IBC 2000 Seismic Forces - whatis "component operating weight"?
IBC 2000 Seismic Forces - whatis "component operating weight"?
(OP)
I am trying to calculating seismic forces in IBC 2000. In Equation 16-17 there is a term "Wp" which is "component operating weight". The definition is not very clear. I was told that for brick wall, it is 50. Could someone please elaborate what "component operating weight" stands for, and how did you arrive at that conclusion? What are the units? And what are the Wp for brick, metal siding, EIFS, etc.? Thanks in advance.
GAEngr05
GAEngr05






RE: IBC 2000 Seismic Forces - whatis "component operating weight"?
I don't follow this - don't you mean Eq. 16-60? Wp is the component weight. I don't know where you got the term "operating", unless it was unrelated to your wall, and referred to an HVAC unit.
I would use simply the dead load, in pounds, as closely as you can calculate or ascertain from a table of building materials weights.
RE: IBC 2000 Seismic Forces - whatis "component operating weight"?
The wp (as in lower case w, mentioned by Sacrebleu) is the weight of the STRUCTURAL element, and by "50" they may have meant 50% of the weight of the wall acts on the floor/diaphragm above and the other 50% acts on the floor/diaphragm below. Make sure you read the Section Headers before jumping to the equations.
RE: IBC 2000 Seismic Forces - whatis "component operating weight"?
The equation is Equation 16-67 in IBC 2000. I am not really sure where it is in IBC 2003.
The equation is used to determine seismic forces, Fp, acting on a wall of a building - lateral loads. One of the terms of this equation is "Wp" and it was stated below the formula that "Wp" is the "component operating weight". Those are the exact words, "component operating weight".
I take it to mean the weight of the wall finish. If my take on this term is correct, I am still not sure how big of the wall should I consider. Should I consider the weight of one square foot of the wall? I was told to use "Wp" as "50". For a one square foot wall with a thickness of 4 in. (or 0.33ft.) and a brick density of 150 PCF, it would work out to be 50#. Am I correct? I am not sure, hence my post.
Any one out that who has worked on lateral seismic forces acting on walls before, appreciate your advice. Thanks again.
RE: IBC 2000 Seismic Forces - whatis "component operating weight"?
I am trying to calculate the seismic forces acting laterally on the brick wall of a building, and Equation 16-67 on Page 376 of the IBC 2000 provided that.
The term Wp was defined as "component operating weight, and I take it that the value of Wp has to do with what type of wall finish it is. For EIFS or metal siding exterior walls, presumably the value of Wp would be different.
I was just trying to get a "clearer definition" of what the term means? Can anyone out there in Structural Land help, please?
RE: IBC 2000 Seismic Forces - whatis "component operating weight"?
The Wp term is the weight (full weight) of whatever you are dealing with. So if you have a wall, it has a weight - perhaps a weight per square foot. That weight is entered into Equation 16-67, 68, or 69, and you get a lateral seismic force developed by that component.
For example, suppose you have a wall that weighs 50 lbs/sq. ft. You use the three equations to get something in the form of:
Fp = P x Wp
The P is the percent of Wp that is thrown sideways in the seismic event.
Suppose your P value is 0.25. That means that 25% of the wall weight is the lateral force that is applied horizontally in the seismic load case. So your lateral load would be 0.25 x 50 = 12.5 psf on the wall, either perpendicular to the wall or parallel to the wall. Every square foot of the wall produces 12.5 lbs. of lateral force in either direction.
RE: IBC 2000 Seismic Forces - whatis "component operating weight"?
Can I take it that the Wp term refers to the weight of one square foot of the wall?
Say, the density of brick wall is 150 PCF and the thickness of the brick wall is 4 in. or 0.333 feet. Then, the weight per square feet of th e wall is:
150 PCF * 0.333' = 50 PSF
The math is not complicated, but the term was not defined clearly. For someone new at the game, the definition "component operating weight" doesn't help a lot.
If the definition was written as, "weight of one square foot of the wall with the units PSF", there wouldn't be too much doubt at all.
Did I get it right?
RE: IBC 2000 Seismic Forces - whatis "component operating weight"?
For a mechanical unit, you may have a single weight - say 500 lbs. Then the Fp would be in lbs, not psf. Its just how you keep track (bookkeeping) of the loads and their path through the structure.
The thing to remember is that all seismic loads are generated by mass and the the resultin seismic load is always placed at the center of mass of the "item" you are dealing with. For your wall, its a big flat uniform thing. So applying a uniform load in psf terms is the natural result. For a mechanical unit, the load would most likely be a point load.
RE: IBC 2000 Seismic Forces - whatis "component operating weight"?
If you are designing the brick wall veneer tie to support 20 sq. ft of brick wall, then Wp is equal to the dead load of 20 sq. ft. of the brick.
Essentially, the Fp seismic load value is 20 times that generated by one sq. ft. of brick wall.
RE: IBC 2000 Seismic Forces - whatis "component operating weight"?
RE: IBC 2000 Seismic Forces - whatis "component operating weight"?
I am actually designing wall studs at 16" apart and the height of the wall stud is 17 feet tall. It is a brick wall and let's take the wall self weight (brick, studs, sheating, etc.) as 54 PSF.
Therefore, my "component operating weight", Wp is:
54 PSF * 16"/12 * 17 = 1224#
With this value, I can work out Fp, the seismic forces, and then compare Fp with the forces caused by the wind load. In my case, the wind load controls.
Did I get it right this time?
RE: IBC 2000 Seismic Forces - whatis "component operating weight"?
When dealing with roof top units (rtu's) the manufacturer will provide the operating weight of the unit. This info you can request from the architect.
Also, try the ASCE 7 for some typical dead load estimates for materials and wall assemblies, brick, cmu, and others.
If you have seismic and wind loads to consider, you may hvae to design with the wind force but I believe you will still have to detail your structure for seismic force effects.
RE: IBC 2000 Seismic Forces - whatis "component operating weight"?
Remember to check your wall/structure for longitudinal Fp as well as lateral Fp.
RE: IBC 2000 Seismic Forces - whatis "component operating weight"?
RE: IBC 2000 Seismic Forces - whatis "component operating weight"?
In my local area, a seismic event has never happened (in recorded hisory). However, the seismic coefficients are much higher than what would be expected. I understand that is based on geological studies.
RE: IBC 2000 Seismic Forces - whatis "component operating weight"?
The "component operating weight" I got is for the "tributary area" covered by one wall stud, i.e. 16" wide and 17' high. And the Fp I got (in POUNDS) is apparently a point load acting on the c.g. on one of my wall studs. I compared this to what equivalent force I would get from the wind, and the larger force controls.
Zo40, could you please elaborate what is longitudinal Fp? I did check the lateral Fp for wall element, body of wall panel connections and fasteners of the connecting system, but I don't think I checked the longitudinal Fp.
RE: IBC 2000 Seismic Forces - whatis "component operating weight"?
Since the outbreak of the IBC Code, seismic load combinations do indeed control in many cases where wind load used to always control. Be careful to not only compare the basic seismic loads, but also seismic demands on connections which are many times required to resist overstrength seismic loads (see IBC 2000 section 1605.4).
Also, your use of Fp as a concentrated load at the c.g. of the stud is technically incorrect. All seismic loads act where the mass is, so technically, the seismic load is a uniform lateral load along the length of the stud. Lumping all the mass, and the resulting lateral seismic load, at the mid-height of the stud is a bit conservative. It probably won't affect your design result that much in this case but I point it out so that you can understand the concept for any future "bigger" designs that you attempt.
Also, I forgot to ask you: Is this a load-bearing stud wall? If so, then you should be in IBC Section 1620, not 1621. And also - what is your Seismic Design Category?
Don't forget to include with the seismic the applicable load combinations of Section 1605. This also requires a determination of E as defined in 1617.1 which includes a vertical seismic effect = .2 x S(DS) x D.
Lastly, you mentioned the "longitudinal" Fp. Keep in mind that the seismic forces work in any direction, both perpendicular (lateral) and parallel (longitudinal) to the wall. For a wall, this longitudinal condition simply forces the wall to act like a shearwall.
RE: IBC 2000 Seismic Forces - whatis "component operating weight"?
Thanks for the explanation, especially the bit that Fp "does not act as a concentrated load on the c.g. of the stud", but rather "is a uniform lateral load along the length of the stud.
In response to the questions you asked, the stud is not a load-bearing stud wall. My seismic design category is C.
Some other information:
Seismic Use Group II
Spectral Response Coefficients:
Sds = 0.24
Sd1 = 0.15
Site Class = C
Basic Struct. Syst. and Seismic Resisting Syst. = Ordinary Steel Concentrical Braced Frame
Design Base Shear, V = 329 Kips
Analysis Procedure = Equivalent Lateral Force Procedure