Jul 5, 2016

General Trexler's Bridge

The 8th Street Bridge is one of the marvels of Allentown.  It was built to facilitate the Liberty Trolley run, from 8th and Hamilton to Philadelphia.  I posted about it before, with its impressive statistics. At the time it was the largest concrete bridge in the world.  It involved two business interests of Harry Trexler,  both the transit company and the local cement industry.

Harrisburg and The Morning Call have been braying about the bridges scheduled for improvement and replacement in the area.  Although, I virtually stopped attending municipal meetings,  I still partake in field trips to the local construction sites.  I don't announce myself, and try to be quick and quiet on these unauthorized inspections.  I would prefer not to vanish like Jimmy Hoffa.  I want to inspect the bridge, not end up in the bridge.

On first glance the work on the bridge looks very impressive. The bridge walls have been replaced with new concrete walls, almost identical to the original, even including the lighting pillars. My question is that the roadbed has been raised about 18 inches, but is still supported by the same arches. Eighteen inches of additional concrete on the roadbed and sidewalk is an enormous additional weight load. Furthermore, I have learned that there was bonding issues between the older base and new concrete. Only the approaches, on both ends of the bridge, have been replaced.  This was done because they are the lowest part of the bridge, and the most feasible parts to replace.  However, they were replaced with pre-stressed concrete beams, and the new arches are only decorative panels.  The original approach bases were massive constructions, which probably would have stood another 1000 years.

Only now is the part of the project which I knew to be necessary beginning.  The massive bridge arches has been showing spalling damage over the last decades.  That is the process where old concrete lets loose from the steel re-bar used as the construction frame.

When the project is completed, I do not expect to be invited to the ribbon cutting.


spencer said...

I don't know much construction, I don't follow what you are saying here about the bridge. What's spalling? Do you mean to say the bridge will be worse of due to the restoration/re-constuction/whatever you want to call it? Sorry, I just don't follow.

michael molovinsky said...

spencer @ 8:05, spalling is when the outer veneer of concrete separates from the iron rods beneath it. please google for fuller explanation. i'm not saying that the bridge will be worse. i'm noting that they replaced the easier or lower parts, but added extra weight to the longer middle part. the spalling was from the underneath portion, and was falling on the roads and property underneath. the bridge repair is a state project, and IMO, susceptible to follies involved in such contracts.

doug_b said...

The Mendota Bridge was completely refurbished about 10 years ago. The state of MN did it right.

Click on the picture of the bridge to see a slide show.


george schaller said...

Like most, everything looks all shiney bright and nue butt the mechanics are truely mal functional meltdowns on the inside?!