Design Assessment of Short-Span Steel Bridges

The assessment of four short-span steel bridges from 24 to 42 m under local overloaded trucks and ground motion records are presented and discussed. Bridges were virtually located in Mexico, and so the vehicular live loads, earthquake loads due to local seismicity, and other local loads were adapted in the design. A realistic condition of the local design truck for Mexico was selected from survey traffic flows reported for local highways. Nonlinear dynamic analyses were carried out using seven historical records associated with the largest vertical intensities from subduction earthquakes in Mexico. The results are intended to evaluate the local practice, which frequently adopts the current AASHTO LRFD Specifications in the absence of an official local design code for bridge structures. This research pretends to provide design recommendations for short-span steel bridges in Mexico, in particular for those related to the influence of local seismicity and overloaded vehicular loading in local highways. Results achieved from the strength and serviceability limit states indicate that the design of the steel plate girders is controlled by the gravity load combination, rather than the combination with both horizontal and vertical ground motion records. Due to disparities in the total vehicular weight, bridges designed for the HL-93 load required by AASTHO are not safe for the overloaded T3-S2-R4 truck that is critical in Mexico. The discrepancies in reliability are minor for the shorter-span bridges due to variances in the number of axes and the total length, but become higher as the span length increases.