Article by Linda Kaplan
Michael D. Flowers, P.E., M.ASCE receives the 2014 Roebling Award for outstanding leadership in construction of the most challenging bridge projects ever attempted by civil engineers in the modern era, particularly the record-setting, single-tower, asymmetrical self-anchored suspension bridge spanning San Francisco-Oakland Bay.
President and CEO of American Bridge, Michael earned a BS from West Virginia University and a MS from University of Pittsburgh. Mr. Flowers has been associated with construction of a series of bridges and bridge retrofits, growing in complexity throughout his career. His penultimate achievement and the basis for selecting him for the Roebling Award is the leadership and construction excellence he brought to the newly completed self-anchored suspension bridge tying Oakland and San Francisco together. With a length of 2,047 feet the SAS Bay Bridge is the longest self-anchored suspension span bridge in the world.
American Bridge Company led a joint venture for the construction of the new $1.9 billion Self-Anchored-Suspension Bridge as a key part of the seismic replacement of the eastern spans of the San Francisco/Oakland Bay Bridge. This signature span involved the construction of a new 625m single-tower, asymmetric, self-anchored suspension bridge. The bridge’s four-legged steel tower is 160m tall, supporting 790mm main cables, from which the cable is suspended. The tower legs at the base weighed 1000mt each. Traffic is carried on twin steel orthotropic box girder roadways, suspended from cables each carrying five lanes of traffic. The massive trapezoidal boxes are nearly 30m in width and over 5m deep, some weighing in excess of 1500mt and spanning 85m in a single piece. The 1,400m long main cable is comprised of 137 prefabricated parallel wire strands of 127 wires each. The cable is a unique continuous loop, anchored in both the westbound and eastbound roadway sections at the eastern end of the bridge, crossing over the tower top through a huge 400mt steel saddle and looping around the pier at the west end of the bridge.
As its name would imply, the bridge had no gravity anchors for the cable, but rather was “self-anchored.” In its final design, this required the roadway sections to carry very large compressive forces in combination with the bending and localized forces. The steel anchorages are roughly 20% of the size of a normal gravity anchorage and are neatly nested below the roadway surface within the box girders. The total weight of the permanent structural steel is about 50,000mt and the tower and roadway sections had to be temporarily supported on 25,000mt of false work to facilitate construction.
Once the tower and the roadways were erected, the cable was installed, and then through a carefully orchestrated complex load transfer process, the roadway sections were lifted off the false work, thereby, transferring the load from the temporary structures into the permanent cables. A build-to-suit marine heavy lift shear leg crane was designed and built as part of the project and facilitated ship unloading and erection of many of the bigger-than-life pieces. The shear leg dubbed the Left Coast Lifter has a 1750mt capacity and was founded on a 400’x100’x22’ custom built barge.
Nearly every aspect of the construction of this one-of-a-kind bridge required careful and thoughtful applications of structural engineering including the completion of all of the stages of our work in a safe seismic condition. The project was awarded in May of 2006 and the seismic safety of the San Francisco Oakland Bay Bridge was restored when we turned traffic onto the new span on Labor Day 2013.
Michael will be presenting this project at an upcoming SEI/ABCD joint dinner event on January 22, 2015. Look for details and registration coming soon.
The Roebling Award recognizes and honors an individual who has made an outstanding contribution to the advancement of construction engineering.