Completed Research 1995 to 2006

Theme 4 Projects (1999-2002):
Innovative Structures with Integrated Sensing

Director: Dr. Sami Rizkalla, University of Manitoba

THEME 4 OVERVIEW

(All project descriptions are provided as proposed in 1998 as part of the NCE mid-term review)

Specific Objectives

1. Assess durability of steel free deck technology through dynamic testing.
2. Establish effectiveness of reinforcement in conventional design through experimentation.
3. Develop FRP restraint system for steel free decks.
4. Develop bridge deck repair schemes based on steel free bridge deck technology and bridge deck behaviour knowledge.
5. Develop alternate innovative bridge deck schemes such as wood laminated decks.

The project will involve four components [Bakht, B., et al., 1996]. The first component will extend the current research to address the issue of increased durability of the system. Specifically, the durability of the concrete under dynamic loading and the use of a durable FRP lateral restraint system to replace the steel strap will be investigated.

The second component will involve the application of the knowledge of bridge deck behaviour to examine an alternative reinforced concrete design for the bridge deck. An experimental program will be developed to establish the function and effectiveness of each layer of reinforcement in a conventional bridge deck. It is believed that only the bottom transverse layer will be required for strength and safety. Once the effectiveness of the reinforcement is established, then a design standard will be developed for reinforced concrete decks based on durability considerations. In this design, FRPs and, in particular GFRPs, can be efficiently utilized for improved durability given that its role as a secondary reinforcement is unified.

The third component involves the application of the expertise developed in the first two components to repair deteriorating bridge decks. Many bridge decks may not require replacement or may only require partial depth replacement. This project will conduct an experimental program to examine repair schemes for deteriorated decks which would include the addition of lateral restraint to an existing superstructure, or the reduction in steel requirements for the top layers, or a combination of both.

The fourth component focuses on the expertise developed by the research on new and distinct innovative bridge deck structural systems. One such system is a stress laminated bridge deck constructed as a grouted post tensioned timber deck.

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The main objective of this project was to develop fibre reinforced cement-based materials for bridge decks. The research was an extension of the work undertaken by the Concrete Canada Network on the development of high performance concrete using steel fibres. This project focused on non-metallic fibres. The research has developed concrete with a compressive strength of 40 to 80 MPa with appropriate workability and adequate resistance to plastic shrinkage cracking. The five fibres considered are non-corrosive synthetic fibres with the commercial names of polypropylene, nylon, polyolefin, polyvinyl alcohol and carbon. The work included characterization of the various composites including flexural toughness, cracking under restrained shrinkage conditions and micromechanical crack growth resistance curves. The work provided data and design procedures for the steel-free deck of Project T4.1 and was used for construction of the Salmon River Bridge in Nova Scotia, the Chatham Bridge in Ontario and the Crowchild Bridge in Alberta.

Working with the Concrete Canada Network accelerated progress of the project and it was completed in March 1997. The experience gained from this project initiated the work in Project T5.6 which uses the same technology for spraying fibre reinforced polymer matrix composite to repair concrete structures. Work in this new project began in June 1997 and is reported within Theme 5.

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The use of FRPs as an alternative to steel reinforcements is one of the most promising solutions to eliminate deterioration of concrete structures due to the corrosion of steel. The high strength to weight ratio and low relaxation, as well as easy handling and installation could introduce economical aspects which could lead to a reduction in construction time and cost. There are fundamental differences between the mechanical properties of steel and FRPs. The latter have a much lower density, a lower modulus of elasticity and higher strength. These characteristics can significantly influence behaviour. The proposed research will also consider innovative reinforcement systems for bridge decks using steel reinforcements as a bottom layer and GFRP reinforcements as the top layer where it is subjected to the most severe conditions due to de icing and dry/wet cycles. This approach could significantly enhance the ductility which is currently lacking due to the linear stress strain characteristics of FRPs up to failure. The following research components are a continuation of the work accomplished during the first three years of ISIS Canada.

1. Use of FRPs for Shear Reinforcements: Stirrups used for shear reinforcements are normally located as an outer reinforcement with respect to the flexural reinforcements and are, therefore, susceptible to severe environmental effects due to the minimum concrete cover provided. The first three years considered the effect of bending of an FRP into a stirrup configuration on the material strength. This research will consider the effect of the diagonal shear crack on the strength of the stirrups since the induced tensile forces will have an angle with the direction of the unidirectional fibres. It is proposed to use specially designed concrete specimens to induce the forces into FRP stirrups with angles of 30, 40 and 60 degrees. The two types of FRP stirrups proposed are CFRP and GFRP. The configuration of the test specimen will also simulate the kinking forces induced into the stirrups due to the inclination of the crack with respect to the stirrups. The research will also investigate experimentally the effect of cyclic loading conditions which simulate the actual and practical use of the structures. Based on the findings, design recommendations will be proposed to use FRPs as shear reinforcements.[Fam, A., et al, 1997].
2. Use of FRP Dowels for Concrete Pavements: Steel dowel bars are used to transfer load from one slab to an adjoining slab across a joint and to provide horizontal and vertical alignment of the slab. Most dowels experience corrosion, particularly in environments where salt is used for de icing roads and highways. This behaviour could cause cracking and chipping of the concrete at the joint location. FRPs represent a possible solution to this problem due to their non corrosive characteristics. The purpose of this research is to examine the feasibility of using GFRP dowels for concrete pavements. The scope of the research encompasses scale models of concrete pavement sections of the slab using FRP dowels subjected to static and cyclic loads. The slab will be loaded on one side of the joint to simulate an equivalent half axle truck load. The behaviour will be compared to steel dowels. Soil conditions will be simulated by a spring system and compacted sands.
3. Long term Behaviour of Concrete Members Prestressed by FRPs: The limited strain of FRPs at rupture and their high cost are currently two major concerns limiting the wide spread use of these materials for civil engineering applications. Partial prestressing of concrete using CFRPs was investigated in the first phase of ISIS Canada and was proven to increase the deformability of the structure at ultimate load and reduce the cost by limiting the amount of reinforcement required in comparison to full prestressing. This principle was implemented in the design of the Taylor Bridge in Headingley, Manitoba, one of ISIS Canada's field applications of Project T3.3.1. In addition, short term deflection and the crack width of beams prestressed by CFRPs have been investigated in the first phase of ISIS Canada. Acceptance of this material is conditional on the knowledge of long term deflection and cracking to predict the behaviour of structures and bridges which are designed for a service life of 50 years or more. The proposed project focuses on the long term deflection of beams partially prestressed by CFRPs and evaluation of the long term prestress losses, including possible stress rupture and relaxation behaviour.
4. Innovative Hybrid Reinforcements for Bridge Decks: Due to a lack of ductility of FRP reinforcements and their high cost, this research proposes a hybrid reinforcement system for bridge deck slabs. The system consists of steel reinforcements as a bottom layer and GFRP or CFRP reinforcement as the top layer. This system will enhance the ductility of the structure while at the same time utilizing the non corrosive characteristics of the FRP in the most critical locations where it is most susceptible for corrosion due to the use of salt for de icing. It is proposed to test a full scale model of a portion of a bridge deck and subject it to an equivalent vehicle loading conditions. Configuration of the slab is similar to the two models, one completed and the other is currently in progress, simulating the design details used for the Headingley and Crowchild Bridges, respectively. Similar to the tested model, different end constraints and boundary conditions will be used to compare the results to the previous model and provide complete information for bridge engineers to optimize their design.
5. Hybrid FRP Concrete Structural Members: This proposed research investigates the feasibility of a new and innovative hybrid FRP/concrete system for structural members. The proposed system consists of FRPs of varying thickness and closed structural shapes such as tubular, rectangular or square with different cross sectional areas and placed one inside the other. The gap in between the two shells is filled with concrete or grout. This system provides advantages of saving the cost of formwork and, at the same time, the outer and inner FRP shell acts as reinforcement. The system will also introduce significant passive confinement effect on the concrete under the effect of applied loads. This innovative structural system is expected to be relatively elastic, considerably light, and could be maintenance free. The proposed work will include the effect of static and cyclic loading conditions. The various parameters to be considered are the direction of the fibres, type of fibres and the reinforcement ratio in terms of the thickness of the shells. The proposed member could be used as supporting elements for structures and girders for bridges.

See Bishop Grandin Bridge Field Demo
See Maryland Bridge Field Demo
See Norwood Bridge Field Demo
See Water Pollution Control Centre Field Demo

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The durability and life cycle cost of FRP reinforced concrete structures are essential aspects which could greatly influence the decision of industry to take full advantage of this new technology. The research program proposed in this project will address the critical issue regarding the use of non corrosive composite FRP reinforcements for concrete structures. Quantification of the predicted service life of these products will play a critical role in the commercialization of this technology. Wide marketplace acceptance of FRPs can be expected only if they are shown to be durable, technically successful and cost effective [Benmokrane, B., et al., 1997]. The specific objectives are:

1. To investigate the durability of FRP reinforcement in concrete with special reference to aggressive environments such as sea water, alkalinity, calcium, chloride, wet/dry and freeze/thaw cycles.
2. To examine the durability of FRP reinforcement in concrete under load environment synergy.
3. To identify the mechanisms of degradation and to examine the effect of resins, fibres, and manufacturing process on the durability of FRP reinforcements in concrete.
4. To develop special durability enhancement techniques and processes and new design approaches for durable composite FRP reinforced concrete structures.
5. To examine and monitor the durability of FRP reinforcements integrated with fibre optic sensors both in the laboratory and for field studies.
6. To prepare working manuals from the results of the research to predict the service life of FRP reinforced concrete structures.

The proposed research plan will include an experimental program to investigate the long term action of the aggressive media and harsh environments of reinforced and prestressed beams and slabs reinforced with FRPs. The principal contents in this study are as follows:

1. Long term durability studies of FRP reinforced concrete structures and FRP prestressed concrete structures under the action of aggressive media, such as high alkalinity, synthetic concrete solutions, distilled water, substitute ocean water and calcium chloride solutions. High temperatures up to 80 °C will be used as an accelerating agent. Arrhenius plots will be used to deduce a safe working lifetime for any specified proportion of short term ultimate stress intensity of the FRP reinforcement.
2. Long term durability investigation of FRP reinforced and FRP prestressed concrete structures under the conditions of harsh environments, such as repeated wet/dry and freeze/thaw cycles.
3. Durability comparison of various FRP reinforced concrete structures by using different types of FRP reinforcement, such as GFRP and CFRP to examine the effects of resins, fibres and manufacturing processes on the durability.

During the period of laboratory investigation, FRP reinforced and FRP prestressed concrete beams and slabs will be put into use for suitable civil engineering applications such as highway bridges, parking garages, quays and underground chambers. The long term behavioural monitoring in the real concrete structures will be investigated by use of FOSs.

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The proposed project is intended to give new life to an old material. By post tensioning masonry, immense structural gains can be made and more efficient masonry structures can be built. The project is well on its way to providing the Canadian masonry industry with a new method to compete with other building forms. The warm aesthetics of masonry will remain popular and the industry will be able to offer those features together with structural capability. On a life cycle basis, masonry is often cheaper than other forms of construction. So, improving the structural capability of masonry will benefit the economy [Sayed Ahmed, E.Y., et al., 1997]. The experimental program is a continuation of the initial phase which remains to be completed, including the following:

1. Prestressed Masonry Diaphragm Wall: The current post tensioned wall needs to be tested under thermal loading. An insulated frame will be constructed around three sides of the wall, leaving one length open to the laboratory. Dry ice will be packed against the opposite length, causing cross wall thermal effects. These will be measured, particularly the changes in the prestress load. Subsequently, the wall will be tested in flexure to failure. Having established the viability of CFRP masonry diaphragm walls as structural entities, discussion will begin with the City of Calgary as to where a retaining wall constructed with the system can be built and monitored. Simple site techniques for post tensioning with CFRP tendons and the new anchorage will be developed.
2. Design Procedures and Manuals: In parallel with the tests and construction above, a manual to help structural designers design CFRP post tensioned masonry walls will be prepared. This will involve the thermal and creep data already obtained. Further creep tests are planned to determine creep effects within practical ranges of temperature and stresses.
3. Metal free Anchorage: The progress in producing high strength concretes has been significantly advanced through the achievements of the Concrete Canada Network of Centres of Excellence. Further development with ceramic and calcined limestone aggregates is expected to produce concrete of sufficient strength and (with the carbon micro fibres) toughness for the anchorage. Tests will then begin to use this new material to develop a non metallic anchorage for FRP strands and bars. A multi strand anchorage is envisaged in addition to a single strand one. This work will be developed in collaboration with Dalhousie University, to use their experience in shaped FRPs, as well as Theme 2, to use their experience in FOSs, to assess the effect of the anchorage on the FRP tendons.

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The objectives of the project over the next three years are to refine the anchor developed in Project T4.4.1, to examine the use of alternative materials and configurations for the anchor, to develop a feasible stressing system utilizing the anchor, and to assess the performance of the anchor in internally unbonded and externally prestressed beams. Input from industry will be sought both to ensure the practicality of the work and to expose the technology to industry. It is envisaged that future work on this project will proceed along five lines, (i) anchor development, (ii) anchor analysis, (iii) use of the anchor, (iv) unbonded construction, and (v) external prestressing.

Alternative materials, such as ceramics and perhaps high performance cement grouts, will be investigated for use in fabrication of the anchor, and alternative configurations, such as embedded anchors, will be studied. An embedded anchor is one which can be cast into the concrete thereby eliminating the need for a barrel capable of resisting high tensile hoop stresses as developed in an anchor which is not embedded. This would allow the use of lower strength and probably cheaper materials but will require a detailed investigation of stressing techniques. The alternative configurations will also include modification of the wedge type anchor to facilitate tendon types other than Leadline. The existing analytical model will be refined to accommodate plasticity of the copper sleeve between the wedge and tendon, and also alternative configurations of the anchorage system.

Performance of the anchor in unbonded construction will be assessed by subjecting simply supported, partially prestressed concrete beams to repeated loading and finally to failure under static loading. The beams will contain carbon fibre prestressing tendons, as well as non prestressed reinforcement of different materials, such as glass fibre and perhaps stainless steel. These tests will not only assess the performance of the anchor but also will generate data on the strength and ductility of partially prestressed, unbonded concrete beams. Subsequently, tests on continuous unbonded beams will be undertaken as there is a paucity of data for such beams even for those prestressed by conventional steel tendons. The behaviour of both the simply supported and continuous beams will be simulated using an analytical model for such beams already developed by the Project Leader but which would require modification for this application. Subsequent to its validation using data from the tests on beams with carbon fibre tendons, this model would be used to extend the data base for such beams.

Use of the anchor in externally prestressed concrete beams will then be studied by carrying out similar tests to those described for the unbonded beams. It is envisaged that a mathematical model developed by other investigators in the Network would be utilized in this part of the project.

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The goal of this project is to establish guidelines for the design of concrete structures reinforced with FRPs. New guidelines are needed for these advanced materials to ensure satisfactory performance of the structures under service loading conditions. Satisfactory performance under service loading conditions is achieved mainly by ensuring that there are no excessive deformations or vibrations and that the cracking is controlled. Due to the modulus of elasticity of FRPs in comparison to steel, deformations in concrete structures reinforced with FRPs is expected to be much larger. Introducing FRPs to the construction industry cannot be achieved without the availability of robust analysis techniques and design guidelines for satisfactory serviceability. The goal of this research project is to provide what is needed in design for serviceability [Hall, T., et al., 1997].
Many experiments have been done on the short term load deflection behaviour of both prestressed and non prestressed concrete members, but few experiments have been done on their long term behaviour. Therefore, the future direction of research in the following three years will be the prediction of long term load deflection behaviour.

A large scale experimental and theoretical investigation will be conducted in collaboration with Project T4.3 to study both prestressed and non prestressed members, with varying concrete strength, concrete cover, reinforcement ratios, span to depth ratios, types of FRP (i.e. glass and carbon) and sustained load. Also, a comparison between tests done in the laboratory with tests conducted on specimens exposed to the elements would be beneficial. The theoretical work of this project will concentrate on the comparison of experimental results with predictions using rational analysis adhering to basic requirements of equilibrium and compatibility. The experimental data should be calibrated with the analysis and with different design codes written for steel reinforced concrete members. The approach that will be adopted for structures reinforced with FRPs will not necessarily follow the approach of the present standard, which is based on empirical rules derived from experiments.

The project will also include modeling of concrete poles post tensioned with externally unbonded FRP tendons housed in the hollow space. The purpose is to achieve a robust computer program tested for all possible practical situations. Computer analysis will be employed to find the optimum design for poles with different heights and different specified forces required in the power transmission industry. Construction and testing of these poles will be conducted at the University of Manitoba as a joint Ghali/Rizkalla project.

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The main objective of this project is to develop procedures and to establish guidelines suitable for inclusion in codes of practice to account for the temperature effect in the design of concrete structures reinforced with FRPs. It is well established that stresses due to temperature can be high enough to cause cracking in concrete structures reinforced with or without prestressing. Although most design codes recognize temperature effects as an important source of stresses and require that they be considered in design, little guidance is given on how this can be done. With the use of FRP reinforcement in place of steel and because of the additional stresses that can be induced due to the difference in thermal characteristics of FRP reinforcement and concrete, guidelines for the design of concrete structures for thermal effects need to be established more than ever.

The proposed research is an extension of the work currently in progress. The present work focuses on the behaviour of concrete members reinforced with FRP rebars only under the effects of elevated temperature (up to 160°C). The experimental work will be extended to include tests on members subjected to cold temperature. Values of temperature as low as 60°C to –80° will be considered. The effects of freezing and thawing will also be investigated.

In concrete members prestressed with FRP tendons, particularly CFRP and AFRP, it is believed that temperature variations and the difference in thermal expansion of the FRP and the concrete may have a significant effect on the level of prestressing in the tendons. Therefore, tests on concrete members prestressed with FRP tendons subjected to temperature differentials will be conducted. Bonded and unbonded CFRP and AFRP tendons will be used. The tests will be conducted under the effects of both elevated and cold temperatures. The effects of freezing and thawing will also be tested.

The current experimental work on concrete cylinders reinforced with FRP rebars will be extended to include the effects of cold temperatures and cyclic freezing and thawing. The tests will determine the effects of cold temperature and the radial contraction of FRP rebars on their bond characteristics and hence on their effectiveness in controlling cracking.

Parallel to the experimental program, the analytical models currently developed will be extended to include the effects of prestressing and the effects of cold temperature and cyclic freezing and thawing. Finite element analyses will also be carried out to investigate the effects of transverse thermal expansion or contraction of FRP reinforcement. Parametric studies will be conducted to develop criteria, guidelines and aids for the design of concrete structures for thermal effects.

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With the experience and the results obtained from the first phase of this project, the research program will continue to investigate the long term durability of FRP ground anchors, with special reference to field applications and smart monitoring, and develop a methodology to predict the bearing capacity and the service life of FRP ground anchors [Benmokrane, B., et al., 1997].

The scope of the program will include three stages: field performance and durability tests on FRP ground anchors, including FOS s for monitoring; analytical studies; and methodology of service life prediction and design recommendations. The scope of the research is summarized as follows:

1. Field Performance and Durability Tests: Field performance tests on FRP ground anchors integrated or installed with optical fibre sensors will be conducted to verify the practical aspects of FRP ground anchors. The FRP ground anchors will be installed in the field on prototype structures such as concrete dams, abutments, slopes and retaining walls. The hole boring, assembly, installation and stressing methods will be developed. The performance of FRP ground anchors and the reinforced structures will be evaluated using two different FOS technologies. The tests include monotonic load tests, proving tests, cyclic loading tests, creep tests and long term relaxation tests.
2. Monotonic Load Tests: Field pull out monotonic load tests will be conducted to investigate the performance and load bearing capability of the ground anchors under given local conditions. Two types of FRP tendons, AFRP and CFRP, are used with different diameters and surface conditions. The CFRP tendons used are produced by a Canadian company, Pultrall Inc. The new potted anchors are used as anchor heads to ensure full development of the tensile strength of FRP tendons. The different numbers of FRP rods consisting of the tendons conducted and the corresponding fixed anchor lengths and free anchor lengths are dependent on the magnitude of anchored load required. The loads are exerted on the anchors using a hollow hydraulic jack. Some of the FOSs will be integrated and others will be attached to the tendons at the anchorage and the fixed anchor length to monitor the strain distributions under different load levels smartly.
3. Proving and Cyclic Loading: Typical anchor systems (three anchors per site) will be tested to check the capability in transmitting the design working load and proof load to the ground under given local conditions. The tensile test procedure conforms to relevant standards. The anchor systems will be subjected to the full load and then unloaded 50 percent, this cycle being repeated many times, without intermission between cycles, so as to investigate the fatigue characteristics of the anchor system. The monitoring systems instrumented as in monotonic load tests for strain variation and displacement in the anchor will be recorded simultaneously.
4. Long term Behaviour: Under sustained load and adverse environments, FRP tendons may suddenly fail over time. The higher the ratio of the applied load to short term tensile strength, the shorter the time will be. This phenomena is called creep rupture or stress rupture when it occurs in air. To investigate the field creep behaviour of anchor systems, constant stress will be applied using a hollow hydraulic jack and monitored with a load cell. The slips at both ends of the anchorage and at the top of fixed anchor length will also be monitored, The anchors will be loaded to 10, 25, 40, 60 and 75 percent of the short term tensile strength for a duration depending on the creep behaviour. After the sustained load, the remaining specimens will be subjected to short term tension tests to evaluate their residual strength. The specimens will be loaded to different percent levels of the short term tensile strength and locked by a nut at the anchor head for a specified time duration. The FOS installed on the surface of the tendon will be used to monitor the relaxation of stress change verse time under the field natural conditions. These tests will provide dates to determine the long term effects of environmental, soil and freeze thaw conditions on the serviceability of the anchor systems.
5. Analytical Model and Design Recommendation: Analytical and finite element studies will be conducted to verify the anchorage devices and to provide parameters for the design. Load transfer mechanisms, anchor creep and relaxation, and long term performance of FRP anchors will be effectively predicted using the finite element method. A comparison between experimental and analytical results will be made. The research findings will provide useful design information, including short term and long term performance, suitable anchorage devices, acceptable prestressing level in the tendon, installation and stressing methods, and critical bond length for FRP ground anchors.

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During the first phase of the ISIS Canada sponsored research program, technology required for the construction of FRP electrical transmission poles was developed and successfully transferred to the industry. The development of this technology was made possible through the establishment of the ISIS FAROEX Filament Winding Research (FWR) Facility. This technology will now be used for other purposes as described in the following two applications proposed for the mandate extension [Lin, Z., et al., 1996]:

1. FRP Wood Pole Extension: The deterioration of wooden poles in the ground, the contamination of the soil by the coating material used in wooden poles, and the high cost of tall poles have prompted the utilities to look at other alternative pole type structures. One such type is a hybrid FRP wood pole consisting of a filament wound FRP bottom part and a wooden upper part. This type of pole has the advantage of prolonging the life expectancy of the pole while at the same time utilizing standard fixtures for cable attachment. This system has been discussed with both Manitoba Hydro and Winnipeg Hydro and both utilities expressed a great deal of interest. The utilities pointed out that such a system will be ideal in areas where the bottom part of wooden poles have been destroyed by fire, or are snapped by heavy loads, as was the case in the recent ice storms in eastern Ontario and Quebec, and it can also be used to increase the clearance between the wires and the ground, as required by the revisions in the electric code.
2. Wood FRP Wood Splice Connection: To extend the height of wooden poles without the additional costs associated with new foundations or to repair broken poles, such as those poles broken by the recent ice storms in eastern Ontario and Quebec, a splice system will be fabricated using the filament winding technique and tested for performance evaluation. Various types of splices will be examined to optimize the design and ensure ease of fabrication and erection. To accomplish both of these tasks, a series of scaled and full sized poles will be tested both in the laboratory and in the field under static and fatigue loading. The testing program will be accompanied by theoretical work as well as by an extensive materials characterization program. Fibre optic sensors will be utilized to monitor the performance of the poles in the field.

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Hog waste storage constitutes a major concern for confined animal production systems. Expanding levels of production are making the conditions even more severe. In some cases, environmental concerns relating to earthen lagoons have led to a requirement for structures more impervious to the elements. In many cases, reinforced concrete has been used for these structures, but the hostile service environment associated with hog waste storage has led to a relatively short useful life, due to the corrosion of the reinforcing steel, which leads to concrete deterioration. This, in turn, releases waste into the soil to the detriment of ground water supplies.

The use of FRPs can eliminate problems related to corrosion and, therefore, enable these structures to withstand such harsh service conditions. This research investigates the use of FRPs when installed in conditions similar to hog waste storage tanks. If they are found to provide improved performance relative to steel, they will provide industry with the knowledge and opportunity to design and build safer and more economical hog waste storage facilities. The research includes developing innovative design procedures for concrete storage tanks reinforced with FRP. The advantage of composite materials as a group is that they are non-corrosive. This research determines the type of FRPs that are most economical and capable of withstanding a severe storage environment.

In addition to the use of FRP reinforcements in storage tanks, this concept could also be applicable for other markets in animal production systems, in particular, reinforcement for slats, floors, and waste handling systems within production buildings.

See Field Demo

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The Ministry of Transportation of Ontario (MTO) has instituted a policy of using stainless steel, rather than epoxy coated steel reinforcing bars, in regions of concrete bridge structures exposed to aggressive environments. This is a result of the Ministry having observed corrosion of the epoxy-coated reinforcement, which has been specified by MTO and other authorities for concrete bridge structures for a number of years in an attempt to avoid deterioration of these structures as a result of corrosion of the reinforcing steel.

Stainless steel bars with strength similar to that of conventional reinforcing bars are readily available and are thus a feasible substitute for epoxy coated steel bars. On the other hand, prestressing steel, which is also widely used in concrete bridge construction, cannot be replaced by stainless steel since it is not available with strength comparable to that of conventional steel used for prestressing. However, fibre reinforced polymer (FRP) tendons, which are non-corrosive and have a sufficiently high tensile strength, are available. It is suggested that a hybrid arrangement of reinforcement, stainless steel for non-prestressed reinforcement and FRP for prestressed reinforcement, would offer a truly corrosion free concrete structure.

Two basic problems exist with the use of FRP prestressed reinforcement in concrete. In bonded construction, FRP tendons, which exhibit a brittle stress strain relationship, have a tendency to fracture at the ultimate limit state resulting in an undesirable brittle type of failure. On the other hand, when unbonded construction is used, there is a total dependence on the integrity of the anchorage to maintain the prestressing force, which has limitations because of the brittle nature of FRP tendons, resulting in an unreliable anchorage system.

These problems may be addressed by a combination of partially prestressed and partially bonded construction. In partially prestressed construction, a combination of non-prestressed and prestressed reinforcement is used while in partially bonded construction the prestressing tendons are debonded in some regions. Debonding of the tendons in high moment regions will decrease the stress levels in the tendons and increase the rotation capacity of the member at the ultimate state, thereby leading to a more ductile failure. Bonding of a tendon in the vicinity of the anchorage will reduce the increment in the force on the anchorage when the member is subjected to loading. Incorporation of non-prestressed reinforcement, in the form of stainless steel reinforcing bars will also enhance crack control in the unbonded region.

The potential of using FRP tendons in conjunction with stainless steel reinforcement will be investigated. The state-of-the-art for the partial bonding concept in prestressed concrete will be established, a test program in which partially prestressed and partially bonded beams will be subjected to static and repeated loading will be carried out and a design methodology for such beams will be proposed.

Fifteen simply supported rectangular beam specimens will be designed and pretensioned construction using carbon fibre reinforced tendons will be utilized. Tests will be conducted at the Structures Laboratory at Queen¹s University. Twelve beams will be tested to failure under static loading, while a representative beam from each debonded pattern will be subjected to repeated loading. Deformations, strains, etc will be measured during the loading of beams.

Stainless steel reinforcement will be provided through the Nickel Development Institute and the possibility of the beam specimens being fabricated by the precast concrete industry will be investigated.

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Completed Research 1995 to 2006