When the 1,000-foot-long bridge carrying U.S. 21 over the Catawba River started to become structurally deficient and functionally obsolete, the South Carolina Department of Transportation selected KCI to design the bridge replacement and roadway improvements. Our team performed an alignment and bridge study comparing cost and impacts of different alternates.
The project consisted of two miles of widening from a two-lane roadway to a five-lane curb and gutter section sidewalks and a 1,000’ eight-span, pre-stressed concrete beam bridge supported on drilled shaft foundations. The new bridge utilizes 74” pre-stressed concrete, bulb-tee beams supported on concrete drilled shaft and rock socket foundations to replace the existing structural steel bridge and includes bicycle lanes, sidewalks and aesthetic features with barrier walls and lighting.
The project also included a corridor analysis and bridge alignment alternate for cost comparison and potential conflicts. Our team provided SCDOT with a matrix and cost comparisons of each alternate while defining: ROW impacts/relocations, traffic staging, utility conflicts, environmental issues, geometric alignments and constructability. Engineers determined that moving the structure upstream rather than replacing it on the same alignment would save more than $1.5 million in mobilization costs and significantly reduce the impacts to the more than 20,000 motorists that cross the bridge every day.
Our team managed all subconsultants for bridge hydrology/hydraulic design, roadway design, environmental documents and permitting, surveying, geotechnical exploration, and utility coordination. KCI also performed the study for architectural features for the new bridge including concrete arches over the river, architectural railings with rock and brick facades, decorative light pedestals and lighting schemes.
Modeling allowed us to define our expectations and when we did a test load, we found that our deflections were within one-eighth of an inch of what we anticipated.
Andrew M. Craig, PEPractice Leader
SCDOT also retained KCI to provide construction inspection while contractor Lane asked the firm to look at alternate construction methodologies. Conventional bridge building approaches called for cranes to lift heavy girders into place; however, during design, engineers determined that the existing structure was unable to support the load associated with cranes and heavy girders. Use of barges was later ruled out because of the low water levels. KCI helped contractors develop a cutting-edge lifting frame to launch beams from the existing structure, which helped to improve safety, minimize environmental impacts and remove any uncertainty with using barges.