Lateral strength force of URM structures based on a constitutive model for interface element

This paper presents the numerical implementation of a new proposed interface model for modeling the behavior of mortar joints in masonry walls. Its theoretical framework is fully based on the plasticity theory. The Von Mises criterion is used to simulate the behavior of brick and stone units. The interface laws for contact elements are formulated to simulate the softening behavior of mortar joints under tensile stress; a normal linear cap model is also used to limit compressive stress. The numerical predictions based on the proposed model for the behavior of interface elements correlate very highly with test data. A new explicit formula based on results of proposed interface model is also presented to estimate the strength of unreinforced masonry structures. The closed form solution predicts the ultimate lateral load of unreinforced masonry walls less error percentage than ATC and FEMA-307. Consequently, the proposed closed form solution can be used satisfactorily to analyze unreinforced masonry structures

Finite element nonlinear analysis of high-rise unreinforced masonry building

A simple efficient algorithm based on compressive diagonal strength of unreinforced masonry walls is presented to determine capacity curve of unreinforced masonry building. The compressive strength is calculated based on a new close form solution. The new close form solution is determined based on predicted results using interface elements for modeling of mortar joints. Finite element method with two-noded linear elements is used for analyses. Different masonry structures, including low- and high-rise unreinforced masonry buildings, are analyzed using the new closed-form solution and the presented algorithm. A comparison of results of the present work with experimental data and other methods similar to the discrete element method show proper accuracy of the analyses in the present work. Consequently, the closed form solution with proposed algorithm can be used to satisfactorily analyze unreinforced masonry structures to predict the ultimate base shear force and the pushover curve. Hence, practicing engineers can determine the behavior of an URM building and its performance level with proper accuracy under seismic excitation using concepts described in the present work

A numerical model for the analysis of masonry walls in-plane loaded and strengthened with steel bars

A novel macro-model for the analysis of masonry shear walls reinforced with steel bar grids is presented. The model is based on the so-called disturbed state concept (DSC), with a modified hierarchical single yield surface (HISS-CT) plasticity model accounting for a distinct behavior in tension and compression. The effect induced by the introduction of different reinforcement ratios is discussed, in terms of increase of both failure load and ductility. With reference to a quasi-square shear wall, an optimal reinforcement ratio is evaluated by means of the numerical model proposed and subsequently compared with recommendations provided by the Canadian masonry design standard. The comparison shows how minimum values proposed by Canadian standard are suboptimal and hence not totally suitable to obtain a proper increase of the seismic performance of shear walls in high seismicity region. A second example, relying into a shear panel with eccentric openings and subjected to horizontal loads, is analyzed in detail. It is assumed to strengthen the structure by means of a light and a heavy reinforcement, to deeply investigate the role played by steel bars in masonry seismic upgrading. A new explicit formula is finally presented, useful to provide a quick estimation of the load carrying capacity of reinforced masonry, to be eventually used in common design

Pushover analysis of large scale unreinforced masonry structures by means of a fully 2D non-linear model

A simple 2D model for the evaluation of the seismic performance of large scale unreinforced masonry structures in-plane loaded is presented. The approach is fully two dimensional and allows performing pushover analyses on large scale structures without the reduction of the walls to an equivalent frame, competing with 1D codes. In the model, a macroscopic approach is used, where the so called disturbed state concept (DSC) with modified hierarchical single yield surface (HISS) plasticity are used to characterize the constitutive behavior of masonry in both compression and tension. Two HISS yield surfaces for compressive and tensile behavior are utilized. The DSC model allows for the characterization of non associative behavior through the use of disturbance, and it computes micro-cracking during deformation, which eventually leads to fracture and failure. The DSC model is validated at both (1) specimen and (2) structural level. At a structural level, three large scale masonry walls subjected to incremental horizontal loads are analyzed and pushover curves obtained with the model proposed are compared to those obtained by means of standard equivalent frames and existing literature models