Twin Basket Tied Arch Design Replaces Iconic Broadway Bridge
On September 28, with a formal closing ceremony, the iconic Broadway Bridge in downtown Little Rock was closed to traffic for the last time, as construction begins on a replacement bridge to be built in place. Also known as the U.S. Highway 70 bridge, the 93-year old structure is one of three bridges (along with the Main Street Bridge and the Interstate 30 Bridge) which cross the Arkansas River and connect downtown Little Rock with North Little Rock. The replacement project is expected to take six months, and in fact, there is a significant incentive for the contractor to complete the project in that 180-day period. Work has already been underway for many months on several components of the project to facilitate the destruction of the old span and the building of the replacement bridge in the shortest possible time.
The Broadway Bridge opened in December of 1922, but the entire project was not fully completed until March 1923, when a grand opening event was held. The original structure is a five-span open spandrel arch concrete bridge with a length of 2,786 feet, a deck width of 40 feet, and a 24.3-foot vertical clearance. In 1974, two spans were removed on the south side and replaced with a single through arch span to provide a navigation channel for the McClellan-Kerr Arkansas River Navigation System. The silver single arch came to be a familiar icon of the Little Rock skyline.
In 2010, the existing bridge was determined to be structurally deficient, and inadequate for a traffic flow that now averages 25,000 vehicles a day. In early 2011, The Arkansas Highway Commission and the Arkansas State Highway and Transportation Department (AHTD) selected engineering firms Garver LLC and HNTB Corporation to design a new bridge; the final design is a four-lane arterial, which incorporates twin basket handle network tied arches. Each of the two arches will weigh approximately 2,000 tons.
From four contractor bids on the project, the Highway Commission and the AHTD accepted a $98.4 million bid from Massman Construction Company of Kansas City, Missouri. Awarded in September 2014, it was at the time the single largest contract ever awarded by the Highway Commission.
Minimizing Construction Timeline
The complexity of the design and the unique steel fabrication requirements, coupled with rising concrete and steel costs and the need for the shortest possible construction timeline, were major concerns for the AHTD going into the bid process, says AHTD Director Scott Bennett. "Contractors were given an extended time to develop their bids. By giving them 12 weeks instead of the typical four, our hope was that they would find innovative ways to keep both the cost and the time down," he explains.
The Massman Construction bid proved to be not only the lowest in terms of cost, but also the shortest as to the time the bridge would be out of service, especially since original estimates projected that the bridge could be out of service for up to two years. Says Bennett, "The length of time for construction was a major concern from the beginning. While the bridge is being replaced, 25,000 vehicles a day will have to use another route to cross the river. Six months is certainly less of a burden than two years."
According to AHTD Public Information Officer Danny Straessle, there is a significant incentive to maintain the bid-specified 180-day timeframe for closing and demolishing the old bridge, erecting the new bridge, and opening it to traffic - Massman Construction will earn a bonus of $80,000 per day for early completion. Conversely, if the project extends beyond 180 days, the firm will be charged $80,000 a day.
Preliminary Work Underway Since 2015
Since preliminary work on the project began in February 2015, a significant amount of upfront and "behind the scenes" work has been underway, such as setting columns, putting cranes in place, and fabricating steel for the two arches. Massman Construction Vice President Paul Scharmer reports, "We've built as much of the substructure for the in-river portion of the bridge as was possible underneath the existing bridge. Additionally, much of the work on on/off ramps outside the new bridge footprint has been completed."
Straessle adds, "The arch construction is being done along the river bank on nearby staging barges. One of the two arches is completed, and the other is currently under construction."
Straessle provides and interesting sidelight - in the early days of the project, when ramps for access to State Highway were being dismantled, sound machines which produced predatory bird noises were installed to help scare away any nesting birds which might cause project delays. "The sound machines were all over the spandrels as well this past spring in anticipation of the demolition work commencing around Memorial Day. These spandrels are now being demolished."
While a Memorial Day 2016 closing was the contractor's original plan, that date had to be put off due to several issues, Straessle adds. "For one thing, the bridge is being replaced in place, which requires extensive coordination. Also, the twin-arch design is very intricate, and there were some challenges in fabricating the steel. And then we had to deal with high water flows on the Arkansas River in the summer of 2015."
It was not until a project partners meeting in August that it was determined that the bridge closing would be on September 28, he reports.
Work on removing the old bridge and the remaining support structures began immediately after the old bridge closed, since extensive preparations had been underway for some time, says Scharmer. "We spent a lot of time with all the project partners, considering all the challenges we might run into and planning for them. We looked at all the "˜what ifs' and how we would handle them."
Straessle anticipates that it will take four to six weeks to bring down the existing bridge, finish the new piers, and then cap them off. "The arches, on their barges, will then be floated into place," he explains. "The arches will be higher than the pier caps, so the barges will be flooded in order to lower the arches to rest in place on the pier caps."
During the six-month construction phase, traffic will be detoured along several alternate routes; 2nd Street and 6th Street in downtown Little Rock will be utilized to route traffic to and from the Main Street Bridge. The Interstate 30 Bridge will also carry some of the traffic flow. A detailed map on the AHTD website shows the available alternate routes in detail.
"The traffic capacity of the Main Street Bridge is such that it can handle this increased traffic flow," says Straessle. "While the Broadway Bridge averages 25,000 vehicles a day, the Main Street Bridge carries less than half of that." (As a comparison, he points out that the Interstate 30 Bridge has a traffic flow of 125,000 vehicles a day.)
High Water Events, Winter Weather Among Potential Challenges
Perhaps even more than the need to reroute a large volume of daily traffic for a six-month period, it is again the weather, which is likely to be the biggest challenge during the construction phase.
As Straessle explains, "Floating the arches into place will likely happen in November, which is typically the wettest month here in Arkansas. The barges will have to be pushed upstream, sideways, against the river's flow, in a "˜choreography' of tugboats and barges. High river flows again, like in 2015, could cause a serious problem.
"Then, of course, the contractor will have to pour the bridge deck, and tie-in ramps and approaches. This six-month timeline runs through March, and winter is an "˜iffy' time for construction. Pouring concrete and paving are very difficult in the winter months. So we'll definitely be hoping for another mild winter like the last one."
Scharmer also cites potential high water events and winter weather as challenges, and adds, "We're planning to accomplish a lot in a short time. We have to make sure we have all the people, materials, and equipment in place to complete the project on time."
Beyond the concerns about weather, water, and short timelines, however, Scharmer emphasizes that the good working relationship between all the project partners has been a positive driving force for the Broadway Bridge project. "We have really had a lot of good cooperation between all the entities and third parties involved, and it's clear how important this project is to Little Rock. It has been a pleasure to work with the cities, the Highway Department, and all the partners. This is the kind of cooperation that you need to make a project really successful."
Photos courtesy of Rusty Hubbard, Arkansas State Highway and Transportation Department