I hereby certify that I am responsible for the work submitted in this project, that the original work is mine except as specified in the references and acknowledgments, and that the original work contained herein was not undertaken or done by anyone other than -specified sources or persons. Current work focuses on the bending behavior of concrete-filled steel pipe (CFST) with carbon fiber reinforced polymer (CFRP) wrapping to minimize the environmental and cost-intensive problems of reinforcing steel pipe. Therefore, this research aims to propose a new method, in which the CFRP is wrapped around the CFST.
The testing is carried out by bending the middle section of CFST wrapped with different layers of CFRP respectively. The results obtained in this research will highlight the flexural behavior of CFST with CFRP wraps. It has been proven that three-layer CFRP-wrapped CFST obtained a higher strength as well as greater ductility compared to two-layer CFRP-wrapped CFST.
I would like to thank all parties involved during my End of Year Project for their guidance and contributions. Johan bin Ariff, for his assistance during the testing of the CFST wrapped with CFRP. Johan also helped me by retrieving the data obtained after the test to write in my results and discussion.
My family members had supported me from day one in my studies as well as during this FYP journey.
INTRODUCTION
Background of Study
- Problem Statement
- Objectives
- Scope of Study
It will be tested with different layers of CFRP to see how they affect the CFST behavior. The varied layers of CFRP will improve the moment capacity, energy absorption capacity and bending stiffness of CFST. Studies show different types of improvements that can be implemented to strengthen CFST, but adding layers of CFRP can improve the condition and performance of the steel pipe.
The behavior of the composite material, which is concrete and steel, is still being studied through experiments. A series of analytical and laboratory steps will be performed to determine the bending behavior of the steel pipeline. The aim of the project is to determine the structural behavior in flexure of CFST using carbon fiber reinforced polymer (CFRP).
CFRP has a high tensile strength, so it will paste in the middle part of the steel pipe. A total of 3 and 5 CFRP layers will be compared and the result will be determined by comparing the forces, resistances, maximum deflections and pipe displacements.
LITERATURE REVIEW
- HIGH PERFORMANCE CONCRETE
- CONCRETE FILLED STEEL TUBE
- STEEL
- CARBON FIBRE REINFORCED POLYMER
- CFST-CFRP
- MECHANICAL PROPERTIES
In some cases, lowering the water/binder ratio below a certain point is not mechanically feasible because the strength of the HPC does not significantly exceed the compressive strength of the aggregate. Furthermore, while HPC with high-strength steel fibers has strong ductility and resilience, the high-strength steel fibers account for about 35% of the total prices of high-performance concrete, resulting in a high initial cost of high-performance concrete. Consequently, lowering the steel fiber content while maintaining or increasing flexural/tensile properties is a problem (Du et. al., 2021).
The axial strength of the infill concrete can be greatly improved due to the confinement provided by the steel tube. In addition, the restraining influence of the infill concrete can avoid or at least delay the local buckling of the steel tube. The interaction of the infill concrete pipe and the steel leads to the high strength and ductility of the structure.
To avoid local buckling, it is first necessary to estimate the dimensions of the steel box and adjust its length. If the concrete is in a steel tube of the right width, good calculations can avoid local inward buckling. Due to the loss of mechanical behavior caused by fire, chemical corrosion and physical aging, the use of multiple CFST columns is considered insufficient to meet essential safety and serviceability standards.
Some of the main reasons for its use are its versatility, durability and flexibility, and the fact that it is a very cost-effective material. Due to its high strength-to-weight ratio, steel can often offer a solution when other materials are insufficient. One of the most commonly used building materials in the construction industry is structural steel, which is also the most researched and well-known.
The types, amount, and position of fiber reinforcement contribute significantly to the strength of FRP. These reinforcements perform exceptionally well in high strength situations, with a modulus of elasticity that rivals that of steel. Contrary to the anisotropy of concrete and the isotropy of steel, CFRP sheath is a type of orthotropic material that can be used to surround a concrete column.
CFRP was used to improve the confinement in the concrete, which improved the bearing capacity and ductility of the CFST columns. 2021) found that the strengthened columns had good ductility, similar to the CFST columns, which could be due to the progressive failure of the strengthened columns. Some of the samples with additional layers of CFRP fiber network showed higher ductility because they did not tear different fiber layers at the same time.
METHODOLOGY
FLOW CHART
MATERIALS USED
- Mix Design
- Concrete-filled Steel Tube
- Carbon Fibre Reinforced Polymer
Carbon fiber reinforced polymer (or CFRP in short) is chosen because of its main properties advantages as explained in literature review. A total of 5 layers of CFRP will be used for the experiment, where each steel tube will be wrapped with 2 layers and 3 layers of CFRP respectively.
EXPERIMENTAL SETUP
- Procedures
- Testing
Different layers of CFRP wrapped in steel pipes will be compared and the result will be determined by comparing the forces, resistances, maximum deflections and displacements of the pipe. The tensile and compressive strength of materials is tested using a universal testing machine (UTM), also known as a universal tester, material testing machine or material testing frame. The analysis for this project will be to determine the tensile strength, flexural behavior, compression and static test of CFRP wrapped CFST.
RESULTS AND DISCUSSION
Physical Results
The CFRP layers in the middle of the two steel tubes were removed after their maximum loads were reached. This small fracture is the result of the tension of the load on the middle part during the testing of the two steel pipes. It is also noticeable that CFST-3L has a high fracture process of CFRP compared to CFST-2L, which indicates that CFST-3L needs a slightly shorter time for CFRP to crack compared to CFST-2L.
This indicates that the more CFRP layers are used, the more sudden the CFRP failure was.
Data and Graphical Results
By comparing the graphs, the load-carrying capacity of CFRP-wrapped specimens appears to increase as the number of CFRP layers increases. Despite the fact that both steel bars were visible, it is safe to say that CFST-3L exhibited a greater ductility compared to CFST-2L. CFST-3L showed a great result during the test, which proves that multiple layers of CFRP can improve and strengthen the concrete-filled steel pipe.
Results Summary
CFRP shear strengthening of reinforced concrete beams in zones of combined shear and normal stresses. Axial compressive performance of CFRP-confined rectangular CFST columns using high-strength materials with moderate fineness. Experimental and Numerical Investigations on the Flexural Behavior of CFRP Reinforced Concrete Filled Stainless Steel CHS Pipes.
Xiong, Design of concrete filled tubular beam columns with high strength steel and concrete, structures, volume 8, subpages 213-226. Behavior of concrete-filled square steel stub columns stiffened with encapsulated I-section CFRP section under biaxial bending. Experimental and analytical studies of CFRP-reinforced circular thin-walled CFST stub columns under eccentric compression.
