Unreinforced concrete bridge

Abstract

During the past decade, durability and sustainability has become more and more important in the building industry. By using no steel reinforcement, which has with high carbon emission and is sensitivity to corrosion, the structure should have a longer life span with less maintenance and a lower carbon footprint.
To get more information on unreinforced concrete structures, a literature study is done, focused on old Roman structures made out of Roman concrete. Besides historic concrete, research is also done on modern concrete and its capacity.
The new bridge is designed for the "Hoofdvaart", a canal in the polder called, "Haarlemmermeer". The design consists of three arches are connecting the two abutments and two piers. In the connection of two arches, above the piers, so called flood openings are placed. Romans used flood openings to let water pass, but in this case they are used for the reduction of weight. Wooden piles form the foundation to the stiffer sand layers. Calculation of the design is done in a few steps. Firstly, the original design, as explained above, is calculated. Results show stresses, that are more than 7 times higher than the capacity of the concrete. The biggest contribution to the stresses are coming from self-weight and load model 1. Load model 1 is a heavy vehicle placed at the most unfavourable position of the bridge. Lowering self-weight is an option, but load model 1 has fixed values, so they cannot be lowered. Next, six optimizations are designed and calculated to create a structure that should fulfil the requirements. It turns out that the structure still exceeding the capacity by approximately 28%. After these optimizations can be concluded that for the given location, this design is not totally satisfying. To find out what contribution soil has to the structure, a few extra calculations are done for the last optimization. Based on overall calculations, the conclusion is that the top soil layers of the "Haarlemmermeer" are not capable of generating enough horizontal support for the unreinforced bridge. To finalize the design, a cost analysis and Life Cycle Analysis, LCA, are made. In both analysis a comparison is made between the new design and a reinforced bridge over the "Hoofdvaart" in "Nieuw-Vennep". The cost analysis show a difference of approximately "170.000,- in advantage of the new design. Especially the material costs of steel and pre-cast elements in the existing bridge, contribute to this difference. So an unreinforced structure has less labour and less material costs, compared to a reinforced structure. Of course this difference is also depending on the type of structure and the design. The LCA shows around 30% less carbon emission for the new unreinforced bridge, compared to the existing reinforced bridge. Especially material use and demolition contribute to this decrease. This shows that an unreinforced structure is 30 to 40% more sustainable than a reinforced structure.