Amir Fam

CONFINEMENT MODEL FOR AXIALLY LOADED CONCRETE CONFINED BY CIRCULAR FIBER-REINFORCED POLYMER TUBES

This paper introduces an analytical model to predict the behavior of axially loaded circular concrete columns confined by fiber-reinforced polymer (FRP) tubes. The model, an extension of an earlier confinement model for concrete confined by steel reinforcement, is based on equilibrium, compatibility conditions, and the biaxial strength failure criteria of FRP tubes. It can be used to predict the behavior of prefabricated FRP tubes totally or partially filled with concrete, as well as concrete wrapped with FRP sheets. The model can account for the case of axially loaded concrete core only as well as the composite section of the concrete core and FRP tube, and is verified by experimental results reported by the authors and other researchers. A parametric study is presented to examine the effect of stiffness of the FRP tube, the effect of loading the FRP tube axially, and the effect of presence of inner hole inside the concrete core. The study shows that increasing the central hole size reduces the confinement effect, increasing the stiffness of the tube improves the confinement, and axial loading of the FRP tube significantly reduces the confinement.

BEHAVIOR OF AXIALLY LOADED CONCRETE-FILLED CIRCULAR FIBER-REINFORCED POLYMER TUBES

The aim of this paper is to describe the structural behavior of concrete-filled glass fiber-reinforced polymer (GFRP) tubes subjected to axial loads. The research included completely- and partially-filled tubes with a central hole as well as a tube-in-tube system with concrete filling between the 2 tubes. The GFRP tubes were designed to provide strength in both axial and transverse directions and were axially loaded with the concrete core. The study showed that the strength and ductility of concrete are improved due to confinement using GFRP tubes. The highest confinement level was achieved for completely-filled tubes. Using a central hole lowers the confinement effect; however, using an inner tube can enhance the confinement for this type of member. Results show that loading of GFRP tubes reduces the confinement effectiveness. The effects of laminate structure, hole size, interface condition between the tube and the concrete core, stiffnes of the tube, and failure modes are discussed.

Influence of Concrete Strength on Confinement Effectiveness of Fiber-Reinforced Polymer Circular Jackets

This article reports on a study of the confinement effectiveness of circular fiber-reinforced polymer (FRP) jackets for axial members with unconfined concrete strength ranging from 26 to 81 MPa. The study included two large-scale concrete-filled FRP tubes and 59 plain and FRP-wrapped concrete cylinders. The cylinders were wrapped with one layer of glass FRP (GFRP) sheet, two layers of GFRP sheet, or one layer of carbon FRP (CFRP) sheet. Specimens were tested to failure under axial compression. The results showed that FRP tubes and wraps provide a substantial increase in strength and ductility for low- to medium-strength concrete. This type of concrete shows a bilinear stress-strain response with strain hardening. For high-strength concrete, however, enhancement in strength is very limited, with hardly any improvement in ductility. The authors present a model to account for the effect of unconfined concrete strength on ultimate strength and strain of FRP-confined concrete. The authors conclude by recommending the use of lower-strength concrete in filling FRP tubes used as axial members.

Experimental and Analytical Modeling of Concrete-Filled Fiber-Reinforced Polymer Tubes Subjected to Combined Bending and Axial Loads

This paper presents test results of an experimental program, and proposes an analytical model to describe the behavior of concrete-filled, fiber-reinforced polymer (FRP) tubes subjected to combined axial compression loads and bending moments. The experimental program included 10 specimens subjected to eccentric axial loads, 2 specimens tested under concentric axial loads, and 2 specimens tested in bending. Glass FRP tubes with 2 different laminate structures were considered, and axial load/bending moment interaction curves are given. An analytical model is presented that accounts for variable confinement of concrete as a result of the gradual change of the biaxial state of stresses developed in the tube as the eccentricity changes. A parametric study was conducted to evaluate effects of diameter-to-thickness ratio and laminate structure of the tube, including different fiber proportions in the axial and hoop directions. The study evaluated the confinement as affected by the eccentricity of the applied axial load as well as the influence of the FRP laminate structure. Findings indicate that the interaction curves are significantly affected by both the laminate structure and diameter-to-thickness ratios of the tubes.

Structural Performance of Sandwich Wall Panels With Different Foam Core Densities in One-way Bending

The flexural behavior of a new sandwich panel proposed for cladding of buildings is studied. The panel is fabricated by laminating two glass fiber-reinforced polymer skins to a prefabricated polyurethane foam core. Two different densities for the core are explored, namely; a 0.31 kN/m3, referred to herein as ‘soft’ foam, and a 0.63 kN/m3, referred to as ‘hard’ foam. Ten 1500 × 300 × 76 mm3 panels were tested in flexure. For each core density, three similar panels were tested to establish the reproducibility of test results as a measure of quality control of fabrication. The panels were tested in three-point and four-point bending as well as under uniform load. The effect of wind pressure and suction was simulated for some panels by applying cyclic bending. It was shown that flexural strength and stiffness increased substantially, by 165% and 113%, respectively, as the core density was doubled. The contributions of shear deformation of the soft and hard cores to mid-span deflection were 75% and 50%, respectively. Panels with soft cores were vulnerable to localized effects under concentrated loads, and suffered inwards wrinkling of the compression skin at a lower ultimate strength. Low cycle fatigue resulted in some residual deflection upon unloading but insignificant stiffness degradation.

Performance of Concrete Beams Reinforced with Basalt FRP for Flexure and Shear

AbstractThe flexural and shear performances are evaluated for concrete beams reinforced with basalt fiber-reinforced polymer (BFRP) rebar and stirrups. Nine 150× 300× 3, 100-mm beams were tested in four-point bending to examine the effect of BFRP flexural reinforcement ratios varying from 0.28 to 1.60 the balanced ratio on the structural performance. The beams were reinforced by either BFRP or steel stirrups, and some had no shear reinforcement. It was shown that ultimate and service loads increased with flexural reinforcement ratio for all shear reinforcement types while the service load levels were not affected by stirrup type. Beams without stirrups and those with BFRP stirrups failed in shear, with the former reaching 55–58% of ultimate flexural capacity and the latter failing by stirrup rupture at 90–96% of flexural capacity. Beams with steel stirrups failed in flexure. Deformability values show that methods that combine strength and curvature digress more from those based on midspan strain energy as...

Large scale testing and analysis of hybrid concrete/composite tubes for circular beam-column applications

Abstract Concrete-filled fiber reinforced polymer (FRP) circular tubes provide an effective structural system for a variety of applications such as piles, columns, overhead sign structures and utility poles. This paper discusses the behavior of concrete-filled Glass-FRP tubes ranging in diameter from 90 to 942 mm, using test results of eight beams, five columns and ten beam-column specimens. The effects of concrete fill, laminate structure of the tube, reinforcement ratio based on the wall thickness, as well as different failure modes are examined. Analytical models have been established and used in a parametric study to examine the effects of fiber orientation within the FRP tubes, thickness of the FRP tube, and the diameter of a central hole, which could be used to reduce the self-weight of the member. The benefits of concrete fill as well as the confinement effects have been demonstrated experimentally and analytically.

Investigating a Structural Form System for Concrete Girders Using Commercially Available GFRP Sheet-Pile Sections

This paper presents a new girder consisting of a trapezoidal pultruded glass fiber-reinforced polymer (GFRP) hat-shaped section commercially available as a sheet pile, but used in this study as a structural form for concrete. It can also offer continuity in the transverse direction through a pin-and-eye connection. Five 610 mm×325 mm and 3,300-mm-long girders were tested in flexure to examine different bond systems, voided and solid concrete cores, and the performance in positive and negative bending. Bond systems were wet adhesive bond to freshly cast concrete, adhesively bonded coarse aggregates, and mechanical shear studs. No slip was observed between concrete and the GFRP section until delamination failure occurred within a thin layer of cement mortar that remained attached to GFRP. The studs failed by pull out from the concrete flange. In general, 47–75% of the full strengths of concrete and GFRP were reached at ultimate bond failure. Wet adhesive bonding was the simplest and quickest to apply, while...

Field Applications of Concrete-Filled FRP Tubes for Marine Piles

The paper discusses an innovative composite pile composed of concrete filled fiber reinforced polymer (CFFT) circular tubes. Also describes is an experimental program that has been conducted over the past six years to study the structural performance of CFFT under axial compression, bending and combined loading in marine environment. Eight field applications of the composite pile are briefly described, along with test results of the experimental program and the design charts.

Flexural Strengthening of RC Beams Using Steel Reinforced Polymer (SRP) Composites

Synopsis: This paper presents the application of a new generation of externally bonded composite material in flexural strengthening of reinforced concrete beams. The steel reinforced polymer (SRP) composite consists of high-carbon steel unidirectional Hardwire® fabrics embedded in epoxy resin, and offers high strength and stiffness characteristics at a reasonable cost. In this paper, the mechanical properties of SRP are evaluated and its application in flexural strengthening of RC beams is investigated. Six beams have been tested in three-point bending to study the effect of SRP retrofitting on flexural behavior, failure modes, and crack patterns. Test parameters include variation of the width of SRP sheets and the use of SRP U-wraps at both ends to prevent premature failure caused by delamination of the longitudinal sheet. Significant increase in flexural capacity, up to 53 %, and pseudo-ductile failure modes have been observed in the SRP-strengthened beams. Failure is governed primarily by concrete cover delamination at the tips of the SRP sheets or crushing of concrete at mid-span. It is also shown that the U-wraps have improved flexural stiffness by means of controlling diagonal crack width and providing anchorages to the longitudinal SRP sheets, which reduces their slip. Shear stress concentration near the cut-off point of the SRP sheet has also been investigated. An analytical model is proposed to predict the nominal strength of the SRP-strengthened beams.