CONCRETE BEAMS

PRESTRESSED CONCRETE I-BEAMS

Prestressed concrete I-beams are usually constructed as simple spans (not continuous over piers) and, after erecting them, made semi-continuous by casting a transverse concrete diaphragm over the piers which also fills the gap between the beam ends. The first prestressed I-beams were constructed in Ohio in 1958, although not widely used until the early 1990s. These types of beams have been relatively maintenance-free thus far, although sealing the fascia beams is recommended on a regular basis.

Preventive Maintenance Recommendations:

  • Seal the fascia beams with a silane/siloxane sealer every 5 years.
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  • On overpass bridges, watch for nicks, gouges and spalls in the beams  caused by overheight traffic passing below.  Patch these areas as noted in the Repair Section of this Manual.

PRESTRESSED CONCRETE BOX BEAMS

Prestressed concrete box beam bridges have been popular in Ohio since the late 1950s. Box beams are set side-by-side, tied together with transverse tie rods along with grouted keyways between the beams near the tops. Many of the bridges up until the early 1990s were waterproofed and covered with a minimum of 2-1/2" asphalt concrete. More recently, the bridges are being topped with a 6"-thick reinforced concrete deck.

Some important aspects of prestressed box beams to remember are:

  • The beams get their strength from 1/2"-diameter high strength steel strands located within 2" of the bottom of the beams and spaced at 2" centers. The strands are uncoated and are vulnerable to corrosion caused by chloride infiltration.
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  • The beams are hollow except at the ends.
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  • The longitudinal joints and keyways between the beams tend to leak.

Preventive Maintenance Recommendations:

  • Seal outside fascias of beams with silane/siloxane every 5 years
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  • Seal any cracks in the wearing surface as noted under Wearing Surface section to keep moisture out of the beams.
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  • If leakage is noted on underside at joints, consider having wearing surface replaced and keyways re-grouted.
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  • On overpass bridges, watch for evidence of collision from overheight passing below, and repair spalls as noted in Repair Section of this manual.