PSI - Issue 44

1000 Roselena Sulla et al. / Procedia Structural Integrity 44 (2023) 998–1005 Sulla et al./ Structural Integrity Procedia 00 (2022) 000–000 3 design axial force, positive if compressive (if  is tensile,   = 0 );   = / is the masonry design compressive strength;  is the masonry mean compressive strength;  is the Confidence Factor defined as function of the knowledge level. 2.2. Pier shear sliding According to (NTC, 2018), the structural element shear capacity is assessed as follows:   =  ′    (2) where:  ′ is the length of the masonry pier compressed part, calculated assuming a compression linear diagram and no tensile strength;  is the masonry pier thickness;   is the masonry design shear strength, given by the following equation:   =    + 0.4   ≤  , (3) where:   is the mean shear strength without normal stresses;   = /   is the mean normal stress on the compressed part of the cross section. The limitation on block cracking, obtained for standard shape blocks, is calculated as follows:  , = .  . (4) where   is the block normalized compressive strength. 2.3. Spandrel bending According to the (NTC, 2018), if the axial load is known, the same strength model adopted for piers may be considered (Eq. 1). If the axial force is unknown, and there are horizontal elements in tension, such as steel tie-rods or RC ring beams, one may refer to the following expression for the ultimate bending strength (NTC, 2018):   =   ℎ  1 −   .∙  ∙∙  (5) where:   is the minimum value between the horizontal element tensile capacity and 0.4  ℎ ;   is the masonry design compressive strength in the horizontal direction; ℎ is the masonry spandrel section height. 2.4. Shear strength with diagonal cracking of piers and spandrels According to (Circolare n. 7, 2019), two masonry groups are identified for the shear assessments, both in the piers and in the spandrels:  masonry with irregular texture, where the diagonal tensile failure is governed by   , representing the mean shear strength with no normal stresses;  masonry with regular texture, where a stair step crack (i.e., a diagonal cracking across the mortar joints) governed by   may occur, or where the diagonal cracking occurs across the masonry blocks governed by the strength parameter  , . In the first case, i.e. masonry with irregular texture, the panel shear strength for in-plane actions is:   =   .    1 +   .   =      1 +     (6)