International Concrete Abstracts Portal

A parametric analysis and experimental study of concrete columns reinforced by steel-BFRP (basalt fiber reinforced polymer) composite bar (SBFCB) were conducted. The relationship between post-yield stiffness of SBFCB and SBFCB reinforced concrete columns was investigated. The influences of reinforcement ratio, axial compression ratio, and post-yield stiffness ratio were explored. The results show that (1) under the same reinforcement ratio, the post-yield stiffness of SBFCB columns increases with the post-yield stiffness ratio of SBFCB; (2) the higher the BFRP content of SBFCB, the better deformation capacity of SBFCB column can be achieved due to the smaller curvature demand of column base; (3) a higher SBFCB post-yield stiffness ratio can delay or prevent the collapse of concrete column caused by P- effect; (4) the residual displacements of SBFCB columns are much smaller than those of ordinary RC columns, that is, the SBFCB column has a more better post-earthquake repairability.

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.

Concrete-filled GFRP tubes (CFFTs) with and without moment connections to concrete footings were tested. The study aims at exploring the combined effect of maximum shear and maximum moment, both occurring at the same location, on the ultimate strength of CFFTs, as well as moment connection behavior in general. Testing involved simply supported and cantilever bending specimens with varying shear spans and fixed end arrangements. End conditions consisted of either direct embedment into concrete blocks with steel dowels, or mechanical clamping. For the GFRP tubes used, the study concluded that the presence of shear at the location of maximum moment near the connection in a cantilever setup does not cause reduction in flexural capacity, relative to the pure bending strength of the CFFT. The study also revealed that achieving tensile rupture of the CFFT tube does not guarantee that the full potential moment capacity of the CFFT member is reached, as slip plays a key role at the moment connection.