Vol.29/No.2 (114) (2014)

作者:

Vol.29/No.2 (114) (2014)

TitleDesign of Shear Strength for Eccentric Beam-Column Joints
AuthorShyh-Jiann Hwang, Erwin Lim, Pu-Wen Weng, Hung-Jen Lee
Keywordsbeam-column joint, effective joint area, effective joint width, eccentric beam-column joint
AbstractThe current ACI 318-11 building code, which adopts many recommendations from ACI-ASCE Committee 352, defines the nominal joint shear strength of a beam-column connection as the product of the average shear stress capacity and the effective joint area. Past experience did indicate that the ACI 318-11 provisions on the effective joint width of the eccentric beam-column joints are too strict. This study critically evaluates four sets of effective joint width provisions, available in ACI 318-11, ACI 352R-02, AIJ Guidelines, and NZS 3101, as well as the companion provisions for average shear stress capacity. Comparisons and experimental verifications have been made among the code provisions; and more general expressions of effective joint width are proposed for design. The proposed effective joint width considers various sizes of rectangular joints and gives consistent strength estimations for both concentric and eccentric beam-column connections. Since the proposed effective joint width possesses the physical meaning of concrete crushing, it can be used both in the ACI 318-11 design method and the associated analytical procedures. Furthermore, based on available research data for concentric exterior (T-shaped) beam-column connection specimens, this study re-emphasizes engineers to extend beam longitudinal bars to the far face of the confined column core.
TitleVerification of seismic preliminary evaluation of school building with brick walls by in-situ test at kou-hu school
AuthorYao-Sheng Yang, Lap-Loi Chung, Tsung-Chih Chiou, Fu-Pei Hsiao, Wen-Ching Jaung, Shyh-Jiann Hwang, Lai-Yun Wu
Keywordsschool building, brick walls, preliminary evaluation, in-situ experiments
AbstractExisting school buildings in Taiwan are numerous and vulnerable under earthquakes so that economical and effective methods to screen those buildings with insufficient seismic capacity is necessary. Preliminary evaluation is a simple and objective screening stage in which seismic capacity and demand of an existing school building can be computed easily. The National Center for Research on Earthquake Engineering has conducted in-situ experiments in four schools. Preliminary evaluation of school buildings without brick walls has been validated. In Taiwan, school building with brick wing walls along the corridor direction is very common. In this paper, in-situ experimental results of a school building with brick walls at Kou-Hu Elementary School are adopted to verify the preliminary evaluation method. In this building, the cross-sectional area of brick walls is as much as that of columns. The material strengths, weight per unit floor area, ultimate base shear strength, fundamental vibration period, allowable ductility capacity and fundamental seismic performance from preliminary evaluation are compared with those from in-situ tests. From the comparison, preliminary evaluation is conservative in material strengths, ultimate base shear strength and allowable ductility capacity. Because of brick walls, preliminary evaluation underestimates the weight per unit floor area. Since the strength contributed by brick walls exceeds 30% of that contributed by columns, empirical formula with shortest vibration period stated in the seismic codes is adopted in the preliminary evaluation. However, it is still longer than the vibration period extracted from the in-situ results. As a whole, the fundamental seismic performance from preliminary evaluation is just 51.7% of that from in-situ experiment. Therefore, the proposed preliminary evaluation method is conservative and feasible.
TitleExperimental Study of Seismic Retrofitting of Low Strength Reinforced Concrete Columns
AuthorShuenn-Yih Chang, Ting-Wei Chen, Chung-Yi Lin, Hung-Yi Lo, Ngoc-Cuong Tran
Keywordslow strength, reinforced concrete column, seismic retrofit, column jacketing, wing wall, cyclic loading test
AbstractIn this paper, the low strength RC columns were seismically retrofitted and cyclically tested. Test results reveal that either the column jacketing or wing walls can effectively increase the lateral shear strength. In addition, The RC jacketing can have a better improvement in capability of energy dissipation and in ductility when compared to installing wing walls. RC jacketing not only increases moment and shear capacity but also results in a flexural failure mode. Thus, the ductility increases. On the other hand, although RC wing walls can increase shear capacity, the original column and the wing walls cannot be integrated together and experience shear failure independently. After yielding the maximum lateral strength, the stiffness and strength are rapidly degraded and thus the specimen results in poor ductility. Apparently, the hysteretic loops can be classified as a typical failure mode, where stiffness degrading and strength degrading in addition to pinching are found. The jacket around the original column can be considered as a hollow column and thus it can resist both flexural moment and shear force. Consequently, RC jacketing can effectively increase the resistance to moment and shear whether the connections between the original column and new jacket are good or not. It is anticipated that the post-installed anchors can integrate the new and existing concrete together to resist seismic force for RC wing walls. However, this goal cannot be achieved due to the low strength concrete. As a result, an independent shear failure is found for the original column and the two wing walls. Even so, it is evident that RC wing walls can still enhance the shear capacity due to the very good mechanism.
TitlePost-earthquake financial loss estimation of an individual RC building through numerical anlaysis
AuthorQiang Xue, Fu-Pei Hsiao, Tian-Hung Chiu, Tsung-Chih Chiou, Chyuan Jhang, Te-Kuang Chow, Jian-Huang Weng, Yeong-Kae Yeh, Cheng-Chung Chen, Lap-Loi Chung
Keywordsseismic performance, nonlinear analysis, loss estimation, repair cost
AbstractThis paper establishes a numerical method to estimate post-earthquake financial loss of an individual RC building. Through nonlinear analysis and seismic performance evaluation, structural behavior subjected to an earthquake excitation can be estimated. Corresponding damage degrees can be determined accordingly. Financial loss in terms of the repair to replacement cost ratio of the most severely damaged storey is estimated based on the post-earthquake damage degree. As a result, the repair cost is obtained and it is clear whether the building needs rehabilitation or rebuilt after demolition. Finally, we take an old building and a lately designed building as examples to establish correlation curves between the spectral displacement and the repair to replacement cost ratio of the most severely damaged storey through nonlinear static pushover analyses. The method proposed in this paper helps decision-making of lifecycle maintenance and management of existing buildings. It also provides a method to control post-earthquake damage consequence and risk for the next-generation of performance-based seismic design.
TitleDevelopment and Validation of a Cross-Anchored Dual-Core Self-Centering Brace: Seismic Test and Finite Element Analysis
AuthorChung-Che Chou, Ping-Ting Chung
KeywordsCross-Anchored Dual-Core Self-centering Brace (SCB), High-Strength Steel Tendons, Cyclic Test, Finite Element Analysis
AbstractThe steel dual-core self-centering brace (SCB) is a novel structural member that provides both energy dissipation and re-centering properties to structures under earthquakes. The axial deformation capacity of the brace is doubled by using two inner cores and one outer box and by serial axial deformations of two sets of parallel tensioning elements. A new cross-anchored dual-core SCB is proposed to reduce half the number of tensioning elements needed for applying the initial post-tensioning work compared to the original dual-core SCB, to investigate the potential use of high-strength steel tendons as tensioning elements, and to examinethe effects of number of cycles on the brace behavior, energy dissipation, and durability of the steel tendon-anchorage system.The mechanics and cyclic behavior of the new brace are first explained; a 7950-mm long cross-anchored dual-core SCB is tested six times. The cross-anchored dual-core SCB exhibits excellent self-centering property up to a lateral drift of 2.5% with a maximum axial load of 1700 kn. No damage of steel tendons, anchors or bracing members is found after three cyclic loading tests by AISC (2010) seismic provisions and 60 low-cycle fatigue tests. Finite element analysis is conducted to furtherverify the hysteretic responses and mechanics of the proposed cross-anchored dual-core SCB in the cyclic tests.
TitleTHE ANALYSIS AND DESIGN OF SHEZI BRDIGE IN TAIPEI
AuthorEng-Huat Teo, Chao-Sheng Huang, Ming-Yi Yu, Yew-Tsang Lin, Dyi-Wei Chang, Yu-Chi Sung
KeywordsCable-Stayed Bridge, Inclined Pylon, Rotating Method, Self-Anchored, Optimum.
AbstractBeing an asymmetric span configuration (180m+70m), the SheZi Bridge in Taipei was designed as an inclined pylon steel cable-stayed bridge.As the asymmetric span configuration has a ratio of main span to side span up to 2.57, the loading of the superstructure generated a huge unbalanced effect to the pylon and the girder. Therefore, the counterweight concrete was designed for unbalanced loading effect, and the inclined pylon and the optimization post-tensioning cable force analysis were used to reduce the unbalanced effects caused by the static load applied and for enhancing the aesthetics design. As the span has a length of 180m, we used a self-anchored cable system for this bridge. Though the static analysis result was used for structural design, the dynamic analysis was also required. For the dynamic analysis of this bridge, both the response spectrum method and the time history method were used. To verify the wind resistance of the bridge and to obtain the aerodynamic parameters, the cross section model and the full model for wind tunnel tests were done to ensure the performance of the bridge’s resistance to wind;and to make a comparison of the wind force during the design stage; and to double check the wind resistant design. In addition, to ensure the safety of the cable anchorage, the finite element analysis was done to verify the stress delivery. This article will take this bridge as an example, carry out the analysis and design of cable-stayed bridge with asymmetric span and inclined pylonhaving unique and difficulty, and provide as a reference for the engineering of related projects.