i have a symmetric structure with symmetric loads..
how does staad generate notional loads?
i used the notional load feature in staad.pro v8i release 20.07.05.15, the generated loads are not symmetric.. why?
below is the input file i used..
STAAD SPACEINPUT WIDTH 79UNIT METER KNJOINT COORDINATES 1 0 5 0 2 0 5 4 3 4 5 4 4 4 5 0 5 0 0 0 6 0 0 4 7 4 0 4 8 4 0 0 9 0 7 0 10 0 7 4 11 4 7 4 12 4 7 0 13 0 7 2 14 2 7 4 15 4 7 2 16 2 7 0MEMBER INCIDENCES 1 1 2 2 2 3 3 3 4 4 4 1 5 5 1 6 1 9 7 6 2 8 2 10 9 8 4 10 4 12 11 7 3 12 3 11 13 9 13 14 10 14 15 11 15 16 12 16 17 13 10 18 14 11 19 15 12 20 16 9 21 1 13 22 2 13 23 2 14 24 3 14 25 4 15 26 3 15 27 4 16 28 1 16DEFINE MATERIAL STARTISOTROPIC STEELE 2.05e+008POISSON 0.3DENSITY 76.8195ALPHA 1.2e-005DAMP 0.03END DEFINE MATERIALMEMBER PROPERTY AUSTRALIAN1 TO 4 13 TO 20 TABLE ST UB150X14.05 TO 12 TABLE ST UC100X14.821 TO 28 TABLE ST A75X75X5CONSTANTSMATERIAL STEEL ALLMEMBER TRUSS 21 TO 28MEMBER RELEASE1 TO 4 13 TO 16 START MY MZ1 TO 4 17 TO 20 END MY MZSUPPORTS5 TO 8 FIXED BUT MX MZLOAD 1 LOADTYPE Dead TITLE LOAD CASE 1JOINT LOAD13 TO 16 FY -1LOAD 2 NOTIONAL XNOTIONAL LOAD1 X 0.002LOAD 3 NOTIONAL ZNOTIONAL LOAD1 Z 0.002PERFORM ANALYSIS FINISH
The following is the answer to your question on how STAAD genertaes the notional load:
Answer :
1. Since notional loads are derived from gravity loads, the first step is in determining the lumped weight at the various nodes of the structure from the corresponding gravity loads. For example, when you declare the notional load as “1 X 0.002”, the program first generates the vertical weights (in the global Y direction) at all the nodes of the structure from the loading data you specified in case 1.
2. Once the nodal weights are obtained, those are then multiplied by the notional load factor, and the resulting value is applied along the direction that you want the notional load to act in. In this example, the vertical weights lumped at the nodes are multiplied by 0.002, and the results are then applied at the same respective locations along the global X direction.
If you want to obtain a report of the notional loads that the program generates, use the PRINT LOAD DATA option with your analysis command. For example,
PERFORM DIRECT ANALYSIS PRINT LOAD DATA
I notice that you are using version 20.07.05.15. I would suggest you to use the latest 20.07.06.34, which has some corrections regarding the Direct Analysis.
Sudip Narayan Choudhury
Use PERFORM ANALYSIS Print Static Loads to see the joint effective loads; these are symmetric. However the results are not symmetric because the cross sections are not aligned symmetrically. This would not matter if Iy and Iz were equal, but they are not.
I WILL LIKE TO GET CLARIFICATION. WHETHER NOTIONAL LOAD IS 2% OR 0.2%.
As per my vague rememberance it is somewhere between 1.5 and 2%.The file posted by Mr Magat speaks for 0.2%. Is it ok?
0.2% as per Appendix 7 of AISC 360-05