Bridge collapse near Pittsburg, PA

[MichSt]

Below are a few articles with photos of a bridge collapse near Pittsburg, PA. The bridge is an adjacent concrete box beam bridge carrying a local road over I-70. From the photos it looks like one of the fascia beams carrying the railing failed at midspan and collapsed. Luckily, the beam collapse happened during a break in traffic on I-70 and no one was seriously injured.

Anyone have additional info?? Thoughts on possible causes of collapse??

http://www.post-gazette.com/pg/05362/628813.stm

http://www.pittsburghlive.com/x/tribune-review/trib/regional/s_408139.html

http://www.observer-reporter.com/main.asp?SectionID=6&SubSectionID=15&ArticleID=7700

 

[wiktor]

There are two possible scenarios for this collapse. One will be a direct hit by an oversized truck (rather unlikely- it would happen already) and the other, more likely, corrosion of the prestressing wires.

 

[Qshake]

A couple of things come to mind.

1. The admission this bridge was rate as structurally deficient.
2. Where are the typical tension rods (to hold them together) that accompany precast deck beams?
3. If it was corrosion of the prestressing strands then at one time they were likely exposed from spalling concrete and patched...seems like someone should have seen this coming.

Terrible tragedy since it shouldn't have happened.

Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[broekie]

Probably not the cause of the collapse, but it seems like the bridge has a fairly high skew as well.

 

[curvbridger]

Critical components for this collapse, from what I have gleaned from news:

1. It was non-composite. No alternate load path for the failed beam.

2. The deck drainage was infiltrating the beams through the asphalt wearing course. Voids in the box contained water!

3. Low vertical clearance led to vehicular impacts.

4. It was, as I understand, a locally-owned rather than a state-owned bridge. Perhaps the inspections were less than they could have been.

Lessons:

Follow basic design rules, i.e. watch where the water is going, provide redundancy, inspect and maintain.

Transverse tensioning rods were either corroded or inadequate to prevent collapse.

"Do not lay up for yourselves treasures on earth, where moth and rust ..." Matt. 6:19

 

[YUF]

Certainly the bridge failed in resisting bending and shear at the critical sections(edge for shear). Maintenance authority is responsible for lack of management of bridges, however the aspects of falling concrete and rebar corrosion on the adjacent carriage way have been noticed earlier according to the sources.

YUF
Bridge Engineer.