Jump to content

Pencil tower: Difference between revisions

From Wikipedia, the free encyclopedia
Browse history interactively
← Previous editNext edit →
Content deleted Content added
VisualWikitext
m Rewording
→Examples: Wikilink. Add example.
Line 47: Line 47:


===Hong Kong===
===Hong Kong===
In Hong Kong, the [[Mid-Levels]] area is home of many pencil towers. The Highcliff tower, located in the neighboring [[Happy Valley, Hong Kong|Happy Valley]] area, was the world's slenderest tower (20:1 ratio) at the time of completion.<ref name=slender-towers/>
In Hong Kong, the [[Mid-Levels]] area is home of many pencil towers, such as the [[Tregunter Towers]]. The [[Highcliff]] tower, located in the neighbouring [[Happy Valley, Hong Kong|Happy Valley]] area, was the world's slenderest tower (20:1 ratio) at the time of completion.<ref name=slender-towers/>


===United Kingdom===
===United Kingdom===

Revision as of 17:35, 27 December 2020

For the skyscraper in France known as The Pencil, see Tour Part-Dieu.
432 Park Avenue (middle), a pencil tower in New York City

Pencil tower (also known as pencil-thin tower, super-slender tower, and super-slim tower) is a high-rise building or skyscraper with a very high slenderness ratio that is very tall and thin.[1][2] There is no universal definition of how slender these buildings have to be in order to be categorized as such, but some definitions of 10:1 or 12:1 ratios and higher have been used.[3][4]

Hong Kong started developing pencil towers in the 1970s. Twenty or more story residential buildings with one unit per floor were built over small lots.[5][6] It has become one of the most common types of buildings in the city, making Hong Kong the world's highest concentration of pencil towers. Hong Kong's most notable towers are the 72-story Highcliff tower that has a slenderness ratio of 20:1 and its neighbor, The Summit, a 65-story residential building.[7][8]

In the 2010s, the pencil towers became a new phenomenon of building designs in New York City real estate market. The newer pencil towers in Midtown Manhattan near Central Park are slender supertall skyscrapers and ultra luxury.[9] The first of this new crop of super-slim towers was the 1,004-foot (306 m) One57 tower.[10] Two pencil towers on 57th Street made the street the most expensive address in the global real estate market, with 41 transactions above US$25 million over the five-year period from 2015 to 2019.[11]

Outside of Hong Kong and New York City, Melbourne has become the center of pencil towers in Australia.[12]

History

Maxluck Court (left) and Fook Kee Court (brown) are examples of typical pencil towers in Mid-Levels[13]
The Summit (left) and the Highcliff (right) in Hong Kong

The early years of slender skyscrapers started in New York City in the late 19th and early 20th century. The designs were driven by an increase in the price of land plots and the use of elevators and steel frame construction that allowed buildings to be built taller. During that time, there were no regulations on building heights until the 1916 Zoning Resolution. The Metropolitan Life Insurance Company Tower, completed in 1911, was an example of the buildings in that era. It has the height of 700 feet (210 m) and the widths of 75 feet (23 m) and 85 feet (26 m).[1]

After an issue of the bulky Equitable Building, the 1916 Zoning Resolution was enacted with setback regulations but left the heights of buildings to be unlimited if the tower is built within 25% of the lot size. This caused the building designs in that era to have a bulky base and slender tower with the floor area of the tower less than 25 percent of the lot area. The Pierre and The Sherry-Netherland are examples of slender towers of the time that were allowed to be built close to the Central Park.[1]

In 1961, another major zoning resolution was enacted. It changed from the setback to Floor Area Ratio formula, and for the first time, it set a limit of heights. However, it allowed transferable development rights, giving birth to the concept of transferring air rights.[1]

In the 1970s, Hong Kong faced with similar challenges of high land values and lax zoning laws.[7] A new housing standard was set in the 1960s when Hong Kong Housing Authority completed the Choi Hung Estate in 1964 for 43,000 residents who suffered from a massive fire in 1953. Those public housing units with sizes from 280 square feet (26 m2) to 450 square feet (42 m2) set a new expectation for sizes of residential units in private developments. The cost of land leasing for residential developments was a big factor in the building designs at that time. Hong Kong's government owned all of the land and leased out for private developments through auctions for various lease terms, such as 50, 75, 99 and 999 years. Developers needed to pay tens of thousands of HK$ for leasing each square metre (11 sq ft) of land. Meanwhile, some innovative building designs emerged. The use of scissor staircases where two fire escape staircases intertwined cut down the width of the fire escape void allowing buildings to be narrower. These factors incentivized developers to build slender residential towers on small lots with one unit per floor. Developers only needed to acquire a lot with a frontage area of two small retail shops (two tong lau buildings) in order to build a tower of 20 stories or more. This was when the term "pencil towers" was used to describe these micro-developments. Currently, a 430-square-foot (40 m2) unit on a pencil tower has an average price of HK$4.3 million.[5][14][15]

Pencil towers became one of the most typical building types in Hong Kong beside tong lau and cruciform apartments.[8] Overall, the buildings with a slenderness ratio of up to 18:1 have dominated the Mid-Levels residential district, giving Hong Kong the world's center of pencil-thin towers. Modern pencil tower developments in Hong Kong started to get much larger in scale than in decades earlier. In 2001, The Summit, a 65-story upscale residential building was completed. It was followed in 2003 by the world's record 20:1 ratio, 72-story building, the Highcliff. These developments highlighted the potentials of tall luxury pencil towers.[7][16]

In the early 21st century, the pencil tower concept for residential towers expanded outside of Hong Kong and circled back to New York City. Developers utilized the transferable development rights with innovative structural engineering to elevate the buildings as high as possible for spectacular views while requiring smallest footprints as possible. The term "pencil towers" has been used to describe a new type of tall and slender buildings in New York City as well.[17][9][4] Early examples of the new trend were Sky House Condominium, a 588-foot (179 m) building on a 45-foot (14 m) lot, and One Madison, a 50-story building with 12:1 ratio. These were followed by more than a dozen of pencil towers built in the 2010s.[1][18]

Challenges

Engineering

Building materials have been improved in recent decades. The strengths of concrete have been changed from 10,000–12,000 psi to 18,000–20,000 psi. The reinforcing steel with higher strengths of 100 ksi became more available. Higher strength materials can reduce thickness of concrete walls, reducing the amount of required interior structures. This is a critical factor that enables super-slender building designs.[3]

A main challenge of super-slender buildings is the management of lateral movements due to wind loads, which can cause discomfort for occupants. Various engineering techniques are used to address this issue. One approach to manage the wind loads is to use an open mechanical floor in the middle of a building allows wind to flow through. This can reduce the wind loads and the resulting movements by 10-15%. An example of this technique can be seen in 432 Park Avenue, a 15:1 ratio building that has many open-air mechanical floors. Another approach is to stiffen the structure to resist the loads. This can be done by using outrigger walls to connect the building core to the perimeter columns on two sides to distribute the loads. The structure of 111 West 57th Street uses shear walls on the east and west facades to stiffen the structure while leaving the north and south views unobstructed.[3]

In term of managing building movements, a tuned mass damper can be used. This is a passive device with a large mass mounted on shock absorbers to slow the movements of the building. Typically they are made of solid mass, but recently liquid damping systems have been used. A liquid damping system or sloshing damper is a tank of water with screens to control the movements of the water, specifically tuned such that when building is moved in one direction, the liquid force goes in the opposite direction to offset the movements. Highcliff is one of the early adopters of such system.[3]

Building footing is another area of concerns. As the slender buildings have smaller footprints, the foundations need to go down deeper.[3]

Fire fighting

Very tall and very narrow pencil towers present new challenges to fire fighting. With narrower buildings, the scissor staircases are narrower and they may need to have five or more turns to rise for each floor. This presents impacts to the performance of the fire hoses that are twisted over a long length, and small areas that can be used for fire fighting operations and medical staging. Another area of concerns is theirs open-air mechanical floors especially those of New York City pencil towers. If the doors are left open, the wind could enter the staircase fueling the fire and endanger people.[19]

Examples

Australia

Melbourne entered the global pencil tower scene with the construction of Phenix Apartments building that rose up on a 6.7-metre (22 ft) wide lot in 2013. The plan originally called for a 40-story building. After oppositions from concerned neighbors, the design was revised down to 28 stories at a height of 88.5 metres (290 ft), still with a high slenderness ratio of 13.5:1.[20][4] That was soon followed by Collins House, a 195-metre (640 ft) skyscraper that has the width of its base at 11.5 metres (38 ft). It slenderness ratio of 16.5:1 was the fourth most slender tower in the world at the time of completion. Collins House incorporated many of advancements in technology including the first of such towers to use prefabrication of 3D structural elements to help navigate narrow project site. A combination of air rights purchase and large cantilevers helped maximizing its floor space.[21] In 2018, a design of a 330-metre (1,080 ft) tower sitting on to of a triangular plot in Melbourne was submitted for planning approval. If built, The Magic would become world's slenderest by a ratio of 26.6:1 based on the shorter side of its widths in a triangular footprint. If it would have a rectangular base, a similar size building would be at 18:1 ratio.[22]

Canada

In 2020, Dutch developers proposed to build an 87-story mixed-use pencil tower at 1200 Bay Street in Toronto to replace a 12-story office building. It follows the form of pencil towers of New York. However, with its 11:1 ratio, the slenderest in Toronto, it falls short of matching those New York towers.[23]

Hong Kong

In Hong Kong, the Mid-Levels area is home of many pencil towers, such as the Tregunter Towers. The Highcliff tower, located in the neighbouring Happy Valley area, was the world's slenderest tower (20:1 ratio) at the time of completion.[7]

United Kingdom

In 2020, Birmingham City Council approved a plan to construct a 9.5-metre (31 ft) wide and 116.5-metre (382 ft) tall building. Tis would be the first super-slender tower in the United Kingdom.[24]

United States

432 Park Avenue (left, farmost), 111 West 57th Street (under construction), One57 (middle, blue), 220 Central Park South (right, gold) and Central Park Tower (righ, blue)

The Skyscraper Museum attributed Sky House, a 55-story building made possible by a purchase of air rights from the Little Church Around the Corner, completed in 2008, as an early example of New York's super-slender towers. One Madison, a 711-foot (217 m) tower that incorporates a concept of seven volumetric pods to extend tower's floor plate, was completed soon after.[1]

There were several more buildings completed between 2014 and 2019. These include: One57, the first supertall pencil tower in New York;[1] 432 Park Avenue, a 15:1 ratio 1,396-foot (426 m) building that has five open air mechanical floors throughout the heights;[1] 220 Central Park South, a 18:1 ratio building that uses its first 200 feet (61 m) of its 950-foot (290 m) hight for mechanical equipment to stiffen the building;[3] 111 West 57th Street, the world's slenderest tower at a ratio of 24:1;[3] and Central Park Tower, a 1,550 feet (470 m) tower that sets aside a total height of 350 feet (110 m) as mechanical space to build taller than it would have been normally allowed.[25]

References

Wikimedia Commons has media related to Pencil towers.
  1. ^ a b c d e f g h "New York's Super-Slenders". The Skyscraper Museum. Retrieved 1 December 2020.
  2. ^ Clines, Francis X. (1 January 2015). "What's Happening to New York's Skyline?". New York Times. Retrieved 7 December 2020.
  3. ^ a b c d e f g Reid, Robert L. "Skinny 'Scrapers". Civil Engineering Magazine. Retrieved 3 December 2020.
  4. ^ a b c Cheng, Linda (16 February 2016). "Melbourne's next 'pencil tower'". ArchitectureAU. Retrieved 3 December 2020.
  5. ^ a b Dewolf, Christopher (6 October 2016). "The Vertical City, Part I: How Hong Kong Grew Up". Zolima CityMag. Retrieved 5 December 2020.
  6. ^ "Try a Little Slenderness: Explorations on the Hong Kong Pencil Tower". Faculty of Architecture, The University of Hong Kong. Retrieved 1 December 2020.
  7. ^ a b c d "Future City:20-21 Slender Towers". The Skyscraper Museum. Retrieved 1 December 2020.
  8. ^ a b "What happens if you inject Hong Kong's density into Zurich's history?". South China Morning Post. 26 January 2016. Retrieved 7 December 2020.
  9. ^ a b Wainwright, Oliver (5 February 2019). "Super-tall, super-skinny, super-expensive: the 'pencil towers' of New York's super-rich". The Guardian. Retrieved 1 December 2020.
  10. ^ Safarik, Daniel; Wood, Antony. "Tall Building Numbers Again on the Rise". Structure Magazone (June 2014). Retrieved 3 December 2020.
  11. ^ Howley, Kathleen (29 December 2019). "New York Tops Ultra-Prime Residential Sales List As 'Pencil Thin' Wins". Forbes. Retrieved 1 December 2020.
  12. ^ Cheung, Alison (17 April 2019). "Why Melbourne will see more skinny skyscrapers". Commercial Real Estate. Retrieved 1 December 2020.
  13. ^ Carlow, Jason F. "Tiny Footprints: Variations on the Hong Kong Pencil Tower". In Ameri, Amir; Dagg, Rebecca O'Neal (eds.). 106th ACSA Annual Meeting Proceedings, The Ethical Imperative (PDF). Association of Collegiate Schools of Architecture. ISBN 978-1-944214-14-2. Retrieved 5 December 2020.
  14. ^ "Hong Kong: Property Tenure/Ownership". JLL. Retrieved 5 December 2020.
  15. ^ "New Tower Designs: Freespace in the City" (PDF). HKIA Journal (75). The Hong Kong Institue of Architects: 86. 2019. Retrieved 7 December 2020. Due to the shortage of land and the small lot sizes, the high-rise "pencil tower" is becoming the most common building type in urban Hong Kong.
  16. ^ "Future City:20-21 Mid-Levels". The Skyscraper Museum. Retrieved 1 December 2020.
  17. ^ 2019/2020 M.Arch Studio Sequence Handbook. NUS Department of Architecture. p. 29. Retrieved 7 December 2020.
  18. ^ "One Madison Park, New York City". Council on Tall Buildings and Urban Habitat. August 2011. Archived from the original on January 28, 2018. Retrieved April 6, 2020.
  19. ^ Roman, Jesse. "Different By Design". NFPA Journal (March April 2017). Retrieved 7 December 2020.
  20. ^ Rollo, Joe (29 November 2013). "Phoenix Apartments brings the skinny tower to Melbourne". The Sydney Morning Herald. Retrieved 3 December 2020.
  21. ^ Whittle, Kristen (2016). "A Case Study on Designing Superslim in Melbourne" (PDF). Proceeding of CTBUH 2016 Shenzhen - Guangzhou - Hong Kong Conference: 1208–1215. Retrieved 3 December 2020.
  22. ^ Block, India (18 May 2018). "Super-skinny triangular tower proposed as Melbourne's tallest skyscraper". Dezeen. Retrieved 3 December 2020.
  23. ^ Mirabelli, Julian (10 June 2020). "Suggested Block Plan for 1200 Bay Supertall Among Details in Planning Docs". Urban Toronto. Retrieved 3 December 2020.
  24. ^ Gerrard, Neil (14 February 2020). "Go-ahead for UK's first habitable 'super-slender' skyscraper". Construction Manager. Retrieved 4 December 2020.
  25. ^ Herzenberg, Michael (7 January 2020). "Part 2: The Loopholes That Help to Send NYC Skyscrapers into the Clouds". NY1. Retrieved 3 December 2020.
Retrieved from "https://en.wikipedia.org/w/index.php?title=Pencil_tower&oldid=996613710"