STAAD FLOOR LOADS

[Hira Malik]

Not a regular user of STAAD and I m really confused by the floor loads. The floor is 3" thick RCC slab. How 2 different floor loads have been applied in dead loads as 50 and 122 psf? The pics are also attached. For 3" slab, shouldn't it be 150*3/12=37.5 psf.

[UmarMakhzumi]

Doesn't Staad consider self weight?

For 3" slab, the weight should be what you said.. are you checking/ vetting this model? If yes, then follow up with he design engineer.

Thanks.

[Hira Malik]

Yes I am checking the model. Thought maybe any of you guys know about the floor loads. Also went through the technical manual. didn't get any answer.

[EngrUzair]

On 4/13/2017 at 0:37 PM, Hira Malik said:

How 2 different floor loads have been applied in dead loads as 50 and 122 psf?

Floor loads may consist of several layers (slab itself, floor finish, ceiling plaster, weight of sand for sunken portion of slab to accommodate  bath/kitchen piping to be laid under normal floor, etc). These may have different load types (e.g., dead or live) as well. 

Moreover, it is practically possible that two adjacent portions of a floor slab have different load values. For example, if one portion of a slab is to be made thicker for creating a raised platform, dead load being carried by thicker slab portion will be higher and different from the one having normal / lower thickness.

All structural software (ETABS, SAP2000, etc.) have capabilities of applying above mentioned loads, through their basic commands & menu options. As such, STAAD surely has this capability too.

I have used STAAD in the past. As such, if you could attach text input file of your model, I might be able to help clear your doubts.

Regards.

Edited April 14, 2017 by EngrUzair
Rectified 2 minor grammatical omissions

[Ayesha]

11 hours ago, Hira Malik said:

Yes I am checking the model. Thought maybe any of you guys know about the floor loads. Also went through the technical manual. didn't get any answer.

Applied loads should be as per architectural drawings. If you are checking someone else work, normally the calculation provided will have a design criteria or load development  summary to provide information about loads assigned in different architecutral area.

 

[Hira Malik]

On 4/14/2017 at 10:26 PM, EngrUzair said:

Floor loads may consist of several layers (slab itself, floor finish, ceiling plaster, weight of sand for sunken portion of slab to accommodate  bath/kitchen piping to be laid under normal floor, etc). These may have different load types (e.g., dead or live) as well. 

Moreover, it is practically possible that two adjacent portions of a floor slab have different load values. For example, if one portion of a slab is to be made thicker for creating a raised platform, dead load being carried by thicker slab portion will be higher and different from the one having normal / lower thickness.

All structural software (ETABS, SAP2000, etc.) have capabilities of applying above mentioned loads, through their basic commands & menu options. As such, STAAD surely has this capability too.

I have used STAAD in the past. As such, if you could attach text input file of your model, I might be able to help clear your doubts.

Regards.

HERE IS THE INPUT FILE. THE LOADS DEFINED IN DL AS FLOOR LOADS CONFUSED ME. THE SLAB IS 3" THICK.

STAAD FILE.txt

[EngrUzair]

Quote

LOAD 3 LOADTYPE Dead  TITLE DL
SELFWEIGHT Y -1 LIST 1 TO 25
ONEWAY LOAD
YRANGE -10 0 ONE -50 XRANGE 0 20  ZRANGE 0 30  GY
YRANGE -10 0 ONE -122 XRANGE 0 20  ZRANGE 0 30  GY

1. Above is an extract from your attached STAAD Input file. The last two lines indicate that two different uniform dead load values have been applied to the same floor area (ranging from 0 to 20 ft in X direction and 0 to 30 ft in Z direction), which is illogical & most probably indicated by mistake. In actual situation, these two load values will be for two different floor areas, for which at least one of the XRANGE & ZRANGE values must be different.

2. Here are two different sample situations for elaborating correct application of given dead loads:

Situation A.   50 psf dead load for XRANGE from    0 to 10 ft and whole ZRANGE from 0 to 30 ft

                     122 psf dead load for XRANGE from  10 to 20 ft and whole ZRANGE from 0 to 30 ft

STAAD commands for this situation are as under:

YRANGE -10 0 ONE -50 XRANGE 0 10  ZRANGE 0 30  GY
YRANGE -10 0 ONE -122 XRANGE 10 20  ZRANGE 0 30  GY

 

Situation B.   50 psf dead load for whole XRANGE from   0 to 20 ft, but ZRANGE from 0 to 20 ft only

                     122 psf dead load for whole XRANGE from  0 to 20 ft, but for remaining ZRANGE from 20 to 30 ft

STAAD commands for this situation are as under:

YRANGE -10 0 ONE -50 XRANGE 0 20  ZRANGE 0 10  GY
YRANGE -10 0 ONE -122 XRANGE 0 20  ZRANGE 20 30  GY

3. Now, what should be the actual values of XRANGE & YRANGE in your case? This will be clear from the floor details, as given in architectural drawings. You may ask the original designer to explain how he/she arrived at the floor load values (and even the other loads & design parameters) used in the STAAD model, if you are still unable to understand their basis.

HTH

Regards.

[Hira Malik]

Thats a great explanation. Thanx a lot. But i am wondering as none of the XRANGE & ZRANGE values are different, is it possible that these are 2 different loads applied on same whole floor? Like one is weight of floor and other is that of some equipment or machine load? In that case the XRANGE & ZRANGE values will remain same. Or the floor loads only include the self-weight of the floor itself? Sorry for any stupid question as load defining is much easier in SAP2000 and ETABS.

[EngrUzair]

58 minutes ago, Hira Malik said:

i am wondering as none of the XRANGE & ZRANGE values are different, is it possible that these are 2 different loads applied on same whole floor? Like one is weight of floor and other is that of some equipment or machine load? In that case the XRANGE & ZRANGE values will remain same.

Yes. It is possible.

But you must make sure, either by confirming from the architectural drawings, or the designer. Because the software model must conform to actual loading requirements, as indicated in architectural plans & relevant loading code.

1 hour ago, Hira Malik said:

Or the floor loads only include the self-weight of the floor itself?

No.

Floor Load is a specific command, indicating two-way load distribution.

For one-way load distribution, STAAD uses ONEWAY command.

Self weight of members defined under MEMBER PROPERTY command is automatically calculated by the software, when SELFWEIGHT command is used (as shown in second line of the following quote).

On 4/17/2017 at 5:45 PM, EngrUzair said:

LOAD 3 LOADTYPE Dead  TITLE DL
SELFWEIGHT Y -1 LIST 1 TO 25
ONEWAY LOAD
YRANGE -10 0 ONE -50 XRANGE 0 20  ZRANGE 0 30  GY
YRANGE -10 0 ONE -122 XRANGE 0 20  ZRANGE 0 30  GY

Hopefully, it should be clear now.

Regards. 

[Hira Malik]

15 hours ago, EngrUzair said:

Yes. It is possible.

But you must make sure, either by confirming from the architectural drawings, or the designer. Because the software model must conform to actual loading requirements, as indicated in architectural plans & relevant loading code.

No.

Floor Load is a specific command, indicating two-way load distribution.

For one-way load distribution, STAAD uses ONEWAY command.

Self weight of members defined under MEMBER PROPERTY command is automatically calculated by the software, when SELFWEIGHT command is used (as shown in second line of the following quote).

Hopefully, it should be clear now.

Regards. 

Yes thanx alot. It was really helpful.