Van Tu Nguyen

The time-history analysis is an important approach in the seismic-resistant design of structures, especially in the increasing use of performance-based seismic designs and seismic protection systems exhibiting nonlinear responses. This method requires input acceleration time-histories that match the seismic characteristics of the site and satisfy the application requirements specified in the design code. This paper focuses on the procedure of selection and scaling artificial accelerograms and natural accelerograms to meet the requirements of Vietnamese code TCVN 9386-2012. The determination of the horizontal elastic response spectra, the application requirements, and the matching criteria specified in the code are first outlined. A proposed procedure of selection and calibration of the time-history accelerations is presented in detail. A typical example is conducted to select and scale a set of accelerograms for a specific seismic region in Vietnam to illustrate the proposed method. The concordance of the calibrated accelerations is validated by matching the response spectral of considered acceleration and the target spectrum and comparing seismic responses between the modal spectral analysis and time-history analysis of two typical linear and nonlinear structures. The results show the high reliability of the proposed procedure and great efficiency in matching the acceleration.

Performance-based design is currently widely applied in the seismic-resistant design of building structures. This approach allows the presence of inelastic deformation in several structural components to dissipate the seismic energy transferred to the building. The paper aims to investigate the inelastic behavior of reinforced concrete structures of a multi- story building subjected to earthquakes. Kent and Park’s model is used to simulate the nonlinear behavior of concrete, including the effect of the confined concrete of column structures. The nonlinear model of Giuffre-Menegotto-Pinto presents the reinforcement behavior. The parameters of the materials used in the modeling are determined from a calibration of the available experimental results by the optimal parameter analysis method. The building structure is modeled by OpenSees software, analyzed with three time-history acceleration records that are selected and scaled to match the target spectrum of a specific location in Vietnam. The seismic inelastic behavior of structures is investigated by the strain-stress relationship response of typical cross-sections of considered columns. The obtained results show the high efficiency of the optimal parameter analysis to accurately identify the behavior model parameters of the reinforcement. Further, the considered models present good effectiveness for the inelastic analysis of reinforced concrete buildings.

The paper presents the seismic analysis method of the reinforced concrete multi-story buildings employing Mander’s nonlinear model for confined concrete behavior and bilinear model for reinforcement behavior. The action of earthquakes on the building is analyzed by using the time-history analysis method. The building structures are modeled by the finite element method based on the OpenSees software. The obtained responses of the internal forces, displacements, strain, and stress are highly consistent with the considered model suggesting that it is practically effective for the seismic-resistant design of the reinforced concrete buildings.

Elastomeric isolation bearing is one of the most commonly efficient devices and widely applied for protecting constructions in the earthquake regions. Its significant lateral deformation during operation, however, may affect its load-carrying capacity, especially the stability of the bearing. The current preliminary design method often focuses on shear behavior without effects of vertical stiffness and stability conditions that do not reflect the practical operation of devices. The paper presents the effect of vertical stiffness and buckling behavior on the seismic performance of lead-rubber bearing (LRB) used for seismic isolation in multi-story buildings. The effective parameters of LRB are estimated by the single-mode spectral analysis method, through a bilinear model, calculated by a typical target spectrum of Eurocode 8. A two-spring equivalent model is employed to study the effects of the vertical stiffness and critical buckling load that is varied as a function of lateral deformation. A set of time history nonlinear analysis is conducted to investigate the effects of vertical stiffness and critical buckling load on the seismic responses of building structures. The findings show the taking into account of the vertical stiffness and buckling behavior results in an increase of lateral displacements and a decrease of the lateral force and the floor acceleration of the isolated building.

Multi-story buildings are important components of urban infrastructures due to their undeniable advantages. However, their structures are characterized by the mass distributed in height and a great slenderness leading to its earthquake vulnerability. Further, their typical structures designed by the conventional method provide low earthquake resistance. The seismic isolation bearings are considered as an effective solution for the structure located in regions of high and moderate seismic activity. The paper presents the procedure to calculate the isolated building structure located in the moderate seismicity areas such as Vietnam. The bilinear hysteretic model is employed to determine the properties of the isolator through the simplified procedure. Three-dimensional model of a typical 11-story building structure is analyzed to evaluate the effect of the isolator on seismic responses of building. The modal analysis and time history analysis are performed using Etabs V17, with the input record taken according to the earthquake ground motion in Hanoi-Vietnam, calculated by the Vietnamese code. The result shows the high effectiveness of isolator on reducing the seismic effect.

The paper presents the analysis of using tuned mass damper system for reducing the response of structure subjected to lateral force, such as earthquake action. The assumed steel eight-story steel frame building is examined. The tuned mass damper system is modeled as 2 joint link in SAP2000, attached to top story of the building. The effect of tuned mass damper system for building under seismic excitation was evaluated by the results of maximum displacement and acceleration of the building. A sensitivity study was also performed to compare the structural response with different mass ratios. From the calculated results, discussions and conclusions are presented.

The paper presents the method of the refined second-order plastic hinge analysis for planar steel frames subjected to dynamic loads. The material model used is the generalized Clough model in consideration of effects of axial and shear force on plastic limit state of cross-sections. Geometric nonlinearities of member and frame are taken into account by the use of stability functions in framed stiffness matrix formulation. Non-linear motional equation of structures was established by finite element method and solved by Newmark method combined with the modified Newton-Raphson method. Based on the obtained algorithms, the author has programmed a computational program and calculated the planar steel frames. From the calculated results, discussions and conclusions are presented.