Thursday, March 30, 2017

Manual checking of Staadpro output


Correct assessment of loads both dead and live loads are important since excessive assumed loads may lead to uneconomical member sizes and footing sizes. Also excessive loads will be adding more weight in the case of seismic forces.
In order to have equilibrium i.e .ΣV=0 under the Load case DEAD LOAD calculate the total dead load on all floor slabs and check it against the output by the program.


Using a single support for the whole structure RUN the ANALYSIS and find out the total support reaction in Y axis i.e FY from the output of the program. Check whether the above two values are in agreement to the manually calculated values. If the results vary then there is some error or mistake took place while entering the input.
The same procedure can be carried out for the LIVE LOAD for both FLOOR LIVE LOAD and ROOF LIVE LOAD cases also.
If the single support is not considered or modeled then use all the supports and copy the values of Fy to EXCEL and get the sum of the FY and check whether it tallies with the manually calculated values.


To find the point load FX or FZ at a joint as nodal wind force calculate the tributary area for the corresponding node and multiply it with the intensity of loading.
For example:
Area = (h1+h2)/2*(L1+L2)/2* intensity of loading.
Please note that the consistence unit shall be used.
Where h1 and h2 are the height above and below the joint in meters and L1 and L2 are the width of the bay on either side of the node in meter units.
If      h1 =4.0m
and h2=3.0m,
and L2=6.0m
then the tributary area for the node is
=(4+3)/2*(5+6)/2 = 19.25sq.m.
Using an intensity of 1KN/sq.m the nodal force shall be =19.25 KN.
This can be verified with the values generated by the program.


Usually while modeling a structure either FIXED or HINGED support condition is proposed. If the support condition is FIXED the there shall be six restraints i.s. FX,FY ,FZ, Mx, My and Mz
For HINGED there shall be no moments. In order to account for the soil spring the modulus of subgrade reaction Ks has to be considered for the support condition.
Ref:  by T.Rangarajan

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