Key Project Details
ClientSolomon Islands Government
ContractorMcConnell Dowel Constructors Ltd
Site WorksSeptember 2011 - March 2012
The Makira Bridge project involves the design and construction of two “High Level” bridges that will cross the Magoha and Maepua Rivers in remote areas of Makira Island in the Ulawa Provence of Solomon Islands. Both bridges have identical superstructures and consist of a 72m single clear span network arch bridge on concrete piers. Both bridges will support a single lane of traffic and footways on both sides of the roadway. The bridges were commissioned and opened in March 2012.
Both the High Level bridges for the Magoha and Maepua Rivers are considered identical except for variations in foundation conditions.
Network arch bridges gain their inherent structural efficiency by the network arrangement of hangers supporting a relatively slender deck between relatively slender arches. The hangers maintain the arch profile and therefore strength, and the arch supports the deck at numerous and regular intervals.
|The bridge design proved very suitable for facilitating the steel fabrication in a quality controlled off-shore fabrication workshop, convenient containerized transport to site, and to span fast flowing tropical rivers without unnecessary impediment.
Given the remote location a comprehensive methodology statement has been produced. The same construction methodology applies to both bridges. The bridge superstructures were detailed to break down into a number of elements 12m long or less for transport. The components were shipped from Batam, Indonesia to Honiara and then to Kaonasugu, Makira and trucked then to the bridge sites.
Working platforms were constructed at each abutment to allow driving of two 1.4m diameter pile casings. Pile driving was done using an 80 ton crawler crane with 5 ton vibrating and hydraulic hammers. A 4 ton drop chisel and air lift was required for the final excavation into sandstone. Following concreting of the piles, the abutment caps, footing and wing walls were constructed.
For each bridge six equally spaced temporary piers were driven in across the rivers. The arch bowstring tie and deck transoms were assembled on sand jacks supported by the temporary piers. The arches were pre-assembled in two halves and lifted into position by the 80 ton crawler crane. Temporary false work props were required to support the half arches from the deck steel work until the splices are complete. The networks of hangers were then fitted between the arches and bowstrings.
Longitudinal steel rails were installed on the deck transoms for placing the approximately 3m by 3m precast concrete deck panels. The deck panels were placed progressively from each end of the bridge so that the deck load is applied symmetrically. As each panel is placed, the gap between panels was a concreted stitch to allow composite action with the transom beams. Outer footway precast panels were then placed.