**1. Introduction**

Viaduct structures and elevated bridges are becoming more common for railways and highways. During the past few decades, partially prestressed concrete has been used for the construction of viaduct structures. Earthquakes have a habit of identifying structural weakness and concentrating the damage at these locations. Elevated bridges and viaduct structures have little or no redundancy in structural systems, and failure of one structural element or connection is thus more likely to result in collapse [1]. Therefore, it is of a great importance to carefully understand the seismic response behavior of viaduct structures. Experimental investigations have been carried out in the past to study the deformation and cracking of partially prestressed concrete beams under static and cyclic fatigue loading [2]. Various loading tests have been carried out to study the inelastic response behavior of the elevated bridges when subjected to ground motions. Since the girders of these bridges are generally hinged to the piers, only the piers are subjected to earthquake

forces. Moreover, few research studies have been carried out to study the effect of prestressing the reinforced concrete piers of highway bridges [3, 4].

On the other hand, because of the monolithic moment-resisting connection between the superstructure and the columns of the viaduct structures, less bending moments were expected in the bottom ends of the columns, and other plastic hinges at the tip of the columns may result to allow for some energy dissipation at these locations. Additionally, not only the columns but also the girders might have some damage. Yet not enough tests have been performed to study the inelastic response behavior of the partially prestressed concrete (hereafter known as PC) girders of the viaduct structures [5–7]. The objective of this study was to obtain the inelastic response behavior of such PC viaduct structures due to severe earthquake excitation.

A study that includes experimental and analytical phases was carried out. Specimens representing the PC girders of the viaduct structures were tested experimentally. Statically reversed cyclic loading and sub-structured pseudo-dynamic testing were conducted. The objective of the statically reversed cyclic loading test was to study the inelastic response behavior of the PC girders and to obtain the hysteretic-load deformational characteristics. During the sub-structured pseudodynamic test, the PC girder was tested experimentally, and the RC columns of the viaduct structure were simulated analytically. Response analyses for the viaduct model in terms of hysteretic moment-rotation curves and time histories were carried out. The plastic deformability expressed in terms of the ductility factor and the dissipated energy was examined. A comparison between the experimental results and results obtained from response analyses was made.
