Transverse Cracking of Deck Slabs 2

71corvette · Nov 9, 2004

Over the past few years, many newly constructed bridges in the Northeast have had issues with transverse cracks developing on the underside of the deck slabs relatively shortly (< 1 year) after construction. Oftentimes the cracks are apparent in all interior bays (full length of bridge, + and - moment areas) and spaced anywhere from 3' to 8' on center. I'm aware of at least one study sponsored by a handful of New England transportation authorities that looked into this problem. As a result, there has been a good deal of debate relating to the cause of this problem. The cracking has been blamed on everying from superplasticizer in the concrete to composite action between the steel stringers and the concrete deck.

I'm inerested to find out exactly how widespread this problem is. Have any of you encountered this in your bridge projects? Have you discovered any means for reducing the frequency and magnitude of the cracking?

bridgebuster · Nov 11, 2004

I worked on two bridge construction projects in CT where effloresence was observed. No one made a big deal about it. I've also seen it on other bridges I inspected. The popular opinion among people that I discussed it with is a little too much water and/or aggregate with a little too much salt.

wiktor · Nov 12, 2004

The problem is apparently wide and current consensus is that's caused by the type of concrete mixture used, cement type, and pouring techniques. The links below provide access to some of the papers on the subject.

http://www.ltrc.lsu.edu/TRB_82/TRB2003-001122.pdf

http://www.transportation.njit.edu/nctip/final_report/CrackingDecksFinal.htm

http://www.utexas.edu/research/ctr/pdf_reports/4098_1.pdf

TpaRAF · Nov 12, 2004

I have seen similar transverse cracks on Florida bridges. It usually occurs with a concrete deck on steel stringers.

I've always thought it was related to flexibility. The steel beams deflect elastically, beyond the concrete deck's tensile capacity. Since the bottom face has too much tension, it cracks transversely near midspan. The situation should be reversed near the supports (cracking on top).

Most every bridge project I've worked on used p/s concrete beams, so I have no design advice for the problem. One potential retrofit is to apply carbon reinforced fibre sheets to either the beam flanges or the deck underside to reduce flexure.

Regards, RAF

VoyageofDiscovery · Nov 16, 2004

Another cause may be shrinkage due to relative humidity.

Regards

VOD

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