Influence of repeated and sustained loading on the performance of layered wood-concrete composite beams

The paper investigates the influence of cyclic and sustained loading on the performance of layered wood-concrete composite beams interconnected by a notched connection detail. A number of composite beams were conditioned in a climate chamber in order to raise the wood moisture content from the ambient value (5-7%) to about 12%. Then the beams were subjected to 21,600 cycles of loading and unloading to simulate the typical live load frequency experienced by the floor of a commercial building over a 30-year service life. Finally, each individual beam was ramp loaded to failure to determine the ultimate load carrying capacity and composite efficiency. Additional beams were subjected to sustained load for 133 days in an unconditioned environment and then tested to failure. The main outcomes of the experimental program were: (1) relatively high beam stiffness and strength were achieved despite the use of few connectors; (2) two types of failure mechanisms were detected: either shear in the wood between the exterior notch and the beam end, or wood bending failure at midspan; (3) the cyclic loading increased the initial elastic deflection by 18% and reduced the beam stiffness by 9%, on average; (4) after 133 days of sustained load, the deflection increased by 59%, on average; and (5) the reduction in stiffness and in load capacity due to sustained loading was greater than that due to the cyclic loading.