Seismic Assessment of RC Frames with Setbacks (original) (raw)
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Setback in elevation of a structure is a special irregularity with considerable effect on its seismic performance.This paper addresses multistory Reinforced Concrete (RC) frame buildings, regular and irregular in elevation. Several multistory Reinforced Concrete Moment Resisting Frames (RCMRFs) with different types of setbacks, as well as the regular frames in elevation, are designed according to the provisions of the Iranian national building code and Iranian seismic code for the high ductility class. Inelastic dynamic time-history analysis is performed on all frames subjected to ten input motions. The assessment of the seismic performance is done based on both global and local criteria. Results show that when setback occurs in elevation, the requirements of the life safety level are not satisfied. It is also shown that the elements near the setback experience the maximum damage. Therefore it is necessary to strengthen these elements by appropriate method to satisfy the life safety level of the frames.
Seismic Performance of 3 Storey Irregular Reinforced Concrete (RC) Frames Under Repeated Earthquakes
Earthquake resistance is one of the most important factors for designing a building in the seismic prone area in order to reduce the earthquake damage on buildings. After earthquake events, the number of damage on buildings with setback is increases, which exhibit inadequate behaviour though they were designed according to the current state of knowledge existing in seismic codes. Most analysis will be carried out based on single earthquake as recommended by codes of practices. In reality, this is not the case, in which earthquake can occur repeatedly in the life span of the buildings. This paper studies three storeys 2D frames with regular three storeys 2D (RC) frames and irregular in elevation (setback) (RC) frame, under repeated earthquakes. Non-linear time history (dynamic) seismic analyses of buildings were employed in this paper. The seismic performance is based on the estimation of important structural parameters such as displacements and inter-storey drifts. Results of single...
Asian Journal of Civil Engineering, 2019
This research study was carried out to analyse the seismic behaviour of ten types of six-storey moment-resisting concrete frames, which were one regular frame and nine setback frames with different building configurations. In this analysis, the setback buildings were mainly studied because they have become increasingly popular in modern multi-storey building construction due to their functional and aesthetic architecture. Incremental dynamics analysis (IDA) was performed on these frames under three sets of repeated ground motion records. Based on the IDA curve, life safety (LS) performance level was considered as the main guideline to develop the fragility curves. The maximum inter-storey drift percentages at each storey level, for all frames and location of plastic hinges for each frame, were clearly determined through IDA. From the fragility curve results, the probability of reaching or exceeding the life safety performance state was determined. The regular frame showed the lowest probability as compared to other frames. Therefore, it is known that the building configuration of frames affects the building's seismic performance, and thus it should be considered in the building's seismic design.
Dynamic Analysis of Multi-storey RCC Building Frames
The important objective of earthquake engineers is to design and build a structure in such a way that damage to the structure and its structural component during the earthquake is minimized. This report aims towards the dynamic analysis of a multi-storey RCC building with symmetrical configuration. For the analysis purpose model of ten storeys RCC with symmetrical floor plan is considered. The analysis is carried by using finite element based software SAP 2000. Various response parameters such as lateral force, base shear, story drift, story shear can be determined. For dynamic analysis time history method or response spectra method can be used .Time-history analysis is a step-by-step analysis of the dynamical response of a structure to a specified loading that may vary with time. The analysis may be linear or non-linear. Dynamic analysis can be performed for symmetrical as well as unsymmetrical building. Dynamic analysis can be in the form of nonlinear dynamic time history analysis. In this paper, a nonlinear time history analysis is performed on a ten storey RCC building frame considering time history of El Centro earthquake 1940 using SAP 2000. The main parameters of the seismic analysis of structures are load carrying capacity, ductility, stiffness, damping and mass. The various response parameters like base shear, storey drift, storey displacements etc are calculated. The storey drift calculated is compared with the minimum requirement of storey drift as per IS 1893:2002.
Evaluation of Seismic Performance of 3 Story Ordinary Moment Resisting Concrete Frames
Most low to medium rise buildings located in low to moderate seismic regions have been designed only for gravity loads. This study is to investigate the seismic behavior of moment frames designed only for gravity loads and detailed by the requirements for ordinary moment resisting concrete frames. In this study experimental test was carried out. For this purpose a three-story frame (prototype building) was designed in compliance to the minimum design and detail requirements in ACI 318 (1999) for gravity loads (1.4D+1.7L). One-third scale specimen of the prototype building was made. Quasi-static cyclic reversed loads were applied. Based on the test results the seismic behavior of the OMRCF is evaluated.
In urban areas, increase in population and scarcity of land, the horizontal development gets restricted that’s why most of the owners, building contractors, engineers are adopting vertical development of buildings for the construction. Natural hazard like earthquake affects the stability of such structures. Performance of structures in different areas of Northern part of India, during the earthquakes, is reviewed. The earthquake caused damage to heritage structures as well as modern buildings. Both masonry and reinforced concrete buildings showed poor performance. Previous studies reveal that major failures of structures occurred due to improper design procedures. Therefore, it is need of time to analyses & designs such hazard resisting structures so as to save human life and avoid property damage. The behavior of a building during earthquakes depends critically on its overall shape, size and geometry. Nonlinear pushover analysis has been used to evaluate the seismic performance of three buildings with four different plans having same area and height. The results of effects of plan aspect ratio on seismic response of buildings have been presented in terms of displacement, base shear. Behaviour parameters of the analyzed moment resisting frames also calculated.
Seismic Performance of Reinforced Concrete Frame Buildings Designed by Iranian Seismic Code
2014
In this paper, the seismic performance of a multi-story reinforced concrete frame building has been studied. A typical reinforced concrete moment-resisting frame building was designed according to the current Iranian seismic code (IS 2800-14). Seven earthquake records were selected and scaled based on IS 2800-14 requirements. In order to assess the seismic vulnerability of the case study structure, nonlinear static (push-over) analysis and nonlinear dynamic time-history analysis have been conducted. The performance has been evaluated based on both the member and global level criteria. Comparison between push-over and nonlinear analyses results shows a relatively good consistency. The numerical results additionally show that the case-study building frames designed by IS 2800-14 satisfy the intended code requirements and meet the inter-story drift and maximum plastic rotation demands suggested byGuide 360 (Instruction for Seismic Rehabilitation of Existing Buildings).
Seismic assessment of RC building frames using direct-displacement-based and force-based approaches
Innovative Infrastructure Solutions, 2020
The conventional force-based design (FBD) method has been in practice for seismic assessment of RC building frames. In the FBD method, the main focus is on the seismic forces over the structure. In recent years, various shortcomings have been pointed out by research works, for example assumed initial stiffness of structural components, inappropriate response reduction factors, etc. To overcome these limitations of FBD, many new techniques have been developed and implemented. One such method is the direct-displacement-based design (DDBD) method. In this, the basic assumption is that strength is less critical than displacement. DDBD is a design theory in which design criteria are articulated for achieving a specified level of performance goals that are subjected to the defined level of seismic hazards. In this paper, the vulnerability of buildings situated in high seismic regions in India has been assessed. Four-and eight-storey RC building frames are taken into consideration. The non-linear time-history analysis is carried out, and the inelastic behaviour of buildings in the form of base shear, inter-storey drift ratio (ISDR) and maximum displacement is assessed. Also, fragility curves have been developed considering the effect of ISDR. It is concluded that the DDBD approach is more reliable and efficient for designing RC building frames as compared to its counterpart FBD approach.
Seismic design factors for RC special moment resisting frames in Dubai, UAE
Earthquake Engineering and Engineering Vibration, 2011
This study investigates the seismic design factors for three reinforced concrete (RC) framed buildings with 4, 16 and 32-stories in Dubai, UAE utilizing nonlinear analysis. The buildings are designed according to the response spectrum procedure defi ned in the 2009 International Building Code (IBC'09). Two ensembles of ground motion records with 10% and 2% probability of exceedance in 50 years (10/50 and 2/50, respectively) are used. The nonlinear dynamic responses to the earthquake records are computed using IDARC-2D. Key seismic design parameters are evaluated; namely, response modifi cation factor (R), defl ection amplifi cation factor (C d ), system overstrength factor (Ω o ), and response modifi cation factor for ductility (R d ) in addition to inelastic interstory drift. The evaluated seismic design factors are found to signifi cantly depend on the considered ground motion (10/50 versus 2/50). Consequently, resolution to the controversy of Dubai seismicity is urged. The seismic design factors for the 2/50 records show an increase over their counterparts for the 10/50 records in the range of 200%-400%, except for the Ω o factor, which shows a mere 30% increase. Based on the observed trends, perioddependent R and C d factors are recommended if consistent collapse probability (or collapse prevention performance) in moment frames with varying heights is to be expected.
Comparative Study of Seismic Behavior of Multistory Reinforced Concrete Framed Structures
A comparative study of the nonlinear behavior of reinforced concrete RC multistory structures is carried out on the basis of measured response of four six-story, three-bay framed structures, namely a regular bare frame, a discontinuous-column frame, a partially masonry-infilled frame, and a wall-frame system. The structures were designed for similar seismic requirements in accordance with Eurocode 8, and their 1:5.5 scaled models were subjected to similar earthquake simulation tests. Experimental observations and numerical analyses show that the distribution of the story shear overstrength is a rather stable indicator of the general inelastic behavior of frames, and hence, can be employed as a characteristic parameter to quantify the frame irregularity for design purposes. Abrupt discontinuity of the geometry or arrangement of structurally effective elements, where unavoidable, may be compensated by strength enhancement targeting a smoothed overstrength profile to allow for distributed inelastic deformation, and this principle applies as well to nonuniformly masonry infilled frames. For the wall-frame system, adequate countermeasures against rocking of the RC wall is shown to be a key to maintaining the effectiveness of the system at advanced inelastic response.