Structural fire design of ear strengthened RC beams

This paper discusses the structural fire design of reinforced concrete beams strengthened in flexure by means of externally applied reinforcement (EAR). It is focusing on the Eurocode approach for fire rating of individual members. Three different fire safety approaches are presented, depending on the strengthening ratio. Applicability of fire design methods, such as the use of the tabulated data and 500°C isotherm methods by EN1992-1-2, is indicated. Results show the importance of a well thought approach in the structural fire design of EAR, being a popular strengthening technique for concrete members. Through this strengthening solution, the load bearing capacity of existing members is strengthened or retrofitted, both in service conditions and at ultimate limit state. The EAR strengthening relies on a good bond interaction between the existing member and the externally applied reinforcement. However, given the weak properties of the bond interface at elevated temperatures, the fire performance is of special concern in the structural design of EAR strengthened reinforced concrete

Bond shear stress-slip relationships for FRP-NSM systems at elevated temperature

In the last years Near Surface Mounted (NSM) reinforcement has mainly been applied at ambient temperature, to strengthen reinforced concrete (RC) beams with FRP (fibre reinforced polymer) materials. Thereby, FRP bars/strips are embedded inside the concrete section by means of grooves filled with adhesive. The behaviour of FRP-NSM strengthening systems at elevated temperature is signicantly influenced by the type of adhesive (e.g. cementitious grout is usually more stable than epoxy resin at high temperature). To characterize the FRP-NSM behaviour two steps are needed: 1) shear tests performed in order to determine the FRP-concrete interaction via bond stress-slip curves and 2) constitutive bond stress-slip relationships for use in structural design (analytical and numerical). Hereby, the bond behaviour is to be considered temperature dependent. During two experimental campaigns, double bond shear tests were performed in order to study the behaviour of FRP-NSM systems at elevated temperature using different types of adhesive, epoxy resin and cementitious grout respectively. The bond shear stress-slip curves are discussed including the effect of different types of adhesive. Simplified bond stress-slip relationships are proposed to model the FRP-concrete interaction at high temperature

Engineering model for SFRC shear strength based on the MC2010 MCFT approach

Recent developments and ongoing research in the field of steel fibre reinforced concrete (SFRC) have led to its implementation into national and international design codes and guidelines. Since fibres are promising as an alternative for (minimum) shear reinforcement, special attention is given towards new shear design provisions for FRC elements. Although these design models are available and validated with respect to research results, the application of fibres as shear reinforcement for both reinforced and prestressed concrete beams is rather limited in daily practice, due to lack of experience in the engineering community with respect to these design guidelines, as well as limited insight in their accuracy. In perspective to a PhD study of the second author, the most important shear design models available for SFRC (RILEM, Model Code, Plasticity Model) are verified in terms of accuracy of the models against a shear test database containing 99 SFRC elements (69 reinforced concrete and 30 prestressed concrete). Based on the obtained insights, a simplified engineering model is proposed for further evaluation by the research community. This model, which predicts the shear capacity of SFRC beams without stirrups, can be regarded as a closed form version of the modified compression field theory (MCFT) approach presented in fib Model Code 2010

Literature review on reinforced concrete members strengthened with FRP at room and elevated temperature

In the last 30 years, composite materials have been successfully applied as structural reinforcement to strengthen existing structures. The success of applying FRPs (Fibre Reinforced Polymers) for strengthening is due to their excellent mechanical properties and durability, their ease of application and the versatility of FRP strengthening systems. In particular Near Surface Mounted (NSM) reinforcement offers an interesting technology in terms of protection of the FRP from external influences compared to the Externally Bonded Reinforcement method (EBR). Based on a literature review, this paper discusses the structural performance in terms of FRP to concrete bond behaviour at room and elevated temperature. To understand and characterize the bond interaction, researchers conducted bond shear tests, though the lack of a standard test methodology makes comparison of results not always straight forward. As such, this study looks into bond influencing factors such as concrete type, adhesive type, FRP roughness, groove dimensions, glass transition temperature and coefficient of thermal expansion

2-span reinforced concrete beam strengthened with fibre reinforced polymer

C