Vol.31/No.3 (123) (2016)
| Title | A Practical Equation for Elastic Modulus of Concrete in Taiwan |
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| Author | W.-C. Liao, C.-C. Lin, Y.-W. Chan |
| Keywords | Concrete, Elastic Modulus, Aggregate, Compressive Strength |
| Abstract | Concrete 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. |
| Title | Performance-oriented two-stage design method for base-isolated structures |
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| Author | Lyan-Ywan Lu, Liang-Wei Wang, Ching-Huei Chen, Kuan Feng Lee, Tzu-Ying Lee, Chun-Chung Tsai |
| Keywords | base isolation, isolation design, performance objective, allowable isolator displacement, allowable base shear |
| Abstract | Base 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. |
| Title | Structural Isolation Design Procedure with Optimal Design Formula of Friction Coefficient |
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| Author | Sheng-Hsuan Wang, Yi-YoTsai, Lap-Loi Chung, Cho-Yen Yang, Pei-Shiou Kao |
| Keywords | isolation systems, frictional coefficient, optimal design procedure, isolation systems simulation |
| Abstract | According 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. |
| Title | Prediction of Lateral Load Displacement Curve of RC Wall with Openings Failing in Shear |
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| Author | Shyh-Jiann Hwang, Weng-Kin Lam, Ren-Jie Tsai, Chien-Chuang Tseng, Yaw-Shen Tu, Fu-Pei Hsiao |
| Keywords | lateral load displacement curve, reinforced concrete, shear deformation, shear strength, wall with opening |
| Abstract | There 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. |
| Title | Comparison of different bridge seismic assessment methods |
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| Author | Chang-Wei Huang, Hsiao-Hui Hung, Chang-Chi Chen |
| Keywords | performance design, pushover analysis, multiple span bridge, dynamic time history,seismic assessment |
| Abstract | Structural 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. |