Design of concrete beams reinforced and unbonded prestressed with FRP bars based on serviceability requirements

Abstract

The serviceability requirements for concrete beams reinforced with fiber-reinforced polymer (FRP) bars usually entail repeated check of deflection and crack width in design process. In this work, a contribution to the development of the design recommendations at serviceability limit state for beams reinforced and unbonded prestressed with FRP bars is presented. To facilitate the design, equations of internal force arm coefficient, nonuniformity coefficient of strain, and position amplification factor were empirically modified using beam test database with the principle of conservation. Accordingly, simplified deflection and crack width models for FRP-reinforced concrete (FRP–RC) beams and unbonded FRP prestressed concrete (FRP–UPC) ones were proposed. Moreover, for FRP–RC beams, safety factors were introduced based on statistical analysis of experimental data. Considering the serviceability-related requirements, reinforcement amount limits and design procedures for both types of beams were provided. Furthermore, to evaluate the cracking behavior of FRP–RC beams, a cracking resistance coefficient was defined. Parametric analysis revealed that the reinforcing layer number of the beam corresponding to the highest cracking resistance coefficient showed a general uptrend with the increase of the beam height. On this basis, a rational method to determine the optimal number of reinforcing layers was proposed.