Sharif Digital Repository

A nonlinear seismic soil-pile-structure interaction (SSPSI) analysis of fixed offshore platforms constructed on pile foundations including both vertical and battered piles is presented. The analysis is carried out in time domain and the effects of soil nonlinearity, discontinuity at pile soil interfaces, energy dissipation through soil radiation damping, formation of soil layers on bed rock, structural material nonlinearity and geometrical nonlinearity are considered. A combination of FEM approach and BNWF approach is used in modeling pile (substructure), platform structure (superstructure) and soil media. Gapping in clay is modeled by a special connector configuration. To find out the... 

Seismic performance of a representative single-story confined unreinforced masonry school building in Tehran, Iran is evaluated by means of incremental dynamic analyses according to FEMA P-58 framework. For this purpose, fragility curves are derived for each of the constituent walls of the building. The in-plane behavior of the walls is considered only. Both flexible and rigid diaphragm conditions are investigated. For comparison purposes, the corresponding unconfined building exactly duplicating the considered confined unreinforced masonry building is also studied. In order to analyze the effects of near-source seismic actions on the performance of masonry buildings, two separate far-field... 

This paper discusses the time-varying characteristics of the output signals resulted from Linear Time Variant (LTV) systems using level-crossing properties. These systems, used for generating synthetic records based on a target record, contain two identification processes: 1) amplitude modulating function; and 2) time-varying Impulse Response Function (IRF) parameters. To track the IRF parameters efficiently, the zerocrossing and positive minima/negative maxima cumulative curves are usually utilized as the measures of the instantaneous spectral power. Using spectral moments, analytic relations for zero-crossing and positive minima/negative maxima cumulative count are developed with respect... 

This article introduces a new time-varying model to generate synthetic non-stationary acceleration records using the modified Kanaii-Tajimi model with time-variant parameters. The proposed method can capture two different dominant frequencies per time which makes it suitable for synthesizing the near-field no-pulse earthquake records. A number of closed-form relationships are developed to describe the frequency dependent time-domain level crossings of the simulated records under white noise excitation. The model parameters are optimized using the crossing and Arias intensity properties of the synthetic and target records. The efficiency of the proposed model is demonstrated using a data base... 

This paper introduces an efficient stochastic method to produce fully nonstationary records having multiple peaks in power spectrum. The zero-crossing characteristics of the acceleration, velocity, and displacement time histories of the output signal are used to estimate the model parameters. This procedure is utilized to resimulate 252 non-pulse-like, horizontal near-field records with rupture distance of less than 10 km and strike–slip mechanism. The model parameters are regressed against moment magnitude, rupture distance, hypo-central depth, and shear wave velocity, enabling the scenario-based simulation of the records. The response spectra of the simulated records are compared with... 

This paper proposes a methodology for generating surrogate single-degree-of-freedom (SDOF) models that can be utilized to estimate the probability distribution of the roof drift ratio of multistory buildings at various ground motion intensity measures. The use of an SDOF model as a surrogate for multistory buildings can significantly alleviate the high computational cost for probabilistic seismic demand assessment considering both model uncertainty and record-to-record variability. The surrogate SDOF model generated herein explicitly accounts for model uncertainties and can be used as an alternative to the nonlinear dynamic analysis of detailed building structures. Applications for such... 

The Endurance Time (ET) method is a time-history based dynamic pushover procedure in which structures are subjected to specially designed, intensifying accelerograms, and their seismic performance is judged based on the time duration needed to satisfy the required design objective. Second generation refers to ET acceleration functions that are generated by application of optimization techniques in order to produce response spectra compliant linearly intensifying accelerograms. In this paper, the major characteristics of a set of second generation ET acceleration functions (ETA20a01-3) are investigated. The template response spectra of this set of ET acceleration functions corresponds to the... 

Dominant Collapse Mechanisms (DCMs) have been reported to play an important role in collapse capacity of structural systems and the seismic losses consequent to it. Therefore, DCMs of Reinforced Concrete (RC) frames have been studied, in this article, considering Record-To-Record (RTR) and modeling uncertainties. Two sets of RC frames have been designed, in this regard, that share the design assumptions but contain different levels of over-strength. Each set contains 26, 4- to 20-story nonlinearly modeled frames. Initially, Incremental Dynamic Analysis (IDA) was used to identify frames' DCMs. Then, the RTR variability reflected through IDA was combined with spectral shape and pulse effects... 

In the present paper, the seismic response of an arch dam subjected to spatial variation of ground motions along the interface with its foundations is investigated. Recorded ground accelerations at the dam foundation interface of an arch dam were used for the purpose of this investigation. Topographic amplification between various points of the interface was studied by obtaining ratios of the response spectral displacement and spectral pseudo acceleration. Time shift and amplification between stations show the nonuniform nature of ground motions for large structures like dams. Recorded ground accelerations were interpolated for different nodes of the finite element model. The seismic... 

This study is about the performance assessment of steel moment resisting frame structures under nearfield strong ground motions. A number of 3 and 9-story, 3-D structural models being designed using the strength method, are considered. A set of 7 near-field earthquake records, scaled according to ASCE- 7(05), are considered for nonlinear dynamic time history analyses using OpenSees program. Park and Ang damage index is considered for quantitative measurement of the performance of structural models. Maximum values of inter-story drifts along with the local and global damage indices are determined to be used in the performance assessment process. Considering the average results of different... 

In the endurance time (ET) method, structures are subjected to a specially designed intensifying ground acceleration function and their performance is judged based on their response at various excitation levels. A range of equivalent intensities can be covered in a single numerical or experimental simulation, thus significantly reducing the computational demand as compared to full nonlinear response-history analyses. The applied excitation intensity at various times has been correlated with those of the scaled ground motions. Response spectra of seven ground motions on stiff soil were used to produce intensifying acceleration functions that at each time window produce a response spectrum... 

The Endurance Time (ET) method is a new dynamic pushover procedure in which structures are subjected to gradually intensifying acceleration functions and their performance is assessed based on the length of the time interval that they can satisfy required performance objectives. In this paper, the accuracy of the Endurance Time method in estimating average deformation demands of low and medium rise steel frames using ETASOf series of ET acceleration functions has been investigated. The precision of the ET method in predicting the response of steel frames in nonlinear analysis is investigated by considering a simple set of moment-resisting frames. An elastic-perfectly-plastic material model... 

The seismic behaviour of a 4-story building is investigated under horizontal excitation of simulated earthquakes. The model has been constructed with a 3D sandwich panel system without any conventional frame system in four storeys on a shaking table. The building has been modelled before construction. Due to the table limit, the scale factor of the model is chosen as 1: 2.35 of a prototype. The shaking table test of the scaled model of the building is carried out under several ground motions to verify the safety of the system. The simulated motions were applied to the model in two-perpendicular directions, simultaneously. The failure mechanism and dynamic behaviour of the model, as a...