scholarly journals Applicability of nonlinear static procedures for low-rise unreinforced masonry buildings with flexible diaphragms

2017 ◽  
Vol 137 ◽  
pp. 1-18 ◽  
Author(s):  
Yasuto Nakamura ◽  
Hossein Derakhshan ◽  
Michael C. Griffith ◽  
Guido Magenes ◽  
Abdul H. Sheikh
Keyword(s):  
Unreinforced Masonry ◽  
Masonry Buildings ◽  
Flexible Diaphragms ◽  
Nonlinear Static

scholarly journals Numerical Simulation of Unreinforced Masonry Buildings with Timber Diaphragms

Buildings ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 205
Author(s):  
Igor Tomić ◽  
Francesco Vanin ◽  
Ivana Božulić ◽  
Katrin Beyer
Keyword(s):  
Failure Modes ◽  
Unreinforced Masonry ◽  
Masonry Walls ◽  
Masonry Buildings ◽  
Seismic Behaviour ◽  
Plane Failure ◽  
Friction Resistance ◽  
Flexible Diaphragms ◽  
Out Of Plane ◽  
Equivalent Frame

Though flexible diaphragms play a role in the seismic behaviour of unreinforced masonry buildings, the effect of the connections between floors and walls is rarely discussed or explicitly modelled when simulating the response of such buildings. These flexible diaphragms are most commonly timber floors made of planks and beams, which are supported on recesses in the masonry walls and can slide when the friction resistance is reached. Using equivalent frame models, we capture the effects of both the diaphragm stiffness and the finite strength of wall-to-diaphragm connections on the seismic behaviour of unreinforced masonry buildings. To do this, we use a newly developed macro-element able to simulate both in-plane and out-of-plane behaviour of the masonry walls and non-linear springs to simulate wall-to-wall and wall-to-diaphragm connections. As an unretrofitted case study, we model a building on a shake table, which developed large in-plane and out-of-plane displacements. We then simulate three retrofit interventions: Retrofitted diaphragms, connections, and diaphragms and connections. We show that strengthening the diaphragm alone is ineffective when the friction capacity of the wall-to-diaphragm connection is exceeded. This also means that modelling an unstrengthened wall-to-diaphragm connection as having infinite stiffness and strength leads to unrealistic box-type behaviour. This is particularly important if the equivalent frame model should capture both global in-plane and local out-of-plane failure modes.

scholarly journals Seismic analysis of in-plane loaded walls in unreinforced masonry buildings with flexible diaphragms

2014 ◽  
Vol 47 (4) ◽  
pp. 275-289
Author(s):  
Yasuto Nakamura ◽  
Hossein Derakhshan ◽  
Jason M. Ingham ◽  
Michael C. Griffith
Keyword(s):  
Seismic Analysis ◽  
Unreinforced Masonry ◽  
Mode Analysis ◽  
Analysis Approach ◽  
Masonry Buildings ◽  
Alternative Analysis ◽  
Response Modification Factor ◽  
Seismic Demands ◽  
Flexible Diaphragms ◽  
Modification Factor

It is well recognised that the dynamic response of unreinforced masonry buildings with flexible timber diaphragms typically contains multiple dominant modes associated with the excitations of the diaphragms and the in-plane walls. Existing linear analysis methods for this type of structure commonly account for the multi-mode behaviour by assuming the independent vibrations of the in-plane loaded walls (in-plane walls) and the diaphragms. Specifically, the in-plane walls are considered to be rigid and the unmodified ground motion is assumed to be transmitted up the walls to the diaphragm ends. While this assumption may be appropriate for many low-rise unreinforced masonry buildings, neglecting the dynamic interaction between the diaphragms and the in-plane walls can lead to unreliable predictions of seismic demands. An alternative analysis approach is proposed in this paper, based on the mode properties of a system in which (1) the mass ratios between the diaphragms and the in-plane wall are the same at all levels, and (2) the periods of the diaphragms are the same at all levels. It is proposed that under these conditions, two modes are typically sufficient to obtain the peak seismic demands of the in-plane walls in elastically responding low-rise regular buildings. The applicability of the two-mode analysis approach is assessed for more general diaphragm configurations by sensitivity analysis, and the limitations are identified. The two-mode approach is then used to derive a response modification factor, which may be used in conjunction with a linear static procedure in the seismic assessment of buildings with flexible diaphragms.

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