Jobsaver
Registered User
To what degree do the IRC prescriptive codes including span tables account for "point loads" or "concentrated loads":
On headers?
On girders?
On headers?
On girders?
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Point Loads
- Thread starter Jobsaver
- Start date
steveray
SAWHORSE
Agree w/ George.....not handled in in IRC...engineering required...or whatever the BO will accept...
fatboy
Administrator
Wasn't going to post, as it may constitute performing engineering, but I've always figured the tables were based on uniform (sorta) loads.
Point loads are extremely important,
I am usually not conserned with point load unless there is a specific load; like a water heater in an attic. Then I am like poop on a stick; you ain;t going to get me off; until you provide proof positive that you have meet all load requirements.
Also, be very attentive in apartment construction; where they build a stand for water heaters to sit on; and the effect on any non-load bearing walls.
Note that the water heaters are to be included as dead loads in the IRC. See Definition of dead loads; 2006 IRC --"and fixed service equipment."
And,
R301.4 Dead Load. The actural weghts of materials and construction shall be use for determining dead load with consderation for the dead load of fixed service equipment.
HVAC units in attic must also be considered; however there is nothing more frightning than seeing two gas fired, 50 gallon water heaters in an attic; directly above a stairway in a two story house; without taking into account the full weight when filled with water. Especially when the water heaters (21" diameter) are centered between 24" on center ceiling joists, supported only by 5/8 OSB.
At a meeting with a major nationwide homebuilder; their engineer said; the water heaters were not considered dead loads, because when you use water; they empty and refill only when the water level in the tank gets too low.
Yes, he is still alive; and, no I did not hit him; but, I did almost lose my job. :grin:
Uncle Bob
I am usually not conserned with point load unless there is a specific load; like a water heater in an attic. Then I am like poop on a stick; you ain;t going to get me off; until you provide proof positive that you have meet all load requirements.
Also, be very attentive in apartment construction; where they build a stand for water heaters to sit on; and the effect on any non-load bearing walls.
Note that the water heaters are to be included as dead loads in the IRC. See Definition of dead loads; 2006 IRC --"and fixed service equipment."
And,
R301.4 Dead Load. The actural weghts of materials and construction shall be use for determining dead load with consderation for the dead load of fixed service equipment.
HVAC units in attic must also be considered; however there is nothing more frightning than seeing two gas fired, 50 gallon water heaters in an attic; directly above a stairway in a two story house; without taking into account the full weight when filled with water. Especially when the water heaters (21" diameter) are centered between 24" on center ceiling joists, supported only by 5/8 OSB.
At a meeting with a major nationwide homebuilder; their engineer said; the water heaters were not considered dead loads, because when you use water; they empty and refill only when the water level in the tank gets too low.
Yes, he is still alive; and, no I did not hit him; but, I did almost lose my job. :grin:
Uncle Bob
Last edited by a moderator:
50 gallons is about 400 pounds. About 9sqft of floor area (based on 40# live load and the 7# of actual dead load - 400/43 = 9). Even as live load not enough weight to worry about.
(My 50 gallon water heater is in a 4'x4' area above my front door. I have no concerns about it. I never even did the math to show the framing - 2x12x16' @ 16" with 1/2" plywood, is sufficient.)
It takes a lot of equipment to make an engineer concerned.
Point loads are usually of importance if they they concentrate major floor or roof loads - like at posts. Even floor joists and jack studs around openings, reasonable sized point loads, don't need to line up with studs too well.
(My 50 gallon water heater is in a 4'x4' area above my front door. I have no concerns about it. I never even did the math to show the framing - 2x12x16' @ 16" with 1/2" plywood, is sufficient.)
It takes a lot of equipment to make an engineer concerned.
Point loads are usually of importance if they they concentrate major floor or roof loads - like at posts. Even floor joists and jack studs around openings, reasonable sized point loads, don't need to line up with studs too well.
George,
You stated;
"It takes a lot of equipment to make an engineer concerned. "
Find an engineer; your configuration and calculations are not even close to the required support in my senario. And your weight approximations is also way off.
Uncle Bob
You stated;
"It takes a lot of equipment to make an engineer concerned. "
Find an engineer; your configuration and calculations are not even close to the required support in my senario. And your weight approximations is also way off.
Uncle Bob
Last edited by a moderator:
We found excess capacity on a couple of spot checks of the table. I'll let you try first. Work out the loads from the table and see what shakes out. Remember the table only checks deflection of live load not total load so you'll need to run the calc both ways. Here is my calc for centered point loads;
http://www.windyhilllogworks.com/Calcs/beamclc_ctrptld.htm
This is for 2 point loads at the third points;
http://www.windyhilllogworks.com/Calcs/2ptbeam.html
http://www.windyhilllogworks.com/Calcs/beamclc_ctrptld.htm
This is for 2 point loads at the third points;
http://www.windyhilllogworks.com/Calcs/2ptbeam.html
Yankee
Registered User
Really? Excessive bending is a structural failure. Your opinion above is one I have to fight daily . . . it doesn't have to fall down and kill someone to be considered a structural failure.GHRoberts said:
The beam could support the load and still not comply with the code.
Wood is interesting in that if you place a heavy load on a wood member for a long term it could eventually fail because of load duration effects. This is recognized by the code provisions related to the design of wood members. Such failures do occur when this issue is ignored. Thus the fact that the member has not failed does not mean that it will not.
Wood is interesting in that if you place a heavy load on a wood member for a long term it could eventually fail because of load duration effects. This is recognized by the code provisions related to the design of wood members. Such failures do occur when this issue is ignored. Thus the fact that the member has not failed does not mean that it will not.
Daddy-0-
Moderator
Point loads are generally a bigger concern with girder trusses and large LVL beams or PSL posts. I also know that when I see a large water heater or a heavy furnace in the attic I look at the extra weight too. I think that UB raises some good points about design issues. There are lots of places to put a water heater and the attic would be my last choice for many reasons.
I was curious. If we take George's water heater and spread it out over 2 joists each one would take 200 lbs of the load. That passes fine on his 2x12's even in the center of span. I then took the 1.33' width (16" oc) x 16' length and multiplied it x 40 psf and got about 850 lbs of uniform load on those joists as well. I wanted to check it quickly so I divided that uniform load in half and added it to the point load in the center of the joist. Remember that a point load in the center produces double the bending moment of a uniform load... long story short, it still passed handily. It sounds like the heater is towards one end of the joists, that makes a huge difference. Not many people have 2x12 ceiling joists, that also makes a huge difference.
Mark K mentioned long term creep deflection. This is part of the adjustment of base design value when you are checking a beam. For "normal" loads considered to be of 10 year duration the design value is unadjusted for duration of load. For a permanent load it is derated 10%. For short term (2 month) loads like snow the base design value can be increased 15%, For 10 minute loads like wind or seismic the increase is 1.6x base design, for impact 2x. Wood can handle large overloads of short duration well, where a constant load of much lesser magnitude will cause it to fail. The failure in long members is often excessive deflection rather than breaking.
Those king sized waterbeds on the narrow pedestal base, depending on which way the pedestal is across the joists, is it on 3 joists or 5... and that's a dynamic equipment load.
Mark K mentioned long term creep deflection. This is part of the adjustment of base design value when you are checking a beam. For "normal" loads considered to be of 10 year duration the design value is unadjusted for duration of load. For a permanent load it is derated 10%. For short term (2 month) loads like snow the base design value can be increased 15%, For 10 minute loads like wind or seismic the increase is 1.6x base design, for impact 2x. Wood can handle large overloads of short duration well, where a constant load of much lesser magnitude will cause it to fail. The failure in long members is often excessive deflection rather than breaking.
Those king sized waterbeds on the narrow pedestal base, depending on which way the pedestal is across the joists, is it on 3 joists or 5... and that's a dynamic equipment load.
RJJ
Co-Founder
Drp: I kinda of agree. I not sure I understand UB point that the load is not as George stated.
even headers... we look at the jack and king studs at each window.. we need to follow that load to the foundation.
Not just because of a big failure.. if the header starts to sag (either from loads above or insufficient support from below), the drywall cracks more than it has to.. the windows don't operate correctly.. etc. Still a failure that we can help avoid.
Not just because of a big failure.. if the header starts to sag (either from loads above or insufficient support from below), the drywall cracks more than it has to.. the windows don't operate correctly.. etc. Still a failure that we can help avoid.
Yankee
Registered User
And this is the road we go down when we start codifying workmanlike construction over shoddy construction, and the difference between safety codes and building codes, and where we most often are likely to go hinky with codifying particular manufacturers specs (or not). Some on this forum feel that codes should only apply to the safety aspect, I disagree. A minimum level of workmanship should (also) be what building codes address.
On the issue of whether the codes should address workmanship issues you need to consider state laws. The laws authorizing adoption of building codes typically state that they are for the purpose of promoting safety and public health and do not mention such items as workmanship. In this context the adopted regulations cannot legaly address issues not authorized by the enabling laws.
We also need ask the question do we want to regulate everything or do we want to minimize government regulations. In addition the more you try to regulate the more complex the codes will become and the more likely that you will find unintended consequences from the regulations.
We also need ask the question do we want to regulate everything or do we want to minimize government regulations. In addition the more you try to regulate the more complex the codes will become and the more likely that you will find unintended consequences from the regulations.
Yankee
Registered User
Or promoting health safety and welfare , , , starting to cover a good deal of ground with that.
mtlogcabin
SAWHORSE
When checking the load path on a raised floor with a rim joist how many stop at the floor plate or do you require additional reinforcment at the rim board where the point load is bearing.
RJJ,
Ok, I'll try to make my point a little more clear;
George's water heater is sitting on 2" X 12"s spaced 16" on center(50 gallon water heater with appox. 22" width; which is more than enough support.
In the case of the homes built in Central Texas by Anonymous Homes (a major nationwide home builder); who has built thousands of homes;
In their two story homes; they placed two Rheem 50 gallon water heaters and two HVAC units in the attic space (all gas fired).
The following is a normal situation concerning their attic installation and support:
The ceiling joists were 2" X 8" with an approximately 14' span on 24" centers.
The 50 gallon water heaters weighted 150 lbs. empty.
Fifty gallons of water weights 417 lbs. for a total weight of 567 lbs.
Not using "Engineering" but, simple math; that is approximately 168 lbs per square foot of weight (DEAD LOAD); which in many instances, the osb carried the total weight of the water heaters.
The water heaters were 21 3/4" wide (ceiling joists were spaced 24" on center).
23/32 (3/4") osb on 24" centers; maximum live load 100 lbs. dead load 10 lbs per sq. ft..
(be patient with the download; it's slow)
http://osbguide.tecotested.com/pdfs/en/el809.pdf
Actually, where the water heaters were supported on one side by a ceiling joist; the weight would bend the osb; and shift most of the weight to the osb.
After seeing several instances of tilting water heaters, overstressed (bending) flooring, and cracked flooring, under the weight of the water heaters; at final inspections; I started researching the problem.
With the help of some very nice Engineers on the old ICC BB; I got the information I needed.
End result: Anonymous Homes began placing the ceiling joists on 12" centers; in the area where the water heaters were installed; which solved the problem for those new homes.
However, I am not sure they went back and made any corrections to homes they had already sold.
On the old BB; I think I posted pictures of two water heaters; totally supported only on the osb; directly above the stairway, in a two story home. Should one of those water heaters go through the floor; they would fall on the stairs; blocking the exit; break flexible gas line feeding the water heater; starting a fire; and trapping the occupants in the bedrooms of the second floor.
As I stated before; in apartment complexes; please check the support under water heaters installed. I have seen many; by major contractors; where the water heaters are not sufficiently supported. Especially where the water heater is above the washing machine or clothes dryer.
Hope this helps,
Uncle Bob
Ok, I'll try to make my point a little more clear;
George's water heater is sitting on 2" X 12"s spaced 16" on center(50 gallon water heater with appox. 22" width; which is more than enough support.
In the case of the homes built in Central Texas by Anonymous Homes (a major nationwide home builder); who has built thousands of homes;
In their two story homes; they placed two Rheem 50 gallon water heaters and two HVAC units in the attic space (all gas fired).
The following is a normal situation concerning their attic installation and support:
The ceiling joists were 2" X 8" with an approximately 14' span on 24" centers.
The 50 gallon water heaters weighted 150 lbs. empty.
Fifty gallons of water weights 417 lbs. for a total weight of 567 lbs.
Not using "Engineering" but, simple math; that is approximately 168 lbs per square foot of weight (DEAD LOAD); which in many instances, the osb carried the total weight of the water heaters.
The water heaters were 21 3/4" wide (ceiling joists were spaced 24" on center).
23/32 (3/4") osb on 24" centers; maximum live load 100 lbs. dead load 10 lbs per sq. ft..
(be patient with the download; it's slow)
http://osbguide.tecotested.com/pdfs/en/el809.pdf
Actually, where the water heaters were supported on one side by a ceiling joist; the weight would bend the osb; and shift most of the weight to the osb.
After seeing several instances of tilting water heaters, overstressed (bending) flooring, and cracked flooring, under the weight of the water heaters; at final inspections; I started researching the problem.
With the help of some very nice Engineers on the old ICC BB; I got the information I needed.
End result: Anonymous Homes began placing the ceiling joists on 12" centers; in the area where the water heaters were installed; which solved the problem for those new homes.
However, I am not sure they went back and made any corrections to homes they had already sold.
On the old BB; I think I posted pictures of two water heaters; totally supported only on the osb; directly above the stairway, in a two story home. Should one of those water heaters go through the floor; they would fall on the stairs; blocking the exit; break flexible gas line feeding the water heater; starting a fire; and trapping the occupants in the bedrooms of the second floor.
As I stated before; in apartment complexes; please check the support under water heaters installed. I have seen many; by major contractors; where the water heaters are not sufficiently supported. Especially where the water heater is above the washing machine or clothes dryer.
Hope this helps,
Uncle Bob
Last edited by a moderator:
Forest
Bronze Member
Jobsaver,
My two cents, IRC 301.1 "transfer of all loads from point of origin through the load- resisting elements to the foundation" then since it not addressed in the tables for point loading IRC 301.1.3 Engineered design required.
My two cents, IRC 301.1 "transfer of all loads from point of origin through the load- resisting elements to the foundation" then since it not addressed in the tables for point loading IRC 301.1.3 Engineered design required.