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Title: FRP Structural Stay-In-Place Formwork for Concrete Slabs
Authors: Goyal, Reema
Supervisor: Mukherjee, Abhijit
Goyal, Shweta
Keywords: FRP;Stay-in-place formwork;bond mechanism;aggregate bonding;adhesive bonding
Issue Date: 28-Mar-2018
Abstract: Development in the use of fibre reinforced polymer (FRP) in the construction industry has led to the development of FRP structural stay-in-place (SIP) formwork system. The concept of using FRP composites for structurally integrated SIP formwork maximises the advantages of both FRP and concrete while simplifying the construction process and reducing construction time and labour cost. FRP SIP formworks plays role of a formwork when concrete is in plastic stage and as reinforcement when concrete has hardened. This thesis investigates the feasibility of FRP plank manufactured in India as structural SIP formwork. The selected plank is a GFRP (glass fibre reinforced polymer) profile consisting of base plate integrated with T-shaped ribs. Experimental investigation regarding the suitability of the plank as SIP formwork was performed in three stages. In the first stage, the FRP plank was selected out of the two commercially available planks. The selection was based on the material and geometrical properties of the plank, viz. moment of inertia, longitudinal tensile strength test and fibre volume fraction test. Further, sand and concrete loading tests were conducted to check if the deflections under concrete weight were within the permissible limits, so that it can be used as a formwork during casting of concrete. In the second stage, the bond between FRP plank serving as structural SIP formwork and cast-in place concrete has been investigated. Bond development between plank and concrete is critical for FRP tension element to be effective. Two different shear tests were used for investigation of bond- Push Tests and Pull Tests. The above mentioned shear tests were performed to investigate two types of bond treatments: aggregate bonding and adhesive bonding. Performance of three different types of adhesives has been compared. The adhesives to be compared were selected based on their viscosity, modulus of elasticity, elongation at break, ease of application and pot life. It was observed that the bond strength and failure mode (interface failure or material failure) varies greatly with the type of adhesive and the bond treatment. It was found that adhesive bonding is more convenient and performed marginally better than aggregate bonding. Moreover, with adhesive bonding, it was possible to shift the failure from the interface to concrete. Finally in third stage, the role of SIP formwork as reinforcement was investigated through cyclic flexural tests on slabs. Two sets of slabs were investigates with different shear span to 7 depth ratio, one being shear critical and other being flexure critical. Each set consisted of two control specimens (one without any bond treatment and second using steel reinforcement in place of FRP SIP formwork) and two bond treated specimens (one each with adhesive bonding and aggregate bonding). The load displacement relationship, ultimate flexural capacity, strain distribution were measured during the test. It was found that ultimate capacity of bond treated FRP plank specimens was higher than that of control specimens. The specimens were analysed using both the ACI Committee 440 recommended flexure and shear design provisions. Non linear finite element method was used for numerical validation of the experimental data. A three-dimensional finite element model was prepared using software ATENA to simulate the behaviour of the bond treated FRP-concrete interface. The aim of the simulation was to have a better understanding of the interface characteristics and determine the interfacial properties that can be used in the full scale simulations. The interface characteristics were then verified by modelling flexural tests.
Appears in Collections:Doctoral Theses@CED

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