Fatigue Design of Modular Bridge Expansion Joints

Experimental and analytical research was recently performed to develop performance-based specifications and commentary for the fatigue design of modular bridge expansion joints (MBEJ). The resulting proposed fatigue-design and test specifications resulting from this research are discussed. These specifications are intended for integration into the present AASHTO Load and Resistance Factor Design (LRFD) Bridge Design Specifications. For consistency with the bridge design specifications, the proposed MBEJ fatigue-design specifications used the same fatigue-design truck as was used by the present AASHTO bridge specifications. However, one important modification of the AASHTO truck loading for MBEJ is the explicit recognition that the rear axles of the HS series trucks actually represent tandem axles. A simplified method to estimate the distribution factor (i.e., the fraction of the range of the design-wheel load assigned to a single “centerbeam”) is recommended. Dynamic impact on both the vertical and horizontal direction is discussed. Also, guidance on structural analysis of MBEJ, good detailing practice, and fatigue resistance and testing are presented. MBEJ designed under the proposed specifications should be resistant to fatigue cracking. The additional material and the improved details, which will be required to comply with the proposed specifications, are not expected to increase the initial first cost of MBEJ substantially.