Lightweight Bridge Crane - beam loading question

[tech7weld]

I am in the formative stages of designing an overhead bridge crane for my shop. With assistance from other threads on this forum and Engineering ToolBox I ran some basic calculations on the bridge beam. The following basis was used:

Beam Size: S8X23
Beam Span: 20ft (240")
Load: 2500 lbs
Calculation: Single Center Load

Based on the above, I came up with a deflection of 0.382" This seems excessive. I am missing a decimal somewhere? Can someone here verify?

Thanks in advance. Sketch of proposed design is depicted below.

 

[dfkrug]

A third of an inch is excessive? That's a pretty shallow beam (8"). Are you designing around
a beam you already have? I have found that W-shapes are easier to find in stock at the steel
disti.

My own beam trolley uses a 12" deep beam spanning 25', but I designed for only about
1200# midspan live load.

 

[tech7weld]

A third of an inch is excessive? That's a pretty shallow beam (8"). Are you designing around
a beam you already have? I have found that W-shapes are easier to find in stock at the steel
disti.

My own beam trolley uses a 12" deep beam spanning 25', but I designed for only about
1200# midspan live load.

Thanks for your feedback. No this construction is brand new - no materials have been purchased so essentially a blank piece of paper right now. As far as deflection, I honestly wasn't sure what to expect. 3/8" deflection certainly won't make the bridge beam come off the rails. In looking at previous posts on a similar subject, I know there are some math and engineering guros on here, so I was hoping that someone could double check my math.

On the 'S' beam choice - I am leaning towards that as I do have a beam trolley that is made for an S beam (it has the tapered rollers).

Thanks again,
RC

PS: Am I correct in assuming that your bridge is pulled back and forward by hand/chain and not power assist?

 

[RedNeckRacin]

Don't forget that those span calculators only spit out an answer. I would greatly suggest having the design looked at by someone. Most cranes have a 5:1 factor of safety on them. There is also impact loading that must be accounted for in the design. I suggest looking up a design manual for bridge cranes or get the AISC book out and start doing some reading. The simplest way is to copy an existing design. The deflection appears to be correct.

 

[tech7weld]

Don't forget that those span calculators only spit out an answer. I would greatly suggest having the design looked at by someone. Most cranes have a 5:1 factor of safety on them. There is also impact loading that must be accounted for in the design. I suggest looking up a design manual for bridge cranes or get the AISC book out and start doing some reading. The simplest way is to copy an existing design. The deflection appears to be correct.

Good counsel. Thank you sir.

 

[RedNeckRacin]

Your welcome.

I did the beam design for my house recently and it took me several hours to get the problem set up to account for all the loading. I actually ended up using deflection to control my design because I didn't want my tile to crack. I may have went a bit overboard, but I had to design the column for the center of the span and the footer to support everything so I wanted to make sure I got it right.

 

[DaveK OR]

Here's a site that will give you pretty good information on beam deflections. You can choose the beam type (including material), the supports, point, uniform, or distributed loads, and so on. I found it very helpful when deciding what beams to use to support the perimeter of a rather heavy deck (It's actually a roof with 2" concrete pavers on the deck surface). My only complaint about their calculator is that it doesn't address things like smaller tubing sizes.

One good thing about the calculator, is that it will give you some indication of "failure mode" (shear, deflection, buckling, etc.).

 

[dfkrug]

PS: Am I correct in assuming that your bridge is pulled back and forward by hand/chain and not power assist?

Mine uses an electric hoist and a manual, chain-controlled horizontal travel. Electric travel was too fast for me. For
the hoist, I used a snatch-block/hook to slow things down. I use it mostly to install/remove engines, and put
tractors back together.

I understand the use of an S-shape, rather than a W-shape if your trolley wheels are tapered.

My trolley runs along my ridge beam, so no bridge. Simpler, but no sideways travel.

 

[LD1]

Late to the party.

Deflection is correct for the loading. But That beam only gives you about a 3:1 safety factor. Most cranes, as mentioned, are designed with 5:1 in mind. Which for THAT beam, and 20' span, would be around 1900# WLL.

The bridge rails and columns are equally important in their design. And i didnt see where you specified what size / shape the rails would be.

An S10x25 beam would be a better choice, and since its only ~20# heaver overall, the difference in cost will be nil. Since steel is ultimately priced by the pound.

 

[tech7weld]

The bridge rails and columns are equally important in their design. And i didnt see where you specified what size / shape the rails would be.

Thank you LD1. This is exactly the feedback I was looking for. In regards to the lateral rail sizing, you are correct - I have not decided on the sizing for these. For the uprights, I am planning on 8" SCH40 mounted on a 1" thick base plate (see sketch on my original post). Still a work in progress... albeit slow.