Civil Engineering Reference
In-Depth Information
present theoretically correct solutions for the structure, but to present a consis-
tent strength estimate based on the engineer
'
s specifications.
This implies that the structure analysis software should be able to represent
different failure criteria for different structural elements as specified by different
codes of practice.
Instead of modeling the structure out of purely geometric considerations, the
modeling must consider the analysis tool that will be used for the nonlinear
analysis, and the mathematical formulation that is embedded within the pro-
gram. Some nonlinear analysis programs have built-in features for calibrating
component failure modes to specific criteria. For other programs, the engineer
must give special consideration during the modeling of the structure in order to
make the program represent the required failure modes or limiting criteria.
Which consideration to take depends on the component as member, joint or
foundation and on the mathematical formulation.
If there is any doubt about the FE formulation, a simple model should be
subjected to a well-defined load and deformation path. This will allow the
results to be judged and calibrated against engineering practice.
This discussion gives a set of modeling recommendations to help make the
nonlinear analysis tool produce reliable results that conform to recognized fail-
ure criteria and design formulations.
Frame Modeling
In frame modeling, the space frame model should describe the three-
dimensional geometry of the platform.
The model for ultimate strength assessment can usually be significantly
simpler than models required for design and fatigue analysis. The primary
framework essential in maintaining overall integrity of the structure for the
in-place condition must be included in the structural model. Secondary struc-
tures and members generating dead loads and/or environmental loading need
only be represented in sufficient detail to introduce the relevant loads on the
primary structure.
The analytical models should consist primarily of beam elements. The struc-
tural members of the framework may be modeled using one or more beam ele-
ments for each span between the nodes of the model of the framework.
Primary Framework
The primary framework of the structure comprises those members that provide
the stiffness and strength of the structures; these are usually the legs, the piles,
the vertical diagonal members and the main plan frame bracing members.
Secondary Framework
The secondary framework consists of members that don
t contribute to the
global stiffness and strength of the framework. In general, their structural
'
Search WWH ::
Custom Search