Showing papers by "Antonio Nanni published in 2002"

Guide for the Design and Construction of Externally Bonded FRP Systems for Strengthening Concrete Structures

Abstract: *Co-chairs of the subcommittee that prepared this document. Note: The committee acknowledges the contribution of associate member Paul Kelley. ACI encourages the development and appropriate use of new and emerging technologies through the publication of the Emerging Technology Series. This series presents information and recommendations based on available test data, technical reports, limited experience with field applications, and the opinions of committee members. The presented information and recommendations, and their basis, may be less fully developed and tested than those for more mature technologies. This report identifies areas in which information is believed to be less fully developed, and describes research needs. The professional using this document should understand the limitations of this document and exercise judgment as to the appropriate application of this emerging technology.

Bond between Near-Surface Mounted Fiber-Reinforced Polymer Rods and Concrete in Structural Strengthening

Abstract: Use of near-surface mounted (NSM) fiber-reinforced polymer (FRP) rods is a promising technology for increasing flexural and shear strength of reinforced concrete (RC) members. As this technology emerges, the structural behavior of RC elements strengthened with NSM FRP rods should be fully characterized, and bond is the first issue to be addressed. Bond is of primary importance as it is the means for the transfer of stress between the concrete and the FRP reinforcement to develop composite action. This research program aimed to investigate bond between NSM FRP rods and concrete. Some of the factors expected to affect bond performance are addressed here, namely: bonded length, diameter and surface configuration of the rod, type of FRP material, and size of the groove in which the rod is embedded. Results are presented and discussed.

440.2R-02 Guide for the Design and Construction of Externally Bonded FRP Systems for Strengthening Concrete Structures

Abstract: and Commentaries are intended for guidance in planning, designing, executing, and inspecting construction. This document is intended for the use of individuals who are competent to evaluate the significance and limitations of its content and recommendations and who will accept responsibility for the application of the material it contains. The American Concrete Institute disclaims any and all responsibility for the stated principles. The Institute shall not be liable for any loss or damage arising therefrom. Reference to this document shall not be made in contract documents. If items found in this document are desired by the Architect/Engineer to be a part of the contract documents, they shall be restated in mandatory language for incorporation by the Architect/Engineer.

Strengthening of short shear span reinforced concrete T joists with fiber-reinforced plasic composites

Abstract: In this work, the results of an experimental study conducted in a 1964-vintage building are presented. Twelve reinforced concrete (RC) T-joists strengthened with fiber-reinforced plastic (FRP) composites were loaded until failure in a short shear span configuration. Different strengthening schemes, including different FRP materials and a new FRP anchorage system, were adopted in order to compare the performance of the different installations. Carbon FRP and aramid FRP sheets in an epoxy matrix were bonded to the RC joists using the wet layup technique. All of the joists were loaded close to one end support and showed similar cracking patterns at failure. The design calculations were based on experimental results. All of the unanchored FRP strengthened beams showed failure due to peeling, while the anchored FRP strengthened members showed failure due to anchor pullout at higher load values. It was found that an increase in the amount of FRP did not result in a proportional increase in the shear capacity, a...

Microwave detection of delaminations between fiber reinforced polymer (FRP) composite and hardened cement paste

Abstract: Fiber reinforced polymer (FRP) composites are increasingly being used for the rehabilitation of concrete structures. Detection and characterization of delaminations between an FRP composite and a concrete surface are of paramount importance. Consequently, the development of a one sided, non-contact, real time and rapid nondestructive testing (NDT) technique for this purpose is of great interest. Near-field microwave NDT techniques, using open-ended rectangular waveguide probes, have shown great potential for detecting delaminations in layered composite structures such as these. The results of some theoretical and experimental investigations on a specially prepared cement paste specimen are presented here.

Designing and constructing with frp bars: an emerging technology

Abstract: This article provides an overview of a new American Concrete Institute (ACI) document that addresses the design of fiber-reinforced polymer (FRP) reinforced concrete structures. Design principles and key concepts such as flexure, shear and development length are summarized. Because this is new technology, future research is needed to provide information in areas that are still unclear, in need of additional evidence to validate performance, or are a real or perceived disadvantage. Application of FRP internal reinforcement is described for two bridge projects. Despite some unresolved issues, the ACI guide should allow the construction industry to take advantage of the potential of FRP internal reinforcement for concrete structures.

Strength and modulus degradation of carbon fiber-reinforced polymer laminates from fiber misalignment

Abstract: Fiber-reinforced polymer (FRP) laminates are being used as external reinforcement for strengthening concrete members. The performance of unidirectional FRP laminates is highly dependent on fiber orientation with respect to applied load direction. In the case of fabrication by manual layup, it is possible to have fiber plies installed with improper orientation. In this project, the degradation of strength and modulus of carbon FRP laminates from fiber misalignment was investigated experimentally using tensile coupons. The specimens consisted of one and two plies of unidirectional carbon FRP impregnated with a two-component epoxy. The misalignment angles varied from 0 to 40° for the one-ply samples, and from 0 to 90° for one ply of the two-ply samples. The size effect on the strength and modulus was investigated for one-ply specimens with misalignments of 5 and 10°. For these specimens, the ply width was maintained constant and the length was varied to that the aspect ratio ranged between 2 and 8. It was concluded that misalignment affects strength more than elastic modulus. However, provided that mechanical parameters are related to the cross-sectional area of laminate with fibers continuous from end to end of the coupon, the degradation of strength can be accounted with a knock-down factor that is independent of misalignment angle.

Near-surface mounted FRP Reinforcement: application of an emerging technology

Abstract: Over 40% of the bridges in the USA need repair or replacement. The use of near-surface mounted (NSP) fibre-reinforced polymer (FRP) for repairing reinforced concrete (RC) structures is described. The technique involves embedding a bar into a groove half-filled with epoxy paste. Demonstration of the technique by the University of Missouri-Rolla on a bridge on Martin Springs Outer Road, Phelps County, Missouri is described. Load restrictions were placed on the bridge in 1985 due to a lack of transverse reinforcing steel. Details are given of the strengthening process to provide the necessary transverse reinforcement and of the approximate costs. The bridge will be field-tested elastically before and after strengthening.

Performance of decommissioned reinforced concrete girders strengthened with fiber-reinforced polymer laminates

Abstract: This study presents experimental and analytical investigations of reinforced concrete (RC) girders removed from a bridge after 40 years of service. The girders were strengthened with externally bonded fiber-reinforced polymer (FRP) sheets and tested, with the main goal of evaluating performance of real-scale members. Comparisons between the experimental data, an analytical model, and the ACI design guidelines are presented to understand the structural performance, allow for prediction, and address potential weaknesses in the design guidelines. In particular, it appears that the FRP tensile strength reduction coefficients presently adopted may be appropriate only if the member does not present D-regions. In the case of members with disturbances or discontinuities, the interfacial shear stresses may require additional analysis and limitations.

Validation of an alternative reinforcing detail for the dapped ends of prestressed double tees

Abstract: Prestressed concrete (PC) dapped-end beams have been used in buildings and parking structures to provide an efficient and economical construction system. The re-entrant corner of a dapped-end beam develops a severe stress concentration, which makes it the weakest point of the connection. If suitable reinforcement is not provided at this location, diagonal tension cracks may propagate rapidly and failure may occur with little or no warning. Reinforcing schemes and associated methods of design, which combine simplicity of application with economy of fabrication and provide the margin of safety required by present building codes, have been developed. This paper describes the experimental validation of an alternative reinforcing detail for the dapped ends of prestressed double tees, which satisfies the requirements of the design method contained in the PCl Design Handbook, Fifth Edition.

Strengthening of Masonry with FRP Bars

Abstract: For the retrofitting of the civil infrastructure, an alternative to Fiber Reinforced Polymer (FRP) externally-bonded laminates is the use near surface mounted (NSM) FRP bars. This technique consists of placing a bar in a groove cut into the surface of the member being strengthened. The FRP bar may be embedded in an epoxy- or cementitious-based paste, which transfers stresses between the substrate and the bar. The successful use of NSM FRP bars in the strengthening of concrete members has been extended to unreinforced masonry (URM) walls, one of the building components most prone to failure during a seismic event. This paper describes three applications of FRP bars for the strengthening of URM and reports on the obtained experimental results. In the first application, FRP bars are applied vertically to resist out-of-plane forces acting on the masonry walls (i.e. flexural strengthening). In the second application, bars are inserted horizontally in the masonry joints to strengthen the wall when subjected to in-plane forces (i.e. shear strengthening). Finally, the third application deals with the retrofitting of masonry walls showing deficient anchorage to the base beam. In this application, FRP bars are placed in the toe region of the wall acting as anchors to increase flexural capacity. In each of these three applications, the strengthening was remarkably effective.

Strengthening and load testing of three bridges in Boone County, Missouri

Abstract: Three bridges in Boone County, Missouri—Brown School Road, Coats Lane, and Creasy Springs Bridges—were selected for strengthening with carbon-fiber-reinforced polymer laminates in both shear and flexure. The objective of the rehabilitation program was to remove the 15-ton load posting that had been imposed on each of the bridges. To verify the results of the upgrade, load tests were performed before and after strengthening on tow of the bridges—Brown School Road and Coats Lane Bridges. This paper presents the procedures followed in the design, installation, and load testing of the bridges. A recommendation regarding the removal of the load posting is made.

Lap splice length and fatigue performance of fiber-reinforced polymer laminates

Abstract: When carbon fiber reinforced polymer (CFRP) laminates are used in strengthening long structural members, lap splicing is usually adopted for the transition of forces. Determination of the effective lap splice length and its fatigue performance is of importance. This study shows that by conducting static and repeated tension tests on CFRP coupon specimens, the strength change and effective lap splice length can be determined. Based on the results, recommendations are made for strengthening concrete structures with lap-spliced CFRP laminates.

Behavior of rc t-beams strengthened in the negative moment region with cfrp laminates

Abstract: The use of Carbon Fiber Reinforced Polymer (CFRP) laminates as an effective and versatile technique for strengthening reinforced concrete (RC) structures has developed into a sizable industry in recent years. Prior research has demonstrated the ability of CFRP laminates to enhance both the shear and flexural capacity of RC structural members. In this context, this research attempts to address an important practical issue that is encountered in strengthening the negative moment regions of RC continuous beams. This is a critical region due to the concurrence of maximum of moment and shear. In addition, there are installation restraints due to the presence of columns (inhibiting continuity for the flexural strengthening) and of the beam flange or slab (inhibit anchorage for the shear strengthening). This paper describes the shear and flexural behavior of RC T-beams strengthened in the negative moment region with CFRP laminates. Three RC T-beams, 14 ft long and 20-in deep with a 4 by 32-in flange, were cast. For all specimens, column stumps were also cast and used as the point of application of the load. One beam served as a control specimen, while one was strengthened for flexure (CFRP laminates applied besides the column) and the other one for flexure and shear (CFRP laminates in the form of U-wraps terminated at the flange intrados). Test results indicated that FRP reinforcement was effective in strengthening for both shear and flexure the negative moment region under the installation constrains encountered in practice. This is comforting news for professionals who are working in the field of structural repair and strengthening.

Finite element analysis of FRP tube assemblies for bridge decks

Abstract: Fiber reinforced polymer (FRP) composite materials have many advantages over traditional building materials. They are becoming more and more popular in civil engineering applications. FRP pultruded tubes are easy to fabricate and can be easily assembled for different applications. In this paper, FRP tube assemblies of variable size, fiber material, tube wall thickness, and different installation are studied using finite element analysis. The deflection and stress distribution are listed for each case. When compared to experimental results, the numerical analysis shows good correlation. Data gained in this study can be used for design and optimization of FRP tube assemblies for bridge deck construction and similar applications in civil engineering.

Performance Evaluation of an FRP-Reinforced Concrete Bridge

Abstract: As part of a larger project to investigate the use of Fiber-Reinforced Polymer (FRP) materials in bridge construction, a short-span FRP-reinforced concrete bridge was installed in central Missouri. The Walters Street Bridge is a precast concrete panel bridge reinforced with both glass FRP (GFRP) and carbon FRP (CFRP) reinforcing bars. It was designed according to the American Concrete Institute’s document “Guide for the Design and Construction of Concrete Reinforced with FRP Bars” to meet the load and deflection requirements of the American Association of State Highway and Transportation Officials. Carbon FRP, as tensile reinforcement, and glass FRP, as shear reinforcement, were utilized. The installation of the bridge is outlined and the results of material testing conducted on the reinforcing bars and concrete are summarized. An in-situ bridge load test was conducted, with a comparison made between the design and experimental values of maximum deflection and a discussion of the load transfer between panels is presented. Testing to determine the flexural and shear capacity of the panels was also conducted on an identical FRP-reinforced bridge panel in the laboratory; results in terms of a load-deflection diagram, ultimate load, and the failure mode of the beam are noted herein. The outcomes of these laboratory tests are further compared to the testing results of a steel-reinforced panel with the same ultimate capacity that was tested in an identical fashion.

Composites in construction: a reality : proceedings of the international workshop, July 20-21, 2001, Capri, Italy

Abstract: This proceedings is a collection of 29 papers presented at the specialty workshop, Composites in Construction: A Reality, held at Villa Orlandi, the International Center for Scientific Culture of Naples University "Frederico II," Capri, Italy. These papers address the state-of-the-art in fiber-reinforced polymer (FRP) composites for use in construction. FRP composites are expected to significantly improve the performance and durability of new or deteriorated constructed facilities. FRP composites can be used as stand-alone structural members, as reinforcement for prestressed and non-prestressed concrete, or in combination with other structural materials for new construction or repair/rehabilitation. The increased interest in FRP composites is fueled by innovative manufacturing technologies as well as significantly more stable, stronger constituent materials. Topics covered include: codes and standards; manufacturing, economics, and construction; materials, durability, and characterization; analysis and design; and outcomes.

Evaluation and Carbon Fiber Reinforced Polymer Strengthening of Existing Garage: Case Study

Abstract: The concrete-repair fiber-reinforced polymer technology emerged in the United States during the past 10 years. Since 1995, carbon fiber-reinforced polymer (CFRP) has been applied to strengthen concrete decks of a troubled posttensioned garage in Atlanta. During the construction of the garage, design deficiencies were found. A remedial repair, involving heavily reinforced, 7.6 cm- (3 in.-) thick Gunite (Shotcrete) beams, applied to the underside of the slab between drop panels in the east-west (E-W) direction, was developed in 1984. Since then, delamination of Gunite beams and other structural problems repeatedly occurred. Epoxy injection and other limited repairs were done over the years in an attempt to remediate the problems. In 2000, due to the growing delamination concerns, backed up with nondestructive impact-echo testing results, and due to the newest set of structural analyses that showed additional design deficiencies, Simpson, Gumpertz & Heger developed a new and comprehensive remedial program. The first phase of this program included an in-depth mechanical in situ load test program to study the strength and stiffness performance of the existing typical slab spans, including the effects of Gunite beams, the loss of Gunite beams due to delamination, and the CFRP strengthening of spans. The tests showed that the CFRP repair of E-W spans with delaminated Gunite beams is warranted and that it performs well. The performance of the existing typical spans in the north-south direction was found to be acceptable without any repairs. Further monitoring of the performance of Gunite beams is required, and additional CFRP strengthening will be done periodically. In addition, structural deficiencies of the typical second-level end bays were repaired using additional steel framing supports.

Characterization of a new frp bar of reinforcement of concrete

Abstract: Dow Chemical and its partners are developing a new glass fiber reinforced polymer (GFRP) bar to be used for concrete reinforcement. The bar needs to be fully characterized in order to be specified as suitable reinforcement for concrete members as per the newly approved ACI 440 design guidelines. The objective of this batter of tests is to provide the first level validation of the product under development. Tests will be conducted on a prototype, 12-mm diameter, smooth GFRP rod samples.