Live Load Reduction for Bearing Walls 1

[strucguy]

Is live load reduction permitted in case of Bearing Walls? If yes, what is the approach?

 

[BAretired]

In the Canadian Code, live load reduction is based on the area supported. If you consider the bearing wall capable of spanning a certain distance between piles or footings, you are entitled to a live load reduction based on the tributary width times the distance the bearing wall can span. Otherwise, don't reduce the load.

BA

 

[strucguy]

That makes sense. Thanks, BAretired. But, I am looking for the approach that needs to be followed per IBC.

 

[KBVT]

I have always factored loads on an interior wall in the same manner as an interior beam. Exterior wall = edge beam. Use K LL factors in accordance with Table 4-2 of ASCE 7.

 

[strucguy]

KBVT, I agree with you on the value of K factor live load reduction. But, how is one supposted to determine the tributary area? Remember, it's a long continuous wall I am talking about. Nothing is mentioned about this in the code. Until now I was assuming 1/3 of the unsupported height of the wall as the tributary width. But, not sure if that's the correct approach. Appreciate if other can pour in their comments. Thanks in advance.

 

[JAE]

structguy - take a look at ASCE 7-05, section 4.8.5 and the corresponding commentary. This is specifically for one-way slabs but I think the principle is similar for one-way walls. A wall is simply a slab on its end right?

In this section they limit the trib. area At to span x 1.5(span).

 

[cap4000]

Taken from NYC Code. Take a look at section(d) for walls.

Link for Code.

http://www.ci.nyc.ny.us/html/dob//downloads/bldgs_code/bc27s11.pdf

ARTICLE 4 LIVE LOAD REDUCTION
§[C26-903.1] 27-565 Roof loads. –
No reduction shall be permitted.
§[C26-903.2] 27-566 Floor live loads. –
The uniform live load to be used for design shall be the
basic value established in reference standard RS 9-2
multiplied by the percentages given in subdivisions (a)
through (d) of this section.
(a) Except as provided in subdivisions (b), (c), and
(d) the percentages in table 9-1 shall apply. Contributory areas
shall be computed in accordance with section 27-567 of
this article.
(b) No live load reduction shall be permitted for the
following: members and connections (other than columns,
piers, and walls) supporting floor areas used for storage
(including warehouses, library stacks, and record
storage); areas used for parking of vehicles; and areas
used as place of assembly, for manufacturing, and for
retail or wholesale sales. For columns, piers, and walls
supporting such floor areas the maximum live load
reduction shall be twenty percent.
(c) No live load reduction shall be permitted for
calculating shear stresses at the heads of columns [sic]
in flat slab or flat plate construction.

(d) In lieu of the percentages given in table 9-1, the
live load reductions for columns, piers and walls may
be taken as fifteen percent of the live load on the top
floor, increased successively at the rate of five percent
on each successive lower floor, with a maximum
reduction of fifty percent; and for girders supporting
two hundred square feet or more of floor area, the live
load reduction may be taken at fifteen percent. The
limitations of subdivisions (b), (c)and (d) of this section
shall apply.

 

[dcarr82775]

To me it depends on the type of wall. If concrete or masonry I would reduce the live loads, but for wood stud walls I wouldn't. My reasoning being a single stud could easily get it's design loading (without LL reduction) and unless the plates/joists/sheathing was detailed to carry the load to to adjacent studs it could fail.