Response Spectrum Analysis in STAAD (Part 2) explanation Video
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- เผยแพร่เมื่อ 29 ส.ค. 2013
- civildigital.com/response-spec...
civildigital.com/?p=1963
STAAD utilizes the following procedure to generate the lateral seismic loads.
User provides the value for Z/2xI/R as factors for input spectrum
Program calculates time periods for first six modes or as specified by the user.
Program calculates Sa/g for each mode utilizing time period and damping for each mode.
The program calculates design horizontal acceleration spectrum Ak for different modes.
The program then calculates mode participation factor for different modes.
The peak lateral seismic force at each floor in each mode is calculated.
All response quantities for each mode are calculated.
The peak response quantities are then combined as per method (CQC or SRSS or ABS or TEN or CSM) as defined by the user to get the final results.
The design base shear VB (calculated from the Response Spectrum method) is compared with the base shear Vb (calculated by empirical formula for the fundamental time period).
If VB is less than Vb, all of the response quantities are multiplied by Vb /VB as per Clause 7.8.2.
How STAAD Calculates of Base Shear in RS Analysis
uThe base shear, for a given mode for a given direction, reported in the response spectrum analysis is obtained as
VB = X*Y*Z*D
where
X = Mass participation factor for that mode for that direction
Y = Total mass specified for that direction
Z = Spectral acceleration for that mode
D = direction factor specified in that load case
BMD for RS Load Case
The member forces are computed correctly only at the 2 ends of the member.
The sign of these forces cannot be determined because the method used to combine the contribution of modes cancels the signs.
Force values do not necessarily occur at the same instant of time.
STAAD plots a straight line joining the max. bending moment values at start and end joints of member, absolute (positive) values.
As per IS code you have to consider both directions, i.e, plan directions, To obtain design forces you have to create load combinations, considering both +ve and -ve effects. Please refer IS1893. To create these combinations in STAAD you can use load combination option or REPEAT load command in load list. To obtain the negative effect use the factor as -1. eg: DL+ EQ+X & DL + EQ-X
can you please tell me that how you have taken combination 1.1dead and live+1.3 earthquake load
Do you have videos done with CQC modal combination method sir..
Loving your great presentation and explanation
what happens when you consider the slabs in the building, you will have a center of gravity and center of torsion therefore you will have a torsion in the slab. Does the response spectrum consider this torsion? Could you explain how would you model and analysis a building with slabs, walls, beams and columns using a response spectrum. Thanks.
How y direction spectral displacement=0.5 and z direction spectral displacement=0.65 is coming?(6.03min in this video)?and how to apply combination rule in x ,y and z direction?
Please upload response spectrum analysis video along with modal generation steps for building resting on 50% slope.
Helpful video. (y)
Sir, I did analyze my structure(that contained shear wall) using Response spectrum method, following the steps in your video, it showed
"RESPONSE SPECTRUM COMPUTES JOINT DISPLACEMENTS THAT REPRESENTS MAXIMUM MAGNITUDE OF THE RESPONSE QUANTITY THAT IS LIKELY TO OCCUR DURING SEISMIC LOADING. ANY RESPONSE QUANTITY LIKE STORY DRIFT, TORSIONAL IRREGULARITY,ETC SHOULD BE CALCULATED FROM ACTUAL DISPLACEMENTS OF EACH MODE CONSIDERED DURING ANALYSIS.THE RESPONSE QUANTITY FROM EACH MODE SHOULD BE COMBINED USING MODAL COMBINATION TO GET THE MAXIMUM MAGNITUDE OF THAT RESPONSE QUANTITY."
What do I do now?
Please help.
is it necessary to combine SRSS in Z and Y direction with other load cases?
Sir please make a video on dynamic Analysis of Retaining wall
good video,
Hi, could you please tell how can we proceed using UBC code... as here we are not using IS code. Thanks in advance
Did Staad pro incorporated latest is codes 183-2016 and 13920-2016.
Yes it has incorporated but only in Staad.pro connect edition...u won't be able to find these latest revised codes in staad v8i.
staad connect edition is having all updated codes and user interface..
Load combinations as per is code not used?
Should we not ASSIGN
EQ +X
EQ _X
EQ Z
EQ -Z
should we not assign
Seismic Loading in + and -
X and Z direction in response spectrum method...?
We have only defined seismic definition