Abstract

Construction of buildings without keeping enough setback from plot boundary is very common practise in India. This lead to very closely spaced buildings with practically zero or few mm gap between them. The intension behind this is to utilize the maximum plot area, without knowing the consequences of damage due to pounding during moderateto-severe earthquake shaking. In this study, an attempt is made to check the adequacy of separation distance clause of IS 1893: 2016 and also a comparison is made with similar clauses in international codes of practise. For this purpose, four low to mid-rise RC buildings located in seismic zone IV were designed as per IS 456: 2000 and IS 1893: 2016. These buildings are assumed to be closely spaced with each other, in pair of two, for four different cases. Further, the linear and non-linear time history analysis (NLTHA) were carried out by considering ground motion time histories of three moderate earthquakes recorded in India. From the study, it was found that the separation distance clauses prescribed in IS 1893-2016 are on conservative side.

Abstract

Buildings damaged in past earthquakes have exemplified the poor performance of reinforced concrete moment resisting frame (RC MRF) buildings due to inadequate design and wrong construction practices. The only way to avoid damage to existing buildings is to retrofit them. There is a large stock of RC MRF buildings constructed as per old Indian standards. With the latest revisions in codal provisions, these buildings are considered to be inadequately designed. Therefore, a large stock of existing buildings needs to be retrofitted. However, retrofitting of houses is not a common practice among the general public in India. To encourage retrofitting among the general public, the efficacy of retrofitting needs to be proven with the well-laid process. In this paper, a case study is done to understand the performance of G+5 storey RC MRF precode building after partial and full column retrofitting. Pushover Analysis (POA) is performed to obtain the capacity of the precode building. The capacity is compared with the seismic demand of that area to decide whether retrofitting is required or not. Initially, ground storey columns are retrofitted and POA is performed to study the damage distribution and obtain the updated capacity curve. It is observed that damage shifted to the first storey. Further, the first storey columns are retrofitted and POA is performed again. From the hinge mechanism, it is observed that the damage propagated to the second storey. Further, the second storey columns are retrofitted and POA is performed again to obtain updated capacity and

Abstract

Buildings on hill slopes are highly vulnerable due to its less resistive lateral load capacity. This type of buildings are unsymmetrical and are of in irregular configuration. There are variations in the column height which gives eccentricity to the structure as the center of mass and center of rigidity doesn’t coincide. This irregularity leads to its torsional behavior and gives us the necessity for analyzing these buildings for its base conditions and its behavior by changing its plan configuration. This paper contain the calculation of Twist which is an effective parameter to decide the behavior of the building, Axial forces on the members that can lead to collapse in the structure and about the twist variation with change in the aspect ratio so that we can know the suitability of the configuration of the building. The building on hill slopes does not behave similar to the buildings which are on plane ground. Change in the Aspect ratio means changing the length of the building in ridge direction. Changing the length in valley direction will disturb the load path of gravity load for each and every change in the structure and after some increment of the length in valley direction will fail the structure for its gravity load path. So we can’t play with the length of the building along the valley direction but changing the length along ridge direction does not effect that much to the load path of gravity load and we can obtain a best aspect ratio of the structure for that region. Keywords: Twist, Axial forces, Slope of the ground

Abstract

In India due to rapid economic development and establishment of new companies, many existing buildings were given permissions to raise the number of floors. This addition of new floors to the existing building will increase the loads on the columns which may not be designed for the additional load. Therefore, such columns need to be strengthened to carry the additional loads. RC jacketing is the most preferred strengthening technique to increase the load carrying capacity of the existing building. In this paper, comparison of two RC buildings i.e., One with columns strengthened only on 2 faces and another with columns strengthened on all four sides with RC jacketing is presented. In 2-face RC jacketing, U shape stirrups are used and for 4-face jacketing closed stirrups are used. Behavior of columns strengthened on all four sides using RC jacketing is more satisfactory in the case of immediate occupancy. In case of high seismic zones under cyclic loading, the seismic performance of RC jacketed columns on 2 sides is not desirable for immediate occupancy.

Abstract

Dams are extremely important lifelines of a country. They aid in the growth of the economy. The large-scale devastation due to an earthquake can generate irreversible losses. 2% of the dam failures all around the world take place due to earthquakes. Earthquakes not only cause immediate damage but are also capable of weakening the structure by decreasing its resistance against further damages. In this work, we study the effect of strong ground motion earthquakes on concrete gravity dams. The strong ground motions lying within shallow depths are felt powerfully by the dams, since the high frequency waves are not filtered. This causes more damage to the dam as there is a high probability of resonance in higher modes, a result of the high frequency content in the ground motion. 5 strong ground motions in the Indian Subcontinent have been selected and applied on the Koyna dam which was constructed in the year 1963. 2D analysis of the dam has been performed in standard software. Qualitative analysis of dams shows that there are 3 regions which are most susceptible to damage within a dam cross-section i.e., neck, body and the heel of the dam. In this paper, the displacement of crest and the formation of tensile stresses at the 3 zones - neck, body, heel of the dam due to these 5 strong ground motions is analyzed. The point of highest tensile stress is most susceptible to damage and failure in the face of an earthquake. When the structure is exposed to the ground motions, under normalized peak ground accelerations (PGAs), the structure behaves differently based on the effect of the frequency content of the input signal. By Normalizing the PGA of the ground motion, we grasp an idea of the effect of frequency content on the dam structure. Keywords: Gravity dam; Stress analysis; Qualitative failure analysis; Frequency Content; Deterministic Analysis

Abstract

Open ground storey buildings are quite popular in India due to availability of parking space and high commercial value of the land. However, these open ground storey buildings become first victims during earthquake ground shaking. The same is evident from the collapse and huge damage in ground story columns during past earthquake events. This led to a huge loss of life and property. Hence, there is an urgent need to take up retrofit activities of open ground storey buildings. There were some instances where retrofit activities were taken up on open ground story buildings. However, the performance of the building was not tested after ground storey retrofit. To build confidence among the general public, there is a need to demonstrate that the retrofitted buildings not only save lives but also resist earthquake with minimum damage. This paper is an attempt to demonstrate the same. In this paper, a case study of G+5 open ground storey building has been taken and nonlinear static pushover analysis (POA) is performed to obtain capacity curve. Later, the building is retrofitted in its ground/first storey and again capacity curve is obtained using the POA. It is found that the performance of the building significantly improved. However, from the hinge formation pattern, it is observed that the damage has propagated to the second storey. To improve the performance further, the second storey is also retrofitted and POA is performed again. Further, as per the damage propagation to upper stories, retrofitting is done to respective stories. It is found from the hinge pattern and capacity curves that in retrofitted buildings, capacity increased up to a certain storey and after that no increment in capacity was observed. It is concluded from the study that retrofitting of open ground storey building does not mean retrofitting of only ground storey but all such columns/stories where damage is getting distributed after the retrofit of open ground storey.

Abstract

Estimating the time, location and the size of an earthquake event using neural networks is an emerging technology. Present study aims to predict the near future earthquake events in each of the regions partitioned as clusters of epi-central locations of earthquakes related to Indian subcontinent. K-means clustering algorithm is applied to develop a catalogue of earthquake epicenters. Two approaches are considered for the purpose of forecasting. In the first approach regions obtained as clusters are considered as the area sources. The distribution of time series of (temporal distribution) events are divided into five time periods viz., 15 days, 30 days, 60 days, 90 days and 180 days. The accuracy of forecasting a magnitude for the next time period is studied using application of Recurrent Neural Network In the second approach the seismic data of each cluster is further grouped into three categories of magnitude viz., minor (≤ 4 Mw), moderate (between 4 Mw and 6 Mw) and strong (> 6 Mw). Accuracy of forecasting for each of the group belonging to the clusters is computed considering the same five time periods. The epicentral locations represented as latitude and longitude is the inputs for recurrent neural network. The results show that accuracy of second approach is significantly more than first approach. Finally, an attempt has been made to compare the accuracy level of Recurrent Neural Network method with the accuracy level of Gutenberg Richter law in predicting the earthquakes for future 60 days. It has been observed that Gutenberg-Richter law poorly forecasts near future earthquake. Keywords: Recurrent Neural Network; Earthquake forecasting, Clustering

Abstract

India is a country which is prone to earthquakes. Many great earthquakes of the world have occurred in India, but still safe earthquake construction practices are not popular yet. This is mainly due to lack of awareness regarding earthquake problems and also earthquake safety features of buildings. On the other hand, India is a country with many diversified building technologies where there is a large variation in selection of building materials and building technologies. Over the ages, building materials and technologies were linked to the geo-climatic conditions of the area and the same is evident from census data of the country. However, during past earthquakes, many buildings collapsed due to the lack of earthquake resistant features in these buildings, resulting in huge life loss. This paper is an attempt to identify the critical earthquake resistant elements in each building typology which is popular in a given region. The same is demonstrated by taking two building typologies i.e., framed buildings and load bearing structures in four different regions i.e., hilly region, plain region, snowfall region and heavy rainfall region. From the above, it is clear that each housing typology can be made earthquake resistant by understanding the role of critical elements and by not deviating from standard design which is safe as well as compatible with geo-climatic conditions of the region.

Abstract

Structural engineering involves clear understanding of characteristics of ground motion used in the design of structures to identify the critical aspects of their behavior. Peak amplitude of response (a, v, or d), predominant frequency and duration of strong ground motion are the most important parameters of ground motion that are required for this purpose. These parameters are influenced by the source, path and site conditions. However, it is also found that for the same distance these characteristics are highly sensitive to the fault direction and the side on which the site lies i.e., hanging wall or foot wall. In this paper, a case study is performed to understand the influence of fault direction and location of site on the characteristics of the ground motion. For this purpose, 371 ground motions recorded during 1999 Chi-Chi, Taiwan earthquake are selected. Initially, these ground motions were arranged in terms of fault parallel and fault normal direction and also according to distance from the fault. Later, ground motion characteristics were obtained using standard procedures. From the above, it was found that, in the near-fault region, PGA and PGV on the hanging wall are higher by at-least 20% than that on the footwall. From this observation, the near-fault region can be defined not by using the distance from the fault, but by observing the ratio of PGA values in fault normal and parallel directions. This method of estimating the near-fault region is reliable because the hanging wall effect is caused only due to the inclined dip-angle of the fault which is inevitable in most of the thrust and normal faults. Keywords: Hanging wall effect; PGA; Thrust faults; Fault Normal; Fault Parallel

Abstract

UN World Conference on Disaster Risk Reduction held in 2015 at Sendai, Japan, reiterated the need for substantial reduction in loss of life and property. Thus, assessing disaster risk and identifying key items for risk mitigation are in focus. Assessment of disaster risk is a multidisciplinary effort, which includes expected tangible physical loss, such as collapse and damage to built environment. In countries with limited resources, prioritizing risk reduction effort across the different parts of the country needs a quantitative (yet simple) approach to bring objectivity into the decision-making process. This paper presents a simple method, called Earthquake Disaster Risk Index (EDRI), for estimating relative earthquake risk across the different regions in a country; it uses three major constituents of risk, namely Hazard, Exposure and Vulnerability. Hazard is taken as the acceleration hazard specified in the national earthquake design standard, Exposure as per the permitted occupancy in the Local Municipal Byelaws, and Vulnerability through a Level 2 Detailed Qualitative Assessment of buildings built in the Town or City (with penalty points for missing features of earthquake resistance compared to an Ideal Building). First, the EDRI of a Town or City is estimated for each typology of building in the Town or City, and then the net EDRI of the Town or City is obtained as a weighted average of the EDRI of each typology of buildings using the number of buildings of each typology present in the city. The EDRI of a city so estimated can be compared with that of another city. Also, disaggregation of risk through its three major constituents of EDRI will increase awareness of the factors which contribute to risk – from expected intensity of earthquake ground shaking, to exposure of people in each building type, to vulnerability of each building typology. The exercise can be undertaken at a large scale across the country. Policy Makers of a prefecture or a state in a nation will find the results of EDRI to be a useful tool for prioritising allocation of earthquake risk mitigation resources and effort across Towns and Cities.