Journal of Composites for Construction

So far, composite materials have found only moderate acceptance in the construction industry. This has been due primarily to technical and economic barriers such as limited information on life-cycle costs and anticipated performance and benefits. To enhance the application of composites in construction, it is important to develop a model that allows life-cycle benefit-cost assessment based on limited available information. This paper presents such a life-cycle benefit-cost model for composites in construction that does not require monetary quantification of benefits for comparison of alternative materials. The model has been explained through an example application for highway bridge column rehabilitation. The example considers composite column wraps versus conventional steel jackets to illustrate the application of the model.

In a recent research and development project a novel prototype pultruded composite structure was designed, fabricated, and tested. The bargelike, box-girder type structure measured approximately 24-ft long by 15-ft wide by 5-ft high (7.3 × 4.6 × 1.5 m). The structure was constructed from commercially available off-the-shelf pultruded structural profiles and panel sections. Tubular steel structural members and steel hardware were used to connect and join the different sections and subassemblies. The structure consisted of three 24-ft-long by 5-ft-wide by 5-ft-high (7.3 × 1.5 × 1.5 m) rectangular box-girder modular units and six 4-ft (1.2-m) wide modular deck panels. A design requirement was that the structure be capable of being transported by conventional, nonpermit trucking and be assembled at a remote site for subsequent testing. The structure was fabricated at a ship building and repair shop in Norfolk, Va., whose primary expertise was with conventional steel ship-structure fabrication methods and which had no prior experience with fabricating a large pultruded structural system. To fabricate and assemble the structure, a set of construction documents was produced. These included a set of written construction and assembly specifications, a set of detailed construction drawings, a detailed parts list, and a schedule. This case study details the construction process and provides a step-by-step explanation of how the engineering design team developed the construction documents for a relatively complex pultruded composite structure. Details of the design, analysis, and testing of the system are provided elsewhere.

Bridge rehabilitation utilizing a hybrid fiber-reinforced polymeric composite has recently been completed in Blacksburg, Va. This project involved replacing the superstructure in the Tom's Creek Bridge, a rural short-span traffic bridge with a timber deck and corroded steel girders, with a glue-laminated timber deck on composite girders. To verify the bridge design and to address construction issues prior to the rehabilitation, a full-scale mock-up of the bridge was built and tested in the laboratory. This setup utilized the actual composite beams, glue-laminated timber deck panels, and the skewed geometry implemented in the rehabilitation. Following rehabilitation, the bridge was field tested under controlled conditions (vehicle load and position). Both tests examined service load deflections, girder strains, load distribution, degree of composite action, interpanel deck deflections, and impact factor. The field test results indicate a service load deflection of L/400 under moving loads and a high factor of safety in the composite members against material failure. The data from the field test serve as a baseline reference for future field durability assessments as part of a long-term performance and durability study.

Recent evaluation of civil engineering infrastructure has demonstrated that most of it will need major repairs in the near future. This justifies the development of innovative rehabilitation and strengthening methods for reinforced concrete structures, especially with composite materials. One of these techniques consists of strengthening columns by confinement with a composite enclosure. This paper reports the results of a research program on this topic and concentrates on the behavior of square and rectangular columns confined with carbon and aramid fiber sheets. Results from a series of tests on small-scale specimens showed that confinement increased the strength and ductility of the concrete columns loaded axially.

The bond mechanism of fiber-reinforced polymer (FRP) rebars to concrete was studied to evaluate the effect of cyclic loading. Five different types of 12.0- and 12.7-mm rebars were tested. The FRP rods were embedded in concrete blocks and were subjected to up to 450,000 cycles at service stress level. The loading was accompanied by immersion in water at 60 and 20°C to accelerate deterioration effects. Pullout behavior of the rods was determined at the end of the loading period. The results indicated a reduction in the bond strength after loading. Three mechanisms of failure were identified: (1) Abrasion of the surface of the rod, which, in the case of uniform resin throughout the rod, may lead to a reduction of 20–30% in the bond strength; (2) delamination of the outer layer of the resin at the surface of the rod, which may lead to a reduction of up to 60% in the bond strength; and (3) abrasion of cement particles entrapped between the rod and the concrete, which serves as the main source of “bond” for smooth rods leading to approximately 70% of reduction in the bond strength. There was no significant change in the effect of curing temperature on the loss of bond.

Currently, considerable interest exists in the use of fiber-reinforced polymer (FRP) reinforcement for concrete structures. Due to the generally lower modulus of elasticity of FRP in comparison with steel and the linear behavior of FRP, certain aspects of the structural behavior of RC members reinforced with FRP may be substantially different from similar elements reinforced with steel reinforcement. In this two-part paper the use of different types of FRP grid reinforcement for concrete slabs is investigated, presenting detailed experimental and analytical work. In the first part, the structural behavior in one-way bending is considered. This paper shows which structural measures are needed to ensure acceptable serviceability behavior. The presented analysis and discussion of test results covers the ultimate state and the ultimate limit state for bending, serviceability limit states, ductility, deformability, and ultimate to service load ratio.

The use of fiber-reinforced polymer (FRP) grid reinforcement for concrete slabs has been investigated, considering the behavior of the slabs in one-way bending and under concentrated loading. The behavior under the latter loading type will be considered in this second part of a two-part paper. From the performed punching tests and the analysis, a fairly strong interaction between shear and flexural effects was noted for most of the tested slabs. For the FRP-reinforced slabs with an increased reinforcement ratio or an increased slab depth (needed to fulfill the serviceability criteria in bending), the punching strength was similar to or higher than the tested steel-reinforced reference slabs. For most slabs, slip of the bars occurred resulting in higher deflections at failure. The calculation of the punching failure load according to empirical-based models (from different codes), a modified mechanical model, and an analytical model is evaluated.