The Martin Luther King Jr. viaduct in Portland, Ore. Will feature precast concrete railing tough enough to withstand 60 mph-plus vehicle impacts – and it will look good too.
By Greg Snapper
Since 1937, the Martin Luther King Jr. viaduct in Portland, Ore., has served as a major traffic artery. A confluence of trade, Portland relies heavily on commercial traffic flowing through the inbound and outbound lanes. But due to years of wear and tear, the viaduct faces a structural overhaul, and in the process, it will become safer and more aesthetically appealing than its predecessor.
Precast architectural bridge railing will line the east and west perimeters, serving not only as an aesthetic spindle-railing touch, but as protection for drivers as well. With a bid letting planned for early 2006, this new design is on the table for Oregon Department of Transportation and Portland officials to mull over, and the Portland community has its finger on this project’s pulse.
Community members leading a design advisory committee had a powerful voice in the viaduct’s architectural elements, and they want to ensure that it will surpass both the beauty and staying power of the current structure. The envisioned precast railing will help accomplish both of these goals.
Designed to deflect, not grab
Making a bridge practical and pretty is a challenge ODOT officials have dealt with since the newly designed viaduct’s inception, says Stacy Codington, senior community affairs coordinator for ODOT. “It’s a huge challenge – we are walking a fine line between visual appeal and functionality, with many interests invested in the process,” she says. One of those interests happens to be the railing design, which features four rails spanning the length of the 1,639-foot viaduct. Two of these railings will line the perimeter – the east and west edges of the viaduct – while the other two will gird a 10-foot-wide space with planters down the center. Each railing segment includes two 5.5-inch galvanized tubes that are tied into the street-facing side and jut out the same distance as the concrete rails. “The purpose of this design is to contain and redirect the errant vehicle back to its lane,” says Tony Stratis, bridge design unit manager for ODOT.
“There’s really no chance for car bumpers to get hung up on the railing,” says Jim Morrison, owner of Pacific Precast Inc., a potential supplier for the project. “The purpose of the design is to deflect, not grab.” Additionally, the railing design has been given a 60 mph-plus highway impact rating, making the precast railing a two-pronged product – pretty and practical.
Terry Shike, bridge design task lead with David Evans & Associates, says the complex installation and placement of the state-of-the-art railing will be a challenge. “By precasting portions of the rail and casting other portions of the rail (on site), we will be able to provide a good finished product and meet the intricate geometry challenges of the project,” he says.
“At each bent of the viaduct, an 8-foot-long pilaster will be installed along with a shorter but similar pilaster installed at midspan,” he says. “Between midspan and each bent there will be a total of four or five intermediate pilasters.” The three types of pilasters will carry the vehicle impact load into the deck. The bent pilaster and midspan pilaster will be a combination of precast and cast-in-place concrete, while the intermediate pilasters will all be cast in place.
The top rail, spindles and curb will be precast in units of four or five spindles. The precast units will then be set in place into blockouts in the previously cast-in-place deck. Once the precast units are placed, the intermediate pilasters and the outside portions for the bent and midspan pilasters will be cast-in-place.
On the west side of the viaduct, the rail will be connected to a raised sidewalk, and on the east side, the rail will be connected to the deck. The effectiveness of installing the rail is vital to the safety of the traveling public.
When the design team considered precast railing for the Martin Luther King Jr. viaduct, it needed something tangible before going any further with a precast design. It needed evidence that the product would meet the strict design demands of the architect, Lloyd Lindley, and the highly involved community surrounding the viaduct. Morrison leaped at the chance to offer his company’s services and promptly cast a model of the railing spindles for ODOT.
“The sample looked great,” says Shike. “We think we will get a better product in the end.”
The original Martin Luther King Jr. Boulevard portion of the structure was built by Hoffman Construction Co. of Portland in 1937 at a cost of $459,000. This Roosevelt-era Works Progress Administration project brought many needed jobs to Portland-area residents. Now the current proposal and construction of the new viaduct could face a high price tag. With federal and state funding, total costs could hit $40 million to $50 million.
After years of design consultation from ODOT and the surrounding Portland community, Dave Thompson, communications coordinator for ODOT, says the robust public involvement coupled with the determination of the viaduct design team will give the city of Portland a bridge it can be truly proud of. “The viaduct will be a welcome replacement upon its opening,” says Thompson. “It will renew the economic lifeblood of Portland once traffic picks up again.”