This was expected for the FRP reinforced concrete beams, but not the steel reinforced concrete beam. The maximum deflection produced by FRP reinforced concrete beams was about 20 mm more than steel reinforced concrete beams.
Introduction
- Background
- Need for Research
- Research Objectives
- Scope of Research
- Summary
Chapter two consists of the literature review on the use of FRP as the main reinforcement in concrete beams. Chapter four consists of the design philosophy of prestressed FRP concrete elements and presents the references used in the preparation of this research proposal.
Review of Design and Construction of FRP reinforced concrete design
Introduction
The probabilistic distribution analysis performed resulted in a probability, shown in Figure 3, that the CFRP bridge is more cost effective, which is 0.54 in 20 years, except for short span bridges. It was stated that the CFRP bridge will be more expensive in this case with a probability of less than 1 in 10,000 in the year 40.
History of FRP
These model analyzes are done to give confidence and real data to the benefits of FRP. The study found that strengthening pre-existing bridge piers was the most standard practice at 44.7%, while bridge decks and girders were at 13.2% and 26.3% respectively.
General Properties of FRP
Types of FRP
Fiberglass is most commonly used in optical cables that run millions of kilometers between continental hubs. The most commonly available types of fiberglass are electrical glass, known as E-glass, and structural glass, known as S-glass.
Current Structural Applications
- Case Study І – Highway Bridge in Wisconsin ,USA
- Case Study ІІ - Cookshire-Eaton Bridge in Quebec, Canada
- Case Study ІІІ - Headingley, Manitoba
- Case Study ІІІІ - Culvert Bridge in Missouri, USA
The only other difference between these two bridges was in the thickness of the concrete. The grid performed as the top reinforcement of the concrete deck and distributed tensile stress across the beams caused by negative bending moments in the transverse direction of the deck.
Summary
Carbon Fiber Reinforced Polymer (CFRP) has a Young's Modulus of 240 - 650 GPa, similar to or even greater than steel, whereas Glass Fiber Reinforced Polymer (GFRP) has a Young's Modulus of 70 - 85.5 GPa, well below that of steel . Since FRP and steel behave differently under continuous loading, it is understandable that the design philosophy of a structural concrete element reinforced with FRP or steel will also be done differently.
Design Philosophy of FRP Reinforced Concrete
The balanced reinforcement ratio uses the tensile strength of the FRP due to lack of distinct yield strength. The strength reduction factor is 0.55 once ρf <ρfb, which indicates that the concrete element will fail due to rupture of the FRP. The strength factor is then implemented in the bending capacity of the concrete element.
Once cracks are observed in the concrete member, the stiffness decreases drastically due to the dependence on the stiffness of the FRP. Deflections are controlled in ACI by limiting the thickness of the concrete member depending on its full length. During the analysis of the load deflection curves, there was a sudden drop in the curve shown below.
The distance from the maximum stress fiber of the concrete to the center of the flexural reinforcement is calculated. The majority of specimens would not pass the crack width requirements adopted by fib, CSA and the ACI. The slip was measured by the probe welded to the bar but not embedded in the concrete that reached outside the specimen.
Design Philosophy of Pre-Stressed FRP concrete elements
The balanced ration can be expressed in material properties as shown in (23) by substituting (19) and (20). 23) can be further simplified in (24) because certain variables can be negligible which can then be considered zero. The strength of the prestressed member will depend on the tensile strength of the tendon used. The moment capacity can be calculated using a rectangular stress block which will accurately represent the stress distribution in the concrete (reference).
The neutral axis can be found by using the force equilibrium of the section. The moment of force can be summed over the prestressed tendons, which will give us the nominal moment capacity of the compression-controlled element. Furthermore, if the section is compression controlled section, the maximum net tensile load that can be reached is greater than or equal to 0.005.
In this way, the fibers can be distributed evenly around the tip to create an anchor point. Load transfer can be improved by adding a threaded sleeve inside the initial sleeve to increase friction at the media-sleeve interface. It is the most functional anchor due to its reliability, reusability and can be easily placed on site or in a controlled environment.
Chapter Summary
Methodology
Design and Details of Steel and CFRP reinforced concrete beam
Lifting hooks were provided so that cranes could be used to lift the beams to any destination. The designed failure mechanism of the control beam was to crush concrete under pressure in the critical moment area and yield the longitudinal reinforcement. The rectangular cross-section of the beams was similar to the dimensions of the reinforced concrete beam.
The tensile strength provided was two 12 mm diameter CFRP bars with a total cross-sectional area of 226 mm2 and two 10 mm diameter steel bars with a total cross-sectional area of 156 mm2 were provided for the longitudinal compression reinforcement. The braces provided for the beams were provided by 10 mm braces with a minimum spacing of 110 mm.
Experimental Procedure
Each batch was tested to ensure that the compressive strength was the same for all the beams. This test is used to understand the behavior of the reinforced concrete beams at certain levels of static load. Since service load is the main concern, research has shown that service load can be considered to be 30% of the bending capacity.
The crack patterns were examined and it was concluded that at approximately 67% of the flexural capacity, no additional cracks were observed on the concrete specimen. One CFRP reinforced concrete beam contained our proposed anchorage method, which was where the ends of the rebar, where they would normally be hook points, were inserted with expanded cementitious grout at the ends of the rebar. The length of the grout that will be applied to each side of the CFRP bars will be 100 mm long.
The thickness of the injection mass was limited to 11 mm, so that separation does not occur during the casting phase. An LVDT will be installed at the center of the beam to track the deflection of the beams during loading. Two load cells will be used as supports to track and record the force exerted by the hydraulic cylinder.
Chapter Summary
Results and Discussion
- Introduction
- Failure Modes
- Deflection
- Strains and Curvature
- Cracking pattern and crack width
- Chapter Summary
CFRC4 is not present due to the malfunctioning of the LVDTs and strain gauges during the experiment. It says that the height of the beam should be 1/3 of the span used for the experiment. This important feature was evident when visual inspection of the failure mechanism was not obvious, i.e.
All girders had a linear differential variable transformer (LVDT) placed at the center of the beam to track the deflection of the girders during the experiment. Figure 46. No load reduction or major shear cracking was recorded or observed in any other beam. The table shows that none of the CFRP bars reached their ultimate strain of 1.7%, but certainly close.
Since none of the beam reinforcements underwent permanent deformation, after the load was released from the beams, all cracks closed immediately due to the elasticity of the reinforcement. They have a similar crack density as shown in Table 9. SRC had fewer flexural cracks than CFRCs, but had much less intermediate crack propagation from large flexural cracks. The intermediate cracks were horizontal to the depth of the CFRP reinforcement in the beam.
Conclusions and Recommendations
- Failure Mode
- Deflection
- Strain and Curvature
- Crack widths and patterns
- Further Research and Recommendations
The maximum deflection of FRP reinforced concrete beams is almost twice that of steel reinforced concrete beams. The difference in values is due to the bonding mechanism between the FRPs and the surrounding concrete, as well as the lower stiffness of CFRCs compared to SRCs. The FRP-reinforced beams consumed around 62% of their ultimate tensile load (1.7%) at failure, and the reinforced concrete beam consumed 90% of their ultimate yield load (0.5%) at failure.
This indicates that the steel reinforcement is more effective as the material is closer to yielding at failure compared to FRP reinforced concrete beams. FRP-reinforced beams have much greater curvature than steel-reinforced beams, which helps determine the severity of failure suffered by a structural member. Crack width and crack density are much larger in FRP reinforced concrete beams than in reinforced concrete beams.
Crack widths are a major problem in steel reinforced concrete beams as this is where chloride intrusion, carbon dioxide and moisture enter the concrete and corrode the steel reinforcement, this is not a problem with FRP reinforcement. The significant crack width of FRP reinforced concrete beams shows a weak bond between the reinforcement and the concrete, which puts it at a disadvantage. Acquisition of more FRP reinforcement to obtain a more statistically robust conclusion on material performance.
2018) "Flexural behavior of full-scale circular concrete elements reinforced with basalt FRP bars and spirals: tests and theoretical studies", Composite Structures. 2000) 'FRP reinforcement for bridge structures', Proceedings of Lectures, Civil Engineering Conference 'FRP reinforcement for bridge structures', (May), p. 7(5), p. 2007) “Strength and serviceability performance of beams reinforced with GFRP bars in bending”, 21, p. 1997) "Constructivity and Economics in April 1400", JOURNAL OF COMPOSITES FOR CONSTRUCTION, 1, p. 2017) 'FRP reinforced concrete panels: a comparative design study', Proceedings of the Institute of Civil Engineers: Structures and Buildings, 170(8), p. Af = FRP reinforcement area. a = depth of equivalent rectangular stress block. mm) b = width of rectangular section.
Ef = design or guaranteed modulus of elasticity of FRP, (MPa) Es = modulus of elasticity of steel, (MPa). Ap = area of internal prestressed reinforcement, mm2 εpe = effective strain in FRP tendon after all losses εpr = loss of strain capacity due to sustained loads.
Appendix
Design Calculation for Beams reinforced with Carbon Fiber Reinforced Polymer
Design Calculation for Beams reinforced with Steel
