Resistance Factors for Ductile FRP-reinforced Concrete Flexural Members

To prevent damage caused by corroding reinforcement, fiber reinforced polymer (FRP) reinforcing bars have been used in place of steel in a relatively small but increasing number of structures in the civil infrastructure. A concern with the use of traditional FRP bars, however, is the resulting lack of ductility. This problem has been overcome with the development of a new generation of composite reinforcement, ductile hybrid FRP (DHFRP) bars. However, standards that address the design of DHFRP bars are unavailable, and appropriate resistance factors for the use of DHFRP reinforcement are unknown. In this study, a reliability analysis is conducted on tension-controlled concrete flexural members reinforced with DHFRP, with the intent to estimate potential strength reduction factors. Flexural members considered include a selection of representative bridge decks and building beams designed to meet AASHTO LRFD and ACI-318 strength requirements and target reliability levels. Nominal moment capacity is calculated from standard analytical models and is taken as first DHFRP material failure. Statistical parameters for load and resistance random variables in the reliability model are consistent with previous code calibration efforts. The resulting resistance factors ranged from 0.61 to 0.64 for tension-controlled sections, which indicates a potential increase in allowed strength over flexural members using non-ductile bars

Analysis of Alternative Ductile Fiber-reinforced Polymer Reinforcing Bar Concepts

Steel-reinforced concrete structural components are often associated with significant maintenance costs as a result of reinforcement corrosion. To mitigate this problem, fiber-reinforced polymer (FRP) bars have been used in place of traditional steel reinforcement for some applications. The non-ductile response of typical FRP bars is a concern, however. To overcome this problem, hybrid ductile FRP (HDFRP) bars have been developed for use in concrete flexural members with resulting ductility indices similar to sections reinforced with steel. In this study, five different HDFRP bar concepts are analyzed and compared in terms of ductility, stiffness, and relative cost. Of primary interest is the effect that the number of materials used in bar construction has on performance. Reinforced concrete beam and bridge deck applications are considered for analysis. It was found that all HDFRP-reinforced flexural members considered could meet code-specified strength and ductility requirements for steel-reinforced sections, although service load deflections were approximately twice that of steel-reinforced sections of the same depth. In general, ductility increased, and overall material cost decreased, as the bar material layers increased from 2 to 4. The 4-material continuous fiber bar approach was found to be most promising, with high ductility as well as relatively low cost

Reliability-based Design Optimization of Concrete Flexural Members Reinforced with Ductile FRP Bars

In recent years, ductile hybrid FRP (DHFRP) bars have been developed for use as tensile reinforcement. However, initial material costs regain high, and it is difficult to simultaneously meet strength, stiffness, ductility, and reliability demands. In this study, a reliability-based design optimization (RBDO) is conducted to determine minimum cost DHFRP bar configurations while enforcing essential constraints. Applications for bridge decks and building beams are considered, with 2, 3, and 4-material bars. It was found that optimal bar configuration has little variation for the different applications, and that overall optimized bar cost decreased as the number of bar materials increased

Reliability model for ductile hybrid frp rebar using randomly dispersed chopped fibers

RELIABILITY MODEL FOR DUCTILE HYBRID FRP REBAR USING RANDOMLY DISPERSED CHOPPED FIBERS Fiber reinforced polymer composites or simply FRP composites have become more attractive to civil engineers in the last two decades due to their unique mechanical properties. However, there are many obstacles such as low elasticity modulus, non-ductile behavior, high cost of the fibers, high manufacturing costs, and absence of rigorous characterization of the uncertainties of the mechanical properties that restrict the use of these composites. However, when FRP composites are used to develop reinforcing rebars in concrete structural members to replace the conventional steel, a huge benefit can be achieved since FRP materials don\u27t corrode. Two FRP rebar models are proposed that make use of multiple types of fibers to achieve ductility, and chopped fibers are used to reduce the manufacturing costs. In order to reach the most optimum fractional volume of each type of fiber, to minimize the cost of the proposed rebars, and to achieve a safe design by considering uncertainties in the materials and geometry of sections, appropriate material resistance factors have been developed, and a Reliability Based Design Optimization (RBDO), has been conducted for the proposed schemes