Behavior of Expanded Polystyrene (EPS) Inclusion at Integral Abutment Bridges

Systems that are rigidly connected to the bridge deck without expansion joints, and by courtesy of this connection, the bridge substructure and superstructure move as one is called integral abutment bridges (IAB). The use of IAB has become reasonably widespread since the 1960s due to low construction and maintenance costs. In addition, studies have shown that IABs show better seismic performance and allow better ride quality. 

There are two types of integral bridges: Fully-integral (F-IAB) and semi-integral abutment bridges (S-IAB). The main difference between the fully and semi-integral abutment bridges is that semi-integral bridges contain an expansion bearing. The focus of my research is to examine the behavior of S-IABs. 

Apart from its advantages, cyclic loadings due to seasonal temperature changes in both fully integral and semi-integral bridge abutments cause excessive settlement of bridge approaches and an increase in lateral earth pressure.  With the increase in temperature during the summer months, the bridge girders expand, and the abutments are pushed towards the backfill. Conversely, contraction in the girders during the winter months cause the integral abutment to be pushed away from the backfill. These movements expose the bridge to cyclic loading during its service life. As a result of these repetitive loads, excessive settlements occur at bridge approaches. Also, because of these movements, the backfill material becomes increasingly dense, and the lateral earth pressure gradually increases. This phenomenon is called stress-ratcheting. 

To mitigate these problems, one of the common practices in Virginia is to install expanded polystyrene (EPS) at the junction of the steel girder and the backfill. The goal of this practice is to create an elastic zone so that the bridge girder could move freely but does not cause excessive settlement or increase lateral earth pressure. However, past field performances indicate that the properties of the EPS used for this purpose plays a very important role in terms of the effectiveness of this approach. The goal of my research is to evaluate and characterize two different EPS materials referred as standard and elasticized and based on the findings, design and implement a long-term cyclic loading test to evaluate the performance of these materials. Findings from my research will lead into revisions of the design of this so-called “elastic zone” and improve the performance of the S-IABs.