STRENGTH CONTINUITY OF DETERIORATED CONTINUOUS SLAB R.C. BRIDGES. FINAL REPORT

Continuous reinforced concrete slab bridges rely on reinforcing steel near the top of the deck over the piers to carry negative moment. However, these negative moment resisting bars and the concrete around them are vulnerable to deterioration from traffic wear, deicing salts and weather. When the concrete around the bars deteriorates, the bars may debond and lose negative moment carrying capacity. This situation may be complicated by a common repair method called variable depth removal. In this method, deteriorated concrete is removed from the deck and the deck is patched. However, when the deterioration is excessive, enough concrete may be removed to completely debond the negative moment resisting bars. If these bars are fully or partially debonded, the continuity over the pier lines may be fully or partially lost. This results in an increase in the positive moments in the spans since the spans now behave like simple, rather than continuous spans. This research tested three bridges to determine if variable depth removal affected the moment distribution and stiffness of bridges under repair. One bridge had only slight damage over the piers, one bridge had moderate damage over the piers and the third bridge had severe damage over the piers. The bridges were tested by truck loading, with the trucks placed to cause maximum deflection in two spans and maximum negative moment over the piers. Deflections and slab strains were measured. Slab moments were inferred from the slab strains. The results show that the bridges lost stiffness during repair, but after repair the stiffness was increased from the prerepair condition. However, in all cases the deflections were an order of magnitude less than those allowed by code. The results also showed that continuity was lost during repair and that slab dead load positive moments may be increased as much as 50%, depending on the amount of damage to the bridge. After repair, the continuity was completely restored and the live load distribution is essentially unaltered. A rating of the bridges was conducted and it was found that repairs increased the bridge rating. It was also found that since moment over the piers is the controlling case for rating for most slab bridges, the redistribution of dead load moment to the positive moment zones does not significantly affect the bridge rating. The study concludes that variable depth removal is effective at restoring stiffness and continuity, but that there may be a redistribution of dead load moment during repair. However, this redistribution is usually not large enough to affect the bridge rating, although it must be accounted for in the rating procedure. Finally, the amount of moment redistribution can be controlled by careful planning of the repair methods.

  • Corporate Authors:

    University of Cincinnati

    Department of Civil and Environmental Engineering
    Cincinnati, OH  United States  45221-0071

    Ohio Department of Transportation

    25 South Front Street
    Columbus, OH  United States  43215

    Federal Highway Administration

    1200 New Jersey Avenue, SE
    Washington, DC  United States  20590
  • Authors:
    • Miller, R
    • Shahrooz, B
    • Saraf, V
    • Godbole, B
  • Publication Date: 1994-2

Language

  • English

Media Info

  • Features: Appendices; Figures; References; Tables;
  • Pagination: 145 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00670384
  • Record Type: Publication
  • Report/Paper Numbers: FHWA/OH-94/010, UC-CII-94/01
  • Contract Numbers: State Job 14501(0)
  • Files: TRIS, USDOT, STATEDOT
  • Created Date: Dec 7 1994 12:00AM