91视频

With updated classrooms and a renovated exterior, Lincoln Hall no longer is the problem child of Portland State University’s downtown campus.

But in 2000, KPFF Consulting Engineers determined that the steel-frame building, and its unreinforced masonry walls and infill, posed a serious danger to occupants if a strong earthquake were to hit the city.

The seismic discovery took a planned renovation of the circa 1911 building to a new level, one that required KPFF and team partner Boora Architects to turn to a relatively new technology.

鈥淲e know that those types of buildings are quite unsafe and so our original direction on the project was to determine how to upgrade the lateral system of the building to replace the reliance on the (unreinforced masonry) walls,鈥� said Jerry Abdie, KPFF’s principal in charge of the project.

KPFF and Boora sought a design that worked on three levels: architecturally, structurally and seismically. The solution included building concrete shear walls, applying shotcrete against stairwells’ existing walls and installing steel, buckling-restrained braces in the center of building.

Unlike conventional braced frames, each buckling-restrained brace has an outer casing and an inner steel core. A layer of grout fills the void between the core and casing, which allows the steel core to elongate slightly and dissipate energy in the event of an earthquake. The core resists compression and tension stresses similarly to conventional braced frames, except the larger steel casing provides the core with buckling resistance.

Buckling-restrained brace technology is relatively new, but growing in popularity according to Abdie. 鈥淭hey provide a better seismic performance and now the costs of the BRBs have come down,鈥� he said. 鈥淲hen you add in the other impacts of BRBs in reducing the need for other steel members, connections and foundations, the overall costs of the lateral system of the building come down.鈥�

For the Lincoln Hall renovation, the BRBs saved about $300,000 and required only 16 braces 鈥� half the number used in a standard brace frame system. 鈥淚t’s definitely something you’ll see more of,鈥� Abdie added.

Aesthetically, it was beneficial that the BRB system required fewer braces. The BRBs remain exposed and are visible from every level of the building because of the opening of previously filled-in interior windows.

鈥淎t the end of day, there is a lot less steel blocking views at the center (of the building),鈥� said Michael Tingley, principal at Boora. 鈥淭he energy and vitality of the events taking place are really evident as people move through the building.鈥�

From a design perspective, the installation of the BRB frame allowed for construction of a dramatic light well running through the building’s core. Although the original building included light wells, they were filled with brick during a renovation in the 1970s. That infill was removed because it was likely to crumble during an earthquake.

After opening the roof to bring in steel for the frame, the team installed a skylight to restore natural light. The addition was seismically beneficial because it reduced the weight of the building’s upper element.

鈥淎ny weight you have above ground level makes the building move more when an earthquake event happens,鈥� Tingley explained.

The seismic upgrade also included pouring a 3-foot-deep, concrete footing in the basement level. In an earthquake, these footings transfer forces in the seismic walls to the ground, to help the walls resist swaying.

Challenges arose out of this structural strategy because the mat footings extended directly under the building’s four original stairwells. If the team were to remove even the bottom of the stairs to pour the concrete, they would have had to rebuild the entire stairwell because of code issues.

The contracting team from Howard S. Wright came up with a creative solution that limited rebuilding costs and preserved the stairs’ historic details. By using cables to suspend the stairs from the floor above, the team was able to dig in, add reinforcing steel, pour the concrete footing and then cut the cables and lower the stairs to the ground.

The project team was also able to reconfigure Lincoln Hall’s mechanical systems to capitalize on the building’s usable spaces. By moving fan rooms to the roof and leveling the basement floor, a new 鈥渂lack box鈥� theater will operate where the boiler room once was and the attic now offers 1,500 square feet of new classroom space.

鈥淲hen we first looked at the project, it appeared that its $30.7 million budget would barely cover the necessary seismic improvements and a few upgrades to the mechanical systems,鈥� Tingley said. 鈥淭he really exciting thing about the project is how our team was able to creatively stretch a deferred maintenance budget into a whole building transformation.鈥�

In September 2010, PSU reopened Lincoln Hall, showcasing the building’s revitalized teaching and performance spaces, which are now filled with natural light and supported by the innovative BRB frame. The hall now is on track to become the first Leadership in Energy and Environmental Design platinum building on PSU’s campus.