Abstract

Seismic resistant design philosophy incorporates the non linear response of the structure by using appropriate Response reduction factor (R). The value of R is directly related to the ductility level provided in the structure. Greater the assumed value of R, grater will be the ductility in the structure. The non linear response of structure will be more than the linear response because of material non linearity, factor of safety in load combinations, structural redundancy and ductility. Use of higher values of R is encouraged because of significant reduction in base shear leading to more economic structure. Value of R for reinforced concrete structure depends on the type of framing system. Proposed IS 1893 draft classifies framing into three categories i.e. 1) Ordinary Moment Resisting Frame (OMRF), 2) Intermediate Moment Resisting Frame (IMRF), and 3) Special Moment Resisting Frame (SMRF). In the paper, study is done to compute the value of R, component wise of a G+4 storey building designed for all seismic zones, considering ductile and non ductile design provisions and the same is compared with the assumed R to check the safety of the structures. R provided is computed from the obtained pushover curves.

Abstract

Past response analyses of structures under earthquake excitations revealed that both the maximum displacement and the number of inelastic excursions cause higher damage to the structure. However, it is observed that the quantification of damage is a difficult task. In the paper, a new methodology is proposed for the quantification of damage of reinforced concrete framed structure. This method is based on the nonlinear energy dissipated by the structure along the complete displacement path. Three methods have been proposed to assess the global damage state of the structure, for any deformation level. In these proposed methods, the damage index is expressed as the ratio of nonlinear dissipated energy at an instant, to the total non-linear energy capacity of the structure. To calculate the energy, pushover curve is plotted between base shear versus displacement at C.G of external force profile, which provides consistent meaning for work done by external forces. The area under the curve represents the energy dissipated by the structure. To illustrate the proposed concept, two cases i.e., G+5 and G+9 story structures have been considered. Keywords: Pushover analysis, expended energy, total energy, damage index.

Abstract

Reconnaissance reports of past earthquakes states that the open ground storey is one the most common problems, causing severe damage in the structural members of ground storey. In majority of the buildings, it was observed that even after proper ductile detailing, there is severe damage to the structure. This is mainly attributed to the presence soft storey. In this paper, a study is carried out to improve the seismic performance of a 5 storey open ground floor building with ductile detailing. The seismic performance is improved by: (a) providing wall infill in some portion, (b) increasing the moment carrying capacity of ground storey columns, and (c) combinations of the above two. The proposed methods can be used for new structures by incorporating the effect in design philosophy or can be implemented in the strengthening of existing structures. The performance of the structure is determined with the help of Non Linear Pushover analysis. The main parameters investigated are interstorey drift and lateral displacement. The study shows, with increase in design moments as per seismic codes for the columns having open ground storey will not improve the performance of the structure significantly. Also the open ground storey columns are severely damaged making their repairing difficult and costly. It is suggested that seismic performance of the structure can be improved more significantly by combination of constructing wall infill and higher design moments in columns; if damage occurs in wall only, it can be reconstructed and structure can be repaired easily. Keywords: Open ground storey, pushover analysis, retrofitting, design provision

Abstract

The use of unreinforced brick masonry as infill material in reinforced concrete frames is inevitable even in higher seismic zone areas. With increasing demands for architectural features in buildings, the provision of soft storey is a common practice in many multi storeyed structures throughout the world, for parking. The standard code of practice in many countries suggests higher design forces for the columns present in the soft storey. In order to understand the affect of increase in design seismic forces on the columns in a structure present in higher seismic zone areas, a study is carried out by taking pushover analysis as a tool for obtaining capacity of the structure. A comparative study between three types of arrangements; type I: structure with infill walls in all floors, type II: structure with open ground storey, type III: structure with open ground storey and columns designed for increased forces. It is observed that there is an increase in maximum load carrying capacity for the type III structure as compared to type II structure with no considerable change in behaviour of the two types of structures. It can be concluded that the increase in design forces of the columns at open ground storey may not lead to the safety as of structure type I. Keywords: Unreinforced brick masonry (URM), multi storeyed structures, higher seismic zone areas, soft storey, pushover analysis

Abstract

According to current seismic zone map around 60% of India’s land area is prone to moderate to severe earthquakes. And earthquake losses, in terms of life and property in last 2 decades have been high, with housing contributing to over 95% of life loss; this failure attributed to improper design and construction practices of housing.Thus, all the three factors influencing earthquake risk of houses in India are above danger levels in many districts of India – hazard, exposure and vulnerability. This paper classifies housing risk in the entire country into four groups; about 47% of population is living in the highest risk. Gigantic effort is required to mitigate the risk. The paper also suggests some steps to move forward to reduce earthquake risk to housing in India.

Abstract

Door and window openings are unavoidable components in RC masonry in-filled frames because of functional and ventilation requirements. The presence of openings in RC masonry in- filled frames reduces the lateral stiffness and strength of the wall, which modifies the actual behavior of structure. If these openings are located in the restricted zones like areas within middle two thirds of a wall panel, then the wall needs to be strengthened by providing necessary structural elements such as lintel or lintel bands (i.e., horizontal/vertical bands) around them. Lack of such strengthening techniques may cause the structure to undergo severe damage during the seismic excitations. In this paper, the change in response of RC masonry infilled frames due to the presence of lintels and lintel bands above the openings is studied. For studying the behavior of the frames, static non-linear pushover analysis using Applied Element Method (AEM) based analysis tool has been used.

Abstract

Buildings in urban areas and metropolitan cities are constructed very close to each other. This is because of the requirement of functional usage and high land value. Because of the insufficient gap between the adjacent buildings or adjacent units of the same buildings, they are most vulnerable for seismic damage like pounding. The adjacent land generally belongs to different land owners, where they construct the buildings for different requirements (residential, public). This leads to different dynamic properties of the adjacent buildings. During the earthquakes these may vibrate in or out-of-phase leading to damages, varying from slight architectural damages to severe structural damages. In this paper the pounding analysis is done for different cases of different building positions like buildings of same height and same floor level to buildings in row, are analyzed using SAP (2000) software package. When the two buildings are placed at different floor levels the impact force is more than buildings with the same floor levels. Also when buildings are in a row exterior building suffers more pounding damage than the interior building.

Abstract

Centre for Earthquake Engineering, Brick mamasory is one of the oldest material used for the construction of load bering

Abstract

Modern research in India on dams has entered a distinct phase subsequent to the damage to Koyna dam, located in hitherto considered stable continental part, due to an earthquake on 11th December, 1967 in Koyna district, India. Out of about 5,100 large dams in India, a significant number are in moderately high and high seismic zones. As such they may be prone to probable instability to the dam’s structure due to earthquake resultant impacts. Even though none of the dams other than Koyna got damaged in India due to high magnitude earthquake activity, since 1967, it is felt necessary to understand the behaviour of dams due to water load coupled with dynamics of faults that are present in the vicinity of the dam, as dam failures due to earthquake activity are reported from different parts of the world. In this paper, damage to Koyna dam due to a fault motion caused nearby has been studied. A concrete gravity dam is selected from the National Importance Dams of India. Structure-1(S1) as a concrete gravity dam with foundation and structure-2 (S2) as a concrete gravity dam with foundation and soil strata are numerically modeled using Applied Element Method (AEM). Displacement at the base of soil strata is given to generate reverse fault effect on the dam. Behavior of dam is studied by direct and sub-structure methods. In the direct method, the effect of fault motion on dam is studied in S2, by modeling dam at different locations on foot wall and hanging wall. In sub-structure method, free-field accelerations are recorded at different locations on foot wall and hanging wall while only the sub-structure is subjected to fault motion. The recorded accelerations on the surface are used as input to analyze super structure S1. Comparison on behavior of dam in models S1 and S2 is later drawn.

Abstract

Analysis and design of high-rise buildings for lateral load such as wind load and earthquake are the major issues which are playing significant role in recent decades. This paper describes a recent application of the computational fluid dynamics technique for wind analysis. Conventional wind analysis suggests wind tunnel experiment for arriving at the wind forces for a given structural form. As a case study a regular 38-story high-rise building (Jamieson place, Calgary Canada1) made of concrete with shear wall, built in downtown Calgary 2010 is selected. It is assumed that the building is located in highly seismic area. The design objective was to develop most cost-effective structural system while meeting building functionality goals and adhering to code requirement. The main structural design issues considered in this building are reviewed: Static analysis, Dynamic Analysis, Wind Analysis and Stability Analysis. Initial static and dynamic analysis is conducted in SAP and later wind analysis is conducted in Ansys as opposed to wind tunnel experiments. The building model is modeled in Ansys workbench and then the mesh file is imported to Ansys CFX for CFD simulation and analysis. After CFD analysis the wind forces on the building model are extracted in Ansys CFX-Post and imported to the structural model in SAP 2000 for the structural analysis.