Reconstruction of Interior Core Including New Learning Stair
the building structure. Where grade extended above level 1, a concrete upturned beam supported the precast columns and structural sidewalk. The new building program called for the grade to be lowered and entry to the building relocated to level 1 on the east, west and south sides. This required the existing structural sidewalks, basement walls, and upturned beams to be demolished above level 1. Permanent steel shor- ing was installed to laterally brace the existing basement wall back to the existing building columns during demolition. In order to remove the precast concrete columns without having to temporarily shore the structure, a new permanent support system was designed consisting of a 16 inch thick cast-in-place concrete basement wall along the north, east and west sides of the building and steel columns to support the floors and roof. The grade along the south side was unchanged, so steel transfer girders were designed to span between existing building columns to support the new steel columns. The steel columns were fabricated with steel “haunches” on the inside face, which permitted the columns to be installed outboard of the floor structure and run full height of the building. Close coordination with the construction manager was required to ensure work was properly sequenced since columns had to be “fished” down the void space in the precast columns with the steel haunches turned parallel to the floor spandrel. Once the columns reached the bot- tom, they were rotated 90-degrees to position the haunches below the floor framing. After the steel columns were plumb and the haunches shimmed, the precast columns were demolished from the top down. Once the precast columns were removed, steel beams were installed between the steel columns around the perimeter of the building at each level, creating a steel “exoskeleton”. Concrete slabs were then installed at each level to extend the floor out to support the new façade, which was outboard of the new steel framing. As the new focus of the ZACH was aimed at “learning by doing,” the large lecture halls in the original building were replaced with smaller active learning classrooms. This required reconfiguring the center core of the building, including demolition of the large concrete-framed lec- ture halls. Since the main entrances to the building were reestablished at level 1, a 12,000 SF section of the post-tensioned waffle slab at level 2 was demolished to extend the new central atrium to level 1.
Completed Active Learning (Seating) Stair and Skyligh. Photo: Randy Braley.
As part of the teaching and research program, the original building housed a 60-year-old, 5W nuclear reactor that had to remain operation- al during the demolition phase until it could be decommissioned and relocated. This required special detailing and sequencing of demolition to work around the reactor room to avoid disturbance. Reconstruction The interior core of the building was reconstructed with structural steel infill framing and a new central “learning stair” between levels 1 and 3 to allow students to study and collaborate. Steel bridges at each level connect the two sides of the atrium and support the stairs. The new infill structure had to be carefully planned and new columns strategically placed to minimize impact on the existing structure. New steel wide-flange columns were “punched” through the post-tensioned waffle slab at level 1 and carried down to the basement. New concrete transfer beams and drilled under-reamed piers were installed to support the new columns. With the precast façade removed, new limestone cladding and curtain- wall was introduced to provide a more transparent and aesthetically appealing structure. Expansion Per the original construction documents, the building was designed to accommodate two levels of vertical expansion. JQ verified this as- sumption by analysis of the structural framing. To better relate with the five-story building additions on the north and south sides, only a por- tion of the existing building was vertically expanded. Structural steel was used for the vertical expansion to reduce weight. Approximately half (32,600 SF) of the existing roof was converted into a new fifth floor level and approximately 6,600 SF consisted of a two-story expan- sion to accommodate a mechanical penthouse.
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august 2020
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