Masonry Finite Element Modeling
Finite Element Modeling, Analysis, and Design for Masonry
This article is Part 1 of a series in which we will discuss the modeling and preprocessing considerations for modeling masonry.
In the January 2021 newsletter, we detailed component-based software programs for structural masonry design. This article will now look in depth at Finite Element Analysis (FEA) for masonry structures. Software programs for structural engineers continue to escalate in complexity as we become increasingly reliant on such tools. They increase accuracy in our analysis and efficiency during the design process. To solve these complex problems efficiently, and to gain a more in-depth understanding of the elements being analyzed, a greater number of structural engineers are using FEA. Of course, each of the different FEA programs have their own idiosyncrasies which require us to pay close attention when we move from one program to another. This article is Part 1 of an article series in which we will discuss the modeling and preprocessing considerations for modeling masonry.
Our next article, Part 2, will delve serve as a guide for post-processing analysis and design of structural masonry. Ensuing articles will also discuss specific recommendations for modeling partial grouting as well as cracking in masonry.
What exactly is finite element analysis? It is the process of reducing (simplifying) a problem with infinite degrees of freedom to a finite number of elements with unique material properties. FEA programs are able to resolve even the most complex of problems in a reasonable amount of time. The process of finite element modeling and analysis is an approximate solution which closely mimics an actual structure in a way that allows structural engineers to safely design for the stresses, forces, and deflections that are determined from these methods.
Some of the more commonly used software programs for FEA with masonry design are RAM Elements (soon to be released as STAAD(X) from Bentley Systems, Inc) and RISA Floor/RISA 3D (from RISA Technologies). Other FEA programs with high end analysis features, such as web: masonry.forsei.com 1 © 2010-2020 FORSE Consulting, LLC
MASONRY INSIGHTS written in conjunction with International Masonry Institute 2021
SCIA Engineer, are important tools for structural engineers because they offer more options for creating elements that more closely represent the actual elements behavior.
Pre-Processing and Masonry Modeling
Many of the analyses used today assume thin plate theory for the plate elements along with linear elastic behavior for the elements. The elasticity of material is described by a stress-strain curve, which shows the relation between internal force per unit area and the relative deformation. Linear elasticity is a simplification assuming linear relationships between the components of stress and strain which is valid only for stress states that do not produce yielding or fracture.
Reinforced masonry and other reinforced concrete elements have the complication of not being elastic. Therefore, once a concrete element cracks, modeled steel reinforcement is then engaged in these elements. Of course, masonry is made up of several different concrete components which closely mimic this behavior when it is reinforced. Many times finite element software gives us element modification factors to account for the reduced stiffness of the concrete or masonry element once it has cracked. In some programs this factor is automatically applied, in some it must be manually defined, and in others it is not an option. Some programs offer multiple element modification factors including: bending in each direction, torsion, shear, and axial deformations. One must confirm that the element modification factor used to account for the reduced stiffness from cracking only applies to the bending stiffness in the the direction of the cracked behavior, and is not used with the shear stiffness or the axial stiffness of the element.