Stiffness and Strength of Metal Bridge Deck Forms

Light gauge metal sheeting is often utilized in the building and bridge industries for concrete formwork. Although the in-plane stiffness and strength of the metal forms are commonly relied upon for stability bracing in buildings, the forms are generally not considered for bracing in steel bridge construction. The primary difference between the forming systems in the two industries is the method of connection between the forms and girders. In bridge construction, an eccentric support angle is incorporated into the connection details to achieve a uniform slab thickness along the girder length. While the eccentric connection is a benefit for slab construction, the flexible connection limits the amount of bracing provided by the forms. This paper presents results from the first phase of a research study investigating the bracing behavior of metal bridge deck forms. Shear diaphragm tests were conducted to determine the shear stiffness and strength of bridge deck forms, and modified connection details were developed that substantially improve the bracing behavior of the forms. The measured stiffness and strength of diaphragms with the modified connection often met or exceeded the values of diaphragms with conventional noneccentric connections. The experimental results for the diaphragms with the modified connection details dramatically improve the potential for bracing of steel bridge girders by metal deck forms.     

CFRP Composite Connector for Concrete Members

Steel plate connections are frequently used in tilt-up and precast concrete building construction to tie adjacent wall panels together for shear and overturning effects, and to provide continuous diaphragm chord connections for wind and seismic loading. These welded connectors perform poorly in regions of high seismicity and are vulnerable to corrosion. Until now, retrofit and repair strategies for in-plane shear transfer strengthening were limited to attaching steel sections across panel edges. In the present paper, an experimental program is described that utilizes carbon fiber reinforced plastic (CFRP) composites to develop a viable retrofit scheme for precast concrete shear walls and diaphragms. Nine full-scale precast wall panel assemblies with CFRP composite connectors have been tested. The results show that the CFRP composite connection is an effective solution for the seismic retrofit and repair of precast concrete wall assemblies and other precast concrete elements, such as horizontal diaphragms, that require in-plane shear transfer strengthening.     

Thermal Compatibility and Durability of Wearing Surfaces on GFRP Bridge Decks

The paper investigates thermal compatibility between wearing surface (WS) materials and glass fiber reinforced polymer (GFRP) bridge decks, and proposes a more durable hybrid WS system for GFRP decks. Wearing surface delamination problems observed on many existing GFRP bridge decks motivated the investigation and the search for a durable WS material that could alleviate the problems. Several WS materials were bonded to GFRP panels, with and without surface preparation, and tested under various environmental conditions. In addition to the standard ASTM C884 method, the testing program included two new methods for thermal compatibility testing to reflect the in-service conditions of WSs on GFRP bridge decks. The proposed methods were developed to account for the influence of freeze–thaw–heat and submerge–freeze cycles on thermal compatibility and durability. The investigation concluded that a hybrid WS system, consisting of two-layered WS materials, has the best bond quality. Applied directly on top of a GFRP deck, the top layer of the hybrid WS system had the best tire resistance, forming a nonskid riding surface.     

Flexural Behavior of Concrete Beams Reinforced with Hybrid (GFRP and Steel) Bars

Reinforcing concrete with a combination of steel and glass fiber-reinforced polymer (GFRP) bars promises favorable strength, serviceability, and durability. To verify its promise and to support design of concrete structures with this hybrid type of reinforcement, we have experimentally and theoretically investigated the load-deflection behavior of concrete beams reinforced with hybrid GFRP and steel bars. Eight beams, including two control beams reinforced with only steel or only GFRP bars, were tested. The amount of reinforcement and the ratio of GFRP to steel were the main parameters investigated. Hybrid GFRP/steel-reinforced concrete beams with normal effective reinforcement ratios exhibited good ductility, serviceability, and load carrying capacity. Comparisons between the experimental results and the predictions from theoretical analysis showed that the models we adopted could adequately predict the load carrying capacity, deflection, and crack width of hybrid GFRP/steel-reinforced concrete beams.     

Static and Fatigue Testing of Hybrid Fiber-Reinforced Polymer-Concrete Bridge Superstructure

This paper presents the experimental results from static and fatigue testing on a scale model of a hybrid fiber-reinforced polymer (FRP)–concrete bridge superstructure. The hybrid superstructure was designed as a simply-supported single span bridge with a span of 18.3 m. Three trapezoidal glass fiber-reinforced polymer (GFRP) box sections are bonded together to make up a one-lane superstructure, and a layer of concrete is placed in the compression side of those sections. This new design was proposed in order to reduce the initial costs and to increase the stiffness of GFRP composite structures. Static test results showed that the bridge model meets the stiffness requirement and has significant reserve strength. The bridge model was also subjected to two million load cycles to investigate its fatigue characteristics. The fatigue testing revealed that the structural system exhibits insignificant stiffness degradation.     

Fabrication and Testing of Cuff Connections for GFRP Box Sections

A new type of connection between beams and columns has been designed and fabricated specifically for use with glass fiber reinforced plastic (GFRP) pultruded box members. The work is built on previous efforts in the area of GFRP connections, which demonstrated that innovative connections between box sections are superior to connections based on concepts from steel construction for connecting I-beams. The new connection element is designed as a monolithic connection for frame members and is fabricated using a vacuum assisted resin transfer molding process. Individual connection specimens have been fabricated and tested to verify their performance under cyclic static loads in a test frame designed to simulate conditions in a moment resisting frame. The connection configuration was found to fare better from the standpoint of both strength and stiffness in comparison with previous attempts at developing GFRP beam-to-column connections.     

Fracture Toughness of Wood Fiber Gypsum Panels from Size Effect Law

This paper addresses the size effect of inplane bending strength as well as Mode I fracture toughness and process zone length of wood fiber-reinforced gypsum panels. Wood fiber gypsum panels represent an incombustible short fiber composite material composed of recycled paper fibers embedded in a gypsum matrix. The material, which is used for sheathing and bracing of timber frame constructions, exhibits marked fracture softening supposedly resulting in a considerable size effect. In the paper presented, in a first step Ba?ant’s size effect law for quasi-brittle materials is derived. The parameters of this size effect law are then determined by means of nonlinear regression analysis applied to a test series with scaled single edge notched beam specimens. Detailed consideration is given to the adequacy of linear confidence intervals of the model parameters in comparison to nonlinear inferential results. Finally, the probability densities of fracture toughness and fracture process zone length are determined from the distributions of the size effect parameters by means of theory of random variables.     

Barrier Wall Impact Simulation of Reinforced Concrete Decks with Steel and Glass Fiber Reinforced Polymer Bars

Many experimental studies have been performed to evaluate the behavior of noncorroding glass fiber reinforced polymer (GFRP) rebars in reinforced concrete (RC) flexural members. Relatively few studies have focused on the behavior of bridge deck overhangs in the event of a barrier wall impact, which subjects this region to a combination of flexure, shear, and axial tension. The objective of this investigation is to evaluate deck overhangs under these forces. Three bridge deck reinforcing schemes were considered in the study: all epoxy-coated steel (ECS), all GFRP, and hybrid made up of a top mat of GFRP rebars and a bottom mat of ECS rebars. Laboratory testing of nine RC specimens was performed. Results showed that all three reinforcing schemes meet the AASHTO requirements.     

Model for Dynamic Analysis of Wood Frame Shear Walls

A discrete three-degree-of-freedom model of a wood frame shear wall has been developed that is suitable for design-type analyses. The model captures the salient features of the wall response, is amenable to exact closed-form solution, and has the flexibility to account for variations in wall geometry, framing and sheathing materials, fastener type, and spacing. Sheathing-to-stud connections are modeled using a linear viscoelastic element; a method is presented for determining the connection properties using the results of full-scale shear wall tests and a closed-form solution for the test excitation. Results show that the model accurately predicts the hysteretic behavior of the wall for low to moderate displacements; at larger displacements the linear model captures the overall behavior (effective stiffness and energy dissipation), but, as would be expected, fails to predict the pinched hysteresis observed in the tests. Finally, a response spectrum analysis is conducted of a single-story wood frame structure to demonstrate how the model can be used for design-type analyses.     

Effect of Intermediate Diaphragms on Decked Bulb-Tee Bridge System for Accelerated Construction

One of the promising systems for accelerated bridge construction is the use of the decked precast prestressed concrete girders or decked bulb-tee girders for the bridge superstructure. Using the calibrated three-dimensional finite-element models through field tests, a parametric study was conducted to determine the effect of intermediate diaphragms on the deflections and flexural strains of girders at the midspan as well as the live load forces in the longitudinal joint. The following diaphragm details were considered: different diaphragm types (steel and concrete), different diaphragm numbers between two adjacent girders, and different cross-sectional areas for steel diaphragms. Five bridge models with different diaphragm details were developed, and the short span length effect on the bridge behavior was also studied. It was found that as long as one intermediate diaphragm was provided between two adjacent girders at midspan, changing the diaphragm details did not affect the girder deflection, the girder strain, and the live load forces in the longitudinal joint significantly. The effect of diaphragms on the midspan deflection was more prominent in the short span bridge; however, the reduction in the maximum bending moment by the diaphragms was more significant in the long span bridge than in the short span bridge. Specific design recommendation is provided in this paper.     

Repair of Cracked Aluminum Overhead Sign Structures with Glass Fiber Reinforced Polymer Composites

Transportation departments have been using aluminum overhead sign structures since the 1950s. It is well documented that cracks develop in the welds between diagonal and chord members due to fatigue stresses from wind-induced vibration of the slender members. The cracks propagate to complete failure of the members, which can cause collapse of the truss and inflict injuries. The original design of overhead sign structures did not consider fatigue as a limit state. In addition, field welding of aluminum structures for any possible repairs is prohibited. A repair method for the cracked aluminum welded connections between diagonals and chord members using glass fiber reinforced polymer composites (GFRPs) is proposed. The static load carrying capacity of the welded connection, and the cracked connection repaired with GFRP composites are established. The paper describes the surface preparation of the aluminum tubular members, and the architecture and application sequence of the GFRP composite to retrofit the connection. Experimental results are presented from static tests of welded aluminum connections, welded aluminum connections retrofitted with GFRP composites, and new aluminum connections that depend only on GFRP composite elements for their strength. The results from monotonic static tests carried out on cracked welded specimens from actual sign structures show that the retrofitted connection with GFRP reinforcement achieved 1.17 to 1.25 times the capacity of the welded aluminum connection without any visible cracks. This result, and the minimal traffic disruption anticipated in the actual field application, makes this retrofit method a good candidate for implementation.     

Field Pullout Testing and Performance Evaluation of GFRP Soil Nails

Glass fiber–reinforced polymer (GFRP) materials provide practical solutions to corrosion and site-maneuvering problems for civil infrastructures using conventional steel bars as reinforcements. In this study, the feasibility of using GFRP soil nails for slope stabilization is evaluated. The GFRP soil nail system consists of a GFRP pipe installed by the double-grouting technique. Two field-scale pullout tests were performed at a slope site. Fiber Bragg grating (FBG) sensors, strain gauges, linear variable displacement transformers (LVDTs), and a load cell were used to measure axial strain distributions and pullout force-displacement relationships during testing. The pullout test results of steel soil nails at another slope site are also presented for comparison. It is proven that the load transfer mechanisms of GFRP and steel soil nails have certain difference. Based on these test results, a simplified model using a hyperbolic shear stress-strain relationship was developed to describe the pullout performance of the GFRP soil nail. A parametric study was conducted using this model to study some factors affecting the pullout behavior of GFRP soil nails, including nail diameter, shear resistance of soil-grout interface, and ratio of interface shear coefficient to the Young’s modulus of the nail. The results indicate that the GFRP soil nail may exhibit excessive pullout displacement and thus a lower allowable pullout resistance than with the steel soil nail.     

Long-Term Compression Performance of a Pultruded GFRP Element Exposed to Concrete Pore Water Solution

A durability study was performed on a pultruded glass fiber reinforced polymer (GFRP) compression element of a hybrid GFRP/steel joint for concrete structures. GFRP elements were immersed in alkaline pore water solutions of different temperatures during 18?months. Moisture uptake occurred very quickly, within a few days, mainly through a wicking effect along the fiber/matrix interfaces and matrix cracks. The loss of matrix stiffness due to swelling led to a first rapid and significant drop in element compression strength, because of the loss of matrix resistance against buckling of the compressed fibers. In the second phase, strength reduction due to chemical glass and matrix degradation occurred at a much slower rate. It was found that the Arrhenius rate law could predict the element strength decrease. Due to the less harsh environment in practice, the strength and stiffness decrease was found to be acceptable, thereby making it possible to assure structural safety and serviceability of the hybrid GFRP/steel joint after 70?years of service.     

Structural Performance of Hybrid GFRP/Steel Concrete Sandwich Panels

Precast/prestressed concrete sandwich panels consist of two concrete wythes separated by a rigid insulation foam layer and are generally used as walls or slabs in thermal insulation applications. Commonly used connectors between the two wythes, such as steel trusses or concrete stems, penetrate the insulation layer causing a thermal bridge effect, which reduces thermal efficiency. Glass fiber-reinforced polymer (GFRP) composite shell connectors between the two concrete wythes are used in this research as horizontal shear transfer reinforcement. The design criterion is to establish composite action, in which both wythes resist flexural loads as one unit, while maintaining insulation across the two concrete wythes of the panel. The experiments carried out in this research show that hybrid GFRP/steel reinforced sandwich panels can withstand out-of-plane loads while providing resistance to horizontal shear between the two concrete wythes. An analytical method is developed for modeling the horizontal shear transfer enhancement using a shear flow approach. In addition, a truss model is built, which predicts the panel deflections observed in the experiments with reasonable accuracy.     

Flexural Load Testing of Concrete-Filled FRP Tubes with Longitudinal Steel and FRP Rebar

The flexural performance of reinforced concrete-filled glass-fiber reinforced polymer (GFRP) tubes (CFFTs) has been investigated using seven specimens, 220?mm in diameter and 2.43?m long. Specimens were reinforced with either steel, GFRP, or carbon–fiber reinforced polymer (FRP) rebar of various sizes. Prefabricated GFRP tubes with most of the fibers oriented in the hoop direction were used in five specimens. One control specimen included conventional steel spirals of stiffness comparable to the GFRP tube and the other had no transverse reinforcement. Test results have shown that CFFT beams performed substantially better than beams with a steel spiral. Unlike CFFTs with FRP rebar, CFFTs with steel rebar failed in a sequential progressive manner, leading to considerable ductility. An analytical model capable of predicting the full response of reinforced CFFT beams, including the sequential progressive failure, has been developed, verified, and used in a parametric study. It is shown that laminate structure of the tube affects the behavior, only after yielding of the steel rebar. Steel reinforcement ratio significantly affects stiffness and strength, whereas concrete strength has an insignificant effect on the overall performance.     

Rehabilitation of Cracked Aluminum Connections with GFRP Composites for Fatigue Stresses

The original design of existing aluminum overhead sign structures (OSS) did not consider fatigue as a limit state. Cracks propagate in the welds of the connection between the main chord and branches of OSS due to fatigue stresses caused by wind-induced vibration, which occasionally lead to complete fracture of the welds. A rehabilitation method for cracked aluminum welded connections using glass fiber-reinforced Polymer (GFRP) composites is investigated for its effectiveness under fatigue stresses. The results of constant amplitude fatigue tests for three types of aluminum connections from actual OSS are presented: (1) connections with no known cracks; (2) cracked connections rehabilitated with GFRP composites; and (3) connections with 90% of the weld removed and subsequently repaired with GFRP composites. The fatigue limits of the three connection types are established for four stress ranges including the constant amplitude fatigue limit threshold. The rehabilitated connections from OSS exceeded the fatigue limit of the aluminum welded connections with no known cracks. The repaired connections with 90% of the weld removed satisfied the constant amplitude fatigue limit threshold. A cumulative damage index is established which leads to a fatigue reduction factor for the rehabilitation design of cracked aluminum connections using the GFRP composites.     

Flexural Strength of RC Beams with GFRP Laminates

The results of an experimental and numerical study of the flexural behavior of reinforced concrete beams strengthened with glass-fiber-reinforced-polymer (GFRP) laminates are presented in this paper. In the experimental program, ten strengthened beams and two unstrengthened beams are tested to failure under monotonic loading. A number of external GFRP laminate layers and bond length of GFRP laminates in shear span are taken as the test variables. Longitudinal GFRP strain development and interfacial shear stress distribution from the tests are examined. The experimental results generally showed that both flexural strength and stiffness of reinforced concrete beams could be increased by such a bonding technique. In the numerical study, an eight-node interface element is developed to simulate the interface behavior between the concrete and GFRP laminates. This element is implemented into the MARC software package for the finite-element analyses of GFRP laminate strengthened reinforced concrete beams. Reasonably good correlations between experimental and numerical results are achieved.     

Development of FRP Short-Span Deployable Bridge—Experimental Results

For military and civilian applications, there exists a need for lightweight, inexpensive, short-span bridges that can be easily transported and erected with minimal equipment. Owing to its favorable properties, fiber-reinforced polymer (FRP) has been shown to be feasible for the construction of such bridges. Investigations into the behavior of a short-span bridge structural concept, adapted to the material properties of commercially available glass FRP (GFRP) pultruded products, are presented. A 4.8-m span prototype was built from GFRP sections, bonded throughout to form a tapered box beam, with a width of 1.2?m and a height at midspan of approximately 0.5?m. The box beam represents a single trackway of a double-trackway bridge, whose trackways could be connected by light structural elements. The quasi-static and dynamic behavior of the prototype box beam was investigated in ambient laboratory and field conditions to assess the design and construction techniques used, with a view to designing a full-scale 10-m GFRP bridge. Laboratory testing of the prototype box beam used single and pairs of patch loads to simulate wheel loading. These tests confirmed that the box beam had sufficient stiffness and strength to function effectively as a single trackway of a small span bridge. Field testing of the structure was undertaken using a Bison vehicle (13,000?kg), driven at varying speeds over the structure to establish its response to realistic vehicle loads and the effects of their movement across the span.     

Multifunctional Hybrid GFRP/Steel Joint for Concrete Slab Structures

A multifunctional hybrid glass fiber-reinforced polymer (GFRP)/steel joint has been developed for the transfer of compression and shear forces in thermal insulation sections of concrete slab structures used in building construction. The new pultruded cellular GFRP element improves considerably the energy savings of buildings due to its low thermal conductivity. The quasi-static behavior of the GFRP element in insulating and load-transferring joints at the fixed support of cantilever beams was investigated. Two loading modes were investigated: a moment dominant mode and a shear dominant mode. Results show that the GFRP element is not critical at the ultimate limit state. Ductile failure occurs either in the concrete during yielding of the steel bars, or only in the steel bars that penetrate the hybrid GFRP/steel joint. In moment mode, the GFRP element only transfers the compressive forces from the bending moments. In shear mode, in addition to the moment transfer, about 43–63% of the shear forces are transferred in the element webs at ultimate limit state due to tilting of the element. The application proves that multifunctionality can lead to competitive solutions for GFRP composites used in load-carrying components and can compensate for the relatively high material cost.     

Cyclic Flexure Tests of Masonry Walls Reinforced with Glass Fiber Reinforced Polymer Sheets

The research work reported here investigates the out-of-plane flexural behavior of masonry walls reinforced externally with glass fiber reinforced polymer (GFRP) sheets and subjected to cyclic loading. A full-scale test program consisting of eight wall specimens was conducted. Nine tests were performed, in which three parameters were studied. These included the level of compressive axial load, amount of internal steel reinforcement, and amount of externally bonded GFRP sheet reinforcement. Of the three parameters studied, varying the amount of GFRP sheets was the only parameter that significantly affected the behavior of the walls. The GFRP sheet reinforcement governed the linear response of the bending moment versus centerline deflection hysteresis. Increasing or decreasing the amount of GFRP sheet reinforcement either increased or decreased both the wall stiffness and the ultimate strength, respectively. Except for visible cracks, the walls maintained their structural integrity throughout the out-of-plane cyclic loading. The unloading/reloading paths for successive loading cycles were similar, indicating little degradation. Thus, the general behavior of the walls was very predictable. The system, therefore, could be used to advantageously rehabilitate older masonry structures that are inadequately reinforced to withstand seismic events. A simple model of the behavior is also presented to allow for the evaluation of the strength and deformation characteristics of these elements.