Keywords: unreinforced masonry, slender towers, strengthening methods, tie-rods, linear time-history analysis..

This paper presents an investigation on the structural role of tie-rods when added to unreinforced masonry towers. Unreinforced masonry towers are slender structures with high seismic vulnerability. A traditional retrofitting and strengthening method put forward is the insertion of tie-rods in critical parts of the tower. This paper presents the results of a parametric analysis on tie-rods in slender masonry structures such as the bell towers. To this end the effectiveness of the tie-rods as a retrofitting scheme is investigated. Two parameters are examined; (i) the position of the tie-rods along the height of the structure; and, (ii) the distance between subsequent tie-rods to better understand the structural behaviour of slender masonry structures. Timehistory analyses are carried out and the maximum top displacement and axial force are detected. These two parameters are a measure of the activation of the tie rod and thus, of the effectiveness of the strengthening employment. Pre-cracks are assumed to run vertically along the height of masonry walls and the rods are expected to tie the intersected wall together against out-of-plane excessive deflection. Seismic action is performed in one direction since these structures are symmetric. In this way rocking behaviour is expected to appear rather than shear failure and so, higher ductility will be achieved. Hence, the basic advantage of the intervention using tierods being a fully reversible technique of strengthening is the control of the failure mechanism in such a way that it exploits as much as possible the high compressive strength of the masonry.

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