Vol.35/No.2 (136) (2020)
| Title | Study of the Influence of Creep and Shrinkage on Concrete-Filled Steel Tubular Columns and Design Suggestions |
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| Author | Ya-Ju Yu, Jenn-ChuanChern, Wen-Cheng Liao |
| Keywords | CFT, creep, autogenous shrinkage, stress transfer,B4-TW creep and shrinkage prediction model |
| Abstract | Concrete-filled steel tubular (CFT) columns show not only high strength and high ductility but also exhibit favorable seismic performance. The primary intent of concrete infill is to increase lateral stiffness of member and delay the local buckling of the steel tubular. Once concrete is subjected to load, development of concrete creep begins. In order to maintain the equilibrium of forces of CFT section, part of axial load of concrete will be transferred to steel tubular which leads to the growth of steel stress. Furthermore, high strength self-consolidating concrete (SCC) with low water-to-cement ratio intensifies the rise of steel stress in CFT columns on account of high autogenous shrinkage.A three-dimensional finite element model of CFT column, which takes account of the phenomenon of concrete creep and shrinkage, is developed to evaluate stress transfer between concrete and steel in ABAQUS. B4-TWcreep and shrinkage prediction model is also applied to reflect a characteristic of high amount of paste in concrete mix designs in Taiwan owing to the soft nature of coarse aggregates. The analysis results show that under the condition of initial steel stress of 0.6݂௬, the final steel stress of CFT column is probably not qualified according to “Design and Technique Specifications of Steel Structures for Buildings” owing to the long term deformation of infilled concrete whether the load is eccentric or not. In the extreme case of high concrete compressive strength of SCC and high diameter to thickness ratio, the steel stress significantly exceeds the original design value with 0.33݂௬. It is suggested that relevant specifications should be revised accordingly in Taiwan. |
| Title | Preliminary Seismic Performance Evaluation Method of RC Buildings Considering the Corrosion Effect of Reinforcement |
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| Author | Chien-Kuo Chiu, Zong-Han Jhan, Yi-Jing Cai |
| Keywords | Preliminary seismic performance evaluation, Visual inspevtion, Deterioration de gree, Corroded reinforcement |
| Abstract | This research establishes a mechanical evaluation model of a corroded RC member and reduces its plastic hinge capacity on the basis of the past research project. In addition to do the comparison and verification with the relevant experiment data, this research collects the general information of the size of column members and reinforcement arrangement in a typical reinforced concrete building and street house for investigation on the reduction factor of strength. Restated, the reduction factor of strength can be used to consider effect of the deterioration or corrosion in the strength or seismic capacity for a corroded RC column member. Therefore, this work can provide a preliminary seismic performance evaluation method for a corroded RC building structure. Additionally, for a corroded column member, its reduction factor of strength is determined based on the deterioration degree, which can be judged based on the visual inspection of deterioration following the technical textbook of the durability assessment of deteriorating RC building structures. Finally, taking an existing school building for an example, TEASPA which is established by NCREE is used to evaluate the seismic performance considering the corrosion and verify the application of the proposed preliminary seismic performance evaluation method for a corroded RC building structure. |
| Title | Verification of Preliminary Seismic Evaluation Methods Using the Damaged Building Data of 2018 Hualien Earthquake |
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| Author | Yi-Hsuan Tu and Tung Yeh |
| Keywords | earthquake damage, seismic evaluation, preliminary evaluation, reinforced concrete |
| Abstract | Data of thirteen buildings that damaged differently in the 2018 Hualien earthquake were collected and used to verify three preliminary seismic assessment methods. The three methods are all widely used in Taiwan, including the Preliminary Seismic Evalureliminary seismic evaluation of RC Buildings (PSERCB), the Preliminary Seismic Evaluation Method for Typical Building Structures of Primary and Secondary Schools by NCREE, and the Preliminary Seismic Evaluation Method for Typical Street-houses by NCREE. Comparison between the evaluation results and the observed damage states of the thirteen buildings showed that all three methods can identify the buildings that were heavily damaged. All three methods can sort the buildings in an approximately reasonable order. However, all three methods tended to give conservative results. The results from different methods for the same building were usually close. Only two buildings obtained different results between the NCREE method for street-houses and the other two methods. The PSERCB and the NCREE method for school buildings showed more conservative results than the NCREE method for street-houses in the two buildings. |
| Title | An approach for probabilistic seismic performance assessment of buildings considering multiple performance levels |
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| Author | Lyan-Ywan Lu, Fu-Pei Hsiao,Yu-Shi Tang,Yin-Nan Huang,Ching-Huei Chen, Kuan Feng Lee |
| Keywords | seismic performance assessment, probabilistic assessment, multiple performance levels, isolated building, performance design, incremental dynamic analysis, nonlinear time history analysis, plastic hinge |
| Abstract | Most of current seismic assessment methods for buildings aim to evaluate the collapse risk of buildings, since the damage criteria of these methods are associated with the mechanism of building collapse. These methods may not be suitable for the assessment of functional facilities or seismic isolated buildings, whose performance objective is usually required to maintain their functionality after a strong earthquake. For this reason, this study proposes an approachfor probabilistic seismic assessment of buildings considering multiple performance levels. This approach adopts the performance levels defined by FEMA 356 and ASCE 41-13, namely, immediate occupancy (IO), life safety (LS) and collapse prevention (CP). For each performance level, both global and local damage criteria are defined according to FEMA 356 and ASCE 41-13, respectively. Based on these damage criteria together with the result of incremental dynamic analysis, the fragility curves for each performance level can be established for seismic assessment. For buildings with isolators, a performance level called isolation limit (IL) is also considered, in order to include safety of the isolation system in the assessment procedure. The damage criterion for IL performance level is defined as when the isolator drift exceeds the maximum total isolator displacement given in the current isolation design code of Taiwan. For demonstration of the proposed assessment method, a 5-story old apartment building was consideredas an example. The building was retrofitted by using sliding isolators, and the seismic performance of the building before and after the implementation of isolation was evaluated using the proposed method and the results were compared, so that the benefit of retrofitting can be quantified. Theassessment results show that the retrofit with the isolators greatly reduces the damage probabilities of the building at all performance levels. This demonstrates that the proposed method can be applied to evaluate seismic performance of either fixed-based or isolated building with consideration of multiple performance levels. |
| Title | Seismic evaluation and strengthening methods for fire protection sprinkler piping systems in hospitals | ||
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| Author | Yung-An Tsai, Fan-Ru Lin, Juin-Fu Chai, Kuo-Chun Chang | ||
| Keywords | Fire protection sprinkler system, fragility curve, numerical analysis, simplified assessment, seismic strengthening design | ||
| Abstract | In recent years, due to the vigorous development of performance design concepts, the seismic capacity of critical building structures (such as hospitals and high-tech factories) has been improved, and the major disasters and economic losses caused by the earthquake have changed from structural to non-structural systems, which include piping systems. This study takes the medium-scale hospital in Southern Taiwan as an example to discuss the effects of installing strengthened elements on sprinkler piping systems which recommended by NFPA13. First, this research uses detailed analysis results to construct the fragility curves, and compares the fragility curves between before- and after-strengthened systems. Second, according to the dynamic characteristics of the sprinkler piping system, the simplified assessment method of original system and strengthened system are proposed in this study. It provides engineers with an alternative, rapid and approximate judgment in the seismic performances of piping systems based on in-situ observations and generic floor response spectrum. |