Bridges are often landmarks. San Francisco has the Golden Gate Bridge, New York City has the Brooklyn Bridge, and Southeast Missouri will soon have a new Bill Emerson Memorial Bridge. Under construction, the Emerson Bridge spans the mighty Mississippi between Cape Girardeau, MO, and Southern Illinois. Supported by cables, the span — the longest in Missouri — crosses the navigational channel of the river. The new bridge will replace the current structure that opened to traffic in 1928.
“All the weight for the cable-stay is supported by two towers,” said Randy Hitt, Missouri Department of Transportation (MoDOT), area engineer. “There’s no interruption to river traffic, and there’s 1,150 feet between the two main piers — that is the longest span for MoDOT. The bridge will require less maintenance. The cable-stay structure is modern and sleek, but it’s a very complex construction process to get all of the cables at the right tensioning. The complexity is due to the large number of cables [up to 52 individual strands]. The tension changes as phases are added. It’s the cantilever method.”
The structure will be supported by a total of 15 piers, including the land abutments in Missouri and Illinois. The first four piers from the Missouri side support most of the structure. Piers 5-15 comprise the Illinois approach span. The piers are positioned from where the cable-stay section ends, and they connect with the Illinois shore. These 10 piers are much closer together than those that comprise the cable-stay.
The Illinois approach, everything but deck, will be complete in May 2000. The main span contract was awarded to Traylor Brothers Construction with a notice to proceed in June 2000 and completion date of June 2003, according to Hitt.
The contract to finalize construction of the bridge’s main span — piers 1-4 from the Missouri side — was awarded in early March to Traylor Brothers Construction of Evansville, IN, for just under $54 million. As part of the main span, Traylor Brothers will complete the massive foundation’s dredged caissons that sink to the bottom of the river. The drilled shaft foundation has 10 drilled shafts each with a diameter of 1.8 meters (6 ft.). The shafts extend all the way into rock, going into 4 to 4.5 meters (12 to 15 ft.) of solid bedrock. Traylor Brothers’ work on the site also includes completing pier 2, building piers 3 and 4, installing support cables, constructing the bridge decking on the first five piers, and putting in roadway and decorative lighting.
Additional work includes jet grouting under high pressures that flush mud out of the fissures in rock and put grout in for reinforcement. Initial corings did not show the fissures. Construction halted after such unanticipated changes in site conditions led MoDOT to discontinue a partnership with Flatiron Structures Co. in December 1997. Presently, the span is 20 percent complete. The Missouri approach is two years off original plans, however, the Illinois approach stayed on schedule. Bids were opened in February 2000 with several qualifying requirements that had to be met before a contractor could bid on the project.
“We pre-qualified contractors for the main span. MoDOT had three requirements: 1) river experience, 2) cable-stay erection experience [this is the first cable-stay bridge project in Missouri where MoDOT has taken the lead], and 3) dredged caisson foundation experience for the main pier and pier 4,” Hitt explained.
According to Hitt, the sequence of work is as follows: completion of the main span (foundation, superstructure, and bridge deck) on the Missouri side, the bridge deck on the Illinois approach, the Illinois approach (foundation, piers and girders), and all roadway connections. The time frame for remaining contracts includes 2001 to 2002 for the bridge deck on the Illinois approach, 2002 for the roadway connection from the bridge to Route 74, and 2004 for demolition of the old bridge.
While Traylor Brothers prepares to continue on the Missouri side, Massman Construction of Kansas City is working on the Illinois approach. Currently 40 to 50 crew members are on site with that number expected to reach 70 at the peak of construction.
Missouri and Illinois Venture
Under a $25.6-million contract, Massman will do the foundations, piers and girders.
Funding for the Bill Emerson Memorial Bridge is 80 percent federal, 10 percent Missouri, and 10 percent Illinois. The project started in the summer of 1996 as a joint effort between the two states with MoDOT taking the construction management lead.
According to Hitt, the two sister states alternate taking the lead on joint projects.
MoDOT is administering the Emerson Bridge project. Illinois Department of Transportation (IDOT) did the grading and abutment on the Illinois approach, and the states collaborated on design issues. The two transportation departments continue to coordinate closely, as the work demands.
“We have used partnering agreements on all contracts to date. We found it to be a good process here. We have weekly meetings that allow us to respond to situations. For example, we worked closely with contractors during the flooding in 1998 when we had to move a lot of equipment,” Hitt explained. “It takes a great deal of coordination to handle the number of cranes needed to move materials or forms and to set girders.”
Flooding, however, has not been a problem during recent dry months. In fact, the opposite scenario has resulted from below average rainfall. The low river has created some problems with equipment. Massman owns most of the equipment on site and transports it via barge on the river.
Project Specs
The project is vast with a foundation of 121 drilled shafts and two dredged caissons. In all, 45,729 cubic meters (60,170 cu. yds.) of concrete will be used, along with 5.9 million kilograms (13 million lbs.) of re-steel and 6.8 million kilograms (15 million lbs.) of girders. Cable strands total over 272 kilometers (170 mi.).
At nearly 1,213 meters (4,000 ft.), the length of the new Emerson Bridge approximates 13 football fields. The cable-stay portion totals 633 meters (2,086 ft.), and the Illinois approach span measures 567 meters (1,870 ft.). The driving lanes of the bridge deck will be located 18 meters (60 ft.) above the river. The suspension cables are attached to towers above the deck that rise over 91 meters (300 ft.) above the Mississippi River.
The new bridge will be nearly five times as wide as the current structure. The 30 meter (100 ft.) width consists of four lanes — two eastbound and two westbound — along with roadway shoulders. “It will have four lanes of 12 feet with outside shoulders of 10 feet and 6 feet for inside shoulders,” Hitt said.
Inspired by the Clark Bridge in Alton, IL, plans also call for 140 lights to welcome motorists to the region. Motorists are anticipating that the wider bridge and brighter lights will improve safety and efficiency. Currently, 14,000 vehicles utilize the bridge daily. By the year 2015, the volume is expected to increase to 26,000 vehicles per day.
Seismic Requirements
Built for maximum efficiency and longevity, the bridge adheres to many seismic requirements. “It is likely that we will have some seismic experience during the life of the new bridge,” Hitt said.
Due to its proximity to the New Madrid fault line, the Emerson Bridge was designed by HNTB of Kansas City to withstand seismic activity of 8.2 on the Richter Scale. For example, the main towers and decks have 16 shock transmission devices that weigh 2,700 kilograms (6,000 lbs.) each and act like giant shock absorbers. The bridge also utilizes a great deal more rebar than is typical.
In addition to meeting seismic design criteria, the Emerson Bridge has the benefit of providing research for the field of earthquake studies. Special research equipment is being installed during construction; it includes ground positioning system instrumentation with recorders to track movements on the bridge and surrounding land. This information will assist engineers in improving future seismic designs on bridges and other structures. Leaders in the field, who gathered in Cape Girardeau, determined the equipment and procedures for gathering data. Meeting participants selected specific location on the structure for the most valuable readings. A $500,000 grant from the Federal Highway Administration is funding the effort.
“The U.S. Geological Survey will place seismic instrumentation sensors on the bridge. They’ll use the data if there is a quake to learn the effects. We’ll put in conduits so that instrumentation is wired to a central spot in hollow towers, but that is really the only modification needed,” Hitt explained.
Today's top stories
