Pull-out tests on bond behavior between timber and near-surface-mounted steel bars

Abstract

Mounting bars on the surface of timber is a kind of special glued-in rod connection, which has great value of practical application. The near surface mounted method can effectively improve the bearing capacity of timber members (timber columns and beams), and the reliable bond performance between timber and bars is the crucial foundation for their collaborative working. To investigate the bond properties between timber and near surface mounted steel bars, pull-out tests of 48 timber specimens with embedded steel bars were conducted. There were four typical failure modes, which were pull-out failure of steel bar, splitting failure of timber, mixed failure and shear failure of timber. The load-slip curves of each specimen group were obtained, and the distribution curves of steel bar strain along anchorage length under different load level were determined, through the test data acquired by internally attached strain gauges. The steel bar strain decreased gradually from loaded end to free end. Distributions of bond stress between timber and steel bar were fitted, which were uneven and exhibited saddle-shaped distribution along the anchorage length. Besides, this paper investigated and discussed the effects of anchorage length, bar diameter, glue-line thickness and groove depth on bond performance between timber and mounted steel bars. Referring to classical equations of glued-in rod in timber, the design model of pull-out load for specimens with mounted steel bars was provided. By comparison the calculation results with other existing models, the newly proposed model had good prediction effectiveness. Based on classical mBPE and CMR models, the bond stress-slip models were established, which was suitable for timber and mounted steel bars. And the model curves and test results were in good agreement, which verified the reliability of the proposed theoretical models.