Issue 50

M. Godio et alii, Frattura ed Integrità Strutturale, 50 (2019) 194-208; DOI: 10.3221/IGF-ESIS.50.17 206 C ONCLUSIONS his study shows by means of numerical simulations that the acceleration capacity of vertically-spanning URM walls decreases when the walls are subjected to a relative motion between the top and bottom supports. The study quantifies this in a systematic way, by looking at two fundamental input motion characteristics: firstly, by including motions that are phase-shifted, i.e. non-synchronous but of equal amplitude; secondly, through motions that are synchronous but of relative amplitude. The effect of the phase-shift and relative amplitude of the support motions have been studied for different wall configurations and by a model where the masonry components are modelled with infinite compressive strength and zero tensile strength. The effect of a limited compressive strength can be taken into account in the model by relating it to the effective wall thickness, see e.g. [10]. The assumption of zero tensile strength, which is not always verified in real situations, allows making a comparison with the results of a previous study [32]. As already observed in [32] for walls subjected to equal support motions, it appears here that for a given phase-shift or relative amplitude, variations in the masonry elastic modulus do not have a significant influence on the acceleration capacity of the URM walls. On the other hand, the wall height-to-thickness ratio, the wall effective thickness and, especially, the vertical stress, or overburden, applied at the wall top appear to be critical parameters that should be carefully evaluated because of their influence on the wall capacity [32]. As a novelty, the study further shows that, because of the relative support motion, the acceleration capacity of URM walls can drop by 10 to 20% for wall configurations with low to moderate overburden ratios and, in cases where the overburden ratio is high, it can drop by more than 50%. In conclusion, the strategies reported in this study allows quantifying the difference in shift and amplitude between the top and bottom wall support motions in efficient way. The support motions used in this study are nonetheless not yet representative of real building configurations as they do not contain any filtering effect due to the shear walls, which provide the wall supports with an input motion whose main period is close to the fundamental period of the structure [2,33,34]. Further studies characterizing the input motion characteristics, i.e. phase shift and relative amplitude, of consecutive floor motions in URM buildings are necessary to put the present study into a real context and decide whether the extension of existing assessment methods to capture the effect of relative support motions is a step to be envisaged. R EPRODUCIBILITY OF THE ARTICLE CONTENT he content of this paper can be reproduced with the files provided at the following permanent repository: https://doi.org/10.5281/zenodo.3187536. The files include outputs of the numerical model, plus Matlab scripts necessary to reproduce Figs. 3-8 presented in the paper. A CKNOWLEDGMENTS he work presented in this paper was funded by the Swiss Federal Office of the Environment and the Construction Department of the Canton Basel-Stadt. R EFERENCES [1] Priestley, M.J.N. (1985). Seismic behaviour of unreinforced masonry walls, Bull. New Zeal. Natl. Soc. Earthq. Eng., 18(2), pp. 191–205. [2] Menon, A., Magenes, G. (2011). Definition of seismic input for out-of-plane response of masonry walls: I. Parametric study, J. Earthq. Eng., 15(2), pp. 165–194, DOI: 10.1080/13632460903494446. [3] Giongo, I., Dizhur, D., Tomasi, R., Ingham, J.M. (2015). Field testing of flexible timber diaphragms in an existing vintage URM building, J. Struct. Eng., 141(1), pp. d4014009, DOI: 10.1061/(ASCE)ST.1943-541X.0001045. [4] Brignola, A., Pampanin, S., Podestà, S. (2012). Experimental evaluation of the in-plane stiffness of timber diaphragms, Earthq. Spectra, 28(4), pp. 1687–1709, DOI: 10.1193/1.4000088. [5] Landi, L., Gabellieri, R., Diotallevi, P.P. (2015). A model for the out-of-plane dynamic analysis of unreinforced masonry T T T