Comparative study on construction cost of same structural system in different seismic zones of Bangladesh

Abstract

Geographical location of Bangladesh makes it ideally suited to natural disasters. Tectonic frame work of Bangladesh and adjoining areas indicate that Bangladesh is situated adjacent to the plate margins of India and Eurasia where devastating earthquakes occurred in the past. The historical seismicity data of Bangladesh and adjoining areas indicate that Bangladesh is vulnerable to earthquake hazards. As Bangladesh is the world’s most densely populated area, any future earthquake shall affect more people per unit area than any other seismically active regions of the world. The pattern of the ground surface acceleration contours having 200 year return period presented in forms the basis of seismic zoning of Bangladesh. In the light of these after various researches BNBC, 1993 has been divided into three seismic zones, namely zone-3, zone-2 and zone-1 with zone-3 and zone-1 being the most severed and at least respectively. The occurrence of earthquakes in an earthquake prone region can not be prevented. So it is suggested to follow seismic code in order to reduce the loss of life. The engineers do not attempt to make earthquake proof buildings that will not get damaged even during the rare but strong earthquake; such buildings will be too robust and also too expensive. Instead, the engineering intention is to make buildings earthquake resistant; such buildings resist the effects of ground shaking, although they may get damaged severely but would not collapse during the strong earthquake. It mainly depends on proper choice of structural system, combination of load, design and detailing, compressive strength and reinforcement used in structure. Thus, safety of people and contents is assured in earthquake-resistant buildings, and thereby a disaster is avoided. This is a major objective of seismic design codes throughout the world. This study has discussed about various structural system and strength of materials for three seismic zones of Bangladesh. The present study is aimed at finding out the variation of costing for a building of same structural system in three seismic zones of Bangladesh. To achieve the aim of this study, three different height of structures 90 feet (27.43 meter), 120 feet (36.37 meter) and 152 feet (46.4 meter) have been selected for two values of R (8, 12). ETABS 9.5 and SAFE 8.1.0 software are used for analysis and design of various structural elements. In the present study effort has been made to critically evaluate the effect of seismic load in same structure in three seismic zones of Bangladesh. It is found that all structural elements of a building are not designed by same load combination. The structural elements of all these height structures have been designed based on wind load combination at seismic zine-1 for both values of R. Few structural elements of these structures are designed based on seismic load combination. Few are designed on wind load combination at zone-2 for both values of R. Most of the structural elements of these structures are designed based on seismic load combination for R equal to 8 and 12 at seismic zone-3. It has been observed that when height of the structures is increased, more structural elements are designed based on wind combination. So, seismic load has more effect comparatively on mid height structures. It has been also found that when a beam designed by seismic load combination, the increment of negative reinforcement at higher seismic zone is comparatively higher than positive reinforcement. Average reinforcement and concrete required for beams and columns in each square feet, has been calculated separately for three seismic zones of Bangladesh. It is found that average reinforcement required per square feet of a building is 1.87 kg, 2.09 kg and 2.29 kg in zone-1, zone-2 and zone-3 for R equal to 8 respectively. In the same way, reinforcement required in each square feet for a building are 1.87, 1.98 and 2.12 kg in zone-1, zone-2 and zone-3 for R equal to 12. Similarly, concrete required per square feet of a building is 0.30 cft, 0.32 cft and 0.34 cft in zone-1, zone-2 and zone-3 respectively for both values of R equal to 8 and 12.