Aseismic Analysis Research Articles

Investigation on Improved Optimal Fixed Time Step in Time-History Analysis for Aseismic Design of High-Speed Railway Bridge-Track System

ABSTRACT Time-history analysis is currently the main approach to the aseismic design of high-speed railway, and the time step significantly affects the calculation efficiency and accuracy. A 5-span high-speed railway bridge-track system was used as an example in this study. The effect of different fixed time steps on maximum seismic response was analyzed. An approach of improved optimal fixed time step was proposed by introducing maximum frequency and sampling frequency multiple. According to the research findings, for a specified ground motion record, the calculation error and efficiency of the improved fixed time step decrease with the increasing sampling frequency multiple. For a specified sampling frequency multiple, the calculation efficiency decreases with the increasing high-frequency components in ground motion record. The calculation error of secondary sampling signal for random ground motion records approximately obeys the normal distribution, and a stable and deterministic upper bound can be constructed based on the random sample of calculation error. The sampling frequency of secondary sampling signal in aseismic analysis for high-speed railway bridge-track system should be set as 4fmax. The improved optimal fixed time step should be set as (4fmax)−1 to simultaneously satisfy both the calculation error and efficiency requirements.

MVLEM MODEL DEVELOPMENT BASED ON ABAQUS AND ITS APPLICATION IN ASEISMIC ANALYSIS OF RC SHEAR WALL

Multiple-vertical-line-element model (MVLEM) is usually used in aseismic analysis of reinforced concrete shear walls. Based on ABAQUS, the multiple-vertical-line-element model (ABA-MVLEM) was developed. The suitable constitutive model of concrete and steel bars for a fiber beam element was established, the origin-oriented hysteresis model was developed, and the parametric modeling program of ABA-MVLEM was carried out. To verify the accuracy of the model provided, the low-cycle reversed loading tests were conducted on three RC shear walls. Comparing the numerical simulation results with the test data shows that the model (ABA-MVLEM) has high simulation accuracy and can meet the requirements of engineering precision. In the aseismic research of RC shear walls, ABA-MVLEM model can represent the structure's overall response and obtain detailed analysis results from the material level. The model has the advantages of high computational efficiency and visualization of simulation results. Furthermore, the influence of aspect ratio and axial compression ratio on aseismic performance of RC shear wall were explored through this model. The results show that: under the same lateral displacement, the bearing capacity of the RC members decreases significantly with the increase of the aspect ratio, but the stiffness degradation is gentle. The bearing capacity of the members with a small aspect ratio increases more obviously with the increase of axial compression ratio n in the case of n≤0.5.

Time-history simulation of civil architecture earthquake disaster relief- based on the three-dimensional dynamic finite element method

Earthquake action is the main external factor which influences long-term safe operation of civil construction, especially of the high-rise building. Applying time-history method to simulate earthquake response process of civil construction foundation surrounding rock is an effective method for the anti-knock study of civil buildings. Therefore, this paper develops a civil building earthquake disaster three-dimensional dynamic finite element numerical simulation system. The system adopts the explicit central difference method. Strengthening characteristics of materials under high strain rate and damage characteristics of surrounding rock under the action of cyclic loading are considered. Then, dynamic constitutive model of rock mass suitable for civil building aseismic analysis is put forward. At the same time, through the earthquake disaster of time-history simulation of Shenzhen Children’s Palace, reliability and practicability of system program is verified in the analysis of practical engineering problems.

Aseismic Analysis on Separation Joint of Atrium Roof and Connection Modes with Tower

The atrium roof system of shared space concerning large public buildingsis studied in this paper. The steel truss roof is wrapped with glass curtain wall which is relatively flexible and it is connected to the tower which is relatively rigid. Different separate means of the atrium roof as well as different connection modes between atrium roof and tower have great effect on mechanical performance of the whole structure. By comprehensive comparing various schemes of atrium roof and connection modes with tower, the internal force, displacement, modal as well as other parameters of roof and tower have been studied. The optimal connection scheme is also determined, which has good reference value for practical projects.

OPERATIONAL MODEL IDENTIFICATION AND CALIBRATION OF CFST ARCH BRIDGE BASED ON AMBIENT EXCITATION

To conduct the aseismic analysis of concrete-filled steel tube (CFST) arch bridges,the initial finite element model of a practical and operational CFST arch bridge is derived. Meanwhile,a more accurate and up-to-state dynamic analysis model for aseismic analysis can be derived through the modal identification and calibration techniques. Thus,this paper is to bridge the gap between the health monitoring techniques and aseismic analysis for large-span bridge structures. With the employment of the ambient response histories from a health monitoring system of this bridge,the operational modal parameters are identified by the FDD method,the FE model has been calibrated using a zero-order approximation method then. Results show that the FDD method can well identify the modal parameters and satisfactory results are observed in using the zero-order approximation method for the model calibration. The error between calculated and measured frequencies can be reduced to 0.11%~3.76%,and the variations of material properties (8.77%~10.21%) have significant effects on the structural dynamic behavior. The calibrated model,reflecting the practical state of a structure,can be used to assess the aseismic behaviors of operational bridge structures in the further.

Seismic Time-History Analysis of Gravity Dam Based on Nonlinear Finite Element Method

A cohesive model (CM) was introduced in this paper. The constitutive response of cohesive behavior depends on a traction-separation description characterized by the initial stiffness, damage initiation threshold, and damage evolution properties.Through the aseismic analysis of a gravity dam, the displacement, stress and anti-sliding safety factor were discussed in the paper, the results were also compared between elastic model (EM) and plastic model (PM). The results shown that the displacement amplitude computed by PM and CM was nearly twice larger than that by EM, and the area of stress concentration became not so obvious. The cohesive model could efficiently simulate the discontinuous structure and the responses of seismic computed by PM and CM were more correspond to actual situation.

Aseismic Analysis on a Strengthened Chinese Ancient Building by Simulation

In order to protect Chinese ancient buildings,a Qing Dynasty building in Sichuan province was taken as example to study its aseismic characters after strengthened. By ANSYS program,semi-rigid character of tenon-mortise joint as well as contact between wooden constitution and walls were simulated.Then by modal analysis basic frequency as well as main modes of the structure were obtained;By response spectrum analysis inner forces as well as displacements of the structure under 7-degree intensity of seldomly occurred earthquakes were obtained.Results show that after strengthened,main modes of the structure are of translation;Under 7-degree intensity of seldomly occurred earthquakes peak values of displacement as well as inner forces of the strengthened building are all within permissible scopes,which proves its good aseismic characters.

Structural optimization and dynamic analysis for double-layer spherical reticulated shell structures

This paper is concerned with the geometrical optimum design and the aseismic analysis of double-layer reticulated shell structures. The characteristic of free vibration of reticulated shell structures, with respect to geometric parameter, is investigated. The variations of the eigenfrequency of shell structures, with respect to the ratio of height-to-span, span, grid division frequency and thickness of shell, are discussed. The Newmark method is used to calculate the stresses and displacements of the reticulated shell structure under earthquake action. The analysis results show that under a specified span, the eigenfrequency of the structure increases with the increase of the height-to-span ratio and then decreases afterwards. Therefore, there exists an optimum height-to-span ratio resulting in an optimum stiffness at the specified span. The optimum value of the ratio is found to be between 1/3 and 1/4 from the simulation study presented in this paper. At a specified height-to-span ratio, the increase of the value of structural span greatly reduces the eigenfrequency of the structure and then decreases the global stiffness of the structure. At the specified span and the specified height-to-span ratio, the eigenfrequency of the structure has a minor increase with the increase of the thickness and the grid division frequency of the reticulated shell structure. The partial double-layer reticulated shell structures have less stability compared with double-layer reticulated shell structures, but more stability in comparison with single-layer reticulated shell structures. The 1/6 partial double-layer reticulated shell structure has a best performance-to-price ratio. In other words, it has a higher buckling load, with smaller material consumption, compared with other partial double-layer reticulated shell structures. It is proposed to adopt the 1/6 partial double-layer reticulated shell structure in engineering if a double layer reticulated shell structure is required.

Seismic Evaluation of Multi-Storey RC Frame Using Modal Pushover Analysis

The recently developed pushover analysis procedure has led a new dimension to performance-based design in structural engineering practices. With the increase in the magnitude of monotonic loading, weak links and failure modes in the multi-storey RC frames are usually formed. The force distribution and storey displacements are evaluated using static pushover analysis based on the assumption that the response is controlled by fundamental mode and no mode shift takes place. Himalayan-Nagalushai region, Indo-Gangetic plain, Western India, Kutch and Kathiawar regions are geologically unstable parts of India and some devastating earthquakes of remarkable intensity have occurred here. In view of the intensive construction activity in India, where even a medium intensity tremor can cause a calamity, the authors feel that a completely up-to-date, versatile method of aseismic analysis and design of structures are essential. A detailed dynamic analysis of a 10-storey RC frame building is therefore performed using response spectrum method based on Indian Standard Codal Provisions and base shear, storey shear and storey drifts are computed. A modal pushover analysis (MPA) is also carried out to determine the structural response of the same model for the same acceleration spectra used in the earlier case. The major focus of study is to bring out the superiority of pushover analysis method over the conventional dynamic analysis method recommended by the code. The results obtained from the numerical studies show that the response spectrum method underestimates the response of the model in comparison with modal pushover analysis. It is also seen that modal participation of higher modes contributes to better results of the response distribution along the height of the building. Also pushover curves are plotted to illustrate the displacement as a function of base shear.

Introduction of structural aseismic research in China in recent four years

The paper mainly summarized the developments on structural aseismic theory, aseismic analysis and design of reinforced concrete structure, lifeline system, several another kinds of structures, site and structure foundation, structure mitigation and isolation of vibration in China in recent four years. This is the introduction of recent research results of Chinese professionals for international organizations and professionals. At the same time, it provides numerous abstract materials for colleagues to realize the trend of the structural aseismic theory and research range needing more study.

A practical coherency model for spatially varying ground motions

Based on the discussion about some empirical coherency models resulted from earthquake-induced ground motion recordings at the SMART-1 array in Taiwan, and a heuristic model of the coherency function from elementary notions of stationary random process theory and a few simplifying assumptions regarding the propagation of seismic waves, a practical coherency model for spatially varying ground motions, which can be applied in aseismic analysis and design, is proposed, and the regressive coefficients are obtained using least-square fitting technique from the above recordings.

Inelastic response of multistory buildings under earthquake excitation

It is well recognized that structures designed to resist strong ground motions should be able to withstand substantial inelastic deformations. A simple procedure has been developed in this paper to monitor the dynamic earthquake response (time-history analysis) of both steel and concrete multistorey buildings in the inelastic range. The building is treated as a shear beam model with three degrees of freedom per floor. The entire analysis has been programmed to run on a microcomputer and can output time histories of displacements, velocities, accelerations and member internal forces at any desired location. A record of plastic hinge formation and restoration to elastic state is also provided. Such information can be used in aseismic analysis and design of multistorey buildings so as to control the damage and optimize their performance.

Aseismic Design of Reactor Enclosure of the Japan Power Demonstration Reactor (JPDR) and Its Actual Behavior for Earthquake

Being situated in a frequent seismic area, aseismic analysis of nuclear reactor to be constructed in this country are strictly required in its safety consideration. For the JPDR, Japan's first nuclear power station, we have analyzed, in its design stage, vibration characteristics of Reactor Enclosure Structure, for the factors such as natural period, damping accleration etc., to check the validity of static design earthquake coefficient. After completion of the plant, many seismic sensors have been mounted on various parts of the Enclosure Structure to observe its vibration characteristics during earthquake. Using the data obtained so far from actual earthquake, the natural period, location of rocking centers, etc. were calculated. The calculated values show good agreement with the above mentioned analytical results.

2076 高層ラーメンの耐震解析における柱軸方向変形の影響 : (第1報・1スパンの場合の4モーメント基本式)

2076 高層ラーメンの耐震解析における柱軸方向変形の影響 : (第1報・1スパンの場合の4モーメント基本式)