Full Session with Abstracts
Strengthening flexurally deficient beams or slabs using externally bonded Fiber Reinforced Polymer (FRP) sheets is an efficient technique due to the lightweight and high tensile strength properties of FRP materials. However, it has been shown that FRP sheets could debond before reaching the full strength of the FRP material. This behavior reduces the efficiency of using FRP sheets and limits achieved strengthening. Spike anchors and other methods of anchorage have been recently investigated to reduce debonding and provide ductility. To date, however, a method to identify the need for anchorage is lacking, and whenever anchors are used their application follows recommendations that stem from past experience. Using supplemental anchorage without determining whether there is a need for it increases the cost of strengthening when strains developed in the sheet do not exceed values corresponding to debonding. In this research, a procedure is proposed to estimate the need and location of supplemental anchors along FRP-strengthened elements. The proposed procedure is based on combining two steps. In the first step strains developed in FRP sheets used to strengthen flexural members are calculated assuming that perfect bond exists between the FRP material and concrete substrate. In the second step the possibility of FRP debonding is considered by limiting the FRP strain using the ACI 440 2.R-2017 procedure. The length of the FRP sheet where anchors are needed is then determined by comparing strain results from the first step with strains determined in the second step. If the debonding strain is exceeded by strains determined assuming a perfect bond indicates the need for anchorage along regions of the entire sheet length. The number and geometry of the anchors required to prevent debonding over these regions of the FRP sheet are then determined based on a new proposed formulation.