Dynamic Effects Caused by SPMT Bridge Moves

This study provides the result of dynamic effects of self-propelled modular transporter (SPMT) movements during a simulated bridge transport. Accelerometers were attached to an SPMT and different transport scenarios were simulated under several loading conditions. For the vertical direction, a traverse of uneven terrain provided the peak platform acceleration (PPA), whereas a rapid start-and-stop motion controlled both longitudinal and transverse directions. The observed PPA increased as the total weight decreased. Vertical accelerations were found to be highly dependent on the SPMT speed. The horizontal accelerations were not affected by the speed of the SPMT, but they were affected by the ability of the operator to perform a braking operation. Response spectra suitable for the design for each direction were constructed from the time history graphs corresponding to these tests. The maximum pseudo accelerations (MPAs) for heavy, medium, and light load cases were 0.68, 1.07, and 2.3g in the vertical direction; they were significantly more than the horizontal direction with 0.32g for heavy, 0.47g for medium, and 0.60g for the light load case. The dynamic forces on the cargo (falsework or bridge) either increased or stayed constant as the stiffness of the system increased. Although vertical accelerations, which mostly affect the bridge superstructure components, can be reduced by limiting the SPMT speed, the horizontal accelerations can be reduced because some ductility and inelasticity within the bracing of the falsework and response modification factors may be applied to the developed spectra. Dynamic dead load impact (DLI) factors were found to be in excess of those often used for the design because of the worst-case nature of the presented results.