seismic analysis in robot structural analysis professional
TRANSCRIPT
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Seismic Analysis in Robot Structural
Analysis Professional
Marius Jablonskis Senior Consultant BIM
Norconsult
In this session we will cover seismic design capabilities
that are included in Robot Structural Analysis
Professional software. We will explore seismic analysis
based on both lateral force and response spectrum
methods, settings, modeling, modal analysis, definition of
automatic design combinations considering static load
cases and dynamic combinations, and specific results for
the core walls and the building stories.
Class summary
At the end of this class, you will be able to:
Learn how to conduct modal analysis in Robot Structural Analysis
software
Explore the results of modal analysis in Robot Structural Analysis
software
Learn how to conduct seismic analysis in Robot Structural Analysis
software
Explore the results of seismic analysis in Robot Structural Analysis
software
Key learning objectives
About the Company
Norconsult is Norway's largest and one of the leading multidisciplinary
consultancy firms in the Nordic region. Our services are geared towards
community planning and design, and we have become a leading player both
nationally and internationally.
More than 50 Years of International Experience
10 000 Projects
2 900 Employees
82 Offices
11 Countries
Business areas
Architecture Buildings Environment Energy Industry
Oil and Gas Planning Risk Management Transport Water
Equivalent Lateral Force Method
The idea of equivalent lateral force method is to distribute part of the
seismic force (base shear) to every floor, which are able to transfer
lateral loads.
As a result of this method, the static forces are generated and
applied to rigid (or semi-rigid) diaphragms or vertical elements
(columns, wall), which can carry calculated forces.
Every code proposes specific limitations of using such method.
Most common limitations are structure regularity and its height.
Equivalent Lateral Force Method
Stories
Defining stories.
Seismic Analysis
Defining seismic analysis load case.
Seismic Analysis
Defining seismic analysis
Parameters.
If Precise Method of Defining
values of fundamental
periods is chosen, Modal
Analysis Parameters become
available.
Modal Analysis
Defining modal analysis parameters.
Load to Mass Conversion
Defining added masses manually
using Load Definition, or by converting
existing load cases to masses.
Code Combinations
Defining design combinations
(manual or automatic ones)
considering static load cases
and dynamic combinations.
Calculations
Running analysis.
Results
Exploring Results.
Live Presentation
Response Spectrum Method
For seismic analysis based on the response spectrum method, all
data is defined the same way as in modal analysis. Additionally,
parameters required by a specific national code to establish the
response spectrum shape must be specified.
Calculations and results are the same as those for spectral analysis.
Response Spectrum Method
Modal Analysis
Defining modal analysis load case.
Load to Mass Conversion
Defining added masses manually
using Load Definition, or by converting
existing load cases to masses.
Number of Modes
Defining appropriate number of modes.
Seismic Analysis
Defining seismic analysis load case.
Code Parameters
Defining code parameters.
Combination Sign
In case of using signed quadratic
combinations it will be necessary to
set main modes for each of directions.
Usually the main criterion to select
such modes is their contribution to
participation mass for given direction.
This contribution can be checked in
Dynamic Analysis Results with
appropriate columns added.
Code Combinations
Defining design combinations
(manual or automatic ones)
considering static load cases
and dynamic combinations.
Calculations
Running analysis.
Results
Exploring Results.
Live Presentation
Preferences Tips
Preferences
Preferences
Job Preferences
Job Preferences
Job Preferences
Modeling Tips
DXF and DWG Backgrounds
Floating comma
Round coordinates
addin
Meshing
In most of the cases, meshing
problems comes from inaccurate
geometry, so instead of changing
meshing options or refining it on
incoherent parts, fix the source of
the problem, which is geometry.
Meshing order (some/all slabs
first, before adjoining walls or vice
versa).
Recommended meshing options
as shown (keep it simple).
Elastic vs Rigid Supports
Elastic (spring) supports can
contribute to mass participation
(e.g. plate foundations).
E Modulus
To account for reduced E
modulus create new material.
During static/modal analysis,
Robot does not account for
reinforcement that was
calculated in design module.
Hollow Core Slabs
Linear Releases
Maximum number of linear releases = number of
panels meeting at the edge -1.
If bar located on such edge maximum number of
linear releases = number of panels meeting at the
edge (but it also depends on bar releases).
Analysis Tips
Mass Matrix Types
Consistent (consistent matrix always with
regard to the rotational degrees of freedom).
Lumped with rotations (diagonal matrix with
regard to rotational degrees of freedom).
Lumped without rotations (diagonal matrix
without rotational degrees of freedom).
Mass Matrix Types
If you use lumped masses, then mass is 'assigned' to
nodes existing in the structure. Adding intermediate
nodes along the bars increases the precision of the
solution.
If you use the consistent mass matrix the mass is
distributed along a bar element rather than assigned
to the nodes.
Active Mass Direction
You may need to deselect a direction when
performing the seismic analysis. If you deselect
the mass in the Z direction, for the modal analysis
that precedes the seismic case, it eliminates local
vertical vibration modes for floor slabs. In the
seismic analysis for such model you will consider
only transversal vibrations.
Mass Participation 90%
Enlarge number of modes.
Change mass matrix type.
Disregard mass direction.
Try Pseudo Modes.
Mass Participation 90%
When using pseudo modes,
Lanczos algorithms has to be used
as requires sequential addition of
new modes (only new are
calculated when the limit is not
reached without the need of
starting from the beginning with
increased number of modes).
Residual Mode
The aim of the residual mode
(pseudomode) option is to consider the
seismic analysis of the total structure mass
without increasing the number of calculated
vibration modes
Pseudomode determines an additional
vibration mode, which includes the missing
percentage of mass participation evaluated
on the basis of the previous vibration
modes
The Residual mode option works correctly only if the modal analysis, preceding
the seismic analysis case, uses the lumped mass matrix without rotations
Filters
Filters determine the number of modes to be
taken into account during dynamic analysis of
structures.
Mass Eccentricities
The tensional effect is taken
into account by adding mass
eccentricity.
You can do this as either
modal analysis parameters
(exact method) or seismic
analysis parameters
(simplified approach).
Instabilities
Type 1 - there is zero value element on the
diagonal of stiffness matrix.
Type 2 - there is zero value element on the
diagonal of inverted stiffness matrix.
Type 3 - some values of stiffness matrix
element are very disproportional.
Instabilities
The first, second and sometimes the third
type of the instability is usually caused by
mechanical instability of a structure.
The third type can also occur due to the fact
that there are big differences in section
profiles of some elements.
Required to have no instability at least type 1
and 2 to get Modal results.
Instabilities
Instabilities might be
reported in calculation
nodes, because of
linear releases, in other
cases on bars - due to
DSC algorithm.
Combinations
Combinations
Handy tool:
http://forums.autodesk.com/autodesk/attachments/autodesk/351/137
89/1/RMI_loadcomb_nested_with_subnatures.zip
Other great API’s:
http://forums.autodesk.com/t5/Robot-Structural-Analysis/useful-
addins-for-Robot-API/td-p/3899448
Results Tips
Torsion Effect
In order to avoid the torsion effect we have
to see in the current mass column a buildup
of at least 60% mass on one direction (X or
Y) in the first mod and the same on the
second mode (Y or X).
Core Walls
Group panels (walls) in
objects called core walls
allows to obtain results for
the reduced forces for each
story.
Base Shear
Take account of the base shear force: calculate it
according to the provisions of the seismic code or
specify it.
The base shear dialog is available for seismic analysis
parameters that use the following codes:
IBC 2009 (IBC 2012), IBC 2000 (IBC 2006)
UBC 97
Canadian NBC 2005, NBC 2010
Indian IS: 1893 - 2002
Australian AS 1170.4
New Zealand NZS 1170.5:2004
Base Shear
The base shear can be obtained as "Sum of
reac." or "Sum of forc."
"Sum of val." should not be used for this purpose because:
It is considering only supports currently filtered (displayed) in the table of
reactions.
Even if the filtering is displaying all supports the sequence of combinations
is incorrect because in such case first CQC combinations from all vibration
modes are calculated for individual supports and then they are all added
(linear combination). So the sequence of combinations (linear and CQC) is
opposite than for "Sum of reac." or "Sum of forc.".
Linear Reactions
Stories and Core Walls Results
Reduced Results for Panels
Panel Cuts Reduced Forces
When Using Reduced forces mesh size is important. By
default it gives values in section of half of the mesh size.
Diagrams for Buildings and Pseudostatic Forces
Calculation Notes
0 . 0 1 . 0 2 . 0 3 . 0 0 . 0
1 . 0
2 . 0
3 . 0
P e r io d ( s )
A c c e le r a t io n ( m / s ^ 2 )
Autodesk Robot Structural Analysis Professional
2015: Essentials
http://www.amazon.com/Autodesk-Robot-Structural-Analysis-Professional/dp/099151811X
Recap Questions
What methods can be used to conduct seismic analysis
in Robot?
What are most common limitations of equivalent lateral
force method?
What instability types have to be avoided during modal
analysis?
The End
*Actually, there are few more slides
*
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