Vol.33/No.2 (130) (2018)

Vol.33/No.2 (130) (2018)

TitleImproving Seismic Performance of Hollow Steel Reinforced Concrete Members with Inclined Bars
AuthorHsieh-Lung Hsu, Ming-Te Hong
Keywordssteel reinforced concrete, flexural-torsional behavior, inclined bars
AbstractThis study focused on the improvement of flexural-torsional behavior of hollow composite members subjected to eccentric cyclic loads. A series of composite members composed of encased steel tubes and reinforced concrete with various inclined bars were fabricated for testing. Member performance was evaluated by the strength, stiffness and energy dissipation during the loading history. Test results showed that the strength of members with inclined bars was significantly increased when subjected to torsion and combined loading coupled with torsion. Enhancement in energy dissipation further validated the applicability of incline bars to the performance improvement of hollow composite members.
TitleThe Effect of Different Transverse Reinforcement Schemes on the Confinement of Encased Concrete-Filled Box Columns
AuthorCheng-Cheng Chen, Pin-Da Wu, Jia-Xi Zhou
KeywordsEncased Concrete-Filled Steel Box Columns, steel reinforced concrete column, SRC column, encased box column, concrete filled box column.
AbstractThe concrete in a concrete-filled steel box column is confined by the box column. However, the confinement of the concrete outside the box column(referred as outer concrete hereafter) in an encased concrete-filled box column need to be provided by the steel cage which is composed of main reinforcement and transverse reinforcement. Due to the existence of the steel box column, the traditional ties used in RC columns can note be implemented here. In this article, the confinement effect of so called corner tie, combined tie and lateral tie are investigated experimentally. Ten large-sized concrete-encased concrete-filled steel box short columns were tested under monotonic axial compression. Based on the test results obtained, the following conclusions are made: (a) the corner tie was unable to provide sufficient lateral support to the longitudinal bar and corner concrete that required by the design code; (b) the use of combined tie can provide sufficient confinement to the outer concrete, (c) the potential of lateral tie in providing sufficient confinement to the outer concrete is high, however, further research is needed to confirm it.
TitleStudy on Short-Stroke Damper Assembled in Tuned Mass Damper
AuthorYong-An Lai, Fan-Yen Meng, Kuan-Hua Lien, Lap-Loi Chung
Keywordstuned mass damper, short-stroke damper, optimal design, damper stroke
AbstractIn the conventional tuned mass damper (TMD), the damper stroke and the mass stroke must be the same, thus the long-stroke dampers are required for implementation in TMD. In addition, a considerable size and higher precision for manufacture of long-stroke damper majorly cause expensive budget for installation and maintenance of the TMD. According to the above features, the“Short-Stroke Damper assembled in Tuned Mass Damper (SSD-TMD)” is proposed in order to reduce the damper stroke in the TMD. In the SSD-TMD, the stiffness of SSD-TMD is separated into two parts. The first part is connected with the viscous damper in parallel. Then, the paralleled system is connected with the stiffness of the second part in series. Afterwards, the mass block is further attached to form the SSD-TMD. This assemblage will produce different strokes between the damper and the mass so that the damper stroke can be significantly mitigated under appropriate design of the stiffnesses and damping coefficient. In this article, the model of the SSD-TMD is firstly proposed. The design formulae and procedure of the SSD-TMD is also proposed by following the optimal design parameters for conventional TMD. The case study of the Taipei 101 structure implemented with the SSD-TMD shows that the damper stroke of the SSD-TMD can be dramatically reduced, so that the short-stroke dampers can be used to replace the long-stroke dampers. Furthermore, with suitable design of the SSD-TMD, both effectiveness of structural vibration reduction and mass stroke of the SSD-TMD can outperform the conventional TMD.
TitleSimplified Seismic Evaluation Method on Old Buildings
AuthorYu-Chih Lai, Tao Lai, Lap-Loi Chung, Guo-Luen Huang, Yao-Sheng Yang, Chien-Chuang Tseng, Sheng-Hsueh Lin, Chu-Yuan Chang
Keywordsseismic evaluation, maximum base shear, in-situ test
AbstractThe earthquakes happen in Taiwan, such as Chi-Chi earthquake, let us know seismic capacity of old buildings is not enough. Because it may cause casualty, it is important to raise seismic ability of those old buildings. School buildings belong to public facility and provide people shelters when their home are damaged seriously by earthquake. Therefore their seismic ability should be raised as soon as possible. National Center for Research on Earthquake Engineering (NCREE) proposed complete procedures for seismic evaluation. The procedures of seismic evaluations include: simple survey, preliminary evaluation and detailed evaluation. After screening out school buildings which have less seismic capacity than seismic demand, we need to do seismic retrofit for them. However, there are lots of other old buildings in Taiwan (such as street houses, hospitals and executive agency) need to raise their seismic ability. In this paper, the method use Ultimate Moment Balanced Method to do Simplified Detailed Seismic Evaluation is proposed. The method first evaluates the lateral strength of each column line and multiplied by reduction factor which decided by failure mode of column. And then add lateral strength of each column after reduction, the result is the maximum base shear strength of building. Also, decides the ductility capacity of each column by its failure mode. The ductility capacity of building can be decided by the ductility capacity of each column weighted its lateral strength. Finally, using the ratio of seismic capacity and seismic demand can get the seismic performance of the building before detailed evaluation. Since Ultimate Moment Balanced Method consider both failure mode of strong beam weak column and strong column weak beam, the method can be used on old building either before or after retrofit. This paper takes Ruei Pu elementary school in Taoyuan county as an example to do Simplified Detailed Seismic Evaluation. It is proved that both maximum base shear and seismic capacity are conservative compared to in-situ test. So the method can be used on existing buildings for seismic evaluation. The Simplified Detailed Seismic Evaluation method can be used on establishing the preliminary evaluation method of buildings in addition to school buildings for engineers to application.
TitleProbabilistic assessment of seismic performance and collapse risk for mid-rise buildings
AuthorWei-Huan Hsieh, Lyan-Ywan Lu, Fu-PeiHsiao, Yu-Shi Tang, Yin-Nan Huang
KeywordsWei-Huan Hsieh, Lyan-Ywan Lu, Fu-PeiHsiao, Yu-Shi Tang, Yin-Nan Huang Mid-rise building, seismic performance assessment, probabilistic assessment, collapse fragility analysis, risk assessment, incremental dynamic analysis, nonlinear time history analysis
AbstractMid-rise buildings, which are usually heavily populated, are very common structures in urban areas. The casualty and social impact caused by the collapse of mid-rise buildings in an earthquake can not be overestimated. Therefore, developing suitable assessment methods to identify the buildings with high collapse risk becomes a critical issue. Even though traditional seismic assessment methods, which usually employ nonlinear static pushover analysis, have been successfully applied to regular low-rise buildings, these methods are unable to reflect higher-mode effect on the responses of mid-rise buildings. Furthermore, a traditional approach usually leads to a deterministic result that could not account for the uncertainty in seismic motions and structural responses of a mid-rise building, which is usually more complicated and involves more structural uncertainties than a low-rise building. To this end, this paper presents a procedure and methodology to assess the collapse risk of a mid-rise building. This methodology is developed based on the collapse fragility analysis proposed by FEMA P-58, the collapse criteria proposed by PEER-TBI and ASCE 41-13, and acceptance criteria suggested by ASCE 41-13 and FEMA 356. To establish the fragility curves, this approach employs nonlinear time history analysis together with the method of incremental dynamic analysis (IDA) to estimate structural response parameters. Finally, for demonstration, the proposed assessment method is applied to assess the collapse risk of a mid-rise building that collapsed in an earthquake.

Vol.33/No.1 (129) (2018)

Vol.33/No.1 (129) (2018)

Title Long-Term Micro-Vibration Monitoring and Seismic Performance Evaluation of an Existing 10-Story Steel Factory in Hsinchu Science Park
Author Chung-Che Chou, Steven Tsuang, Yu-Ting Ling
Keywords Steel factory, Micro-vibration, Seismic performance, Moment connection
Abstract The Hsinchu Science Park was opening in 1979 and becomes a very important high-tech area in Taiwan to support the economic growth. This work supported by the MOST, Taiwan focused on the micro-vibration and seismic performance of an existing 10-story steel factory that was designed in 1991 and completed in 1995 in Hsinchu Science Park, Taiwan. A few velocity and acceleration meters were used to monitor the building micro-vibration and performance during earthquakes and typhoons. The monitoring duration is from January to October, 2015 while Typhoons Soudelor and Dujuan and several small earthquakes hit the building. The recorded data was used to (1) evaluate the factory performance in terms of micro-vibration in vertical and longitudinal directions, and (2) adjust the building computer model such as the fundamental period and damping ratio. Then, the nonlinear pushover analysis and time history analyses were conducted on the factory model to obtain seismic demands on design-based and maximum-considered earthquake levels.
TitleMaximum probable moment strengths of reinforced concrete columns
AuthorYu-Chen Ou, Tung-Chun Tsai
Keywordsreinforced concrete, columns, maximum probable moment strength, high strength, axial force
AbstractIn seismic design, the maximum probable moment strengths of columns need to be calculated for shear design. The maximum probable moment strength is the maximum possible moment strength considering material overstrengths (e.g. actual strengths higher than specified ones, concrete confinement, strain hardening of reinforcement, etc.) and the range of factored axial load acting on the column. Both the codes for design of reinforced concrete structures and seismic design of bridges have include their own provisions to calculate the maximum probable moment strength. Earlier studies have shown that both the code methods tend to show unconservative results with increasing axial compression, particularly for compression-controlled sections. In this research, the ratios of measured moment strength to nominal moment strength of 297 column specimens were examined. The examination confirmed that the ratios increased with increasing axial compression and found that it is mainly due to the effect of concrete confinement. To account for the phenomenon, a general equation for maximum probable moment strength of normal and high-strength columns was developed based on actual material strengths. Comparison with the test data of the 297 columns showed that the proposed equation produced conservative predictions for most of the columns. In contrast, current code equations for reinforced concrete structures and for seismic design of bridges produced unconservative predictions for most of the columns. Moreover, the predictions by the proposed equation showed smaller standard deviation than those by the current code methods. Based on the general equation, two equations were developed based on specified material strengths for normal and high-strength columns. Comparison with the test data of the 297 columns showed the two equations produced results similar to the proposed general equation.
Title Experimental Study of Non-ductile Frame Infilled with RC Shear Wall with Openings
Author Chien-Chuang Tseng, Li-Ping Chen, Shyh-Jiann Hwang
Keywords reinforced concrete, shear wall with openings, window openings, door openings, shear strength, experimental study
Abstract In this study, six specimens of non-ductile RC infilled frames with openings were designed according to the typical low-rise buildings in Taiwan, and these specimens were tested in NCREE. Specimens were categorized into three series, such as single window opening, double window openings and single door opening, and each series has two specimens. Test results indicated that the smaller width of window opening can increase shear strength significantly due to the contribution of wing wall. For the specimens of double window openings, shear strength of vertical wall segments between two window openings is significantly lower as compared with its height-to-length ratio. For the specimens of single door opening, the experimental results showed shear strength only increased slightly by its overhanging wall. In addition, it was indicated that the ductility of the specimen is significantly improved because the larger vertical dimension of door opening can yield higher height-to-length ratio of vertical wall segment. ACI 318-14 building code has equations to predict the shear strength of RC wall with openings. In this paper, ACI 318 building code was used to calculate shear strength and compared with the experimental results to check the applicability of ACI 318-14 code on predicting the shear strength of RC wall with openings applicability.
Title Seismic Design and Tests of the Beam-column Joint in a Buckling-Restrained RC Braced Frame
Author Ting-Li Lin, An-Chien Wu, Kung-Juin Wang, Keh-Chyuan Tsai
Keywords buckling-restrained brace, reinforced concrete structure, corbel, beam-column joint, nonlinear response history analysis
Abstract In this study, the brace connection performance in the new reinforced concrete (RC) frame buildings with buckling-restrained braces (BRBs) arranged in a zigzag configuration is investigated. A 12-story buckling-restrained braced RC building is proposed following the model building codes as a prototype. In order to verify the constructability and the seismic performance of the proposed connection, the beam-column joint at the tenth floor selected as the sub-assemblage specimen was designed and fabricated. The full-scale sub-assemblage, including the BRB gusset bracket and a pair of RC corbels, in the proposed BRB-RCF structural system was tested using cyclic loading procedure. Test results demonstrate that the proposed BRB-to-RC connection details performed very well without failure in the steel gusset bracket or the RC corbels. The design and construction of the sub-assemblage specimen show the feasibility of the proposed system for practical applications. In order to further gain insights into the seismic performance of the BRB-RCF system, nonlinear response history analyses were conducted using a total of 240 (SLE, DBE and MCE) ground accelerations. Analysis results indicate that the mean maximum total BRB shear to base story shear ratios are about 23%, 21% and 19% for SLE, DBE and MCE, respectively. The maximum inter-story drift ratios under the DBE and MCE events are 1.82% and 2.32%, respectively. Analysis results also suggest that the high mode effect is moderate. It is found that the peak demand of the horizontal tension force on the gusset bracket can be estimated by considering 70% of the sum of the horizontal force components computed from the maximum tension strengths of two adjacent BRBs.
Title Development and Analysis of Creep and Shrinkage Database of Concrete in Taiwan
Author Jenn-Chaun Chern, Wen-Cheng Liao, Ting-Kai Liu, Wei-Yi Chin
Keywords Concrete, Creep, Shrinkage, Slag, Fly Ash, Database
Abstract The present study begins with the organization of recent half a century data on the shrinkage and creep testing, and proceeds to refer the parameter formation and data structure in international databases, and combines those with present concrete databases in Taiwan to create the Database on Creep and Shrinkage of Taiwan Concrete. The database incorporates 82 documents, 156 data sets for concrete creep tests, and 303 data sets for concrete shrinkage tests. The material properties, the mix designs, the admixture amounts, the geometry of the test specimens, and the test conditions, for each test, are well documented in this database. Through comparisons with international database analyses and literature reviews, this study has verified that the mix design of concrete in Taiwan, for comparable design strength targets, tends to have the following characteristics: high cement amounts, and low elastic moduli of local aggregate. Finally, this study, in addition to incorporating the Taiwan database into the international concrete databases, is also expected to serve as a base to facilitate the development of the worldwide database with a cloud-based web platform for the world.

Vol.32/No.4 (128) (2017)

Vol.32/No.4 (128) (2017)

TitleStudy on the Shear Behavior of Chemical Anchors in the Low Strength Concrete
AuthorJia-MingHsu, Yuan-Liang Zheng, Fu-Pei Hsiao, Wen-I Liao, Pu-Wen Weng, Tai-Kuang Lee, Guo-Luen Huang
Keywordslow strength concrete, adhesive anchors, post-installed rebars, shear, retrofit
AbstractIn order to increase seismic capability of structural system, retrofit techniques are usually applied. Traditional RC retrofit methods include adding RC shear wall, wing wall and RC jacketing. In addition to connect new structural members to old structural members,adhesive anchors (post-installed rebars) are used. From the investigation results by National Center for Research on Earthquake Engineering (NCREE), it was found that concrete strength of old school buildings is very low due to poor construction quality. Therefore, the behavior of post-installed rebars in low strength concrete is very important. In this study, the concrete strength of specimens are 5MPa, 10MPa and 15MPa.According to the minimum edge distance and depth of ACI code, this study proposed a series of anchorage and shear test, a total of 192 specimens. Control parameters are the embedded depth of the rebar, the distance to edge, and concrete strength. The results of those experiments are compared with the calculated values of ACI code. It was found ACI calculated values remain conservative in strength 10MPa and 15MPa, but in the 5MPa calculated values is very close to experiment results.So,the formula of ACI code used in low strength concrete may not be conservative. From the experiments of this study,it was also found a new failure mode as steel bending failure. Finally, the importance of the shear strength of the interface between the post-installed rebar and concrete was addressed with an actual experiment of RC shear wall and the results of the reconnaissance of earthquake disaster in Taiwan.

 

TitleLoading Test Analysis of An Earthquake-Damaged Bridge
AuthorChun-Chung Chen, Yu-Chi Sung, Zheng-Kuan Lee, Chia-Chung Hsu, Fang-Yao Yeh, Yu-Chi Sung, Feng-Kai Chang, Yi-Tsung Chiu, Ping-Hsun Huang, Jia-Ying Chen, Wan-Long Wu
KeywordsGene Algorithm, Response Surface Method, Loading Test
AbstractThis paper conducts an analysis on loading tests of the earthquake-damaged bridge. The study uses the commercial finite element program to build a bridge analytical model, and the analysis result is compared with that of the field load testing to verify the proposed model. Generally, in order to improve the reliability of the finite element model, it is needed to adjust some modeling parameters using field experimental data to realize the representative characteristic of the bridge structure. However, the structural model usually involves numerous elements which lead the poor analysis efficiency of modeling parameters adjustment work. In view of this, this study applies the response method of experimental design function to take place of the finite element model by statistical experimental design theory and integrates the genetic algorithm to optimize modeling parameters which were used in the model and can make the model gives the reliable results which close to static and dynamic characteristics of the actual bridge.
TitleStudy and Establishment for Cloud Platform of Preliminary Seismic Evaluation of Reinforced Concrete Buildings
AuthorYu-Chi Sung, Ming-Chun Lai, Yi-Tsung Chiu, Chun-Jung Chen, Hong-Syuan Lin, Chih-Liang Yen, I-Chau Tsai, Chien-Jung Chen, Chang-Yu Chen
KeywordsCloud Operation System, Quantitative Evaluation, Disaster Prevention
AbstractThe numerous existing buildings maynot behave qualified seismic performance satisfied with the current seismic design code as a result of material deterioration or outdated design, etc. It needs a significant cost and time to do the detailed seismic evaluation of existing buildings for determination on necessary seismic retrofit. Therefore, development of a preliminary seismic evaluation system giving a rapid and reliable result is very important currently in Taiwan. This paper focused on developing the preliminary seismic evaluation of reinforced concrete buildings (PSERCB), based on research of Profs. Tsai and Sung 2014, granted by Architect Research Institute, Taiwan. Both qualitative and quantitative evaluation results are involved in this framework. A cloud platform was established for the engineers to input the inspection of current status of buildings and the evaluation report is able to be downloaded as technical report. All the data on the cloud platform are collected as the basis of big data analysis for strategy of disaster prevention to government in the future.
TitleA Simplified Seismic Analysis Procedure for Vertically Irregular Buildings
AuthorChih-Chia Tsaur, Jui-Liang Lin, Keh-Chyuan Tsai
Keywordsvertically irregular building, setbacks, nonlinear response history analysis, modal pushover analysis, modal response history analysis
AbstractMost seismic building design codes describe the features of vertically irregular buildings. In addition, these building design codes prescribe that dynamic analysis should be adopted in the seismic analysis and design of these irregular structures. Besides the finite element method (FEM), which performs inelastic dynamic analysis to complete finite element models, the modal pushover analysis (MPA) method is one of common simplified seismic analysis procedures. The force-deformation relationship of each vibration mode obtained from the MPA method is employed to construct the corresponding single-degree-of-freedom (SDOF) modal system. The modal response histories are obtained from performing nonlinear response history analysis to each SDOF modal system. The total seismic responses of the building are estimated by adding up the seismic response histories resulting from all vibration modes. This study designates the aforementioned simplified method as the single-degree-of-freedom modal analysis method (SDM). Some research literatures showed that using SDM leads to overestimated seismic responses of the lower parts of the vertically irregular buildings, which have stronger or stronger-and-stiffer bottom story or lower half. Instead of the SDM, the complicated and time-consuming FEM was thus suggested for the seismic analysis of this type of buildings. Nevertheless, this type of vertically irregular buildings is common. It would benefit engineering practice if there are simplified seismic analysis methods available to this type of irregular buildings. In light of the incompetence of using the SDOF modal systems to simultaneously reflect the seismic responses of the super- and sub-structures of the buildings, this study proposes the two-degree-of-freedom modal analysis method (2DM). 2DM is basically the same as SDM, except that 2DM represents each vibration mode as a two-degree-of-freedom modal system. One 9-story and one 20-story regular moment resisting frames are selected as the prototype building in this study. Each of the two prototype buildings are further varied into four vertically irregular buildings as the target buildings. The four variations include buildings with stronger, stronger-and-stiffer first story; stronger, stronger-and-stiffer lower half. FEM, SDM, and 2DM are applied to the eight target buildings subjected to the selected 60 ground motions. This study shows that the analysis results obtained from 2DM are the same as those obtained from SDM as long as the structures remain elastic. While the structures become inelastic, 2DM generally results in more accurate estimations of inter-story drifts, compared with those obtained from SDM. The overestimated peak inter-story drifts of the substructures by using SDM are effectively reduced by using 2DM.
TitleInterference Effects on High-rise Building Based on Aerodynamic and Aeroelastic Tests
AuthorYuan-Lung Lo, Chi-Rou Chen
KeywordsHigh-rise building, Aero-elastic test, Interference effect, Interference factor
AbstractWind effects on high-rise buildings are one of the most important topics in safety designs of structures, especially the target building is neighbored by another or even multiple high-rise buildings. This study intends to compare the differences between the results from the aerodynamic test and the results from the aeroelastic test. Physical scaling tests are planned in three parts: firstly the aerodynamic test is conducted in order to understand mean and fluctuating force coefficients of a square prism model with interference effects; secondly the aeroelastic test is conducted in order to examine the displacement variation under various velocities and terrain flows; thirdly the results from both tests are compared to find the differences by means of displacement estimation methodologies. It is found that, adopting the aerodynamic test for wind-induced response is not reliable compared to the aeroelastic test since the wind-induced response with/without interference effects are much more complicated and need more investigations in systematic aeroelastic test works.

Vol.32/No.3 (127) (2017)

Vol.32/No.3 (127) (2017)

TitleStudy of Prediction Equation for Modulus of Elasticity of High Strength Concrete in Taiwan
AuthorWen-Cheng Liao, Wei-Xiu Hu
KeywordsHigh Strength Concrete, Modulus of Elasticity, Compressive Strength, Silica Fume, New RC
AbstractThe modulus of elasticity of concrete is an important factor in design of RC structures. Modulus of elasticity is also essential for engineers to estimate deflections and stiffness of RC members. Nowadays, Taiwan New RC project is developing to reduce the member sections and increase the available space of high rise buildings by using high strength concrete (f’c > 700 kgf/cm2) and high strength rebars. However, the prediction and calculation of modulus of elasticity of high strength concrete in Taiwan is still mainly referred to ACI318 or ACI363. It was confirmed that modulus of elasticity of high strength concrete is usually overestimated due to less coarse aggregate amount and high paste volume. In order to gain precise modulus of elasticity, it is necessary to find out an equation which can reflect materials characteristic in Taiwan.This study collects 471 data sets of high strength concrete in Taiwan. By regression analysis with certain key parameters, such as silica fume, a new and practical prediction equation based on the ACI318 is proposed. This equation is easy to calculate and reflects the low modulus of elasticity characteristics in Taiwan. It can offer more accurate estimation of modulus of elasticity for New RC member design.
TitleThe seismic performance of reinforced concrete columns using horizontally lap-spliced crosstie
AuthorTai-Kuang Lee, Cheng-Cheng Chen, Ming-Chin Ho
Keywordshorizontally lap-spliced crosstie, lap splice length, RC columns, seismic performance
AbstractA lap-spliced crosstie consists of two J-shaped steel bars (rebars) that have a straight end and an end featuring a 180° hook. In this study, a lateral cyclic load test was conducted on three specimens of large-sized reinforced concrete (RC) columns to investigate the seismic resistance capability of RC columns comprising horizontally lap-spliced crossties with less than Class A splice length. The research results are presented as follows: (a) The confinement effect of horizontally lap-spliced crosstie with less than Class A splice length, was comparable to that of the specimens using crossties featuring a 180° hook on the two ends and conventional crossties. (b) According to the reading data of strain, the horizontally lap-spliced crosstie can develop the required strength and provide satisfactory confinement effect. (c) In order to be safe and conservative, Class A splice (1.0 times the development length) for lap-spliced crossties is recommended. (d) Using lap-spliced crossties in construction is easy and produces a low possibility of construction errors. Therefore, the construction quality of RC column reinforcement and the seismic resistance capability of RC structures can be substantially increased. The case discussed in this study shows that the use of lap-spliced crosstie would increase the amount of transverse steel in each plastic hinge by 11.5 kg and in the clearance height of columns by 17%.
TitleFeasibility Study on Building Mass Damper Using Optimum Dynamic Response Control Algorithm for Practical Application
AuthorPei-Rong Chen, Yu-Fang Liu, Bo-Han LEE, Tzu-Kang Lin, Kuo-Chun Chang
KeywordsMid-story isolation system, Tuned mass damper, Building mass damper, Objective function, Optimum Dynamic Response Control Algorithm
AbstractIn a mid-story isolated building, the isolation system is incorporated into the mid-story rather than the base of the building. The effectiveness of mid-story isolation design in reducing seismic demands on the superstructure above the isolation system has been verified in many researches. However, the response of substructure may be amplified due to the flexibility and the contribution of the higher modes. On the other hand, although tuned mass damper has been recognized as an effective energy absorbing device to reduce the undesirable vibrations of the attached vibrating system subjected to harmonic excitations, the mass ratio of most TMD was not enough for earthquake resistance due to the limitation of the building space. Therefore, the concept of building mass damper (BMD) design has been developed, which incorporates the TMD design concept into the mid-story isolated building to control the seismic response of both substructure and superstructure. In the BMD design, the superstructure serves as a tuned absorber mass while the stiffness and damping can be provided by the isolation system composed of elastomeric bearings and additional dampers, as the advantages of conventional TMD and mid-story isolation systems can be integrated. A simplified three-lumped-mass structure model, in which three lumped masses are respectively assigned at the building mass absorber, the control layer, and the primary structure, is rationally assumed to represent a building structure with a BMD system. The reason for doing this is that the inherent dynamic characteristics (fundamental modal characteristics of vibration) of both the building mass absorber and the primary structure can be considered comprehensively in the simplified structure model. The feasibility of the optimum BMD (OBMD) design method has been verified in previous studies. In this research, the 57 story steel frame is used to be a bare frame. According to 2% inherent damping ratios of the TMD, BMD and OBMD can be designed respectively. Six real earthquake records with distinct seismic characteristics adopted in this research are selected for the ground acceleration inputs along the longitudinal and transversal direction. On the other hand, the acceleration transfer functions of the simplified three-lumped-mass structural model and the FFT of each ground motion are used to describe the seismic behavior of the TMD, BMD and OBMD. Then, the seismic responses of the OBMD system are thoroughly investigated and the practicability and effectiveness of the OBMD system for seismic design are verified.
TitleEvaluation of composite floor vibrations induced by moving loads
AuthorJian-Huang Weng, Chi-Hang Li
Keywordsfloor vibration, composite floor deck, moving load, generic vibration criteria, one-third octave spectrum, SCI P354
AbstractIn the laboratories or research centers, the vibration-sensitive equipments are often placed on the basement floors. The reason is the impact of environmental vibrations outside the building can be reduced. Another reason is the influence on the structural design will be smaller if the slab thickness needs to be increased because the lateral seismic force of the slab is directly borne by the basement exterior wall. However, basements are often used as parking or loading/unloading spaces so that the vibration induced by vehicle pass-bys may affect the equipments. Although the full height RC partition wall can be used to reduce the vibration and it is also effective to keep the equipments far away from the lane, the result should be confirmed with floor vibration analysis. In this paper, the moving load analysis in SAP2000 is applied to evaluate the floor vibration induced by vehicle traveling inside the building. The publication of Steel Construction Institute: Design of Floor Vibration – A New Approach (SCI P354) is referred as a guideline for structural simulation of the composite floor deck which is commonly used in steel structures. This paper contains simulation of moving load, modeling of composite floor deck and calculation of the generic vibration criteria which is commonly used for high-tech facilities. Finally, an example, design of floor vibration in an animal research facility, is provided to illustrate the design details.
TitleDesign and Construction of Carbon Fiber Reinforced Polymer Composite Jacketing for Seismic Retrofit of National Freeway Bridges
AuthorKang-Yu Peng, Ming-Shing Wu, Chien-Hung Chen, Chi-Shan Wang, Sheng-fa Lin, Jun-Jjie Zheng
Keywordsbridge, seismic retrofit, carbon fiber, jacket, construction
AbstractChi-Chi earthquake measuring 7.3 on the Richter scale struck Taiwan on September 21, 1999, and caused severe property losses and casualties to central Taiwan. After the earthquake, the seismic safety of the bridge structure has become a very important issue in the national disaster prevention plan. The national freeway is the main traffic artery connecting the north and south in Taiwan, which has great influence on the national economic development and the people’s livelihood. Taiwan Area National Freeway Bureau (TANFB) actively took preventive measures for the bridge structures. The bridge columns jacketing can effectively increase the flexural ductility and shear strength of the bridge in large earthquake. The reinforced concrete jacketing and steel jacketing are the most widely used in the domestic bridge columns seismic retrofit project. In view of the ever-changing materials technology, carbon fiber material has the characteristics of bearing the load, limiting the micro-crack extension, improving the material strength and rigidity. The material can also improve the material anti-fatigue, anticreep performance and service life. When the space is limited, the landscape requirements or construction conditions are not applicable reinforced concrete jacketing and Steel Jacketing , the seismic retrofit program of national freeway bridges using carbon fiber reinforced polymer composite jacketing (CFRP jacketing). With carbon fiber materials’ light weight, high strength, easy constructed and other characteristics, increase the seismic capacity of freeway bridges, and accumulate the experience of domestic design, construction, testing and maintenance. Looking forward to provide more choice for future domestic bridge seismic retrofit project.

Vol.32/No.2 (126) (2017)

Vol.32/No.2 (126) (2017)

TitleSeismic Design, Tests and Analysis of Steel Panel Dampers for Steel Moment Frames
AuthorChung-Hsiang Hsu, Chao-Hsien Li, Pu-Yuan Chin, Keh-Chyuan Tsai
Keywordssteel panel damper, capacity design, seismic design, finite element model analysis, non-linear structural analysis
AbstractA ductile vierendeel frame can be constructed by incorporating the steel panel dampers (SPDs) into the moment resisting frame (SPD-MRF). Thus, the lateral stiffness, strength and energy dissipation capacity of the building can be enhanced.This paper presents the mechanical properties, capacity design procedures and the buckling-delaying stiffeners for the proposed 3-segment SPDs using two specimens subjected to cyclic increasing deformations. This paper also discusses the seismic design procedures of the SPD itself and the boundary beams connected to the SPDs in typical SPD-MRFs. Tests confirm that the proposed SPDs possess excellent ductility and energy dissipation capacities. The cyclic force vs. deformation relationships of the two SPD specimens can be accurately predicted using either the ABAQUS or PISA3D model analyses. This paper also investigates the seismic performance of a 6-story example SPD-MRF by using nonlinear response history analysis procedures and 240 ground accelerations. Results indicate that under the 80 MCE ground accelerations, the mean plus one standard deviation shear deformation of the SPD inelastic core segment is 0.055 radian, substantially less than the 0.11 radian capacity observed from both two SPD specimens. In addition, the cumulative plastic deformation of the proposed SPD is 127 times the yield deformation, capable of sustaining the MCE at least 4 times before failure. This paper concludes the method of using one equivalent element for effective modeling of the 3-segment SPD. The effects of the core segment relative length and stiffness on the overall SPD elastic, post-elastic stiffness, elastic deformation limit and inelastic deformational demand are discussed.
TitleSeismic Tests and Nonlinear Time History Analyses of Full-Scale Two-Story Steel Frames with DC-SCBs and SBRBs
AuthorChung-Che Chou, Chia-Hung Hsiao, Ze-Bang Chen, Ping-Ting Chung, Dinh-Hai Pham
KeywordsDual-core self-centering brace (DC-SCB), Sandwiched buckling-restrained brace (SBRB), Tests of two-story steel braced frames
AbstractTraditional seismic resisting systems in a large earthquake can experience significant damage and residual drifts due to energy dissipation of some structural members, which leads to difficult or expensive to repair after earthquakes. A steel dual-core self-centering brace (DC-SCB), which utilizes three steel bracing members, two friction devices, and two sets of tensioning elements that are in a parallel arrangement for doubling its axial deformation, has been proposed and validated to provide both the energy dissipation and self-centering properties to seismic resisting systems. A prototype three-story steel dual-core self-centering braced frame (DC-SCBF) was designed, and its full-scale one-bay DC-SCBF was tested to validate the system response. The DC-SCB was then replaced by the sandwiched buckling-restrained brace (SBRB) in a full-scale two-story frame, so the seismic performance of the DC-SCBF and the special mixed braced frame (SMBF) that has both the DC-SCB and SBRB in a frame could be evaluated. The full-scale two-story DC-SCBF, SMBF and BRBF subassembly specimen performed well up to an interstory drift of 2% after multiple tests. Nonlinear time history analyses were also performed on the prototype braced frames to obtain seismic demands.
TitleCurvature effect on seismic responses of pendulum sliding isolators subjected to vertical and horizontal bi-directional ground excitations
AuthorChun-Chung Tsai, Lyan-Ywan Lu, Liang-Wei Wang, Lap-Loi Chung
Keywordsbase isolation, sliding isolation, pendulum isolator, curvature effect, bi-direction excitation, centrifugal force
AbstractFriction pendulum system (FPS) isolator is one of most widely used sliding isolators, presently. This type of isolators usually has a spherical sliding surface with constant radius, in order to produce a restoring force for the isolation system. The energy dissipation of the isolator is provided by sliding friction force. The common model adopted for an FPS isolator usually contains a constant-stiffness spring and a friction element placed in parallel. This model assumes that the isolator displacement is much smaller than the radius of the sliding surface, therefore the curvature and slope effects of the spherical surface on the restoring and friction forces can be neglected. This simplified model may not be applicable for FPS isolators under earthquakes that produce large isolator displacements or sliding velocities, since in these earthquakes the curvature and slope of the sliding surface may have significant effects on the dynamic response of the isolation system. In order to capture the actual response of a FPS-isolated structural system under an extreme earthquake, in this paper, complete dynamic equations of motion for the isolation system under vertical-and-horizontal bi-directional ground excitations were derived by using Lagrange’s equation. It is shown that the derived governing equations in both horizontal and vertical directions contain high-order nonlinear terms related to the slope and curvature of the sliding surface. These terms that are functions of horizontal sliding velocity and acceleration cause the coupling effect between horizontal and vertical motions and result in extra vertical acceleration and isolator axial load. The existence of the coupling effect was further verified by the shaking table test conducted in this study. In addition, by using the derived complete dynamic equations, the time responses of a FPS-isolated rigid structure under 168 ground motions with different intensities and characteristics were simulated. The simulation result demonstrates that the high-order terms have less effect on the horizontal response (acceleration and isolator drift) of the isolated system, but are more influential on the vertical responses (acceleration and isolator axial load). Neglecting the high-order terms may underestimate the vertical response by about 20-40% in a sever earthquake.
TitleInvestigation on Safety Problems of SRC Structures used in Construction
AuthorJui-Lin Peng, Chung-Ming Ho, Wen-Jinn Lee, Liang-Jenq Leu
Keywordscritical load, direct analysis method, second-order analysis, steel reinforced concrete structure
AbstractThe steel reinforced concrete structures (SRC) integrate into the merits of steel structures (SS) and reinforced concrete structures (RC). The steel reinforced concrete structures, combined by reinforced concrete and steel structures, have a good ductility, earthquake resistantce and fire resistance. In recent years, some construction projects with high safety and seismic requirements have considered the design of steel reinforced concrete. However, in the construction of SRC structures, an unexpected construction load may cause the collapse of SRC structures if the correct construction procedures is not considered. This study investigates the construction safety of SRC structure based on the collapse of a SRC structure using a second-order analysis and a simplified model of composite columns. The study result of the second-order analysis shows that designers might fail to consider the overall steel self-weight of the SRC construction structure to exceed the critical load of this structure. This caused that the SRC construction structure buckled and then immediately collapsed after a slight disturbance. The analysis result of the simplified model of the composite column shows that the self-weight of SRC may exceed the critical load of the SRC construction structure and then the structure fails finally. The analysis result implies that the SRC construction structure collapses if the construction procedure of SRC only follows that of SS regardless of the setup progress of reinforced concrete beams and columns at the bottom. In order to avoid the collapse of SRC construction structure, this study proposes that, in terms of construction, the government authorities should develop a safety assembly procedure of SRC structures so that the hoisting of steel beams and columns can combine reinforced concrete operations perfectly. In terms of design, the government authorities should add the direct analysis method or the second-order analysis into the domestic design specifications of steel structures based on those used in advanced countries.
TitleNumerical simulation of shaking table tests on dynamic response of a bridge model with scoured piled foundation
AuthorKuang-Yen Liu, Zheng-Hong Chen, Chia-Han Chen, Kuo-Chun Chang
KeywordsShaking table test, Pile foundation, Scouring effect, Soil springs
AbstractThe simplified analysis process of soil-structure interaction is proposed in this research to study the response of the bridge with scoured piled foundation under earthquake. The simplified analysis applies soil spring to simulate soil-structure interaction behavior. Both soil shear wave velocity and dynamic shear modulus are used to estimate initial value of linear soil spring. Given two assumptions: (1) the shear strain of the soil near the pile is consistent to the strain of the pile, and (2) modification of dynamic shear modulus of soil follows the relationship of effective shear strain and maximum shear modulus, proposed by Seed and Idriss, the parameters of soil springs can be determined iteratively. Furthermore, a simplified approach to identify the soil layers subjected to seismic loading was also introduced by the predominant frequencies of soil layers by the transfer function analysis. Based on the proposed method, the SDOF bridge model with equivalent linear soil springs was built to simulate behavior of soil-pile-structure interaction in the shaking table test. The acceleration and relative displacement of superstructure, the strain of pile top, and the maximum strain of pile can be effectively predicted by the proposed method, either in the condition of exposed or no exposed pile foundation. In addition, the analyzed result of the model considering the double layers of soil can obtain better accuracy than that of the model with single layer of soil.

Vol.32/No.1 (125) (2017)

Vol.32/No.1 (125) (2017)

TitleSeismic Behavior of Reinforced Concrete Beams with Rectangular Spiral Reinforcement
AuthorPing-Hsiung Wang, Kuo-Chun Chang, Yu-Chen Ou, Samuel Y. Yin, Jui-Chen Wang, Chih-Hsuan Chen, Chen-Wei Wu
Keywordsrectangular spiral, beam, plastic hinge, cyclic loading
AbstractThis paper presents an experimental study on reinforced concrete beam with continuous rectangular spiral as transverse reinforcement. Three exterior beam-column joint specimens with different beam detailing were devised to exhibit beam hinging and to examine their seismic performance under pseudo-static cyclic loading. Two beams with single and double rectangular spirals were introduced to compare with the one with traditional hoops. Test results show that beam specimen with single rectangular spiral has comparable hysteresis behavior compared to the traditional one, while the one with double rectangular spiral exhibits more degradation due to inadequate detailing at the end of spiral. Without the need of anchored hooks on each hoop, beam with rectangular spiral can save around 25% of transverse reinforcement in comparison with traditional hoops. Moreover, rectangular spiral can be automatically produced and easily erected with less labor effort.
TitleSeismic Tests of High Strength Concrete Filled Box Columns under Large Axial Loads
AuthorChung-Che Chou, Sung-Cheng Wu
KeywordsHigh strength material, Concrete filled box column, High axial load beam-column specimen
AbstractThe cyclic behavior of high strength Concrete Filled Box Column (CFBC) under large axial loads was experimentally investigated. The parameters in the study included the width-to-thickness (b/t) ratio, axial load level and section type. Total six beam-column specimens were tested under a constant axial load and an increasing cyclic loading. The CFBC specimens were 280 to 420 mm in width and 2000 mm in height. Nominal b/t ratios varied from 11 to 30. All specimens were made of high strength steel SM 570M with a nominal yield strength of520~580 MPa.Three specimens were filled with high strength (80 MPa) concrete. Experimental results indicated that ductility decreases significantly with an increase in either axial load level or b/t ratio of the steel. The ductility does not change significantly whether concrete is infilled in the steel box column. Eurocode (EC 2004) and Architectural Institute of Japan (AIJ 2010) have good prediction in the flexural strength of high strength CFBC. AISC-LRFD (2010), ACI 318 (2011) and Taiwan Steel Design Code (2010) are too conservative in predicting the flexural strength of high strength CFBC. All the design codes are conservative in predicting high strength steel column moment capacity, especially for small b/t ratios.
TitlePerformance-based design for earthquake-resistant coupled structural walls
AuthorChung-Chan Hung , Yu-Hsiang Cheng ,Wei-Ting Lu
Keywordscoupled structural walls, performance-based design, nonlinear time-history analysis
AbstractCoupled structural walls are often used in the buildings located in regions with high seismic risk. A coupled wall structure consists of two or more structural walls linked by coupling beams. It is able to provide efficient lateral strength and stiffness, which effectively reduces the drift response of buildings under earthquakes. Current seismic design codes are based on strength methods. Although they are able to prevent structures that are designed accordingly from collapse, the designers and users have limited knowledge about the seismic behavior of the designed structures under different levels of earthquakes. The objective of the present study is to develop a performance-based design method for coupled walls. The developed method allows engineers to pre-select the desirable coupling ratio and performance objectives for coupled walls, and then design the structures accordingly. In addition, it also facilitates the ideal yielding mechanism of coupled walls under earthquakes. Four example coupled wall structures are designed in this study using the proposed method. Their computational models are also built and analyzed using nonlinear time history procedures. The results show that the designed coupled walls are able to exhibit satisfactory structural yielding mechanisms and show the seismic behavior satisfying the pre-selected performance objectives for different seismic hazard levels.
TitleOptimal Design Formula for Viscous Damping Ratio in Isolation System with Consideration of Site Classification
AuthorCho-Yen Yang,Yang-Chih Fan, Lap-Loi Chung, Bao-Jyun Lu
Keywordsdesign formula, isolation, viscous damping, optimal, site classification
AbstractIn this paper, the optimal viscous damping ratio for isolation system is studied. The linear restoring and damping force are considered. According to the previous literature in optimal design formulas, the white-noise excitation is considered. However, the case analysis in previous study was not doing well because the formulas could not retain the regional feature. Therefore, the numerical analysis intended to input several ground motion records in Taiwan. After that, the rigid and non-rigid superstructures for isolation system with various structure parameters are numerically simulated. The root mean square of absolute structure acceleration is selected to be the objection function for obtaining optimal isolation damping ratio. Repeating the optimal process with various structural parameters, the proposed simple design formula was developed by regression of those optimal isolation damping ratios from numerical simulations. Finally, we conducted the case analysis to verify the feasibility of proposed optimal design formulas.
TitleSeismic Analysis of Ceiling Lateral Bracing and Vertical Motion Effects on Suspended Ceilings
AuthorGeorge C Yao, Wei-Chung Chen, Ching-Yao Lin
Keywordssuspended ceilings, lateral bracing assembly, bracing wire, shaking table experiment, vertical motion
AbstractPast earthquakes have shown widespread damage to the suspended ceilings. Despite their frequent use in Taiwan, many suspended ceilings experienced damage in earthquakes owing to the lacked proper seismic design or efficient installation. In 2011, Taiwan Building Code issued the seismic installation of the suspended ceiling systems which are similar to the ASTM E580-09. However, the construction of the lateral bracing assembly has always been a difficult challenge. Problems include slack installation or omission of the bracing wires due to obstructions result in uneven quality of the bracing system in-situ. In recent years, some researches have demonstrated that the lateral bracing assembly may not adequately resist the lateral force. The other researches have even shown that unbraced ceiling systems may perform well when providing both sufficient clearance and wide closure. Therefore, there is an increasing concern about the necessity of the bracing system. In order to understand the dynamic behavior of bracing systems of the suspended ceilings, full scale shaking table experiments of suspended ceiling systems were conducted in this study. The first series of experiments on 5.7m × 2.7m ceiling systems looked into the seismic effects of the bracing assemblies. Some ceiling specimens were subjected to unidirectional ground motions while the others were subjected to a horizontal and a vertical ground motions acting together. The results clearly showed that the bracing wire bore only a small portion of the inertial force, and this situation became more obvious while the ceiling systems were subjected to vertical excitations. The second series of experiments on 5.7m × 2.7m ceiling systems compared the seismic performance of the braced and unbraced ceilings. The preliminary observations revealed that the use of the lateral bracing including compression post may not improve the seismic performance of the ceiling system. The unbraced ceiling systems performed well just as the braced ceiling systems when excited only by horizontal ground motions, and it performed better when the vertical ground motions were added to the ceiling systems. In this study, a conceptual computer model was developed based on the experiment data. The accuracy of the computer model was verified by using modal analysis. In comparison with the experiment results, this computer model provides the time-history analysis with reliable accuracy and helps simulate the dynamic response of different conditions of ceiling systems.

Vol.31/No.4 (124) (2016)

Vol.31/No.4 (124) (2016)

TitleA Computer Program for Axial Load-moment Interaction Diagram for New High-strength Reinforced Concrete Columns- New RC-PM
AuthorYu-Chen Ou, Tung-Chun Tsai
Keywordsreinforced concrete, high strength, columns, axial load-moment interaction diagram, New RC, computer program
AbstractTo address the need for high-rise reinforced concrete buildings in Taiwan, Taiwan New High-Strength Reinforced Concrete (Taiwan New RC) project was initiated. The project integrates the resources of academia and industry of Taiwan to develop the New RC structures for use in Taiwan. The longitudinal and transverse reinforcement used in the project are SD690 (yield strength of 685 MPa) and SD790 (yield strength of 785 MPa), respectively. The concrete compressive strength is typically ≧ 70 MPa. To support the Taiwan New RC project, a computer program, referred to as New RC-PM, was developed in this research to calculate the axial load-moment (PM) interaction diagram for New RC columns as well as for conventional RC columns. The theoretical background and verification of the New RC-PM are presented and discussed in this paper. Moreover, a test database with 18 New RC columns were established. The New RC-PM was used to analyze the PM interaction diagrams of the columns, which were then compared with the test results. The comparison showed that the New RC-PM could conservatively estimate the axial-bending strengths of the columns. The New RC-PM was further used to evaluate the methods for calculating the maximum probable moment strength (Mpr) of the current building and bridge codes. Evaluation results showed that the Mpr calculated by the current building code was unconservative for all the columns. The method of the current bridge code significantly improved the degree of unconservatism of the method of the building code. However, the Mpr was still unconservative for most compression-controlled columns. To address the issue, a new method to calculate the Mpr was proposed in this research. Comparison with the test results showed that the Mpr calculated by the proposed method was reasonably conservative for most of the columns.
TitleSeismic Retrofit by External Reinforced Concrete Frames – Using School Building of HOU-JIA Junior High School as Example
AuthorSheng-Hsueh Lin, Yu-Chih Lai, Tao Lai, Lap-Loi Chung, Guo-Luen Huang, Chien-Chuang Tseng
Keywordsretrofit by external frames, seismic retrofit, pushover analysis, shear capacity of slab
AbstractIn Chi-Chi earthquake, the school buildings in Taiwan were damaged seriously. Because rebuilding school buildings will be uneconomical and that will be a tremendous amount of work, seismic retrofit methods are usually adopted to raise seismic performance of buildings. The typical retrofit methods of school buildings in Taiwan include RC jacketing, wing wall and shear wall etc. However, those methods above will affect the function of the existing building during the construction. In this paper, retrofit method with adding external frames, seldom seen in Taiwan, is proposed. The advantage of this method is that the function of the existing building will not be affectedduring the construction. We first use a school building to discuss the feasibility of the method. And it is suggested that the method can be used on the buildings whose functioncannot be affected during construction, such as hospitals. We use a school building of HOU-JIA junior high school to apply a retrofit design of this seismic retrofit method using slabs to connect existing building and external frames. After the retrofit design, we do pushover analysis to make sure the seismic capacity of the retrofitted school building is enough. Finally, we check the shear capacities of slabs to make sure they can completely transfer the earthquake load from the existing building to external frames. By the design example, we prove that the retrofit method of RC external frame is fit to the common squat school buildings.
TitleSeismic Performance of Large BCR Steel Columns
AuthorCheng-Cheng Chen, Shu-Hao Lin, Pin-Da Wu
Keywordscold formed structural tube, steel structure, steel column, earthquake-resistant structures
AbstractThis study examined the ductility development of large cold-formed square tube columns through cyclic loading test of five full-sized specimens. Specimens included crack-sensitive and local-buckling-sensitive specimens. In addition, specimens using internal diaphragm and external diaphragm were employed to weld the columns to the beams. Based on the test results, the following conclusions can be drawn: (1) The cold-forming process caused considerable plastic strain on the cross sections of the steel columns, however, by controlling the heat input in the welding passes, premature cracks can then be suppressed. (2) For the specimens with a column wall width-to-thickness ratio equals to 10.9, a story drifty ratio capacity no less than 7% and a plastic hinge rotation capacity no lower than 4.5% can be reached. (3) For the specimens with a column wall width-to-thickness ratio of 23.9, which is much larger the code limitation of 15.6, a story drift ratio capacity between 4.2%–4.4% and a plastic hinge rotation capacity between 2.1%–2.2% can be reached; generally, the specimens satisfied the requirements for seismic structures. (4) Although a more restrict with-to-thickness ratio for cold-formed square section than for box column is specified by the code, the ductility of the structural tube and the box column with the same section width and wall thickness is similar.
TitleOptimal Design of Viscous Dampers for Two and Three-Dimensional Building Structures
AuthorPeng-Tai Chan, Chih-Shen Cheng, Liang-Jenq Leu
KeywordsViscous dampers, optimal placement of dampers, shear type buildings, three-dimensional asymmetric buildings
AbstractNowadays, passive energy dissipation devices are widely used in building structures. Design codes such as FEMA273/274 suggested that the equivalent damping ratio of supplemental viscous dampers be used. However, how to place viscous dampers optimally was not addressed. Several optimal damper placement methods have been proposed to improve the seismic performance of structures but they usually involve complicated procedure and therefore are not suitable for practical applications. The goal of this study is aimed at finding the optimal placement of viscous dampers using proposed simple methods. The proposed methods and other optimal damper placement methods are applied to different shear type buildings and a three-dimensional asymmetric building. Their performance and applicability are compared using statistical methods under a series of spectrum-compatible ground motions.
TitleEffect of Vibration Reduction of Bidirectional Suspension-type Tuned Mass Damper
AuthorJing Jhang, Wei-Ru Liao, Yong-An Lai, Kuan-Hua Lien, Lap-Loi Chung, Chien-Chuang Tseng
KeywordsTuned Mass Damper, bidirectional analysis, wind-induced vibration control, high-rise building
AbstractThe tuned mass damper (TMD) is widely utilized for civil engineering to control wind-induced vibration in high-rise building. In this research, the design and analysis procedures of the bidirectional suspension-type tuned mass damper are proposed and demonstrated. The main structure is simplified as a shear building model to install the suspension-type tuned mass damper for simulation by the dynamic time history analysis. For common pendulum tuned mass damper, the suspension position and viscous damper implement location are located at different floors. Therefore the reaction force and damping force of the tuned mass damper are acting on different degrees of freedom of the main structure. Although the damping force of a damper is acting in both the two horizontal directions because the damper is implemented with an angle to the floor plane, the damping force is independent in the two horizontal directions if the dampers are allocated in symmetric layout. Therefore, the damping matrix can be decoupled. The feasibility of the bidirectional suspension-type tuned mass damper is illustrated by the high-rise building subjected to the design wind force with return periods of 1 year and 50 years, respectively. Following numerical verification, the effects of vibration reduction for the high-rise building subjected to the design wind forces are demonstrated.
TitleSelection of modal frequencies adopted in ambient vibration method for determination of stay cable force
AuthorWen-Hwa Wu, Chien-Chou Chen, Yi-Ren Wang
Keywordsstay cable, cable force, ambient vibration method, modal frequency, anchorage system
AbstractThe ambient vibration method is typically employed in engineering practice to determine the tension of a stay cable and its precision strongly depends on the appropriate selection of cable frequencies. In general, the modal frequencies of a stay cable are close to an arithmetic sequence and these well separated frequency values are not difficult to be identified. From recent measurements on different stay cables by this research group, however, it is found that the identification of cable frequencies is possibly disturbed by the frequencies of bridge deck, the biased constraint of anchorage system, and the coupled interaction for the cable with its anchorage system. This study is consequently aimed to systematically explore these three types of difficulties such that the goal of clarified cable frequency identification and accurate cable force estimation can be attained. For the confusion caused by the frequencies of bridge deck, it is suggested to conduct the cable frequency identification over a wider frequency range and then exclude the interference of the deck frequencies in the lower frequency range based on the equally spaced relationship of cable frequencies conveniently observed in the higher frequency range. Regarding the biased constraint of anchorage system to induce a pair of frequencies for each vibration mode, it is recommended to consistently adopt the higher or lower frequency value in each pair for the computation of cable force established on a basis of common boundary constraints. Finally, the phenomenon that a particularcable frequency within a specific frequency range can irregularly splitinto two is confirmed to result from the coupled interaction between the cable and its anchorage system. Under such circumstances, special attention should be paid to choose the cable frequencies not influenced by this coupling for evaluating the cable tension.

Vol.31/No.3 (123) (2016)

Vol.31/No.3 (123) (2016)

TitleA Practical Equation for Elastic Modulus of Concrete in Taiwan
AuthorW.-C. Liao, C.-C. Lin, Y.-W. Chan
KeywordsConcrete, Elastic Modulus, Aggregate, Compressive Strength
AbstractConcrete is a composite material consisting of water, cement, fine and coarse aggregates. The elastic modulus of concrete is highly affected by the properties of its components. The estimation of elastic modulus of concrete in Taiwan is mainly referred to the empirical equation provided in America Concrete Institute, ACI 318. However, it can be found that the elastic modulus of concrete in Taiwan is considerably lower than that in US according to the experimental results due to differences of aggregate properties. The aggregate phase is predominantly accounted for the elastic modulus of concrete. In addition, notable amounts of pozzolanic materials, such as fly ash and slag, are widely used in concrete mixtures in Taiwan. Since the elastic modulus directly influences the stiffness of RC structures, a more accurate prediction of the elastic modulus of concrete in Taiwan to reflect all these characteristics is essential. This paper proposes a formula to estimate the elastic modulus of concrete in Taiwan by collecting and analyzing the related test data. The parametric analysis is also carried out to verify the validity of this formula. This practical formula of elastic modulus of concrete has good agreement with that obtained from the experiments.
TitlePerformance-oriented two-stage design method for base-isolated structures
AuthorLyan-Ywan Lu, Liang-Wei Wang, Ching-Huei Chen, Kuan Feng Lee, Tzu-Ying Lee, Chun-Chung Tsai
Keywordsbase isolation, isolation design, performance objective, allowable isolator displacement, allowable base shear
AbstractBase isolation is an effective means for improving seismic resistance capacity of structures. Design codes for base isolation have been given in many countries for many years. However, most of existing codes only provide generic formulas that determine the parameters of an isolation system as a whole, rather than the parameters for individual isolators. Consequently, design engineers have to perform the design task based on the isolator parameters selected according to past experience. Moreover, since most of existing isolators are nonlinear devices, conventional design methods usually involve iteration and trial-and-error procedure if certain performance demand has to be satisfied. In order to simplify the design procedure so the tedious iteration procedure in a conventional design approach can be averted, in this paper, a performance-oriented two-stage design method is proposed. Without iteration, this method is able to determine a set of isolator parameters that meet the two pre-selected performance objectives, namely, the allowable isolator displacement and base shear. The proposed method includes two design stages. In the first stage, the formulas specified in the current design code are employed to compute the linearized parameters of the whole isolation system, i.e., the effective period and effective damping, so that the two performance objectives can be satisfied. Based on the linearized parameters determined in the first stage, in the second stage, the nonlinear parameters for each individual isolator, such as the yield force and post-yield stiffness in a LRB isolator, are computed. For the convenience of applications, in this work, the complementary design formulas are derived and design steps are also outlined. Finally, the feasibility of the proposed design method is demonstrated by an example that involves a 5-story RC building isolated by LRB isolators.
TitleStructural Isolation Design Procedure with Optimal Design Formula of Friction Coefficient
AuthorSheng-Hsuan Wang, Yi-YoTsai, Lap-Loi Chung, Cho-Yen Yang, Pei-Shiou Kao
Keywordsisolation systems, frictional coefficient, optimal design procedure, isolation systems simulation
AbstractAccording to the concept of earthquake response spectrum, the structure which equips with isolation system reduces seismicforce by extending the period.For isolation design, the friction coefficient is one of the main design parameters. Based on the experience, the isolation displacement get lower with larger friction coefficient, however, the structural acceleration get larger with lower or larger friction coefficient.In the conventional isolation design procedures, the energy dissipation parameters, like friction coefficient, is not determined by some certain criteria but engineers’ practical experience. Because structure may suffer nearfult earthquake orearthquake of which intensity is larger than design earthquake. This article incorporates the optimal friction coefficient into isolation design process which called optimalisolation design process of friction coefficient. In order to verify effect of the process, the article choosesdesign earthquake, 1.5 times design earthquake and nearfult earthquake as input to do time history analysis in an imaginary case. The simulation result indicates that structural acceleration reduce effectively but isolation displacement may be larger than displacement limit except under design earthquake. Therefore, the article change design logicthat fixes displacement first and designs with non-design earthquake response spectrumto develop modified optimal isolation design process and chooses non-design earthquake as input to do the timehistory analysis in an imaginary case.According to the analysis results, the isolation displacement will be lower than design displacement andstructuralacceleration reduce effectively. Because the difference between the optimal design procedures of friction coefficient and the conventional one is insignificant, engineers will feel comfortable to adopt the optimal design procedures to determine isolation parameter. The modified optimal isolation process’s steps are concise and base on non-design earthquakeresponse spectrum, so the article refer the process as credible.
TitlePrediction of Lateral Load Displacement Curve of RC Wall with Openings Failing in Shear
AuthorShyh-Jiann Hwang, Weng-Kin Lam, Ren-Jie Tsai, Chien-Chuang Tseng, Yaw-Shen Tu, Fu-Pei Hsiao
Keywordslateral load displacement curve, reinforced concrete, shear deformation, shear strength, wall with opening
AbstractThere are plenty of RC walls with openings in the low-rise residential buildings. Due to unawareness of the behavior of RC walls with openings, their effects are often ignored or undervalued during seismic assessment and design. In consequence, the seismic capacity of residential buildings is greatly underestimated, which is detrimental to the work of seismic design, evaluation and retrofitting for the low-rise residential buildings. In this paper, a lateral load displacemen tcurve of the RC walls with openings subjected to shear failure is proposed. The turning points in the structural behavior are defined as shear cracking, shear strength and collapse point. The proposed model correlates well with the available test results of RC walls with openings. Calculations of the proposed model are greatly simplified to fit in the purpose of design in practice. For the pushover analysis, the proposed model can simulate the properties of shear plastic hinge of the RC walls with openings.
TitleComparison of different bridge seismic assessment methods
AuthorChang-Wei Huang, Hsiao-Hui Hung, Chang-Chi Chen
Keywordsperformance design, pushover analysis, multiple span bridge, dynamic time history,seismic assessment
AbstractStructural seismic design and seismic assessment are important issues in the sustainable development. Today, the concepts of performance-based design have been adopted in the building codes of European Union, Untied of States, Japan and other advanced countries. As a result, the performance-based seismic design provisions and commentary for highway bridges has also been introduced in Taiwan from 2009. The aims of the new seismic design provisions are to ensure the serviceability, retrofit, and safety of highway bridges under seismic hazards. In addition, the new seismic design provisions focus on the real responses of structures suffer from different levels of earthquakes, which can guarantee the new bridges, according to the performance-based design, achieving the reliability of anticipated targets and decreasing the damage ricks. In this paper, the draft of the new seismic design provisions for highway bridges is introduced and compared with other two existed method (ATC-40 and refined seismic assessment method). Pushover analyses with uniform lateral load pattern for four numerical multiple-span bridges are carried out. Then the pushover curves are transformed to the corresponding capacity spectrum curve with multiple monitoring points. Then the performance points are obtained by three seismic assessment methods and can be used to estimate the maximum lateral displacements. Compared with the results from nonlinear dynamic analyses, one can know the differences between three seismic assessment methods.

Vol.31/No.2 (122) (2016)

Vol.31/No.2 (122) (2016)

TitleThe seismic performance and crosstie unity of reinforced concrete columns using the lap-spliced crosstie under various axial loads
AuthorTai-Kuang Lee, Cheng-Cheng Chen
Keywordslap-spliced crosstie, RC columns, seismic performance
AbstractA lap-spliced crosstie consists of two J-shaped steel bars (rebars) that have a straight end and an end featuring a 180° hook. In this study, a lateral cyclic load test was conducted on four specimens of large-sized reinforced concrete (RC) columns to investigate the seismic resistance capability and crosstie unity of RC columns comprising lap-spliced crossties under various axial loads. The research results are presented as follows: (a) The ductility of the specimens that adopted the lap-spliced crossties was comparable to that of the specimens using crossties featuring a 180° hook on the two ends. (b) Without axial load, the straight end of the J-bars did not slip toward the inside of the column, suggesting that two J-bars were effectively spliced to be a crosstie featuring a 180° hook on its two ends and maintaining good unity. (c) The ductility of RC columns comprising lap-spliced crossties and crossties featuring a 180° hook on the two ends is significantly decayed with increasing axial load ratio.
TitleSeismic Behavior of Exterior Beam-Column Joints with Headed Bars
AuthorKer-Chun Lin, Chien-Kuo Chiu, Kai-Ning Chi
Keywordsbeam-column joint, headed bar anchorage length, shear of the panel zone
AbstractThis paper presents the seismic behavior of 12exterior RC beam-column joint specimens that headed bars were adoptedas main bars of their beam members and anchored into theirpanel zone. Two types of net spacing of 2 times and 2.2 times diameter of headed bars were used. All specimens meet the requirements of the strong column-weak beamof the ACI 318-11 Code.Other main parameters included the anchorage lengths of headed bars and the shear demand-to-capacity ratioof the panel zone.The results showed that when the net spacing of headed bars used 2.2 times their diameter and anchorage lengthplaced long enough, the seismic performance of specimen that used headed bars was so well as that of using the standard 90-degree hooked bars.It proved an applicability of the headed bar replacing the hooked bar. Based on seismic assessments of ACI 374.1-05 and proposed by this paper, assessed results indicated that specimens with net spacing of 2 times diameter of headed bar were able to meet their assessed criteria of strength, stiffness and dissipating energy at 4% radian of drift ration as long as the anchored length of headed bar satisfied the development length stipulated in ACI 318-11. However, a specimen with an unexpected failure mode of shear friction slide was excluded. Analysis results of specimen strengths presented that if anchored lengths of headed bar exceeded the development length of headed bar required by the ACI 352-02 Code, the developing average stress of the headed bars was able to reach 1.25 times its nominal yield stress of seismic design requirement.
TitlePreliminary Seismic Evaluation of School Buildings Retrofitted with Reinforced Concrete Jacketing
AuthorLap-Loi Chung, Sheng-Hsueh Lin, Yao-Sheng Yang, Shyh-Jiann Hwang, Fu-Pei Hsiao, Tsung-Chih Chiou, Lai-Yun Wu, Yu-Chih Lai
Keywordsschool building, reinforced concrete jacketing, preliminary evaluation, in-situ test
AbstractPreliminary evaluation is an important screening procedure for the seismic performance of school buildings so that the magnitude of the problem of seismic deficiency of school buildings can be reduced effectively. According to the seismic zone, importance factor and dimension of the vertical members in the first floor, seismic capacity and demand of a school building can be evaluated. Base on the score (capacity to demand ratio), the priority of the school building to enter into the stage of detailed evaluation is determined. However, a simple and quick evaluation method for the school buildings after retrofit has not been proposed yet. In this paper, a preliminary evaluation method is developed for the school buildings retrofitted with reinforced concrete jacketing. First of all, lateral strength of the reinforced concrete jacketing region per unit cross sectional area is established. Experimental results of two structures are adopted to investigate the feasibility of the proposed method including material strength, ultimate base shear strength, allowable ductility ratio, weight of building, fundamental vibration period and basic seismic performance. After comparison, the preliminary seismic evaluation for school buildings retrofitted with reinforced concrete jacketing proposed in this paper is effective and conservative. Before retrofit design, the amount of retrofit can be estimated by this method. After retrofit design, the rationality of the design can be confirmed by this method.
TitleDevelopment and Cyclic Tests of Circular RC Columns Confined with a GFRP-Wrapped Spiral Corrugated Tube
AuthorChung-Che Chou, Kai-Yi Wu, Chung-Sheng Lee
KeywordsGlass Fiber Reinforced Polymer (GFRP), Spiral Corrugated Tube, Confined Reinforced Concrete Column, Seismic Tests
AbstractThis paper presents the cyclic behavior of novel circular reinforced concrete columns confined with a FRP-Wrapped Spiral Corrugated Tube (FWSCT). In order to analyze the behavior of FWSCT concrete columns in axial and lateral loads, a load-displacement analysis program was also developed by the authors. Three specimens that had no transverse hoops were constructed and tested under small and large axial loads to investigate their seismic performances. Specimen FWSCT-0 was confined with only a spiral corrugated tube without Glass Fiber Reinforced Polymer (GFRP); Specimens FWSCT-5 and FWSCT-8that were made in Taiwan were confined with 5 and 8 layers of GFRP, respectively. Test results showed that Specimen FWSCT-0 experienced shear failure, while Specimens FWSCT-5 and FWSCT-8 exhibited rupture of longitudinal steel bars at story drifts of 6% and 8%, respectively. It was also found that the plastic hinge of the new column was developed on both ends of the column gap and extended into the footing. The analytical program reasonably predicts test results by using the observed plastic hinge length.
TitleSeismic Design, Tests and Analysis of a Full-scale Two-story Reinforced Concrete Frame with Buckling-restrained Braces – Part I: Specimen Design and Seismic Tests
AuthorHsun-Horng Yang, Jie-Luen Huang, An-Chien Wu, Chao-Hsien Li, Ching-Yi Tsai, Kung-Juin Wang, Keh-Chyuan Tsai
Keywordsreinforced concrete frame, buckling-restrained brace, steel embedment, hybrid test, seismic design, softened strut-and-tie model
AbstractBuckling-restrained braces (BRBs) have been widely used nowadays in steel structures as it can provide high stiffness, strength and ductility without compression buckling. Researches on using BRBs for seismic retrofit of existing reinforced concrete (RC) buildings have been reported. It is found the construction of BRB and RC member interfaces are often difficult, mostly due to the tensile and shear strengths of post-installed anchors in concrete are limited. As a result, the size and effectiveness of the BRBs are restricted. Nonetheless, researches on applying BRBs for new RC constructions are rather limited. This research investigates the seismic design and analysis methods of using the proposed I-shape steel embedment as the interface for the BRB and RC members. Steel embedment is designed to transfer the BRB normal and shear forces in order to secure the seismic performance of the RC buildings. In this study, a full-scale two-story RC frame with BRBs (BRB-RCF) is tested using hybrid and cyclic loading test procedures. The BRBs are arranged in zigzag configuration. The design of gussets incorporates the BRB axial and RC frame actions, while the beam and column members comply with ACI 318-14 seismic design provisions. The results are divided into two papers to discuss the design and construction methods of the steel embedment, seismic performance of the BRB-RCF, and seismic responses of the BRBs, gussets and RC members. A typical PISA3D numerical model of the BRB-RCF was constructed to predict the test responses and select the earthquake ground motions for hybrid tests. Analytical results indicate that the seismic responses of the BRB-RCF can be satisfactorily predicted only under the small earthquake. After all tests, a calibrated PISA3D numerical model is validated. It is illustrated with details in the Part II paper that the experimental responses of the BRB-RCF can be accurately simulated using the proposed procedures.
TitleSeismic Design, Tests and Analysis of a Full-scale Two-story Reinforced Concrete Frame with Buckling-restrained Braces – Part II: Test Results and Response Analysis
AuthorHsun-Horng Yang, Jie-Luen Huang, An-Chien Wu, Chao-Hsien Li, Ching-Yi Tsai, Kung-Juin Wang, Keh-Chyuan Tsai
Keywordsreinforced concrete frame, buckling-restrained brace, steel embedment, hybrid test, gusset buckling, nonlinear analysis
AbstractSeismic design and analytical response predictions of the full-scaled two-story BRB-RCF are introduced in the Part I paper. This Part II paper discusses the experimental observations, test results and analytical simulations using a refined PISA3D model. In the 50/50 earthquake, the ratios of peak BRB and BRB-RCF shear are 52% and 71% for the first and second stories, respectively. Similar ratios can be obtained if a factor 0.7 is applied on the gross moment of inertia for RC members in the ETABS elastic model. In the 10/50 and 2/50 events, the ratios become about 60% and 70% for the first and second stories, respectively. These indicate that BRBs can provide a high lateral stiffness and strength. The hysteresis energy dissipated ratios in the four hybrid tests are ranging from 60% to 94% for the two stories, confirming that BRBs can effectively dissipate seismic input energy. When the 2.75% inter-story drift ratio (IDR) cycles were completed during the cyclic loading test, the cumulative plastic deformations were more than 476 and 680 for the first- and second-story BRBs, respectively. When both two stories reached an IDR of 3.5%, the frame’s lateral force versus deformation response was still very stable. Up to the first IDR=4.5% loading cycle, the first story top gusset buckled, caused the subsequent flexural buckling of the first story BRB to occur. This is consistent with the predicted results as this gusset’s demand-to-capacity ratio DCR is 1.05 for the buckling limit state when the effective length factor Kcr=2.0 is considered. Nonetheless, the buckled BRB have a DCR=0.95 in the steel casing. No failure of the steel embedment is observed in the tests. Test results confirm that the ACI provisions and the simplified softened strut-and-tie model can be effectively applied to prevent the RC discontinuity region failure. This study demonstrates that the proposed design and construction methods for the steel embedment are effective and practical for the real applications. The response analysis of the refined PISA3D model calibrated from using the test results is conducted to demonstrate the accuracy enhancement compared to the typical model.

Vol.31/No.1 (121) (2016)

Vol.31/No.1 (121) (2016)

TitleDevelopment of Windows-Based Automatic Design and Drawing Integrated System on Prestressed Concrete Bridges
AuthorPing-Hsun Huang, Chi-HengChiang, Shu-Jen Chi, Yu-Chi Sung, Chun-Ying Wang, Jim-Ming Nian,Yu-Yang Lai, Yun Chuang, I-Chau Tsai
KeywordsPrestressed Concrete Bridge, Windows-based platform, Visual C# .NET
AbstractPrestressed concrete bridge is the commonly used type of bridges in Taiwan. According to the planning considerations of this bridge, the longitudinal and cross-section analysis results need to be checked repeatedly in the design process to determine the span lengths, cross dimensions, load combinations, working procedure restrictions, tendon profiles and tensioning sequences, etc., and the interrelated work activities of engineering drawing, structural computation statement and quantity estimation would be very complicated and cumbersome. Hence, once the civil engineering drawing software has been connected with structural analysis program, the design process can be expedited to identify sketches and quantities automatically. As a consequence, based on the basic design theory and construction methods of prestressed concrete box girder bridge, this paper aims at progressing an automatic design and drawing system performed by the Visual C# .NET programming language and further development technology of AutoCAD. As practical bridge design course, the window-based platform and devisable results presented in this paper are expected to provide a useful perception in structural engineering.
TitleLateral Load Displacement Curves of Low-Rise Reinforced Concrete Shear Walls
AuthorPu-Wen Weng, Yi-An Li, Ren-Jie Tsai, Shyh-Jiann Hwang
Keywordsreinforced concrete, shear wall, lateral load displacement curve, shear strength, shear deformation, low-rise
AbstractReinforced concrete shear wall is commonly used as a structural member and possesses the characteristics of high stiffness and strength. During earthquake attacks, shear walls usually receive the major lateral forces and are prone to fail in shear. Therefore, prediction of the lateral load displacement curve of shear walls is essential for the seismic assessment of existing buildings. In accordance with the Technology Handbook for Seismic Evaluation and Retrofit of School Buildings published by National Center for Research on Earthquake Engineering, this paper employs the Softened Strut-and-Tie Model to estimate the seismic behavior of low-rise shear walls. By using the simplified strut-and-tie index and shear deformation estimated from the associated strain field at peak load, the proposed curve is greatly simplified and correlates well with the available test results. The current ACI 318-14 Code over-estimates the contribution of shear strength from the shear reinforcement and the proposed model can correct this drawback. In addition to predicting the shear strength of existing shear walls, the proposed model can also provide estimation of shear strength of RC infilled walls in new construction buildings. This application can assist engineers to evaluate accurately the influence of RC infilled walls on the seismic behavior of frames.
TitleSeismic Tests of Full-Scale Dual-Core Self-Centering Braces (DC-SCBs) and Sandwiched Buckling-Restrained Braces(SBRBs)
AuthorChung-Che Chou, Ping-Ting Chung, Yu-Tsen Cheng
KeywordsDual-core self-centering brace (DC-SCB), Sandwiched buckling-restrained brace (SBRB), Seismic tests
AbstractThis paper presentsseismic tests of full-scale dual-core self-centering braces (DC-SCBs) and sandwiched buckling-restrained braces (SBRBs). The DC-SCB has a flag-shaped hysteretic response with high axial stiffness and minimal residual deformation, exhibiting a self-centering mechanism. The SBRB like conventional BRBs has much higher energy dissipation capacity than the DC-SCB, but larger residual deformations are expected for structures equipped with SBRBs. The primary objective of the study was to conduct seismic tests that established a direct comparison basis between two DC-SCBs and two SBRBs designed with similar axial capacity and length. A total of DC-SCBs and SBRBs that were about 7.5 mlong and had maximum axial forces from 1500 to 6000 kN were tested to evaluate their cyclic behavior and durability. In general, these tests showed that the DC-SCB and SBRBexhibit robust cyclic performanceswith good deformation capacity and durability. The axial elastic and post-elastic stiffnesses of DC-SCB were around two and five times those of SBRB, indicating that DC-SCB is more effective to resist lateral forces than SBRB in structures. Some new buildings in Taiwan and China have adopted SBRBs as main earthquake-resisting members.
TitleDynamic Stability of Frictional Isolation Systems Excited by Simple Harmonic Waves
AuthorSheng-Hsuan Wang, Lap-Loi Chung, Yong-An Lai, Cho-Yen Yang
Keywordsfrictional isolation systems, simple harmonic waves, dynamic stability
AbstractAccording to the equivalent damping ratio formula of frictional isolation systems, the damping ratio becomes lower as the isolation displacement gets larger. Therefore, if the excitation is a simple harmonic wave with constant amplitude and ongoing input energy, then the displacement response of isolation systems will increase with time; on the contrary, the equivalent damping ratio of isolation system will decrease with time. The relationship between isolation displacement and damping ratio will make frictional isolation systems fall into the vicious circle and become dynamic unstable finally. To investigate the issue about dynamic stability of frictional isolation systems, we assumed the super-structure is rigid and the excitation is simple harmonic, and transformed the motion equation of isolation systems into the dimensionless form. We also set the response indices to help practical engineers preliminarily estimate the isolation design. Actually, real ground excitations will not make isolation systems dynamic unstable, but the vicious circle between displacement response and equivalent damping ratio of isolation systems is undoubted. For the reason that we proposed practical engineers take the characteristic into consideration to enhance the safety of isolation design.
TitleSeismic Vibration Control of Off-Shore Wind Turbines
AuthorLyan-Ywan Lu, Hsuan-Teh Hu, Tzu-Yao Lin, Bo-Hua Lin
KeywordsOff-shore wind turbines, seismic mitigation, mass damper, anti-resonance, energy dissipation, wind energy
AbstractSince Taiwan has one of the best wind-farms in the world, it is beneficial to develop renewable energy by using off-shore wind turbines. Nevertheless, since Taiwan is prone to earthquakes, the problem of seismic protection for the offshore wind turbines becomes an important issue. On the other hand, although current Taiwanese seismic design code is very stringent, it aims to ensure live safety in a major earthquake rather than the functionality of equipment in the structural system. In order to simultaneously ensure the safety and functionality of a wind turbine during a major earthquake, in this study, the possibility of using a mass damper (MD) system for mitigating the seismic response of offshore wind turbines is investigated. A MD system is established by introduced a soft and energy-dissipative layer between the nacelle and the supporting tower structure of a wind turbine. As a result, the interacting motion between the nacelle and underneath tower structure creates a significant anti-resonant phenomenon that is able to avert the seismic energy transmitted into the system. Different from a traditional tuned mass damper (TMD), the MD uses the mass of the nacelle itself as the reactive mass and its frequency may not be tuned to that of the structure. In this study, the seismic performance of a 5MW mono-pile off-shore wind turbine with the MD subjected to 16 seismic excitations is simulated. The simulation results have demonstrated that by properly selecting the MD parameters, i.e., the frequency and damping ratios, the acceleration of the nacelle and the base shear and moment of the supporting structure can be significantly reduced, as compared with a TMD-controlled or uncontrolled wind turbine. This implies that the MD technology is able to maintain the safety and functionality of a wind turbine in a major earthquake, simultaneously.