Sharif Digital Repository

This paper puts forth a wavelet-based methodology for generating endurance time (ET) excitations. Conventional simulating practice expresses signals by acceleration values which are then computed via unconstrained nonlinear optimization. Dynamic characteristics of signals, including frequency content, are not represented directly in this type of variable definition. In this study, a new algorithm is developed to generate ET excitations in discrete wavelet transform (DWT) space. In this algorithm, signals are represented by transform coefficients. In addition, objective functions are modified in order to obtain transform coefficients and return the objective function values. The proposed... 

Endurance Time (ET) method is a response history based analysis procedure that can be used for estimating the seismic response of structures at different excitation levels in each response history. This seismic analysis method utilizes specific intensifying acceleration functions to analyze seismic behaviors. One of the potential applications of the ET method is in the seismic assessment of shell structures. In this study, a procedure for linear seismic analysis of shell structures is proposed and applications of this method is investigated for several cases of shell structures. These structures are analyzed under three ET acceleration functions in one direction and the results are compared... 

Endurance Time (ET) method is a new dynamic analysis procedure that aims at estimating seismic performance of structures by subjecting them to predesigned intensifying acceleration. These acceleration functions are designed in a way that they approximately simulate earthquakes with different intensities through their duration. Performance of the structure is judged based on its behavior for different intensity measures through time. A set of three acceleration functions have been produced using the ET concept by applying optimization techniques. These acceleration functions are designed in such a way that their response spectrum, while complying with typical code design spectra, intensify... 

The endurance time method is a time history dynamic analysis in which structures are subjected to predesigned intensifying excitations. This method provides a tool for response prediction that correlates structural responses to the intensity of earthquakes with a considerably less computational demand as compared to conventional time history analysis. The endurance time method is being used in different areas of earthquake engineering, such as performance-based assessment and design, life-cycle cost-based design, value-based design, seismic safety, seismic assessment, and multi-component seismic analysis. Successful implementation of the endurance time method relies heavily on the quality of... 

Earthquakes are natural phenomena that damage structures and buildings and their equipment. Preventing the transfer of earthquake vibration to the buildings is important to protect the residents and reduce the damage. Base isolation with lead rubber isolator is one of the desirable methods to prevent the transfer of seismic to buildings. Many parameters are involved in the design of these isolators and some of them are unknown at the beginning of the design. Therefore, iterative methods are required to design these isolators. This research described two procedures for isolator design, First, usual design procedure based on AASHTO and ASCE7 codes and second, design based on the performance... 

This study aims to develop a low computational cost framework to optimize the seismic performance of the steel moment-resisting frames (SMRFs) equipped with friction dampers at different performance levels. To achieve the optimal design of dampers in a structure, a novel approach called adaptive optimisation technique (AOT) is adopted. The basis of this method is to achieve a uniform distribution of damage (UDD) in the structure to exploit the maximum energy dissipation capacity of the dampers. The optimisation objective is to obtain the best position of friction dampers and minimize their slip-threshold force to satisfy a predefined inter-story drift (i.e. selected performance target). The... 

In this paper, considering horizontal components of seismic excitation, an algorithm for the nonlinear multi-component analysis of building structures by the Endurance Time (ET) method is proposed, and results of the ET method for various steel moment frames with one to seven stories are verified by comparing with the results from Nonlinear Time History Analysis with use of two different sets of ground motions. In addition, several parameters such as eccentricities and irregularities in structure, rotational and lateral stiffness, effect of hysteresis type and ductility have been considered for sensitivity analysis on results, obtained by ET method. Results show that on the basis of... 

Endurance Time (ET) method has been introduced as a lime-history based dynamic analysis procedure. In this method, structures are subjected to a gradually intensifying acceleration function. Performance of the structures is assessed based on the length of the time interval that they can satisfy required performance objectives. In this study, some fundamental concepts of ET method are explained and the potentials and limitations of this procedure in nonlinear seismic analysis of SDOF structures are investigated. A numerical optimization procedure for generating ET acceleration functions that are compatible with ground motions are explained. Results of ET analysis for inelastic SDOF systems... 

The end diaphragm of bridges are normally designed to resist lateral seismic forces imposed on the superstructure in earthquake prone regions. Using ductile diaphragms with high deformation capacity could reduce the seismic demands on the substructure and prevent costly damage under strong ground motions. The end diaphragms of steel tub girder bridges with high lateral stiffness and dominant shear behavior have a potential to be used as ductile fuse elements. In this study, a steel plate shear diaphragm (SPSD) is introduced as an external end diaphragm of tub girder steel bridges to reduce the seismic demands imposed on the substructure. Quasi static nonlinear analyses were conducted to... 

Nonlinear static methods are simplified procedures in which the problem of evaluating the maximum expected response of a MDOF system for a specified level of earthquake motion is replaced by response evaluation of its equivalent SDOF system. The common features of these procedures are the use of pushover analysis to characterize the structural system. In pushover analysis both the force distribution and the target displacement are based on the assumptions that the response is controlled by the fundamental mode and that the mode shape remains unchanged after the structure yields. Therefore the invariant force distributions does not account for the change of load patterns caused by the plastic... 

Endurance time method is a dynamic analysis in which structures are subjected to increasing excitations. These excitations are generated to be compatible with ground motions. Conventional excitation generating processes take into consideration the dynamic characteristics related to intensity and frequency contents of ground motions; however, duration-related characteristics have never been considered directly. In this study, the existing methodology is extended to include Cumulative Absolute Velocity as a duration-related parameter in the generating process. These newly generated excitations are then employed to estimate nonlinear responses of three concrete structures as case studies....