Structural Design and Materials Selection Considerations

Marie Fisk, P.E.,

Bridge Division, TxDOT

Bridge Summary

• Total Length = 11,010’

• 93 spans

–92 spans of Tx54 in 120’ and 100’ lengths

–1 span of Tx70 at 150’ channel crossing

• Horizontal curve in first 5 spans, rest straight

• ~3% grade crossing channel

• Minimum Vertical clearance at channel 75’

Bridge Bents

• Three bent types

– Trestle on square piling

– Trestle on cylinder piling

– Pier w/ cylinder piling, footing, cast-in-place (CIP) columns

• Dependent on location and height

Trestle on Square Piling

Trestle on Cylinder Piling

Pier w/ cylinder piling, footing, CIP columns

Two Types of Deterioration

• Sulfate attack

– Deterioration of concrete

– Mitigate w/ a sulfate

resistant cement (Type 2 or 5 )

• Corrosion

– Deterioration of reinforcing steel

– Mitigate with:

• High performance concrete (HPC)

• Corrosion inhibiting admixtures

• Increased clear cover

• Epoxy-coated reinforcement

Sulfate Attack

• Elements using Type 2 or 5 cement:

–Square piling

–Cylinder piling

–Footings

• Or all elements in constant contact with seawater

Corrosion Resistance

• CRP historically hasn’t used these measures • HPC

– Abutments – Bents – Footings – Slab – Girders – Square Piling

• Corrosion inhibiting admixtures – Calcium nitrite – Precast elements only - piling and girders

Corrosion Resistance

• Increased clear cover – Deck (also PMDF disallowed)

– Abutment and bent caps

– Columns

• Epoxy-coated reinforcing (ECR) steel – Deck

– Rail

– Abutments

– Bent caps and tie-beams

– Columns above elevation 13’

Stainless Reinforcing Steel

• “Splash Zone” below El 13’ – MHW = El 1’

– Plus 12’ wave height

• Epoxy Coated Reinforcing is questionable in wet conditions

• Use stainless reinforcing steel in CIP elements – Columns below 13’ elevation

– Footings

– Pile-footing connections

Stainless Reinforcing Steel

• Cost comparison

– Black $0.35/lb., Stainless $2.47/lb.

– $541,000 increase for 175,000 lbs.

– 0.6% of estimate

• Included in SP440-004

Cylindrical Piling

• Long-Term Durability

• Least Environmental Impact

• Construction Impact

Spun-Cast Cylindrical Piling Long-Term Durability

• We considered 36” sq. piling with voided center

• Spun-cast cylinder piling have high density & their shape reduces inclination to crack

• Other Gulf Coast states regularly use and have had outstanding performance with spun-cast cylinder piling

Least Environmental Impact

• Drilled shafts were not feasible

• Cylinder piling reduce footprint

• Cylinder piling are alternate

Construction Impact

• Soil profile extremely soft for considerable depth – drilled shafts not an option

• Reduce the amount of CIP over open water

• Vessel impact – bents needed lateral resistance

• Cylinder piling replace standard sq. piling in a ratio of 1:2 or 1:3

Cylinder Piling

• Need sulfate and corrosion resistance

• Require sulfate resistant cement (Ty 2 or 5)

• Extremely low permeability concrete

– maximum chloride ion penetrability of 500 coulombs, per ASTM C1202

• Use calcium nitrite admixture

Static Cast Cylinder Piling

• During planning process, the precast industry wanted a statically cast option. The SS for the cylinder piling was modified to include statically cast pile sections.

Cylinder Piling

Our Plan: Spun-Cast,

Post-tensioned

Full Length Static Cast Cylinder Piling

Plans vs. Shop Drawings

Plans vs. Shop Drawings

WB Full Length Static Cast Spun Cast

Full Length Static Cast Cylinder Piling

Spun-Cast Cylinder Piling