Relaxing the Stud Spacing Limit for Full-Depth Precast Concrete Deck Panels Supported on Steel Girders (Phase I)

The AASHTO LRFD Bridge Design Specifications state that the spacing between the shear connectors for steel girders should not exceed 610 mm (24 in.). This decision was made based on research conducted more than three decades ago. The goal of this research is to investigate the possibility of extending this limit to 1,220 mm (48 in.) for stud clusters used with full-depth precast concrete deck panels installed on steel girders. This paper presents the history of the 610 mm (24 in.) limit, various formulas developed to calculate fatigue and design capacity for stud clusters and concerns about extending the current LRFD limit. This paper also presents information on the first phase of the experimental investigation, which is conducted on push-off specimens to validate extending the limit to 1,220 mm (48 in.).     

Large Shear Studs for Composite Action in Steel Bridge Girders

Shear studs used in composite steel bridge construction are typically 19.1 mm (? in.) or 22.2 mm (? in.) in diameter. This paper presents the development and implementation of the 31.8 mm (1??in.) stud diameter. Because the 31.8 mm (1??in.) stud has about twice the strength and a higher fatigue capacity than the 22.2 mm (? in.) stud, fewer studs are required along the length of the steel girder. This would increase bridge construction speed and future deck replacement, and reduce the possibility of damage to the studs and girder top flange during deck removal. Studs also can be placed in one row only, over the web centerline, freeing up most of the top flange width and improving safety conditions for field workers. This paper provides information on the development, welding, quality control, and testing of the 31.8 mm (1??in.) stud. Information on the first bridge built in the state of Nebraska with the 31.8 mm (1??in.) studs is provided.     

Response of Conventional Steel Stud Wall Systems under Static and Dynamic Pressure

This research effort focuses on the evaluation of existing design standards for cold-formed steel stud?walls and the development of retrofit wall systems. Full-scale wall systems are tested under uniform static pressure using a vacuum chamber. The resistance functions obtained are used to model the dynamic behavior of the walls and to predict performance under blast conditions. This paper focuses on defining the static resistance of nonload-bearing steel stud walls with slip track connections and their performance under external explosions. Simple modifications to existing design practice have significantly improved the blast performance of the steel stud walls. Maximum blast resistance is achieved by using steel angles connected to the studs and anchored to the floor and ceiling. The static and dynamic performances of five full-scale steel stud wall systems are presented in this paper.     

Effect of Transverse Reinforcement on the Flexural Behavior of Continuous Concrete Beams Reinforced with FRP

Continuous concrete beams are structural elements commonly used in structures that might be exposed to extreme weather conditions and the application of deicing salts, such as bridge overpasses and parking garages. In such structures, reinforcing continuous concrete beams with the noncorrodible fiber-reinforced polymer (FRP) bars is beneficial to avoid steel corrosion. However, the linear-elastic behavior of FRP materials makes the ability of continuous beams to redistribute loads and moments questionable. A total of seven full-scale continuous concrete beams were tested to failure. Six beams were reinforced with glass fiber-reinforced polymer (GFRP) longitudinal bars, whereas one was reinforced with steel as control. The specimens have rectangular cross section of 200×300??mm and are continuous over two spans of 2,800?mm each. Both steel and GFRP stirrups were used as transverse reinforcement. The material, spacing, and amount of transverse reinforcement were the primary investigated parameters in this study. In addition, the experimental results were compared with the code equations to calculate the ultimate capacity. The experimental results showed that moment redistribution in FRP-reinforced continuous concrete beams is possible and is improved by increasing the amount of transverse reinforcement. Also, beams reinforced with GFRP stirrups illustrated similar performance compared with their steel-reinforced counterparts.     

Compound Shear-Flexural Capacity of Reinforced Concrete–Topped Precast Prestressed Bridge Decks

Modern concrete bridge decks commonly consist of stay-in-place (SIP) precast panels seated on precast concrete beams and topped with cast-in-place (CIP) reinforced concrete. Such composite bridge decks have been experimentally tested by various researchers to assess structural performance. However, a failure theory that describes the failure mechanism and accurately predicts the corresponding load has not been previously derived. When monotonically increasing patch loads are applied, delamination occurs between the CIP concrete and SIP panels, with a compound shear-flexure mechanism resulting. An additive model of flexural yield line failure in the lower SIP precast prestressed panels and punching shear in the upper CIP-reinforced concrete portion of the deck system is derived. Analyses are compared to full-scale experimental results of a tandem wheel load straddling adjacent SIP panels and a trailing wheel load on a single panel. Alone, both yield line and punching-shear theories gave poor predictions of the observed failure load; however, the proposed compound shear-flexure failure mechanism load capacities are within 2% accuracy of the experimentally observed loads. Better estimation using the proposed theory of composite SIP-CIP deck system capacities will aid in improving the design efficiency of these systems.     

Experimental Validation of a Shear Stud Connection between Steel Girders and a Fiber-Reinforced Polymer Deck in the Transverse Direction

A fiber-reinforced polymer (FRP) deck-to-girder connection was evaluated for fatigue resistance and residual capacity in the transverse direction. The connection consisted of three shear studs cast into a trapezoidal cell of a FRP sandwich deck. Steel spirals were positioned around each shear stud to aid in grout confinement. Test fixturing consisted of multiple girders and tie downs to induce realistic loading of the connection due to wheel loads. The connection was fatigued according to AASHTO LRFD Specifications for 10.5?million?cycles (75?year design life) and tested for residual capacity. The connection survived fatigue testing without failure. The haunch exhibited minimal debonding and cracking. Connection capacity after one lifetime of fatigue cycles exceeded strength limit state requirements.     

Seismic Damage Thresholds for Gypsum Wallboard Partition Walls

A series of 11 tests of full-scale partition walls were conducted to determine the behavior of nonstructural gypsum wallboard partition walls during lateral deformation as might be expected during a major earthquake. The partition walls were constructed as double-sided, 1/2?in. (13?mm) gypsum wallboard partition walls with wood stud framing. The walls deformed laterally in one of two ways: either as a joint-failure mode with racking of the individual gypsum wallboard panels, or by a pier-rotation mode where all the gypsum wallboard panels in a pier rotated as a unit. In all of the tests, the fasteners failed by pulling through the back of the wallboard panel, cutting of the gypsum, or tearing out through the edge of a wallboard panel. In some tests, the strength of the tape and compound was seen to provide adequate support to cause the walls to roll as a single unit, especially when the spacing of fasteners was large. The maximum load resisted varied from 512?N/m (378?lb/ft) to 1,177?N/m (869?lb/ft) and occurred at drifts between 0.68 and 1.87%. The drift when specific damage thresholds occurred was monitored during testing. Damage initiated with slight cracking of the panels at the wall opening at drifts of 0.25%, followed by increasing damage up to drifts of 2%, and minimal additional damage at drifts above 2%. Damage thresholds for cyclic loading often occurred at lower drifts than comparable specimens under monotonic loading.     

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.     

Fatigue Behavior of RC Beams Strengthened with GFRP Sheets

The objective of the presented study is to examine the effects of glass fiber reinforced polymer (GFRP) composite rehabilitation systems on the fatigue performance of reinforced concrete beams. Experiments were conducted on beams with and without GFRP composite sheets on their tensile surfaces. The specimens were 152 × 152 × 1,321 mm reinforced concrete beams with enough transverse reinforcement to avoid shear failure. The results of this study indicate that the fatigue life of reinforced concrete beams with the given geometry, subjected to the same cycling load, can be significantly extended through the use of externally bonded GFRP composite sheets. An interesting finding is that, although the fiber strengthening system increases the fatigue life of the beams, the failure mechanism, fatigue of the steel reinforcement, remains the same in both strengthened and nonstrengthened beams. Thus, it is possible to predict the fatigue life of a cyclically loaded beam using existing fatigue models.     

Fatigue of Reinforced Concrete Beams Strengthened with Steel-Reinforced Inorganic Polymers

Steel-reinforced polymer (SRP) composite materials are very attractive due to their low weight and high strength. The ease of installation which significantly reduces repair time and expense is another major advantage. One of the main disadvantages of SRP materials is that the matrices used for their fabrication are typically organic and thus they are susceptible to fire. In this study, a newly developed retrofit system is being used. It consists of high strength steel fibers impregnated in a fireproof inorganic matrix. The objective of this study is to examine the effects of this hybrid rehabilitation system on the fatigue performance of strengthened reinforced concrete beams. Sixteen 100?mm×150?mm×1200?mm reinforced concrete beams with enough transverse reinforcement to avoid shear failure were used in this study. Nine beams were strengthened with steel fiber sheets on their tension faces. The results from the present study indicate that the fatigue life of reinforced concrete beams, subjected to the same cycling load, can be significantly extended using externally bonded sheets. A rather important finding is that although the strengthening system increases the fatigue life of the beams, the failure mechanism remains the same in both strengthened and nonstrengthened beams. Thus, it is possible to predict the fatigue life of a cyclically loaded beam using existing fatigue models. Furthermore, no delamination failures were observed due to fatigue loading.     

Evaluation of Flexural Behavior and Serviceability Performance of Concrete Beams Reinforced with FRP Bars

Flexural behavior and serviceability performance of 24 full-scale concrete beams reinforced with carbon-, glass-, and aramid-fiber-reinforced-polymer (FRP) bars are investigated. The beams were 3,300?mm long with a rectangular cross section of 200?mm in width and 300?mm in depth. Sixteen beams were reinforced with carbon-FRP bars, four beams were reinforced with glass-FRP bars, two beams were reinforced with aramid-FRP bars, and two were reinforced with steel, serving as control specimens. Two types of FRP bars with different surface textures were considered: sand-coated bars and ribbed-deformed bars. The beams were tested to failure in four-point bending over a clear span of 2,750?mm. The test results are reported in terms of deflection, crack-width, strains in concrete and reinforcement, flexural capacity, and mode of failure. The experimental results were compared to the available design codes.     

Cracking and Reinforcement Corrosion in Short-Span Precast Concrete Bridges

A nationwide survey revealed 14 states having bridges comprised of precast, nonprestressed, concrete channel beams. Currently, the Arkansas State Highway and Transportation Department (AHTD) bridge inventory includes approximately 389 in-service bridges using 5.79?m precast channel beams that were constructed using 1952 AHTD bridge details. Results from a statewide inspection of these bridges conducted by the writers revealed bridges with extensive concrete longitudinal cracking at the flexural reinforcing steel level and exposed reinforcing steel. Approximately 2,000 beams in 95 precast concrete channel beam bridges were inspected during a statewide investigation; longitudinal cracking at the reinforcing steel level was observed in 60.4% of the beams and exposed flexural reinforcement in 21.2%. A combination of flexure cracking from the live-load overloads and the presence of moisture has led to this high level of beam deterioration. The source of this moisture is humidity and water seepage at joints between adjacent beams. This paper examines the causes of longitudinal cracking deterioration by examining the influences of water permeation and humidity on the corrosion of flexural reinforcement in precast concrete channel beams.     

Fatigue Flexural Behavior of Corroded Reinforced Concrete Beams Repaired with CFRP Sheets

This study investigated the flexural behavior of corroded steel reinforced concrete beams repaired with carbon-fiber-reinforced polymer (CFRP) sheets under repeated loading. Thirty beams (152×254×2,000?mm) were constructed and tested. Fatigue flexural failure occurred in 29 of these beams. The study showed that pitting of the steel reinforcement due to corrosion occurred only after about a 7% actual mass loss which coincided with a decrease in the fatigue performance of the beam. The controlling factor for the fatigue strength of the beams is the fatigue strength of the steel bars. Repairing with CFRP sheets increased the fatigue capacity of the beams with corroded steel reinforcement beyond that of the control unrepaired beams with uncorroded steel reinforcement. Beams repaired with CFRP at a medium corrosion level and then further corroded to a high corrosion level before testing had a comparable fatigue performance to those that were repaired and tested after corroding directly to a high corrosion level.     

Fatigue Behavior of Carbon Fiber Reinforced Polymer-Strengthened Reinforced Concrete Bridge Girders

This study examines the effects of one-dimensional fiber-reinforced polymer (FRP) composite rehabilitation systems on the flexural fatigue performance of reinforced concrete bridge girders. Eight 508?mm deep and 5.6?m long reinforced concrete T-beams, with and without bonded FRP reinforcement on their tensile surfaces, were tested with a concentrated load at midspan under constant amplitude cyclic loading. The objective of this investigation is to establish the effect that these repair systems have on the fatigue behavior and remaining life of the girders. Results indicate that the fatigue behavior of such retrofit beams is controlled by the fatigue behavior of the reinforcing steel. The fatigue life of a reinforced concrete beam can be increased by the application of an FRP retrofit, which relieves some of the stress carried by the steel. The observed increase in fatigue life, however, is limited by the quality of the bond between the carbon FRP and concrete substrate. Debonding, initiating at midspan and progressing to a support, is common and is driven partially by the crack distribution and shear deformations of the beam.     

Improved Longitudinal Joint Details in Decked Bulb Tees for Accelerated Bridge Construction: Fatigue Evaluation

This companion paper focuses on an investigation of improved continuous longitudinal joint details for decked precast prestressed concrete girder bridge systems. Precast concrete girders with an integral deck, which are cast and prestressed with the girder, provide benefits of rapid construction along with improved structural performance and durability. Despite these advantages, the use of this type of construction has been limited to isolated regions of the United States. One of the issues limiting more widespread use is the perceived problem with durability of longitudinal joints used to connect adjacent girders. Four full-scale slabs connected by No. 16 (#5) headed reinforcement detail using a 152 mm (6 in.) lap length were fabricated and tested. An analytical parametric study was conducted to provide a database of maximum forces in the longitudinal joint. These maximum forces are then used to determine the loading demand necessary in the slab testing due to the service live load. Static and fatigue tests under four-point pure-flexural loading, as well as three-point flexural-shear loading, were conducted. Test results were evaluated based on flexural capacity, curvature behavior, cracking, deflection, and steel strain. Based on these test results, the improved longitudinal joint detail is a viable connection system that transfers the forces between the adjacent decked bulb tee girders.     

Use of Precast Concrete Walls for Blast Protection of Steel Stud Construction

This research study examines the use of a precast concrete panel system for blast protection of facilities with exterior light gauge metal stud walls. The structural retrofit is designed for the specific case where internal operation of the facility cannot be interrupted. To meet this design requirement, a series of precast concrete panels are installed exterior to the building envelope with connections to the foundation at ground level and to the steel building frame at upper floor levels. To validate the retrofit concept, two explosive detonations representing relatively low and high blast threat levels are examined. An exterior insulation and finishing system (EIFS) clad stud wall and a precast concrete protected stud wall are examined under each demand level. The measured responses of both systems are compared with each other and with basic dynamic predictive models. In addition, a finite element study of the connection is conducted to estimate support demands for the blast retrofit. The research results show that the precast wall system provides effective protection of the exterior wall. The research also shows that EIFS clad metal stud wall systems retain significant resilience under blast demands. The dynamic responses of the systems are predictable using standard elastic-plastic dynamic modeling assumptions.     

Interface Shear Connection Analysis of Ultrahigh-Performance Fiber-Reinforced Concrete Composite Girders

The purpose is to analyze the interface shear connection behavior for ultrahigh-performance fiber-reinforced concrete (UHPFRC) and normal concrete (NC) composite girders. The shape and dimension of the shear stud in the conducted tests are referenced from the traditional interface connection design and engineering experiences. The interface shear connection parameters, i.e., initial stiffness and slippage capacity of a single shear stud, are measured from three groups of lateral direct push test specimens with different numbers of studs. Based on the UHPFRC tensile failure characteristics and cracked section rotational mechanisms of the UHPFRC-NC composite structures with flexural, or flexural and shear failure, the limit state is defined as a full pullout from the bottom fiber of the UHPFRC girders. Pseudostrain hardening behavior of the UHPFRC is simplified as an equivalent rectangular stress block. From this mechanism, the interface equilibrium equations are constituted and the interface shear connection degree of the UHPFRC-NC composite girders is derived. It is recommended that the interface shear connection degree may be used as minimum design standard for UHPFRC-NC composite interface shear connection design.     

Evaluation of GFRP Honeycomb Beams for the O’Fallon Park Bridge

This paper presents a study on the evaluation of the static performance of a glass fiber-reinforced polymer (GFRP) bridge deck that was installed in O’Fallon Park over Bear Creek west of the City of Denver. The bridge deck has a sandwich panel configuration, consisting of two stiff faces separated by a light-weight honeycomb core. The deck was manufactured using a hand lay-up technique. To assist the preliminary design of the deck, the stiffness and load-carrying capacities of four approximately 330 mm (13 in.) wide GFRP beam specimens were evaluated. The crushing capacity of the panel was also examined by subjecting four 330×305×190?mm?(13×12×7.5?in.) specimens to compression tests. The experimental data were analyzed and compared to results obtained from analytical and finite element models, which have been used to enhance the understanding of the experimental observations. The failure of all four beams was caused by the delamination of the top faces. In spite of the scatter of the tests results, the beams showed good shear strengths at the face-to-core interface as compared to similar panels evaluated in prior studies.     

Behavior of Field Splice Details in Precast Concrete-Filled Steel Grid Bridge Deck

Redecking operations executed on urban bridges that experience large traffic volumes frequently require carefully orchestrated construction sequences carried out during times of nonpeak traffic. In such a construction environment, only bridge deck options that exhibit a high degree of modularity in conjunction with ease of installation are considered as viable options for a given redecking operation. As a further requirement, the deck installation must also be expected to perform essentially trouble free, with minimal maintenance, for very long periods of time in extremely harsh environments. The present research investigates the behavior of two new deck splice details for use in bridge applications involving precast concrete-filled steel grid deck panels. The research is primarily experimental in nature and is carried out using full-scale deck panel specimens. However, in an effort to better understand the experimental results, 3D finite-element models of the deck specimens are also constructed and studied. This paper summarizes the results from this experimental and analytical program of study.     

Fatigue of Concrete Beams Strengthened with Glass-Fiber Composite under Flexure

A detailed investigation on the fatigue performance of concrete beams strengthened with glass-fiber composite (GFC) is performed in this study. Cyclic load tests were conducted on reinforced concrete beam specimens strengthened with two layers of GFC bonded to the beams’ bottom surface using a special epoxy resin. Midspan-deflection and cracks were measured at different numbers of load cycles and varying fatigue loading levels during the tests. Investigated parameters include total midspan-deflection, residual midspan-deflection after unloading, crack width, crack length, and crack distribution at different loading stages. The fatigue performance of concrete beams strengthened with GFC was evaluated by comparing the deflections, crack sizes, and crack distributions with unstrengthened beams. The concrete beams strengthened with GFC investigated in this study showed significant improvement on fatigue performance.