New Phra Nang Klao Bridge

New Phra Nang Klao Bridge is located in Nonthaburi province of Thailand and was constructed adjacent to the existing bridge. The bridge, carrying six traffic lanes crossing the Chao Phraya River, is recognized as the prestressed concrete box girder bridge with the longest main span in Thailand. The main span of 229 meters is constructed by balanced cantilever method. Due to the geometric constraint, the alignment needs to be horizontally curved toward the upstream of the existing bridge. Thus, this introduces high torsion in the box girder superstructure and transverse bending in the piers. If a symmetrical pile arrangement is adopted, the downstream piles will sustain considerably larger axial compression forces than the upstream piles. To overcome this issue, an analysis by finite element method (FEM) was performed and showed that the unsymmetrical pile arrangement, which corresponds to the torsion direction in the box girder, will result in a rather uniform axial load distribution on piles both during the construction and after the bridge was completely constructed. The unsymmetrical pile arrangement was proved to be effective and can reduce the size of foundation and the number of piles. The analysis also indicated using double-wall piers instead of single stocky column can decrease the magnitude of axial loads in the piles due to its lower flexural stiffness.