PEDESTRIAN SUSPENSION BRIDGE

[LUISGUTIERREZ]

The attachment shows a pedestrian suspension bridge built in a resort area in Central America. The span is about 90 meters. The main cable (on either) side is composed of three cables of about 1 inch in diameter. Would the participants in this forum provide technical references with guide lines for design and construction of this kind of bridge. I will appreciate information. Also, do you notice the two small wires bracing the columns of the tower? It seems they were needed during construction, but do they serve any purpose after completion of the structure? Will appreciate your insight.

Thanks

 

[BigH]

I think that you would do better posting in Structural Engineering and Other Technical Topics. This really isn't an earth retention (i.e., retaining wall) problem

 

[JAE]

Google mania!!!!

https://mcedc.colorado.edu/sites/de...ridge-Design-for-Rural-Construction_FINAL.pdf

http://www.ilo.org/public/english/employment/recon/eiip/download/footbridges.pdf

https://wildcatman.wordpress.com/category/building-a-small-cable-suspension-bridge/page/2/

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[hokie66]

Luis,

Full disclosure is best on this site. You didn't tell us that you were investigating a failure.

http://delsurnewsonline.com/san-juan-del-sur-foot-bridge-collapses/

 

[hokie66]

Now that we know that it collapsed, perhaps you can share with us which of the questionable details failed. These folks would like to know.

thread507-385689

 

[BigH]

I still fail to see why this post is in this forum

 

[LUISGUTIERREZ]

To hokie 66,
Thanks for your response and your interest on the subject. It is interesting to learn how structural failures happen. However, I would say that rather than performing an investigation, I have been trying to gain some insight on the failure and, in connection with that, how to prevent that failure to happen again, and how that bridge could be reconstructed (or how it should not be reconstructed).

The attachment to my original message shows the condition of the south anchorages before failure. I am attaching now a picture of the north anchorages. You will notice a difference. In the north anchorage the three steel bars at each cable appear to be on the same plane. In the south anchorage, one of the bars is out of the plane of the other two. Force diagrams at the node of the connection show that the load on the bar out of plane can be as high, or even higher than the tension in the cable, depending on the alignment of the cable relative to the bars, see attachment. This may have been a construction error. The over load on that bar may have caused the failure.

I have not been able to get a picture of the failed anchors (I am thousands of miles from San Juan del Sur). Pictures from digital editions of the local papers have very poor resolution, but it seems that the cables were disengaged from the anchors. It seems that the failure happened at the "eye" of the anchors, not on the straight leg of the anchor. Did the bar break at the eye? Did the weld attaching the two legs of the loop failed?

In any case, the type of anchors they used seems very fragile and highly vulnerable to misalignment. The bridge should not be reconstructed using the anchors of the north end, even if they didn't fail.

By the way, how do I transfer this thread to the structural section?

 

[hokie66]

That is a photo of the same anchorage, if not the same photo.

You can't transfer to another forum, as far as I know. But some of the same people will see this one. For any future use of the site, just check for an appropriate forum.

 

[LUISGUTIERREZ]

TO: JAE,

Thanks for the technical references.

 

[LUISGUTIERREZ]

hokie66,

My reply to you in this thread is missing two files: NORTH ANCHORAGE.JPG & BRIDGE ANCHORS STRESSES.PDF. Apparently you can only attach one file to your reply.

Here is one of them, I will send the other in a separate reply, in case you continue interested.

Thanks

 

[LUISGUTIERREZ]

To Hokie66,
Here is the missing photo of the NORTH ANCHORAGE. This file together with the BRIDGE ANCHOR STRESSES.PDF will help you to make sense out of my previous message. I still will appreciate your comments on my message if you continue interested.

Thanks.