Fatigue behaviour of timber-concrete composite connections and floor beams

摘要

In recent years. timber-concrete composite systems have become more widely used as a new constructiontechnique for buildings and bridges. The main advantage is that the compressive strength of concreteis exploited through the use of composite action while timber beams are able to resist the tensile stresses.The level of composite action. which can be achieved by the system. is dependent on the type of shearconnector used. There is a lack of knowledge. however, on the performance of these types of connectionswhen subjected to cyclic loading, which is typical for bridges. Testing was performed in the StructuresLaboratory of the University of Canterbury to analyse the fatigue behaviour of two types of timber-con-Crete connections via push-out specimens, and two beam specimens representing strips of compositefloor with the same connection types. The two types of connection investigated were: (i) a rectangularnotch connection reinforced with a coach screw (also known as lag screw); and (ii) a connection withtoothed metal plates punched into laminated veneer lumber (LVL). The stiffness of the connection wasmonitored throughout the cyclic loading along with the total amount of slip occurring between the concreteand timber. After the application of 2 million cycles, the push-out and beam specimens were loadedto failure in order to quantify their maximum strength. The strength of the rectangular notched connectionafter cyclic loading was 0.95 times of the one without cyclic loading, while for the metal plate connectionwas 0.60 times. For the metal plate connection. a continuous increase in slip was observed withincreased cycles possibly due to accumulated damage from repeated loading. The rectangular notch connectiondisplayed more resistance to changes in slip. strength and stiffness than the metal plate connection.No obvious loss of stiffness was observed in the rectangular notch connected floor beams after2 million cycles, and when tested to failure the stiffness was very similar to the same floor beam thathad not been cyclically loaded. The floor beam with metal plate connections did not perform well andfailed after 350.000 cycles. The loss pf strength, stiffness and composite action in this floor beam comparedto the one without cyclic loading was significant In this respect. the rectangular notch connectionsystem is recommended for use in bridge design as opposed to metal plate connections.