Abstract
This paper presents an innovative anti-seismic device for controlling the out-of-plane rocking motion of masonry walls with traditional tie-rods, called LInear COntrolled Rocking Device (LICORD). LICORD is a low-impact box connected to the extremity of the traditional tie-rod designed to mitigate rocking for medium–high intensity earthquakes. Additionally, the paper widens the knowledge about the dynamic behavior of rocking walls through the interpretation of the results of an extensive experimental campaign performed on masonry specimens composed by clay brick and cementitious mortar. Firstly, the LICORD’s single components are tested to identify their stiffness and damping properties. Secondly, free vibration tests provide actual values of coefficients of restitution on free-standing walls and walls restrained by LICORD, where the walls vary for the height to thickness ratio. For the stockier wall, the ratio of experimental/analytical coefficient of restitution varies from 88 to 98%, whereas for the slender wall, the results are less scattered, with a minimum value of 95% and a maximum value of 96%. The restrained walls are characterized by coefficients of restitution from 5 to 25% less than the values found for unrestrained walls, depending on the equivalent viscous coefficient of the shock absorbers. Moreover, LICORD demonstrated to properly absorb and damp the oscillations of the wall and control its rocking motion, strongly reducing the number of impacts and the rotation amplitudes up to 70%. Considerations about the effect of one-sided motion on the assessment of coefficient of restitution are also given. The equivalent viscous damping coefficients are observed to be on the range 4% (unrestrained wall) and 7–20% for walls restrained by LICORD.
Highlights
The analysis of out-of-plane (OOP) mechanisms of masonry buildings is a key issue in the seismic vulnerability assessment of existing structures, whose characterization through experimental tests is fundamental for the correct selection of mechanical properties and boundary conditions (Alecci et al 2019; Alecci et al 2020)
The most common model for rocking masonry consists in a single degree of freedom (SDOF) system rocking about the two corner points on the ground
The analysis of Displacement time histories (DTH) shows that the equivalent damping ratio passes from 4 to 20%
Summary
The analysis of out-of-plane (OOP) mechanisms of masonry buildings is a key issue in the seismic vulnerability assessment of existing structures, whose characterization through experimental tests is fundamental for the correct selection of mechanical properties and boundary conditions (Alecci et al 2019; Alecci et al 2020). This paper presents an innovative anti-seismic device, called LICORD (LInear COntrolled Rocking Device), designed to overcome these issues by controlling the rocking of masonry walls This device consists in coupling traditional restraint techniques such as steel tie-rods, frequently used in historic buildings during the last centuries, with an individual or multiple shock absorbers coupled to a re-centering system. For masonry specimens of clay brick (Sorrentino et al 2011) and rubble masonry with historic mortar (Giresini et al 2018a), the ratio of experimental coefficient of restitution to analytical coefficient of restitution was found to be between 80 and 95%, with lower values (about 80%) referring to walls restrained by equivalent tie-rods, and from 85 to 95% for free-standing walls. The effectiveness of LICORD is discussed through the comparison of the dynamic responses between the free-standing walls and the restrained walls
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