Ductility and deformability of fibre-reinforced polymer-strengthened reinforced concrete beams

Abstract

This paper discusses the definition of, and the distinction between, deformability and ductility of reinforced concrete (RC) beams that are strengthened by advanced composites. The study examines the suitability of a new, design-based method for the determination of deformability, as well as an energy-based process, which is found to be suitable for quantifying the ductility levels of fibre-reinforced polymer (FRP)-strengthened RC members. Ten FRP-strengthened RC beams and four slabs have been load-tested to ultimate failure in the current study. The test results, together with the load–deflection data of an additional 26 beams from literature, form the basis of analyses and discussions. The paper concludes that high deformability does not necessarily lead to good ductility, as very brittle failure modes of such beams have been observed in the experimental studies and reported in literature. It was found that a ductility index of between 2·0 and 2·5 reflects 25–33% of elastic energy stored in the strengthened system. This level of elastic energy is considered to be the maximum acceptable in FRP-strengthened concrete flexural elements for ductile behaviour. It was also found that for ductile failure modes the deformability and ductility indices tend to converge, whereas for brittle behaviour the deformability index could be up to 33% higher. The results presented in this paper provide a rationale for the ductility considerations to be incorporated into the development of design equations for FRP strengthening.

Flexural property and design method evaluation of BFRP and steel bars hybrid reinforced concrete beams

“…Tann et al 33 suggested utilizing the deformability index D df to describe the loaded FRP bar RC beams subjected to large deformations, however, are not necessarily highly ductile. …”

Deformability of concrete beams with unbonded FRP tendons

“…(6) There is no general agreement on how much deformability is enough with respect to the available deformability indices. Further study is necessary to provide a scientific basis for determination of the requirement.…”

“…According to Grace et al [5], if the energy ratio is 75% or greater, then the beam will exhibit a ductile failure. As pointed out by Tann et al [6], the Grace model is actually a reversed form of the Naaman model. If the energy ratio of Grace et al is 75%, then E tot /E el would be 1/(1−0.75) = 4, and the deformability index as determined by Eq.…”

“…Eq. (6), is sensitive to the change of concrete strength and the level of prestressing. It is also desirable to verify if Zou's conclusions are also valid for UPPC beams with FRP tendons.…”

Methods to Determine Ductility of Structural Members: A Review

“…Research by Barrera et al (2012) and Spadea et al (2001) used two or more methods. Several types of ductility methods have been demonstrated in previous studies (Tann et al, 2004;Ghallab, 2014;Zou, 2003;El Zareef and El Madawy, 2018;Oudah and El-Hacha, 2012). However, only a few common methods have been identified, and many previously used ductility methods remain unidentified.…”