Experimental and numerical investigation of steel-timber composite beams under concentrated load

  Objective  Replacing the web of I-shaped timber beam with steel can solve the problems of web shear failure and low bending stiffness of bare timber beam. This helps to reduce the component size and increase its application in large-span buildings.

  Method  The steel-timber composite (STC) beam was prepared by connecting two timber slabs on the H-shaped steel flanges with bolts. The influence of different bolt spacing and shear-span ratio on the structural behavior (failure modes, stiffness and load capacity) of STC beams were studied. Three-point bending tests were carried out on 11 STC beams. Four push-out tests were carried out to investigate steel-timber interface slip.

  Result  The bending stiffness of the STC beams was 201% higher than that of the rectangular timber beam with the same section size. The steel upper flange was prone to buckle by concentrate load. Increasing the shear-span ratio, the failure converts from brittle to ductile, the initial failure transforms from top timber slab to bottom. Increasing the shear-span ratio or decreasing the bolt spacing, the bending stiffness was declined, the ductility coefficient was improved and the peak load decreased by more than 15%. The formulations of yield load and mid-span deflection considering interface slip between steel and timber were proposed, the error of most specimens was less than 10% between calculated and experimental results. In addition, referencing material properties and push-out test, the finite element models of STC beams were established. The errors between simulated and experimental values of bending stiffness and yield load were basically within 10%.

  Conclusion  Steel used as the web can significantly improve the bending stiffness of beams and prevent shear failure of webs. Considering the interface slip, the theoretical calculation and simulation results of flexural performance of STC beams are accurate.