Finite Element (FEM) Model

Introduction

This chapter is to provide a closer information about the behaviour of the finite element model.

Features

Eccentricities on curved structural members are discussed "FEM - eccentricity and curved elements".

Hinges are in more detail explained " FEM - Hinges".

Rotational stiffness along local z axis (normal) of 2D finite element is discussed " FEM - 2D finite element - rotational stiffness along local z axis (normal)".

Behaviour of coincidently positioned finite element nodes is discussed " FEM - connecting of FE nodes".

Expected differences between SCIA Engineer versions

New 2D element formulation in 21.1. patch 2

A new formulation of 2D finite element has been introduced since SCIA 21.1.2013 (internal release, hence for customers this is to be accounted since 21.1. patch 2). Different results while keeping the same mesh size are expected (and some differences in general as well). In order to obtain more comparable results between the performance of the older and newer 2D element formulation, finer mesh needs to be introduced since this change (approximately 2 times finer). New projects created since 21.1. patch 2 have the default mesh size already finer, but opening older project in newer version might result in some differences. An example of what kind of differences are expected is provided "FEM - expected differences - New 2D element formulation since 21.1. patch 2".

Neglecting the Moments of Inertia for beam elements since SCIA Engineer 24.0.

Since SCIA Engineer version 24.0, there is a change in the FEM solver. The Moments of inertia (mass inertia Imx, Imy and Imz) based on the self-weight of the beam members are neglected. In detail the description and some examples are provided " FEM - Neglecting of the moments of inertia of the beam members".

Reducing the types of eigenvalue solvers since SCIA Engineer 24.0.

Since SCIA Engineer version 24.0, these types of eigenvalue solvers have been removed: Subspace iteration, Iterative (ICGC), as no longer recommended by FEM. Lanczos and Polynomial are recommended to be used in general. More info " FEM - Types of eigenvalue solvers reduction".

Mass group based on self-weight load case - since SCIA Engineer 24.0.

Since SCIA Engineer version 24.0, the behaviour of the mass group based on self-weight has been changed. Before v 24.0, for each combination of mass group, the mass from self-weight of the structure was automatically considered in the background with multiplier 1.0, independent on the multiplier defined by the user within the content of the combination. Since SCIA Engineer v 24.0, the mass from self-weight respects the explicit user definitions, making it more transparent. More informations " FEM - Mass group based on self-weight load case".

Normalization of the direction vector for "general" direction within seismic LC - since SCIA Engineer 24.0.

Since SCIA Engineer version 24.0, there is a change in the FEM solver. In order to unify the approach for the direction vectors, all the user-defined direction vectors (for direction general) are normalized. Some examples are provided " FEM - Direction vector normalization - since SCIA Engineer 24.0".

Changes in rigid links and line rigid links - since SCIA Engineer 24.0.

Since SCIA Engineer version 24.0, due to certain change in the FEM solver, the behaviour or rigid links and line rigid links has changed, as explained in more detail " FEM - Changes in rigid links - since SCIA Engineer 24.0".

The nonlinear stability analysis has been reworked and improved - since SCIA Engineer 24.0.

Since SCIA Engineer version 24.0, the settings for nonlinear stability analysis have been reworked, due to switch to the new versions of FEM solver. The whole process is in detail explained " Nonlinear stability analysis (improvements since SCIA Engineer version 24.0)".

New features in SCIA Engineer versions

Use Lagrange Multipliers setting since SCIA Engineer v 24.0

A new global analysis setting found in the "advanced solver settings" is available since version 24.0, and is described " FEM - Multi Freedom Constraints (MFC) - Lagrange Multipliers".