Nonlinear Finite Element Analysis of Strengthened Masonry Buildings subject to Seismic Action

Masonry structures are always used from the past until modern times but due to material degradation, imposed displacements, and structural alterations some members need strengthening to re-establish their performances. In this frame, fiber-reinforced polymer (FRP) composites in the form of bonded laminates applied to the external surface are an effective solution [1,2]. Despite research efforts in the last years, for the seismic analysis of the strengthened masonry system, there is still lack of numerical models, which have the advantages of accurate, high-efficiency and good-convergence [3,4]. In the first part of this paper, numerical approaches to model FRP strengthened masonry structures are discussed and in particular a material model suitable for micro-modelling of the interfacial behaviour FRP-masonry implemented in the Diana finite element (FE) program using a user subroutine is presented [5,6,7]. This micro-modelling approach based on interface elements is then used to develop and validate the global behaviour of a different type of FE that was implemented in the Opensees finite element framework. This new element is extremely effective for the seismic analysis of masonry buildings because of the significant advantage of drastically reducing the number of DOF of the FEM model [8,9,10]. Numerical results are validated by comparison with experimental results from tests performed at the University of Pavia and the Georgia Institute of technology. In particular, it shows a satisfactory degree of accuracy to analyse complex assemblages of masonry buildings including cyclic loads effects and FRP strengthening influence.