This document discusses architecturally exposed structural steel (AESS) in the context of pedestrian bridges. It provides an overview of benefits of AESS for pedestrian bridges such as artistic potential, urban activation, and minimized disruption during construction. It discusses factors to consider for pedestrian bridges using AESS like viewing distance categories, corrosion protection, prefabrication, and maintenance requirements. Examples of pedestrian bridges from around the world illustrate different AESS categories and design considerations.

1. WHEN AESTHETICS GOVERN:
PEDESTRIAN BRIDGES AND
ARCHITECTURALLY EXPOSED
STRUCTURAL STEEL
PDH #

2. B9 Wednesday, April 11, 5:30 to 6:30 PM
Speaker:
Terri Meyer Boake BES, Barch, MArch, LEED AP
University of Waterloo
Moderator:
Ryan Sherman PhD
University of Nevada at Las Vegas

3. Overview
• The presentation will address:
• Benefits of AESS for pedestrian bridges
• Pedestrian Bridge as Public Art
• Erection and fabrication issues and
potential
• Corrosion protection systems and
application
• AESS based detailing
Mimico Creek Bridge, Toronto

4. Coimbra, Portugal

5. Poplar DLR | London, UK

6. Toronto, Canada

7. What is AESS?
• Architecturally Exposed Structural Steel is steel that has been
purposefully left exposed
• It must fulfill structural functions
• It is normally part of the Architectural aesthetic of the space
• It usually requires detailing, finish and handling that requires
more attention and care than regular structural steel
• It adds to the cost of the contract
• When used in Pedestrian Bridges extra care must be taken to
ensure durability, good drainage, and the careful selection and
application of finishes
Arganzuela Bridge, Madrid

8. Viewing distance is noted as the
differentiating factor between the high and
low end AESS Categories.
Grinding
permitted $$
No
Grinding!!

9. Selecting Your AESS Category
• Choices are most often AESS 3 – Viewing Distance < 6m
or AESS 4
• High degree of welded prefabrication
- Often no need to grind or remediate welds
• High degree of custom sections for very artistic bridges
• Numerous curved elements, including cones and tapers
• Stainless steel fittings for railings and guards
• Higher level finishes on tensile elements than might be found
in regular suspension type bridges
8
Canoe Bridge, Vancouver

10. Benefits of AESS for Pedestrian Bridges
• Artistic potential
• Urban activation
• Prefabrication of near complete elements prior to
erection/installation
• Transportation to site of large bridge elements
• Minimization of disruption to normal traffic flows during
erection
• Durability and ease of inspection for maintenance
Canary Wharf, London

11. To Combine or to separate?
• Pedestrian access has typically been included alongside
existing vehicular bridges
• Pedestrians have been completely excluded from vehicular
and rail bridges
• Pedestrian precincts that parallel high traffic on bridges are
non ideal
• Recent increase in dedicated pedestrian bridges can be
seen as good
Jubilee Bridge, London

12. Guangzhou, China

13. San Francisco, USA Toronto, Canada

14. Winnipeg, Manitoba

15. Artistic Potential – Bridge as Public Art
• Many municipalities are developing dedicated funds for public
art
• Possible to add budget to the bridge if it is also seen as
“public art”
• Pedestrian/cycle bridges can be used “as” art
• The improvement of the human condition by design
Kurilpa Bridge, Brisbane

16. Peace Bridge | Calgary, Canada
ALL custom platework,
curvature, welding, means
AESS 4

17. Arganzuela Bridge | Madrid, Spain
ALL custom platework,
curvature, welding, means
AESS 4

18. Simone Beauvoir Footbridge | Paris, France
ALL custom platework,
curvature, welding, means
AESS 4

19. London, UK Welded tubes, AESS 3

20. Toronto, Canada
Curvature, welding, means
AESS 3

21. Urban Activation
• Encourage public use if the bridge is an
attraction
• Entails designing the spaces of the
bridge for activities
• May necessitate more width or points of
overview or for lingering
• May require the separation of cyclists
from slower moving pedestrians to avoid
accidents
• Some bridges will preclude cyclists for
this reason
• Must ponder bridge access for the
disabled and cyclists (ramps)
Olympic Bridge, London

22. Brooklyn Bridge | New York City, USA

23. Millennium Footbridge | London, UK Highly custom steel AESS 4

24. Gateshead Millennium Bridge | Newcastle, UK Highly custom steel AESS 4

25. Simone de Beauvoir Footbridge | Paris, France Predominantly AESS 3

26. Peace Bridge | Calgary, Canada
ALL custom platework,
curvature, welding, means
AESS 4

28. Cycle access ramp to bridge | Guangzhou, China

29. Prefabrication
• AESS/steel is easily shop fabricated
• Steel can come to site prefinished
• Able to reduce the time spent on the
site
• POSSIBLE to reduce/eliminate site
welding
• POSSIBLE to promote quicker bolted
connections on site
• Depends on aesthetics, member types,
span
Photo: Ziggy Welsch

30. Auckland, New Zealand

31. Minimized Disruption to Traffic
• Erection is quicker so traffic is less
disrupted than for work that requires
extensive scaffolding and formwork
• Need to understand implications of
span
- Clear span versus multiple spans
- Over water, clear span or supports
possible?
- Over streets, highways or rail lines,
stoppage of traffic
· Lift in segments and join or launch
entire bridge?
· Premiums paid for stoppage can be
reduced
Photo: Ziggy Welsch

32. Skytrain Bridge | Vancouver, Canada
Photo:ZiggyWelsch

33. John Street Bridge | Toronto, Canada

36. Puenta de Luz | Toronto, Canada
Custom platework, curvature,
welding, means AESS 4

37. Image: Walters Inc. Hamilton

39. Durability
• Extremely important to understand
the atmospheric conditions and
risk of corrosion
• Ascertain type of de-icing agents
as some are far more corrosive
than others
• Need to obtain higher up front
spending on corrosion system to
prevent longer term repairs
• Ensure maintenance schedule
• Detailing for drainage and against
pigeons, etc.
Denver, USA

40. Amgen Bridge | Seattle, USA
Custom platework, curvature,
welding, means AESS 4

41. Galvanization
• Likely the most popular and cost
effective solution for corrosion
resistance
• Need to understand limits of size of
galvanizing bath as may mean
constructing of smaller elements
• Need to ensure drainage holes and
coating hollow sections on inside
(more $)
• Complex shapes and thin steel not
well suited to galvanizing
• Hot process so can cause
deformations
• Presence of SO2 will accelerate
corrosion

42. 1.1 Surface preparation to SSPC-SP 6
photo: Dry-Tec website - www.drytec.ca
AESS 1
SP 15
SP 3 : Power Tool Cleaning
SSPC-SP 6 for complete removal
of visible oil, mill scale, rust, paint.
SP 6 : Commercial Blast Cleaning

43. Miyazaki, Japan Unremediated welds, tensile fittings, AESS 3

45. Toronto, Canada Unremediated welds, tensile fittings, AESS 3

46. Polysiloxane coating
Webb Bridge | Melbourne, Australia Members too small and complicated to galvanize

48. 47
London, UK Combination of galvanization and zinc paint

49. Olympia, Greece

50. Problem with improper fasteners!

51. Metallization
• Zinc / aluminum wire is melted
and sprayed
• Usually shop applied
• No limits on member sizes
• Relatively cold process (150C) so
no issues of deformation for thin
members
• Need to verify applied thicknesses
• Aluminum better for high SO2
levels (industrial pollutants)

53. Auckland, New Zealand

54. Curvature and welded tubular
truss means AESS 3

55. Weathering Steel
• Material most commonly sourced as plate good
• Infers a high level of custom fabrication
• Achieves patina through cycles of wet/dry
• Need to ensure good detailing and drainage
• Keep debris and leaves away as these will trap moisture and accelerate corrosion
• Not suited to harsh marine climates as salt spray will accelerate corrosion
• Concern for staining of surfaces below the steel

56. Melbourne, Australia

57. Simple design, bolted
connections means AESS 2

58. Glass Bridge | Perth, Australia

59. ALL custom platework,
welding, means AESS 4

60. Stratford Town Centre Link | London, UK

61. ALL custom platework,
welding, means AESS 4

62. Stainless Steel
• Not all stainless steels are equal
• Rough finishes will rust faster
• Must also be cleaned on a regular basis to prevent staining
and pitting
• Marine climates and presence of de-icing agents will require
higher level of steel
• Use at least 316 for basic corrosion prevention
• Severe marine climates will need Duplex 2205
Helix Bridge, Singapore

63. Helix Bridge | Singapore
Curvature, complexity, welding, grinding,
stainless steel, means AESS 4

65. Paddington Basin | London, UK
Curvature, simplicity, welding, grinding,
stainless steel, means AESS 3

66. Vancouver, Canada
Welded connections, mixed materials,
tolerances, means AESS 3

67. Toronto, Canada
Curvature, welding, means
AESS 3

68. Maintenance and Staining
• Understanding the environment cannot be stressed enough
• Impacts the ultimate choice of corrosion system
• Bridges are not easy to clean due to their locations
• Consider colour choice as you understand the potential
cleaning and finishing schedule, particularly when using a
painted type finish
• White might not be the greatest colour choice….
Mimico Creek Bridge, Toronto

69. Vancouver, Canada All welded, AESS 3

72. Support Type
• The abutment conditions will
influence the type of bridge
• Mast types need clearances
• Arch supports need good abutments
• Long low bridges require special
foundations/support
• Similar considerations to larger
vehicular bridges but the supports
may need to be more aesthetically
integrated into the overall design
• Mid span supports not always
possible
Denver, Colorado

73. Skytrain Bridge | Vancouver, CanadaWelded tubular truss means AESS 3

74. TransCanada Overpass | Vancouver, Canada Welding, curvature, means AESS 3

75. Amgen Helix Bridge | Seattle, USA
Welding, curvature, complexity,
means AESS 3 and 4

76. Pedro e Ines Bridge | Coimbra, Portugal
ALL custom platework, completely remediated
welds, curvature, means AESS 4

77. Solferino Footbridge | Paris, France
Custom platework, remediated welds, curvature,
complex geometries means AESS 4

79. St. Patrick’s Bridge | Calgary, Canada
Welding, custom sections, curvature,
some weld remediation means AESS 4

80. The underside of the bridge is finished to
AESS 3 as less visible.

81. Peace Bridge | Calgary, Canada
ALL custom platework, curvature,
welding, means AESS 4

82. Millennium Bridge | London, UK

83. ALL custom steel, large tensile
members, welding, means AESS 4

84. Jubilee Bridge | London, UK

85. Mostly standard sections, some
tapers, no weld remediation, AESS 3

86. Canary Wharf Footbridge | London, UK Predominantly welded, AESS 3

87. Dalian, China

90. Yufuin, Japan Galvanized, tensile fittings, AESS 3

93. Span Length and Clearances
• Span length important
• Ability to include mid span supports
• Clearance below the deck for traffic
• Height limitations
• Clearances for transportation to the site
• Type of transportation to the site
Millennium Bridge, London

94. Museum of Flight | Seattle, USA Curved tubes, no weld remediation, AESS 3

97. Simone de Beauvoir Footbridge | Paris, France
Mix of standard shapes and custom,
no weld remediation, AESS 3

98. http://www.linternaute.com/savoir/grands-chantiers/06/dossier/passerelle-bercy-tolbiac-simone-de-beauvoir/3.shtml

99. Gateshead Millennium Bridge | Newcastle, UK

101. Section Types and Detailing
• Most bridges will use either hollow structural sections or
custom fabricated plate
• Tensile systems require good weather detailing for
durability
• Budget usually will determine
• You can actually make a pretty interesting bridge with
minimal custom work
• AESS 3: uses many standard shapes
• AESS 4: predominantly custom plate work

102. Skytrain Bridge | Vancouver, Canada Welded tubular truss means AESS 3

104. Prefectural Art Museum | Oita, Japan

105. Welded wide flange, no remediation
means AESS 3

106. Canoe Bridge | Vancouver, Canada
Welded tubes, no remediation means
AESS 3

108. Kurilpa Bridge | Brisbane, Australia
Complicated, but tubes with no weld
remediation means AESS 3

111. Paddington Basin | London, UK
Welded tubes, no remediation means
AESS 3

112. Wells Fargo Bridge | Salt Lake City, USA
Welded curved tubes, weld
remediation, AESS 4

113. Humber River Bridge | Toronto, Canada
Welded tubes, no remediation means
AESS 3

114. Amgen Helix Bridge | Seattle, USA
Welded tubes, no remediation means
AESS 3

115. Custom Fabrication
Or, how to create a corner using plate steel…
Three options:
• Brake form the steel (corners will be rounded)
• Butt weld the corners (corners will be crisper)
• Inset the plates as they meet and fillet weld (corners will be crisp with a shadow line)

116. Peace Bridge | Calgary, Canada
ALL custom platework,
curvature, welding, means
AESS 4

117. Arguanzela Bridge | Madrid, Spain
Welded curved plates, no remediation
means AESS 3

119. Pedro e Ines Bridge | Coimbra, Portugal
Welded custom plate, full
remediation, AESS 4

120. Puente de Luz | Toronto, Canada
Welded curved plate, complex
shapes, means AESS 4
Tubes with unremediated
welds, AESS 3

121. Design of Guards and Railings
• Style and height will depend on the risk of fall
• Taller and more dense (non climbable) guards are
required over highways and rail corridors
• Lower guards possible over landscaped areas and
rivers
• Important to preserve the sense of view as not to
make pedestrians feel imprisoned
• Possible to use stainless steel meshes and glass
where falling must be safely restricted
Glass Bridge, Perth, Australia

122. Prefectural Museum | Oita, Japan

123. Arguanzela Bridge | Madrid, Spain

124. Simone de Beauvoir Footbridge | Paris, France

126. Puente de Luz | Toronto, Canada

127. TransCanada Overpass | Vancouver, Canada

128. Amgen Bridge | Seattle, USA

129. The Solution is in the AESS
Architecturally Exposed Steel can be used to create vital
pedestrian bridges that are capable of reconnecting the
disparate parts of our urban centers.
Take care to choose and detail for your correct AESS
Category, for durability, and a fantastic user experience.

130. Assessment Question
"When should welded connections be subject to grinding
and full surface remediation?
a. Always
b. When specified as AESS 3 or AESS 4
c. When specified as AESS 1 or AESS 2
d. Never

131. Assessment Question
b. When specified as AESS 3 or AESS 4

132. PDH #
Terri Meyer Boake BES, Barch, MArch, LEED AP
University of Waterloo
tboake@uwaterloo.ca
www.tboake.com
Thank you!