Controlled failure warning and mitigation of prematurely failing beam through adhesive

Abstract

In plated beam, an adhesive is used primarily to adhere the external plate to the concrete beam to achieve a composite action. Even though some work has been found to indicate that the choice of softer adhesive increased the capacity of beam (MacDonald & Calder, 1982), relatively stiffer adhesives have been largely assumed to provide better strengthening. Largely, due to the fact that adhesive has been widely consid-ered as an insignificant structural component towards the capacity of a composite beam; material capabilities (if not structural) of adhesive have also been ignored for further research towards studying its effects on premature failures (particularly debonding). Under mixedmode loading, the adoption through discretisation of Cohesive Zone Model as a bulk material (indicative of adhesive component) and to simulate interfacial cracks is shown here to achieve the objectives. The outcomes of the research indicate the critical material properties of adhesive in all directions, such as stiffness, strength and crack energy, play crucial role in controlling the behaviour of modes of failure. Further, based on this study, recommenda-tions have been proposed on the choice of adhesive type at different locations of plated beam so as to capture a failure warning and avoid catastrophic failure.

Bond parameters for peeling and debonding in thin plated RC beams subjected to mixed mode loading – Framework

“…In recent years, the use of CZMs has become frequent in fracture problems as these overcome the reported limitations by combining elements of strength and fracture mechanics to calculate fracture loads (Campilho et al, 2007;Cavalli and Thouless, 2001). Cohesive zone models are based on cohesive (Feraren and Jensen, 2004;Petrossian and Wisnom, 1998) or spring (Cui and Wisnom, 1993) elements, placed at regions where damage is prone to occur, or these are also used to define a cohesive continuum medium like an adhesive (Khan et al, 2017c) without the requirement of initial flaw. In an adherend, it is difficult to pre-identify regions or paths of damage, while in bonded assemblies the damage is largely restricted to common interfaces due to accumulation of stresses.…”

“…Elliptical crack initiation criterion is considered, and failure criterion to be energy based. The discretization of CZM is elaborated by Khan el al. (2017c), and is not repeated here due to space limitations.…”

“…However, in most cases, the expected capacity of the retrofitted structure is adversely affected by the formation of premature cracks; thereby, leading to premature failure such as plate debonding (without or slightly damaging concrete surface) or peeling (ripping off concrete cover, exposing internal rebars) from soffit of the beam. Studies (Camanho et al, 2003;Khan et al, 2017c;Khan, 2021b;Li et al, 2005;Oh et al, 2003a) in general have indicated that adhesive can profoundly control the transfer of stresses between the plate and main structure, mainly determining debonding. Therefore, in spite of being a structurally insignificant component (to contribute towards the beam capacity), adhesive layer is a critical element of structural integrity.…”

Relative behaviour of premature failures in adhesively plated RC beam using controllable and existing parameters

“…The effect of adhesive material properties, such as normal stiffness K gr and transverse stiffness K gs , normal strength t n and transverse strength t s , and interface fracture energy G fc interface , are also studied using cohesive zone model by [39]. As they primarily focussed on debonding, therefore the effect of such parameters is briefly extended here towards studying other types of failures as well (including peeling).…”

“…This indicates that the overall brittleness of beam (rapidness of failure) is directly dependent on the behaviour or brittleness of failure mode(s). Therefore, in addition to focussing on the relative response of critical sections, the relative effect of parameters (primary, secondary or local) on modes of failure are also analysed and discussed based on achievable percentage of the ultimate carrying capacity of the beam at the appearance of first crack F 1 =F u  100%, which is brittleness of failure mode(s) [39]. In Fig.…”