Journal of Composites for Construction

The application of concrete is severely limited in construction in cold areas. However, the local ice has functioned as a potential substitute for concrete for a long time. In order to make efficient use of ice to overcome its weaknesses of low strength and poor ductility, an innovative type of ice-filled large rupture strain (LRS) fiber-reinforced polymer (FRP) tube column was developed. The system consists of external LRS FRP tubes filled with plain ice or sawdust-reinforced ice. This paper presents an experimental investigation into the axial compressive behavior of such composite stub columns with circular sections. The test results confirmed that the axial compressive behavior of the ice cores was greatly improved because of the LRS FRP confinement, as well as the addition of sawdust in ice. The axial stress–strain curves of the LRS FRP-confined ice exhibited monotonically ascending bilinear shapes. Both the compressive strength and the ultimate axial strain of the confined ice were significantly enhanced with an increase of the thickness of the LRS FRP tube. A theoretical model for the LRS FRP-confined ice is proposed, in which the dilation properties (i.e., lateral strain–axial strain relation), as well as the entire axial stress–strain responses of the inner ice cores, are explicitly modeled with reasonable accuracy.

The accuracy of existing compressive strength models for fiber–reinforced polymer (FRP)-confined concrete might vary significantly since most of them were established empirically, without a clear understanding of the confinement mechanisms. Previous studies have suggested that the compressive behavior of confined concrete depends on its confining stress path. However, the confining stress path of FRP-confined concrete and its corresponding effect on the behavior of FRP-confined concrete has not been investigated, to the best of the authors’ knowledge. In this paper, the confinement mechanism of FRP-confined concrete will be investigated for the first time by investigating the confining stress path and the relationship between the confining stress path and the compressive strength of FRP-confined concrete. The results indicate that the FRP-confined concrete that has different column parameters generally yields different confining stress paths, which leads to different compressive strengths. The influence of the confining stress paths on the compressive strength was observed to be less significant for the specimen that was confined by a stress path with a larger lateral stress dominant index. Based on the theoretical and experimental results of this paper, a confining stress path-based compressive strength model will be developed for FRP-confined concrete. The developed model yielded more accurate predictions than existing models based on the results of this paper and previous tests.

Masonry columns often exhibit a lack of load-carrying capacity that is due to overloads and do not provide any ductility or dissipation capacity under seismic forces. Column confinement has been extensively studied as an effective technique, which could mitigate these structural vulnerabilities. The confinement of masonry columns will be studied in this paper, by considering fabric–reinforced cementitious matrix (FRCM) materials as external jackets. Due to the lack of information in the scientific literature, a new analysis-oriented model (AOM) for the prediction of the axial stress–strain law will be presented and discussed in this paper. The proposed AOM consists of a system of equations that make several assumptions: crossing the predicted peak point (strength and relative strain), crossing the ultimate point (80% residual strength and relative strain), and the horizontal tangent at the peak point and the initial (linear elastic) slope derived from the geometry and mechanical properties of the materials involved. The AOM was demonstrated to be simple and accurate, based on Pearson's test (χ²); therefore, the proposed approach could be considered for future design equations. In addition, this paper will illustrate and discuss the validation of two available design-oriented models (DOMs), which could predict the axial strength of FRCM jacketed columns, by comparing the theoretical results with a database of experimental results that is available in the scientific literature. Novel formulas for the computation of both the peak and ultimate axial strains will be further proposed, as the basis for a design procedure. Their accuracy was demonstrated by considering an experimental versus theoretical comparison.

In reinforced concrete (RC) columns, the efficiency of confinement that is provided by fiber–reinforced polymer (FRP) composites is usually limited by the buckling of longitudinal steel bars. This situation is even more critical in noncircular columns in which the FRP ruptures due to a combination of buckling of the steel bars and FRP stress concentrations at the corners. The main objective of this study is to observe the effect of internal steel bars on the axial compressive response of noncircular RC column specimens confined with polyethylene terephthalate (PET) FRP, which possesses a large rupture strain (LRS) capacity. In total, 32 specimens were tested under monotonic axial compression. The parameters considered are the number of PET FRP layers, the stirrup spacing, and the cross-sectional aspect ratio. The test results indicate that the strength and deformation capacities of the confined specimens were significantly influenced by the parameters that were considered. Of interest, with an increase in PET FRP confinement, the effect of buckling length became less significant. In addition, the test results indicate that the PET FRP confinement provided a weak but prolonged constraint on the buckling of longitudinal bars. Moreover, PET FRP efficiently sustained the stress concentrations of bar buckling at corners that led to a considerable ductile response before failure.

The stress–strain relationship of concrete is different under different boundary conditions, load paths, and environments. Identification of the stress–strain relationship of concrete for different structures and design conditions is critical to the engineering design of structures. Because direct measurement of local stress is impossible without interrupting the original local stress–strain condition, various indirect methods have been developed to derive stress–strain relationships of concrete. An analytical method for deriving the stress–strain relationship of concrete from eccentrically loaded column tests is extensively studied in this paper, through rigorous mathematical derivation and rational analytical studies. Detailed and rigorous equations and computational procedures for columns with an arbitrary shape of cross section are obtained. Instability of the calculated stress–strain curve or large scattering of results, a critical problem of the analytical method, is resolved through proper selection of equations and computational procedures. Application of the method reveals the real shape of the stress–strain relationship of fiber–reinforced polymer (FRP)-confined concrete under eccentric loading for the first time.

Nowadays retrofitting and strengthening of masonry buildings are important challenges for structural engineering to ensure the structural safety under seismic or exceptional loads. This paper aims to clarify the effects of strengthening systems on out-of-plane mechanisms activation, such as horizontal and vertical bending mechanisms, by analyzing P-M interaction diagrams according to available international design guidelines. They enable the assessment of structural behavior of strengthened masonry walls under different external loads. Dimensionless equations of maximum bending moment capacity of masonry cross sections retrofitted with composite strengthening systems are derived, assuming different failure modes such as crushing of masonry and rupture of the strengthening system. Parametric analyses are performed to assess the impact of the mechanical parameters of the strengthening systems in terms of strength. The results show that the strengthening systems play a fundamental role in terms of cross section capacity and, if not well designed, the strengthening systems may be ineffective or deleterious in cultural heritage.

A series of finite-element analyses for slab­–column edge connections reinforced with fiber-reinforced polymer (FRP) reinforcement and subjected to reversed-cyclic lateral load is conducted and discussed. A three-dimensional nonlinear finite-element model (FEM) is constructed using a commercially available software. The FEM is validated against the results of experimental studies conducted previously by the authors. Subsequently, the validated FEM is used to carry out an extensive parametric study investigating the influence of key parameters including the gravity shear ratio (0.2–0.8), flexural reinforcement type [glass and carbon FRP (GFRP and CFRP, respectively)], column aspect ratio (0.25–4.00), flexural reinforcement ratio (0.7%–1.4%), and slab thickness (150–400 mm). The results showed that the drift capacity of edge connections reinforced with either GFRP or CFRP reinforcement is reduced when the applied gravity shear ratio increases. However, GFRP-reinforced concrete (RC) connections were able to undergo larger drift ratios than their CFRP-RC counterparts. In addition, increasing the slab thickness reduced the punching shear strength of GFRP-RC connections, even for slabs with an effective depth less than 300 mm.

In this paper, a formulation based on the moment–curvature diagrams was proposed to calculate the effective flexural stiffness (EFS) of fiber-reinforced polymer (FRP) reinforced concrete (RC) beam members. A parametric study was carried out to encompass the effect of different factors, such as tensile reinforcement ratio, concrete compressive strength, modulus of elasticity, and aspect ratio. The proposed formulation was verified with numerous experimental data reported by various researchers. To extend the validation of the formulation into the beams of RC frames, the EFS (EI_e) of cracked GFRP (glass FRP) and CFRP (carbon FRP) RC beam sections for four types of frames were calculated. Based on the analytical study, experimental approach, and frame analysis approach, the EFS of FRP RC beams is less than 0.184 times the gross flexural stiffness (E_cI_g). According to the results obtained from various approaches, the range between 0.05 and 0.18 for the EFS ratio (EI_e/E_cI_g) of FRP RC beams is proposed.

The combined use of a fiber-reinforced polymer (FRP) tube with steel and concrete to form hybrid structural members has attracted increasing research attention. Hybrid FRP-concrete-steel multitube concrete columns (MTCCs) are a new form of such members, comprising an external FRP tube and a number of internal steel tubes, with all the space inside the tubes filled with concrete. Hybrid MTCCs allow the use of small-scale standard steel tube products to construct large-scale columns, and these possess many advantages including excellent ductility, as demonstrated by recent studies. The existing studies on MTCCs, however, have been limited to the testing of small-scale specimens. For a new column form particularly suitable for large-scale construction, the potential size effect on the behavior of MTCCs needs to be clarified. This paper presents the first-ever experimental study on large-scale MTCCs through the testing of specimens with an outer diameter (for circular specimens) or a side length (for square specimens) of 500 mm and a height of 1,500 mm. The configuration of steel tubes in these specimens, designed to be similar to real columns, is different from those in the small-scale MTCCs reported by the existing studies. The test results show that the large-scale MTCCs all possess excellent structural performance including ample ductility and that the size effect appears to be negligible for MTCCs with sufficient confinement. The test results also show that the configuration of steel tubes may have a significant effect on the behavior of the confined concrete in MTCCs. In addition, an analytical method based on the transformed section approach and an existing model for FRP-confined concrete-filled steel tubes is presented and shown to provide close predictions of the test results in the present study.

The use of fiber-reinforced polymer (FRP) to repair and seismically strengthen existing deficient or damaged structural elements is now widespread. FRP anchors have become an important component of such FRP strengthening. However, while reasonable quality control and field quality assurance measures exist for FRP fabrics and plates, such attention has not yet been given to FRP anchors. It seems logical to expect that poor FRP anchor installation will adversely impact the performance of the repaired element. This experimental program was envisaged to assess the level of such an adverse impact. It consists of six RC columns subjected to axial load and quasi-static cyclic load. Of the six columns cast for the experimental work, three columns had good concrete placement, while the remaining three showed poor consolidation, with substantial honeycombing and segregation at the base. It was decided that the latter columns could be used as examples of damaged concrete and so they were repaired by a local contractor by removing the poor concrete and replacing it with a commercially available bagged concrete repair material. One column of each set of three was designated as a control column without any FRP strengthening, while the four remaining columns were strengthened using longitudinal FRP sheets for flexural strengthening, anchors to develop the FRP into the foundation, and transverse FRP sheets for confinement. It was observed that the concrete repair did not adversely affect the behavior of the columns or the interaction between the concrete and the FRP. The FRP anchors were installed to replicate poor installation in the field. Those with improperly placed fans, or splays, did not perform at all as intended and it is recommended that such anchors be removed and replaced without exception. Inadequately saturated anchors were able to achieve their design rupture capacity but failed in a more brittle manner than adequately saturated anchors. Based on the observations from the experimental program, several ideas and options are proposed to enhance the quality of FRP anchors. Accompanied with onsite testing and mockups, these suggestions will substantially contribute to the mitigation of the associated variability in the performance of the rehabilitation.

Small-diameter fiber-reinforced polymer (FRP) bars have great potential in certain applications, such as concrete sandwich panels, ties, and shear connectors. In this study, the development lengths (L_d) of basalt FRP (BFRP) deformed bars of 4–8 mm diameter (d_b) will be determined through a series of 44 notched beam tests with concrete of 41–70 MPa compressive strength. The beams measured 101 × 203 mm in cross section and varied in length from 610 to 1,980 mm to accommodate various embedment lengths (L_e). Depending on d_b, L_e varied from 5 to 109 d_b and the clear concrete cover was 30 mm. Bond failure of the 4 and 6 mm bars was by pullout and that of the 8 mm bar was by concrete splitting. The bar axial stress at failure will be plotted against L_e for each set and linear regression will be used to establish L_d based on the guaranteed tensile strength. It was shown that as concrete strength increased from 41 to 70 MPa, L_d reduced from 32 to 20 d_b for the 4 mm bar, from 30 to 25 d_b for the 6 mm bar, and from 52 to 23 d_b for the 8 mm bar. The average bond strength increased as the L_e shortened, and as concrete strength increased. ACI 440.R1 (ACI 2015) and CAN/CSA S806 (CSA 2012) design guides grossly overestimated L_d of these small-diameter bars. Alternative equations are proposed for both splitting and pullout bond failure that provided more accurate predictions of L_d.

This paper discusses the design of a marine dock in Miami, Florida reconstructed after sustaining damage from Hurricane Irma in 2017. This pioneering structure implements accelerated bridge construction methods using prefabricated bridge elements and systems. The structure is made of precast concrete members with basalt fiber-reinforced polymer and glass fiber-reinforced polymer bars, and concrete mixed with seawater. The structure is designed to withstand hurricane loading and the choice of materials is intended to leverage sustainability and resilience.

The harsh Australian environment makes the use of steel reinforcement in concrete structures problematic on account of corrosion. The probability of corrosion damage will significantly increase in the years to come and will become a major problem not only in coastal regions but also in inland parts of Australia due to increasing carbon dioxide concentration, temperature, and relative humidity as a consequence of climate change. In the last two decades, glass fiber-reinforced polymer (GFRP) composite bars have become an alternative to steel reinforcement for reinforcing concrete structures exposed to harsh environments. The reinforcing material is noncorrodible, nonmagnetic, lightweight, and has high tensile strength, thus making it a viable reinforcing material for concrete structures. This paper provides the state-of-the-practice in the research, development, and application of GFRP bars, with the aim of properly informing the engineering community about this alternative, noncorrodible reinforcing technology. The paper also presents a strategy toward the development of fiber-reinforced polymer bar material specifications with the aim to ensure quality use and application of the GFRP material in a wide range of applications in Australia in the years to come. Moreover, the best practices and data presented in this paper will be very useful in the development of unified international standards and specifications for GFRP bars.

Hollow-core concrete columns are widely used as structural members to reduce the cost and self-weight of concrete structures. This study investigates the axial load–axial deformation behavior of glass fiber-reinforced polymer (GFRP) bar- and helix-reinforced hollow-core circular concrete columns. Four specimens of 214-mm outer diameter and 56-mm circular inner hole diameter with a height of 850 mm were tested under axial compression. One specimen was reinforced with steel bars and steel helices, and the remaining three specimens were reinforced with GFRP bars and GFRP helices. It was found that, for a similar amount of longitudinal and transverse reinforcements, the GFRP bar-reinforced specimen achieved 15% and 4% higher effectiveness of confinement reinforcement and ductility, respectively, than the steel bar-reinforced specimen. The effectiveness of confinement reinforcement and ductility of the GFRP bar-reinforced specimen was higher for the smaller pitch of GFRP helices. The GFRP bar-reinforced specimen with helices of 30 mm pitch achieved 46% and 66% higher effectiveness of confinement reinforcement and ductility, respectively, than the GFRP bar-reinforced specimen with helices of 90 mm pitch.

Widespread acceptance of textile-reinforced mortar (TRM) systems for various applications would require a universally accepted procedure for the qualification, characterization, and design of TRM. Based on several independent studies, it is well established that the tensile strength of TRM is not just dependent on the type and volume fraction of the textile but also on the bond characteristics of the textile with the cementitious binder. The customization possibilities for selecting the textile and binder according to various product applications makes it necessary to characterize the tensile behavior independently when deriving design parameters. This paper is aimed at developing a methodology for the design of textile-strengthened masonry panels that accounts for its flexural behavior. In the proposed methodology, first predictions of the tensile strength and efficiency of various textiles in TRM are made, and the possibilities of adopting artificial neural networks (ANNs) to this aim are explored. The method is independently validated using experimental data of uniaxial tensile characterization. Further, the flexural capacity predicted for masonry panels strengthened with TRM has been validated against the experimental results to prove the feasibility of the proposed methodology.