An investigation of the structural capacity of the Alabama Department of Transportation’s standard prestressed precast concrete piles
Prestressed precast concrete piles (PPCPs) are commonly used in bridge foundations throughout the southeastern United States. The Alabama Department of Transportation (ALDOT) particularly uses them in the coastal regions in non-cohesive soils and where corrosion would be expected from salt or brackish water. ALDOT’s currently listed pile design capacities in their structural design manual (SDM) were found to be lower than those for similar PPCP pile sizes used in surrounding states. This prompted the question as to why these values were lower, and whether they could safely be increased. A joint research project involving researchers from the University of Alabama and the University of South Alabama set out to answer this question, considering the structural and geotechnical implications respectively. This thesis particularly investigates the structural capacity of ALDOTs PPCPs through a series of tasks. First, an in-depth review of the practices of surrounding DOTs was conducted, evaluating how ALDOT’s practices are similar and where they diverge, to arrive at plausible explanations for ALDOT’s current standard capacities. Next, a simple analysis program was developed using Microsoft Excel, to calculate the combined axial and moment capacities of the standard ALDOT piles. Following this, to evaluate the expected demand on pile bents using the current bridge loading (HL-93), three prototype bridges were modeled and analyzed using standard structural analysis software. Using the analysis, the demand on pile bents under different load combinations were estimated and compared with the previously determined capacities. Based on this analysis, the listed structural capacities of ALDOT’s standard PPCPs could be increased.