Question 1
What is the difference between instancing a wall as an 'element_surface_plane' or an
'element_surface_complex' and using 'plane' for surface_definition?
Answer to Q1
An 'element_surface_plane' simply constrains the type of surface used to define the
element to be a plane. Any good toolkit will check any STEP physical file for rules such
as the WHERE Rule in the entity element_surface_plane.
There is of course, nothing to stop developers of CIS translators using a plane to
define an 'element_surface_complex'. However, the type of the surface will not be checked.
The two entities above show a construct that is common throughout LPM/5 and STEP
Application Protocols; that is, a generic construct is specialized through subtyping.
Here, we are following the logic that a 'plane' is a special case of a (generic)
'surface'. Similarly, a 'line' is a special case of a 'curve'.
In general, translators should implement the LPM at the most detailed level possible.
The most detailed information is contained in the lowest level subtypes.
Question 2
Must I have multiple analysis models for the same structure, or can a node
have more than one boundary condition?
Answer to Q2
No. At any given moment in time, a node may only have one boundary
condition. Think of a populated product model as a "snap shot",
capturing information at a given moment.
To model several different cases, use as many instances of analysis_model as
is required. The definition of a node must be unique within an analysis
model. However, several node in different analysis models may be in
the same position.
Question 3
How many nodes may the different surface elements
contain?
Answer to Q3
Surface elements may 'contain' (or rather - be defined by) any number of nodes. The
minimum number is 3 for a plane triangular element. There is no upper limit defined in
LPM/5.
Question 4
How does one associate multiple analytic models with a single design model?
Answer to Question 4
Use the entity analysis_model_mapping to relate an instance of analysis_model
to a set of one or more instances of assembly. (See page 107 of SCI-P-268)
Question 5
How does one associate different Load_Cases or Load_Combinations to a
design_part?
Answer to Question 5
There is no direct relationship between the entities design_part and
load_case, between design_part and loading_combination. However, you can
use the entity element_mapping to relate an instance of element to an
instance of part, design_part or located_part. Then apply the load to
the element. (See page 138 of SCI-P-268).
Alternatively, use the entity loaded_product to relate an instance of
applied_load to an instance of structural_frame_product (or one of its
subtypes). (See page 197 of SCI-P-268). Then use the design_part to
associate the part with its design_assembly.
Question 6
How do I set up multiple loading conditions with a design model, so
that I can generate multiple design models (and results) from them?
Answer to Q6
I would not recommend this approach. Design models are represented by
instances of assembly_design, and are composed of design_parts and
design_joint_systems. Forces may be applied directly to assemblies
through the entity loaded_product. Loading_combinations are applied to
analysis_models, and are made up of load_cases.
A loading_combination may be made up of any number of load_cases. A
load_case can be used in any number of loading_combinations. Thus we use
the intersection entity load_combination_occurrence. A load_case is made
up of a number of loads (which are either applied to nodes or to
elements.)
Question 7
What are examples of using
multiple analysis models? According
to LPM there is only one “root” analysis model with analysis_child
models. How would a frame
and a floor analysis models be written to the same file?
Answer to Question 7
LPM/5 shows that the entity 'analysis_model' has a subtype 'analysis_model_child'.
However, this does not mean that a CIS/2 data set (physical file) can
only hold one 'root' analysis model. Indeed, there can be many
instances of 'analysis_model', and any one of them can have any number
of child analysis models.
Thus, it is possible that a particular structure is represented by
several analysis models - each represented by an instance of 'analysis_model'
(or one of its subtypes). Each analysis model may be (but need not
be) distinct and separate. For example, a frame may be modelled
with pinned bases or fixed bases. In CIS/2 these would be
represented by 2 different instances of analysis_model. (Obviously, some
of the common characteristics such as the section profiles may be
reused.)
CIS/2 is flexible enough to allow the user to create simple models or
more complex models, reflecting the functionality of the application
software. When representing frames and floors, the simple approach would
be to create 2 distinct analysis models, each represented be an instance
of 'analysis_model' (or one of its subtypes). With more advanced
software, it is possible to represent the relationship between the 2
models using an instance of 'analysis_model_relationship'. One
could even go as far as defining a third analysis model which represents
the complete structure. The first 2 analysis models would then be
created as 'children' to the third.
Question 8
How is a loaded_product
used?
Answer to Question 8
'Loaded_product' is a generic construct that allows a load to
applied to a generic product. It does this by creating an association
between the two high level entities 'applied_load' and 'structural_frame_product'.
The load can be any force, displacement or pressure, while the product
could be an assembly, part, or structure. (See page 197 of
SCI-P-268).
Question 9
This is a question on representing element orientation as a vector.
What is the orientation vector for an inclined member with slope 30
degrees to the horizontal? Is it [0,0,1] ? The lines on page 125 and 130
of CIS 2 volume 4 states "That is, the direction of the re-oriented
local z-axis relative to the global coordinate system". If that is
correct then the vector will be [sin30,0,cos30]. This is the way we were
writing our model. But , we have been told that it is not correct. Could
you please let us know the correct way of representing it?
Answer to Question 9
The attribute element_orientation is concerned with the rotation of
the section profile around its own longitudinal (x) axis. It is the
equivalent of a 'Beta angle' used in many analytical programs. It does
NOT provide the location of the element in space. For example, for an
UNROTATED prismatic element the element_orientation = 0.0 (the
orientation vector = [0.0, 0.0, 1.0]. Note - as it is a 2-dimensional
transformation - 1 of the parameters will always be zero). The
definition of element_orientation uses a plane generated by the
projection of the local x-axis in the direction of the global Z axis.
Thus, consider the angle between this plane and the local z-axis.
The fact that the element is sloping is not at issue. This slope is
defined by the connecting nodes - not be element_orientation.
