Safe and reliable pedestrian access is a frequently neglected aspect of rural life in South Africa. In many areas, adults and children are forced to traverse rivers via unsafe paths along river courses, low level bridges prone to flooding, or unmaintained and dangerous pedestrian bridges. The Western Cape Department of Rural Development and Land Reform has identified this as an area requiring intervention after numerous accidents and fatalities caused due to unsafe river crossings and poorly designed and maintained infrastructure.
Near Clanwilliam in the Cederberg Mountains is the small town of Wupperthal, located in a pristine valley in an unspoilt part of the Country. Wupperthal is split by the Dassieboskloof River. The existing pedestrian bridge over the river was poorly maintained and is no longer in a usable condition. For most of the year, the river is easily traversed on foot, however, during heavy rains, the river floods and crossings are no longer safe. The Western Cape Department of Rural Development and Land Reform appointed iX Engineers (Pty) Ltd to assess whether the existing bridge was adequate to meet its intended purpose. It was found that the bridge was not safe and a new bridge was required.
SMEC South Africa (Pty) Ltd were appointed as a sub-consultant to iX Engineers (Pty) Ltd to propose possible replacement options for the existing bridge and to provide the detailed design of the approved proposal.
The aim of the new crossing was to provide a simple structure that would blend in with the natural surroundings. It was decided to traverse the river with a single span, preventing the need for piers within the river course and the consequent environmental disturbance which could arise as a result there of. A concrete beam bridge was judged to be too heavy to span the long distance, which might have appeared out of place in the natural setting. Steel provided the perfect solution to enable a simple and slender structure, yet still robust enough to withstand debris impacts during flood events. The applicability of the use of steel in rural and remote contexts was illustrated by the fabrication of the structure in Cape Town and subsequent transport to the site. The colour of the steelwork, which was chosen through a participative process with the local community, ensured that the bridge blended in with the local surroundings, and to create stewardship for the bridge among the community. A steel solution also presented the opportunity to be innovative with the design and sculpt a unique and creative form.
The chosen solution is a tapering, 36 m single span, steel plate through girder bridge.
The deck superstructure consists of two girders created from an assembly of welded plates to form a varying depth beam. A semi-circular void in the girders was introduced at mid span to give the bridge an arch feel, a natural form that suited the setting. A compression box was provided on the top flange at mid span to prevent buckling of the compression fibre. The transverse members are steel I-beams with diagonal circular hollow section plan bracing, both of which are bolted to the longitudinal plate girders.
The bridge is a simple and basic structural solution, consisting of a simply supported beam. However, the open form and intricate geometry required a complicated analysis and design process. A three-dimensional finite element plate model was created to perform a detailed buckling analysis and stress check on the plate elements.
The Contractor appointed for the construction of the bridge was Guerrini Marine Construction, who were responsible for the construction of the bridge substructure and transport and erection of the superstructure. The deck superstructure was fabricated in Milnerton by Just Engineering and transported to site in three separate parts with a maximum length of 13.7 m. The three parts were erected on temporary supports on the river bank where they could be spliced together. The splice joints consisted of a temporary bolted connection used to secure and position the structure. A full penetration weld could then be performed to conclude the permanent connection. The completed 36 m long deck could then be lifted and rotated into position on top of the reinforced concrete supports.
The handrail consists of an 80 mm diameter circular hollow section, with a custom-made mesh of 8 mm diameter solid bars, which could be bolted onto the bridge in modules on site. This unobtrusive design was chosen so that the handrail does not detract from the elegant lines created by the aesthetically pleasing form created by the steel plate girders below.
The bridge was positioned with a 0.5 m freeboard above the 1:100 year flood line to reduce the risk of debris impacts during a flood event on the lightweight steel superstructure. A timber walkway was provided to link the bridge with the 1:5 year flood line to ensure that the river could be safely crossed even in minor flood events. The total construction cost of the project was R5.265 million.
The bridge in Wupperthal highlights the potential for steel to be used in an innovative way to achieve social and developmental objectives for the community, combining function and aesthetics, without impacting on the environment. The steel bridge provides a positive landmark to the small town that the local community and Client can be proud of.
|Tons of structural steel used||37 tons|
|Structural profiles used||Plates, I Beams, CHS|
|Project Team Role||Company|
|Nominator||SMEC South Africa (Pty) Ltd|
|Client/ Developer||Department of Rural Development and Land Reform|
|Architect||Not provided by nominator|
|Structural Engineer||SMEC South Africa (Pty) Ltd|
|Engineer||SMEC South Africa (Pty) Ltd|
|Quantity Surveyor||Not provided by nominator|
|Project Manager||iX Engineers (Pty) Ltd|
|Main Contractor||Guerrini Marine Construction|
|Steelwork Contractor||Just Engineering|
|Steel Erector||Guerrini Marine Construction|
|Cladding Manufacturer||Not provided by nominator|
|Cladding Supplier||Not provided by nominator|
|Cladding Contractor||Not provided by nominator|
|Not provided by nominator|
|Not provided by nominator|
|Photographer, Photo competition||SMEC South Africa (Pty) Ltd|
|Photographer, Other submitted images||SMEC South Africa (Pty) Ltd|
If you were a part of this project, and your company details are incorrect or missing – please notify the SAISC so that the error can be corrected.