Experimental And Theoretical Study On Bearing Behavior For Timber Beams Strengthened With CFRP

The Palace Museum is the largest and most complete in the ancient building group and is an outstanding representative ancient wood building ,with high cultural relic , historical and artistic value. The Palace Museum was built so far, since 1407 year, and experienced repeated rebuilt and expansion, and now is under the largest maintenance since the revolution of 1911. Now with the present situation that seven frame beam and its following beam have excessive deflection in CiNing Palace in the Palace Museum, the research works on reinforcement wooden beams are carried out.In the tests, through the tests of 20 single timber beams and composite timber beams(3000mm×180mm×240mm) strengthened with carbon fiber reinforced polymer(CFRP) sheets, the structural behaviors are analyzed in terms of ultimate bearing capacity, deflection, failure modes, strain distribution of cross section , the stress state of CFRP ring hoops, and etc.Ultimate bearing capacity of reinforced single timber beams is increased by about 25 percent, and ultimate bearing capacity of reinforced composite timber beams is increased by 65 to 79 percent, and the rigidity of reinforced beams is also increased in certain degree.The load-deflection curves for reinforced timber beams and unreinforced beams, show a linear trend in the early loading stage, and nonlinear with different degrees in the later stage. In the test, flexural failure occur for the most timber beams, and shear failure parallel to grain and shear-bending failure for others.Bending failure will occur,when axial tension and compression stress of wood reach to ultimate strength.And shear failure occur ,when the shear stress parallel to grain of wood in longitudinal section reach to ultimate strength.Shearing-bending failure occur, when axial tension of the mid-point cross-section in shearing-bending zone reach to the diagonal tensile strength. At the same time, based on elastic-plastic theory and strength reduction method, the simple and practical formulas of bending and shearing capacity for the beams are proposed.Through the comparative analysis of testing programs, the impact to carrying capacity , bending stiffness and the coordination of the upper and lower beams of the composite beams with different reinforcement methods,such as the interface structural adhesive reinforcement, CFRP reinforcement on the bottom of the beam, CFRP hoops reinforcement around the beam, etc., was studied.The bearing capacity and deformation of the unreinforced and reinforced beams are analyzed with finite element software ANSYS.By calculation, load-deflection curves and the stress contour pictures of the timber beams have been created, and through the compareing with the experimental load- displacement curves and ultimate load,it was proved that the element numerical model can simulate reinforced and ureinforced timber beams .