235 NW Park
Structural Rehabilitation of Existing Unreinforced Masonry and Concrete Building
The existing one story unreinforced masonry and concrete building at 235 NW Park in the North Park Blocks needed a lot of work. The entire structural system of the building needed to be brought up to meet the current building code requitements. While parts of the vertical framing system were found to be adequate, the entire lateral force resisting system needed to be redesigned and rebuilt.
Several things were discovered during the initial planning phase of this project. The original design documents at the City of Portland indicated the existing basement was to be abandoned and filled in during a renovation in 1918. Becuse that never happened, Ogren Engineering needed to investigate the structural adequacy of the basement for potential use in the new configuration of the building. In the end, reusing the existing concrete walls in the abandoned basement saved a significant amount of money in new footing costs.
The seismic upgrade for the existing building at 235 NW Park consisted of installing wood shearwalls on two sides of the ground floor and steel concentrically braced frames on the two street-facing sides of the building. Because the sides of the building on NW Park Avenue and Everett Street are almost entirely glass windows and doors, there was not any place for shearwalls.
The steel braced frame along the Park Avenue side of the building is connected to a series of steel beams that support the roof and tie the building together to resist both vertical and lateral loads. This concentrically braced frame is in integral part of the new lateral force resisting system for the building.
The steel concentrically braced frame at the NW Everett street side of the building is also intrgral to how the newly upgraded structure will perform. This braced frame not only supports the wind and seismic forces for one side of the building, it carries one of the main 16 x 30 old growth timbers that are part of the original roof framing system. These timber beams are not anything you will find anymore - 16"x30"x50 feet long.
Second Story Framing
The second story walls were largely built on the roof deck and then stood up with a crane. Connectors were installed at the top of the wall to give the crane something to connect to while lifting the wall.
When the walls were stood up, the 32 foot long GluLam beams that are more than 2 feet tall were flown into place with the crane. These GluLam beams allow the entire second story to be open and not have any columns to interrupt the interior space, which will be a roof-top bar.
Making all of the architectural requirements a reality to take an existing building that was in need of a siginificant amount of repair find a way to create a structure that meets all of the building code requirements was the challange for Ogren Engineering. The existing building needed to keep it's old building charm while designing a new structural system that meets modern building code requirements.