In situ free‐vibration tests on unrestrained and restrained rocking masonry walls

Abstract

Summary In the out‐of‐plane assessment of rocking walls, a relevant and yet uncertain aspect is the influence of energy dissipated during motion due to impacts and restraints, such as a floor or tie rods. Therefore, in situ rocking tests on unrestrained and restrained unreinforced masonry walls, made of composite (rubble + blockwork) masonry, were performed and analyzed. The restraint is given by steel springs of assigned stiffness, simulating a floor connected to full‐scale (4 × 1 × 0.6 m3) specimens from a dismantling building. The specimens are displaced from a static equilibrium position and released, allowing to evaluate energy dissipation. The coefficient of restitution is estimated as the square root of consecutive peak velocities of the same sign, to take into account nonhomogeneities in walls. For unrestrained walls, experimental coefficients of restitution vary between 81 and 88% of analytical ones, confirming the latter as conservative. For restrained configurations, experimental coefficients of restitution are between 74% and 83% of analytical values of unrestrained walls. Hence, an additional energy damping can be ascribed to the springs. Equivalent viscous damping ratios of a nonlinear rocking system are calculated by considering a velocity logarithmic decrement, resulting between 6% and 8% (unrestrained condition) and between 8% and 10% (restrained condition). An analytical formula is proposed for estimating the coefficient of restitution for restrained walls if the dynamic properties of the unrestrained wall and the horizontal restraint are known. Finally, the relevance of a refined estimation of energy dissipation is discussed by means of numerical time history analyses.

Seismic fragility assessment of nonstructural components in unreinforced clay brick masonry buildings

“…The horizontal diaphragms in these buildings are constructed of timber, with the diaphragms providing out-of-plane restraint along the wall horizontal edges only in the inward F I G U R E 2 Assumed two-way spanning wall prototypes for a two-storey building. (A) Prototype 1; as-built (AB) and (B) prototype 2; retrofitted (R) direction (Cross and Jones 8 ; Giresini et al 21 ; Noor-E-Khuda and Dhanasekar 38 and Sorrentino et al 52 ). As an exception for these connections, the wall horizontal edge support at the first floor line (above the openings) was assumed to be provided in both directions by the lateral stiffness of the lintel, which includes the frames of the ground floor openings.…”

Masonry Walls Retrofitted with Vertical FRP Rebars

“…The effectiveness of the intervention is analysed in terms of level of seismic improvement, defined as the ratio between the seismic capacity of the reinforced and unreinforced walls.Buildings 2020, 10, 72 2 of 17 with the current state of the art, the masonry element, when subjected to out-of-plane actions, assumes a monolithic behaviour and cracks subdividing into distinct macro-elements. A model of rigid body excited into a rocking motion can be adopted to simulate the behaviour of the masonry element [12][13][14], whose effectiveness has been recently proved through dynamic tests performed on real walls [15] and by the subsequent comparison with analytical and numerical models [16].Depending on the typology of restraints and on the location of the masonry element within the structure, different mechanisms may take place [17]. It is nowadays well assessed that, in presence of poor connections with external or internal perpendicular walls, out-of-plane behaviour of masonry piers and spandrels represents the greater structural vulnerability of existing masonry building [18][19][20][21][22].…”

“…It is nowadays well assessed that, in presence of poor connections with external or internal perpendicular walls, out-of-plane behaviour of masonry piers and spandrels represents the greater structural vulnerability of existing masonry building [18][19][20][21][22]. Advanced analysis techniques, involving both theoretical approaches [15,[23][24][25][26][27][28][29][30][31] and numerical models [11,16,[32][33][34], allow to accurately evaluate the seismic capacity of the masonry element and to direct engineers to the definition of proper retrofitting interventions, required to ensure an adequate safety level in case of low structural capacity. Well-designed classical retrofitting interventions can improve the seismic strength of the masonry macro-element but, on the other hand, they can change the collapse mode, inhibiting the simple overturning mechanism and then modifying the structural behaviour of the entire structure.…”

“…Buildings 2020, 10, 72 2 of 17 with the current state of the art, the masonry element, when subjected to out-of-plane actions, assumes a monolithic behaviour and cracks subdividing into distinct macro-elements. A model of rigid body excited into a rocking motion can be adopted to simulate the behaviour of the masonry element [12][13][14], whose effectiveness has been recently proved through dynamic tests performed on real walls [15] and by the subsequent comparison with analytical and numerical models [16].…”

The role of different sliding resistances in limit analysis of hemispherical masonry domes

“…Finding the ultimate load factor, together with the stress state and failure mechanisms for models with basic geometries, is a classical problem also solved through other structural analysis methods such as Finite Element (FE) analysis, including detailed and simplified finite element micro models [27][28][29], and Discrete Element (DE) analysis [30][31][32]. On the other hand, further approaches have been proposed to simplify the static and dynamic analysis of masonry structures assumed as assemblages of rigid blocks, such as equivalent macro-elements constituted by a set of trusses to describe masonry vaults [33] and one-sided motion of rocking rigid blocks [34,35]. However, limit analysis approach is less computationally expensive still highly accurate, compared to other computational methods.…”