The Mays Center roof includes vertical wood compression members in an otherwise steel Pratt truss.
The key finding was a structural system (clay-tile formed ribbed con- crete floors) that Datum’s staff recognized from renovations to a local circa 1930s San Antonio high school. The team even found a concrete slab cast on draped, wire-reinforced synthetic fabric. Further research into the ribbed slabs led to recovery of a portion of the existing con- struction documents from a structural firm doing work from the 1920s through the 1960s on the Witte campus. With the help of these draw- ings, it was possible to illustrate (and date) most of the previous phases of work and to understand the extent of expansion joints and load paths within the building. The proposed exhibit designs included a large space on the ground floor to showcase the museum’s Texas Wildlife collections. Ideally, this space would be column-free, but its location within the existing plan put it at the intersection of three phases of prior building construction, which required outside corner columns to stay in place. Datum took on the task of removing as many of the other columns as structurally feasible. Working with the architects and exhibit designers, the team identified six (non-corner) removable columns. Logically, elimination of these columns resulted in additional loads to the remaining foundations. Unfortunately, the existing building drawing set did not include foundation details. From experience with this era of construction in San Antonio, the Datum team expected the foundations to consist of deep spread footings supporting cast-in-place columns — an early version of a belled pier. Linbeck helped to expose a corner foundation on the museum once the adjacent building was demolished, confirming this foundation type; but the existing condi- tions complicated the discovery of reinforcing patterns in the founda- tion and further study was abandoned. Understanding the geometry was enough, and Datum recommended supplementing the remaining column footings to account for the increased loading, and provided detailing for new battered helical piers and pier caps to be installed through small holes in the existing ground floor framing.
Renovation to the second floor and roof were considerably less com- plicated, though not without challenges. In addition to bridging the abandoned columns with steel reinforcing, directions were provided to trim as much as 12 inches from the bottoms of the second-floor con- crete beams to increase space for lighting and ductwork. Reinforcing was also provided around a new, large circular hole in the second floor. One of the most memorable tasks was repurposing an existing riveted roof truss. This truss spanned a single-story wing of the museum in the initial 1926 construction and was removed and reused when a second story was added in the 1960s. Although moved only a few feet north of its prior position, this was the third use of the same truss in the building. Jim Michel of Project Control and the Witte’s project manager said, “The rehabilitation of the [existing] space was an enormous task. Datum’s engineers proved their worth from the forensic investigation through the final structural reinforcement of the multiple construction types presented by the composite building types. The removal of col- umns — reducing the beam depths — creating an Oculus hole in the concrete slab are worthy of their own exhibit.” Susan Naylor Center: Dinosaurs and dresses Following demolition of the original north wing and during interior renovations, Linbeck began work on the main building addition, the Susan Naylor Center. This addition provides a 26,000-square-foot lateral expansion to the existing facilities and adds classrooms, shops, display galleries, and two separate two-story volumes — an indoor/ outdoor exhibit area and the Valero Great Hall. The primary space of this addition is the dinosaur-filled Valero Hall. The architect wanted to introduce significant, albeit controlled, day- light into this space. Their designs included a south-facing monitor at the roof level and faceted walls on the north side. As mentioned, the
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april 2018
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