Concrete Cover Separation Of FRP Strengthened RC Beams With Anchorage System

Nowadays, many strengthening methods including FRP strengthening method、 steel strengthening method、enlarging section method and so on are popularly applied in strengthening of reinforced concrete (RC) sturctures. Premature debonding failure such as debonding between FRP-concrete interface or concrete cover separation is commonly observed. The applications of FRP strengthening are restricted seriously because of debonding. Anchorage system has been proved to efficiently enchance the debonding strength of FRP-concrete interface, while the effectiveness and related mechanism of anchorage system on concrete cover separation remains unclear and a general design model is unavialble. This thesis aims at preventing concrete cover separation by steel anchors or U shape FRP anchors, and clarifying the mechanical principle of concrete cover separation. The main work is listed as follows:(1) Based on "concrete tooth model" theory, the "artificial tooth" cantilever-beam specimens of bottom-anchor-implanted RC beams strengthened with CFRP sheet are applied, and the experimental research on mechanical principle of concrete cover separation of bottom-anchor-implanted RC beams strengthened with CFRP are conducted. The concrete cover separation strength of each specimen is determined though inflection point of CFRP and the crack propagation diagram of concrete cover separation. The mian test parameters include the implanted depth、 location and numbers of anchors and their effect on concrete cover separation of bottom-anchor-implanted RC beams strengthened with CFRP are discussed. The experiment results revealed that anchorage implanted depth and anchorage location from near bearing supports showed more effect.(2) The same theory is applied in "artificial tooth" of U-shape-FRP-anchored RC beams strengthened with CFRP sheet. The effect of the depth and width of U shape FRP stirrup on experimental result are investigated. The experimental result proves that the more U shape stirrup implanted depth and width resulted in a better anchorage effect.(3) We designed five HR-FRP RC beams strengthened with CFRP sheet anchored by four mechanical anchors spaced at 100mm in order to investigate its effect on the flexural performance of beams. We concluded that the first anchor contributes most to the concrete cover separation, while arranging several anchors with reasonable spacing is necessary to restrain the interface debonding, which increased the stiffness of RC beams.(4) We built the concrete cover separation mechanical model of RC cantilever beams strengthed with CFRP under HB-FRP or U shape stirrup anchorage systems. The accuracy of these mechanical models is proved by comparing the results of cantilever-beam tests. Considering several kinds of failure models, we built the load bearing capacity model of RC beams strengthened with CFRP sheet with anchorage systems and verified its reliability against the experimental data.