R. Gordon Wight

Innovative System for Prestressing Fiber-Reinforced Polymer Sheets

Strengthening with bonded prestressed fiber-reinforced polymer (FRP) sheets combines the benefits of excellent durability and structural improvement in terms of serviceability and ultimate conditions. The method offers the benefits of both a prestressed system that contributes to load-carrying capacity before further deformation occurs and a bonded system that sustains a major portion of load under further deformations. This work outlines a strengthening technique that involves prestressing carbon FRP (CFRP) sheets using a new external anchorage system to directly add tension to the sheets by jacking and reacting against the concrete beam itself. Results indicate that the CFRP sheets can be effectively prestressed using the developed anchorage system.

Bond and Short-term Prestress Losses of Prestressed Composites for Strengthening PC Beams with Integrated Anchorage

This article presents modeling of bond performance and short-term prestress losses of prestressed carbon fiber-reinforced polymer (CFRP) composite sheets for strengthening prestressed concrete beams, using an integrated anchor system that consists of steel plates bonded with CFRP sheets. A simple fracture mechanics model, validated with the experiment, is developed to examine the bond performance of the CFRP sheets for the plate-type anchor system. To predict the short-term prestress losses of the prestressed CFRP sheets used in the integrated anchor system, a closed-form solution is developed. Seven prestressed concrete beams strengthened with prestressed CFRP sheets are used to validate the proposed model. Fracture energy and tensile modulus of the CFRP sheets are the most critical factors affecting debonding failure of the plate-type anchor system. For design purposes, it is recommended that the short-term prestress loss be 10% of the applied prestress using the proposed anchor system.

Punching Shear of Two-way Slabs Retrofitted with Prestressed or Non-prestressed CFRP Sheets

This study presents punching shear behavior of two-way slabs strengthened with prestressed or non-prestressed carbon fiber reinforced polymer (CFRP) sheets. Four two-way slabs (2360 × 2360 × 150 mm3) with a steel reinforcement ratio of 1.44% are tested under concentric load. All slabs exhibit a punching shear failure mode. The strengthened slabs show an increase of up to approximately 20% in load-carrying capacity and an increase of up to 25% in cracking load with respect to the unstrengthened control slab. A detailed stress analysis in reinforcement is conducted along the loading span of the slabs, including the critical shear perimeter surrounding the column stub. The effective strain zone near the slab—column connection, where a sudden increase of strains in the reinforcement is observed, is also studied. The development of shear stresses in the vicinity of the slab—column connection is examined. A non-linear 3D finite element analysis is conducted and analytical predictive models for the punching shear failure are evaluated as well.

Load Configuration and Lateral Distribution of NATO Wheeled Military Trucks for Steel I-Girder Bridges

This paper presents the lateral load distribution of various North Atlantic Treaty Organization (NATO) wheeled military trucks on a simple-span steel I-girder bridge (L=36 m). The military trucks are classified into the military load classification (MLC) system. The MLC trucks demonstrate different load configurations when compared to the standard HS20 truck in terms of wheel-line spacing, number of axles, and weight. A calibrated three-dimensional finite-element analysis is conducted to examine the MLC load effects. The applicability of the AASHTO LRFD provisions is evaluated using 72 different load models. The wheel-line spacing and weight of the MLC trucks cause different flexural behavior and load distributions of the bridge when compared to those of HS20. The current AASHTO LRFD approach to determine live load distribution factors may be reasonably applicable to the MLC trucks, including approximately 20% of conservative predictions.

Recent Advances in Performance Evaluation and Flexural Response of Existing Bridges

This paper presents a comprehensive overview of recent developments in the performance evaluation and flexural response of existing bridges from fundamental concepts to advanced topics. The focus is particularly on the structural evaluation to enhance the quality assessment of constructed bridge superstructures, taking into account a synthesis of the most important contributions to the flexural behavior of existing bridges, such as dynamic responses and lateral load distributions. This state-of-the-art paper provides a critical review of published literature and existing assessment methodologies in conjunction with corresponding analysis techniques, including technical comments on the code provisions. Detailed descriptions of the important parameters influencing flexural responses of existing bridges are discussed, such as the geometric effect, loading configuration, present condition of a bridge, and contribution of secondary structural elements. The review also includes the investigation methodologies, namely, the diagnostic and proof load tests. Finally, the current research needs to further advance the performance evaluation technologies for existing bridge superstructures are recommended.

Research on the Use of FRP for Critical Load-Bearing Infrastructure in Conflict Zones

Research into the use of fiber-reinforced polymers (FRPs) in structures at the Royal Military College of Canada (RMC) during the past two decades has largely focused on two important military engineering goals—mobility and survivability. FRP research in the area of mobility has included the strengthening and repair of reinforced concrete beams and slabs and the development of portable lightweight bridges suitable for most wheeled and tracked vehicles. With respect to survivability, a particular interest is in the use of FRPs to enhance the blast resistance of structural columns and beams. Such research may be equally pertinent to improving the blast resistance of a broad range of critical domestic infrastructure worldwide, given both the increasing concerns about terrorist acts and the desire as well to improve resistance to accidental explosion. This paper will report on the experimental work of two of the most recent FRP research projects carried out at the RMC in support of military objectives—the development of a lightweight portable glass FRP bridge and the use of FRP to strengthen reinforced concrete structural columns against blast. A full-sized FRP box beam was constructed and tested in the laboratory and 28 half-scale reinforced concrete columns, some strengthened with either steel reinforced polymer (SRP) or with FRP, were tested in the field under blast load. From this research, it can be seen that FRP as a structural material offers significant advantages to military forces working in conflict zones, whether for traditional strengthening of damaged or understrength structures, lightweight portable bridge options, or as a means of strengthening structures against blast effects.

Prestressed fiber-reinforced polymer (FRP) composites for concrete structures in flexure: fundamentals to applications

Abstract: This chapter presents a comprehensive overview of prestressed fiber-reinforced polymer (FRP) composites for concrete structures. Of interest are the prestressing methods and flexural responses of such structures. This state-of-the-art review provides a synthesis of all existing prestressing applications for reinforcing or strengthening concrete members, including bonded and unbonded FRP composites. The review examines published codes and design manuals with their limitations, prestressing operation, failure modes, design methods, bond characteristics, and deformability (or ductility) of various prestressed FRP applications. Current research needs are discussed to further improve an understanding of the behavior and application of prestressed FRP composites for concrete structures.

Design and Site Application of Prestressed Carbon-Fiber-Reinforced Polymer Sheets for Strengthening Concrete Structures

The application of carbon-fiber-reinforced polymer CFRP sheets for strengthening deteriorated concrete structures is becoming widely accepted around the world Bakis et al. 2002; Teng et al. 2003 . The system uses high-strength, light-weight, and corrosion-resistant materials. Benefits of this type of strengthening include minimized maintenance expenses, good chemical resistance, and rapid on-site installation with little requirement for heavy equipment Kim et al. 2006, 2008a . The CFRP sheets may be prestressed to enhance the effectiveness of strengthening, which gives them the ability to support dead load, to use material strength more efficiently than non-prestressed sheets, and to achieve greater load-carrying capacity and serviceability Meier 1995; El-Hacha et al. 2001; Kim et al. 2008b,c . The following criteria should be carefully considered before using prestressed CFRP sheets to strengthen reinforced concrete structures.