While the Visitor Center overall is a split level, each of the two levels is basically a one story structure. The level above the floor slab in our case is the roof plane. So taking it to the next level and for us the highest level of the project means topping out the building with the roof structure.
The lower level houses office space that has a traditional suspended ceiling with cavity space above for mechanical and electrical systems. The roof structure of the lower roof consists predominantly of bar joists with wide flange beams interspersed that are on average 4’-6” on center.
The upper level of the facility is the true Visitor Center with the Gallery space, reception/information station, gift shop, viewing room, toilets, break room and conference room. The design of the high volume Gallery drives a solution that is clean with simple lines culminating overhead with a rich wood ceiling. Because minimal engineering is integrated into the Gallery ceiling and structural beams are exposed, there is very little cavity space provided above the ceiling; only enough to weave in the fire sprinkler piping and electrical conduit while keeping them concealed.
The high roof beams are spaced at 7’-6” on center and spanning over them are cold-rolled steel purlins (8Z2.5×090) at 5’ on center. The cold-formed manufacturer, however, is allowed to provide lighter framing if they submit calculations for approval that include load summaries and deflection criteria set forth in the construction documents.
The main diaphragm for both roofs is the metal decking. The deck is fastened to the joists and beams on the lower roof and is fastened to the purlins on the upper roof. In each case, once fully adhered, the deck acts as a structural diaphragm that keeps the steel frame from twisting and racking.
The process of steel erection has been ongoing for some 9 weeks and is essentially done. And while the topping out of a building, which is where the last and uppermost structural member is put into place, is usually a big celebrated event on multi-story structures, it is somewhat anticlimactic on a one story building. Despite the fact that this facility is a one story structure, with areas of exposed structure and complex connections including many that needed to create thermal breaks, this was not your ordinary post and beam assembly. The structural steel fabricators and erectors will attest to that.
When the structural skeleton of the building is assembled, you can really see for the first time the mass and form of the building. The high roof over the Gallery gracefully slopes upward as the cantilevered beams extend effortlessly beyond the columns. When completed, the roof assembly will seem to float magically over the large areas of vertical glass. Seeing the design slowly take steps towards its creative shape and beauty is the reward we all look forward to.
As the project moves forward, it will now be a matter of wrapping the exterior with the envelope of materials that consist of stone, metal cladding and glazing that varies from single openings of 6’ by 6’ and large openings of 20’ by 70’. The interior systems will begin populating the spaces inside the building. These will include mechanical systems (ductwork, plumbing) fire protection systems, electrical and data distribution, the interior wall systems and eventually the ceiling systems.