Sunday, June 28, 2020

Steel is stronger in tension than compression

I've talked before about members in a truss bridge that are in tension are cheaper to build than members that are in compression. When I saw this photo I was reminded that steel is weaker in compression.
John Snyder posted
And when I saw this photo a week later, I decided that was close enough for my "2 in 2" rule to write about steel in compression.
William HBaird posted
Covered Hopper MOCX 426425 appears to be the victim of a very hard shove or a collision. Andy Cassidy took this shot in the CP yard in Coquitlam BC in June 2020.
Cameron Blanchard Looks like hump damage.
Tom Srb Looks like a Trinity Industry built car, they never did hold up even in normal usage situations.
Dave Drake Took more than a hard shove . Iol
John White Hit pretty hard to bend the sills like that.
Jerry Maddax I’m thinkin,a smidge over 4 mph

Rick Carpenter commented on William's post
And the demonstrations just kept on coming.
Walter A. Keil A fully loaded reefer like I assume that one is need to spread a bar across the top so it picks up straight up not towards the center.
Jim Snowy With the slings angled like that, there is compressive force created in the container. Normally they are lifted with a spreader so the force is purely lifting.
David Carnes commented on the above video
Containers are designed to be lifted from bottom 4 corners when loaded. Top will overstress and buckle them.
Brett Patrick David Carnes They're always top lifted at container terminals, but the jigs they lift with eliminate the included angle component which caused this failure.
Paul Marcati Directions on the side lol
Never pick loaded container from top pick points
Always use lower pick points
Any old truss bridge shows that members in tension are much cheaper (less metal and less fabrication) than members in compression. This is an example of v-lacing compression members.
Old Renwick Road
HAER explains that the truss members were fabricated in their shop and then shipped to the site and assembled using a local work crew under the supervision of a field agent who worked for the bridge company.

Morris Terminal RR Bridge over I&M Canal
This Big Four Bridge over the Ohio River is so big that even the "simple" members are rather substantial.
20151009 1090
Another bridge that has been converted to pedestrian use and allowed me to get up close and personal with the truss members was the 135th Street Bridge in Romeoville, IL.
20200313 1689

20170121 7700, Abandoned C&NW in Carpentersville, IL
This bridge is basically a Warren Truss. They evidently don't have pure tension members. But the vertical members are thinner than the diagonal members.
HV/C&O over Hocking River

The swing span is a Warren Truss, but the approach spans are Pratt trusses and the diagonals have just tension so they are simple bars.
Wabash Cannon Ball over Wabash River

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