Abstract

Symatically analyzied b- value variation in space as well as in time

Abstract

Ports are lifeline systems that function as storage and maintenance facilities for the transport of cargos. The port structures are frequently exposed to failure under severe seismic loading, for example, 1995 Kobe, 1989 Loma prieta, 1999 Kocaeli and 2001 Bhuj earthquakes. The scenario is more critical if the port sites are located within the seismically vulnerable area like Gujarat state of India. This clearly indicates the importance of port buildings and stability that can withstand natural disasters particularly earthquakes. The main objective of this paper is to perform the nonlinear dynamic analysis of Kandla port building subjected to ground motion. Ground motions generated by Institute of Seismological Research (ISR), Gujarat at four locations on Katrol Hill Fault (KHF) and Kachchh Mainland Fault (KMF) were used in the analysis. Finally, the damage of the Kandla port building is estimated though fragility curves. The damage values obtained from fragility curve are 0.46, 0.17 and 0.88 for KHF Mandvi, NKF Jodiya and KMF Jhangi ground motions respectively.

Abstract

Masonry is one of the most common types of construction materials in India. It is commonly used for infill walls in Ordinary Moment Resisting Frames. The strength based design in the code considers the masonry wall as non-structural element and its load is considered on the corresponding elements. The numerical modeling of infill is completely disregarded during analysis of the structure. To design a building realistically, the behaviour of all the primary components is needed and the load carrying capacities are required to be properly assessed. Apart from the strength based design adopted in the code of practice, the modern and advanced approach to design, the performance based design, needs a proper understanding of the behaviour of all the structural elements. Analytical modeling of infill is attempted by many researchers using equivalent strut and tie models which can idealize the behaviour of masonry infill to some extent. The effect of masonry wall on RC frame can be well understood by continuum modeling. Numerical modeling of masonry infill wall is done using Finite Element Method. This paper attempts to simulate the nonlinear behaviour of URM infill frames with varying storeys using Applied Element Method (ARM). Two bay ordinary moment resisting frame is considered with and without infill and capacity is obtained using Nonlinear Static Pushover analysis. One, two and three storey frames with and without openings are also analyzed to understand the differences in drift ratios and the strength of the frame. It is observed that the bare frame carries lesser drift when compared to the frame with infill. This clearly proves the increase in ductility of the frame when provided with infill. In the analyses of infill frame without door and window openings, the maximum base shear of the frame decreased and the drift carrying capacity increased with the increase in number of storeys. Almost the similar behaviour is observed when the infill frame with openings is analyzed.

Abstract

The usefulness of shear walls in the structural planning of multi-story buildings has long been recognized. When walls are situated in advantageous positions in a building, they can be very efficient in resisting lateral loads originating from wind or earthquakes. Reinforced concrete framed buildings are adequate for resisting both vertical and horizontal loads acting on them. Extensive research has been done in the design and analysis of shear wall highrise buildings. However, significance of shear wall in highrise irregular structures is not much discussed in literature. A study on an irregular highrise building with shear wall and without shear wall was studied to understand the lateral loads, story drifts and torsion effects. From the results it is inferred that shear walls are more resistant to lateral loads in an irregular structure.

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

The overall capacity of a structure depends on the strength and deformation capacity of the individual components of the structure. This paper deals with the prediction of effect of a member on global performance of the structure. The performance of a 5 storey RC frame, designed for Indian standard codes has been presented. Non linear pushover analysis is used to draw the capacity curve. During the pushover analysis when the structure becomes unstable, the failed members are identified. In the present study, end columns of the bottom storey which exists in failed members are strengthened by increasing the longitudinal reinforcement, increasing the c/s area and reducing the shear reinforcement spacing. Increase of longitudinal reinforcement or decrease of shear reinforcement spacing not effected much the strength capacity, but the ductility is increased in both the cases. Increasing the c/s area of two columns increased the strength and stiffness of the frame, but the ductility is increased up to a certain limit and then decreased. Parametric study also done for individual column performance with same geometric and material properties as it exists in the frame. The performance of individual column is completely different with frame performance though the geometric and material properties are same this is because of the frame action where redistribution of forces takes place when the member fails in the frame.

Abstract

Tall building construction is booming in India. There are several earthquake safety issues involved in planning, designing and constructing these buildings. Some issues related to seismic behaviour are still not resolved even in developed countries, like USA and Japan. Researchers all over the world are continuously working towards development of latest techniques for improving earthquake safety of tall building. The situation in India is that there are few codes which specify guidelines for earthquake resistant design of structures. However, the guidelines given in this code are useful for regular and relatively small, low-rise buildings. When it comes to tall buildings, every structure is special, several parameter needed to be considered. One such parameter is T. Existing empirical natural period equation given in IS 1893 is suitable only for small to medium rise buildings. There is a serious need for proposing equation for high rise buildings. In this paper an attempt is made to compare empirical equations for natural period of different countries. Study gives that there is a need to propose the new time period formula exclusively for Tall structure based on Indian condition.

Abstract

Response of a structure subjected to gravity and lateral loads depends on the boundary conditions assigned at the base of structure in numerical modeling. Most of the structures are analyzed considering fixed base, but in reality, foundation is not fixed. The fixity depends on the interaction between the soil and foundation. In most of the cases base of a structure undergoes small amount of rotation because of flexibility induced by soil especially at the time of earthquake. Difference in boundary conditions used in analysis and in actual conditions will lead to improper estimation of the design forces, to reduce such effects in numerical analysis fixed base of structure can be replaced by springs or structure base resting on soil to obtain results closer to that of actual base conditions. Stiffness of the spring depends on geotechnical parameters as well as on the dimensions of the foundation. In the present paper an attempt is made to understand the difference between the Linear and Non Linear response of a frame having fixed base, spring base and with soil. Stiffness of springs for spring base structure is calculated as per ATC-40 [1] and JICA [7]. Analysis of structure with soil modeling is complex, specifically for Non Linear behavior for this Applied Element Method is used. Linear and Non Linear response is compared in terms of stress resultants and capacity of the frame respectively, for non linear response static pushover analysis is done. From the study, it is observed that the actual capacity of structure is overestimated assuming fixed base. The fact that the initial stiffness of the structure is governed by the soil stiffness can be clearly stated from the obtained pushover curves. It is also recommended that analysis of structure should be done considering spring base in place of fixed support.

Abstract

The earthquake resistant design of structures according to the existing design philosophy aims to ensure that during their lifetime, the structures resist the maximum possible earthquake without collapse. This philosophy ignores the fact that for the allowable damage at the end of the design life, it is necessary to account for the seismicity of the area in a comprehensive manner i.e., in terms of magnitudes with proper spatial distributions around the site. It is also necessary to estimate damage due to each of these events and also cumulative damage till date. Such a procedure is proposed in the paper and it is applied to heritage structures which stand for longer duration compared to ordinary buildings. As a case study, the proposed methodology is used to evaluate damage to Golkonda Fort located in Zone II according to IS 1893-2002. Proposed approach is based on the estimation of Power spectral density function (PSDF) of earthquakes already occurred and then estimation of damage to the structure during each of these events. Golkonda Fort is modeled using Applied Element Method (AEM). Pushover analysis of the AEM model is also carried out. The damage computed from the proposed approach is plotted on the fragility curve obtained from the push over analysis for comparison.

Abstract

In this paper an attempt has been made to understand the Soil Structure Interaction behavior of pile supported framed buildings under transient loading by taking the interface effects between the pile and soil. For this purpose a three dimensional Finite Element Method is used for modelling the soil-pile structure interaction using SAP 2000. A single bay five storey framed structure with a pile group foundation is modelled. First the significance of soil foundation structure interaction over fixed base analysis is studied, it has been observed that the presence of soil and foundation make a considerable change in response with a shift of natural period of the system. Next, a parametric study has been done to understand the significance of interface behaviour on soil foundation structure interaction. From the results it has been observed that under transient loading the acceleration response of top floor is reduced by two times, when contact between pile and soil has been modeled.