Sharif Digital Repository

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... 

A new procedure is proposed to quantify uncertainties involved in the seismic response of structures including ground motion and modeling variability. The advent of performance-based earthquake engineering (PBEE) and probabilistic seismic risk analysis necessitates consideration of uncertainties in predicting seismic responses. However, the high computational cost of conventional methods restricts their application to only simple numerical models. The present study employs the endurance time (ET) method concept to predict the response distribution which requires much less computational efforts than conventional methods. The proposed procedure for the quantification of record-to-record... 

In this study, a performance-based optimisation framework is proposed for optimal cross-sectional distribution of steel moment resisting frames (MRFs) subject to earthquake excitations. For the first time, the concept of uniform distribution of damage (UDD) is adopted for the complex optimisation of moment resisting steel frames under dynamic earthquake excitations. To enhance the computational efficiency of the optimisation process, a novel adaptive algorithm is proposed, where the power functions change based on the demand to capacity ratio of the structural elements. The framework is then used for optimisation of 3, 5, 7, 10 and 15-storey steel MRFs under a set of representative... 

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 the Endurance Time (ET) method, structures are subjected to a calibrated intensifying accelerogram and their performance is assessed based on their response at various equivalent intensity levels. Application of the ET method in performance-based design of structures has been studied by introducing a continuous performance target curve, which expresses the limit of the proper seismic performance of a structure along various times of the ET accelerogram. The correlation between time in the ET method and the return period for different structural periods is investigated. The procedure is based on the coincidence of response spectra obtained from the ET accelerogram at different times and... 

Various durations of Endurance Time Acceleration Functions (ETAFs) associated with different seismic hazard levels are presented to enable Endurance Time (ET) method for use in probabilistic seismic demand assessment studies. Various Intensity Measures (IMs) were, first, considered for establishing multiple "IM-duration" relationships. A set of 30 RC moment resisting frames were, then, subjected to IDA analysis using 44 ground motion records and the median IM values corresponding to different structural response levels were extracted. These values were compared with the ET-derived IMs by computing the errors corresponding to various demand levels and summating these errors over a complete... 

In performance-based geotechnical earthquake engineering, the required degree and spatial extent of ground densification for mitigation of liquefaction beneath a structure should be determined based on the acceptable levels of performance of foundation. Currently, there is no solution for evaluation of the amount of settlement and tilt of footings constructed on a densified ground which is surrounded by a liquefiable soil. This implies the need for numerical procedures for simulation of seismic behavior of shallow foundations supported on both liquefiable and densified subsoil. In this paper, the dynamic response of shallow foundations on a densified ground is studied using a 3D fully... 

Structures with inappropriate distributions of strength and stiffness have performed poorly in recent earthquakes, and most of the observed collapses have been related to some extent to configuration problems or a wrong conceptual design. Shear building models of multi-story structures are considered in this study and are subjected to a group of severe earthquakes. It is shown that the strength distribution patterns suggested by the seismic codes do not lead to a uniform distribution and minimum amount of ductility, drift, and damage. A new pattern is proposed that is a function of the period of the structure and the target ductility. An iterative approach is also developed to determine the... 

A methodology is presented for optimization of the dynamic response of concentrically braced steel frames subjected to seismic excitation, based on the concept of uniform distribution of deformation. In order to obtain the optimum distribution of structural properties, an iterative optimization procedure has been adopted. In this approach, the structural properties are modified so that inefficient material is gradually shifted from strong to weak areas of a structure. This process is continued until a state of uniform deformation is achieved. It is shown that the seismic performance of such a structure is optimal, and behaves generally better than those designed by conventional methods. In... 

Endurance Wave Analysis (EWA) is a novel, simple, economical but yet reliable method for the integrity assessment of offshore platforms against extreme irregular waves. The current paper presents a framework for the probabilistic assessment of offshore platforms based on EWA. The stochastic nature and the uncertainties in the ocean waves were taken into account by introducing a set of artificial, random and gradually intensifying wave trains. To simulate other uncertainties in the loading and the strength of the structure a Latin Hypercube Sampling (LHS) type of Monte Carlo Simulation (MCS) was employed. The EWA methodology and different structural performance criteria were considered. The... 

In this paper, the significance of soil–structure interaction (SSI) in optimal placement of viscous dampers in steel frames is studied. Optimal placement of dampers is determined with the purpose of achieving performance objectives at three hazard levels using genetic algorithm optimization. Endurance time method is used for seismic nonlinear response analysis of the fixed-base and SSI included frames. The soil beneath the structures is considered as a homogeneous elastic half-space, and the soil–structure systems are modeled by the substructure method. Results indicate that at low excitation intensities, consideration of SSI results in maximum drift ratio reduction at all stories of the...