Seismic effects of elevating bridges with steel pedestals in the southeastern United States

Steel pedestals have been used in the southeastern parts of the United States to elevate highway bridges and decrease the likelihood of vehicle collisions with bridge decks. However, the seismic performance of bridges elevated with steel pedestals is still unknown. To investigate the effect of elevating bridges with steel pedestals, this paper uses the results of previously conducted experimental tests to model the hysteretic behavior of three types of steel pedestals in a detailed 3D finite element model of a representative bridge. One short pedestal (with a height of 500 mm) and two tall pedestals (with a height of 850 mm) are studied. The structural responses of the studied bridge with the addition of steel pedestals are compared to the structural responses of the same bridge before elevation, where elastomeric bearings support the deck. This study considers five different locations in the southeastern United States and for each of them selects 20 artificial ground motions at two hazard levels of 2% and 10% probability of exceedance in 50 years. The selected artificial ground motions are applied to the representative bridge model in four cases: one case with elastomeric bearings and three cases with three studied pedestals. Because of the large amount of resulting data, a statistical effects model is employed. The statistical effects model is a statistical tool that uses the statistics of the data to investigate the effect of each studied parameter such as bearing type, bridge location and hazard level on the structural responses. Results show that elevating bridges with the studied steel pedestals decreases longitudinal and transverse deck displacements, longitudinal shear and moment in columns, cap beam moment and pounding force. In the transverse direction, elevating the bridge leads to an increase in the abutment force. Also, results show that the studied tall steel pedestals are more effective than the studied short steel pedestal in decreasing longitudinal shear and moment in columns and decreasing transverse deck displacements while offering a height advantage. A study of the stability of the pedestals in this paper shows that the three types of studied pedestals may become unstable in earthquakes, thereby serving as a means to help determine where the installation of steel pedestals would not seem detrimental. ► We study the seismic effects of elevating a typical bridge with steel pedestals. ► Elevating the studied bridge with the steel pedestal