Live Load in Office

[bookowski]

I am trying to figure out the logic behind a 50psf uniform live load for an office, and how this accounts for larger concentrated loads.

I have an existing office space, mid-60's steel frame with slab on deck. I do not have any structural drawings or info other than measuring beams, and the access is limited even for that.

The question from the client is how many fire-safe file cabinets they can move into an area safely. Without getting into a lot of destructive probing and testing I am trying to come up with a reasonable answer. Each cabinet is 900lbs and works out to about 200psf directly below the cabinet.

I would guess that the 50psf loading is intended to account for some lower uniform loading mixed in with concentrated loads or areas of higher loading. I have read the commentary to ASCE7 but it has not shed any light on this.

With the current layout they are looking at it would work out to a blended average load of about 65psf in the affected beams (other areas are unaffected, so columns would see minimal increase). Maybe a bit high... but what if it was 60? 55? Not looking for a black and white answer - just curious what people would be comfortable with.

The ASCE commentary has some intersting info on surveys of actual live loads. For offices it looks like they had mean of about 10psf steady and 8psf transient, so less than 20psf mean live load for offices.

 

[woodman88]

This is from this link

http://www.spacefile.com/ad/loading.html

“The Load is an Average Value
The requirement to design a floor for a uniform load of 50 PSF over the entire tributary area for a particular member does not mean that this is the largest load that can be placed on the floor.
The load is an average value for a typical office space with desks, filing cabinets, aisles, etc. As can be seen by the concentrated load requirement, the 2,000 pounds in 6.25 square feet (2 ½ x 2 ½ ft) is a load of 320 PSF. This high loading assumes that the area around the concentrated load is unloaded. This would occur if the heavy object was surrounded by aisle space. Each loading condition must be reviewed individually.
The typical floor load for high density filing is 250 PSF. This is greater than the 50 PSF uniform design load. Since the design load is assumed over every square foot of floor area, including aisles, the floor is not overloaded if there is four square feet of aisle area for each square foot of file storage floor area. This statement is a simplification of the issue and cannot be used as a basis of approval for every high density storage application.
Each installation must be considered as a separate case. To avoid the danger of overloading the floor, the approximate weight of the system and the materials to be stored should be calculated and evaluated individually by a licensed architect or engineer.”


and from this link

http://www.bgstructuralengineering.com/BGASCE7/BGASCE7005/index.htm

“Certain occupancies, such as office space, have the potential for a larger concentrated load (such as a large copy machine) being located in a space.  This space may also be designed for uniformly distributed loads, but it is not probable that both the uniformly distributed load and the large concentrated load will occupy the space at the same time.  Consequently the space must be designed to accommodate, separately, the uniformly distributed load and the point load, with the point load being moved around the space so as to cause maximum effect on the supporting elements.  ASCE 7-05 Table 4-1 lists the specified concentrated loads that are associated with with occupancies where the concentrated loads are likely to occur. “

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.