Bond repair of cracked beams

摘要

The repair of cracked timber beams on site frequently involves crack injection with adhesives followed by the application of the chosen strengthening system, involving bonded or bolted metal plates or rods or bonded pultruded GFRP or CFRP profiles. Although strengthening design will not generally take into account the contribution of injecting adhesives in the crack volume region it is felt that this contribution to overall strengthening of the component or structure may be of some significance. A test programme was therefore developed at LNEC to assess the strength and stiffness of timber beams which were treated with epoxy adhesives after they had developed failure in a 4 point bending test. It is recognised that partially broken beams may have very narrow, almost invisible, fissures, which are difficult to impregnate. As well as the forgoing partially separated broken beams may present extremely irregular split ends, which are difficult to bring back into perfect alignment and contact. These two factors may reduce the effectiveness of the strength restoration and were considered in the experimental study. However, the specific beam failure appearance is not likely to give a clear indication of how efficient the consolidation turns out to be. Test results show that epoxy adhesive injection of cracked timber beams may lead to a not insignificant, but somewhat variable, strength recovery (0.45 to 1.11) and to a significant stiffness recovery (0.74 to 0.99) of broken beams. Having these results in mind, although on site repair of broken timber beams should not rely on epoxy adhesives injection only, its contribution to the stiffness of strengthened beams is significant and one should make use of this advantage.