International Concrete Abstracts Portal

This paper investigates the design of fiber reinforced polymer (FRP) reinforced concrete based on ACI 440.1R serviceability requirements related to deflection control of one-way slabs and rectangular beams, and uses this information as the basis for evaluating the minimum member thickness requirements needed to satisfy ACI 318 deflection limits. Serviceability is shown to govern design in most cases, as flexural members designed for deflection control are usually stronger than required. Slabs satisfying deflection requirements have a service load that ranges from 20 to 30% of the nominal member capacity, while service loads for beams range from 35 to 45% of the member capacity. Recommended minimum member thickness values for slabs are too conservative and require revision, while those for beams appear reasonable. A practical approach for design of FRP reinforced concrete members is proposed based on selection of member thicknesses needed to satisfy deflection and strength criteria.

The structural reliability of concrete flexural members reinforced with fiber reinforced polymer (FRP) reinforcement is investigated. Reliability indices based on the equations for flexure in ACI 440.1R-03, which uses the load factors from ACI 318-99 are presented. Choice of a resistance factor for flexure for ACI 440.1R-06, which uses the load factors from ACI 318-02 is also presented. Flexural designs using either ACI 440.1R-03 or ACI 440.1R-06 provide sufficient reliability, with reliability indices between 3.5 and 4.8, with the older versions of ACI 440.1R yielding higher reliability. An analysis of curvature of the beams at failure showed that flexural members that fail by FRP reinforcement rupture have ductilities similar to those that fail by concrete crushing, indicating that FRP reinforcement fracture is not necessarily a more brittle failure mode than concrete crushing.

This paper presents the results of an experimental investigation on the strength and behavior of thirteen RC and CFFT columns. The effects of two parameters and their interactions on the buckling behavior were investigated; namely, the type of internal reinforcement (steel or CFRP bars) and the slenderness ratio. CFFT 152 mm, (6 in.)-diameter columns with different slenderness ratios 4, 8, 12, 16 and 20, were tested under pure compression load. Filament-winded FRP tubes with 2.65 mm (0.10 in.) thickness were used as a stay-in-place structural formwork for the CFFT columns. The axial compressive capacity of steel and CFRP-reinforced CFFT columns was reduced by 13% to 32% with increasing the slenderness ratio from 4 to 20. The behavior of CFRP bars as a compression reinforcement was generally similar to conventional steel bars. The test results indicated that the axial capacity of CFRP-reinforced CFFT columns is 13% lower compared to steel-reinforced CFFT columns.

The results of an experimental investigation on the effects of prestressing on the flexural behavior of GFRP-reinforced SCC slabs are presented. A total of six one-way slab strips were tested up to failure, including one steel-reinforced control slab. The five remaining slabs were reinforced with GFRP bars, three of which also contained two CFRP post-tensioned tendons. Steel stirrups were included in one prestressed and one non-prestressed slab to ensure a flexural mode of failure. The slabs were tested under four-point bending. Results were compared to analytical models for ultimate flexural and shear capacity as well as load-deflection behavior. Prestressing effectively increased the cracking load and post-cracking stiffness of the FRP-reinforced slabs and significantly reduced crack widths at service loads. Slabs without shear reinforcement failed in shear in a brittle manner prior to reaching their full flexural capacity. All of the GFRP-reinforced slabs failed at higher loads than the control slab.

This paper presents a new concept for an FRP-Concrete composite floor system. The system consists of a moulded glass fiber reinforced polymer (GFRP) grating adhesively bonded to rectangular pultruded GFRP box sections as structural formwork for a concrete slab. Holes cut into the top flange of the box sections at a variable spacing allow concrete ‘studs’ to form at the grating/box interface. During casting, GFRP dowels are inserted into the holes to further connect the grating and box sections. Following preliminary component tests on two concrete blocks, experimental results show that the concrete filled grating provides a 100% increase in strain capacity when compared to a plain concrete block. It is therefore feasible to provide ductility to the complete system through the concrete in compression. Four push-out GFRP grating-box section specimens were then tested in double shear to assess the shear behavior of the proposed GFRP dowel shear connector in both partially concrete-filled and fully concrete-filled box sections. From the resulting load-slip curves, a progressive longitudinal shear failure was seen to be provided by such a connection. The experimental results indicate that this type of shear connection can provide robustness and reasonable ductility to the system. Research is now underway to test a complete prototype system under variable load conditions to examine whether the behavior is as predicted.