RNS
Browse Projects > Detailed View

Cracking of Decks on Deep Plate and Tub Girders

Description:

Cracking of Decks on Deep Plate and Tub Girders – (Similar to what has been observed on curved ramps of Marquette)

Cracking of concrete decks supported by steel girders has been a perennial problem in the industry that despite all research performed to date seems to be eluding a concrete (no pun intended) and satisfactory solution. We have a clear pattern of transverse deck cracks on several Tub and Plate Girder Bridges - Need Solution. The problem seems to be even more pronounced in the case of deep and stiff girders such as steel tub or deep steel plate girders. This research would propose to study them first to identify at least the structural part of the problem. This would compare actual performance of bridge decks that have cracked with the analytical models to determine if we are capturing the actual stresses at hand. Other structural aspects to be researched would be:

  • Curvature of structure,
  • stiffness differentia, (deep steel girders are way stiffer than the deck they’re carrying, especially if girder is expanding and deck is resisting the expansion)

  • effects of eccentricity: if a girder is expanding due to temperature rise, the deck is resisting but at fibers that are further away from the neutral axis in these types of structures. Therefore, the stress they would see would be larger, potentially taking them above the modulus of rupture threshold.

  • temperature differentia

  • differentia of the coefficient of thermal expansion, which is at least about 10%, but new studies sponsored by Caltrans show the concrete coefficient of thermal expansion as low as 0.0000055 or lower. That would make for about 12% difference.

  • differentials in heat conductivity and ambiance differentials such as temperature and sun exposure,

  • bending, longitudinal and transverse (for more flexible bridges), etc. This could also address the placement, curing, and shrinkage aspects.

Objective:

The main objective is to understand the problem fully, the real causes of cracking, which might be singular but might also be a combination of all the mentioned basic cases. What causes a deck that has been designed to not see any tension in the deck from dead and live load to end up in the first few months of service with evenly spread cracks at every 2’-4’ frequency.

Once the problem is understood, it should be easier to mitigate the causes accordingly.

Research should be mostly analytical, combined with ambiance data from specific projects, but it may also involve some experimental testing/monitoring of new bridges.

Benefits:

Concrete decks in the USA crack. We have not figured it out yet as to what would be the right solution. Billions of dollars are spend replacing decks within 35-45 years, when their life should match that of the bridge to at least 75 years. Even when special mixes and protection are specified for the concrete mix, they usually assume concrete models with no cracks. That would indicate that even with special concrete mixes, and for bridges where decks have been designed for zero tensile stress based on the conventional service combinations of basic loads, the decks still crack and in frequencies that are similar from structure to structure, and are not easily explained from conventional practice of load combinations.

Related Research:

Usually using conventional methods and focusing on concrete mix design and concrete pouring and curing implementation .

Tasks:

A combination of field measurements, lab testing and a lot of finite element studying of the issues included here below:

  • Curvature of structure,
  • stiffness differentia, (deep steel girders are way stiffer than the deck they’re carrying, especially if girder is expanding and deck is resisting the expansion)

  • effects of eccentricity: if a girder is expanding due to temperature rise, the deck is resisting but at fibers that are further away from the neutral axis in these types of structures. Therefore, the stress they would see would be larger, potentially taking them above the modulus of rupture threshold.

  • temperature differentia

  • differentia of the coefficient of thermal expansion, which is at least about 10%, but new studies sponsored by Caltrans show the concrete coefficient of thermal expansion as low as 0.0000055 or lower. That would make for about 12% difference.

  • differentials in heat conductivity and ambiance differentials such as temperature and sun exposure,

  • bending, longitudinal and transverse (for more flexible bridges), etc. This could also address the placement, curing, and shrinkage aspects.
Implementation:

Bridges should be studied as follows:

  • Bridges already built should be studied and modeled in full FEM. Issues mentioned above should be individual studied in the numerical models. Comparisons should be made with field findings.

  • Some full-size tests should be included in the research, but these might require significant expenses and large labs with special capabilities. Once the problem is better understood and comparisons with already built bridges seem to match, then new bridges should be identified at least to be monitored from day one, but potentially if mitigation solutions are proposed they can also be implemented in this stage.

Relevance:

All bridge owners

Sponsoring Committee:AFF20, Steel Bridges
Research Period:Longer than 36 months
Research Priority:High
RNS Developer:Tony F. Shkurti, PhD, PE, SE
Date Posted:02/14/2017
Date Modified:03/19/2018
Index Terms:Bridge decks, Girder bridges, Cracking, Stiffness, Shrinkage,
Cosponsoring Committees: 
Subjects    
Highways
Construction
Design
Maintenance and Preservation
Bridges and other structures

Please click here if you wish to share information or are aware of any research underway that addresses issues in this research needs statement. The information may be helpful to the sponsoring committee in keeping the statement up-to-date.