Seismic site characteristics of shallow sediments in the Bangkok Metropolitan Region,and their inherent relations

Bulletin of Engineering Geology and the Environment - This paper presents the site characteristics of soft deposits in Bangkok Metropolitan Region, and their inherent relations, which were explored...     

Alternative approach to compute shear amplification in high‐rise reinforced concrete core wall buildings using uncoupled modal response history analysis procedure

The seismic response of the high‐rise reinforced concrete (RC) wall structures is really complicated as several vibration modes other than the fundamental mode normally contribute significantly to the response—commonly recognized as ‘higher mode effects’. Response spectrum analysis (RSA) procedure, which can account for higher mode effects, is usually employed to compute the seismic design demand for the high‐rise structures. Recent studies show that the inelastic seismic force demands obtained from the rigorous nonlinear response history analysis procedure are much larger than the seismic force design demands obtained from the code‐based RSA procedure for the high‐rise RC wall structures. Though, the nonlinear response history analysis procedure is widely accepted for its ability to provide the most accurate estimate of nonlinear seismic responses, the obtained responses are generally so complex that it is quite difficult for engineers to grasp the overall picture of the responses and gain some insight into them and use them to understand the cause of high seismic demands. Another important issue related to the nonlinear seismic response prediction of the high‐rise RC wall structures is the realistic and accurate numerical modeling of RC walls. In this study, a simplified but reasonably accurate procedure called the uncoupled modal response history analysis procedure is used to interpret the complex nonlinear behavior of high‐rise RC wall structures. Moreover, a finite element model based on modified compression field theory is employed for accurate numerical modeling of RC walls by incorporating the axial‐flexure‐shear interaction. This study, by making use of a better computer modeling approach and an in‐depth analysis by modal decomposition, aims to resolve some of the unanswered questions regarding realistic prediction of nonlinear seismic demands of high‐rise structures.     

环形调频液体阻尼器（TLD）的计算模型

本文建立了液体在刚性环形容器内晃动的计算模型，这一模型可以用于调频液体阻尼器（ＴＬＤ）及结构─ＴＬＤ相互作用的研究。为了验证计算模型，进行了一系列的振动台试验，研究液体晃动第一振型的频率和动力反应。用模型计算的结果与试验结果符合良好，计算模型基本合理。     

用TLD减小电视塔动力反应的振动台试验研究

本文介绍了用环形调频液体阻尼器（ＴＬＤ）减小电视塔动力反应的模型结构振动台试验研究。结果表明，ＴＬＤ能有效地减小第一振型的位移共振反应；在地震激励下，ＴＬＤ减小峰值反应的效果不十分显著；但地震停止后，ＴＬＤ使模型结构的自由振动迅速衰减。     

Dynamic analysis of three-dimensional bridge–high-speed train interactions using a wheel–rail contact model

A formulation of three-dimensional dynamic interactions between a bridge and a high-speed train using wheel–rail interfaces has been developed. In the interface, contact loss is allowed, the vertical contact is represented by finite tensionless stiffness and the lateral contact is idealized by finite contact stiffness and creepage damping. Such stiffness and damping are nonlinearly dependent on normal contact force. The relative rotations of a wheelset to the rails about its vertical and longitudinal axes are included. Bridge eccentricities and deck displacement due to torsion are accounted for in bridge deck modeling. A numerical algorithm using separate integrations for bridges and trains, and iterations for interface compatibilities is established. A case study of a ten-car train passing over a two-span continuous bridge at various speeds and rail irregularity wavelength ranges is analyzed. The responses of the bridge, car-bodies and wheelsets are investigated for their behavior, acceptability and relations with the wavelengths. Analytical and numerical evaluations of resonant speeds are in good agreement, and the exit span vibration is more amplified than the entrance one at those speeds. The computed relative displacements of all wheelsets to the rail facilitate an explicit assessment for derailment risk.     

Optimal reduction of inelastic seismic demands in high‐rise reinforced concrete core wall buildings using energy‐dissipating devices

Recently, the issue of large inelastic seismic force demands at severe ground shakings such as maximum considered earthquake level has been highlighted in the conventionally designed high‐rise reinforced concrete core wall buildings. Uncoupled modal response history analysis was used in this study to identify the modes responsible for the large inelastic seismic force demands. The identification of dominant modes and mean elastic design spectra of seven representative ground motions for different damping ratios has led to the identification of three control measures: plastic hinges (PHs), buckling‐restrained braces (BRBs) and fluid viscous dampers (FVDs). The identified control measures were designed to suppress the dominant modes responsible for the large inelastic seismic force demands. A case‐study building was examined in detail. Comparison of the modal as well as the total responses of the case‐study building with and without the control measures shows that all the control measures were effective and able to reduce the inelastic seismic demands. A reduction of 33%, 22% and 27% in the inelastic shear demand at the base and a reduction of 60%, 22% and 26% in the inelastic moment demand at mid‐height were achieved using the PHs, BRBs and FVDs, respectively. Furthermore, a reduction of about 30–40% in the inelastic seismic deformation demands was achieved for the case of the BRBs and FVDs. The study enables us to gain insight to the complex inelastic behavior of high‐rise wall buildings with and without the control measures. Copyright © 2011 John Wiley & Sons, Ltd.     

Investigating the vulnerability of nonductile reinforced concrete columns in moderate seismic regions to gravity load collapse

Reinforced concrete (RC) columns are important components of the lateral load‐resisting structural system of RC buildings. In moderate seismic regions, where stringent seismic reinforcement detailing requirements are usually not considered, RC columns are categorized as nonductile. Postearthquake studies have shown that gravity load collapse of RC columns can trigger the progressive collapse of RC buildings. The current study presents the seismic response behavior of nonductile RC columns in moderate seismic regions, with a particular focus on gravity load collapse. Six RC columns, three with lap splices and three without lap splices with variable aspect ratios, were tested under reversed cyclic loading. Experimental results show that the column failing in shear could tolerate the maximum drift in order of 2.7–3.5%, whereas the columns failed in flexural mode could achieve the maximum drift of 4.5%. For the columns with lap splice, the lateral strength was significantly degraded, but all spliced columns could sustain gravity load even when their displacements were more than 4% drift. This very large drift without axial collapse, observed in the current study, is associated with the splice slip causing the large rotation just above the splice region.     

A BEM formulation for inelastic transient dynamic analysis using domain decomposition and particular integrals

This study deals with the domain decomposition method and particular integrals for multi-region inelastic transient dynamic analysis. The particular integral formulation for single-region inelastic transient dynamic analysis is obtained by eliminating the acceleration volume integral and treating the initial stress term by volume cell. The Houbolt time integration scheme is used for the time- marching process. The Newton-Raphson algorithm for plastic multiplier is used to solve the system equation. In order to extend to multi-region problems, the domain decomposition method is examined. The domain of the original problem is subdivided into subregions. The interface boundary conditions are updated by using the iterative coupling employing Schwarz algorithm. Numerical results of two example problems are given to demonstrate the validity and accuracy of the present formulation.     

A modified response spectrum analysis procedure to determine nonlinear seismic demands of high‐rise buildings with shear walls

The standard response spectrum analysis (RSA) procedure prescribed in various design codes is commonly used by practicing engineers to determine the seismic demands for structural design purpose. In this procedure, the elastic force demands of all significant vibration modes are first combined and then reduced by a response modification factor (R) to get the inelastic design demands. Recent studies, however, have shown that the response of higher vibration modes may experience much lower level of nonlinearity, and therefore, it may not be appropriate to reduce their demand contributions by the same factor. In this study, a modified RSA procedure based on equivalent linearization concept is presented. The underlying assumptions are that the nonlinear seismic demands can be approximately obtained by summing up the individual modal responses and that the responses of each vibration mode can be approximately represented by those of an equivalent linear SDF system. Using 3 high‐rise buildings with reinforced concrete shear walls (20‐, 33‐, and 44‐story high), the accuracy of this procedure is examined. The inelastic demands computed by the nonlinear response history analysis procedure are used as benchmark. The modified RSA procedure is found to provide reasonably accurate demand estimations for all case study buildings.     

Prediction of nonlinear seismic demands of high‐rise rocking wall structures using a simplified modal pushover analysis procedure

This study presents a simplified analysis procedure for the convenient estimation of nonlinear seismic demands of high‐rise rocking wall structures. For this purpose, the displacement modification approach used in the nonlinear static procedure of ASCE/SEI 41‐13 is adopted. However, in the current study, this approach is extended to every significant vibration mode of the structure whereas the displacement modifying coefficients for different modes are calculated using the typical flag‐shaped hysteresis behavior of rocking walls. The parameters of this hysteresis behavior are selected to represent rocking walls with a practical range of energy dissipation capacity and postgap‐opening stiffness. The computed peak inelastic‐to‐elastic displacement ratios are presented as mean spectra, which can be used for the convenient estimation of pushover target displacement for every significant vibration mode. The accuracy of proposed procedure is examined using the seismic demands obtained from the nonlinear response history analysis of a 20‐story case study rocking wall structure. Furthermore, a modal decomposition technique is used to determine the individual modal seismic demands. The proposed procedure is found to predict both the combined and the individual modal demands with a reasonable accuracy and can serve as a convenient analysis option for the design and performance evaluation of high‐rise rocking wall systems.