Comparative structural design of a Timber Concrete Composite bridge - LCA and LCC comparison between TCC and concrete integral bridge

Abstract

Timber concrete composite (TCC) bridge is a structure system composed of three main structural elements: timber elements, concrete slab and connections to enable composite action. TCC bridges main advantage is the structural efficiency. The materials are used in an efficient manor, with concrete in compression and timber in tension. To be able to profit from the efficiency of the system, a capable connection is essential. This means a connection that can provide enough stiffness to create a good composite action between the materials, strong fasteners to carry the load subjected to the connection and ductility to prevent brittle failure of the structure. This thesis investigates the possibility of designing a TCC integral bridge based on the prerequisites of an existing concrete integral bridge over a small river. Three connection types are studied: a combination of notches and dowels, dowels alone and a hybrid of adhesive and dowels. These alternatives are evaluated under both short and long term loading to assess their structural performance. The study resulted in a preliminary design of a TCC bridge. The analysis revealed that the governing stage was the initial service period. Notably, a composite action of approximately 30% led to the lowest material utilization, highlighting a complex relationship between connection stiffness and structural efficiency. Long term effects varied depending on the connection type. For low composite action, utilization decreased over time, while for high composite action, utilization ratio increased. To compare the bridge alternatives, a life cycle assessment (LCA) and life cycle cost (LCC) analysis are conducted to evaluate whether TCC bridges are environmentally and economically competitive with conventional concrete bridges. The LCA results from the case study indicate that TCC bridges have a lower climate impact than conventional concrete integral slab bridges when comparing CO2e emissions throughout the construction and maintenance phases. The results from the LCC assessment show that the TCC bridge has a similar expected cost compared to the integral concrete slab bridge from the case study. However, the cost estimates for the TCC bridge shows greater uncertainty, resulting in a wider range between the lower and upper bounds.