A problem about the note *** NOTE: THE TOTAL WEIGHT OF THE STRUCTURE CONSIDERED FOR BASE SHEAR
CALCULATION ALONG GLOBAL Z DIRECTION IS NEGLIGIBLE.

Question

Dear Members, 
 Please help me to learn about the problem BASE SHEAR CALCULATION ALONG GLOBAL Z DIRECTION IS NEGLIGIBLE. 
 I mention the brief information about my model as follows in pewit to point:......... 
 01) I create RC model in V8i SS6. 
 02) The frame of model is not fully orthogonal in X and Z axes. 
 03) Use Reference Load type Mass without -ve sign, Rigid Floor Diaphragm, UBC-94 Seismic definition 
 04) Provide Seismic weight by Reference Loads in X, Y. and Z directions with the factor 1 for DL and 0.5 for LL 
 05) I try to find out, a) Soft Story as per ASCE7, b) Story Shear c) Story Drift with Limit L/250 
 06) I provide Static Seismic Analysis. 
 My confusions in this model are........... 
 A). Why the Base shear calculation along Global Z direction is negligible? 
 B). Why the Story Shear is missing? 
 C).Am I right in the case of soft story checking? 
 Please, help to know me also, which are the out of my questions but helpful. 
 NB: For more information, I attached my STAAD file here. STR_RE-05_07_Frame.std 
 Thanks

Sye · Accepted Answer

You mentioned about having floor diaphragms, reference loads in your points 3 and 4 but I do not see these in the model you attached. Softstory check as per ASCE can only be carried out if floor diaphragms are defined. The base shear in Z is comparable with that in X for the model you attached. Story shear is missing as you do not have the PRINT LOAD DATA with the PEEFORM ANALYSIS command. So basically use PERFORM ANALYSIS PRINT LOAD DATA instead of just PEERFORM ANALYSIS and you should have the Story shears reported in the analysis output file. To get Story Drift you need to add PRINT STORY DRIFT command. So here is what you can use 
 &hellip; 
 PERFORM ANALYSIS PRINT LOAD DATA 
 PRINT STORY DRIFT 0.004 
 ...

Sye · Answer

I did not see any generated seismic loads applied in your cases 1 to 4. As part of these cases, you have only specified reference loads. There has to be a UBC load applied to get the software to do the seismic load generation. For example as part of your load case 1 you have specified 
 
LOAD 1 LOADTYPE Seismic TITLE EQ +VE X 
REFERENCE LOAD 
R1 1.0 R2 1.0 R3 1.0 R4 1.0 
PERFORM ANALYSIS 
CHANGE 
 
You should instead specify 
 
LOAD 1 LOADTYPE Seismic TITLE EQ +VE X 
UBC LOAD X 1 
PERFORM ANALYSIS 
CHANGE 
 
You do not need to add the reference loads again as part of the seismic load case. Similar changes need to be made to the other seismic cases as well. 
 
Also for equivalent static seismic load generation, you do not need to specify seismic weights in X and Z within the Seismic definition. Specifying these in Y is good enough. So you may take out the ones in X and Z as shown next 
 
DEFINE UBC LOAD 
ZONE 0.15 I 1 RWX 8 RWZ 8 CT 0.073 PX 1.072 PZ 1.072 S 1.5 
REFERENCE LOAD Y 
R1 1.0 R2 1.0 R3 1.0 R4 1.0 R5 1.0 R6 0.5 R7 0.25 R8 0.5 
*REFERENCE LOAD Z 
*R1 1.0 R2 1.0 R3 1.0 R4 1.0 R5 1.0 R6 0.5 R7 0.25 R8 0.5 
*REFERENCE LOAD X 
*R1 1.0 R2 1.0 R3 1.0 R4 1.0 R5 1.0 R6 0.5 R7 0.25 R8 0.5 
 
I think I already answered your other queries in my last post.

A problem about the note *** NOTE: THE TOTAL WEIGHT OF THE STRUCTURE CONSIDERED FOR BASE SHEAR CALCULATION ALONG GLOBAL Z DIRECTION IS NEGLIGIBLE.