Bi‐directional collapse fragility assessment by DFEM of unreinforced masonry buildings with openings and different confinement configurations

Abstract

Unreinforced masonry (URM) buildings that are characterized by brittle, heterogeneous, and anisotropic responses have complex nonlinear dynamic behavior and high vulnerability under seismic loading. While masonry confined by tie‐columns and lintel beams can achieve better ductility and stability, the wall openings induce stress concentration around the corners and diminish the strength. Furthermore, the interacting in‐plane and out‐of‐plane responses of masonry walls could significantly affect the post‐cracking behavior and increase the collapse risk. To attain reliable seismic design of confined masonry buildings with openings, the collapse fragility under bi‐directional seismic loading shall be addressed and thoroughly investigated in this study. Advanced discrete finite element models (DFEM) with coupled damage‐plasticity traction‐separation law, which can simulate complex nonlinear dynamic behavior such as disintegration and progressive collapse, were developed for the masonry structures and validated against experimental results. Four one‐storey residential masonry buildings: (1) unconfined (UCM), (2) confined by tie‐columns at four building corners (CM‐I), (3) confined by toothed tie‐columns (CM‐II), and (4) confined by toothed tie‐columns and lintel beams (CM‐III) were considered. A series of incremental dynamic analyses (IDA) with 15 bi‐directional ground motions and fragility analyses were performed to investigate the dynamic characteristics, base shear, hysteresis behavior, failure mechanism, collapse probability, and exceedance probability for different drift limits were studied in‐depth. CM‐II with toothed tie‐columns had the lowest collapse probability and fragility at different drift limit states. The introduction of lintel beams to CM‐III lead to an increase of the storey‐drift‐based fragility compared to CM‐II, as a result of the increased maximum base shear of CM‐III with higher post‐damage stiffness. The lintel beams also inflicted short‐column effects on the tie‐columns. Nevertheless, the lintel beams could delay the out‐of‐plane collapse of the masonry walls by shortening the effective wall arching length. In some cases, the CM‐III could achieve better performances than CM‐II even in terms of storey drifts. The response variations of CM‐III to the changing of the non‐intensity related ground motion parameters are also lower than CM‐II.

Variable Factors Affecting Progressive Destruction of Composite Steel Tall Building

“…where f E c elastic strain at the peak stress; ε the total strain; ε p plastic strain with stiffness degradation; d the damage factor; σ the tension or compression stress; f is either the tensile or compressive strength of concrete as appropriate. The values of the concrete damage parameters are suggested based on [39][40][41][42][43]. The parameters are introduced in Table 2.…”

A robust computational strategy for failure prediction of masonry structures using an improved multi‐surface damage‐plastic based interface model

“…Thus, there is a growing trend towards the use of precise numerical modeling approaches for simulating masonry structures because they are capable of solving complex nonlinear problems. [3][4][5][6][7][8][9][10] In this context, Lourenco 11 has classified the modeling strategies of masonry structures into three groups: (1) detailed micro-modeling, 12 where bricks and mortars are discretely modeled using continuum elements and brick-mortar interfaces are modeled with zero thickness cohesive elements;…”

“…Though empirical based approaches 2 can provide an easy solution of this problem, they only give an approximate solution that may not be adequate to assess the safety of large masonry buildings with complex architectural forms. Thus, there is a growing trend towards the use of precise numerical modeling approaches for simulating masonry structures because they are capable of solving complex nonlinear problems 3–10 . In this context, Lourenco 11 has classified the modeling strategies of masonry structures into three groups: (1) detailed micro‐modeling, 12 where bricks and mortars are discretely modeled using continuum elements and brick‐mortar interfaces are modeled with zero thickness cohesive elements; (2) macro‐modeling, 13,14 where bricks and mortars are homogenized as a single continuum utilizing a representative volume element (RVE); and (3) simplified micro‐modeling, 15 where bricks are modeled using continuum elements, while cohesive elements are used for mortar joints (entire thickness) and artificial joints placed inside bricks to simulate the potential crack in bricks.…”

Lateral behaviour of unreinforced masonry walls with different types of opening and effect of strengthening measures: A computational approach

“…Following these behavioral mechanics, considerable research efforts have been made to evaluate the in-plane resistance of the URM walls. (Nayak and Dutta 2016a;Deb et al 2021).…”