An Analysis of Bridge Abutment Shear Key Behavior due to Embankment Modeling and Earthquake Intensity

The importance of proper abutment modeling is often overlooked in the analysis of a bridge. Properties such as nonlinearity of the embankment or a lack of embankment mass can lead to unrealistic behavior along the bridge. These shortcuts in modeling can lead to more conservative residual displacement demands in the bridge deck and abutment shear keys, causing improper design and, ultimately, behavior during an earthquake. Current design standards in California allow bridge abutment shear keys to be designed as structural fuses; shearing horizontally with minimal damage to the abutment stem wall. However, if the bridge model fails to account for certain embankment properties, these shear keys may be improperly designed. This study investigates the importance of proper embankment modeling and will show that inaccurate modeling will result in overly conservative displacement demands. In addition, it is difficult to predict the level of shear force experienced in shear keys during an earthquake unless capacity design principles are used. As a result, current design philosophies also suggest that shear keys should be resistant to damage at the design earthquake level. An incremental dynamic analysis of earthquake intensity will show that at low intensity earthquakes, shear key displacement demands are notably large and performance criteria should be developed to prevent such damage at low intensitie