Timber concrete composite (TCC) floor systems are relatively new to Australia and satisfactory performance requires a rigorous design procedure addressing both ultimate and serviceability limit states. TCC structures have a degree of complexity, since they combine two materials that have very different mechanical properties and respond in different ways to their environment. In addition, most TCC structures exhibit partial (not full) composite action.
There are several design procedures for TCC structures. Among these, the Eurocode 5 (EC5) procedure is relatively straightforward and has been successfully implemented in Europe. It uses a simplification for modelling the complex timber–concrete interaction known as the ‘Gamma coefficients’ method, which manipulates properties of the concrete member to predict the cross-section characteristics of the structure. This Guide presents a design procedure for TCC floor structures that is based on the Gamma method and AS 1720.1 Timber structures Part 1: Design methods.
The Eurocode 5 approach has been adopted as the underlying basis for the design procedures presented in this document; modified to comply with current design codes and practices in Australia. It comprises normative parameters for the strength and safety (ultimate limit state) and informative guidelines for appearance, deflection limits and comfort of users (serviceability limit states). While the latter must be defined by designers to meet the specific functional requirements of the floor under consideration, it is recommended that the serviceability guidelines in this document should be adopted as a minimum standard for TCC floors.
At the time of publication of this Guide, there is still uncertainty about some aspects of long-term deflection of TCC floors. As such, it is recommended that designers exercise caution when applying the design procedures contained in this document to floors exceeding 8 m in span, utilising the notched connections and crossed screws. This caveat restriction is due to a lack of research data at this stage to support the behaviour of floors and connections for spans exceeding 8 m. Some general considerations for manufacturing the notched connections are presented in this Guide.