This paper examines differences in performances of a range of torsionally stiff and flexible single story buildings designed with the provisions of Iranian Standard 2800. Seismic nonlinear dynamic time history behavior of eight building models subjected to seven horizontal bi-directional design spectra compatible ground motions are investigated. These models cover a wide range of very torsionally stiff to very flexible buildings. Response parameters are element ductility demand and building story drift ratio. These criteria are appropriate indices for structural and nonstructural damages, respectively. This investigation shows that the linear static analysis of building code such as Iranian Standard 2800 is not generally adequate for structures with very low torsional stiffness.

This article provides a comparison process on how to calculate seismic forces by the static analysis method stated both in the international Building Code (IBC) 2003 and in the Iranian Seismic Code (IS 2800-05). The seismic coefficient for the equivalent lateral force is specified by the following factors: fundamental period, importance factor, spectral response acceleration, and building response modification factor. In this article the above-mentioned parameters are obtained through the IBC 2003 and are compared against those covered in the IS 2800-05. Studies and comparison of factors would lead to significant differences in the results obtained using the two codes. In order to clarify the problem, design base shear of a building with combined system (special moment steel frames + eccentric bracings) in four different soil types and vertical distribution of base shear at story level is obtained, in accordance with both codes; and the results are compared with diagrams and tables. The results prove the need to review the IS 2800-05 and develop more appropriate relations towards achieving economic and functional objectives.

The performance of buildings designated as very high importance buildings (such as hospital buildings) according to Iranian Seismic Code (Standard 2800) is that, these buildings maintain their operational level in major seismic ground motions (design level earthquake) without major structural damage. This paper discuses the design requirements to reach the purposes in this code and shows that the code regulations can not provide the enough strength for the buildings to operate acceptable during sever earthquakes. To evaluate the code requirements, some R/C moment resistance frames with difference in stories numbers (designated according to standard 2800) was selected and their strength was evaluated based on Instruction for Seismic Rehabilitation of Existing Buildings (No. 360), by pushover analysis. The results indicate that the buildings designated as very high importance according to standard 2800, do not remain operationally after sever earthquake.

Nowadays, performance evaluation of buildings against earthquakes is one of the common debates among researchers. Old buildings designed on the basis of previous versions of seismic codes are exposed to more damages in earthquakes. To evaluate vulnerability of existing buildings for earthquakes, Instruction on Rapid Earthquake Evaluation of the Existing Buildings (Code No. 364) has been proposed. By this code, a building can be rapidly evaluated by easily available data such as structural type, designing and construction date, appearance, etc., with very low cost. One of important parameters for such evaluation is the version of the seismic code (Standard 2800) which had been applied in the designing process of inspected building; later version has greater score.  However, the rapid evaluation code (Code No. 364) has been prepared before releasing version 4 of Standard-2800 and therefore do not have the score of designing with this version. Therefore, this paper is focused on comparing version-3 and vetsion-4 of Standard 2800 in designing buildings. For this, three buildings, having 3, 5 or 7 story, with regular plane is considered. Each is designed twice, based on the version-3 and vetsion-4  and then their fragility curves are calculated. The obtained fragility curves are compared in two levels of earthquakes having return period of 475 years and 2475 years (PGA of these earthquakes are assumed as 0.35g and 0.5g, respectively). To achieve the fragility curves, 50 earthquake records, recommended by FEMA-P695, are considered. They include 22 far field ones, 14 near field ones having pulse and 14 near field records without pulse. To consider nonlinear behavior of the structural elements, concentrated plasticity is assumed at two ends of each element by Opensees software. Properties of the plastic hinges are introduced in the software based on Lignos model. The obtained results show that in IO performance level, there is no meaningful difference between the structures designed on the basis of version 3 and version 4 of Standard-2800. However, in Life Safety (LS) and Collapse Prevention (CP) performance levels, version 4 leads to much better structure. Furthermore, the difference between these two versions of standard is greater for 475 year earthquakes, in comparison with 2475 year earthquakes, and also for LS rather than CP performance level.

Many high-rise buildings have been constructed near fault lines around the world, and some have suffered significant human and economic losses during strong seismic events. Given the growing trend of high-rise construction in Iran, it needs to see about how the behaviour of tall buildings that are equipped with buckling-restrained braces is in an earthquake event. To this purpose, it is necessary to obtain such behaviours in different branches of seismic excitations, near-field, long-period, multiple earthquake, etc., then compare them with the ordinary seismic events. This study evaluates the effect of near-fault ground motions on the seismic performance of tall reinforced concrete buildings with special moment-resisting frame systems equipped with buckling-restrained braces (BRBs), using the acceptance criteria defined in the Iranian Standard 2800. To this end, structural models were first fully designed using ETABS software, in accordance with the Iranian National Building Regulations and the seismic provisions outlined in Standard 2800. Subsequently, the nonlinear behavior of 3D models of 12-, 16-, and 20-story frames was developed in detail and then analyzed using nonlinear analysis methods in OpenSees software based on nonlinear faber-based elements and needed material and geometric nonlinearities, based on the criteria specified in Appendix 2 of Standard 2800. The seismic responses of structural elements were evaluated separately under nonlinear static and nonlinear time-history analyses at the design-level earthquake intensity. Although this type of seismic record has more effect on low-rise structures than tall ones, the tallest model of the study is the most vulnerable model, because of the components of near-field excitations as pulse-like motives, forward directivity, and vertical earthquake components. Thus, the 20-story model exhibited the highest vulnerability under near-fault ground motions. Furthermore, seismic performance variations due to near-fault excitations ranged from approximately 2% to 18%, depending on the specific earthquake and structural configuration. Based on the acceptance criteria in Appendix 2 of Standard 2800, the application of this structural system is validated in terms of both strength and deformation requirements. It is of utmost importance that this acceptance criterion that had been achieved in this study is just to satisfy the performance objective of the 2800 seismic standard, which is limited life safety. In fact, it needs to perform such investigations for each seismic code and see whether the performance level of the code is satisfied. However, the performance level of the structures should be constant. In addition, BRB-equipped frames develop a wider stable post-elastic capacity with greater energy dissipation, without strength or stiffness degradation up to 125% of target displacement. Base shear at first plastic hinging is ~17% higher than in the unbraced frame,resisting force at peak roof displacement rises by 13%, 11%, and 8% for the 12-, 16-, and 20-story models. BRBs delay inelastic onset and OP/IO/LS/CP exceedance and allow 10% larger roof displacement. Nonlinear story drifts remain within limits and below 2%, even at 1. 2 intensity. A probabilistic assessment and the derived R-factor validate constructability,given lower weight than shear-wall alternatives, BRB-SMRFs are recommended for near-fault regions.

Most researches on masonry infill walls have shown that the presence of such walls in framed structures increases their stiffness and resistance. However, the presence of panels is not always beneficial and may lead to a brittle failure in some cases. To quantitatively investigate this issue, it is necessary to consider the infill wall as a structural member and explicitly model it in framed structures. Recently, the Building Design Code against Earthquake (IS 2800) has provided an approach for the explicit analysis and design of infilled frames in its sixth appendix using an equivalent strut model. In this solution, by reducing the response modification factor of the structural frame with infill walls to 3 and modeling the infill walls using the equivalent strut method and redistributing the forces in the equivalent truss system, the structural adequacy of the beams, columns, and infill walls in the entire frame is checked. In the present study, five reinforced concrete moment frames, including one bare frame (with intermediate ductility) and four infilled frames with different infill wall arrangements according to the sixth appendix of IS 2800, are analyzed and designed, and subsequently, the seismic performance of their members is investigated using the nonlinear static analysis method (the coefficient method). The results show that although the addition of masonry panels to the structures increases their stiffness and resistance and improves the performance of the beams, however, the lower columns exceed the life safety performance level and sometimes reach the collapse prevention level. Therefore, considering a response modification factor of 3 for all infilled frames with different infill wall arrangements on the floors does not seem to be accurate.

This article intends to investigate the effects of site-to-fault distance on the earthquake intensity measure (basic design acceleration, A, and response spectra, Sa) where is not taken into account in Iran standard No. 2800. Regarding that the relation between site-to-fault distance and the design-base acceleration (A) parameter (or Sa) in currently used attenuation relations is highly non-linear, thus assigning the same value of such parameters to different site-distances in big cities, particularly at near fault sites, seems to be quite challengeable. In order to make this problem clear, forty series of site specific seismic hazard analysis in the two cities, Ahwaz and Kerman, are performed over ten sites having four different site-soil conditions and the “A” parameters are calculated and discussed. The results of this study showed that the site-to-fault distance can significantly influence upon the site’s intensity measure (A) parameter (about several times as distance become smaller) and have significant differences with those of the Standard No. 2800. This problem also highly affects the effectiveness of “N” parameter presented in thee 2800 standard as the representative of near fault directivity parameter.

The significance of earthquake effects on storage tanks compels researchers to investigate tanks seismic responses. In spite of the recent design codes developments, there is no accepted procedure to scale ground motions to perform time-history analysis for these very stiff structures. Nevertheless, standards for conventional structures have long been minimized in a predefined range of periods the difference between the response spectra of chosen records and the target spectrum. Since design specifications have important differences in their scaling procedures, it gives rise to affect on seismic response of structures. In this paper, the various seismic responses of several existing cylindrical tanks in an oil storage complex in Kashan, Iran are evaluated. The earthquake records have been separately scaled according to the procedure described in Iranian Standard No. 2800 and ASCE/SEI 7-10. The results indicate the different consequences of the scaling procedures for the tanks responses.

This paper assesses three definitions of eccentricity employed in the description of asymmetric multistory buildings. Other definitions of static eccentricity in multistory buildings fall essentially into one of the above categories. Using the three approaches, formulae are developed to evaluate the asymmetry of shear-type buildings where the deformation is governed by the lateral and rotational rigid-floor displacements arising from the seismic design loadings. Finally by modelling three concrete buildings according to Iranian concrete code (ABA) and investigating these three definitions and comparing them, the best method for representing Iranian 2800 Standard was selected. Simple comparisons and comments on the alternative approaches are presented with the aid of these appropriate examples. This clarification of the definition of eccentricity isneeded for improved understanding of the application of codified torsional design procedures. It is also a prerequisite for advanced studies of the inelastic seismic response of multistory shear buildings.

Progressive collapse studies generally assess the performance of the structure under gravity and blast loads, while earthquakes may also lead to the progressive collapse of a damaged structure. In this study, the progressive collapse response of concentrically braced dual systems with steel moment-resisting frames was assessed under seismic loads through pushover analysis using triangular and uniform lateral load patterns. Two different bracing types (X and inverted V braces) were considered, and their performances were compared under different lateral load patterns using the nonlinear static alternate path method recommended in the Unified Facilities Criteria (UFC) guideline. Eventually, the seismic progressive collapse resistance of models was compared to their progressive collapse response under gravity loads. These studies showed that models under the seismic progressive collapse loads satisfied UFC acceptance criteria and limited rehabilitation objective. The structures had better performance under seismic progressive collapse than models under gravity loads because of more resistance, ductility, suitable load redistribution, and more structural elements that participated in load redistribution. Furthermore, despite studies on progressive collapse under gravity loads, the dual system with X braces showed better progressive collapse performance (more resistance, residual reserve strength ratio and ductility) under seismic loads than the model with inverted V braces.