PSI - Issue 78

Ingrid Boem et al. / Procedia Structural Integrity 78 (2026) 457–464

461

Fig. 2. Experimental behavior of 350 mm thick rubble-stone masonry (a) piers, with axial stress 0.5 MPa, and (b) spandrels, with axial stress on adjacent piers 0.33 MPa, subjected to in-plane cyclic action. Main features, capacity curves (shear force vs. drift) and crack pattern at the end of the tests, in the unstrengthened (URM) and CRM strengthened configuration (R2). 4.2. Account for CRM in the procedure To account for the CRM contribution into the procedure of §0.1, accordingly with the experimental evidences, the in-plane lateral response of the RM piers has been updated by improving their secant stiffness, lateral resistance and ultimate displacement capacity. In particular, when evaluating the secant stiffness, the Young’s and shear moduli shall be increased by considering the average values of masonry and mortar coating, weighted according to their respective thicknesses. The lateral resistance, V P(RM) , is evaluated accordingly to the analytical approach suggested in CNR-DT 215 (CNR, 2020) and, specifically:  for the diagonal shear cracking mechanism, the contribution of the FRP mesh is added to the resistance of the unstrengthened masonry pier, V P,d(URM) :   f t fd f f Vf Rd ) P,d RM P,d(URM E l n t V V            1 , (1) with  Rd model coefficient, n f number of strengthening layers, t Vf equivalent fibres thickness in the direction parallel to the shear force (= A f / s , ratio between the dry cross section of a single fiber yarn and the grid pitch), l f design dimension of CRM,  t reduction factor for shear stress,  fd design value of the tensile limit strain of the strengthening system, E f fibers Young’s modulus. In this study: n f = 2, t Vf = A f / s = 3.8 mm 2 / 66 mm,  t = 1,  fd · E f = 1345 MPa,  Rd = 1.5, l f = pier height, but not greater than 1.5*pier width;  for the in-plane bending mechanism, the resistant bending moment is that of a cracked reinforced section subjected to combined axial and bending action, evaluated by solving the equilibrium for translation and for rotation under the following assumptions: composite action of CRM and the masonry (monolithic cross-section), planar sections remain planar (Bernoulli hypothesis), bilinear response in compression and no tensile strength for masonry, linear tensile response in tension (Young’s modulus E f ), up to failure (at reaching the tensile limit strain  fd ) and no compressive strength for the fibres, no contribution from the mortar. Based on the experimental evidence for the considered CRM strengthening technique, the ultimate drift is set 1.0% or 2.0%, respectively, for the two cases. A residual strength of 80% is also considering till a drift of 1.6% for the shear failure mechanism.