Performannce Base Analysis of Multy Storied Building

In India multistoried buildings are widely designed with the method suggested by Indian Standard IS1893: Part-1:2016, Criteria for the Earthquake resistance design of the structures: General Provision and Buildings for the calculation of equivalent horizontal load generated during earthquake. Response Spectrum method is widely used for the multistoried buildings with base shear scaled to get the equal value as calculated with the time period obtained by the empirical formula of time period of the buildings. The approach of the dynamic analysis is basically a linear approach. In this scenario we are totally relying on ductility of the structure. The concept for performing the Pushover Analysis is to analyze a structure with non linear approach and to find the behavior of structure beyond its ductile limit. Pushover analysis can help to demonstrate how progressive failure in building really occurs and to identify the mode of final failure of the buildings. Pushover analysis is commonly used to evaluate the seismic capacity of existing structures and appears in several recent guidelines for retrofit seismic design. It can also be useful for performance-based design of new buildings that rely on ductility or redundancies to resist earthquake forces. So basically Pushover analysis is non linear approach to estimate the strength capacity of the structure beyond Limit State. In this analysis we can predicts the weak areas in the building and keeping track of the sequence of damages of each and every member in the building/structure, thus can be performed for existing structure and also for performance base design, similarly for progressive collapse analysis. The approach is easy to understand, when we designed or analyze a moment resisting frame as per IS 1893:2016 by Response Spectrum method with response spectrum method with the response reduction factor 5 i.e. R=5, we are basically designing the structure with 1/5th horizontal load (calculated with the empirical formula given in IS 1893:2016), the rest 4/5th load is basically taken care by the ductile behavior of the building. The ductile detailing suggested by the 13920:2016 will resist the full impact of seismic load without collapse. The distribution and impact of the full horizontal load can be analyzed with the non linear approach, and pushover analysis is one of them. METHODLOGY: A pushover analysis is performed by subjecting a structure to a monotonically increasing pattern of lateral loads, representing the inertial forces which would be experienced by the structure when subjected to ground shaking. Under incrementally increasing loads various structural elements may yield sequentially. Consequently, at each event, the structure experiences a loss in stiffness. Using a pushover analysis, a characteristic non linear force displacement relationship can be determined. Key elements of the pushover analysis 1) Definition of plastic hinges, it includes hinges for uncoupled moment, hinges for uncoupled axial load, hinges for uncoupled shear force, hinges for coupled axial force and hinges for biaxial bending moment. 2) Definition for control node, the node used to monitor the displacement of the structures. Pushover curve is obtained from the displacement verses base shear. 3) Developing the pushover curve which includes the elevation of the forces distribution 4) Estimation of the displacement demand. 5) Evaluation of performance level for the structure

Construction Sequence Analysis and Conventional Lumped Analysis considering P-Delta Effect by Using Etabs

While analyzing a multistorey building frame, conventionally all the probable loads are applied after modeling the entire building frame. But in practice the frame is constructed in various stages. Accordingly, the stability of frame varies at every construction stage. Even during construction freshly placed concrete floor is supported by previously cast floor by formwork. Thus, the loads assumed in conventional analysis will vary in transient situation. Obviously, results obtained by the traditional analysis will be unsuitable. Therefore, the frame should be analyzed at every construction stage taking into account variation in loads. The phenomenon known as Construction Sequence Analysis considers these uncertainties precisely. Therefore, the building structure should be analysed at every stage of construction taking into account the load variations. In this project two cases have been considered. Whereas in Case 1 the multistoried building (G+22 storied) with floating columns and transfer girder will be analysed by response spectrum method and considering P-delta effect as a whole for the subjected loading and in Case 2 the multistoried building (G+22storied) with floating columns and transfer girder will be analysed by response spectrum method with reference to the construction sequence or staged construction and considering P-delta effect. In the present study a G+22 storey multistoried R.C.C building model is modelled using Etabs 2019 software. Response spectrum analysis is made by considering building situated in zone III.Building models are analyzed by Etabs 2019 software to study the effect of maximum positive moment, maximum negative moment, maximum shear forces, maximum deflection, maximum torsion moment of transfer girder beam and total axial load under transfer girder and floating column etc

A study on earthquake performances of reinforced concrete buildings with various number of stories

Seismic codes generally require that the Equivalent Seismic Load Method or the Modal Response Spectrum Method is adopted in the design of buildings. In the equivalent seismic load method, the equivalent seismic static force applied to the building is determined depending on the seismicity of the region where the building is located, the usage class of the building, the fundamental period of the building and the building mass. Later, this equivalent seismic load is reduced by the seismic load reduction factor to take into account the increase in the capacity of the system and the decrease in the seismic demand due to the nonlinear and inelastic behavior of the system, i.e., by accepting limited inelastic deformations in the building subjected to the design earthquake. Then, structural system of the building is analyzed under the reduced seismic forces in addition to the vertical loads by using the load combinations given in the design codes. The process is completed by designing the sections and the structural elements of the building. Similar processes can be implemented by using the modal response spectrum method. The difference between these two methods is consideration of the higher modes of the building instead of the first mode only and the use of the modal masses of the building for each mode, instead of the total mass of the building. In the latter method, the contributions of the higher mode are combined by using specific superposition rules. The codes assume that the structural systems designed in this way will exhibit the almost same level of inelastic deformation, i.e., the controlled damage state, regardless of the building parameters, such as the number of stories. In this study, an attempt is made to investigate the validity of this implicit acceptance. For this purpose, the buildings with a various number of stories are designed by satisfying the bare minimum requirements of the code only, as much as possible. The seismic behavior and the lateral load capacity of these buildings are examined by the static and dynamic nonlinear analyses. The ratio of the nonlinear load capacity to the reduced equivalent seismic load is evaluated depending on the number of the stories of the buildings. The results which are presented in detail yield that the buildings with a low number of stories have relatively larger nonlinear lateral load capacity-to-the reduced elastic seismic load ratio, which is not compatible with the general implicit assumption made in the seismic codes.