Arend benkert defilippis tillmaand by HUSSIEN MANSOUR

John Arend, Mike Benkert, Audrey deFilippis, Saretta Tillmaand

Commerzbank Tower

-Overview-

-Integrated Strategies-

-Structure-

-Environment-

-Construction-

Overview Commerzbank Tower Program Architectural Intent Construction Ethic

01 02 03

Integrated Strategies Structure, Environment, and Construction - Exterior Office Glazing Structure and Construction - Mega-Column Structure and Environment - Sky Garden Glazing System

01 02 03

Structure Primary Structural Members Conjecture and Structural Diagrams Structural Strategy Hypothesis

01 02 03 04

Environment Climate Data Climate Data Climate Data Climate Data Climate Data Climate Data Climate Data: Responses Environmental Responses: Envionrmental Responses: Environmental Responses: Environmental Responses:

01 02 03 04 05 06 07 08 09 10 11

Daylighting and Views Ventilation Ventilation Sky Gardens

Construction How the Building Meets the Ground - Foundation How the Building Meets the Ground - Foundation How the Building Meets the Sky How the Building Meets the Sky - Cladding How the Building Meets the Sky - Cladding Social Responsibility The Corner The Corner - Mega-Column and Vierendeel Frame The Corner - Cladding Response to Water - Exterior Office Glazing Response to Water - Exterior Office Glazing Response to Water - Mega-Column

01 02 03 04 05 06 07 08 09 10 11 12

Works Cited

Table of Contents

-Overview-

-Environment-

-Construction-

Commerzbank Tower FosterArend, & Partners, Arup andAudrey Krebs & (SE), J. Roger Preston w/ P&A Petterson Ahrens (ME), Schad & Hölzel (EE) John Mike Benkert, deKiefer Filippis, Saretta Tillmaand

Site

Project

Building Facts

HVAC

Passive Systems

Envelope

While Commerzbank Tower has a distinctive presence on the Frankfurt skyline, it is also anchored into the lower-scale city fabric, with restoration and rebuilding of perimeter structures reinforcing the original scale of the block. The developments at street level provide shops, carparking, apartments and a banking hall, and forge links between the Commerzbank and the broader community. At the heart of the scheme is a public galleria with restaurants, cafes and spaces for social and cultural events. [fosterandpartners.com}

-Structure-

Building Facts

Structure

When construction wrapped up on the 53-story Commerzbank Headquarters in 1997 it stood as the tallest building in Europe, but what made it revolutionary, was its combination of form, inventiveness, and technical expertise to create an entirely new building type: the humane and socially responsible skyscraper. Breaking away from the American model of deep-planned, air conditioned structures with a central service core and identical, spatially separated floors; Commerzbank tower is flooded with daylight and naturally ventilated, has a full-height atrium, and four-storey landscaped gardens evenly distributed over the height of the building. Working in conjunction, these architectural elements unlock the internal space of Commerzbank, transforming the entire work environment. {Davies 9}

-Integrated Strategies-

Overview 01

Floor Area sq.ft/floor

1.3 mill total (≈23,000 per floor)

Occupant load

2,100 workers

Cost Program

$300,000,000 US 53-story high-rise office building

Site Description (acres?)

approximately 3 acres; site shared with old Commerzbank building

Site Type urban, rural, etc

urban

Parking spaces #

multi-story parking garage holds 300 cars and 200 bikes

Foundation type

pile raft foundation

Gravity force systems type

perforated tube structure (corner columns with link frames)

Lateral force systems type

vierendeel truss system

secondary structure/backup

continuous floors at every fourth floor act as a stiffening diaphragm

Glazing type, identify

double-glazed operable window w/ outer skin of fixed glass & ventilated cavity

Skylights

full-height atrium with glass decks every twelve floors

Cladding type, identify

double-skinned aluminum framed curtain wall

Roof

glazed roof over plaza & atrium, high albedo concrete above remaining program

Daylighting

sky gardens, atrium, & floor-to-floor glazing

Heating

passive solar gain, heat generated from office machinery & building occupants

Cooling

natural ventilation, stack effect

Equipment list

cooling towers, absorption chillers, central building management system (BMS)

Cooling system type

water-cooled, chilled-panel ceiling system

Heating system type

thermostatically controlled radiant heating system

Duct

yes/no yes

Vertical Chases

yes/no no

Sources 1. http://www.skyscraperpicture.com/commerzbank_tower.htm 2. Commerzbank Frankfurt: Prototype for an Ecological High-Rise

(Davies 51)

(Davies 46,47)

Sources: “Commerzbank Frankfurt: Prototype for an Ecological High-Rise” (Davies), www.fosterandpartners.com

Commerzbank Tower Program

-Overview-

-Integrated Strategies-

-Structure-

-Environment-

Overview 02 -Construction-

Architectural Intent Although Norman Fosterʼs Commerzbank design was the tallest building in Europe at the time of its completion, its height was an after-thought to the true intentions driving its creation. Commerzbank is a social, economic, and ecological statement in architecture. Foster considered the lives of the users, clients, and neighbors of the building when formulating his design. Fosterʼs social, economic, and ecological goals often overlapped. Foster could have designed a cheaper building than what Commerzbank is today, but he asked his clients to consider additional investments to realize long-term gains. The buildingʼs program enhances its users lives and because of this increases their productivity. The ecologically friendly design lessens the energy costs required to maintain the building over time. Even the decision to build in the urban core of Frankfurt rather than on cheaper land in the suburbs, continued the growth of Frankfurtʼs development and contributed to the strength of the city as a whole.

Structure The structure of Norman Fosterʼs Commerzbank Headquarters is essentially a perforated tube in the shape of an equilateral triangle. The structural components work together to form this shape and to resist both gravitational and lateral forces. The three corners of this triangle are made up of 2 H-section columns connected with large steel “link frames” covered with reinforced concrete. These columns carry the load of the building and transfer it into 101 telescoping piles that bear on the porous limestone below. Supporting the winter gardens that are cut out of the tube are eight storey Vierendeel trusses. These trusses, made up of eight horizontal and four vertical members, also form the eight floors between gardens. Because of the tube form, the structure of the Commerzbank Headquarters is made up of a very few standardized pieces. All of the Vierendeel frames support the same load, and therefore are made of the same members. The corner columns are also the same from the bottom floor to the very top, with their strength changing depending on the amount of reinforcing in the concrete encasing them. The core columns, Vierendeel frames, and link frames work together to form a structure of great stiffness and stability.

Environmental Response Considered to be the worldʼs first ecological office tower, Commerzbank Headquarters relies heavily on passive strategies to create a pleasant work environment for its occupants. These strategies include a triangular (doughnut) floor plan, ʻskyʼ gardens, and a full-height atrium that allows for every office in the tower to have operable windows for views, natural ventilation, and daylight. The four-storey ʻskyʼ gardens (which spiral up the sides of the tower) provide fresh air and allow for passive solar gain, while the central atrium space acts like a natural ventilation chimney for the inward-facing offices. Despite the effectiveness of passive systems in Frankfurtʼs temperate climate zone, Foster recognizes the potential for technical (active) systems to maximize the buildingʼs efficiency. A computer controlled building management system decides whether passive or active systems are most appropriate for use at a given time and adjusts openings and shading devices accordingly. Commerzbank tower also uses water, instead of air, to condition the building, which saves a tremendous amount of energy over the life of the building. (http://inciarco.com)

Sources: Lambot, Ian. Commerzbank Frankfurt: Prototype for an Ecological High-Rise. Boston : Watermark Birkhauser. 1997.

Overview

-Overview-

-Integrated Strategies-

-Structure-

-Environment-

Overview 03 -Construction-

Construction Ethic Foster deemed the social and environmental responsibility of the building as the driving force behind the structure and construction assembly. The Commerzbank defied traditional construction methods used for high-rise buildings in Germany. Typical construction involved the use of a reinforced concrete structure, while the Commerzbank is made of a simple all steel structure. Even though the use of concrete had been the original intent Foster deemed that the lightweight form of the building outweighed the importance of traditional construction methods. The use of concrete would have required the floor slabs of the building to be far deeper than that a simple steel frame construction. The depth of these floors would decrease the transparency of the building, reducing its connection to the exterior environment and its interaction with surrounding buildings. The use of a simple all-steel structure and Vierendeel trusses allows for a repetitive lightweight construction assembly. This in turn increased the use of curtain wall glazing, leading the overall transparency of the building. The expression of form as a twisted perforated tube, in which natural light and ventilation can penetrate, emphasizes the lightweight structure and transparent materials, which create a relationship with the natural world. The Commerzbank building receives continuous praise for being the tallest building in Europe, and also distinguishably one of the most environmentally responsive office buildings. Yet in the context of Frankfurt, Germany, the Commerzbank building is social responsive by both creating a distinctive presence in the skyline while also assimilating itself into the city fabric.

(Davies)

Sources: Lambot, Ian. Commerzbank Frankfurt: Prototype for an Ecological High-Rise. Boston : Watermark Birkhauser. 1997.

Overview

Integrated Strategies 01 -Overview-

-Integrated Strategies-

-Structure-

-Environment-

-Construction-

Exterior Office Glazing Panels The exterior glazing to the office spaces integrates structural, environmental and construction strategies. The extruded aluminum Aerofoil sections are included in the glass panels in order to increase the lateral stability of the panels, allow air ventilation within the double glazed window panel system, and to avoid rainwater penetration within the interior of the panel systems.

Air Intake Transom

During the design of the glazing panels the deflection and thermal movement of the structural frame had to be taken into account. Projecting from the glazing panels the bracing provides a tolerance of up to 20mm of vertical movement (Lambot 168). Aerofoil provides structural bracing that increases lateral stabilty during thermal expansion

Ventilation slots are included allowing air to enter through the bottom sill of the insulated glass and exit at the head. These slots have been designed slightly below the opening casement of the glass in order to avoid rainwater penetration. The fixed exterior glass within the operable window system slows the flow of air avoiding the creation of a draught or the entry of water when the interior portion of the window is opened.

Air Exit Transom Water is shed away from the glazing due to the Aerofoil sections Aerofoil provides structural bracing that increases lateral stabilty during thermal expansion

(Lambot 160)

Air Intake Transom Water is shed away from the glazing due to the Aerofoil sections Air Exit Transom

Glazing Vented Cavity

Water is shed away from glazing to to Aerofoil sections and the location of the operable glazing

Ventilation allows air intake at the bottom sill and exits at the head of the window

Structural bracing provides lateral stability

(Davues 28)

Glazing Panel Axon

Exterior Office Glazing Panels Sources: Lambot, Ian. Commerzbank Frankfurt: Prototype for an Ecological High-Rise. Davies, Colin ed. Birkhauser and Jenkins, David ed. Norman Foster Works Vol. 4. Munich ; New York : Prestel, c2002

-Overview-

-Integrated Strategies-

-Structure-

Integrated Strategies 02

-Environment-

-Construction-

Mega-Column The “mega-columns” of the Commerzbank tower encompass a response to structural, environmental, and construction ideas. Even though the buildingʼs foundation consists of piles bearing on fairly stable limestone, it has to be as light as possible. The “mega-columns” of the building consist of two vertical steel ʻHʼ-section members that rise from the foundation to the top of the building. The members are stabilized by beams and diagonal bracing and encased in reinforced concrete. This creates a very light but strong structure to carry the gravitational loads of the tower. Consequently, the concrete also acts as a damper to reduce vibration in the steel from wind. The concrete and steel approach to the structure also has roots in the construction of the building. Since the steel members are erected before being encased in concrete, the equipment used to construct the building can continue to build the structure while finished portions below are being encased in concrete. This is a much quicker process than if the building were completely reinforced concrete ensuring a shorter construction time. Also, the concrete acts both as fire protection for the steel and as a water barrio to protect it from corrosion.

Diagram of how concrete can be poured while steel frame is still being constructed above it.

Sources: Lambot, Ian. Commerzbank Frankfurt: Prototype for an Ecological High-Rise. Boston : Watermark Birkhauser. 1997.

Diagram of wind vibration in structure with or without concrete encasement

Mega-Column

-Overview-

-Integrated Strategies-

-Structure-

Integrated Strategies 03

-Environment-

-Construction-

Sky Garden Glazing System The glazing system of the sky gardens was designed to be both a structural and environmental response. Structurally, the system consists of a series of vertical bowstring trusses that are connected to the steel of the floor levels with slip joints that allow the structure above to deflect and still provide lateral restraint. The bowstring trusses also integrate the hollow vertical mullions of the glazing grid. Environmentally, the hollow trusses are filled with water and connected to the building始s heating system. This transforms them into large radiators for the gardens and ensures that condensation and down drafts do not occur in the atrium during winter months.

Diagram of truss used in radiant heating.

Sources: Lambot, Ian. Commerzbank Frankfurt: Prototype for an Ecological High-Rise. Boston : Watermark Birkhauser. 1997.

Diagram of heat loss if trusses aren始t used as radiators.

Detail of slip-joint

Sky Gardens Glazing System

-Overview-

-Integrated Strategies-

-Structure-

-Environment-

Structures 01 -Construction-

Perforated Tube Structure GRAVITY LOADS

The perforated tube structure of the Commerzbank is made up of two primary structural elements: the eight-storey Vierendeel trusses, and the corner columns. These two elements provide the primary gravity and lateral load resisting members of the building. To add stiffness and stability to the structure, every fourth floor is continuous throughout the building.

LATERAL LOADS

(Below): Plan diagram of gravity and lateral load resisting members Base image: Davies, 44

Vierendeel trusses resist lateral wind loads (Above): Exploded axon of major structural members: red corner columns blue Vierendeel frames green floor structure

Vierendeel trusses that support gravity loads from winter gardens and floors

Corner columns carry concentrated gravity load to ground

(Above): Diagram of gravity resisting members and gravity load paths Base image: Davies

Continuous floors provide stiffness and stability

Horizontal floor structure creates stiffness and helps resist lateral wind loads

(Above): Diagram of lateral load resisting members Base image: Davies

Primary Structural Members

Sources: Davies, Colin ed. Birkhauser and Jenkins, David ed. Norman Foster Works Vol. 4. Munich; New York: Prestel, 2002. ; Fischer, Volker. Sir Norman Foster and Partners: Commerzbank, Frankfurt am Main. Stuttgart: Axel Menges, 1997.

Structures 02 -Overview-

-Integrated Strategies-

-Structure-

-Environment-

-Construction-

Structural Conjecture The structure of the Commerzbank works as a tube to resist lateral wind loads. This tube functions like a cantilever out of the ground. When resisting gravitational loads, the structure pushed loads to the perimeter. It is basically supported by the three corner columns and the Vierendeel frames. As â&#x20AC;&#x153;frameâ&#x20AC;? assumes fixed connections, the structure works as a very large column/beam structure with fixed connections. (Above): Diagram of moment in a Vierendeel Frame (Below): The gravity resisting structure functions as a column/beam structure (with Vierendeel frames functioning as beams between corner columns) with fixed connections.

(Above): The lateral load resisting structure functions like a cantilever rising out of the ground. Shear and moment diagrams for cantilever.

(Above): Floor structure showing steel floor beams that connect Vierendeel frame to courtyard structure as well as providing lateral stability. Wise, 117

(Above): The perimeter tube formed by Vierendeel frames and corner columns, thus forming tube. Wise, 114

Conjecture and Structural Diagrams Sources: Fischer, Volker. Sir Norman Foster and Partners: Commerzbank, Frankfurt am Main. Stuttgart: Axel Menges, 1997. Wise, C. M. et al. "The new Commerzbank headquarters, Frankfurt, Germany." The Structural Engineer 74.7 (1996): 111-22.

Structures 03 -Overview-

-Integrated Strategies-

-Structure-

-Environment-

-Construction-

Conjecture

Vierendeel Frame

Atrium Structure

The structure of the Commerzbank is essentially a perforated tube made up of corner columns and Vierendeel frames. These members work together in a combination of compression and tension. In order to increase stiffness and stability, the vertical loads are concentrates at the perimeter to create a large footprint instead of a structural center with floors moving outward. The four story gardens are supported by eight story Vierendeel frames. These twelve story structural sections are located so that the garden space spirals around the building, leaving the floor plane intact every four stories. This intact floor plane contributes to the overall stiffness of the building.

The Vierendeel frames are made up of eight horizontal and four vertical elements. These horizontal and vertical elements work together to distribute loads equally and absorb lateral forces in rigid moment joints.

The atrium is defined by a secondary structure that supports the inside edges of the floors. A vertical member links the eight end beams at the center of the span so that they can share the loads on each of the floors. This vertical member allows the end beams to have less depth without losing resistance to deflection.

The horizontal elements correspond with the floor levels, supporting the outside edge and allowing an open plan inside. These horizontal elements, in conjunction with the floor structure behind them, add depth and stiffness to the frame system, creating more resistance to wind loads. The vertical elements could be arranged in two different ways. To most effectively counteract wind loads, they should be equally spread out on the face of the building. To effectively support gravity loads, these members should be concentrated at the corners. The final design supports a combination of both strategies. The vertical elements are distributed across the face of the building, but are slightly shifted toward the corner columns. This way the Vierendeel frame is able to support both gravity loads and wind loads.

Edge beams

(Above) Looking up through atrium, diagram of edge beams and vertical load-sharing members Lambot

(Above): Commerzbank from the street

Corner Columns

Vertical members

Fischer, 31

The three corners of the Commerzbank contain two columns each. These columns are made up of two H-section vertical steel pieces that are connected by beams and diagonal bracing. The two columns that make up each corner are connected by a link frame and enclosed in reinforced concrete. While the structure of most tall buildings tapers toward the top, the steel in the Commerzbank remains the same throughout. There is a variation in strength of the column, however, but this variation is caused by a change in the amount of reinforcement used in the concrete.

Foundation The foundation consists of 111 telescoping piles that are concentrated at the corners, where the load of the building above is concentrated. These piles bear on a porous layer of limestone located beneath the clay that supports most buildings in Frankfurt. (Above): Optimum vertical element (Above): Actual vertical element spacing for Vierendeel frames spacing for Vierendeel frames Davies, 45

Fischer, 34

Structural Strategy Sources: Davies, Colin ed. Birkhauser and Jenkins, David ed. Norman Foster Works Vol. 4. Munich; New York: Prestel, 2002. ; Fischer, Volker. Sir Norman Foster and Partners: Commerzbank, Frankfurt am Main. Stuttgart: Axel Menges, 1997.; Lambot, Ian. Commerzbank Frankfurt: Prototype for an Ecological High-Rise. Boston: Watermark Birkhauser, 1997.

Structures 04 -Overview-

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Designer’s Strategy The designer’s strategy was to create a structure that would support the four-story-tall winter gardens without the space being infiltrated by columns, as well as creating an open floor plan, also without interruption by columns. The designer also wanted to utilize as much of the envelope of the building for natural daylight and ventilation as well. The use of the Vierendeel frame allows all of these strategies to be feasible. By spiraling the winter gardens around the building and creating twelve story “villages,” the designer is able to realize all the project goals. A Vierendeel frame is engineered in such a way that the members of the frame can be space far enough apart that they can encompass an entire floor. In essence, the support structure under the winter garden (the Vierendeel frame) contains eight individual floors of office space.

(Above): Drawing of open floor plan office spaces Fischer, 25

The corner columns serve as circulation space between floors also allowing the interior spans between corner columns to be free of secondary support columns. Structural expression appears to be an important element. When looking at the building, the structure and the load paths are apparent. The Vierendeel frame is clearly visible in both the articulated floors and the vertical elements. This is partially due to the placement of glazing in the envelope: glazing is used wherever possible, which coordinates with the structural elements of the Vierendeel frame.

(Above): A twelve-floor village, showing Vierendeel frame elements spaced to support floors and the rotation of Winter gardens. Fischer, 24

(Above) The structural members can be seen clearly in this elevation Fischer, 32

Hypothesis Sources: Davies, Colin ed. Birkhauser and Jenkins, David ed. Norman Foster Works Vol. 4. Munich; New York: Prestel, 2002. ; Fischer, Volker. Sir Norman Foster and Partners: Commerzbank, Frankfurt am Main. Stuttgart: Axel Menges, 1997.

-Overview-

Climate Facts Commerzbank Tower

Days Observed

Wind

Sky

H u m i d i ty

Temperature

Project

FosterArend, & Partners, Arup andAudrey Krebs de & Kiefer (SE), J. Roger Preston w/ P&A Petterson Ahrens (ME), Schad & Hรถlzel (EE) John Mike Benkert, Filippis, Saretta Tillmaand Building Name

Commerzbank Tower (or Commerzbank Headquarters)

Construction Period

1994 to 1997

Client

Commerzbank

City

Frankfurt, Germany

Latitude

50.07 N

Longitude

08.41 E

Elevation

367 ft

Normal Climate Data Heating Degree Days Cooling Degree Days Extreme High Normal High Normal Average Normal Low Extreme Low Dew Point Max %RH Min %RH % Days with Rain Rain Inches % Overcast Sky % Clear Days Prevailing Direction Speed, mph Percent Calm Rain Fog Haze Snow Hail Freezing Rain

Jan 588 0 56 F 38 F 34 F 30 F -4 F 30 F 90 80 32 1.7 67 33 SW 9 6 10 19 12 -

Feb 508 0 63 F 41 F 36 F 30 F -1 F 29 F 88 69 25 1.5 61 39 NE 8 9 7 18 8 -

Mar 427 0 75 F 50 F 43 F 36 F 9F 34 F 87 60 30 1.9 60 40 SW 9 6 9 16 5 -

Apr 317 0 77 F 56 F 48 F 39 F 20 F 37 F 84 53 28 1.7 57 43 NE 9 8 9 12 2 -

May 185 0 88 F 66 F 57 F 47 F 28 F 45 F 83 53 32 2.4 56 44 NE 8 12 10 14 0 -

Jun 110 7 93 F 71 F 62 F 53 F 34 F 51 F 83 54 34 2.4 57 43 SW 9 11 10 13 0 -

Jul 51 32 97 F 75 F 66 F 57 F 38 F 54 F 83 51 30 2.6 56 44 SW 9 11 9 12 0 -

Aug 48 31 96 F 75 F 66 F 56 F 37 F 54 F 87 51 25 2.1 54 46 SW 8 14 8 15 0 -

Sep 130 2 90 F 68 F 59 F 51 F 32 F 51 F 91 59 27 2 60 40 SW 8 12 8 18 0 -

Oct 271 0 82 F 57 F 50 F 43 F 25 F 45 F 93 70 30 2.1 66 34 SW 8 11 9 21 0 -

Nov 457 0 63 F 45 F 41 F 36 F 16 F 37 F 91 78 32 2 71 29 SW 9 6 10 19 4 -

Dec 558 0 61 F 40 F 37 F 32 F 3F 33 F 90 82 32 2.2 70 30 SW 9 6 10 20 9 -

Year 3650 72 97 F 57 F 50 F 43 F -4 F 42 F 88 63 30 24.6 61 39 SW 9 9 109 197 40 -

-Integrated Strategies-

-Structure-

Environment 01

-Environment-

Germany's climate is relatively constant. The summers are generally warm with frequent rainshowers and winters are generally cold. The amount of snowfall and average temperatures are typically influenced by altitude moreso than by climatic region. The weather is continental in that it varies from year to year, meaning a chilly spring and rainy summer one year can be followed by a warm spring and sunny summer the next. Therefore, it is recommended that environmental building systems in the region be versitile in response to the constantly changing conditions.

-Construction-

Frankfurt

The city of Frankfurt has a temperate continental climate characterised by warm summers with occasional wet days, and cold winters. Temperatures are not extreme and never severe, but winters can bring occasional violent storms. (www.earth.google.com)

Sources 1. http://www.myforecast.com/ 2. http://www.worldweather.org/

3. http://www.gaisma.com 4. http://www.eosweb.larc.nasa.gov/

Sources: www.about-germany.org, (see tables above for additional sources)

Climate Data: Frankfurt, Germany

-Overview-

Temperature

average high in Frankfurt, Germany

-Integrated Strategies-

-Structure-

Environment 02

-Environment-

-Construction-

average low in Frankfurt, Germany source: http://www.myforecast.com

Death Valley, CA (high)

Fargo, ND (low) High Avg Low

38˚F 34˚F 30˚F

41˚F 36˚F 30˚F

50˚F 43˚F 36˚F

56˚F 48˚F 39˚F

66˚F 57˚F 47˚F

71˚F 62˚F 53˚F

75˚F 66˚F 57˚F

75˚F 66˚F 56˚F

68˚F 59˚F 51˚F

57˚F 50˚F 43˚F

45˚F 41˚F 36˚F

40˚F 37˚F 32˚F

Jan.

Feb.

Mar.

Apr.

May

Jun.

Jul.

Aug.

Sep.

Oct.

Nov.

Dec.

110 100 90 80 70 60 50 40 30 20 10 0

Indoor and outdoor air temperature can be modified through a combination of “passive” or active design strategies. Daily average temperatures remain pleasant in Frankfurt, Germany for a good portion of the year, However, temperature is only part of the equation when considering occupancy comfort as relative humidity is also a contributing factor.

Relative Humidity

average morning high

average afternoon low source: http://www.myforecast.com 100

New Orleans, LA (high)

80 60

Death Valley, CA (low)

40 20 Morning

90%

88%

87%

84%

83%

87%

91%

93%

91%

90%

Afternoon

80%

69%

60%

53%

54%

51%

59%

70%

78%

82%

Jan.

Feb.

Mar.

Apr.

May

Jul.

Aug.

Sep.

Oct.

Nov.

Dec.

Jun.

Frankfurt, Germany is a rather humid climate when compared to those in the USA. Fortunately, the relative humidity levels are highest during the cool fall and winter months when it’s more desirable, and considerably lower in the warm spring and summer months when it causes the most discomfort. For further explanation, please refer to the psychometric chart that follows.

Sources: http://www.myforecast.com

Images: www.corbis.com

Climate Data: Frankfurt, Germany

-Overview-

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Environment 03

-Environment-

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Heating Degree Days Fargo, ND (high)

1000 800 600 400 200

Miami, FL (low)

degree days

588

508

427

317

185

110

130

271

457

558

Jan.

Feb.

Mar.

Apr.

May

Jun.

Jul.

Aug.

Sep.

Oct.

Nov.

Dec.

A Heating Degree Day (HDD) is defined as 65 degrees Fahrenheit minus the mean daily temperature. In Frankfurt, Germany heating is required throughout the year, even in the summer months. Annually there are 3,650 HDD. (For comparison: Miami, Florida has 40 HDD, and Fargo, North Dakota has 5,550 HDD)

Cooling Degree Days 500 400 300 200

Miami, FL (high)

100 Fargo, ND (low)

degree days

Jan.

Feb.

Mar.

Apr.

May

Jun.

Jul.

Aug.

Sep.

Oct.

Nov.

Dec.

A Cooling Degree Day (CDD) is defined as the mean daily temperature minus 65 degrees Fahrenheit. In Frankfurt, Germany very little cooling is required, even during the summer months. Annually there are 72 CDD. (For comparison: Miami, Florida has 2,451 CDD, and Fargo, North Dakota has 82 CDD)

Sources: http://eosweb.larc.nasa.gov/sse

images: www.corbis.com

Climate Data: Frankfurt, Germany

-Overview-

-Integrated Strategies-

Wind Potential

Average Speed and Direction at 50m Above Earth Surface

-Structure-

Environment 04

-Environment-

-Construction-

7.8 knots is recommended speed for effective use of wind energy

14 12 10 8 6 4 2 Knots m/s Direction

13.5 6.96 SW

11.4 5.85 SW

13.4 6.88 SW

11.6 5.96 SW

10.3 5.31 SW

10.2 5.27 SW

10.8 5.54 SW

10 5.16 SW

9.9 5.11 SW

10.4 5.35 SW

12.2 6.27 SW

12.7 6.53 SW

Jan.

Feb.

Mar.

Apr.

May

Jun.

Jul.

Aug.

Sep.

Oct.

Nov.

Dec.

The average annual wind speed in Frankfurt, Germany is 11.4 knots with the breezes typically coming from the southwest. The velocity is strong enough in the region for wind energy to serve as an effective means of power generation and passive cooling via cross-ventillation and stack effect. Southwestern winds from the Mediterranean keep the region relatively mild throughout the year.

Average Rainfall

Monthly Averaged Precipitation (mm/day)

7 6 5

Birmingham, AL (high)

4 3 2 Las Vegas, NV (low)

mm/day

3.5

2.88

2.84

2.22

2.49

3.28

2.65

2.25

2.94

2.49

3.34

3.67

Jan.

Feb.

Mar.

Apr.

May

Jun.

Jul.

Aug.

Sep.

Oct.

Nov.

Dec.

Frankfurt, Germany receives a relatively high amount of precipitation throughout the year. The rainfall is fairly consistent from month to month and allows for the implementation of rainwater capture systems throughout the region. Unfortunately, the massive program and limited roof area makes such a system somewhat impractical for Commerzbank Tower.

Sources: http://www.eosweb.larc.nasa.gov/, http://www.iht.com/

Images: http://www.corbis.com

Climate Data: Frankfurt, Germany

-Overview-

Solar Potential

-Integrated Strategies-

-Structure-

Environment 05

-Environment-

-Construction-

Monthly Averaged Insolation Incident On a Horizontal Surface

7 6 5 Miami, FL

4 3 2

Seattle, WA

1 kWh/m2/day 0.8

1.55

2.42

3.69

4.73

4.62

4.95

4.15

2.87

1.72

0.92

0.61

Jan.

Feb.

Mar.

Apr.

May

Jun.

Jul.

Aug.

Sep.

Oct.

Nov.

Dec.

Statistics for average insolation (the combination of clear sky insolation and average daylight cloud amount) indicate that the use of photovoltaics in Frankfurt, Germany is not an effective means of power generation. Frankfurt only receives an average annual insolation of 2.75 kWh/m2/day. By comparison Seattle, WA receives 3.77 kWh/m2/day, while Miami, FL receives 5.18 kWh/m2/day. Commerzbank Tower utilizes the low solar insolation in the region as a means to effectively daylight the entire building with minimal glare and overheating from direct gain. At the same time, the orientation of the building allows for passive solar heating for the majority of the year, as well as the growth of sky gardens, which spiral up the interior of the structure. The sky gardens themselves are a direct response to solar orientation with the warmer south facing gardens containing plants and trees which are prevalent in the temperate Mediterranean, the western gardens containing species from North America, and the cooler east facing sky gardens containing plants more native to the Frankfurt region. Commerzbank tower has no overhanging sun shades to protect the building from the hot summer sun, but rather utilizes shading devices sandwiched between the double-glazed glass curtain wall.

(Quantril 165)

Sources: http://www.eosweb.larc.nasa.gov/, â&#x20AC;&#x153;Commerzbank Frankfurt: Prototype for Ecological High-Riseâ&#x20AC;?

(www.earth.google.com, Lechner)

Images: www.corbis.com

Climate Data: Frankfurt, Germany

-Overview-

% 70

% 30

K 20%

H F

10%

D C

B I

J 40ºF

50ºF

60ºF

70ºF

80ºF

90ºF

100ºF

110ºF

Winter: December

Spring: March

Summer: June

Fall: September

am:

pm:

32º F 90% relative humidity 40º F 82% relative humidity

A B

pm:

Sources: Lechner, http://www.myforecast.com

36º F 87% relative humidity 50º F 60% relative humidity

pm:

Images: Lechner

D. Internal Gains: Conditions are close enough to the comfort zone that internal loads (heat provided by electrical and human sources) will provide the heat needed for comfort.

53º F 83% relative humidity 71º F 54% relative humidity

D E

F. Ventilation: Though temperatures and humidity levels are high, comfort may be obtained through the direct evaporation of perspiration, if enough air movement is available. G. Thermal Mass: Radiant cooling and night-flushing of the internal air with cool outside air will store "coolth" for the next day.

30ºF

C. Passive Solar: Direct gain, indirect gain and hybrid systems, combined with infiltration and heat-loss control, can provide the heat required for comfort.

E. Comfort: No strategy is necessary, except to prevent further solar heat gain in summer or loss in winter

20ºF

-Construction-

B. Active Solar: Heat needed to achieve comfortable levels in this zone can be effectively supplied by solar collectors or any other active solar system supported by backup high efficiency conventional heating systems.

By plotting the temperature and humidity ranges of Frankfurt, Germany over the course of a year on the chart, one can determine which passive and/or active heating and cooling strategies are most effective for Commerzbank tower when it comes to creating a comfortable work environment for its occupants. Frankfurtʼs temperature and humidity ranges are represented on this chart by the dashed green polygons.

10ºF

-Environment-

A. Conventional Heating: Conditions occurring in this zone are too cold to rely on passive and active solar heating; high efficiency conventional heating systems are required.

% 80

Psychrometric charts graphically represent the relationship between temperature and humidity, the two factors that determine human comfort. On the chart, the "comfort zone' indicates conditions in which most people will be thermally comfortable. The boundaries of the zones are not absolute, as human comfort will vary by season, metabolic rate and culture.

-Structure-

Strategies:

The Psychometric Chart:

-Integrated Strategies-

Environment 06

pm:

51º F 91% relative humidity 68º F 57% relative humidity

D E

H. Thermal Mass plus Ventilation: Some passive or active internal ventilation is required to extract heat, in addition to night flushing and radiant cooling. I. Evaporative Cooling J. Humidification: Moisture must be added to the air for comfort. K. Air Conditioning: Humidity levels are too high to achieve comfort levels without the use of high-efficiency conventional systems.

Climate Data: Frankfurt, Germany

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Environment 07

-Environment-

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Commensurate Tower: Thermal Strategies

(Please refer to previous page for clarification of psychometric chart and corresponding letters)

A. Conventional Heating: Conditions in Frankfurt, Germany are sometimes too cold for a building to rely solely on passive heating strategies as a means for creating thermal comfort: Commensurate tower utilizes high efficiency heating systems throughout the majority of cold winter months. C. Passive Solar: Direct gain, Indirect gain and hybrid systems inherent in the buildingĘźs massive glass facades, combine with infiltration and heat-loss controls to meet a majority of Commensurate's heating requirements for the spring, fall, and portions of the summer season as well. D. Internal Gains: Conditions in Frankfurt, are oftentimes close enough to the comfort zone that internal loads (heat provided by electrical and human sources) will provide all the heat necessary for comfort. H. Thermal Mass plus Ventilation: When conditions call for a level of cooling in Commensurate tower, passive and active internal ventilation is utilized to extract heat along with night flushing and radiant cooling.

A. Conventional Heating: When conditions are too cold for passive strategies to be an effective means for creating thermal comfort, heating is provided by ordinary, thermostatically controlled panel radiators below the windows. (Davies 204)

C. Passive Solar: Large glass facades surrounding the sky gardens and offices allow for direct and indirect solar gain throughout Commensurate for the majority of the year when heating is desired. Shading devices and ventilation systems are utilized to counter overheating. (Davies 287)

Sources and Images: â&#x20AC;&#x153;Commensurate Frankfurt: Prototype for an Ecological High-Riseâ&#x20AC;?

(Lechner)

H. Thermal Mass plus Ventilation: Natural ventilation as a means for aiding in thermal comfort in Commensurate is possible for roughly 60% of the year. This is a result, thanks in large part to four twelve-story atrium spaces in which windward and leeward sky gardens take in and exhaust fresh air using cross ventilation and stack effect. (Davies 196)

Climate Data: Responses

-Overview-

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Environment 08

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When analyzing the environmental systems within Commerzbank Tower, itʼs worth noting that the number one goal of Fosterʼs design is to create a pleasant work environment for the buildingʼs 2,000+ occupants as a means of increasing worker productivity. While this significantly increases up-front building costs of the skyscraper, in the grand scheme of Commerzbankʼs expenses, worker salaries significantly outweigh any construction costs over a prolonged period of time. Therefore, it can be assumed that the documented increases in worker productivity from abundant daylighting and views to the outside makes Fosterʼs scheme financially justifiable. Commerzbankʼs use of the doughnut plan in conjunction with the four-story sky gardens allows for every office in the building to be daylit with an unobstructed view to the outdoors. Full height windows and shallow floor plates ensure that the amount of natural light penetrating into the building is sufficient enough to substitute for artificial lighting through the majority of the workday. Frankfurt, Germanyʼs low solar insolation and diffuse lighting conditions make daylighting an incredibly effective environmental response in that glare and unwanted direct solar gain in the region is minimal. Daylit sky gardens with views to the outdoors Daylit offices with views to outdoors

(Above) Daylight/Views Floor Plan (Davies 248) (Left) Daylight/Views Section (Davies 46,47)

Sources and Images: “Commerzbank Frankfurt: Prototype for an Ecological High-Rise” (Davies)

Daylight/Views Perspective Sketch (Davies 15)

Environmental Responses: Daylighting and Views

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Environment 09

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While the majority of modern skyscrapers rely heavily on the use of massive mechanical systems to heat, cool, and circulate air within the building, Commerzbank Tower utilizes natural ventilation as a primary means for creating year-round thermal comfort. Natural ventilation in Commerzbank occurs at multiple scales ranging from individual rooms to several building stories, all of which vary based on climatic conditions. When looking at the building section as a whole, it appears as though the entire central atrium space acts like a giant chimney with air being exhausted out the top of the building by way of stack effect. While this was Fosterʼs original intention when designing the building, the incredible scale of the space would have resulted in a powerful updraft of air that would have been undesirable for the building patrons. Consequently, in the final design, the atrium is segmented by glass decks into four twelve-story spaces, each consisting of three deliberately positioned sky gardens. In this particular scheme, fresh air enters the building through windward gardens at the bottom of every twelve-story segment, and exhausted out of leeward gardens at the top of them. The glass decks are completely sealed off from the atrium space below, divorcing them from the towerʼs natural ventilation process, which includes both cross-ventillation and a limited amount of stack effect. The means by which natural ventilation occurs in the tower section varies for the cold winter and warm summer months. In cold winter conditions, sky garden windows are closed to store heat, but are reopened to let in desirable breezes when conditions warm up. In both circumstances, warm air rises up and out of the building to naturally ventilate the interior.

Central Atrium Ventilation (Quantril 165)

Winter Sky Garden Ventilation (www.architectureweek.com)

Sources and Images: “Commerzbank Frankfurt: Prototype for an Ecological High-Rise” (Davies)

Summer Sky Garden Ventilation (www.architectureweek.com)

Environmental Responses: Ventilation

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Environment 10

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One of the main reasons as to why Commerzbank Tower is considered to be the first “ecological skyscraper” is that passive strategies are utilized at all scales ranging from window detailing to the full-height atrium. Typically, modern office buildings full of heat-producing machinery have a higher demand for cooling, but Frankfurt winters typically require heating as well. Foster responds to this dichotomy of needs in the cladding system by utilizing double skin glazing with ventilated cavity spaces, operable casements, and Venitian blinds. Whenever heating is desired, exterior vents are closed to allow heat to build up in the cavity spaces, which protects against cold winds while improving the thermal insulating properties of the windows by as much as 20%. When cooling is required, the cavity vents and operable casements are opened to allow for natural ventilation with cool air entering low and warm air exiting high after circulating through the office. While passive strategies for heating, cooling, and ventilation are effectively implemented in Commerzbank office spaces for the majority of the year, Frankfurtʼs cold winter months and hot summer period require active systems as a means to create thermal comfort within the tower. When in active modes (as determined by the central building management system), Commerzbank offices utilize radiant floor heating to effectively warm objects instead of air, and chilled (water) panel ceilings to cool the space in a more energy efficient manner than the forced-air alternatives.

Glazing Vented Cavity

Building Skin Ventilation Detail (Davies 160)

Sources and Images: “Commerzbank Frankfurt: Prototype for an Ecological High-Rise” (Davies)

Passive Heating/Cooling/Ventilation Systems (Davies 201)

Active Heating/Cooling/Ventilation Systems (Davies 200)

Environmental Responses: Ventilation

-Overview-

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Environment 11

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Spiraling up the sides of the building, Commerzbank towerĘźs nine four-story sky gardens occupy three different faces, which all have distinct solar orientations. With gardens oriented to the south, east, and west, the design team recognized early on that plantings from different climates would be required to respond to the varying levels of solar exposure. The south facing gardens, which receive the most amount of solar gain throughout the year consist primarily of Mediterranean plantings including olive trees, cypresses, and a ground cover of thyme. The west facing gardens, which receive a significant amount of afternoon sun throughout the year are filled with north American plants including acarias, evergreen oaks and ornamental grasses.

(Davies 248)

The northeast facing gardens, which receive very little to no sun over the course of the year are composed of various Asian plantings that thrive in shaded environments such as bamboo. To ensure that all of the plant life stays alive, the sky gardens are always naturally ventilated, even when the office interiors are being air conditioned. As a result, these environments act more as sheltered exterior spaces than interiors, meaning that there are times in the year when they may be too cool for people in indoor clothing. This is somewhat supplemented with underfloor heating, but is an adjustment that would probably not be as widely accepted in America as it is in western Europe. West facing gardens filled with North American plant life. (Davies 278)

South Facing Gardens filled with Mediterranean plant life. (Davies 279)

Sources and Images: â&#x20AC;&#x153;Commerzbank Frankfurt: Prototype for an Ecological High-Riseâ&#x20AC;? (Davies)

Environmental Responses: Sky Gardens

Construction 01 -Overview-

Construction: The Foundation

-Integrated Strategies-

-Structure-

-Environment-

-Construction-

Due to Frankfurt’s location on a soil mostly made up of clay, with a layer of sand and gravel above, Foster and Partners along with the foundation engineers, Ingenieursozietat katzenbach und Quick, had to consider in depth the possibility of settling and its effects on surrounding buildings. They had found that other high-rise buildings of the area had settled between 100mm to 300mm. The engineers predicted that a settlement of 150mm might have been drastic enough to cause the existing Commerzbank building, due to its proximity to the new tower, to tilt. The solution arose when determining the size of the pile-raft foundation. It was decided that the piles would be drilled into the ground about 45 meters deep, in order to pass through the clay soil and embed themselves in the limestone “inflata” layer located below. Piled raft foundations traditionally evenly spread the piles around the footprint of the building. The new Commerzbank tower, due to its distribution of loads to the six mega-columns at the corners of the building, led to the 111 piles being concentrated at these three corners rather than evenly through the footprint (Davies 63).

Location of Piles

Sand and Gravel Layer

Clay Soil Layer

Porous Limestone Layer

Construction of the Foundation

(Lambot 71)

Construction of the Foundation

(Lambot 72)

Section Diagram of the Foundation and Soil Condition

(Lambot 70)

Meeting The Ground Sources: Lambot, Ian. Commerzbank Frankfurt: Prototype for an Ecological High-Rise. Davies, Colin ed. Birkhauser and Jenkins, David ed. Norman Foster Works Vol. 4. Munich ; New York : Prestel, c2002

Construction 02 Construction: The Foundation

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The long piles led to high torsion stresses during drilling, causing restrictions on their overall diameters. The decision was made to use telescopic piles. At the base of the slab the piles were designed to be 1.8 meters in diameters. This would be used for the initial 20 meters. Following this the piles diameter would be reduced to 1.5 meters. The location of the piles became a concern for in traditional construction methods piles are evenly distributed at the footprint. The design of the Commerzbank had located the cores of the building at the 3 corners thereby concentrating the vertical loads in these corners. This required the unconventional distribution of 111 piles, in groups at the three corners of the building. A 12 meters high cellular box structure is used to transfer the loads. This structure is made up of wall 3 meters deep and a horizontal slab that ranges from 2.5 to 4.5 meters. A second issue arose with the realization of the porosity of the limestone bed, which led to large cavities where the piles were supposed to be imbedded. This would significantly weaken the piles. The decision was made that liquid concrete would be injected, at a high pressure into the subsoil of each pile strengthening the foundations connection to the subsoil. The pile cages incorporated the pipes and valves of the concrete injection system. The concrete was injected around the base of each pile as much as 10 meters below and around the piles. Over 2,000 tones of concrete was injected around the piles strengthening the foundation. The design and construction of the foundation has led to a measured settlement of the new towers of about 2 cm and only 0.6 cm in the old tower. This is far smaller than any of the tall buildings of Frankfurt, who have had settlements ranging from 10 to 30 cm. The use of a deep piled foundation has led to the success of the integration of such a large building within a tight framework of existing buildings on unstable soil (Davies 67).

Clay Region

(Lambot 66)

Model of Foundation and Piles

Porous Limestone Region Liquid Concrete Injected Around the Base of the Pile

Clay Intact Limestone Weathered Limestone Foundation and Structure Model

(Lambot 69)

Construction of Foundation

(Lambot 73)

Typical Pile Detail

Construction 03 -Overview-

-Integrated Strategies-

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-Environment-

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Transparency: Skylight

Spacial Composition of Frankfurt’s Skyline

Perforated Design: Sky Garden The perforated form of the buildings, along with the extensive use of the curtain walls allows for a transparency, not often attainable for a building of its size. The use of gardens within the perforations creates the link between the exterior environment and the building. By bringing the park inside, Foster has allowed this office building to integrate itself not only with the existing city fabric but also with nature and the surrounding environment. Initially Foster had design the Commerzbank building by located all of the gardens on the southern side. This he felt decreased the connection of the building to his surroundings. He decided to then cut the building after every four floors and twist the level above, resulting in a spiraling garden. This increases the amount of light and ventilation through the building along with increasing the overall transparency within the skyline (Davies 69).

The overall form of the building is a simple curved triangular monolithic tube. The different functional areas are distinguished on the exterior façade by changes in color, texture and cladding systems. This expression and function through the structures give the building a human scale. Glass ‘decks’ or skylights at levels 7, 19, 31, and 43 along with the enclosing top skylight divide the atrium. The use of multiple skylight enclosures has more than one function. A half-hour fire and smoke barrier is created between sections of the building along with managing and control the fresh air ventilation in the building. The skylights divide the stack and chimney effect leading to an increase control of air quality management. The skylights are divided into triangular panels (1.5 meters on each side by 2.5 cm thick glass). A neoprene gasket is used to seal the joints between the glass and steel frame. The interior and exterior of building use glazing and reflective panels in order to reflects views from the sky allowing the building to be imbedded within its setting. The overall structural appearance can be seen as light and transparent, in relation to other high-rise buildings in the city, leading to the reduction in social scale of the building (Lambot 176).

Perforated Tube Design Iterations

Penetration of the Sky

Skylight in Atrium

Final Design

(Lambot 153)

Atrium Skylight Locations

(Lambot 46)

Meeting The Sky Sources: Lambot, Ian. Commerzbank Frankfurt: Prototype for an Ecological High-Rise. Davies, Colin ed. Birkhauser and Jenkins, David ed. Norman Foster Works Vol. 4. Munich ; New York : Prestel, c2002

Construction 04 -Overview-

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Transparency: Cladding Types The exterior cladding system for the office area is made up for repetitive individual panel units that interlock with each other. These panels are suspended from brackets fixed to the Vierendeel beams. The typical panel has two main parts, a fixed spandrel of insulated grey glass and an operable window. Each panel is a thick double glazed system included a variety of smaller components within the glazing, including motors and operable blinds. Ventilation slots are included allowing the air to enter through the bottom sill of the insulated glass and exit at the head. These slots have been designed slightly below the opening casement of the glass in order to avoid rainwater penetration. The fixed exterior glass within the operable window system slows the flow of air avoiding the creation of a draught when the interior portion of the window is opened. A â&#x20AC;&#x2DC;tongueâ&#x20AC;&#x2122; projects from the top of each panel which allows for the location of the next panel above, while also allowing for vertical movement caused by thermal expansion. The slip joints along the vertical edge also allow for movement, while retaining a tight joint system though neoprene gaskets (Lambot 168).The cladding located between the offices and the atrium is relatively the same system, yet is slightly simplified. These is no second skin, but the windows are still operable, creating a cross ventilation. There are also no blinds located in these panels, from direct light does not access these spaces, only the diffused light from the skylight and exterior glazing (Lambot 156). Vierendeel Frame I-Beam Bolted Attachment to I-Beam

Bolted Attachment to I-Beam

Attachment Clip for Glazing Attachment Clip for Glazing

Glazing Panels Interlock Glazing Panels Interlock

Interior Office and Atrium Cladding

Exterior Office Cladding

Construction 05 -Overview-

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Transparency: Cladding Types The core columns are first protected by a layer of intumescent paint then clad in reinforced concrete. A layer of waterproofing is then attached, followed by frameless, story height toughened white glass panels. These are fixed to the reinforced concrete through bolted connections.

Vierendeel Frame

The cladding used to enclose the corners of the tower is a simple frame-and-infill curtain wall. A variety of panels are used including: transparent, clear or enamel-backed glazing, opaque glazing, louvered, insulated and un-insulated, some ventilated and other unventilated. As this building is more often viewed from far away the paneled differences are only moderately perceived allowing a continual unity within the rounded corners. A vertical aluminum frame conceals the edges of the column glass and paneled corner in order to create a continuous tower element at all three corners of the building. The transparent and reflective cladding of these masses increase the buildings intearction with its surrouding environment and create a relationship between the building and human scale (Lambot 155)

Vierendeel Frame Reinforced Concrete

Aluminum Frame

Panelized Glazing

Waterproofing Membrane Toughened White Glass Panels

Mega Column Cladding

Building Corner Cladding

Construction 06 -Overview-

Transparency: Construction

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The decision to use a steel structural frame allowed the Commerzbank Tower to gain and increase transparency. The use of Vierendeel truss system, created a standardized structural frame, that could be prefabricated and simply assembled on site. The efficiency of this structure along with the thinner floors increased the ability to use curtain wall glazing, both transparent and reflective. The overall structural appearance can be seen as light and transparent, in relation to other high rise buildings in the city, leading to the reduction in social scale of the building. The use of these panels reflects views from the sky allowing the building to be imbedded within its setting.

Sketch of City Fabric

Social Responsibility: The Urban Fabric The plaza and cross through that was created at the ground floor of the office buildings, has created an area of social gathering that has linked the building the city surroundings, reducing the social scale of such a building.

Commerzbank Plaza

(Lambot 34)

Commerzbank Plaza

(Lambot 31)

Sketch of City Fabric

Social Responsibility Sources: Lambot, Ian. Commerzbank Frankfurt: Prototype for an Ecological High-Rise. Davies, Colin ed. Birkhauser and Jenkins, David ed. Norman Foster Works Vol. 4. Munich ; New York : Prestel, c2002

Construction 07 -Overview-

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Mega-Column Cladding

Column Cladding

Office Cladding Construction

Vierendeel Frame Construction Column Cladding Construction

Office Cladding

Mega-Column Frame Construction

Vierendeel Frame Construction Mega-Column Cladding

Location of the Cladding Detail

(Lambot 46)

Cladding Types Sources: Lambot, Ian. Commerzbank Frankfurt: Prototype for an Ecological High-Rise. Davies, Colin ed. Birkhauser and Jenkins, David ed. Norman Foster Works Vol. 4. Munich ; New York : Prestel, c2002

Construction 08 -Overview-

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The Corner: Mega-Columns The decision to use a steel structural frame allowed the Commerzbank Tower to gain an increased transparency. The use of steel allows for increased openness and speed of erection of the frame. The use of a Vierendeel truss system, created a standardized structural frame that could be prefabricated and simply assembled on site, as a â&#x20AC;&#x2DC;kit of partsâ&#x20AC;&#x2122;. Originally the structure was intended to be made out of reinforced concrete, as is the building tradition of Germany, but studies showed that beams would of had to be near two meters thick to accommodate the load. This would have drastically affected the amount of free space for glazing. The steel structural frame was proposed, with reinforced concrete located around the mega-columns allowing 65 percent free space to glazing as opposed to 40 percent allowable with the use of a concrete frame (Lambot 68) The efficiency of this structure along with the thinner floors increased the ability to use curtain wall glazing, both transparent and reflective. The overall structural appearance can be seen as light and transparent, in relation to other high-rise buildings in the city, leading to the reduction in social scale of the building (Lambot 68)

Mega-Column Frame Construction

(Lambot 86)

Vierendeel Frame Construction Mega-Column Frame Construction

(Lambot 93)

Mega-Column Frame Detail

Corner Detailing Sources: Lambot, Ian. Commerzbank Frankfurt: Prototype for an Ecological High-Rise. Davies, Colin ed. Birkhauser and Jenkins, David ed. Norman Foster Works Vol. 4. Munich ; New York : Prestel, c2002

Construction 09 -Overview-

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The Corner: Cladding The core columns, the heaviest mass of the building are first protected by a layer of intumescent paint, which is applied on all parts of the structural frame. The columns are then clad in reinforced concrete, which increases structural stability as well as protects from weathering and corrosion. A layer of waterproofing is then attached, followed by frameless, story height toughened white glass panels. These are fixed to the reinforced concrete through bolted connections. A vertical aluminum frame conceals the edges of the column glass in order to create a continuous tower element of all six columns. Every fourth floor and wider horizontal joint is used in order to break up the mass and create a scale and hierarchy within the buildings facade. This coincides with the location of the interior gardens.

Vierendeel Frame

The cladding used to enclose the corners of the tower is a simple frame-and-infill curtain wall. A variety of panels are used including: transparent, clear or enamel-backed glazing, opaque glazing, louvered, insulated and un-insulated, some ventilated and other unventilated. Some panels have internal lining walls, while others do not. The type of panel used in a specific location is in direct correlation with the programmatic function housed on the interior. As this building is more often viewed from far away the paneled differences are only moderately perceived allowing a continual unity within the rounded corners (Lambot 155). Reinforced Concrete Aluminum Frame

Panelized Glazing

Waterproofing Membrane Toughened White Glass Panels

Building Corner Construction

(Lambot 165)

Cladding Types

(Lambot 164)

Building Corner Cladding Detail

Construction 10 -Overview-

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-Environment-

Exterior Office Glazing System

-Construction-

Fixed External Glazing

The extruded aluminum Aerofoil sections are included in the glass panels in order to increase the stability of the panels and to avoid rainwater penetration within the interior of the panel systems. Ventilation slots are included allowing air to enter through the bottom sill of the insulated glass and exit at the head. These slots have been designed slightly below the opening casement of the glass in order to avoid rainwater penetration. The fixed exterior glass within the operable window system slows the flow of air avoiding the creation of a draught or the entry of water when the interior portion of the window is opened (Lambot 161).

Double Glazed Opening Casements Ventilated Cavity

Extruded Aluminum Aerofoil Section Slip-Joint Between Panels 6mm Toughened Glass on Felt Underlay

80mm-Thick Thermal Insulation

Vierendeel Frame

Water is shed away from glazing to to Aerofoil sections

8mm Toughened Glass

40mm-Deep Ceiling Panel

Extruded Aluminum Aerofoil Section Venetian Blinds

Casement Motor

Office Glazing System

(Lambot 158)

Office Glazing Detail

(Lambot 161)

Exterior Office Glazing Section

(Lambot 160)

Response To Water Sources: Lambot, Ian. Commerzbank Frankfurt: Prototype for an Ecological High-Rise. Davies, Colin ed. Birkhauser and Jenkins, David ed. Norman Foster Works Vol. 4. Munich ; New York : Prestel, c2002

Construction 11 -Overview-

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Exterior Office Glazing System In order to avoid rainwater penetration within the interior of the panel system the air intake transom is located slightly below the opening casement of the glass. The air exit transom is located at the top of the exterior clear glazed portion of the panel. This allows for the controlled movement of air within the panel system and avoids the entry of water into the interior portions when the operable window is in use (Lambot 161). Air Intake Transom

Structural Steel

Holorib Concrete Slab Fire Protection

Air Exit Transom

Chilled Ceiling Panels Movable Double-Glazed Window Element Fixed Outer Glass

Air Intake Transom

Convection Heater

Fixed Spandral (Low Iron Glass with RAL Enamel Coating) Raised Floor

Office Glazing System

(Lambot 159)

Office Glazing Detail

(Lambot 168)

Exterior Office Glazing Section

(Davues 28)

Construction 12 -Overview-

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Mega-Column The reinforced concrete surrounding the mega-columns is not only used for structural stability but also to protect the steel column from corrosion and weathering. The initial layer of intumescent paint, which is applied on all parts of the structural frame, provides a layer of protection while the reinforced concrete provides another. A waterproofing membrane is added between the reinforced concrete and the glass panels. To protect the columns from rain, the glass panels shed, rather than absorb water, as the reinforced concrete would. Due to the location of joints in the glass panels, rainwater is able to infiltrate this first layer of glass. Behind this is located the waterproofing, creating an additional barrier. The thicker layer of reinforced concrete becomes a moisture barrier along with the last layer of intumescent paint that protects the structural steel from corrosion (Lambot 165).

Vierendeel Frame Reinforced Concrete

Waterproofing Membrane

Toughened White Glass Panels

Mega-Column Waterproofing

(Lambot 164)

Mega-Column Cladding

(Lambot 159)

Mega-column Waterproofing Detail

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Works Cited Cramer, Ned. “Europe's Tallest Tower”. Architecture August 97, Vol. 86 Issue 8, p26. Davey, P. “High expectations”. The Architectural Review July 97, Vol. 202 Issue 1205, 26. Davies, Colin ed. Birkhauser and Jenkins, David ed. Norman Foster Works Vol. 4. Munich ; New York : Prestel, c2002. Fischer, Volker. Sir Norman Foster and Partners : Commerzbank, Frankfurt am Main. Stuttgart : Axel Menges, 1997. Lambot, Ian. Commerzbank Frankfurt: Prototype for an Ecological High-Rise. Boston : Watermark Birkhäuser, 1997. Wigginton, Michael, and Jude Harris. Intelligent skins. Oxford : Butterworth-Heinemann, 2002.

Works Cited