Journal of Composites for Construction

For posttensioning tendons consisting of prestressing steel in many countries comprehensive mechanical tests for the general acceptance are required. The relevant test rules vary from country to country. The Fédèration Internationale de la Précontrainte (FIP) recommendations from 1993 for acceptance testing represent a significant step toward international harmonization. With the first applications of fiber-reinforced plastic (FRP) for posttensioned structures the need for corresponding test rules became evident. This paper presents a draft of such rules elaborated on by a working group of FIP Commission 2.

Corrosion of the steel reinforcement in a cold and saline environment leads to the overall deterioration of reinforced concrete structures. To avoid such deterioration, fiber-reinforced polymers (FRP) rebars are used in place of steel reinforcement. In the present paper, test results of 12 concrete beams reinforced with FRP rods are reported. The main parameters investigated in the study include the reinforcement ratio and the concrete strength. Theoretical models are proposed for the prediction of crack width, crack spacing, load-deflection response, ultimate capacity, and modes of failure. The concept of deformability is also discussed.

An exploratory study was carried out to support the development of standard test methods for fiber reinforced plastic (FRP) bars for use as concrete reinforcement. The principal objectives were to develop a simple, economical, and effective system to permit tensile loading of the bars in a universal test machine; to evaluate the influence of the free-length-to-bar-diameter ratio on the measured tensile strength; and to explore the potential of measuring the elastic modulus using available nondestructive test methods. A successful system for applying tensile load was developed. The ends of a bar were embedded in steel tubes using a high-strength gypsum cement mortar. The bars were loaded by gripping the tubes in the conventional wedge friction grips of a tensile testing machine. No statistically significant influence of the free-length-to-diameter ratio was observed for ratios varying between 40 and 70. However, large within-test variability of tensile strength was observed. Dynamic modulus of elasticity was determined using two stress-wave propagation methods: ultrasonic pulse velocity and resonant frequency. The dynamic values compared favorably with static values obtained from tensile stress-strain curves. Recommendations are provided for additional studies to support the development of standard test methods.

A new ductile hybrid fiber reinforced polymer (FRP) bar has been developed at Drexel University. This new bar is unique in that it has equivalent bilinear stress-strain characteristics, with a Young's modulus approaching that of steel. It has improved bonding characteristics through the direct introduction of ribs during the in-line braiding and pultrusion process used in its manufacture. When used as reinforcement in new or repaired concrete structures, it attains ductile characteristics similar to those of steel and permits limit states design methodology. The new FRP bar, which fails in a gradual manner, has an equivalent bilinear stress-strain tensile curve with a definite yield, an ultimate strength higher than the yield, and an ultimate failure strain between 2% and 3%. It has the distinct advantage of being noncorrosive, it is light in weight, nonconductive, and nonmagnetic, and has high strength. It can be tailored to strength levels that are compatible to current grades of steel reinforcing bars or prestressing tendons. This paper briefly describes the method of designing and manufacturing the new FRP bars. It compares the predicted and experimental stress-strain characteristics of the new bars manufactured using a prototype braiding/pultrusion process, and compares the behavior of these new bars to steel reinforcement in flexure. It examines the implications of the bilinear stress-strain relationship of the reinforcement on the load-deflection and moment-curvature behavior of flexural members. Finally, it describes the ductile behavior of beams reinforced with the new FRP and with steel bars.

Damage and fracture progression in carbon-fiber reinforced plastic (CFRP) composite I-beams subject to three point bending are evaluated via computational simulation. An integrated computer code that scales up constituent micromechanics level material properties to the structure level and accounts for all possible failure modes is used for the simulation of composite degradation under loading. Damage initiation, growth, accumulation, and propagation to fracture are included in the simulations. Three I-beams with different layup configurations are evaluated. Simulation results are compared with experimental data. Design implications with regard to damage tolerance and residual strength of CFRP composite beams are examined.

The shear coefficient in Timoshenko beam theory is derived for thin-walled beams constructed of orthotropic laminated composite panels and new formulas for the common forms of thin-walled section are presented. The results are identical to Cowper's for the case of isotropic beams. Comparison is also made with the shear coefficient presented by Bank (1987). A parametric study is conducted to evaluate the effect of cross section dimensions and the mechanical properties of the laminated panels on the shear coefficient. The transverse shear deformation and its relative importance compared to bending deformation is investigated for this class of composite beams. For thin-walled sections constructed from laminated panels made of a combination of 0° unidirectional and angle-ply laminae, the optimal ply angle for different percentages of angle-ply laminae, is found to minimize the total static deflection of the beam. This lay-up configuration is the most practical and effective distribution of plies in laminated composite thin-walled beams to meet the design serviceability requirements (i.e., deflection and vibration).

This study describes the fatigue performance of pultruded glass fiber reinforced plastic (GFRP) box and wide flange (WF) beams without and with flexural connections. A total of 51 tests were conducted under cyclic bending loads to monitor stiffness degradation, failure progression, failure patterns, and fatigue performance. The test data revealed that sections showed no stiffness reduction till they reached 70–80% of their fatigue life. Fatigue performance of GFRP sections versus steel has been presented. The effect of load application mode (uniform across flange and over a part of flange) on the fatigue performance of box sections is described. The WF sections showed better fatigue performance than the box sections. Failure modes revealed that the web-flange junction on the compression side was the principal location of fatigue failure. A total of 35 tests were conducted on sections with connections to study the performance and efficiency of sections with splice connection as compared to those sections without any connection.