Journal of Composites for Construction

This paper introduces a new design procedure for the strength prediction of pultruded glass fiber–reinforced polymer (pGFRP) angles subjected to compression through a parametric analysis. Experimental results were used for the calibration of a finite-element numerical model according to linear and nonlinear analyses. Sensitivity to the initial geometric imperfections, material damage, and leg-junction rotational stiffness was then investigated for an evaluation of the influence of material and geometric nonlinearities on the column behavior. A parametric study including 100 pGFRP angles within slenderness ranges not covered by previous tests was developed for increasing the available data, and the results were evaluated by two normative and four nonnormative design procedures. Finally, a new design procedure based on the direct strength method (DSM) is proposed. It adopts modified global and local strength curves of the original American Specification for the Design of Cold-Formed Steel Structural Members (AISI) from the adjustment of the original expressions based on a large database, including experimental data collected from the literature and numerical data obtained from the parametric study. The proposed DSM approach led to accurate ultimate strength estimates for columns covering a wide slenderness range.

This study presents the results of a comprehensive experimental program on the compressive behavior of hybrid fiber-reinforced polymer (FRP)–concrete–steel double-skin tubular columns (DSTCs) filled with ultrahigh-performance concrete (UHPC) or engineered cementitious composites (ECC). The use of UHPC or ECC, being a novel engineering material with unique characteristics, leads to many advantages of such hybrid DSTCs compared with conventional hybrid DSTCs with normal strength concrete (NSC). Particularly, the tendency of cracking of the FRP tube and NSC in conventional hybrid DSTCs could be reduced through the use of ECC with high tensile ductility and high tensile toughness, leading to excellent corrosion resistance. To understand the compressive behavior of DSTCs with UHPC or ECC, 12 DSTC specimens with different types of concretes (i.e., NSC, UHPC, and ECC) were prepared and tested, and the test results are presented in this paper. The test results demonstrated that DSTC specimens with UHPC or ECC could exhibit highly ductile behavior when a sufficiently large FRP confinement is provided, but the expected beneficial effects of fibers in UHPC or ECC are insignificant in the axial compressive behavior of DSTC specimens. Finally, the axial load resistances of different components of the test hybrid DSTC specimens were investigated, which demonstrated the beneficial effect of interaction of different components in the hybrid system, especially for DSTC–NSC and DSTC–ECC specimens.

The use of fiber-reinforced polymers (FRPs) in the construction of FRP-confined concrete columns (FCCs) is increasingly common for both new construction and the strengthening of existing structures. Given the current need to reduce the environmental impact of concrete construction and the ability of FCCs to minimize the overall dimension of columns by enhancing performance through confinement, it is now necessary to better understand the relationship between the mechanical performance of FCCs and their environmental impact. To achieve this outcome, cradle-to-gate life-cycle assessments (LCA) are performed on a large number of tested and simulated specimens to quantify the global warming potential and embodied energy of FCCs constructed with FRPs and concretes with a range of mechanical properties and to link environmental impact with observed performance. Analysis is conducted using a set of five functional units to first identify the environmental impact of FRP at the material level in relation to composite mechanical properties. It is observed that basalt and carbon fibers have superior environmental and mechanical performance when compared with aramid and glass fibers. The analysis is then repeated at the member level where it is observed that basalt fibers deliver the best environmental performance relative to the stress and strain enhancement provided to the concrete core.

This paper discussed the effectiveness of the hybrid use of fiber-reinforced polymer (FRP) reinforcement for the seismic retrofitting of substandard reinforced concrete (RC) columns. Four columns, except for the reference, were retrofitted with externally embedded FRP (EE–FRP) bars in a longitudinal and external FRP jacket in the transverse directions. The test parameter was the configuration of the FRP bars that were used for retrofitting along the longitudinal direction (e.g., single or hybrid use of different types of FRP bars, such as aramid (AFRP), glass (GFRP), or carbon fiber–reinforced polymers (CFRP). The test results indicated that a significant enhancement in the lateral load capacity (≤198% in the unstrengthened column) could be achieved through the hybrid use of FRP bars under reversed cyclic lateral displacement and a constant axial load without a significant sacrifice in deformability. In addition, the test results yielded insights into the strain (ɛ) capacities of longitudinal FRP bars in tension and their contribution to compression resistance under reversed cyclic lateral loading conditions. In addition, an analytical study was conducted to predict the cyclic flexural behavior in substandard RC columns that were retrofitted through the single or hybrid use of EE–FRP bars that considered the debonding behavior of longitudinal CFRP bars with a smooth surface.

This study entailed axial cyclic loading tests conducted on full-scale diagonal tension members of steel deck-truss bridges to evaluate the effects of seismic retrofitting methods using carbon fiber–reinforced polymer (CFRP) sheets. The loading tests were performed on CFRP-retrofitted specimens with varying anchoring lengths of the CFRP sheets. The results indicated that the proposed retrofitting methods, which employed the intermediate-modulus CFRP type (390–450 GPa) and polyurea putty (a ductile adhesive), delayed the plastic buckling of the flanges and substantially increased the load-carrying capacities, stiffnesses, and ductility capacities of the retrofitted diagonal tension members. Additionally, the polyurea putty effectively suppressed the peeling failure of the CFRP sheets. It maintained the cross-sectional integrity between the steel members and CFRP sheets even after the plastic buckling of the flanges and rupture failure of the CFRP sheets. Further, finite-element analyses accurately reproduced the loading test results by considering the nonlinear bond-slip performance of polyurea putty, anisotropic characteristics of the CFRP sheets, and cyclic plasticity properties of steel.

Millions of tons of glass-fiber-reinforced polymer (GFRP) composite wind turbine blades are expected to age out of service over the next 30 years. Research is being conducted on repurposing these structures as new civil infrastructure products. The GFRP material in these decommissioned wind blades has been shown to retain significant strength and stiffness for second-life applications. However, for repurposing as new products, they will need to be connected to other structural members. The connections employed for this need to be designed, evaluated, and tested prior to their use. Here, we present the results of detailed testing of bolted connections for load-carrying appurtenances that will carry the phases and shield wires (e.g., insulators, crossarms, davits, guy wires, posts) to the spar cap of an 11-year-old 1.5 MW GE37 wind blade, intended for use as a repurposed transmission pole (i.e., a BladePole). Details of ASTM-type pull-out and bearing capacity tests using different types of blind bolts, and tests of a full-scale steel bracket connection called a “universal connector,” are reported. The effects of the different blind bolts, pin diameters, and loading directions relative to the composite laminate structure (longitudinal or transverse) for both the coupon- and full-scale connector bracket tests are described. The ability to design and construct robust connections for repurposed wind blade structures was demonstrated.

This paper addresses a theoretical investigation of the undamped free vibration of slender fiber-reinforced polymer (FRP) beams. While previous studies have focused on global vibration modes in the range of excitation frequencies reported in typical civil engineering problems, the present one discusses the influence of local modes, which can be useful for nondestructive indirect characterizations of materials and detection of damage in bridges and frames. Appropriate shape functions for flexural, flexural–torsional, torsional, and local vibration modes were chosen, and Lagrange’s equations of motion were derived after determination of the energy components. The formulation accounts for C and I sections, different end conditions, and enriched shapes for local modes, and transverse shear deformation is neglected. The results from the proposed equations for a C section were compared to those from generalized beam theory (GBT). Overall, an excellent agreement with GBT was achieved, except for global modes in beams of relatively short equivalent length, in which transverse shear deformation is relevant. Regarding local modes, the associated natural frequency tends to stabilize with increasing lengths and the transverse stiffness component plays a major role in the modal behavior. A study of the influences of flange width and cross-sectional shape (C and I) revealed that frequency drops significantly when flanges become wider. The influence of transverse shear was negligible for beams with a higher than 40 slenderness ratio. The formulation was successfully compared to a previous experiment performed by the authors.

Externally bonded reinforcement with fiber-reinforced polymer (FRP) laminates is a popular method for repairing and strengthening reinforced concrete structures. Failure due to premature debonding poses the challenge of accurately estimating the FRP-to-concrete bond capacity. Such a challenge, premature debonding, exhibits the significance of accurately estimating the FRP-to-concrete bond capacity. Therefore, many lap shear tests have been conducted to evaluate the behavior and capacity of FRP-to-concrete bonds. Based on these tests and theoretical studies, numerous bond capacity estimation models have been proposed. These models, however, do not have the same levels of accuracy and performance. In this study, the accuracy and performance of available models for bond capacity are evaluated based on various criteria. For this purpose, 31 bond capacity prediction models were chosen. A database containing 345 test specimens that were used in none of the models was collected. The models were initially scored through the four methods of log-likelihood, Euclidean distance ranking, Bayesian factor, and variance reduction. The final ranking was then determined by applying the results of these methods to a multicriteria decision-making process using the data envelopment analysis technique. The results show that most models ranging from 1st to 10th are the models employed by strengthening provisions or based on fracture mechanics. The models’ coefficient calibration tests have a considerable effect on the ranking results. The effective bond length has a significant impact on the accuracy and score of the models and is the most important parameter.