UBC live load reduction for seismic load.

[erginc]

I am new to the forum so hi to all.

Here is my first question. We are designing some office buildings using UBC. I am new to UBC. In our own seismic design code in Turkey, we have a factor for reducing live load contribution to the seismic weight . For office building it is n=0,3.

So for an office seismic weight is calculated as,
W=D+n*L

But UBC 1997 in Section 1630.1.1, W is the total dead load and applicable other loads listed in 4 items.

From this I understood that for only storage areas I need to include live load for 25% but for office use, live load contribution is zero to seismic weight.

I would like to be sure if my interpretation is correct.

Thanks...

 

[WillisV]

Your interpretation is correct. Note that is the MINIMUM seismic weight - you are free to use some of the live load at your discretion.

 

[OldPaperMaker]

Sukolik,

Since the last version of the UBC was published in 1997 I am a bit fuzzy on the specifics of what was included in the Effective Seismic Weight of a structure.

But, the in ASCE 7-05, which is referred to in the 2006 IBC, directs that the effective seismic weight shall include the total dead load and "other loads listed below".

In Section 12.7, Modeling Criteria, 12.7.2 one of those "other loads" is "#2 Where provisions for partitions is required in the floor load design, the actual partition weight or a minimum weight of 10 psf (0.48 kN/m2) of floor area, which ever is greater."

As I noted above, I really don't remember if the 97 UBC had a similar directive.

 

[erginc]

Thanks WillisV. I was quite unsure due to the big difference between two codes. The reason we are using UBC is new Jordanian code is taken from UBC and revised a bit to fit local requirement. So I will advice customer for his directions in case their code differs in this matter.


OldPaperMaker, they look same. Actually there is item one as below,
1. In storage and warehouse occupancies, a minimum of 25 percent of the floor live load shall be applicable.

But this only tells us about storage type buildings. For office use, UBC does not state any live load contribution to seismic weight. That’s where I was stuck. I felt uncomfortable with zero live load as Turkish code requires min 30% for office. For storage it more demanding goes to 80%.

 

[msquared48]

You also have snow in Turkey, and the UBC required a certain percentage of any snow load over 30 psf to be included in the seismic calcs too.

Mike McCann
MMC Engineering

 

[erginc]

Hi msquared48, thanks for the comment.

Yes we do snow in Tukey. But project is in Amman and snow load is given by the customer is 125kg/m^2 which is less than ~150kg/m^2 (1.44kN/m^2).

 

[weab]

Sukolik,

Just to be clear, the idea is that most live loads are people and items that are not bolted to or integral with the building. During an earthquake, these thing will not move with the building.

Any unusual items which may be bolted down or otherwise attached to the building structure will move with the building during an earthquake. These items should be included in W.

 

[erginc]

jsdpe25684,

I agree with you. We have added items connected to the structure to dead load. However, for minimum live loads which are taken from UBC table 16-A, in my opinion, are not attached to the building completely. Friction between floor system and item is the only means of transfer for horizontal force. Therefore, should be reduced in seismic weight calculation. Yet it is clear in UBC for storage type usage it not clear for office use, or residencial use. It looks like it is left to designers discretion.

Thanks...