Seismic performance analysis of steel frame structures with separated three‐dimensional isolation

Distributed plasticity analysis of steel frame structures comprising non-compact sections

Application of “advanced analysis” methods suitable for non-linear analysis and design of steel frame structures permits direct and accurate determination of ultimate system strengths, without resort to simplified elastic methods of analysis and semi-empirical specification equations. However, the application of advanced analysis methods has previously been restricted to steel frames comprising only compact sections that are not influenced by the effects of local buckling. A concentrated plasticity formulation suitable for practical advanced analysis of steel frame structures comprising non-compact sections is presented in this paper. This formulation, referred to as the refined plastic hinge method, implicitly accounts for the effects of gradual cross-sectional yielding, longitudinal spread of plasticity, initial geometric imperfections, residual stresses, and local buckling.

In recent years, various seismic isolation devices have been developed to prevent earthquake damage to valuable art works. The purpose of this study is to develop a vertical seismic isolation system that both reduces the natural frequency and solves the problems of vertical seismic isolation systems in previous studies. In this study, we developed a vertical seismic isolator that supports the load with inclined springs without using vertical springs. A motor is mounted on the ball screw that constitutes the central axis of each crank mechanism. The vertical stiffness of this seismic isolator can be changed using the motor. In this study, the seismic isolation performance was improved by using the negative stiffness property to set the natural frequency lower. The vertical seismic isolation system was modeled using SimulationX. The characteristics of the vertical seismic isolation system were verified and its performance was evaluated by various experiments and simulations. The MBS model of the newly developed device was used to accurately simulate the loading characteristics of the vertical isolator such as negative stiffness characteristics. The performance of this vertical isolator was verified by vibration experiments and simulations assuming typical seismic waves in Japan. The average response factor of acceleration in the experiment was 17.8%, and the average response factor in the simulation was 15.9%, which exceeded the performance of the device in the previous study. Finally, in the resonance avoidance test, the acceleration of the top plate of the vertical base isolation system was reduced by 57% by using the vertical natural frequency adjustment mechanism to avoid resonance.

Shaking table test of space double-layer cylindrical reticulated shell with three-dimensional isolation bearing

The study analyzes the seismic performance of spatial steel frame structures by creating a three-dimensional nonlinear finite element model and designing vibration table model experiments. This is done to ensure the seismic performance of the steel framing-bracing system in spatial steel frame structures and to raise the level of seismic and disaster prevention technology of steel structures. The outcomes revealed that under the experimental load consisting of simulated seismic waves generated by the shaker, the initial natural frequencies of the bidirectional bracing arrangement in white noise in the X and Y-directions were larger, 53.18 Hz and 72.49 Hz, respectively. The decrease of the vibration frequency of the bidirectional bracing arrangement structure was smaller under the increase of the excitation acceleration. In El Centro seismic waves, Taft seismic waves and Wenchuan seismic waves, the changes of damping ratio, acceleration amplification factor and relative displacement of bidirectional bracing arrangement were smaller than those of unidirectional bracing arrangement. The bidirectional bracing was beneficial to the overall stiffness and seismic performance of the structure, and helps the steel frame structure to resist lateral displacement. At the same time, the bidirectional support was more favorable to the seismic performance if the support structure was arranged according to the wave, which could effectively reduce the strain. Under the simulated seismic action of the 3D non-linear finite element model, the finite element model results were tested by inputting the parameters of Wenchuan seismic wave, the fit between the finite element model results and the vibration table experiment results was high, and the acceleration time-course curve and displacement time-course curve were basically the same. The simulation errors of the maximum values of acceleration and displacement were 7.0% and 4.0%, and some of the larger errors were within the acceptable error range. This study provides reference and theoretical guidance for the research on the seismic performance of steel framing - bracing system under seismic action, which is conducive to the expansion of the application field of steel seismic structures.

Time domain intrusive probabilistic seismic risk analysis of nonlinear shear frame structure

A detailed nonlinear finite element analysis (FEA) model of a radial-ply truck tire, 295/75R22.5, has been developed using explicit FEA simulation software, PAM-SHOCK. For the validation of the model, the tire model predictions of contact patch area, vertical stiffness, and cornering characteristics, such as cornering force and aligning moment versus slip angle, at different vertical loads are in good agreement with available physical measurements. For complete vehicle simulations, a simplified rigid ring tire model is required for efficient analysis throughput. The behavior of such a tire model can be verified and improved by comparing responses with the developed FEA model. Moreover, the in-plane and out-of-plane tire parameters needed for the simplified rigid ring tire model could be virtually determined at various vertical loads by testing the FEA tire model instead of performing expensive tire parameters measurements. The in-plane and out-of-plane tire parameters are implemented into a simplified rigid ring tire model to perform durability tests. The durability tests are conducted to examine dynamic behaviors by using the FEA truck tire and the rigid ring tire models during running on a water drainage ditch at various vertical tire loads. The ditch is 12.0-cm (4.72-in) deep and lies in 45-degree angle against tire traveling direction. The dynamic responses such as vertical displacement, forces, and moments at tire center are predicted using both tire models. The results obtained from both models are in reasonable agreement.

Seismic performance of recentering energy dissipation bracing with pendulum in prefabricated steel frame structure systems

To improve the seismic design of steel frame structures, the empirical formula for evaluation of fundamental periods of steel frame structures was investigated and a new formula was presented in the paper. A total number of 36 moment resisting steel frame structures were selected for the statistical analysis, and all the structures obtained seismic response records during past earthquakes. The fundamental periods of all structures before damaged were identified by using ARX method, and the new empirical formula for fundamental period of steel frame structure was obtained through nonlinear least square regression. The result shows that the fundamental period of steel frame structure can be expressed in terms of the height to the power of 0.6 and multiplied by the modified factor 0.12. The proposed empirical formula can be referenced for the seismic design code revision, steel frame structures seismic design and related researches.

The seismic performance of braced steel frame was simulated by the finite element software ANSYS based on the passive energy-dissipation under the low-cycle repeated load and the time-history analysis under seismic load for the energy-dissipation braced steel frame structure, no-brace steel frame structure, and conventional braced frame structure. The energy dissipation and seismic performance of three kinds of frame were compared, the results show that the energy-dissipation braced structure can produce strong energy-dissipation control force to enhance energy dissipation capacity of the whole structure significantly, and weaken the seismic load of the main frame. It follows that the energy-dissipation braced steel frame can achieve the purpose of energy dissipation for structure, and has good seismic performance.

The rail vertical displacement of CRTSII slab track structure under vertical static loads was analyzed in this paper by using 1:1 full-scale track model, based on which the WJ-8 fastener vertical static stiffness was calculated, and the rationality of the fastener vertical stiffness values and the relationship between the values and load were studied. According to the beam-plate theory and beam-solid theory for slab ballastless track, a finite element analysis model of CRTSII slab track structure was established. The rail vertical displacement under the same case as test was calculated by using the measured fastener vertical stiffness value. The rationality of the method for testing and the fastener vertical static stiffness is verified through comparing the calculated values with experimental ones.

Mechanical behaviors of Tou-Kung in historic timber structures subjected to vertical load

PurposeIn recent years, three-dimensional (3D) seismic base isolation system has been studied extensively. This paper aims to propose a new 3D combined isolation bearing (3D-CIB) to mitigate the seismic response in both the horizontal and vertical directions.Design/methodology/approachThe new 3D-CIB composed of laminated rubber bearing coupled with combined disk spring bearing (CDSB) was proposed. Comprehensive analysis of constitution and theoretical derivation for 3D-CIB were presented. The advantage of CDSB is that the constitution can be flexibly adjusted according to the requirements of the bearing capacity and vertical stiffness. Hence, four different combinations of CDSB were designed for the 3D-CIB and employed to isolate nuclear reactor building. A comparative study of the seismic response in terms of seismic action, acceleration floor response spectra (FRS), peak acceleration and relative displacement response was carried out.Findings3D-CIB can effectively reduce seismic action, FRS and peak acceleration response of the superstructure in both the horizontal and vertical directions. Overall, the horizontal isolation effectiveness of 3D-CIB was slightly influenced by vertical stiffness. The decrease in the vertical stiffness of the 3D-CIB can reduce the vertical FRS and shift the peak values to a lower frequency. The vertical peak acceleration decreased with a decrease in the vertical stiffness. The superstructure exhibited a rocking effect during the earthquake, and the decrease in the vertical stiffness may increase the rocking of the superstructure.Originality/valueAlthough the advantage of 3D-CIB is that the vertical stiffness can be flexibly adjusted by different constitutions, the vertical stiffness should be designed by properly accounting for the balance between the isolation effectiveness and displacement response. This study of isolation effectiveness can provide the technical basis for the application of 3D-CIB into real engineering of nuclear power plants.

Infill walls consisting of materials such as hollow concrete, hollow clay and autoclaved aerated concrete bricks are not only preferred in reinforced concrete buildings but also in steel frame structures. It is a well-known fact that infill walls limit the displacement of frames under horizontal loads. However, they may also bring about certain problems due to being placed randomly in horizontal and discontinuously in vertical directions for some architectural reasons. Moreover, cracks in frame-wall joints are observed in steel frame structures in which ductile behaving steel and brittle behaving infill walls are used together. In this study, the effect of infill walls on steel frames has been investigated. In the steel frame structure chosen for the study, four different situations consisting of different combinations of infill walls have been modeled by using ETABS Software. Later, the pushover analyses have been performed for all the models and their results have been compared. As a result of the analyses done by using the equivalent diagonal strut model, it has been found out that infill walls limit the displacement of steel frames and increase the performance of a structure. However, it has been also determined that in the steel frame structure in which the infill walls have been placed discontinuously in vertical and asymmetrically in horizontal, infill walls may lead to torsional and soft story irregularities. As a result, it is possible to observe cracks in the joints of infill walls and steel frame, the deformation properties of which differ, unless necessary precautions are taken.

Base isolation is an effective seismic design strategy that has received considerable attention in recent decades. This research is dedicated to developing a response spectrum method (RSM) for analysis of base-isolated structures under seismic excitation. A novel analytical model consisting of a linear superstructure under equivalent base excitations is proposed in the present study. To determine the response spectra corresponding to the base excitations, termed as the base response spectra, a sufficient number of samples of base excitations comprising base responses need to be obtained through time-history analysis of the nonlinear base-isolated structure in conjunction with the Monte Carlo simulation (MCS). To improve the efficiency for each sample analysis, the recently proposed explicit time-domain method (ETDM) is utilized for fast analysis of the base acceleration and velocity responses with a dimension-reduced iteration scheme. Once the base response spectra are obtained, the mean peak values (MPVs) of structural responses of the linear superstructure can be conveniently evaluated through the complete quadratic combination (CQC) rule. A 4-story nonlinear base-isolated frame structure was analyzed to validate the effectiveness of the proposed analytical model and the feasibility of the present approach for seismic response analysis of nonlinear base-isolated structures.