ABSTRACT
The demand for minimum traffic disruption during bridge rehabilitation or replacement resulted in development of innovative project delivery methods classified under Accelerated Bridge Construction (ABC). Two ABC methods that reduce traffic interruptions typically under 12 hours are: Slide-In Bridge Construction (SIBC) and Self-Propelled Modular Transporter (SPMT) move. Several pilot SIBC projects have been completed in Michigan. For SIBC, the superstructure is typically pulled in place or pushed on the permanent substructure. In the latter case, the superstructure is slid directly on the bearings installed on the substructure. Sliding forces are directly applied to the superstructure and the friction forces are transferred to the substructure. Quantification of loads acting on the substructure during the slide is necessary in order to assess the potential for structural damage, and to develop recommendations towards standardizing SIBC. With this purpose, one of the SIBC project in Michigan was monitored during the lateral slide operation.
The project consisted of one 2-span bridge designed to be pushed in sliding tracks on to the permanent substructure (Figure 1). The abutments of the bridge were supported on piles while the pier was supported on a spread footing. Using load cells for the quantification of loads was impractical because the loads were primarily created from frictional resistance. A quick analysis of the sliding mechanism and substructure configuration indicated measurable movements of the pier when the superstructure was being moved onto it from the temporary substructure. Therefore, the pier was instrumented with high precision crystal targets to measure the movements in three perpendicular directions using a non-contact high-precision laser equipment, the Laser Tracker. Then, an analysis model was developed to calculate the loads acting on the substructure based on soil-structure interaction, force-deformation relations, and the field measurements (Aktan & Attanayake 2015). Sliding bridge and Laser Tracker targets. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315207681/cd556cd4-4dcf-4efe-8e29-56fc67b8bfbd/content/fig144_1.tif"/>
Elastic settlement formulation of a foundation under uniform pressure (NCHRP 1991), settlement expressions for shallow foundations subjected to eccentric loading (Algin 2009), geometric parameters of the pier foundation, and properties of soil below the foundation were utilized in the analysis model.
The force calculated in the slide direction was between 294 kips (1308 kN) and 313 kips (1392 kN). The analysis results indicated that a force couple was developed rotating the superstructure (yaw) and pushing the substructure in the transverse direction to slide (Y direction), which was unexpected. The transverse force was calculated between 158 kips (703 kN) and 357 kips (1588 kN).
