Bridge#2

[Transit]

Geeee....... I wonder why that failed? Oh, wait ...I think I might have an Idea. The bridge opened in 1936 and has appox 270,000 cycles per day. That would be 719,415,000 cycles before stress failure.

Mock me if you will. The Oakland Bridge was designed and built by PROS that know of such things and a testament to their skills, no such thing as CAD modeling in 1936. Nothing was said about the pitfalls of Stress Concentration until I tabled the subject of being careful where holes are being drilled. Choosing to ignore or be unaware of the subject does not offer protection from a stress crack failure. Will the bridge collapse next week, no? Maybe in the next five years? One day Buggyman will be crossing and will he have an oh-zhit surprised look on his face. [hope not]

Not a believer? I'll see if I can access the photo files at work. About seven years ago, maintenance was being done on the bridge crossing the Passaic River in Newark, my office over looks the bridge. All the train traffic from New York City Penn Station going north-south passes over that bridge, Washington, Atlanta, Florida, etc., the bridge can not be taken out of service.
To work safely, sections of the bridge were blocked off into safe work zones and when that zones work was completed the zone would be moved to the next section. The trains would run slowly and the work crew would stop-start to accommodate the traffic by the safety director. One of the workers was killed; he stepped beyond the safe zone coming into contact with the overhead catenary line that powers the electric trains at 42,000 volts. His body was hanging on the bridge in plain sight for hours until he could be safely taken down, we don't need any more killed in the recovery. The point is, you get to screw-up only one time and that will be the very last time.

 

[BlacknTan]

How did humankind ever get things built before rafts of college boys with their slide rules and calculators?? I just don't know! Oh wait, I do know... They used good old fashioned common sense and overbuilt from there. Just like the OP did here!
Ever wonder why old structures survive, and some modern ones that are only built to design specs don't??
Overbuilding!!
Things were built far beyond there design limits for safety's sake, because folks didn't have the answers, and college educated engineers to back them up.. Today, structures a built closer to the edge, and judging by the bridge failurse we've seen lately, I think I'd prefer to put my trust in old, seat of the pants technology over the handiwork of the college boys with their degrees hanging on the wall.

 

[harpoonalt]

Your bridge came out great. Very well thought out and done. I'd cross it anytime. I get a kick out of all this engineer stuff. They can and do some great stuff. We have engineers at work who can tell you all sorts of stuff, like the world is black and white. We also have some guys without college degrees that get stuff done when the "theory" just doesn't work. What they lack in formal education they more than make up for in real world experience. I can't tell you how many times we've told a new engineer that something wouldn't work only to have them go ahead and do it anyway. I guess they have to learn somehow. I'm not knocking engineers. We've had some great ones. But the real world isn't all numbers and calculations. I know of many similar bridges built by individuals that have been around forever and take higher loads than his tractor. And history is full of engineering disasters. And lest we forget, a lot rests with who builds the bridge. The best designs executed poorly can be just as bad. My .02.

 

[wedge40]

I still like how we trying to compare the OP's bridge to something commercial, that carries 10's of thousands vehicles over it every day. We have an over pass in town that was built in the last 15 years. In my book that's a brand spanking new bridge. Yet if I'm stopped in traffic in the middle of the bridge waiting to make a turn I can feel a good deflection as the cars and trucks roll by.

Wedge

 

[foggy1111]

Mock me if you will. The Oakland Bridge was designed and built by PROS that know of such things and a testament to their skills, no such thing as CAD modeling in 1936. Nothing was said about the pitfalls of Stress Concentration until I tabled the subject of being careful where holes are being drilled. Choosing to ignore or be unaware of the subject does not offer protection from a stress crack failure. Will the bridge collapse next week, no? Maybe in the next five years? One day Buggyman will be crossing and will he have an oh-zhit surprised look on his face. [hope not]

Not a believer? I'll see if I can access the photo files at work. About seven years ago, maintenance was being done on the bridge crossing the Passaic River in Newark, my office over looks the bridge. All the train traffic from New York City Penn Station going north-south passes over that bridge, Washington, Atlanta, Florida, etc., the bridge can not be taken out of service.
To work safely, sections of the bridge were blocked off into safe work zones and when that zones work was completed the zone would be moved to the next section. The trains would run slowly and the work crew would stop-start to accommodate the traffic by the safety director. One of the workers was killed; he stepped beyond the safe zone coming into contact with the overhead catenary line that powers the electric trains at 42,000 volts. His body was hanging on the bridge in plain sight for hours until he could be safely taken down, we don't need any more killed in the recovery. The point is, you get to screw-up only one time and that will be the very last time.

Get a grip man. His bridge is very well built. I bet you would absolutely freak at loading 9 foot wide combines on an 8 foot wide flat bed like we used to do!! Their is lots of stuff done that just requires common sense.

 

[SuperDuty335]

The 1/8 inch deflection is not what I was concerned about. Remember the Oakland Bridge in California that was closed this weekend? Did you see the Dog Bone Link that cracked at the Eye? That crack was the result of stress-concentration as opposed to average stress. That type of crack starts at the inside of the hole [a point of discontinuity] that the link-pin secures and works its way outward.[ first discussed in 1864 by Barre de Saint-Venant] Now that bridge and its components are many times stronger than it has to be [safety factor] and that link could have completely failed, other links in the catenaries would have safely taken up the extra load. Drill holes in the wrong place and you setup a very local overload that will fail some day. I could bore you for hours with the details of Mores Circle, Dynamic and repeated loading, etc.
Bottom line is, Buggyman ends up in the ditch crushed with the tractor on him.

PS, not kidding.

I knew that would get you fired up. But do realize I agree with you about punching holes in the wrong places. Bore me all you want.

 

[sld]

If a guy looks at a very, very small probability of failure with fear he will never get anything accomplished.

Almost every part or system on an aircraft is proven that it will fail at some point. When that probability is below an acceptable level is it fine.

If Transit's logic of "it just takes one time" was the golden rule of aviation there is not an aircraft in existence that would be allowed to fly.

I am an engineer in the aircraft industry and I will be the first one to tell you that common sense is the best quality to have in designing anything.

 

[schmism]

some suggestions i noticed for the next one that is built.

instead of drilling ten thousand holes in the I beam for attachment of deck material. Instead bolt single 2x ontop of the beam with a bolt every few feet. then lagbolting or screwing the decking material to the top of that material.

i curious if you budgeted your build. did you price out any other options/variants?

For instance the second span of 10' looks as if a small section of retaining block could have been layed and that portion back filled with dirt/gravel eliminating that section of "bridge" leaving the larger 25' span. At which point many people (myself included) have discussed useing old flat bed semi or the like for small span bridges. For someone who would have actually DONE it, im curious if you spent any time investigating it.

 

[buggyman1]

some suggestions i noticed for the next one that is built.

instead of drilling ten thousand holes in the I beam for attachment of deck material. Instead bolt single 2x ontop of the beam with a bolt every few feet. then lagbolting or screwing the decking material to the top of that material.

i curious if you budgeted your build. did you price out any other options/variants?

For instance the second span of 10' looks as if a small section of retaining block could have been layed and that portion back filled with dirt/gravel eliminating that section of "bridge" leaving the larger 25' span. At which point many people (myself included) have discussed useing old flat bed semi or the like for small span bridges. For someone who would have actually DONE it, im curious if you spent any time investigating it.

If you look back at the build, that is pretty much what i did, i used 4x4's instead of 2x4's but the same idea. I just couldn't not tie-in the i-beams, for my own overbuilding ego...its hard to explain..maybe i have a drilling fetish...lol. In my mind, bolting the slats directly to the beams makes me feel safer when i cross it with the K. I know that prob. don't make it stronger...it just makes me feel better. As for the budget, i really didn't set a price range, i knew it would be costly, and it cost more than i thought (as everything does). Again, if you look back at the start, and the lay of the land, backfilling the 10 foot section was really not an opition...I think my photo's are lackluster at least. The flat bed trailer is a great idea...I barely had enough room to get a single i-beam to my location. I did put quite a bit of thought into this..and yes i prob. spent to much and didn't think of everything.. I kinda went by my seat of the pants on this, as i do most things...Think of all them stress-fractures on the semi trailers...if i could have got one cheap, and had the room to move it to my place...SOLD.. The bottom line is, do you feel safe crossing it...I do. I'm happy with it.

 

[schmism]

the lay of the land, backfilling the 10 foot section was really not an opition...I think my photo's are lackluster at least.

Intresting. From this photo (and others like it)

it makes it look as if only a small section of retaining wall would need to have been built with a total elevation of no more than about 3' (useing your peer as the main headwall)

regardless the finished product is impressive!