COMPOSITE BRIDGES IN SADC. KEVE RIVER BRIDGE.
To build composite bridges in countries belonging to the SADC – Southern Africa Development Community – is totally different from building in Europe since there are specific difficulties that constrain the final solution, such as: 1) difficulty in finding skilled labor for welding works; 2) the high cost of the solution when it is imported from foreign countries; 3) the high cost of formwork; and 4) qualified hand labor for the erection process. Consequently, VESAM has developed a solution with the objective of adapting the traditional composite bridge construction vesamin Africa, thus creating a truly rapid assembled bridge, with a longer lifetime and a lower production cost.
Some of these innovations have been incorporated into the Keve River Bridge in Angola, Fig. 1, and are herein described: 1) splice connections with composite action; 2) use of corrugated steel deck for the execution of the slab; and 3) border girder with direct incorporation of guards.
Shipping is the most economical way to put the structural members, fabricated in Europe, on site. Combining this with the fact that transportation of girders above 12 m is significantly more expensive, « 40 ‘Open Top » shipping containers are currently adopted. However, girders have to be spliced. The interruption of these structural members requires the creation of a structural joint.
In contrast to the welding work, splice connections with pre-stressed bolts are significantly cheaper and simple to execute . However, in areas with high bending moments the number of bolts makes the solution too expensive. The incorporation of the composite action can help solving this problem.
The principle of splice connection with composite action is, in all aspects, identical to the metal splice connection. The unique difference is the contribution of the concrete slab that must be considered in the distribution of normal stresses. The bending moment is divided between the web and the top and bottom flanges of the steel profile and the concrete and reinforcement bars.
Another development is related with the execution of composite bridges slabs. It can be performed in several ways, namely with traditional timber formwork or with precast slabs. The corrugated sheet metal is probably the most attractive solution. The raw material (steel deck) is economic and the assembly process is very fast and simple. It should be highlighted that even the tops of the steel deck can be deformed to avoid the need of placing a closing and thus avoid the outflow of the concrete.
The plates of corrugated steel deck are cut in factory, with the exact length and width, applied on site with metallic nails between main girders and fixed to the upper flange. This solution presents a difficulty for spans larger than 1,5 m since it is necessary to use a temporary support. To overcome this, a cold formed profile is added, see Fig. 2, increasing the strength of the steel deck but also its stiffness. The profile it is connected by the process of spot welding. This solution present the advantages of being low-cost, fast to execute, flexible and several profiles can be added to increase the stiffness as necessary to meet the loads imposed.
The corrugated steel deck is stopped at girders, including the lateral area. Normally this is typically cantilevered. The adopted solution comprises a deck supported in the main girder and the border girder. This border girder has three functions: 1) a metallic structural member in the composite and bare steel phases; 2) a formwork member during the concreting of the slab; and 3) an aesthetic effect.
On the border girder the hand rails are assembled with a tuning system that allows the correction of any altimetry errors. Angles with holes spaced differently were placed, allowing the correction of any deviations in the alignment, see Fig. 3.
To build bridges in Africa is a true challenge due to local conditions and constrains. The absence of qualified and skilled manual labor and the high cost of raw materials are two of the major difficulties found. To overcome these it is necessary to develop new solutions that should be modular, simple, fast to execute and above all, competitive in cost.
The solutions herein presented meet these needs. Splice connections with composite action allows to have smaller joints with the same strength and stiffness; the use of corrugated steel deck for the execution of the slab is an economic solution for the fast erection of bridge decks; and the use of a border girder with direct incorporation of guards combining a triple function (structural, formwork and aesthetic) is a high competitive solution in relation to traditional systems.
Filipe Santos 1, Pedro Santos2, Luis Simões da Silva3
1 VESAM Engenharia SA, Zona Industrial de Cantanhede, Lote 69, Cantanhede, Portugal | firstname.lastname@example.org
2 VESAM Engenharia SA, Zona Industrial de Cantanhede, Lote 69, Cantanhede, Portugal | email@example.com
3 ISISE, Department of Civil Engineering, University of Coimbra, Rua Luis Reis Santos, Coimbra, Portugal | firstname.lastname@example.org
Paper presented in EUROSTEEL 2014, September 10-12, 2014, Naples, Italyretour