1 TIMBER VEHICULAR BRIDGES IN GHANA – THE PROGRESS TO DATE K. A. Solomon-Ayeh Building and Road Research Institute (BRRI) Kumasi, Ghana [email protected]Abstract The infrastructure in Ghana is relatively low because of, among other factors, the lack of crossing structures like bridges. Existing bridges are predominantly of reinforced concrete and as the cost of the imported steel and cement became expensive, research, particularly at the Building and Road Research Institute (BRRI), started on the possibility of using Lesser Used Timber Species (LUS) for vehicular bridges, at least on low-volume feeder roads in Ghana. A prototype 7.6 metre-span, I-sectioned timber girder vehicular bridge was built by the BRRI over the Subin stream at Kaase, in Kumasi, Ghana, in 1991. This bridge is successfully performing its designed functions to date. The structural forms used then and the likely spans achievable, brought to the fore likely problems should spans beyond 8 metres be bridged and, together with the Timber Research and Development Association (TRADA), the possibility of the use of timber truss bridges was looked at. The form of the prototype I-girder bridge, the technical problems inherent in taking this structural form beyond 8 metres and the consequent truss bridge proposed, are presented in this paper. Problems that arose during the design of the truss bridge were those to d with the size f transverse beams, the design of couplers and the need to proof test the integrity f the proposed joints. Design solutions t some of the foregoing problems are given. However, lack of relevant equipment such as loading rams and strain/displacement transducers have meant that the research efforts at validating the design options adopted for the joints have not been possible. Future collaborative research and testing efforts are required if more bridges are to be provided as crossing structures on low-volume roads, if more efficiency in use is to be made of LUS and a likely industry in pre-fabricated timber bridge components engendered in Ghana. Keywords: Bridges, girder, timber, truss, couplers 1.0 INTRODUCTION In 1991, following research carried out at the Building and Road Research Institute (BRRI) on scaled timber I-girders (Allotey, 1990, 1992), a prototype timber bridge was built over the Subin Stream at Kaase, in Kumasi, Ghana. Considerable problems arose with the construction of the bridge and these problems and their solutions are briefly highlighted.
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DESIGN OF TIMBER TRUSS BRIDGES: THE SITUATION IN GHANA
THE USE OF LESSER USED TIMBER SPECIES IN THE DESIGN OF VEHICULAR BRIDGES, THIS TIME A LOG TRUSS BRIDGE IS REPORTED ON. THE ADVANTAGES OF AFENA SPECIES SUCH AS RELATIVELY SMALL DIAMETER AND UNIFORM TAPER ARE MENTIONED. PROBLEMS SUCH AS THE USE OF THE LOGS OF ADEQUATE STRENGTH AND NUMBERS FOR TRANSOMS AND THE TYPE OF COUPLERS ARE HIGHLIGHTED. THE FOR WILL BE BY THE USE OF STEEL FLITCH BEAMS AND THE LATTER WILL VERIFIED BY LABORATORY TESTING OF FULL SIZE JOINTS.
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1
TIMBER VEHICULAR BRIDGES IN GHANA – THE PROGRESS TO DATE
K. A. Solomon-Ayeh Building and Road Research Institute (BRRI) Kumasi, Ghana [email protected]
Abstract
The infrastructure in Ghana is relatively low because of, among other factors, the lack of crossing structures like bridges. Existing bridges are predominantly of reinforced concrete and as the cost of the imported steel and cement became expensive, research, particularly at the Building and Road Research Institute (BRRI), started on the possibility of using Lesser Used Timber Species (LUS) for vehicular bridges, at least on low-volume feeder roads in Ghana. A prototype 7.6 metre-span, I-sectioned timber girder vehicular bridge was built by the BRRI over the Subin stream at Kaase, in Kumasi, Ghana, in 1991. This bridge is successfully performing its designed functions to date. The structural forms used then and the likely spans achievable, brought to the fore likely problems should spans beyond 8 metres be bridged and, together with the Timber Research and Development Association (TRADA), the possibility of the use of timber truss bridges was looked at. The form of the prototype I-girder bridge, the technical problems inherent in taking this structural form beyond 8 metres and the consequent truss bridge proposed, are presented in this paper. Problems that arose during the design of the truss bridge were those to d with the size f transverse beams, the design of couplers and the need to proof test the integrity f the proposed joints. Design solutions t some of the foregoing problems are given. However, lack of relevant equipment such as loading rams and strain/displacement transducers have meant that the research efforts at validating the design options adopted for the joints have not been possible. Future collaborative research and testing efforts are required if more bridges are to be provided as crossing structures on low-volume roads, if more efficiency in use is to be made of LUS and a likely industry in pre-fabricated timber bridge components engendered in Ghana. Keywords: Bridges, girder, timber, truss, couplers
1.0 INTRODUCTION
In 1991, following research carried out at the Building and Road Research Institute (BRRI)
on scaled timber I-girders (Allotey, 1990, 1992), a prototype timber bridge was built over
the Subin Stream at Kaase, in Kumasi, Ghana. Considerable problems arose with the
construction of the bridge and these problems and their solutions are briefly highlighted.