Experimental study on hysteretic behavior of circular timber columns strengthened with wrapped CFRP strips and near surface mounted steel bars

Considering that the strengthening of historical timber columns is urgently required, and the composite material elements could be applied to modern timber structures, the composite reinforcement method with wrapped CFRP strips and near surface mounted steel bars is proposed. In order to verify the strengthening effectiveness of newly proposed method, the hysteretic performance of timber columns was explored. Taking the number of mounted steel bars and wrapped CFRP strips as influential factors, lateral cyclic loading tests on eight strengthened timber columns were carried out. Test results indicated that specimens showed tensile rupture failure of timber parallel to grain, and the hysteretic curves and skeleton curves of specimens illustrated that the proposed method could improve the bearing capacity (32.3-60.1%) and deformation performance (67.9-89.4%) of timber columns. Furthermore, the location of the mounted steel bars had effect on the timber columns' bearing capacity, and fully jacketed CFRP strips showed better strengthening effectiveness than the interval wrapped ones. Composite reinforcement method can slow down the stiffness degradation of strengthened timber columns, and enhance the specimens' energy dissipation capacity. The hysteretic curves of steel bars reflected the working performance of strengthened timber columns, which indicated that the steel bars could work together with timber column to improve its seismic performance. There was good bond property between CFRP strips and timber, which could ensure the confinement of CFRP strips for timber columns. The experimental investigations can provide vital references for the seismic design and practical application of the composite reinforcement method.