"Fatigue behavior of notched connections in wood-concrete composites"

In a wood-concrete composite structural member the wood layer overlapped by the concrete layer are interconnected to prevent the relative slip. The stiffness of the interlayer connection determines the degree of the composite behavior achieved. In this research notched shear-key connections were used with an embedded anchor detail. Wood-concrete composite structural members are usually applied in building structures. There are a relatively small number (in the low 100s) of known bridge applications involving wood-concrete composites. A problem with using these novel composite members in bridges with high traffic is that the fatigue behavior of the composite member under long-term repeated loading is not known. This paper presents the result of a research at Colorado State University and Metropolitan State College of Denver, performed in coordination with work at University of Stuttgart, attempting to establish the S-N curve for fatigue loading of notched wood-concrete connections based on low/high-cycle, repeated loading tests. Experimental results are obtained on fourteen 1524 mm span composite beam specimens of 191 mm width, with a 89 mm thick wood layer consisting of five “2x4” boards and a 63 mm concrete layer, which are interconnected by embedded anchor screws at the notch locations. Five specimens are only statically loaded while the others are cycled to failure with a maximum to minimum pulsating load ratio of 10. Points on the S-N curve are determined for three levels of the maximum load as a function of the average static failure load. Typical observed failure modes are block-shear of the wood at the notch and tension failure of the wood at mid-span. As a result, the obtained S-N curve could be proposed for future consideration in drafting design codes addressing the timber-concrete composite structures.