Upload
jonathan-wardrop
View
231
Download
0
Embed Size (px)
Citation preview
8/22/2019 Seismic Analysis Using Robot Software
1/30
SEISMIC ANALYSIS USING ROBOT SOFTWARE
The following report contains direction guidelines about how to performseismic analysis (modal response spectrum analysis) using ROBOT software.
A simple 3-D structure was used containing only 30x30cm RC columns and
300mm thick RC slabs. C40 concrete was used for all the elements.
This process is indicative and can be generalised in order to carry out seismic
analysis for any kind of structures.
It can also be used as a general guideline for seismic analysis irrelevant to the
software used, just by using the same commands on the desired software.
8/22/2019 Seismic Analysis Using Robot Software
2/30
MODAL ANALYSIS
8/22/2019 Seismic Analysis Using Robot Software
3/30
Select "New" to create a
new Analysis Case
8/22/2019 Seismic Analysis Using Robot Software
4/30
Select "Modal" as type
8/22/2019 Seismic Analysis Using Robot Software
5/30
Select the desired number of modes (depending on
the type and the complexity of the structure).
Select the mass matrix type. In principle, consistent
mass matrix gives more accurate results and should
be used. When lumped mass matrix is used, a
portion of the structure's mass is allocated to thesupports and therefore not taken into account for
seismic calculations since the nodes at the supports
have no seismic degrees of freedom (see following
pages for illustration).
Select the desired active mass directions.
In principle all directions are active mass directions but sometimes it may be
desired to check specific directions only. For instance:
-When modelling a strip (eg. 1m wide) of a structure we are not interested in the
out of plane mass direction and it should not be selected.
-The vertical (Z) mass direction can generally be neglected, unless there is a
specific interest in looking into effects such as uplift of pre-cast slabs. When the
vertical mass direction is active it will give vertical modes which can be disturbing,
especially when slabs are not held by columns for long distances and so they are
free to oscilate vertically.
However these modes have almost zero impact on the results (assuming that the
vertical translation is not of interest) since their effective modal mass is only activeon the vertical direction.
See next page for advanced parameters.
8/22/2019 Seismic Analysis Using Robot Software
6/30
By selecting "Advanced parameters" there are a couple of more
options available.
Probably the most useful is the option of setting an analysis limit
based on the percent of mass participation. Most codes only require
90% mass participation (participating mass/total mass).
This option can be useful, or save some calculation time when the
number of modes can not be foreseen. ROBOT will only use as
many modes required to get 90% participating modal mass for each
active mass direction.
It should be noted that ROBOT will only use up to the number of
modes defined by the user. It may be required to increase thisnumber in order to get 90% participating modal mass in all active
mass directions.
The analyses hereafter were run with
this limit set as Inactive
8/22/2019 Seismic Analysis Using Robot Software
7/30
After running the analysis, select Modal analysis relults.
8/22/2019 Seismic Analysis Using Robot Software
8/30
It can be observed that because the stiffness of this structure is
symmetrical (square columns and equal spans at both directions)
we get flexural modes with equal period/frequency.
Eg, mode 1 (flexural, x direction) has a period of 0.37sec, same as
mode 2 (flexural, y direction).
See following pages for modes illustration.
Note the difference between the total mass here and on the
following page. In this analysis half of the ground floor columns
mass is lumped at the supports, therefore being inactive seismically.
Analysis run with
Lumped mass matrix
8/22/2019 Seismic Analysis Using Robot Software
9/30
Analysis run with
Consistent mass
matrix
Note that the total mass is equal to the total weight of the structure
(see next page) divided by the gravity acceleration.
Cumulative Participating modal mass for each direction.Modes with zero
participating translational
modal mass are torsional
modes.
8/22/2019 Seismic Analysis Using Robot Software
10/30
Total weight
8/22/2019 Seismic Analysis Using Robot Software
11/30
Select display-maps-deformation-active to
display the modes.
8/22/2019 Seismic Analysis Using Robot Software
12/30
Mode 1 - flexural - x direction.
8/22/2019 Seismic Analysis Using Robot Software
13/30
Mode 2 - flexural - y direction.
8/22/2019 Seismic Analysis Using Robot Software
14/30
Mode 3 - torsional.
8/22/2019 Seismic Analysis Using Robot Software
15/30
Mode 4 - flexural - x direction.
8/22/2019 Seismic Analysis Using Robot Software
16/30
Mode 7 - vertical mode.
8/22/2019 Seismic Analysis Using Robot Software
17/30
MODAL ANALYSIS USING ADDITIONAL LOADS
8/22/2019 Seismic Analysis Using Robot Software
18/30
Define a new load case for
the load that should be used
as additional seismic mass
(for instance backfill).
8/22/2019 Seismic Analysis Using Robot Software
19/30
Go to Analysis - Analysis Type and select
the tab "load to mass conversion"
8/22/2019 Seismic Analysis Using Robot Software
20/30
Select the desired case to convert and assign any
coefficient (for instance 50% of the load).
Assign mass direction with the same principle as
when defining the modal case.
Click add.
8/22/2019 Seismic Analysis Using Robot Software
21/30
Modal analysis results.
Note the total mass is now the sum of DL plus the
roof load.
8/22/2019 Seismic Analysis Using Robot Software
22/30
MODAL RESPONSE SPECTRUM ANALYSIS (ASCE7-10)
8/22/2019 Seismic Analysis Using Robot Software
23/30
Select tools-job preferences
8/22/2019 Seismic Analysis Using Robot Software
24/30
Go to design codes and select"more codes"
8/22/2019 Seismic Analysis Using Robot Software
25/30
Under "seismic loads" choose
the desired code and add it (forthis case IBC 2006)
8/22/2019 Seismic Analysis Using Robot Software
26/30
Go to analysis types-new and
select "seismic" and the newly
defined code.
8/22/2019 Seismic Analysis Using Robot Software
27/30
Define the parameters according to the desing code.
Here the analysis is according to ASCE7-10, using site class
C, S1=0.2g, Ss=0.47g, TL=8sec, R=4 and I=1.25 (note: be
careful between S1-Sd1 and Ss-Sds when using ASCE).
See next page for direction.
8/22/2019 Seismic Analysis Using Robot Software
28/30
By default ROBOT will apply the earthquake to all 3
directions (not simultaneously).
If one direction (eg. Z) is set to zero then ROBOT will not
apply the earthquake to this direction.
8/22/2019 Seismic Analysis Using Robot Software
29/30
Automatically 2 components of the earthquake analysis
were created (no component for Z since it was set to 0 in
the previous step).
8/22/2019 Seismic Analysis Using Robot Software
30/30
The tab combination sign allows for definition of the
positive sign of each seismic case (if desired to define
one), as well as the combination rule used for the
directions of the motion (if excitation is applied at different
direction during the same case or combination)