31' Bridge across Creek

[crazyal]

Some more food for thought:
Why not price a W18 x 35 I-beam. Since steel is usually priced according to weight they would be cheaper. And they would also be stronger. Each beam would be able to carry just shy of 15000 LB in the center. Making the bridge safe to almost 30k. Being lighter, they may also be easier to set(not as big of equip. required). @39' long they would weigh 1365 lbs instead of 1950 lbs.

I was just about to post the same thing, not the calculated loads but that it could be cheaper and handle more weight. I'm just starting to build a garage and since I don't want any posts in the center I'm going to run an I-beam to support the second floor. The local steel company said I could use a w18x46 or as an option a w21x44. Since the w21 is a special order there would be no savings.

My suggestion was going to be a w16 in one of the lighter weights. I know you can get a 26, 31, 36, and 40. I know I would rather have a larger but easier to move beam. Of course that's assuming that the extra height will work where you want it to.

 

[LD1]

I was just about to post the same thing, not the calculated loads but that it could be cheaper and handle more weight. I'm just starting to build a garage and since I don't want any posts in the center I'm going to run an I-beam to support the second floor. The local steel company said I could use a w18x46 or as an option a w21x44. Since the w21 is a special order there would be no savings.

My suggestion was going to be a w16 in one of the lighter weights. I know you can get a 26, 31, 36, and 40. I know I would rather have a larger but easier to move beam. Of course that's assuming that the extra height will work where you want it to.

The w16 x 26 and 31 are not as strong as the w12x50. And the next one that I was was a 38, and that is heavier and not as strong as the 18 x 35.

When looking up the scale of beams, I was shooting for as strong as, or stronger than the 12 x 53. The 18x35 was the lightest one while still being at least as strong. I think it was a 14 x 45 or heavier, the 16 x 38 or heavier and the 18 x 35 or heavier to be as strong. Above 18 " there are no beams ligher than 35lbs.

The shorter the beam, the much heavier it needs to be to carry the load. The main reason for shorter and heavier is if you have hight restraints. Like for ceilings. If I had a 21" beam in my basement, sure the absence of jack posts would be nice, but not when I have to duck under the beam.

For this situation, I see no reason to use a short/heavy beam when a tall/lighter one will do the job.

 

[deanfitz]

Might just do that LD1, we'll see when the buying times come. Take a look a what they have here:
Surplus Steel Beams

 

[LD1]

12" X 10" X 53 LB Surplus Painted Beams 2@ 39' 10k per beam
14" x 8" x 48 LB Surplus Painted 37' Thru 50' 12k per beam
14" X 10" X 61 LB Surplus Painted Beams 38' Thru 50' 18k per beam
14" x 10" x 74 LB Surplus Painted 39' thru 50' 21k per beam
14" X 89 LB Surplus H Piles 4@ 40.3' 24k per beam
18" X 11" X 86 LB Surplus Painted Beams 37' Thru 50' 38k per beam



I copied and pasted the only beams they list that would be long enough for your span, and that would hold at least 10k per beam. And then listed the max point load @15.5' for each beam assuming the previously stated 60lb per foot dead load.

Is that place close to you? I bet shipping woudl be expensive, but worth a look. The 14 x 48 would probabally be your cheapest route, allthough if the price is right you could dang neart drive anything across a w18 x 86.

If you are not in a hurry, keep your eyes out for a good deal.

Just kinda as a general rule for you so you know what to look for

12" beam 50lb/ft and up
14" beam 43lb/ft and up
16" beam 36lb/ft and up
18" beam 35lb/ft and up
Anything bigger and/or taller is just icing on the cake. 21" beams and up don't come any smaller than 44lb/ft.

 

[crazyal]

Too bad they are too far from me. I could use that W21x44 40' beam.

 

[deanfitz]

Yes LD1, The place is 30miles away. We a 30' Gooseneck dual axle trailer & dually. I will watching this inventory until its time to buy.

 

[LD1]

Yes LD1, The place is 30miles away. We a 30' Gooseneck dual axle trailer & dually. I will watching this inventory until its time to buy.

What kind of prices do they have on them beams? Most places like that sell by .xx cents per lb. Just curious as to what there rate is on some of the above mentioned beams.

Use this site as a reference Wide flange beams

At the top, click properties. Under Axis X-X, The moment of Inertia is denoted as I. It is expressed in IN^4. If you scroll down, you'll see that a w12 x 50 beam is 394. (I noticed that they do list WAY more beams than in the beamboy program, maybe beamboy only lists the more popular ones). Any beam on that list that has an I value of 394 or greater, will be as strong as the w12 x 50 or stronger. You can use this as a reference if the get a beam in and you are unsure if it will be strong enough.

If they dont charge too much extra for the painted or galvanized beams, that might be the way to go, and save yourself a lot of work.

Also keep an eye on your local C-list. I was looking for 2 beams ~ 30 foot long to span the upstairs in my polebarn. Minimum spec was W10x19. New price was $900. I found a guy 2hrs away that had a bunch of W12 x 26, 30, and 35lb beams. They were 26' long. I told him I Needed 60 total feet. $500. When I got there, They had a shorter peice ~21'. He gave me that and 2 26' for $500. After cutting what I needed and lengthening the 26'ers, I had 14' of w12x35 left, which I had no trouble reselling on c-list for $200. So My 2 12" beams 29-30' long only cost me $300.

There are good deals out there, and you have time to your advantage if you aren't in a hurry.

 

[rutwad]

some friends just did something similiar. They used 3"x8" rough cut oak timbers.

 

[dodge man]

My degree is in civil engineering but I am by no means a structural engineer. I have done construction layout on many bridges and one thing about your design bothers me, but maybe I am misreading your post? Are the I beams going to be set in concrete? Most of the time at least one side, and often both sides just rest on the abutments. This allows them to flex as a load is driven across the bridge. Often one side is even set on a roller or bearing plate that allows the beam to slide on the abutment. This is probably not a big deal on your bridge, but I would allow at least one side of the beams to be free on the abutment.

 

[LD1]

My degree is in civil engineering but I am by no means a structural engineer. I have done construction layout on many bridges and one thing about your design bothers me, but maybe I am misreading your post? Are the I beams going to be set in concrete? Most of the time at least one side, and often both sides just rest on the abutments. This allows them to flex as a load is driven across the bridge. Often one side is even set on a roller or bearing plate that allows the beam to slide on the abutment. This is probably not a big deal on your bridge, but I would allow at least one side of the beams to be free on the abutment.

Very good catch. I must have missed that somewhere. Encasing them in concrete is not the greatest Idea.

My suggestion would be when you are pouring your 12' x 8' x 4' concrete anchors, build some forms that are the width and depth of the beam by however long the beam will be in/on the concrete. When you have about 18" of your 4' thickness done (or however tall the beam is) set the forms in where you want the beams to lay and finish pouring. That way, the top of your 12 x 8 pad will have 2 channels in them that are the depth and width of the beams. Then just set the beams in. They will be able to slide longways but cant flop over on their side or shift sideways at all. Make sure to use plenty of re-bar in/around where the beam will be setting.