فهرست مطالب hamed roohbakhsh

Height of the buildings directly affects the seismic performance and behavior of the structure during the earthquakes. This parameter is also significant when the structure is excited by two consequent ground motions. This paper presents the results of a study on the effect frame height on the seismic performance under two successive strong ground motions. It has been shown that, when the consequence of the first event remain in the structure as damage, the building often shows different dynamic characteristics as well as more vulnerability during the second seismic event. Three RC moment resisting frames with 4, 8 and 15 stories are designed based on the latest version of Iranian code of seismic design of buildings referred as Standard No. 2800 (STD 2800). The frames are then simulated in OpenSees software to perform nonlinear dynamic analysis. Twenty natural ground motion sequences each including two seismic events were selected from previous studies for the purpose of nonlinear incremental dynamic analysis. Maximum inter-story drift was employed as a damage index, to capture the performance of the RC frames under sequences. The accepted performance level for collapse level was taken from Iranian instruction for seismic rehabilitation of existing buildings, PBO-Publication No. 360, 2007, which is similar to ASCE 41-13. Seismic fragility values are calculated for the buildings under the second event when being damaged in first event. Assuming a log-normal distribution for failure probability function, corresponding values of median, μ and standard deviation, β, for each case are calculated and discussed for frames with different heights. The results indicate how the main parameters of the seismic fragility function may differ with frame height.

Developing fragility and vulnerability functions are important tools in seismic reliability assessment of buildings and are widely used in regional seismic risk studies. To date sufficient studies for developing analytical fragility functions for Iranian code-conforming buildings have not been carried out. Performing such studies are necessary to assess the adequacy of Iranian seismic design codes. 

In this paper, by designing 4, 8 and 15 storey concrete reinforced concrete buildings based on the latest three editions of Iranian Standard 2800, seismic fragility functions will be estimated for the 9 different design results. For this purpose, after designing the structures defined in accordance with the procedures in Iranian Standard 2800 and the National Building Code, Chapter 9, a nonlinear model of each case was developed in the OpenSEES finite element software. Nonlinear material properties as well as P-Δ effects were considered in the models. Twenty-two reference ground motion records were used to perform the incremental dynamic analyses. The relative performance criteria according to publication No. 361 of the Planning and Budget Organization of Iran were employed in the evaluation of the results of nonlinear analyses.

The results were applied in statistical analysis to estimate the seismic fragility functions and corresponding parameters.

The results show the trend of change in the seismic fragility for the frames with different height and conforming different editions of the Standard No. 2800.

Estimating the vulnerability rate of urban textures in seismic incident following a major earthquake (aftershocks) is crucial in decision making and crisis management. For this purpose, it is necessary to calculate the vulnerability of buildings due to the successive incidents and to use them in the vulnerability estimation for probable future aftershocks. Seismic fragility in reinforced concrete buildings with shear wall affected by a secondary incident due to seismic continuity is calculated in this paper.

The studied buildings have 4, 8 and 15 floors. Opensis software was used for nonlinear analyzes. For this purpose, twenty seismic sequences which presented in previous valid studies were used. Seismic fragility curves to collapse level following increasing nonlinear time history analysis were estimated; for this, numerical models of studied constructions following the first incident damage were analyzed.

According to the results, in addition to present the seismic fragility of reinforced concrete sheets with shear wall and the effect of the first incident amount on this parameter, the changing process of this index due to Iran 2800 Standard Change in three recent editions has been studied; the results showed that the probable demolishing of studied frames affected by the second incident, is significantly increased if the frame were damaged in first incident.

It is essential to consider the aftershock impacts on damaged structures under the first incident in order to risk management and decrease the damages. The results of this study showed that increasing the amount of demolishing due to main earthquake the probability of the structure collapse will increase significantly following the aftershock. On the other hand, recent editions of Iranian seismic guidelines in choosing design method, has a significant impact on the reduction of aftershock damages.