International Journal of Advanced Structures and Geotechnical Engineering ISSN 2319-5347, Vol. 06, No. 02, April 2017 IJASGE 060201 Copyright © 2017 BASHA RESEARCH CENTRE. All rights reserved Lateral Strength and Safety Evaluation of Piers of Kadamtali Flyover in Chittagong, Bangladesh MOHAMMAD RAIHAN MUKHLIS 1* MD. ABDUR RAHMAN BHUIYAN 2 1 Institute of Earthquake Engineering Research, Chittagong University of Engg. and Tech, Bangladesh 2 Department of Civil Engineering, Chittagong University of Engg. and Tech, Bangladesh Email: raihan.ce@live.com Abstract: Chittagong, the only sea port city of Bangladesh, situated in seismically active region near Chittagong-Tripura Fold Belt (CTFB) may experience certain strong earthquakes resulting severe damage of existing bridges like Kadamtali flyover. The current study mainly aims at safety evaluation of piers of Kadamtali flyover. To the end, failure mode, lateral strength and displacement ductility of piers have been evaluated as recommended by Japan Road Association (JRA). Ultimate flexural strength of piers has been computed from the force-displacement relationships obtained by the moment curvature relationships of piers as per JRA and using SeismoStruct. Moment curvature relationships of piers are derived from nonlinear sectional analysis of pier sections. Shear capacity of piers have been calculated by the equations provided by JRA. Lateral strengths have been determined depending on the three failure mode of the piers where displacement ductility have been computed using yield and ultimate displacement of flyover piers obtained from the force- displacement relationships. Three spectral accelerations corresponding to three peak ground accelerations (PGA) related to the seismic zoning of Bangladesh are used in safety evaluation. Lateral force demand of piers corresponding to spectral acceleration is determined using the displacement ductility and seismic weight. Finally, safety of the piers is evaluated according to ductility design method described by JRA. Keywords: Flyover; Failure Mode; Lateral Strength; Displacement Ductility; Pushover Analysis; Safety Evaluation. Introduction: Flyovers are generally those bridges which are constructed at intersections of highways that cross over another road to separate the vehicles of different direction and to form a grade separation. In recent years, flyovers have become the easiest alternative to compensate traffic jams at intersections of major cities in Bangladesh. A number of flyovers are being constructed in Dhaka and Chittagong metropolitan cities with a view to reducing the traffic congestions. Bridge structure plays very important role for evacuation and emergency routes for rescues, first aid, medical services, fire-fighting and transporting urgent disaster commodities (Alim et. al., 2014). Highway bridges are vulnerable to earthquakes proved by past earthquakes, such as the 1971 San Fernando earthquake, the 1994 Northridge earthquake, the 1995 Great Hanshin earthquake in Japan, and the 1999 Chi-Chi earthquake in Taiwan (Hwang et. al., 2001). A number of highway bridges have collapsed or have been severely damaged by some previous earthquakes, even though they were subjected to earthquake ground shaking of an intensity that has been frequently less than the current code intensities (Khan et. al., 2014).When the rocks along a weak region in the earth’s crust reach their strength, a sudden movement takes place and opposite sides of the fault suddenly slips and release the large elastic strain energy stored in the interface rocks. The sudden slip at the fault causes the earthquake. A violent shaking of the earth when large elastic strain energy released spreads out through seismic waves that travels through the body along the surface of the earth. Most earthquakes in the world occur along the boundaries of the tectonic plates (UPSeis, 2016). By its geographical position, Bangladesh is being treated as very vulnerable country with its high risk of earthquake hazard. The Indian plate is moving 60 mm/yr in a northeast direction and subducting at the rate of 45 mm/yr under the Eurasian and 35 mm/yr under the Burmese plates in the north and east, respectively (Bilham, 2004). Bangladesh stands on the northeastern corner of the Indian plate while Chittagong is situated over Chittagong-Tripura Fold Belt (CTFB). Most of the active faults within CTFB is thought to be secondary faults and deformations related to the rupture of the Tripura segment shown in Fig. 1. However, a part of these faults may generate large earthquakes separately from the plate boundary fault like the 1918 Srimongal earthquake. However, it is difficult to separate active structures from the secondary structures. Some active faults within Chittagong have been shown in Fig. 2 among which Sitakund fault, Patia fault, Sitapahar fault, Kalabunia fault have potentials to produce some significant earthquakes. Sitakund fault zone is located at Northwest side of Chittagong city and the nearest fault from main city (Mukhlis et. al., 2016).