Non-dimensional axial load-moment interaction diagrams for FRP strengthened masonry walls

Abstract

Masonry is a material with poor capacity to withstand tensile loads, for this reason it results so vulnerable against destabilizing accidental loads, such as earthquakes. External FRP (fibre reinforced polymer) reinforcements can improve out-of-plane flexural capacity of masonry walls. For practical applications, we need to study the critical sections to check Ultimate Limit State is not exceeded. In this sense, non-dimensional axial load-moment interaction diagrams are a useful tool for the design/assessment of the FRP reinforcement, as well as for analyzing the incidence of the main variables on the ultimate cross sectional capacity. The diagrams included in this work have been prepared from a calculation procedure similar to that used for reinforced concrete sections but adapted to the particularities of the strengthened masonry ones. For masonry, an idealized bilinear stress-strain relationship is used. For FRP strengthening, linear elastic up to failure, the design strain for flexural applications is limited by a >bond reduction factor> taking into account some aspects, such as intermediate FRP debonding failure, that causes the FRP sheets can't reach their ultimate tensile strength although their ends were properly anchored. Non dimensional axial load-moment interaction diagrams are presented, which main parameters have been chosen to be representative of different FRP strengthening systems. These diagrams allow analyzing the predictable failure mode (due to masonry or FRP) and the improvement of flexural sectional cross capacity obtained by means of the strengthening depending on axial load level supported by the wall.