International Concrete Abstracts Portal

Fiber reinforced polymer (FRP) composites in the form of laminates or bars have been proven to be effective for the strengthening of unreinforced masonry (URM) walls subjected to overstresses. Two installation techniques have been proposed: externally-bonded FRP laminates (i.e. manual lay-up or adhesion of pre-cured laminates) and near surface mounted (NSM) FRP bars. The latter technique consists of placing a bar in a groove cut into the surface of the member being strengthened. This paper presents a field application on flexural strengthening with NSM FRP bars of two cracked URM walls in an educational facility. Design considerations and the results of an experimental program conducted to validate the strengthening are described.

The earthquake of June 23, 2001, that affected most of the southern part of Peru, put in evidence the seismic vulnerability of icons of the cultural heritage of the country. The historical downtown of the city of Arequipa (located at 1000 km to the South of Lima) was heavily affected by the earthquake, with forty percent of its representative buildings suffering damage ranging from moderate to severe with partial collapse. The towers of the cathedral of Arequipa, built integrally with a volcanic stone called sillar, suffered extensive damage. As a consequence, the left tower partially collapsed, whereas, the right tower remained standing but in an unstable condition. This paper describes the reinforcing strategy of the right tower with Carbon Fiber Reinforced Polymer (CFRP) laminates, which were used to provide tensile strength and confinement to the central stone core of the tower. After completing the CFRP installation, carved stones were placed on top of the laminates to keep the original appearance.

A detailed evaluation, combined with a new snow and wind study, was carried out on the Olympic Saddledome to confirm its ability to support heavier suspended loads. The results of the study confirmed that the main roof cables have sufficient capacity to resist the increased load. However a new snow loading condition, identified in the snow study, had the potential to overstress specific roof panel elements. A finite element analysis of the roof panels supported the conclusion that under the newly identified snow/wind load combination, several roof panels of the Saddledome will face demands that are above the ultimate roof capacity according to the National Building Code of Canada (NBCC 1995). Therefore, it was decided to strengthen selected roof panels of the Saddledome using FRP plates. Special consideration was given for analyzing the effect of creep on the strengthened concrete panels. This was due to the relatively high creep stress expected in the roof panels as a result of using lightweight concrete. It was feared that such high stress might result in creep of the epoxy resins and system debonding under loads lower than that predicted by the analysis. In this paper, Design considerations for the effect of creep are discussed and the results of full scale tests are presented. Performance design for serviceability and deformability of the roof panels was considered. Special provisions in the project specifications were used to ensure satisfactory surface preparation to achieve adequate bond between the FRP laminates and the roof panels. Performance specifications were also developed for the required mechanical and durability characteristics of the FRP strengthening system rather than specifying the type of FRP material.

Maintenance, rehabilitation and change in use of existing structures have become more and more important the number of new structures decreases. More than 10 years ago FRP strengthening systems were introduced into the construction industry. External flexural strengthening of reinforced concrete structures using bonded CFRP plates was first utilized in 1991 on the Ibach Bridge near Lucerne, Switzerland [1]. After the first pilot applications in the early 1990's and introduction to the market in 1994, flexural strengthening by bonding CFRP plates to many structures has become accepted world-wide and is now commonplace [2]. Systematic testing undertaken by Sika AG, Switzerland in co-operation with the independent laboratories of EMPA (Swiss Federal Institute for Materials Testing and Research) offers a new solution for shear strengthening using CFRP L-shaped plates. To guarantee the expected long-term behaviour of the strengthening system, it is necessary that the CFRP plate and the structural adhesive be designed and installed as a complete system.

Use of ACM in the form of FRP laminates in rehabilitation of concrete structures is the prime application of ACM in Egypt. FRP laminates are applied for strengthening reinforced concrete slabs or beams in flexure and shear as well as for confinement of reinforced concrete columns. This paper briefly introduces selected projects to demonstrate the current practice of FRP in Egypt. In the first application, carbon FRP (CFRP) laminates in the form of strips and sheets were applied to strengthen a public building suffering from differential settlement of the foundation. In a different application, CFRP laminates were used to upgrade a residential building to be used for commercial purpose. The paper summarizes the design aspects, construction details and recommendations for future application of ACM.

To prevent future blowouts of sections of the 50-year-old pipe, the Providence Water Supply Board decided to evaluate the condition of a main water pipeline. Non-destructive testing (NDT) investigations revealed that certain sections of the pipe were potentially deficient due to corrosion and breakage of the prestressing system. Strengthening of deficient sections was necessary to maintain the pipeline operational. A carbon fiber in-situ lining appeared to be the fastest, least disruptive, and most cost-effective upgrade solution. The specialty concrete repair contractor conducted full-scale tests to validate optimum FRP repair and waterstop termination design. In these tests, after the carbon fiber liner was installed, the prestressing strands of the FRPstrengthened section were cut leaving the FRP to be the only reinforcement. The test pipe was progressively pressurized until failure occurred at approximately 2-1/2 times the pipe service and surge pressures. The full-scale test proved the integrity of the system beyond theoretical prediction and assured the owner that strength was added to the pipe sections. The lightweight, flexible carbon fiber material along with thorough planning helped overcome challenging working conditions and provided a fast and effective upgrade solution.

In 1997, a precast, prestressed T-beam in the Ala Moana Shopping Center parking garage, in Honolulu, Hawaii, was strengthened in flexure using carbon fiber reinforced polymer (CFRP) strips epoxy bonded to the soffit of the beam. When the parking garage was demolished in June 2000, this beam and two control beams were salvaged and brought to the University of Hawaii for testing. This paper presents the retrofit procedures used during field application of the CFRP strips. It also describes the beam recovery and preparation for laboratory testing. The test program and results of the flexural testing of both unstrengthened and strengthened beams under four-point loading are presented in detail. The CFRP retrofit significantly increased the flexural capacity of the beam while also increasing its flexural ductility. The failure moment was well in excess of the nominal moment capacity predicted using the strain-compatibility procedure described in the ACI 440R-02 report.

The use of externally bonded FRP (Fibre Reinforced Polymers) reinforcement for strengthening or rehabilitation purposes is becoming a well documented and often applied technique world-wide. A particular application of this technique in Belgium, is a rehabilitation project at the Antwerp Zoo, where an innovative strengthening system based on multidirectional carbon fibre reinforced polymer (CFRP) composites was applied. This system, offering new possibilities for strengthening of structures, consists of PC CarboComp Plus laminates and sandwich prefab composite beams. A two-way slab and supporting beams were successfully repaired and strengthened in only 38 days, with a minimum of disruption (animals were not relocated and the building remained open for public) and respecting the restraints typical for a protected historical building. In a second phase of the project, masonry columns at the basement level were wrapped with aramid FRP (AFRP) and the supported beams were strengthened with CFRP sandwich prefab elements. In order to achieve sufficient efficiency of the wrapping, transverse links were provided through the rectangular columns. Related to the first part of this project, experimental verification of the system was performed.

The Gentilly-1 nuclear power plant, in Quebec, Canada, was decommissioned in 1978. Since that time, the containment structure has been used for the storage of the moderately contaminated nuclear reactor. The enforcement of more rigorous environmental regulations, as well as economic considerations, have raised the decommissioning period from 40 to 100 years, thus severely increasing the durability requirements for the structure. The containment structure, constructed of thick prestressed concrete, was in good condition except for the secondary concrete. The latter is a keystone for the durability of the structure because it fills the recesses and protects the terminations of the tendons against corrosion. The differential shrinkage caused cracking and debonding and, with freeze-thaw cycling over the years, the secondary concrete had to be removed and replaced. The ringbeam, at the top of the containment structure, was severely affected because the numerous tendons of the roof terminate at that level. The retrofit of the ring-beam consisted of replacing the secondary concrete with highquality shrinkage-compensated mortar and concrete, followed by FRP wrapping. The layout of the FRP wrap was designed to mitigate the adverse effects of the new secondary concrete shrinking-induced cracks. Most of the concrete cold joints were covered by the FRP wrap, which was anchored on the dome roof to provide an effective support.

It is the intent of this paper to update developments in the fascinating field of composites. Special topics will include, masonry walls, blast effect technology, and bridge column and bent rehabilitation and arch bridge restoration. "Technology is a queer thing, it brings you great gifts with one on hand and stabs you in the back with the other" (C.P. Snow). It remains for us to keep abreast of the latest developments in composite technology to stimulate our thinking and keep us ahead.