Modelling Options
Ruaumoko allows a wide range of modelling variables
to be utilized, which is one of the strengths of the program. A brief
description of each option is available below. If you select the modelling
title an additional information window will open.
Hystresis::
Over 40 hysteresis rules for modeling member behaviour are provided
in the Ruaumoko suite. Many of the rules allow for degradation
of the strength of the members. The Yield Forces or Yield Moments
may degrade as a function of the member ductility or the number of cycles
of inelastic action. This is independent of the stiffness degradation
associated with a hysteresis rule itself. There are, however, some hysteresis
rules that have their own built-in degradation of strength.
Mass:: The
mass of the structure is input in the form of weights and internally
converted by the program to mass units by dividing the weights by the
acceleration of gravity. The mass may be provided by both specified
nodal weights or by member weight/unit length or element material density.
Damping::There are several
damping options available. The traditional approach has been to use
a Rayleigh or Proportional model, Ruaumoko also incorporates the Caughey
and the Wilson & Penzien models, as well as specific translational
and rotational damping members.
Stiffness:: The program offers a number of ways of
describing member stiffness. Elements may be defined as one of the following:
All members are represented by a four-node definition, node I,
J, K and L. These are the four corner nodal points for the Quadrilateral
Finite Elements and the Masonry Panel Elements. For all other members,
which are line or one-dimensional elements, the first two nodes
I and J are the nodes by which the member is connected to in the
structure.
The second two nodes K and L, which are usually dummy nodes with
no displacement degrees of freedom, are used to define the inner
ends of rigid links connected to first two or outer nodes. The
deformable part of the member is that between the inner two nodes
K and L.
In Ruaumoko3D the line members use a 5th node, node M, or a global
coordinate direction i.e. +x, -x, +y, -y, +z or -z, to help define
the principal axis directions of the member’s cross-section.
The local z axis lies in the plane of nodes K,
L and M.
Loading:: Loads may be applied to the structure
in a number of ways including:
Analysis:: There
are several types of analysis available. These range from small displacement
analysis to evaluations that allow for P-delta effects. Options include:
- Static Analysis only
- Static Analysis and Frequency Analysis (mode
shapes and frequencies of free vibration)
- Static Analysis, Frequency
Analysis and Time-history Analysis
- Earthquake ground acceleration
input (relative displacement formulation or total displacement
formulation and traveling wave input.)
- Earthquake ground displacement
input
- Force history input (includes standard pushover analyses)
- Adaptive Pushover
- Cyclic Adaptive Pushover
Slaving:: To enable the modelling of rigid floor diaphragms and
coupling of degrees of freedom Ruaumoko allows the slaving of degrees
of freedom of one joint, or node, to be slaved to those of another
node in the structure. This removes the necessity of using very stiff
members in the model with the inherent risks of loss of precision
in the analysis. In Ruaumoko3D if the rotational degrees of two joints
are slaved then there is implicitly a coupling of the associated
translational degrees of freedom to model a rigid floor diaphragm.
