ABSTRACT
Current materials engineering trends put forward the development of efficient structural solutions. The steel replacement with fiber-reinforced polymers (FRP) exemplifies the key to the corrosion problem. However, the relatively low deformation modulus of typical FRP materials raises the deformations of the structural components. Together with the self-weight reduction increasing the kinematic displacements, the latter issue makes developing hybrid structures comprising compression-resistant concrete and high-performance in tension FRP profiles important. Although such hybrid systems are applicable for bridge engineering, the uncertainty of the inter-component bonding properties complicates developing these innovative structures, including the design models. The typical solution focuses on the local bond improvement, e.g., employing FRP profile perforation and mechanical anchorage systems. However, this study introduces an alternative solution, using the stress-ribbon bridge structural system for creating the hybrid beam prototype, which combines the synthetic fiber-reinforced concrete slab and pultruded FRP profile fixed on the supports. This work exemplifies the structural development concept when the finite element (FE) modeling outcome defines the target reference of the design procedure. Thus, on the one hand, this innovative structure simplifies the corresponding numerical (FE) model, which assumes the perfect bond between the components of the hybrid beam system. On the other hand, the solution to the support problem (resulting from a low resistance of pultruded FRP profiles to transverse loads) improves the structural performance of the bridge prototype, doubling the structure's flexural stiffness and load-bearing capacity regarding the weak concrete supports' system. The bending tests proved the adequacy of this solution in describing the design reference for further development of the proposed structural concept.
ABSTRACT
Strength and stiffness are the key parameters characterising the bond performance of fibres in concrete. However, a straightforward procedure for estimating the bond parameters of a synthetic macro-fibre does not exist. This study employs pull-out tests to investigate the bond behaviour of synthetic macro-fibres. Two types of macro-fibres available in the market were investigated. A gripping system was developed to protect the fibres from local damage. The experimental campaign consisted of two stages. At the first stage, 32 concrete specimens were manufactured for performing 96 pull-out tests (three fibre samples were embedded in each cube perpendicular to the top surface and two sides). Two types of macro-fibres with either 10 or 20 mm embedment length were tested. The obtained load-displacement diagrams from pull-out tests demonstrate that the bond performance (characterised by the strength and deformation modulus) of the "top" fibres is almost 20% weaker than fibres positioned to the side surfaces. At the second stage, one type of macro-fibre was chosen for further experimentation of the feasibility of improving the bond performance through the use of colloidal silica or steel micro-fibres. This investigation stage employed an additional 36 concrete specimens. The use of steel micro-fibres was found to be an efficient alternative. The success of this solution requires a suitable proportioning of the concrete.
