John P. Newhook

PUNCHING SHEAR STRENGTH OF RESTRAINED CONCRETE BRIDGE DECK SLABS

This paper focuses on the development of a theoretical model for predicting the behavior of laterally restrained, fiber-reinforced concrete bridge decks. Based on observations of the failure modes in experimental testing and a review of models used for the punching failure of reinforced concrete slabs, a rational model is developed. The assumptions and equations used in the model development are presented along with the solution algorithm. The theoretical model is checked through comparison with several half-scale and full-scale tests on laboratory bridge decks. The results of the experimental programs are recorded elsewhere and listed in the references.

Durability of GFRP Reinforced Concrete in Field Structures

Synopsis: Recently, ISIS Canada studied the durability of GFRP in concrete in several field structures across Canada. The objective of the study was to provide the engineering community with the results of the performance of GFRP materials that have been exposed to the concrete environment in built structures. Cores of GFRP-reinforced concrete were removed from five field structures. Analytical methods, namely optical microscopy, scanning electron microscopy and energy dispersive x-ray, differential scanning calorimetry and infrared spectroscopy, were used to determine the composition of GFRP after being subjected to the alkaline environment of concrete for five to eight years. Three research teams from four Canadian universities performed microanalyses of the GFRP and surrounding concrete independently. Results indicate that no deterioration of GFRP took place in any of the field structures. No chemical degradation processes occurred within the GFRP due to the alkalinity of the concrete. The overall conclusion of the study is that GFRP is durable in concrete. Also, it was concluded that the CHBDC was conservative in its first edition by not permitting GFRP as primary reinforcement. As a result of the study, the second edition of the CHBDC, currently in the final stages of approval, permits the use of GFRP as primary reinforcement.

PRECAST CONCRETE DECKS FOR SLAB-ON-GIRDER SYSTEMS: A NEW APPROACH

Fiber-reinforced concrete (FRC) deck slabs without internal tensile reinforcement are also known as steel- and corrosion-free deck slabs. The cast-in-place version of these slabs was applied to 5 highway bridges in Canada. This paper describes the significant design details of a 150 mm-thick precast steel-free deck slab supported on girders at a spacing of 3.5 m. Results of tests on full-scale models of the precast slab are also reported. It was found that the precast panels, made composite with the supporting beams, were able to sustain concentrated loads that were several times larger than the factored design loads. The experimental investigation included the study of the panels performance to sustain construction loads when it is not connected to the girders. This investigation led to an improved design of the panel, also reported herein. When a precast panel without any reinforcement was incorporated in a forestry bridge some years ago, it developed several wide cracks. While these cracks have not impaired load-carrying capacity of the deck, it is now believed that unsightly wide cracks should be avoided by including a crack-control grid of nominal reinforcement in the panel, either made of steel or glass fiber-reinforced polymer.

Behavior of Externally Restrained Noncomposite Concrete Bridge Deck Panels

Externally restrained concrete bridge deck slabs, sometimes referred to as steel-free bridge decks, have been employed in at least 12 highway bridges in North America. These decks are normally made composite with the supporting bridge girders to promote arching behavior. This paper describes research conducted to develop a precast noncomposite panel, which behaved in a similar manner as the composite externally restrained system. Five full-size deck slab panels were constructed and tested under concentrated static loading conditions. Various parameters, including strap strain, deck deflection, and crack width, were monitored during testing. The results show that proper confinement of the deck panels resulted in the desired punching shear behavior and compared favorably with theoretical models. These panels can be used for rapid construction of field structures but also create economic full-scale laboratory specimens for further research on externally restrained deck systems.

Investigation of Fatigue Damage in Steel-Free Bridge Decks with Application to Structural Monitoring

The steel-free deck system is a unique concrete deck slab for girder bridges. The system does not require internal reinforcement for strength. This paper reports the results of an investigation into the fatigue behavior of this system. For this purpose, two sets of five precast steel-free decks with two different concrete strengths were constructed and tested under differing levels of fatigue loading to study their behavior. The behavior of parameters, such as the strap strain, deck deflection, and crack width, which could be monitored in field bridges with steel-free decks, was studied. Based on these experimental results, an S-N curve was suggested for the precast steel-free decks and a generic format for the monitoring parameters of the structural model was produced.

Residual Strength of Precast Steel-Free Panels

In this paper, the residual strength behavior of steel-free decks under truck wheel loads was studied. Steel-free decks are free of internal reinforcement; instead, they rely on arching action created by a series of external straps. Residual strength is defined as the remaining strength of the slabs after a limited number of fatigue cycles are applied. The change in residual strength with increasing fatigue cycles was experimentally investigated by testing five identical steel-free slabs. A varying number of fatigue cycles were applied to each slab and then ultimate static testing was conducted. During the testing, various physical parameters, including deflection, strain, and crack width, were monitored. It was determined that the residual strength begins to decrease as the fatigue damage enters the transition from stable crack growth to the final rapid crack propagation stage. A general residual strength relationship was proposed for use in field monitoring and management decisions.

Synthetic Fiber-Reinforced Concrete Bridge Decks: Redefining Bridge Deck Design and Behavior

Researchers at the Technical University of Nova Scotia have pioneered the development of concrete slab on girder bridge decks totally devoid of all internal steel reinforcement. The decks are constructed of synthetic fiber-reinforced concrete on composite steel girders restrained by external steel straps. The discrete reinforcing fiber used is a collated fibrillated polypropylene fiber. The major benefit of this approach is the reduction of long-term maintenance costs and the increase in bridge deck lifespan. An overview of the concepts behind this technology, theoretical and experimental work that has been undertaken, and some the practical aspects of designing a fiber-reinforced concrete mix with high volume fractions of synthetic fiber are presented.