live load reduction

Hi,
I'm designing a 4 stories condo's and i would like to find out how the live load reduction apply's too what i'm doing for the column, beams and wall loading.


PS. any one have any tips on Inverse T beams designs.


thanks,
altec

Consult your local building code or ASCE 7-98. They all have provisions and formulas to compute live load reduction. For certain loadings, LL reduction is not applicable.

What I am trying to say, Read the code.

i agree to lutfi i m not sure if u can really reduce the live load just for four stories.if allowed in ur code than u have to see the load combinations under which the reduction is permitted.i think for dynamic analysis this reduction is not existing

ARIF ALI SIDDIQUI
STRUCTURAL DESIGN ENGINEER
IMCC 8 JANTAR MANTAR MARG
NEW DELHI INDIA

Most codes only allow the reduction of floor loads in commercial establishments and in common areas of multiple tenant residential above the SECOND floor. The floor load for the residential unit itself should not be reduced at all, but areas such as common corridors, common meeting places, common balconies etc, that have historically required upwards of 100#PSF LL are able to be reduced when they are not the ground floor. I will note however that in recent years we have all heard of crashes where balconies and walking bridges collapsed because of undue stress and many engineers are erring on the side of caution, taking care not to seal off on the next catostophic event.

Thanks for the info.

ASCE 7 allows for two or more transient live loads to be reduced by 0.75, with no reduction in live load.  For example D+L+S can be considered as D+0.75(L+S).  It is important to consider the effects of load duration when using these combinations if you are designing with timber.  What you'll find is that members supporting two floors and roof usually don't need to be designed for roof loads at all, if the roof load is relatively light.  This may seem counterintuitive, but is perfectly consistent with the stochastic basis of the uniform loads in ASCE 7 and provides for more uniformity between ASD and LRDF design.  

For multiple stories of live load ASCE 7 does not provide clear guidance, however HUD has published some intresting 'Residential Construction Design Guide' and 'Structural Design Loads for One- and Two-Family Dwellings' which provide intresting perspective on load combinations and reductions.  It provides a floor LL reduction equation developed for residential floors.  It also recommends greater load combination reductions and presents the load combination of D+L1+0.7(L2+L3+...), where L1 is the story for which members are being designed and L2, L3 are the live loads imposed by floors above.