47 Journal of Structural Engineering and Geotechnics, 7 (1), 47-54, Winter 2017 QIAU The Effect of Compressive Strength Reduction of Column Section Expose due to Freezing-Thawing Cycles on the Seismic Performance of Bridges Saeideh Alsadat Mousavi *,a , Mehran Seyed Razzaghi b a Department of Civil and Architectural Engineering, Qazvin Branch Islamic Azad University, Qazvin, Iran b Assistant Professor, Qazvin Branch, Islamic Azad University, Qazvin, Iran Received 10 April 2016, Accepted 20 July 2016 Abstract One of the serious damages of tremendous earthquakes is the damage to bridges as the major components in an arterial road network, as relief operation is interrupted following cutting roads. Regardless of the magnitude and severity of an earthquake, other factors are also important in the strength and seismic performance of concrete bridges. Freezing-thawing cycles are among the factors, which erode the piers of concrete bridges over time. Therefore, it is necessary to evaluate the seismic vulnerability of bridges for future designs. This research aims at discussing the effect of freeze-thaw cycles on the seismic performance of concrete bridges using fragility curves. Fragility curves express the conditional probability to reach or exceed a level of damage as a function of ground motion parameters. The curves have been developed analytically using a probabilistic method. Ground motion parameter, peak ground acceleration, structural criterion, and relative displacement of piles were considered. The non-linear time history analysis in OpenSees was used for demand determination. The curves were drawn for the slight, moderate, and extensive damage levels in two modes of before and after damage caused by thawing and freezing, i.e. the mode in which the compressive strength of column section expose reduced. With respect to the fragility curves, the strength reduction increases bridge vulnerability, especially on slight damage levels. Comparing with the cyclic curves of the most vulnerable column in two modes of before and after the damage showed that energy absorption capacity lowered with the expose compressive strength reducing. Keywords: Concrete Bridges, Concrete Compressive Strength, Freezing-Thawing Cycles, Seismic Vulnerability, Fragility Curve, Nonlinear Time History Analysis, Damage Levels, Peak Ground Acceleration 1. Introduction Bridges, as specific structural systems, have particularly attracted attentions of designers because their structural shape is a simple expression of their functional requirement. Therefore, the structural solutions considered for them should be confirmed as far as bridge function and elegance are concerned. Most bridges with simple structure, especially those made of RC or prestressed concrete, failed to withstand at the expected level in different earthquakes [1]. Preparing high-strength concrete, manufacturing high yield strength steel, employing high spans using modern implementation methods, easy ductility, elegance, and other concrete specifications have made concrete bridges into one of the most common bridges. On the other hand, * Corresponding Author Email address: mousaviss@yahoo.com concrete is exposed to the damages including cracking, abrasion and erosion, sulfate damage, reinforcement erosion, etc. The damage caused by continuous freezing and thawing of the water inside concrete is one of the common causes for vulnerability of concrete structures in cold climates [2]. Many studies have been conducted on the effect of freezing-thawing cycles on concrete specifications [3-8]. In 2006, Sheng et al. studied the strength and deformation behavior of plain concrete under 2-axial and 3-axial pressures [9, 10]. Lee and Gu estimated the lifetime of a concrete structure under thawing and freezing cycles [11]. Thawing and freezing cycles throughout the day and during years lead to continuous damage of the walls of piers of concrete bridges, which challenges the seismic performance of bridges against earthquakes. Generally, the seismic performance of the systems,