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Archive for October 1st, 2019

Monthly Science: Concrete Bridge Flexing

Riding south on Rt 376 takes us across the Mighty Wappinger Creek on a four-lane concrete bridge built about 1995. This Dutchess County Aerial Access photo shows it in 2016:

Rt 376 - Wappinger Bridge - 2016 overhead
Rt 376 – Wappinger Bridge – 2016 overhead

A pothole opened up on the south end of the span last year:

Rt 376 bridge deterioration - marker 1102 - 2018-05-07
Rt 376 bridge deterioration – marker 1102 – 2018-05-07

NYS DOT patched it a while ago:

Rt 376 - Wapp Bridge - 2019-09-11 - 0490
Rt 376 – Wapp Bridge – 2019-09-11 – 0490

This year, we’ve been avoiding a new pothole opening on the north end:

Rt 376 - Wapp Bridge - 2019-09-11 - 0295
Rt 376 – Wapp Bridge – 2019-09-11 – 0295

It’s difficult to ride between the right side of the hole and the weeds growing from the curb joint under the guide rail, so we take the lane whenever we can. The extensive vegetation growing in the bridge structure can’t possibly be a good thing.

The bridge deck rests on steel beams across the creek, with plenty of corroded concrete along the edge:

Red Oaks Mill bridge - dangling concrete
Red Oaks Mill bridge – dangling concrete

The concrete seems to be failing by tension overload as the beams flex downward under traffic loading and pull the top surface apart. The surface has irregular transverse cracks across the deck width, not all of which look like control joints.

With potholes and surrounding cracks allowing brine into the deck, we expect much worse deterioration during the next few years.

My Professional Engineer license has long lapsed, not that I ever knew anything about bridge design, so this is mostly observational.

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