Steel I-Beam

[HARLEYRIDER]

Question for those of you that know steel.......there is a bridge...2 Steel I-beams 5.5" x 12" x 10' with X brace between.  It has a 10 ft span, and a wood deck. The steel  is 15 years old, but looks good.  How much weight can this bridge handle?

[Furby]

Gonna need to know how thick the steel is as well I would think.

[isassi]

Beams are scaled according to weight per foot. You can find the tables online by a quick search and also, the allowable span for a given beam size. Off the top of my head (without checking) a 5.5" X 12 is 18# per ft or 26 per foot, depending on thickness of the webb and flanges and across a 10ft span, would probably support 8 tons per beam, center load point (worst case scenario) on loading.

[Don_Papenburg]

Should  hold a couple of ton , 20 if you drive over real real fast

[maple flats]

you also need the grade of steel. Too many unknowns yet and after all the specs are on the table I still won't know the answer. 8) ;D

[Don P]

Can you get very accurate measures of the flange and web widths and thicknesses? From there you can get to joasis' weight per foot  and then the safe load tables. That 2 ton rating will drop to 500 pounds if you hit the brakes don't forget its a dynamic load. I doubt its high strength steel, I'd check very carefully to make sure it isn't low strength rust  ;).

[isassi]

I have still not dug out my steel tables and loading book...I can't even think this clearly in the early mornings  :D But for all you reading this that haven't palyed with steel before, Don is right on the money about grade of steel. Most heavy iron used to come from US Steel, or Bethlehem, ect. Import steel from Japan is rated by American standards. BUT...Mexican iron has lots of carbon, same with Chinese steel and Taiwan..actually any nation that recycles a lot of scrap without good quality control. As long as our domestic steel industry was a powerful giant, I bet engineers never had to look at these issues, but now, with steel being imported and in many cases, very poor quality, it is an issue.

When we erect steel buildings, we use I and H beams, typically oversized by 50% (loaded at half of failure load) and they are usually American Made. I know the engineer will not stamp a building unless it has American steel for the support structure. Now when it comes to the purlins and girts, they typically come from Mexico, and can be a real bear to weld, due to the carbon content and impurities in the steel.

[HARLEYRIDER]

 I'll measure again and mic thickness. I dont know how I'd find out the grade. Would it be stamped on it?

[HARLEYRIDER]

Should  hold a couple of ton , 20 if you drive over real real fast

thats what i was thinking :D

[WH_Conley]

Joasis, don't ya just love weldin on that stuff and a piece the size of a quarter blows back at ya? Down the collar and up the sleeve. That'll wake ya up in the morning.

[isassi]

What got my attention more then anything was years ago, I was cutting a beam, probably a 12 wide by 24 web, very large beam with 3/4 inch flanges, and ran into a pocket I could not cut through...turned out there were UN-MELTED ball bearings in the beam...I have no explanation unless the mill furnace was a little cooler then normal (?) and the ball bearings were introduced right before the poor into the pigs...beats me, but I saw it...

It is very common with Mexican steel to have slag pockets in structural steel and also to be welding 11 or 16 gauge purlin and be scooting along and suddenly have a blow-out cause by a pocket of high carbon steel in the run.  >:(

[Fla._Deadheader]

 Sounds like when I started cutting and welding, using Bed Rail angles. Hacksaw would melt through, and then, use 3 blades to finish the last 1/4" of the cut. Chunks blow out when you are welding.

  Sure learned how to sharpen drill bits, too.  : : :

  Maybe that's why I over-design things now  : : :D :D

[ely]

harold i have noticed the same things about bed rails. sometimes they do not weld well at all.

[scsmith42]

If the grade of the metal is not cast into it (and it probably is not), then it can be determined by chemical analysis.  The lab will need some small samples of the beams.

However, this may be overkill.  Typically (but not always) structural shapes are manufactured in one of two yield strengths - 36ksi and 50ksi. 

What is your intended application for the beams? 

Scott

[HARLEYRIDER]

If the grade of the metal is not cast into it (and it probably is not), then it can be determined by chemical analysis.  The lab will need some small samples of the beams.

However, this may be overkill.  Typically (but not always) structural shapes are manufactured in one of two yield strengths - 36ksi and 50ksi. 

What is your intended application for the beams? 

Scott

This is a bridge in the woods, probably put in in late 80's when a logging road was installed (with very good drainage and culverts).  Again, I didn't have a tape with me, but it looked like 5.5 or 6" by 12" high I-beams 10 ' long, heavy cross bracing, and 10/4 decking (which is rotted).  Decking will be replaced with black locust.  Abuttments are very large rocks that have no  sign of movement.

I just want to know if I drive a pick-up  with 1000 pounds of quickrete in the back, (3 tons total) will be stressing the steel too much. The approach on either side of the bridge is smooth and flat.

[isassi]

For your intended load, I think you will be on the safe end of things...really ;D

[mometal77]

To test the strenght of the steel and hardness just use a center punch and a hammer.  With steel today there are hard spots.  Most steel comes from other countries and have a lower grade.  One reason alcoa aluminum plant started back up.  Stuff coming from china was poor grade.  I even hear guys in shops that have problems with drilling steel.  Usually they incounter hard spots and the drill bits break.  Even more expensive when the bits range up too a few hundred dollars. You will find out more info when you take the decking off.  With the new boards your going too put on in the tire tracks i would put expanded metal nailed down or something.  Friend did the same and it was slippery even too walk on.
Some food for thought. 
steel weight
http://www.pacific-recycling.com/steelsize.html
Forum on welding and steel
www.shopfloortalk.com
googled this one
http://www.efunda.com/math/areas/IbeamIndex.cfm

[HARLEYRIDER]

Alright...I'm a total steel dummy. can someone explain this wieght per foot thing?  if a beam has 50 wt/ft, what does that mean if the beam is 10 feet long? How much weight could it handle?

[jgoodhart]

50lbs per ft is the weight of the beam per ft. That why the guys are asking for the web thickness many beam have the same width and height but the web thickness changes changing the lbs per ft and the capacity of the beam.

[isassi]

Unless you really want to know... :D...it is simple. #50 per ft means exactly that, 50 pounds per foot and 10 feet would be 500 pounds total weight of that particular beam.  Those figures originated from the need to calculate weights and strength without actually weighing every piece of steel. As Scott pointed out, and I wasn't thinking about, the "yield" or strength of steel is based on psi or pounds per square inch. 36ksi or 56ksi litterally means 36,000 pounds per square inch yield on the strength. Another thing to give thought to is that old saying "the weld is stronger then the metal" which is true in most cases, but only to the degree of shear or compression strength, not in the bending moment, which steel will bend, the weld will bend less, but I digress Go to the links Mometal posted after you know the exact beam size, and compare the loading to the very light weight you intend to use it for, and smile and say it is way overkill  :D

[rebocardo]

Assuming a 3/16 wall and at least 1/4 - 5/16 in the web (corner radius) it will easily support 3 tons.

> probably put in in late 80's when a logging road was installed

I would assume they were probably driving things much heavier then three tons over it.

What you can do is get a log arch, use a tree or rock as an anchor on the other side for the pulley block, and drag five tons of wood (which would not be a lot) unto the bridge and leave it there for a week. If nothing has moved I would call it good.

As someone noted about the bridge being slippery, I would add 12" high rails to prevent the truck from sliding off when wet or muddy.  1/4" wall lolly columns or 3" channel welded or bolted to the existing I beams would be more then enough at low 3 mph speeds when crossing.

[HARLEYRIDER]

I'll measure flange thickness today or tomorow.  When I first saw this bridge, I thought it was strong enough for a pick-up, but the owner of this property (who might chime in here)  felt it was only good for an ATV or suzuki samuri.  If we find that these 2 beams, when new, were good for 16 tons, then we'll both feel better about driving 3 or 4 tons on it.
I'll mic up the thickness and post it later.
Thanks

[scsmith42]

Lots of good feedback from a lot of folks here.

To cut to the chase though, from what you describe of the steel, if the steel appears to be in good shape and not seriously rusted I would not hesitate one second to take up to 20 tons over that bridge with new decking.

To be more specific, a steel I-beam in the dimensions you describe is probably between 26 and 35 lbs / foot.  The flange thickness for 26lb/foot is .360, with a web thickness of .230.  35 lbs/foot i-beam has a .520 inch thick flange, and a .300 thick web.

Without going into engineering overkill (which is easy for a lot of us to do, me included!), simply compare your bridge to any dual tandem trailer.  A 40' 25,000 lb load rated trailer will use 12" x 19lb i-beam - which is significantly lighter than what is on your bridge.  This same trailer will have about 25' span between the loadpoint at the hitch and the concentrated load point at the front axle mount - over double your bridge span.

And I'm being conservative too.  12", 26lb  I-beam over a 10' span should support significantly more than 20 tons.  I've personally rolled 10 ton equipment over an eleven foot span with 8" 15 lb/ft I-beam covered with 2" oak decking.  All ten tons was on the span too.

Some additional things to look at - will the load crossing the bridge be relatively centered over the I-beams?  If not, then you need to reduce the capacity based on the strength of the decking and how far the load will be away from the i-beam.

From what you describe, with 10/4 decking and 12" i-beam I would imagine that this bridge was built and installed for heavy logging equipment such as skidders, etc to use. 

Bottom line - as long as the steel looks good and you replace the wood decking, use it without worry.

Scott

[wiam]

I have driven a 10 ton truck over 3 ton bridges to go further up the road to put up gaurdrail.  I was very nervous until I heard that they had driven the crane that set the new bridge up further over them.  These 3 ton bridges hsd wood timbers under them and a bunch of wood cribbing.  I saw triaxle loads of maple to the top of the stakes go over them.  The deflection was scary.

Will

[Stan P]

Well Harley,  if your next post is from the bottom of the creek, we will know you had a bit more rust than you thought