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very purpose. This is consistent with the observed behavior of the elevated piping run; specifically, there was no upwind or downwind drift accumulation immediately adjacent to the obstruction. As mentioned above, in relation to Figure 5, the gap between the piping run and the snow surface is about 2 feet. Hence, the wake region behind the pipes was reasonably close to the saltating snow particle layer adjacent to the snow surface. If the gap between the piping run and the snow surface were much larger (say 10 feet or more), the wake region would be well above the saltating snow layer. For such a case, this type of snowdrift would be much smaller or non-existent.

Summary

This article describes a newly observed roof-top piping-run drift and compares it to common windward and leeward drifts in ASCE 7. Since there is currently only a single reasonably well-documented case history, the specific influence of certain key parameters is not well understood. If and when additional case histories become available, future versions of ASCE 7 may well address this new and interesting snowdrift.■

Michael O’Rourke has been a Professor in the Civil Engineering Department at Rensselaer Polytechnic Institute since 1974. He served as the Chair of the ASCE 7 Snow and Rain Subcommittee from 1997-2017 and currently serves as the Vice-Chair. (orourm@rpi.edu) Chris Letchford is an international expert in Wind Engineering with experience documenting wind-induced structural failures, simulating novel wind phenomena, and codifying findings for practicing engineers in codes and standards. (letchc@rpi.edu)

Adhesives Technology Corporation

Phone: 754-399-1057 Email: atcinfo@atcepoxy.com Web: www.atcepoxy.com Product: ULTRABOND® and CRACKBOND® Adhesives Description: America’s #1 structural adhesive specialist off ers four IBC compliant, wind- and seismic-rated adhesives, including HS-1CC, the world’s strongest anchoring epoxy. Our CRACKBOND grout and chock adhesives were designed with wind farm applications in mind. ATC is a Meridian Adhesives Group Company.

ASDIP Structural Software

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CAST CONNEX

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SEISMIC/WIND guide

ENERCALC, Inc.

ENERCAL C

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IES, Inc.

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MAX USA Corp.

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SkyCiv

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Trimble

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The Academy Museum of Motion Pictures

Designed by the Renzo Piano Building Workshop, the Academy Museum of Motion Pictures consists of a major renovation to the 1930s May Company Building (renamed the Saban Building) plus a soaring spherical addition that includes the 1,000seat Geffen Theater. The Saban building is connected to the new theater with three steel and glass bridges. Connecting this base-isolated structure with an existing building introduced significant challenges for Buro Happold, the project’s structural engineer, as well as MEP engineer, lighting and environmental designers, energy modelers, and IT consultant. The two buildings required very different structural solutions. The theater and terrace are composed of reinforced concrete. To construct the curves, a partial steel structure was introduced to support the exterior precast concrete panels, which then provided formwork for the structural shotcrete on the inside – a time-saving strategy. A glass-curtain-wall canopy encloses the terrace, completing the spherical form. For the 150-foot-diameter, orb-shaped spherical addition, in-depth analysis argued for an unusual base-isolation system. The theater is supported by four mega-columns, seismically isolated from the ground. The unique design employs just eight base-isolators set 15 feet above grade and exposed as a design element. Base-isolators allow the Sphere to move up to 30 inches in any direction during an earthquake. The Saban Building’s retrofitting is designed to limit movement to address the seismic challenges. Because the buildings are designed to move so differently during an earthquake, building components between the two structures –including circulation bridges and stairs –required flexible connections to allow one building to move and the other to stand still. The bridges – the main pathways to and from the Saban Building and Geffen – are anchored to the Saban Building and designed to pivot and slide, moving with the Sphere during an earthquake. At the Saban Building, the bridges connect to pivot and bearing connections that provide vertical and horizontal restraint but also allow the bridges to rotate about a vertical axis when the Sphere moves during an earthquake. At one corner of each bridge, a cylindrical “pivot” connection acts as the center of rotation and locks the bridge to the Saban Building. There is a simple bearing connection at the other corner of each bridge, allowing the bridge to move freely in horizontal directions. At the Sphere, the bridges connect with sliding tracks that provide restraint in the vertical and horizontal east-west directions and move freely in the north-south direction. When the Sphere moves east or west, the tracks push on the bridges and cause them to rotate about the pivot connections at the Saban Building. When the Sphere moves north or south, the bridges slide along the tracks, allowing the theater to move freely without applying any load to the bridges. All the connections were custom designed to accommodate the forces and displacements that were determined during the structural analyses of the Sphere, the Saban Building, and the bridges. The connections are also architecturally exposed, and, as such, form and function were both given equal weight during the design process. The two stair towers, one on either side of the Sphere, are designed to provide egress to the Geffen Theater and Dolby Terrace in the event of an emergency. However, the stair towers sit on the ground. They must also connect to the sides of the Sphere at multiple levels – a significant design challenge because of the differential movement that is anticipated between the Sphere and the ground during an earthquake, up to 60 inches in any direction. Buro Happold developed a structural solution that decouples the gravity and lateral load-carrying systems of the stairs. Vertical gravity loads are transferred to the ground through long slender columns that anchor to “stationary” foundations. Lateral earthquake loads are transferred to the Sphere through beams at each floor level. These beams also push on the stairs when the Sphere moves on its isolators. Lastly, hinges are introduced at the top and bottom of each column to prevent lateral loads from being transferred through them and accommodate the Sphere’s movement without damaging the stair structure. In an earthquake, the Sphere moves on the base isolators below; these hinges allow the stair columns to “lean over” so that the upper portion of the stairs can go along for the ride. These joints are hinged in two perpendicular axes, which effectively allows rotation and translation in any direction. The column hinges that were developed for the stairs were custom designed to accommodate the anticipated displacements of the Sphere and the calculated gravity forces from the stairs above. The finished column hinges were cast from high-grade carbon and stainless-steel alloys, providing a streamlined construction and fabrication process and ensured a highquality final product that is aesthetically pleasing and will perform over the life of the building. The Academy Museum of Motion Pictures will be the world’s premier institution devoted to the art and science of movies and moviemaking. The unique design of the spherical addition, the renovation of the Saban building, connecting the two structures, and an unusual base-isolated system all contribute to this unique Museum’s appeal.■

Buro Happold was an Outstanding Award Winner for the Academy Museum of Motion Pictures project in the 2020 Annual Excellence in Structural Engineering Awards Program in the Category – New Buildings over $200M.