Precast Beam Bridges with a Buffer–Gap–Elastomeric Bearings System: Uncertainty in Design Parameters and Randomness in Ground Records

The buffer–gap–elastomeric bearings system used in precast girder bridges with relatively short piers is one of the efficient hybrid seismic isolation schemes. However, there are many uncertain environmental, material, and geometric parameters affecting gap size and, hence, the response of the bridge to earthquakes. To investigate, four different configurations of a three-span continuous bridge were designed for a high-seismicity site in Egypt, considering short or tall bridge piers of high or limited ductility. The performance of each bridge configuration was studied using nonlinear dynamic analysis under ground motions selected to be compatible with the site hazard. Two different treatments of parameter uncertainty were used: a mean parameter model, in which uncertainty was essentially disregarded, versus a random parameter model, represented by 60 realizations of each bridge generated via Latin Hypercube Sampling. Different intensity measures were also studied, showing that the geometric mean of multiple spectral ordinates over a period range that encompassed the vibration characteristics of both a closed-gap and open-gap model best satisfied both efficiency and sufficiency requirements. All in all, parameter uncertainty was shown to be an important issue for such bridges, requiring appropriate consideration for accurate assessment.