Hello everyone,
I'm trying to understand the Seismic Loads using SRA in STAAD.
The Code Goes:
STAAD SPACESTART JOB INFORMATIONENGINEER DATE 28-Jul-16END JOB INFORMATIONINPUT WIDTH 79UNIT METER KNJOINT COORDINATES1 0 0 02 0 5 03 5 0 04 5 5 0MEMBER INCIDENCES1 1 22 3 43 2 4DEFINE MATERIAL STARTISOTROPIC STEELE 2.05e+008POISSON 0.3DENSITY 76.8195ALPHA 1.2e-005DAMP 0.03TYPE STEELSTRENGTH FY 253200 FU 407800 RY 1.5 RT 1.2END DEFINE MATERIALMEMBER PROPERTY AMERICAN1 TO 3 TABLE ST W10X30*1 TABLE ST W8X15CONSTANTSMATERIAL STEEL ALLSUPPORTS1 3 FIXEDDEFINE UBC LOADZONE 0.075 I 1 RWX 3 RWZ 3 STYP 1 NA 1 NV 1SELFWEIGHT -1 LOAD 1 LOADTYPE Seismic TITLE LOAD CASE 1UBC LOAD X -1LOAD 2 LOADTYPE Seismic TITLE LOAD CASE 2UBC LOAD X 1LOAD 3 LOADTYPE Dead TITLE LOAD CASE 3SELFWEIGHT Y -1 LOAD 4 LOADTYPE Seismic TITLE EZ AUTO RESPONSE SPECTRUMSELFWEIGHT Y 1 SELFWEIGHT X 1 SELFWEIGHT Z 1 SPECTRUM SRSS X -1 ACC SCALE 9.8 DAMP 0.0350 0.1188; 0.1 0.2931; 0.45 0.2931; 1.2 0.1178; 2 0.0733; 2.8 0.0623;3.6 0.0575; 4.4 0.0527; 5.2 0.0478; 6 0.043;LOAD COMBINATION 114 -1.0 PERFORM ANALYSISFINISH
The thing is on Load Combination 11, i wanted to get a value of the EQ Load opposite the direction of Load 4,but it just simply negated the resultant values
I also tried Changing the X Factor from 1 to -1 in the spectrum but to no avail. How can I make Seismic Load opposite the direction of Load 4.
I'm using SS4.
Thank you,Regards.
The response spectrum loading represents seismic acceleration applied at the base of the structure and this dynamic loading would vibrate the structure in both directions. The nature of RSA is such that the responses are all absolute maximum responses. So you don’t need to apply it in the positive and negative direction as you would typically do for a static seismic case. You should rather define two combination loads to combine these with the gravity loads as shown below
LOAD COMB 100 DL + EL
3 1.0 4 1.0
LOAD COMB 101 DL - EL
3 1.0 4 -1.0
That was my initial assumption too. But applying a negative factor for the Seismic L/C in the Load Comb only negates the results of the Seismic L/C, I'd expect that the Load Comb 100's deflection would just be the opposite direction of Load Comb 101's Deflection along the X-Axis, but no, it also negated the deflection of the horizontal beam, I know I just could use the negative Y reaction in Load Comb 101 and pair it with Load Comb 100 to provide the tension-compression couple forces, but my real problem is this... What if the frame of my structure is assymetrical? and Locating the Point of Rotation of the structure would be difficult, How would I know which column would be in tension, and which would be in compression? Also I've tried Modeling a simple frame with induced failure in the member to have a predictable outcome, and the result was not as I expected, if you change one column to a smaller section, you'd expect the structure to deflect that way, but that was not the case, the deflection would always go to the positive X-axis regardless which column was smaller.
Hi I too have the same question. Any update in your query??