EVALUATING THE GAP SIZE IN BRIDGE STRUCTURES BY CONSIDERING THE EFFECTS OF POUNDING AND SOIL-STRUCTURE INTERACTIONS

In order to reduce the cost and time of seismic analyses, due to lack of correct understanding of structural characteristics and the forces acting on, usually simplified assumptions are applied in the structural modeling that could lead to unrealistic responses. One of these simplified assumptions in bridge modeling is ignoring the pounding phenomenon and soil-structure interaction. Nowadays, the bridges are considered as a vital component in urban and inter-urban transportation systems that the disruption in their operation due to partial or full collapses could lead to disruptions in the transportation system and heavy costs and consequences. One of the major factors, which is considered by the researchers after some earthquakes such as Northridge, Kobe and Chi Chi and their destructive effects on bridges in recent decades, is the pounding phenomenon. This phenomenon is a result of a collision
between two parts of the deck and/or deck and lateral piers (abutments) in the gaps during the earthquake. The pounding in bridges could cause damage in the deck and abutment or the dislocation of deck from the pier. In conventional bridge designs with a few centimeters gap, pounding in severe earthquakes will be unavoidable. Therefore, in this study, with modeling two- and three-span bridges with different periods and considering the gaps of 2.5, 5, 7.5, 10, 12.5 and 15 cm, the effects of the gap size on seismic parameters, including maximum absolute displacement of the deck, the maximum pier bending moment, the maximum pounding force, and the number of pounding, are analyzed. The bridges are subjected to 8 far-field and 8 near-field accelerograms. The results show that increasing the size of gap reduces the number of poundings and increases the maximum deck displacement. However, the trend of changes in maximum pounding force is subject to the bridge period and applied earthquake specifications. In addition, the near-field earthquakes lead to greater seismic responses than that of the far field ones.