뉴욕 허드슨 야드의 유리 전망데크 VIDEO: Structural Glass Challenges: Hudson Yards Observation Deck

Structural Glass Challenges: Hudson Yards Observation Deck

Date:19 NOVEMBER 2019

Structural, architectural and installation demands must all be considered in glass structures. The best solutions do not form a compromise between these demands but integrate them into one solution.

This paper presents a case study of three glass structures with varying challenges on the Observation Deck of Hudson Yards in New York – a 3m, cantilevered Windscreen subject to wind gusts of up to 4.7 kPa, an outdoor Glass Floor with high traffic, and a combination glass floor and window structure.

뉴욕 허드슨 야드의 유리 전망데크    건물의 구조적  설치 요구 사항은 모두 유리로 고려되어야 한다. 최선의 해결책은 이러한 요구들 사이에 타협을 형성하는 것이 아니라 그것들을 하나의 해결책으로 통합시킨다. 본 보고서에는 최대 4.7kPa의 돌풍을 받는 3m 캔틸레버식 윈드스크린, 교통량이 많은 실외 유리 바닥 및 창문의 조합된 유리 바닥 구조 등 뉴욕 허드슨 야드의 관측 데크에 다양한 도전이 있는 3개 유리 구조물에 대한 사례 연구를 제시한다. 본 보고서에서는, 335m 높이에서 한 쪽에서 접근하여 구조 안전과 성능을 보장하고, 명확한 건축 비전을 충족하며, 높은 허용오차에 유리를 설치하는 등, 적층 연결의 과제를 살펴본다. 프로젝트 개요 허드슨 야드는 뉴욕시의 중심부에 있는 25억 달러의 혼합 부동산 개발사업이다. 이 개발은 미국 역사상 가장 투자가 많이된 민간 부동산 개발로  모두 16개의 건물로 구성되어 있다. 이 건물들 중 가장 높은 건물은 386m의 30허드슨 야드다.  이 마천루와 관련된 또 다른 구조물이 있는데, 그것은 335m 높이를 자랑하는 전망대를 가지고 있다는 것이다. Schlaich Bergermann Partner는 관련 30 Hudson Yards에 있는 전문 분야의 파사드 엔지니어로서 고용되었다. KPF는 허드슨 야드의 마스터 플랜과 30허드슨 야드의 설계자다. 특수 면에는 관측 갑판 이차 구조와 외피, 본 논문의 주제인 전망대 바닥 위의 3가지 구조 유리 프로젝트가 포함된다. 이 세 가지 구조물은 윈드스크린, 테라스 유리 바닥, 헐 창이다. 월스트리트저널(WSJ)의 논평에 따르면, 이 전망대는 "미국 어느 건물보다도 장관을 이루고 있다"고 한다. 이러한 관점을 달성하기 위한 핵심은 앞에서 언급한 유리 구조를 통해 이루어졌는데, 물리적 장벽과 시각적 연결이 동시에 존재한다. 3개의 유리구조물 윈드스크린은 3m 높이의 캔틸레버로 수직으로부터 9°로 경사져 있다. 이것은 관측 데크의 투명한 주변을 형성하고 돌풍이 보행자에게 미치는 영향을 줄인다. 유리는 단단하고 아연도금된 강철 모멘트 슈즈로 지지된다. 테라스 유리 바닥은 아래 도시 경관을 방해받지 않고 볼 수 있으며, 4개의 반복적인 유리 삼각형 세트로 구성되어 있다. 스테인리스강 빔은 위의 유리와 아래에 걸려 있는 가려진 전면 유지보수 레일을 모두 지지한다. 스테인리스강 빔은 관측 데크의 일차 구조와 연결되는 연강 주변 프레임에 연결된다. 중략 황기철 콘페이퍼 에디터 큐레이터 Ki Chul Hwang, conpaper editor, curator

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In this paper, we look at the challenges of laminated connections, ensuring structural safety and performance, meeting a clear architectural vision, and installing glass to high tolerances with access from one side at 335m height.

Project Overview

Hudson Yards is a $25bn mixed real estate development in the heart of New York City. The development is the most expensive private real estate development in US history and comprises a platform over a working rail yard, and 16 buildings on the platform. The tallest of these buildings, at 386m, is 30 Hudson Yards. There is another superlative associated with this skyscraper, and that is that it has the highest (335m) outdoor observation deck in the Western Hemisphere.

Figure 1: 30 Hudson Yards Observation Deck

Schlaich Bergermann Partner was hired by Related Hudson Yards, as the façade engineers for the specialty facades on 30 Hudson Yards. KPF is the architect for both the Hudson Yards master plan and 30 Hudson Yards. The specialty facades include the observation deck secondary structure and cladding, and the subjects of this paper – the three structural glass projects on the observation deck. These three structures are the Windscreen, Terrace Glass Floor and Hull Window. According to a review by the Wall Street Journal, the observation deck “offers the most spectacular vista of any building in America.”

The key to achieving these views was through the aforementioned glass structures, which are simultaneously both physical barriers and visual connections.

 

Figure 2: Glass Structures

 

The Three Glass Structures

The Windscreen is a 3m high cantilever, sloped at 9° from the vertical. This forms the transparent perimeter of the observation deck and lessens the impact of wind gusts on pedestrians. The glass is supported in a stiff, galvanized steel moment shoe.

 

Figure 3: Windscreen

The Terrace Glass Floor offers unobstructed views to the cityscape below and is composed of a set of four repeating glass triangles. Stainless steel beams support both the glass above and the obscured façade maintenance rails which hang below. The stainless steel beams connect into a perimeter framing of mild steel, which itself connects to the primary structure of the observation deck.

 

Figure 4: Terrace Glass Floor

The Hull Window offers similar views to the Terrace Glass Floor, but from an interior space. Three independent panels – a glass floor and two sloping triangular panes – form a faceted shape.

The two sloping panels are supported at far edges. This means that no additional dead loads act on the glass floor panel, and the vertical panels do not produce a constant shear load on the adjoining panel from their dead loads. Supporting these panels at their far edges also allows for a minimal joint at the interfaces.

 

Boundary Conditions

As unique structures in a unique space, the Windscreen, Terrace Glass Floor and Hull Window also have peculiar requirements. As with all glass structures, it is essential to think about redundancy, especially at 335m high.

Similarly, access for installation, maintenance, and replacement must inform the design. Due to the expected high pedestrian traffic and the large wind loads at this elevation, the structures also experience high loading. These aspects all played a role in the design.

 

Figure 5: Hull Window

 

Loading

One of the primary functions of the Windscreen is to form a barrier to resist the high wind loads, which exist at this height. As such, it is estimated to be exposed to 4.7 kPa wind pressures and 3.4 kPa wind suction. As a 3m glass cantilever with high loading, it is crucial to control deflection and ensure a robust design.

Both the Terrace Glass Floor and Hull Window were designed for 4.8 kPa uniform live loads on the horizontal surfaces and for 1.3 kN concentrated live loads over 50x50mm areas, in keeping with the requirements of ASCE 7-05 and New York Building Code.

Access

The observation deck was constructed in a modular system, with modules up to 35,000 kg assembled in Italy, shipped to New York, craned up to 335m and installed together on site. Once the structure of the observation deck was in place, there would be no raft or installation platform in place to allow access to both sides of the Windscreen.

Therefore, all access for installation, replacement and maintenance was required to be performed with access from the terrace and a limited access from the exterior using the façade maintenance machines. As a signature element of the building, it was essential that it would be possible for future contractors to be able to install the structure to a high degree of tolerance. The possibility of damage to exposed edges and coatings means that replacement of panels must be accounted for. 

With these in mind, sbp devised installation and replacement narratives to ensure each step was thought through in the design stage. The Terrace Glass Floor has access on all sides and is almost horizontal, with only a minimal slope for drainage assumed. Therefore, there are not the same difficulties with installation as with the other structures. However, the footfall expected on the upper surface means that the surface treatment is likely to become worn away after continuous use. The microfractures initiated and propagated by scratches on the surface of glass lead to compromising the compression layer of heat-treated glass and eventual fracture of that layer. If the top layer is damaged in a multi-layer laminate, the entire laminate must be replaced.

At an early stage in design, the idea of a removable layer or laminate was explored. This idea is in use in some interior glass floors but was not appropriate for this project. It was not pursued due to several reasons:

• The difficulty of forming a hermetic seal (for load transfer) on site during replacement

• Increased deflections

• Monolithic layers are less safe and not structurally sufficient for wind suction and concentrated live loads

The Hull Window had similar design parameters to the Windscreen, in that access was only possible from the interior. The sequence was determined to be that the hung panels would be installed first since they would need space to be rotated into place in a limited interior space. After these were installed, the glass floor would complete the structure and the structure would be sealed.

Transparency is key for all these structures, and so regular cleaning is expected. Titanium based self-cleaning coatings were not used due to the possibility of degradation of these over the glass lifetime, and the need to use exterior surfaces for different coating products.

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The Edge Hudson Yards Observation Deck NYC

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