Hope somebody can point me to tables that show the load a steel I-beam will take. I’ve got a friend that owns some rental property which has cottages on a hill. One cottage has a garage underneath part of it and the structure needs to be rebuilt/reinforced. The garage currently has two wooden supports which he’d like to remove … to give unhindered access to the garage area … and replace the wooden beam above with something that will carry the load upstairs, which is one end of the cottage. The span is about 25 feet and the cottage is one story. Short of getting a structural engineer to figure this out, is there a less expensive way to figure this out? He’s got access to all sorts of I-beams at a metal supply house but doesn’t know how to size it.
Thanks in advance,
John
Replies
Why steel? Why not take a sketch, with dimensions, to your local lumber yard and have them size a glulam or similar? Or take the sketch to a steel fabricator and see if they would do the same. I would bet the the steel fab would not touch it without an engineers approval. Sounds like your friend os trying to get something for nothing...hope you're not in the way when things go south.
Whenever you are asked if you can do a job, tell'em "Certainly, I can!" Then get busy and find out how to do it. T. Roosevelt
Edited 1/13/2004 8:42:38 PM ET by ELCID72
"Why steel? Why not take a sketch, with dimensions, to your local lumber yard and have them size a glulam or similar?"
ELICID72,
$ for $, if you have the tools and knowledge, for a span that long, steel is the way to go. I've been there, done the research and cost analysis. Off the top of my head, I'm thinking W10x26 (very common) but I'm not an engineer so.............
Easy enough to do your homework on the net.
Edited 1/13/2004 9:18:37 PM ET by WorkshopJon
Dollars and dimensions both - steel beats wood.
Excellence is its own reward!
But I did say he needed to ask an engineer, I think I derseve part credit
nuthing but happy thought.
Lotsa web sites for struc. steel shapes, look for section modulus. M= 20,000 * section modulus, where M is the moment the beam takes. You gotta figure out what the load is above (if a floor ONLY, figure 60 # sq ft to start and figure pounds per inch beam load) . Once you figure out how many pounds per inch the beam is loaded (=w), M = w*span^2/8. Go get the beam. If you can't follow the above, well???
BIG gotcha maybe lurking also -- the support of the end of the beam prolly need to be beefed up to have the same total sq ft. as the ends now do PLUS THE AREA OF THE FOOTINGS OF THE POSTS REMOVED - otherwise, you could end up with a tilted floor.
"Hope somebody can point me to tables that show the load a steel I-beam will take"
John,
Hope this helps.
http://members.fortunecity.com/911/wtc/I-beams.htm
Jon
Good God... People go to school for years to learn this stuff and you want to do it yourself.
Practice now that preplexed look of " well it should have worked"
Hey anyone know a good site for at home brain surgery? I think some here could use it but then again maybe it's me.
Good God... People go to school for years to learn this stuff and you want to do it yourself.
You right people go years to school to learn this and everything else that goes along with engineering, math, science, chemical, business law, everything.
But the question he ask they learn in three and half days. I do agree you need to ask an engineer but its not a major thing, its listed in most steel books.
nuthing but happy thought.
"But the question he ask they learn in three and half days"
BROWNBAG,
I'm thinking more like one lecture and one chapter, But hey, I went to B-school, not engineering.
Jon
He wants to remove 2 posts and replace a supporting beam.
Ok so it may be learned in 2 1/2 days but unless he wants to devote 20 hours to understanding loads and footings, I'd suggest leaving the brain surgery to the pros.
A question is simply a question, this place is about productive support. It's not for someone who had a bad day to step up and piss on someone else who mearly wanted help sizing. Which, by the way, is pretty easy for people who can do advanced math; sorry you don't have any idea how to.
"Which, by the way, is pretty easy for people who can do advanced math; sorry you don't have any idea how to."
If it is so easy why did you provide the answer.
BTW, no "pissed on him".
In fact I am surprised. We have a couple of threads on structural sizing and everyone is being nice, FOR A CHANGE.
Thanks Bill. I guess my reply sounded know-it-all-ish. I didn't mean for it to be that way and I certainly wasn't trying to "piss" on anyone. The point of all that verbal diahrea wasn't to make anyone feel stupid but just to point out to some of the participants in this discussion that engineering isn't simply looking stuff up and structural design sure as hell isn't learned in one lecture or even one semester. I'm sure most of you guys already know that but apparently not everyone here does. And yes, my spelling leaves a lot to be desired- I meant "shear", not to be confused with the "sheer" that some of you pervs may have been daydreaming about. One final thought to someone's suggestion of overbuilding by picking a bigger beam- if you don't know what the minimum is, how can you a pick a bigger one?
"One final thought to someone's suggestion of overbuilding by picking a bigger beam- if you don't know what the minimum is, how can you a pick a bigger one?"
Stone,
That's why we have tables. But you do make very good points, especially in light of the fact we're taking California here.
Jon
>> ... if you don't know what the minimum is, how can you a pick a bigger one?
Well, without knowing what the minimum is for the situation described in the original post, I wouldn't hesitate to specify a beam 16" wide by 48" deep, 1 1/2" cross section.
Yeah sure that's reasonable- probably 300 lbs per foot. Figure a 50 ton crane to get it into place and some monstrous end supports. The cost of an installation for something that big would far exceed the cost of doing it right in the first place by having an engineer size it.
Edited 1/16/2004 9:38:02 AM ET by stonebm
Oh now you're changing the terms. You didn't specify reasonable. :) Overengineering, even gross overengineering, is a time honored way of dealing with uncertainty and lack of knowledge.
"Overengineering, even gross overengineering, is a time honored way of dealing with uncertainty and lack of knowledge."
Sounds like the shade tree engineers version of the redneck's famous last words."Hey y'all, watch this!"
Jon Blakemore
This discussion is pointless. You cannot conclusively go with a larger beam unless you know the minimum. We both know that a beam like what you're talking about is fine- you could hang a semi off it but you're client isn't going to pay for something like that. Think of how stupid it would look in a house. The point is that a beam of that size (if it were made, which it is not- the largest W beams are 44 -inches deep) would cost maybe $5,000 plus shipping. At 5 tons, you'd need large cranes and special supports- no idea how much that all would be but I've got to believe you could have an engineer size a beam for way less than that so what's the point in going with something like that? Are you seriously recommending to the original poster that he install a 5-ton 48-inch deep beam? I'm not "changing the terms"- reasonableness should always form the basis for an argument.
>> This discussion is pointless.
So why did you continue it? :o) Or do you mean just my part of it pointless?
I agree with the point you're trying to make (or the point I think you're trying to make). For a person in the situation described by the original poster, expending any effort and resources to avoid paying a structural engineer entails too many risks and has a fair chance of costing more than the engineer's fee. Yes, someone it that position should consult a structural engineer and follow his recommendations.
The point I was trying to make is that we are not helpless without engineers. Buildings were built using intuition and experience for many thousands of years before structural engineering gained a solid scientific footing. A remarkable number of them are still standing. Builders today also gain experience, and over time, integrate their experience into intuition.
Suppose there were a Breaktime poster living in the Pacific Northwet and going the the handle SCRAPYARD. And suppose he had a couple dozen steel beams neatly stacked in the back yard. And suppose that a poverty stricken builder needed a steel beam for the garage in his own house, and could not afford to buy one, nor to pay an engineer to tell him which one to buy. And suppose that he gathered together a hundred of his best buddies who were experienced builders and told them, "SCRAPYARD said he would give me a beam, but we need to go out to his place and pick the right one." So they go out there and each experienced builder designates which of the two dozen beams is the right one. I would bet money that most of the picks would be clustered on a very few beams, the median beam would be the optimum choice out of the selection available or not more than one beam away from the optimum choice. And this is without any of the builders knowing what is the engineered minimum beam for that location.
If a builder is paying attention, I think he can hardly fail to notice what beams the engineers specify for different circumstances.
>> (if it were made, which it is not- the largest W beams are 44 -inches deep)
I'm surprised I came that close. I was plucking numbers out of the air to match my intuition of what would be a really big beam.
John; re:
"devote 20 hours to understanding loads and footings"
YOU WILL HAVE THAT KNOWLEDGE THE REST OF YOUR LIFE. !!! GOOD INVESTMENT!
Once spent 3 weeks (200 hours?) of own time learning just basics needed to get corp of Eng approval for building an earthen dam for a 5 acre pond and did do the surveying and plans (surveying learned on a previous endeavor) and got engineering approval only to find that the Ecology dept didn't want 5 fingerling salmon disturbed ... good leason though, just need to learn where to start, at least you are asking questions.
PS: don't forget the footing part of the problem.
Johnhardy, don't know of any table as you requested. To many variables and to many possebilities. However here are some options for your problem. Assuming the garage width/span is 25'. The garage debth/length is 24'. The live and dead load is 50#/sf. There is no roof load tranfering to the beam or the joist supported by the beam. The allowable deflection of the beam is 1/360th of beam length =7/8". Here are some possibilities. Steel:W8x58 (8-1/4x8-3/4); W10x45 (8x10); W12x30 (6x12); 14x26 (5x14). Wood:4-1-3/4x18 LVL; 6-1-3/4x16; 8-1-3/4x14 LVL. Hope this helps.
OK- you guys asked for it... Sizing a beam usually requires looking at a few likely failure modes (generally shear and bending). Given the length of the span (25 feet), bending failure should occur first- shear is usually only the failure mode for short spans. (Notice I'm saying things like "generally" and "usually"- you really need to check both to verify which occurs first). Bending failure occurs when the bending moment (a moment is basically torque and is measured in foot-pounds or similar units) applied to a beam causes a stress in the beam that exceeds the allowable stress of the beam material.
A maximum allowable bending moment, "M", can be determined for a beam using the formula S=M/Z. "S" is the allowable stress for the material (for steel this is usually taken as the yield stress of the material (there are different types of stell but I believe most structural shapes are constructed of steel having a yield stress of 36 ksi (36,000 pounds per square inch). "Z" is the section modulus (difficult to explain but easily looked up from tables). "Z" is really a measure of the bending resistance of the beam. I have a book from the American Institute of Steel Construction (AISC) that includes "Z" values for all types of structural shapes (W, S, H beams and C channels).
That was the easy part. Now you need to determine what kind of bending moment is being applied to the beam. This depends on how the beam is loaded- is the load distributed along the length of the beam, are there any point loads or cantilevers? If the load is distributed along the length of the beam and there are no point loads and there are no cantilevers and the beam is simply supported (hey this is all easy right? can be covered in one lecture right?), the maximum applied bending moment, M', is calculated as M'=w*(L^2)/8. "w" is the load on the beam per unit length and "L" is the span of the beam. Remember all the units have to be consistent (use inches and pounds everywhere to make it easier).
So now you know the maximum applied bending moment on the beam (M'). If you use this value in the first equation to solve for a required section modulus (Z), you'll get a minimum required section modulus. You're going to want to add in a factor of safety which in itself requires equations to determine which factor of safety is appropriate (depends on the severity of live loads and dead loads). This factor of safety is multiplied by the maximum applied bending moment to get a "design bending moment". If you solve the first equation using the "design bending moment" you can get your design section modulus and pick a shape that provides at least that value.
My point here is to not to offend or to toot my own horn (OK maybe just a little) but to enlighten and illustrate the complexity of the process. It can be done and probably some of you guys without engineering backgrounds have done it in the past. However, if you think this is complicated, keep in mind that there were several simplifying assumptions that most engineers woudn't make without first evaluating the actual loading and support conditions. I think it's been said before on this site- hire an engineer.
Edit: Almost forgot- as some have pointed out in this post, there are also deflection considerations. These may or may not govern the design- another thing you should check.
Edited 1/14/2004 1:24:54 PM ET by stonebm
"My point here is to not to offend or to toot my own horn (OK maybe just a little) but to enlighten and illustrate the complexity of the process..........I think it's been said before on this site- hire an engineer."
Stone,
You are definitely correct in that attempting to calculate every force and variable is indeed complicated. But, sometimes it is just more cost effective to go for overkill vs. "hiring an engineer." The info the originator of this thread is asking for is pretty basic. Sure you can go through all the work (cost) of calculating the "theoretical" failure point, that may occur if the structure is subjected to some force, some day, based on historical data. Then apply a X-times margin for safely.
Or spend an extra $200. on a bigger beam.
Jon
Here's a little story on "hiring an engineer". After our GC went bankrupt, and I wound up playing GC to finish the house, the one remaining issue the inspector had was that there was one window and one door located such that there was a doulbe and a triple girder truss directly over the door and window openings. (Keep in mind that the house is two storeys, and the openings in question are on the first floor. So there is a whole storey in between the roof trusses and the headers in question).
Apparently, when a doubled or tripled girder truss or a load carrying beam are located over a door or window, the inspector needs to see an engineer's stamp approving the loading on the header. This I can understand.
So, once I determined that our GC hadn't done anything about this issue before going bankrupt, I asked another contractor that I knew who would be the best engineer to deal with. I called the engineer, and described my problem.
He wanted to know if I had the truss drawings, my building permit number, and some basic data (what was the header made out of). Once he knew who the GC was who had done the work so far, he had NO concerns. I went home, pulled out the drawings, gave him the spans, described the house, told him the permit number, and by the time we were off the phone, he had the letter written.
He knew exactly what assumptions to make, based on the house construction used around here, and he knew how to simplify and take "worst case" numbers for loading. It cost me $70, and was the best money I've spent in a long time.
Sometimes, "hiring an engineer" is a matter of finding the right person who knows what he is doing and will simplify the process.
"Sometimes, "hiring an engineer" is a matter of finding the right person who knows what he is doing and will simplify the process"
Cario,
Good point, and $70 well spent. On the other hand, unless you're hooked up, few "engineers" will go through the trouble for $70. Geez, out here it cost $300 for a plumber to make a night time house call (Wisconsin).
Jon
Uh, professor Stone, can you start over at the beginning and go a little slower? Sheer...isn't that what my girlfriends nightie looks like?
Whenever you are asked if you can do a job, tell'em "Certainly, I can!" Then get busy and find out how to do it. T. Roosevelt
Stone,
The AISC Steel Manual, ASTM, and almost all mills use 'F' for allowable stress (small 'f' is actual stress) and 'S' as Section Modulus. 'Z' is used for the plastic modulus, which is for non-elastic design and well beyond the scope of garage beam design. Someone looking for those symbols in any steel table (AISC, ASTM, etc.) may be confused by your designations....that's not a mistake, it's rustic
About that sizing yourself/hirinbg an engineer thing. Few inspectors are going to accept internet schooling for beam sizing over calcs sealed by a PE....that's not a mistake, it's rustic
None wrote: The allowable deflection of the beam is 1/360th of beam length =7/8".
this may be so, but what will 7/8" look like across the top of the garage door? Depending on how the door is constructed, the sag could be very obvious. It could also be a problem with the internal dry wall.
If it were me, I'd design for a maximum sag of 3/8" or maybe less. In sizing the beam, I'd be guided by what amount of sag would look "wrong" across the opening, even if the sag was less than that allowed by the codes.
Ian
In sizing the beam, I'd be guided by what amount of sag would look "wrong" across the opening, even if the sag was less than that allowed by the codes.
EXACTLY. That's why you get a local guy who does this for a living; he can usually whip it together in no time, and he'll know what he SHOULD do as opposed to what he CAN do.
Thanks to everybody who contributed here. I'll pass along the information and am recommending that he contact an engineer.
John
Since this is in Los Angeles, I can recommend my engineer. He works out of his house in West Hollywood. Not only can he do the wet stamped design, he also pulls permits.
Reply here if you want the info, because I don't get incoming e-mail any more. My account was spammed out. But I can send outgoing mail. (IIRC, one of the Taunton rules is that we can't post anybody's name and phone number here on the board.)
-- J.S.
If you'd be so kind as to send the information to my e-mail account I'll pass it along.
[email protected]
Thanks in advance.
John
John --
I e-mailed the info this AM. Let me know if it doesn't get thru.
-- J.S.
John, I wrote to you 3 times and got no reply. I have something you might like for your project in exchange for those beams.
Joe H
I'm sorry, but my corporate e-mail account had to be put out of its misery. It was getting 300 spams a day, which made it unusable. I've e-mailed you my wife's home e-mail address, let me know here if it doesn't come through. Thanks for the offer.
-- J.S.
The short answer is to have a competent professional engineer evaluate the problem. It may or may not need to be a structural engineer (depending on code) but it will need to be a PE competent in steel design. There are many variables to consider, some of which have not been mentioned in others' answers. The PE certification will probably be a requirement anyway by the building inspector.
"I-beam," (actually wide flange) selection involves several steps. Loads must first be determined and proper factors applied to those loads. The loads to be considered in this design would include dead loads, live loads, live roof loads, snow loads, wind loads, rain or ice loads and earthquake load. I noticed from you profile that you are from Los Angeles so the earthquake load could be a factor. After the loads are determined, design factors are applied to them in various configurations to determine what the design load must be. This method is called the LRFD Method and is much too involved to go into here.
Once design loading is known, bending moment in the beam can be calculated or determined from tables of the Manual of Steel Construction Load and Resistance Factor Design, a publication of AISC. BUT this is only part of the analysis. In addition to bending moment, the beam can also fail as the result of: 1. Lateral-torsional buckling, (LTB) 2. Flange local buckling, (FLB) 3. Web local buckling (WLB) or 4. unacceptable deflections. All of these are significant and must be checked. The manner in which the beam is connected to the floor above it and to its supports at the ends, is significant in how much load it will be able to withstand. What comes into play is refered to as the "unsupported length." Do not assume that a beam can be considered fully supported because the top flange is affixed to the structure above. Deep, narrow beams might take the moment but could fail due to LTB, LFB or WLB.
I remember an illustration given by a professor who is a recognized structural engineering expert. He once designed a long beam which would be used as a hoisting rail at a maintenance facility. The beam was quite substantial because of the long span and high loads anticipated. The general contractor saw that the beam was quite heavy and proceeded to select another beam "from the table" which would carry the same amount of moment but be lighter in weight. Well, it failed in LTB and actually would not even support its own weight because it just rolled over!
After the beam is properly sized, there is the matter of the end connections, column support and the footings...
Steel shapes are a wonderful material to use for long span - high load conditions. Hope this has been helpful.