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JUMBO GLASS BY GSW

Introducing the Jumbo Glass by GSW. The modern structural glass facades are including larger glass panels and less hardware than ever before. The aesthetic creates transparency and it presents a design challenge when it comes to accommodating for seismic drift. Richard Kaire and David Dunham, engineering manager and director of business development, respectively at Sentech Architectural Systems, provided some solutions to this issue during their presentation, “Seismic Design of Jumbo Glass Structures: Interstory Drift Analysis of Modern Facades,” during Façade Tectonics Institute’s 2020 World Congress.

 

Until a few years ago, glass manufacturing limitations restricted panel and fin sizes. Fitting hardware and numerous internal system joints were required to support the system. Technology has allowed for increasing large panels and minimal or concealed hardware, like shown in the past decade.

“The only distinction between the interior and the exterior are the entry doors within the wall and sparsely spaced vertical sealant joints across the opening,” he said.

Due to the number of joints being minimized and the use of structural silicone, are the result of the trends of stiffer glass walls in planes. This helps the transfer loads back to the find or other support elements. Kaire said this planar stiffness has created the performance system where the depended on insuring the joints are not stretched beyond their limitation and they they provide maximum load resistance.

Richard Kaire, engineering manager at Sentech Architectural Systems, explains the two typical design methods to address in-plane drift.

“The dead load system at the head or the base is very important to the design to ensure that adequate stiffness is built in to mitigate racking and create even and accurate joints,” he said. “For most all systems, out of plane drift can still be accommodated by allowing translation at the head and pivoting about the base, causing the wall to rotate out of plane as the building deforms.”

 

There are two typical design methods, to address in-plane drift.

  1. Connect the base and head of the wall to the structure and to force the panels to rack as the building moves. In the scenario, joints are sized to stretch and the glass’ engagement is detailed to ensure there’s no fallout or collision.
  2. Isolate the facade completely from in-plane movement at one level, detailing sliding brakes that allow movement along the will direction while still resisting loads out of plane.

The glass collision and fall are still a concern, but those typically are addressed at the perimeter connections where relative movement occurs between the facade wall and the building.

Dunham explained that the seismic design of facades with jumbo panels creates challenges because it’s flexible out of plane of the façade but is extremely rigid in plane.

“So as the buildings are moving we see that the rigidity of the glass is much higher than the rigidity of the building. This creates huge differential movement between the façade and the building itself,” he said. “As these facades get larger, that differential has increased more and more.”

 

David Dunham, director of business development at Sentech Architectural Systems, explains how to account for in-plane movement when designing curved glass facades.

Dunham said he’s focused on how to accommodate drift rather than the seismic load applied to the panels because the panels themselves can handle those seismic loads adequately. He explained that facades with smaller glass panels typically transfer seismic loads in plane through the façade itself. To isolate it from the building was a matter of adding slots to the base plate in plane of the façade. As the glass panels get larger, the slots must also get larger. Dunham said it’s not uncommon to have larger projects where there’s close to 12 inches of drift or beyond.

“The space to accommodate slots quickly goes away and becomes impractical,” he said.

Dunham gave an overview of several design solutions, such as slide brackets in which the base plate is not bolted to the structure, but instead captured in a Teflon-coated slide bracket. This allows the building to rack without causing added stress.

Another challenge is seismic design for curved and complex geometries. In these cases, Dunham said his company breaks the façade down into individual units by tying two fins together with a single bracket, which can be isolated from the building movement within its plane but move with the building out of plane. The next two fins in the façade are also connected, but at a different primary angle or axis, creating what Dunham called separate “mini facades” that go around the curvature.

Cantilevered fins with tall glass panels create another issue and Dunham said the attachment complexity becomes more difficult, but it can be achieved with a unique slide bracket design.

“There are different approaches, but using the glass as structured to accommodate its own loading in seismic events to isolate it from the building movement has allowed for much larger facades that can support very high drift criteria,” he said.

Jumbo Glass Requires Innovative Seismic Solutions