Load-Bearing and deformation behaviour of concrete beams reinforced in combination of both steel bars and bars made of glass fibre reinforced plastic (GFRP

Abstract

A series of 5 trusses have been tested for bending stress at the Technical University Kaiserslautern. Trusses with steel reinforcement, GRP-reinforcement and combined reinforcement have been comparatively investigated. The GFRPreinforcement has been located close to the soffit surface. Facing the ultimate limit state a clear increase of load-bearing capacity could be notified with trusses reinforced by GFRP-bars and at trusses with combined reinforcement. In comparison to the reference truss the double reinforced type of truss provides a favourable solution proving an increased stiffness in the cracked condition as well as an improved load bearing capacity after the yielding of reinforcing steel. Comparing the deflections the double reinforced option supplying a higher bending stiffness in the cracked condition provides a better deformation behaviour at limit state of serviceability. A plainly GFRP-reinforced option effects the deflection in a lessfavourable way. Looking on the crack patterns, it becomes obvious, that the criterion for serviceability related to the crack width will most favourably be impacted by GFRP-reinforcement located with minor concrete cover close to the surface. Apart from the double reinforced trusses only the GFRP-reinforced trusses show a distinct crack distribution together with much smaller crack widths. Along with these signifying consequences it could be observed, that even less additional GFRP-reinforcing bars could originate a strong improvement of crack control. To sum up it can be said, that trusses comprising steel reinforcement combined with surface reinforcement made of GRP-bars will behave better than concrete trusses plainly reinforced by steel reinforcement. Especially the crack distribution and the crack widths will positively be improved. In many cases the limitation of crack widths will become determinant for the design of reinforced concrete members. Therefore, it is recommendable to investigate combined reinforced concrete elements more precisely. Some more basic tests have already been started at the Technical University Kaiserslautern.