This presentation was given at the CISC Western meetings and at NASCC in Dallas in the spring of 2012. It looks at the use of unusual steel shapes and geometries in contemporary design

1. Terri Meyer Boake
Associate Director of the School of Architecture
University of Waterloo
CISC Saskatchewan Region – 4 April 2012

2. The design of buildings has changed, from traditional, through the “rectilinear”
Modern period, to the current period where any geometry goes.

3.  We will look at applications of steel in
various non rectilinear forms:
› Curved systems
› Castings
› Diagrids
› Tension structures

4. Content of the presentation will also be derived from my recent
book, “Understanding Steel Design: An Architectural Design
Manual”, Birkhäuser, 2012.

5. We will be referencing the new AESS Documents, including the AESS Categories

6. Each of the AESS Categories includes additive subsets of Characteristics.

7. Wells Fargo Building, Salt Lake City, Utah

8.  bend the steel
› Using a 3 point smooth bending machine
› Using a brake press
› Heat applied bending
 facet the building to give the
appearance of curves while using
straight members
 cut curved forms out of plate material

9.  Member type
 Orientation of
member
 Length of member
 Shipping
considerations
 Sourced out work
 Accuracy of curve
 Multiple curves

10.  Different shapes are
more or less “easy”
to bend
 Tendency for
buckling on tighter
curves
 Thin steel likely to
buckle
 Heavier steel
harder to bend

11. Dies have to be tooled for each shape and changed between jobs. Smaller runs
have higher costs. Bender must have the dies in order to do the job.

12. There is always a straight piece at the end as a result of the bending process that
is cut off and recycled. So the length of “raw” member must be longer than the
bent one.

13. The straight steel that is shipped INTO the bending facility may NOT fit on the same
truck for transport back to the fabricator. Detailing must account for this and
include splices if required.

14. These curved tubes for the Canadian Museum for Human Rights were to the limit
for the bending facility. These will be AESS4 quality in the finished project as the
“Cloud Rails” will be used to support the specialty glazing system.

15. The curved stairs on the Art Gallery of Ontario were fabricated using round HSS. There
were difficulties in ascertaining approval of the splices as unavoidable deformations
happen when bending tubes, so guarantees on the welds were difficult.

16. When splicing tubular steel so that the joins are not evident, it is typical to use an
inset sleeve to form the backstop for the weld. Given the angular splice and
deformation of the material, this proved to add a challenge to the splice.

17. Although workmanship was not a large issue in making the splices, the contractor
could not use plates or bulkier methods as the cladding for the stair was to be very
tight to the steel.

18. The Abilities Centre in Whitby, Ontario, uses curved steel to create the top and
bottom chords of these large, long span trusses over the rink area of the sports
facility.

19. The connection between the curved “vertical” truss and the long horizontal
members have been done as to be invisible. Although similar methods are used as
in the AGO stair, the AESS4 level of this project requires impeccable workmanship.

20. It is not always necessary to hide connections. Here plates are used between the
joining elements of the truss to accentuate the detail. This is easier to accomplish
than a fully blended weld, and truly adds elegance to the detail.

21. Frank Gehry’s Experience Music Project in Seattle, Washington used W sections to
create the complex curves for the project.

22. Although the steel exposed, it is quite high up and the aesthetic might only call for
an AESS2. Here more evident splices were permitted as they added to the rugged
aesthetic of the interior.

23. In brake forming, sheet steel is carefully marked with “lines” and then the brake
press puts pressure on the lines to create creases. Much skill is required by the
operator to determine the correct pressure and line placement.

24. These oversized cylinders have been created using brake forming. The lines are
evident on the interior but not the exterior. Brake forming is used for oversized
members as well as plate that has complex or non uniform curves.

25. Here on the AGO, brake forming was used to form the large plate sections into the
complex curves required for the stair. Weld seams can be seen to join the wedges
of the large flat portion that will provide support for the steps.

26. The grand stair at the Boston Society of Architects was created using brake
forming. The stair (tread portion to handrail) was installed/shipped in one piece.
The side piece/hanger is separate. Bolted joint visible at left.

27. The treads were fabricated separately – brake forming used for the curves. The
treads were then welded to the side panels and the welds completely concealed.
This is AESS4 level workmanship.

28. The stadium designed by Peter Eisenman may appear to be curved, but is actually
created from all flat sections. Faceting is used in the design to give the illusion of a
smooth curve. This saves greatly on fabrication and erection costs.

29. It can be seen that the exposed members are quite straight, the curved geometry
being resolved towards the exterior cladding by a sequential decrease in the span
distance.

30. The Chinese National Theatre in Beijing is a large “egg” shape. The exterior
cladding is faceted. The interior structure uses cut sections of plate to create true
curves.

31. Each of the trusses that forms the amazing structure for the theatre is created from
plate sections that have been cut to true curves and welded to create larger
entities.

32. The welds within the trusses have been cleanly done, carefully filled and sanded to
AESS4 levels in order to provide a clean, seamless appearance. They are in close
range to sight and touch.

33. The round bracing members that connect the plate trusses are attached via a
“ball” joint as it most readily adapts to the continually changing geometry of the
structure.

34. Here you can see the “secret” behind this joint! Here a fully welded “appearance”
was desired, but a bolted connection has been used – subsequently covered with
filler, sanded and then painted.

35. University of Guelph | Young+Wright 2009

36. Cast iron or steel used to be synonymous with the requirement for high levels of
ornamentation, made cost effective through the use of articulate forms. This is no
longer the case. Castings are now used to SIMPLIFY connections!

37.  Used for special connections
 Can be one-of large pieces formed with
expendable molds (i.e. Structural)
 Can be smaller die cast pieces made in
great quantity (i.e. glazing attachments)
 Can be solid or hollow depending on
size and purpose

38.  It is said that when the fabrication costs
for a connection become 4 times as
expensive as the materials used to
create the connection, then castings
begin to make economic sense.

39. Some of the first large structural castings to be seen in Canada were used in the
construction of the atrium for the Caisse de Depot et Placements in Montreal.

40. The castings at the CDP were connected to round HSS that comprised the
balance of the vertical trusses using variations of non hidden welded connections
or evident welded connections. There was no attempt to hide the connections.

41. This steel “tree” at the University of Guelph was created using hollow castings to
join the branches. The branches were made from mechanical pipe rather than
HSS, for both structural and textural reasons.

42. The main casting node was attached at the shop as it is easier to have access for
preheating. The connections are welded. Contemporary castings are quite
weldable.

43. The casting is hollow in the centre but the wall thicknesses are not uniform. They
vary in order to locate the steel where the load transfer stresses require it.

44. The expendable molds are often made from sand in resin, based on a form in this
case driven by a CAD/CAM device. The casting technique leaves the surface of
the casting with an orange peel like texture.

45. This close view of the casting reveals the very different surface. In the case of the
Guelph Tree, it was important that the connection between the casting and the
branch was seamless, so this required extra care in fabrication and erection.

46. For these unique connections it is important that adequate testing be carried out.
The steel must go through very controlled cooling in order to prevent the build up
of problematic stresses in the material.

47. The cast connection used at Hauptbahnhof Station in Berlin does not try to hide
the connection between the casting and the connecting HSS members. This
reduces the cost and difficulty of site fabrication to an extent.

48. These tree like supports were repeated throughout the terminal. There is greater
economy when producing repetitive elements as there are savings in fabrication
as well as testing.

49. The renovation to King’s Cross Station in London uses tree forms as columns.
Castings are used to attach the branches to the trunk. A reveal is used as the
connection detail.

50. The cast node in this instance has an unusual geometry and is not as smooth or
uniform in its geometry. The level of quality in the project will depend on the quality
of the translation of the geometry of the design smoothly into the casting.

51. At Shanghai International Airport, Terminal 2, castings are combined with curved
steel and tension trusses to create a vibrant structural system.

52. The attachment of the diagonal to the roof member is achieved through a
casting. This created a much smoother and better looking transition. The pin
connection also improved constructability.

53. Tension members are used to hang the spiral ramp system for the Reichstag from
the ribbed steel dome.

54. Smaller die-cast connectors are used at the Reichstag in Berlin to attach the
tension support system.

55. Three different cast connectors are used in the system. The one at the left that
accepts two incoming members is quite innovative and the detail allows for a very
tidy connection. This project also uses a significant quantity of bent plate steel.

56. London GLA| Foster+Partners 2004

57.  Started as diagonal reinforcement to a portal frame typology
 Evolved to exclude the braced frame
 Elimination of vertical columns
 Replacement by diagonal members
 In theory material savings in the range of 20% over traditional braced frame structures

58.  Similar to a space
frame, the diagrid is
formed by
connecting straight
members to nodes
 Nodes can be fixed
(moment resisting)
or hinge-type (non
moment resisting)
 Fixed most often
used for fabrication
and erection
control

59. The Royal Ontario Museum, by Studio Libeskind, used fixed nodes to join the straight
segments and required very little in the way of temporary shoring during the construction
of the project. Intermediate members were sized for eccentric loading during erection.

60.  Most current diagrid
buildings use fixed or
prefabricated nodes
 Preferred as it makes
erection simpler
 Reduces need for
temporary bracing
 Allows for repetitive shop
fabrication
 Minimizes on site welding
of the node itself
 Introduces some stiffness
into the overall structure
during erection

61.  In a “simple” diagrid
structure, the diagonals
take the place of
columns
 Diagonals form a tube
that braces the exterior
 Beams at the edge of
the floor connect to the
diagrid and serve as
braces
 The floor plate is clear of
columns, the floor
framing system spanning
from the core to the
exterior diagrid
Hearst Building | Foster+Partners w/ ARUP 2006

62. The Hearst Tower uses a diagrid frame whose diagonals span 4 floors of the
building. The exterior beams for the floors serve to brace the diagonals. The nodes
are shop fabricated for maximum accuracy.

63. http://www.e-architect.co.uk/new_york/hearst_tower_new_york.htm
The prefabricated nodes of the Hearst Tower were attached to the straight W
shaped segments of the diagrid using bolted connections. This made for very fast
erection with little “extra” access for fixing the connections.

64. The diagrid framing for the Hearst Tower was not intended to be exposed, so the
choice of member shape and the bolted connections of the straight segments to
the nodes, had no aesthetic considerations.

65. Foster+Partners’ Swiss Re Tower in London was constructed shortly after the GLA
and made use of a true diagrid. Here the outside diagrid formed the primary
structure to support both floor plates and facade.

66. http://www.architectureweek.com/
The plan of Swiss Re shows the open floor plan between the exterior diagrid and
the central core.

67. The South Face of the Bow Encana Tower DOES expose its diagrid, so where the
steel is exposed to view, it needed to be of AESS4 quality.

68. The straight segments have been welded to the fixed nodes to meet AESS4
expectations. Only the two sides of the triangular members that are exposed to the
inside of the atrium have been fabricated to AESS4. The hidden rear face has not.

69. Here you can see the weather protection provided at the nodes to allow the high
quality welding to be accomplished. This obviously adds cost to the project over
bolted connections. But the aesthetic requirements overrule in this case.

70. The diagrid on the north side of the Bow Encana Tower is concealed by finishes, so an entirely
different set of criteria has been applied to member selection, erection and fabrication. Welded
connections are still used, but the straight members are simpler W sections.

71. The fixed nodes of the Bow Encana were fabricated in Hamilton and trucked to
Calgary. Bracing between the stubs ensured accuracy through transportation and
erection.

72. The straight segments, although extending over 6 floors in height between
nodes, needed to be cleanly spliced at the mid point due to shipping limitations.
Not all diagrid straight sections span over the same number of floors. This varies by
job.

73. The Aldar Headquarters in the UAE, designed by MZ Architects and ARUP, is the first
circular diagrid building.

74. https://picasaweb.google.com/lh/photo/EUz-8DR3HES38c4l6LbqVg
The straight sections of the diagrid frame extend only over 4 floors in this case. They
are attached by fixed nodes. Placing the nodes closer together allows for the
incorporation of the curves in the design.

75. Aldar Headquarters’ diagrid was designed to be concealed, so member choice was based on
structural considerations. You can see how the exterior floor beams are being used to brace the
length of the angular diagrid. There is a clear (albeit short) floor span from the concrete core to
the edge.

76. http://innovativebuildings.net/2010/06/20/capital-gate-abu-dhabi/
It is the strength of diagrid framing that allows Capital Gate Tower in the UAE , by
RMJM Architects, to lean backwards 18 degrees.

77. http://www.zawya.com/story.cfm/sidZAWYA20090114101526/
Here, due to the unusual eccentricity of the structure, we see that the fixed nodes happen at
every floor level and that the straight members are much larger than we saw on Aldar. The
concrete core runs vertically up the building and must offset the floor loading.

78. http://www.panoramio.com/photo/46687499
The eccentric geometry of the building has forced a very tight floor plate, with an
inefficient ratio of core to usable area. For this signature building, this was obviously
not a concern!

79. The white lines indicate the location of the diagrid. The glazing has been
subdivided into triangles, some of which you see are open permitting natural
ventilation.

80. A sun shading screen is a major feature of the south facade. Round HSS is being
used to attach the facade back to the diagrid structure at the nodes.

81. The Orbit Tower for the 2012 Olympics in London uses a diagrid type structure
made up completely from prefabricated nodes. These are joined to each other
without any straight interconnecting members.

82. http://www.flickr.com/photos/arcelormittalorbit/
However complex the sculpture might appear, it is reduced to the replication of this element.
Designed by artist Anish Kapoor and structural engineer, Cecil Balmond, the 115m high
ArcelorMittal Orbit will be the tallest sculpture in the UK and will offer unparalleled views of the
Olympic Park and London’s skyline.

83. http://www.flickr.com/photos/arcelormittalorbit/
Although the nodes were prefabricated with joints between each node, larger
aggregated elements were prefabricated prior to lifting to make the construction
more efficient.

84. http://www.flickr.com/photos/arcelormittalorbit/
As with all projects it is important that the designers keep in mind the issues of scale
– size of elements and types of connections – to be sure that the design of the
connections is appropriate to the AESS level of the project.

85. The new Peace Bridge in Calgary, designed by Santiago Calatrava, uses a diagrid
type of “Chinese Finger Tube”, in a fully welded scenario, to create a very slender
span across the Bow River. Span 130 m.

86. The end of the tube has been substantially thickened to provide support at the
end. The bridge is created from sections of bent plate with internal reinforcement.

87. The floor has been built into the tube (constructed first). Plate steel ribs have been
welded to a plate steel floor to provide reinforcement. The bottom of the bridge
shows the small HSS stubs that have been welded into the diagrid halves.

88. The smooth finish of this AESS4 structure, in combination with the large open panels
and translucent glazed panels, give a light and airy feeling to the bridge interior.
The interior was to have been painted white.

89. Very small traces of show through weld are visible, indicating where the internal
reinforcements are positioned. The rounded edges of the final product would have
made the proposed white painted interior rather impossible to achieve.

90. Night lighting can be strategic, but it will have impact on the requirement of the
forming and finishing of high level AESS work.

91. A note of caution when choosing both a forming method and a finish. Night
lighting can highlight imperfections in the steel that are not evident with regular
day lighting. Here the lines of the brake forming translate through the finish.

92. La Defense Paris | 1989

93.  Many unusual geometries are possible
through tension support systems
 Tension vs. compression can allow
designers to differentiate member size
and type
 Systems can include:
› Rods
› Cables
› Smaller sections
 Standard or high strength structural steel
 Stainless steel

94. Tension systems can be used for far more than the support of fabric structures as
seen in the tent canopy at the Grand Arch at La Defense in Paris, France.

95. What is interesting in the use of tension systems at La Defense is the ability of the
trusses to both push and pull the fabric into shape. Clear differentiation of tensile
versus compression members is evident.

96. The Olympic Stadium in London is using differentiated member sizes and types to create
an energetic exposed steel structure to support the roof. Within the truss, larger HSS is
used for compression members. Actual tension cables are used as well.

97. The practice of using cables and masts to support “cantilever” situations is
widespread.

98. The large glazed canopy at the Aria Hotel in Las Vegas, by Cesar Pelli, uses a
complex tension system to “assist” the cantilevered glass.

99. For the most part the main tension members that assist are hidden from view. The
ceramic frit on the glass also makes it difficult to see through and limits the
understanding of the support system.

100. Such detailing requires the use of very fine fittings, both to allow for on site erection,
potential replacement of broken panes, and tension adjustment of the entire
system during erection.

101. The relatively lightweight pedestrian bridge platform is achieved by the use of
tension cables to support and thereby break up the effective span.

102. The railing design on the “support” side of the bridge is slightly more opaque and designed to
hide some of these details. Tension cables in exposed conditions must be protected from
weathering. This is often done by overwrapping both cable and connection.

103. Rather than using a more typical die cast anchor, this bridge creates the
connection point through welded plate “boxes” that hide the more standard
bolted connection inside (also weather protected).

104. This fully glazed room achieves a clear, column free span through the use of a
tension assisted roof. The tensile members criss-cross the room and are use to push
up through the centre point, allowing the compression members to be quite light.

105. The custom fabrication for the central support system is quite elegant. If you look
closely you can see the weld lines on the roof beams as they were attached to the
“star”. London, England. No snow loading!

106. Much of the detailing and expression that we see in tension systems came about in
the architecture of the High Tech Movement. We need to learn from the mistakes
made here to show that steel is indeed a durable material.

107. The design and detailing on Waterloo Station, designed by Nicholas Grimshaw, are
innovative and exemplary – but this fussy, exposed, exterior structure was
impossible to maintain, and the train shed is set to be demolished.

108. The train shed at Hauptbahnhof Station in Berlin uses an exterior tensile structure, but the
detailing and materiality are far simpler than for Waterloo Station. The choice of colour here also
impacts cleaning. The glass on the shed is able to be cleaned using fairly standard methods.

109. The trusses continue on the interior to allow for the clear spanning curved beams to
be lighter through this “assistance”. The square steel framing that supports the glass
roof is also reinforced with X type tension reinforcing.

110. Here you can see the many different levels of structure in the station. The larger
tension system is comprised of cables with cast clevis attachment systems. The
station is recent so it will be interesting to see how easy it is to maintain.

111. The large glazed facade at Poly Plaza in Beijing, designed by SOM, is supported by
a cable net system. This eliminates mullions. The “box” at the left is supported by a
large cable system, to effectively hang the structure.

112. Looking through the glass the ghost of the hanging system can be seen. The major
lines on the facade glass are the connection points of the facade to the
suspension system.

113. Looking up the atrium the cable net system for the glazed facade is visible and the
suspension system for the “box” barely visible. It is up 15 floors.

114. Zooming in, you can see the large cast clevis like element that is being used to
hang the floors.

115. The cables that are used to hang the floor system are bundled. The cable net
system for the facade is attached to the larger cable to provide wind bracing.

116. The scale and high level of finish of the clevis can be seen in this close up image.

117. Castings combined with custom fabricated elements are used in this instance to
provide a very clean and controlled appearance, function and assembly for the
structure.

118. http://www.som.com/content.cfm/the_new_beijing_poly_plaza
This detail of the clevis attachment for Poly Plaza illustrates the type of tight
tolerances and complexity when creating such an innovative project.

119.  Steel design today is far different than it
was even 10 years ago
 Architects present fabricators and
engineers with complex problems
 With a good understanding of the goals
of the project, and the tools and
standards available, high quality work is
quite achievable!
 A high level of COMMUNICATION
between the Architect, Engineer and
Fabricator is essential!

120. Terri Meyer Boake
tboake@uwaterloo.ca
“Understanding Steel Design:
An Architectural Design Manual”
is available from Amazon.com