Minimum thickness of concrete members reinforced with fibre reinforced polymer bars

To avoid excessive deflection most design codes specify the ratio (l/h)(s), the span to minimum thickness of concrete members without prestressing. Us e of the values of (l/h)(s) specified by the codes, in selecting the thickn ess of members, usually yields satisfactory results when the members are re inforced with steel bars. Fibre reinforced polymer (FRP) bars have an elast ic modulus lower than that of steel. As a result, the values of (l/h)(s) sp ecified in codes for steel-reinforced concrete would lead to excessive defl ection if adopted for FRP-reinforced concrete. In this paper, an equation i s developed giving the ratio (l/h)(f) for use with FRP bars in terms of (l/ h)(s) and (epsilon (s)/epsilon (f)), where epsilon (s) and epsilon (f) are the maximum strain allowed at service in steel and FRP bars, respectively. To control the width of cracks, ACI 318-99 specifies epsilon (s) = 1200 x 1 0(6) for steel bars having a modulus of elasticity, E-s, of 200 GPa and a y ield strength, f(y), of 400 MPa. At present, there is no value specified fo r epsilon (f); a value is recommended in this paper.