Sharif Digital Repository

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... 

A simple Dynamic-based Pushover analysis for Plan Asymmetric buildings (DPPA) is proposed with the aim of properly considering the effects of torsional behavior as well as the higher modes in the applied lateral load pattern. According to the proposed method, the peak story drifts obtained from the response spectrum analysis (RSA) can be resolved into their translational and rotational components, and the related equivalent static lateral forces and torsional moments can be calculated. Consequently, for accurate estimation of the maximum drift demands of plan-asymmetric buildings, it is proposed that the drift responses obtained from the RSA for the stiff and flexible edges of the building... 

Pushover analysis is a simplified nonlinear analysis technique that can be used to estimate the dynamic demands imposed on a structure under earthquake excitations. One of the first steps taken in this approximate solution is to assess the maximum roof displacement, known as target displacement, using the base shear versus roof displacement diagram. That could be done by the socalled dynamic pushover analysis, i.e. a dynamic time history analysis of an equivalent single degree of freedom model of the original system, as well as other available approximate static methods. In this paper, a number of load patterns, including a new approach, are considered to construct the related pushover... 

In this paper, a relatively novel approach is established to estimate different limit states and accurate behavior of jacket platforms against environmental wave loading. This novel approach which is called Incremental Wave Analysis (IWA) can be an appropriate substitute to current pushover practice. The IWA can take into account the effects of variation in wave height and wave-in-deck loading in the estimating of platforms' behavior. This paper aims to introduce the applications of this approach in deterministic assessment of offshore platforms, comprehensively. The IWA can estimate the collapse-prevention limit state of jacket platforms properly. In addition, an appropriate parameter for... 

As steel plate shear walls are typically used in the building central cores around the elevators and stairs, introduction of an opening as door seems to be inevitable in steel plate shear wall spans. Due to the weakening of the steel plate shear walls’ performance caused by this particular type of opening, the use of stiffeners around the opening is necessary. Nevertheless, introduction of stiffeners around all sides of the opening, which does continue to boundary elements, is very expensive and inefficient. Therefore, the study on the effect of different arrangements of stiffeners on the behavior of steel plate shear walls is significant. In this research, a number of steel plate shear... 

Nonlinear behavior of jacket platforms is important in both design and rehabilitation issues that depends on the bracing arrangement. Both ductility and strength of the structures derived from pushover analysis are highly related to configuration of the braces. Considering a suitable criterion such as constant weight or constant stiffness and period of the structure in all arrangement cases, one can compare the capacity curves and find the best configuration. In this paper a simple logical method for investigating the strength and ductility of the jacket structure is presented, it is shown that global geometry and configuration of the braces are very important and effective in both strength... 

The seismic performance of diagrids equipped with buckling restrained braces (BRBs) is investigated. In that regard, the effects of BRBs on the seismic performance characteristics of diagrids such as response modification factor, R, overstrength factor, Ω0, ductility ratio, μ, and median collapse capacity, S^CT, are evaluated. To this end, 6 three dimensional diagrid structures with various heights and diagonal angles are modeled using OpenSees program and are equipped with BRBs in a novel arrangement. Utilizing nonlinear static analysis, the seismic performance factors of models are evaluated. Subsequently, the median collapse capacity (S^CT) of the models are determined by performing... 

Recent studies have indicated the need of considering aftershocks in the seismic design/assessment of structures. This article investigates the effect of sequential mainshock and aftershock earthquakes on eccentrically braced steel frames with vertical energy-absorbing links. To achieve this, 4, 8 and 12-storey frame buildings are modelled in Perform3D® software considering non-linear behaviour of materials and components. The frames are subjected to a set of 12 main earthquake records corresponding to the required hazard level, and then subsequent aftershocks are applied using incremental dynamic analysis (IDA). To reduce the computational cost, an alternative approach is also adopted by... 

The present study aims to reliably quantify the seismic response parameters of steel diagrid structural systems. To this end, in addition to the conventional Static Pushover Analysis (SPA), Dynamic Pushover Analysis (DPA) based on Incremental Dynamic Analysis (IDA) technique was taken into account. FEMA P-695 recommends a methodology for establishing Seismic Performance Factors (SPFs). The objective of the present study was to propose a simpler framework for estimating and validating SPFs while applying the concepts of FEMA P-695 guideline. The results showed that the R factors obtained through SPA procedure for steel diagrid systems were conservative and the IDAbased probabilistic method... 

The endurance time (ET) method is a time history-based dynamic pushover analysis procedure that utilizes special intensifying acceleration functions for estimating the seismic performance of structures at different excitation levels. One of the potential applications of the ET method is in the three-dimensional analysis of buildings considering multidirectional excitation. In this paper, a procedure for multi-component analysis by the ET method has been developed. Several steel moment frames with heights from 9.6 to 48 m were designed according to the Iranian National Building Code. By applying the proposed algorithm for three-dimensional analysis of structures by the ET method, these frames... 

In this research, four types of concrete moment frame were designed with glass fiber reinforced polymer (GFRP) bars according to ACI 440.1R-15 and the seismic behavior was assessed using pushover analysis. The frames were three and five stories with two and three bays. A computer code was developed to calculate the amount of fiber reinforced polymer bars in beams of the frames. In order to evaluate nonlinear behavior in plastic hinge regions, sections of beams and columns were analyzed on the basis of moment-curvature diagram and also P-M interaction curve for columns. Performance levels of frames were determined considering ATC-40 criteria. Behavior of concrete moment frames reinforced with... 

As the result of safety factors considered in load and resistant values for the design of new offshore platforms, a higher resistance compared to the 100 year return period environmental loading, is achieved in the structure. This type of design is usually performed using linear methods of structural analysis. In this case the structure practically has a high reserve capacity which is disregarded in the design phase but may be considered in special cases. One of these important cases is when an existing structure is assessed and evaluated after elapse of its structural life. In this case using the platforms reserve capacity, through a non-linear analysis such as push-over, would be logical... 

As steel is highly sensitive to temperature variations, fire exposure is more destructive in the case of steel structures in comparison to the concrete ones. The performance of an intermediate three-story steel moment frame with 4 spans was studied under the service load, thermal load and post-earthquake fire in this paper. Also, the effects of passive fire-protection materials such as ordinary cement-based and fire-retardant coatings were investigated. To model and analyze the structure; Abaqus software is utilized. In order to apply the earthquake effect, the push-over analysis method is employed. Changes in the stories deflection, endurance time and growth of nonlinear regions due to... 

In this paper, application of the Endurance Time (ET) method in the performance-based design of steel moment frames is explained from a conceptual viewpoint. ET is a new dynamic pushover procedure that predicts the seismic performance of structures by subjecting them to a gradually intensifying dynamic action and monitoring their performance at various excitation levels. Structural responses at different excitation levels are obtained in a single time-history analysis, thus significantly reducing the computational demand. Results from three analyses are averaged to reduce the random scattering of the results at each time step. A target performance curve is presented based on the required... 

In nonlinear static (pushover) methods of analysis as an alternative to time history analysis, the capacity curve of the structure is established with respect to the roof displacement. Disproportionate increases in the roof displacement and even outright reversals of the higher modes can distort the capacity curve of the equivalent single degree of freedom system in these kinds of method, including MPA. To overcome this problem, recently, "Energy-Based" the Modal Pushover Analysis (Energy-Based MPA) method has been introduced. In this method, the absorbed energy and/or the external work in the pushover analysis is considered. Accordingly, the assessment of the Energy-Based MPA method is...