UBC 97 load combination

[perfectaccess]

I am revising design report.
it is professional one I think, but the load combination is not similar to you ubc97 ,although he is telling that combination is form ubc 97
see attached ubc 97 load combination form report.

 

[perfectaccess]

especially wind load factor (i do understand that 1.2+0.12 D and 0.9-0.12 D for earthquake case)

 

[perfectaccess]

up

 

[joncle10]

it is correct. The earthquake is divided into horizontal and vertical component. the vertical component is 0.5xCa and should be added to the effect of dead load. so u add it to the 1.2DL to have 1.32DL (Ca i guess is 0.24 in your case).
For the 0.9DL, you subtract since the vertical earthquake effect can be positve or negative.

 

[perfectaccess]

thank you,

i mentioned that earthquake portion is fine( i agree with)
but why wind load factor is different.

am i missing something?

 

[joncle10]

sorry. i did not read correctly your thread.
According to UBC combinations, the load factor for the wind is 1.3 not 1.6.
It became 1.6 in the ASCE where a directionality factor has been introduced.

 

[perfectaccess]

Thank you

in ASCE 2005 THE Factor is 1 , but in ASCE 2010 THE Factor is 1.6(as mentioned in ACI 318-11,COMMENTARY)
But ubc is still 1.3.

any further comment on this guys

 

[JAE]

Older UBC (and ASCE 7) versions used a wind speed based on a "fastest mile" reading and the wind factor was 1.3.

In the IBC (and later ASCE 7 versions like 7-05) they changed to a "3 second gust" wind speed and included a separate directionality factor (per joncle10 above). This changed the wind factor to 1.6.

In the later version of ASCE 7-10, wind was revised again to be "3 second gust" but with the importance factor included in the wind speed along with the fact that ultimate values of wind speed were then used, reducing the load factor to 1.0.

So the proper wind load factor to use depends very much on the particular code you are using.


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