1. Better
Buildings
From Better
Fasteners
Gregg Melvin – Senior Applications Engineer
Elco Construction Products
An Infastech Company
2012

2. AIA Credits
Elco Construction Products an Infastech company, is a Registered Provider
with The American Institute of Architects Continuing Education Systems. Credit
earned on completion of this program will be reported to CES Records for AIA
members. Certificates of Completion for non-AIA members available on
request.
This program is registered with the AIA/CES for continuing professional
education. As such, it does not include content that may be deemed or
construed to be an approval or endorsement by the AIA of any material of
construction or any method or manner of handling, using, distributing, or
dealing in any material or product. Questions related to specific materials,
methods, and services will be addressed at the conclusion of this presentation.

3. Copyright Materials
This presentation is protected by US and
international copyright laws. Reproduction,
distribution, display, and use of the
presentation without written permission of
owner is prohibited.
Copyright © 2012 by Elco Construction Products, An Infastech Company

4. Learning Objectives
1. Identify situations requiring A/E to specify fasteners instead of
leaving product selection to contractor or supplier.
2. Learn techniques for reducing fastener damage due to rust and
galvanic corrosion.
3. Be able to explain causes of hydrogen embrittlement and HASCC.
4. Be able to specify high performance fasteners that are HASCC
resistant.
5. Explain the role of fasteners in building sustainability.

5. For want of a fastener…
“For want of a nail, the shoe was lost,
For want of a shoe, the horse was lost,
For want of a horse, the rider was lost.
For want of a rider the battle was lost.
For want of a battle the kingdom was lost.
All for the want of a nail.”

6. For want of a fastener…
This old rhyme about a battle
being lost due to one missing
nail is a parable about making
sure of the details.

7. For want of a fastener…
Yet it’s specifically about
fasteners, because they are
a particular kind of detail:
a small thing that holds
together larger and more
seemingly important things.

8. For want of a fastener…
Compared to the horse and
even the shoe, the fastener is
small. Yet without it…

9. For want of a fastener…
“God is in the details.”
Mies van der Rohe

10. Your reputation hangs on
specifying the right fasteners.
Fastener specification is
critical to project success.
The Petronas Towers in Kuala
Lumpur, the world’s tallest
building, required careful
engineering to ensure none of
the millions of fasteners used to
install cladding would be the
installation’s weakest link.

11. Your reputation hangs on
specifying the right fasteners.
Standard types and grades of
fasteners are sufficient in many
construction applications.
In these instances, fastener
selection can usually be based
on industry standards, building
code requirements, and design
loads.

12. Your reputation hangs on
specifying the right fasteners.
It may be acceptable in some
cases to leave fastener selection
to contractors or building product
fabricators, allowing them to
select fasteners based on cost,
convenience, and trade practice.

13. Your reputation hangs on
specifying the right fasteners.
Other times, fastener selection
can be one of the most crucial
aspects of building design.
Professional judgment is required
to specify fasteners that:
• Perform as intended
• Are dependable & economical
• Last the life of the building

14. A big job for such a small part
Factors affecting fastener performance
include:
• Structural capacity and safety factor.
– Static and dynamic load resistance.
– Pull-out and pull-over resistance.
– Shear resistance of fastener and attached
materials.

15. A big job for such a small part
Factors affecting fastener performance
include:
•Corrosion resistance in conditions of use.
•Seal against liquid or gas leakage (if required).
•Constructability, practicality, and inspectability.
•Compatibility with design intent and aesthetics.
•Removability, or other special requirements.
•Service life exceeds that of attached materials.

16. A big job for such a small part
Specifying fasteners is part of designing
safe, durable, and practical connections
between building components.

17. HASCC
A “New” Threat to Fasteners
HASCC = Hydrogen-Assisted Stress
Corrosion Cracking.

18. HASCC
A “New” Threat to Fasteners
HASCC has only been identified as a
fastener failure mechanism within the past
few decades.

19. HASCC
A “New” Threat to Fasteners
Since then, “Best Industry Practices” have
changed to protect fasteners against
HASCC.

20. VISIBLE CORROSION

21. VISIBLE CORROSION
Before considering HASCC, let’s review
some basics of ordinary fastener corrosion:
Oxidation (Rusting)
Galvanic Corrosion

22. Must it Rust?
Most architectural fasteners
are made from grades or
alloys of steel that will react
with oxygen to create ferrous
oxide, commonly know as
rust. Rust is a type of
corrosion that weakens and
deteriorates steel.

23. Must it Rust?
Rusting is accelerated when
steel is also exposed to
moisture, especially if the
moisture contains chlorides
(salts), a condition that is
common in marine, industrial,
and urban atmospheres.
Once rust starts, it can spread
rapidly to adjacent exposed
steel surfaces.

24. Must it Rust?
When designing steel-to-steel
connections, both the
fasteners and the items being
joined must be protected
against rusting.
Steel building panels, for
example, can be protected by
using zinc galvanizing and a
high-performance coating.

25. Must it Rust?
As a general guideline,
fasteners should have
greater corrosion resistance
than items being joined so
that fasteners do not become
weakest link in connection.

26. Corrosion-Resistant Plating
Fasteners are often protected
with metallic plating.
For example, zinc plating helps
protect steel against exposure to
air and moisture and provide a
sacrificial, galvanic protection to
steel.

27. Corrosion-Resistant Plating
Hot-dipped galvanizing is widely
used for large fasteners such as
anchor bolts. The thick layer of
zinc deposited in this process
clogs the threads of smaller
screws.
On the other hand, thin coatings
of electro-plated zinc applied to
some screws do not provide
sufficient corrosion resistance for
exterior or high performance
fasteners.

28. Corrosion-Resistant Plating
Other types of metal plating,
such as cadmium and
chromates, provide greater
corrosion-resistance than zinc.
These materials are decreasing
in usage, however, due to
environmental concerns about
heavy metals toxicity.

29. Corrosion-Resistant Plating
Plating is no longer considered
acceptable protection for high
performance fasteners.
In fact, it is counter-indicated for
case-hardened fasteners, as will
be discussed later in course.

30. Corrosion-Resistant Plating
Fasteners are often protected
with metallic plating. For
example, zinc plating helps
protect steel against exposure to
air and moisture and provide a
sacrificial, galvanic protection to
steel.

31. Corrosion-Resistant Coatings
New types of anti-corrosion
coatings can be considered
to protect high-performance
fasteners.

32. Corrosion-Resistant Coatings
This type of coating is eco-
friendly, minimizing the use of
heavy metal in fasteners.

33. Corrosion-Resistant Coatings
In addition to corrosion
resistance, the coatings
lubricate threads, making
fastener insertion and removal
easier. Easier removal is a big
plus when doing repairs,
remodels, and retrofits.

34. Corrosion-Resistant Coatings
The coatings can be
pigmented to color-match
other building materials or to
simplify product identification.

35. Corrosion-Resistant Stainless Steel
300-series stainless steel provides even
greater levels of corrosion resistance.

36. Corrosion-Resistant Stainless Steel
It should be considered for critical structural
connections and in locations with corrosive
environments.

37. Corrosion-Resistant Stainless Steel
Note that even stainless steel requires a coating
for protection against galvanic corrosion, as will be
discussed later in this course.

38. Galvanic Corrosion
Galvanic corrosion occurs when dissimilar
metals, such as aluminum and steel, are in
contact in the presence of an electrolyte, an
electrically conductive medium, and form a
galvanic cell. H+
H+ H+

39. Galvanic Corrosion
These galvanic cells are similar to those in
electric batteries. In batteries, however, cells are
sealed so galvanic reactions only occur when the
cells are part of a controlled electrical circuit.
H+
H+
H+

40. Galvanic Corrosion
The same reaction occurs in buildings when two
pieces of metal form an uncontrolled short circuit.
It occurs because of the electro-chemical
relationship of the metals.
H+
H+ H+

41. Galvanic Series
Cathode (Least Active) Metals conduct electricity
Gold because they have a
Silver
Stainless Steel
tendency to give up
Bronze electrons easily.
Copper
Brass
Nickel Some metals give up
Lead
Steel & Iron
electrons more easily than
Aluminum others.
Zinc
Magnesium
Anode (Most Active)

42. Galvanic Series
Cathode (Least Active) They can be listed in order
Gold of their potential to yield
Silver
Stainless Steel
electrons, a table known as
Bronze a Galvanic Series.
Copper
Brass
Nickel
Lead
Steel & Iron
Aluminum
Zinc
Magnesium
Anode (Most Active)

43. Galvanic Series
Cathode (Least Active) They can be listed in order
Gold of their potential to yield
Silver
Stainless Steel
electrons, a table known as
Bronze a Galvanic Series.
Copper
Brass
Nickel
Lead
Steel & Iron
Less “noble” Aluminum
(sacrificial and Zinc
more Magnesium
corroded)
Anode (Most Active)

44. Galvanic Series
Cathode (Least Active) They can be listed in order
Gold of their potential to yield
More “noble”
(protected and
Silver
Stainless Steel
electrons, a table known as
less corroded)
Bronze a Galvanic Series.
Copper
Brass
Nickel
Lead
Steel & Iron
Less “noble” Aluminum
(sacrificial and Zinc
more Magnesium
corroded)
Anode (Most Active)

45. Galvanic Series
Cathode (Least Active) Aluminum is more active
Gold (anodic) than steel or
More “noble”
(protected and
Silver
Stainless Steel
stainless steel.
less corroded)
Bronze
Copper
Brass
Nickel
Lead
Where aluminum and steel
Steel & Iron form a galvanic cell,
Aluminum
Less “noble”
(sacrificial and Zinc aluminum will corrode,
more
corroded)
Magnesium
sacrificing electrons that
will deposit onto and
Anode (Most Active)
protect the steel.

46. Galvanic Corrosion
This aluminum plate received two screws made from
300-series stainless steel, a grade that is highly
resistant to oxidation and rusting.

47. Galvanic Corrosion
It was then exposed to 1000 hours of salt-water spray
that acted as an electrolyte to form a galvanic cell
between the aluminum plate and stainless steel
fasteners. The screws were them removed to allow
examination of the plate.

48. Galvanic Corrosion
Stainless Steel Stainless Steel
Screw: Screw With
The aluminum Anti-Corrosion
sacrificed electrons Coating:
to the steel. The Coating prevented
surface of the formation of a
aluminum is visibly galvanic cell and
deteriorated. prevented corrosion
of the aluminum
plate.

49. Galvanic Corrosion
Stainless Steel
Stainless Steel
Screw With
Screw:
Anti-Corrosion
Coating:
Using ordinary steel fasteners in architectural
aluminum elements (such as windows, curtain walls,
or wall cladding) can create galvanic corrosion of the
aluminum, weakening the connection until it fails at
well below design loads.

50. Galvanic Corrosion
Stainless Steel
Stainless Steel
Screw With
Screw:
Anti-Corrosion
Coating:
Avoid this problem by specifying fasteners with
high-quality anti-corrosive coatings.

51. Galvanic Corrosion
Dissimilar metal
combinations are common
in construction. For
example:
• Aluminum framed glazing
units and cladding get
attached to structural steel
framing using steel self-
drilling, self-tapping screws.

52. Galvanic Corrosion
Dissimilar metal
combinations are common
in construction. For
example:
•Aluminum parts are often
attached to concrete or
masonry with self-tapping
screws made of steel.

53. Galvanic Corrosion
Dissimilar metal
combinations are common
in construction. For
example:
•Even steel-to-steel
connections can involve
dissimilar metals, if either of
the steel parts, or the
fasteners joining them, has
been coated with zinc.

54. Galvanic Corrosion
The Schermerhorn Symphony
Center looks like solid stone,
but it is clad with a thin
veneer attached with self-
drilling fasteners.

55. Galvanic Corrosion
It is difficult to prevent electrolytes from contact
with fasteners.
Moisture can enter construction due to:
–Rain or dew during Construction.
–Condensation inside a wall or roof.
–Leaks in building envelope
–Water from building maintenance or operations.
–Plumbing failures.
–Flooding and spills.
–Perspiration from workers that install the parts.
–Air pollutants can make atmospheric moisture more
conductive.

56. Galvanic Corrosion
If dissimilar metals are in contact,
assume that an electrolyte will also
be in contact with the fasteners.

57. Galvanic Corrosion
Specifying fasteners with adequate
corrosion resistance protects against
catastrophic failure, loss of use, injury,
death, and liability.

58. HASCC
The Invisible Corrosion

59. HASCC
The Invisible Corrosion
Hydrogen, a by-product of galvanic corrosion, can
weaken standard fasteners and cause failure. It
produces a type of corrosion that is not readily
apparent…until it is too late.

60. A Case Study
20 years after installation,
screws began snapping for
no apparent reason.
The screws complied with
building code load
requirements.
While they had been exposed
to weather due to roof
damage, they were not visibly
corroded.

61. A Case Study
They simply appeared
to have broken in half.

62. A Case Study
Scanning electron
micrographs (SEM) revealed
fractured fastener surfaces
and separated grain
boundaries in the steel. The
screws had also lost ductility.

63. A Case Study
The Culprit: HASCC!

64. Hydrogen Embrittlement
HASCC starts with hydrogen
embrittlement, which is
associated with galvanic action.
However, steel fasteners are
not weakened by galvanic
corrosion itself.
Rather, hydrogen generated
Screws attacked by
by galvanic action attacks the
hydrogen embrittlement
typically show no visible
steel.
corrosion.

65. Hydrogen Embrittlement
Even if steel is protected from
galvanic corrosion, hydrogen
can attack it rapidly.
Specialized fasteners have
been developed to avoid this
risk.
Screws attacked by
hydrogen embrittlement
typically show no visible
corrosion.

66. Source of Hydrogen
1. Galvanic action creates electrical
current.
2. Water in electrolyte separates into
oxygen and hydrogen.
H+
H+
H+

67. Source of Hydrogen
1. Oxygen bonds with anode and oxidizes
metal. Oxides have little structural
strength, the anode weakens and
corrodes.
2. Hydrogen is attracted to the cathode
and penetrates into the metal.
H+
H+ H+

68. Source of Hydrogen
This process is similar to the
laboratory procedure for
separating water into hydrogen
and oxygen by passing electrical
current through it, a process
called electrolysis.

69. Hydrogen Diffuses into Steel
Hydrogen, the smallest
atoms, can penetrate
“solid” steel.
Atoms lodge in voids in
steel’s crystal structure.
This scanning electron microscope
(SEM) image of steel shows enlarged
grain boundaries indicative of hydrogen
embrittlement.

70. Hydrogen Diffuses into Steel
Single hydrogen atoms
are unstable and bond
with other hydrogen
atoms.
The larger H2 molecules
This scanning electron microscope
put pressure on the (SEM) image of steel shows enlarged
grain boundaries indicative of hydrogen
surrounding steel embrittlement.
molecules.

71. Hydrogen Diffuses into Steel
This creates internal
tension in steel, enlarging
its grain boundaries and
reducing ductility.
The steel can no longer
This scanning electron microscope
bear its normal tensile (SEM) image of steel shows enlarged
grain boundaries indicative of hydrogen
load and becomes brittle. embrittlement.

72. The Role of Case Hardening
Case
Rockwell
hardness Hydrogen has little
HRC 52 min. effect on “mild” (soft)
steel.
Many architectural
Core fasteners, however,
Rockwell are case hardened.
hardness
HRC 32-40

73. The Role of Case Hardening
Case
Rockwell
hardness In case hardening,
HRC 52 min. low-carbon steel is
heated in a high-
carbon environment to
infuse extra carbon
Core
Rockwell
into metal’s surface.
hardness
HRC 32-40 This hardens steel’s
outer layer (“case”)
and makes it brittle.

74. The Role of Case Hardening
Case
Rockwell
hardness Case hardening
HRC 52 min. makes self-drilling
screws hard enough
to drill and tap into
structural steel or tap
Core
Rockwell
concrete.
hardness
HRC 32-40

75. The Role of Case Hardening
Case HASCC affects steel
Rockwell
hardness of Rockwell hardness
HRC 52 min. ≥ HRC 35.
The harder the steel,
the more
Core susceptible is it to
Rockwell HASCC.
hardness
HRC 32-40
Case-hardened
fasteners are typically
HRC 52 on the case
and HRC 32 to 40 in
the core.

76. Hydrogen Embrittlement &
Stress
In case-hardened
fasteners, only the
brittle outer layer is
vulnerable to HASCC.
However, a weakening
outer layer places the
entire load onto the
core of the fastener, a
significantly smaller
diameter of steel than
the original design.

77. Hydrogen Embrittlement &
Stress
The design load can
overwhelm this reduced
fastener diameter,
leading to failure.

78. Hydrogen Embrittlement &
Stress
This cross-section of a
failed case-hardened
fastener shows the
hardened outer case,
which was embrittled by
hydrogen, and the inner
ductile core, which
failed under the design
load.

79. Hydrogen Embrittlement &
Stress
A. Application Induced
Hydrogen Assisted Stress
Corrosion Embrittlement
Mode
B. Ductile and Embrittlement
Mode/ Strength loss
C. Complete ductile failure
due to reduced cross-
sectional area of fastener –
unable to sustain application
load.

80. Stress Concentration
Stress increases steel’s susceptibility to hydrogen
embrittlement.
Stress concentration occurs at screw heads for 3
reasons:
1. MANUFACTURING: Deformations required to form steel
rod into screw heads induces stress into metal.

81. Stress Concentration
2. CLAMPING FORCES
When screws are
tightened, their heads
bear on the surface of
the object being
attached.
This places the area of
the shank immediately
under the head into
tension, inducing stress.

82. Stress Concentration
3. OUT OF ALIGNMENT
Screw holes are rarely
perfectly perpendicular to
the surfaces they are
attaching.
When tightened, uneven
pressure is put on the
screw’s head.
This puts additional stress
on one side of the fastener
at juncture of head and
shank.

83. Stress Concentration
A standard test for
resistance to hydrogen
embrittlement mimics this
real-world situation.
The fastener is screwed
through two plates of
dissimilar metals. A shim is
placed under one edge of
the top plate, creating an
angle between the two
plates and placing the screw
at an oblique angle with
respect to one of them.

84. Stress Cracking
Embrittlement at stress points leads to microscopic
cracking.
Micro-cracks further concentrate stress points.
Once propagated, cracks can spread quickly
through hardened steel.
Metallurgists call this cracking “Hydrogen Assisted
Stress Corrosion Cracking” (HASCC).

85. Plating and HASCC
Case hardened fasteners must still be protected
against rust and galvanic corrosion.
Plating should not be used with most case
hardened fasteners because the plating process
generates hydrogen that contributes to HASCC.
Instead, case hardened fasteners should be
protected with a high-performance anti-corrosion
coating or with new innovations such as those
described in the next section.

86. HASCC Recap
• Galvanic action between dissimilar metals
generates hydrogen.
• Hydrogen penetrates steel and creates internal
stresses that embrittle and weaken fasteners.
• This process occurs primarily in case hardened
parts.
• Stress concentrations initiate micro-cracking that
can propagate across fastener.
• HASCC can occur years after fastener installation
if connection is exposed to moisture.
• Failure is often sudden and without warning.

87. The Remedy for HASCC
Self-Drilling Fasteners have to be case
hardened in order to drill and tap
substrates – but case hardening makes
them vulnerable to failure.
Fortunately, there is a solution to fastener
HASCC hazards.

88. Benefits of Self Drilling Screws
Why use self-drilling screws?
Self-drilling screws require just a few
percent of installation time and Installed with
screw gun.
labor required by nuts-and-bolts,
rivets, and other fasteners requiring
pre-drilled holes.
Fasteners install in single, fast
operation using a power driver.

89. Benefits of Self Drilling Screws
They are much faster than
two-handed bolt-and-nut
installations, and more
practical where the back
side is not accessible for
installing a nut.
With hundreds of thousands
of fasteners used in large
buildings, this represents
an enormous savings in labor.

90. Benefits of Self Drilling Screws
Use to install windows, cladding,
curtain wall, framing, anchors,
equipment, fixtures, and other
building components.
Substrate becomes the nut

91. Design of Self Drilling Screws
Select head for
easy installation,
Attaching into Metal: Lead threads acceptable profile,
and pull-over
tap threads into substrate, so the resistance.
substrate acts as a nut without Select
thread
requiring the time to tighten a nut. style to
hold in
substrate.
They are available in many
specialized configurations to suit a
wide range of construction Lead threads
cut threads
applications. into (tap)
substrate for
pull-out
resistance.
Tip drills hole and
removes shavings.

92. HASCC-Resistant Fasteners
High performance structural drill screws:
Lower hardness (HRC 28-34)
Load-bearing threads for ductility
Virtually immune to embrittlement
failures.
Increased hardness (HRC 52 min)
point and lead threads for drilling
and tapping

93. HASCC-Resistant Fasteners
High performance structural drill screws:
Lower hardness (HRC 28-34)
Load-bearing threads for ductility Vir
tu
Virtually immune to embrittlement all
to y Im
HA m
failures. SC un
C e
Increased hardness (HRC 52 min)
point and lead threads for drilling
and tapping

94. A Metallurgical Marvel
There are two ways to achieve this
performance:
2. Selectively Hardened Fasteners
3. Bi-Metal Fasteners
Hardened for Ductile for structural performance
drilling and tapping. and HASCC-resistance.

95. 1. Selectively Hardened
Fasteners
Selectively hardened
fasteners are made from
DUCTILE WHERE special, high-carbon
NEEDED
steel.
Since the alloy already
contains the carbon
HARDENED
needed to harden the
WHERE NEEDED
steel, fasteners do not
have to be placed in a
high-carbon environment
during heat treatment.

96. 1. Selectively Hardened
Fasteners
This makes it possible to
selectively harden
DUCTILE WHERE fastener tip.
NEEDED
The tip of the screw is
passed through an
electrical induction coil
HARDENED
that heats and hardens
WHERE NEEDED
drill-point and lead-
threads without affecting
the rest of the shank.

97. 2. Bi-Metal Fasteners
Use where stainless steel
is required for increased
Stainless
resistance to corrosive Steel Head
environments. and
Shank
High-Carbon
Steel Tip,
Selectively
Hardened
Recommended for
exposed fasteners.

98. 2. Bi-Metal Fasteners
Stainless steel is not
suitable for selective
Stainless
hardening. Instead, a high- Steel Head
carbon steel tip is fused and
Shank
onto a stainless shank.
High-Carbon
Steel Tip,
Selectively
Hardened
Recommended for
exposed fasteners.

99. 2. Bi-Metal Fasteners
The high carbon tip is then
selectively hardened
Stainless
using induction-coil Steel Head
heating. and
Shank
High-Carbon
Steel Tip,
Selectively
Hardened
Recommended for
exposed fasteners.

100. Corrosion-Resistant Coatings
Even stainless steel is not immune to galvanic
corrosion and the elements.
Non-metallic, anti-corrosion coatings are
recommended on both selectively hardened and bi-
metal fasteners to provide additional protection and
lubricate the threads.
Bi-Metal Fastener: Before coating, above. After coating, below.

101. Corrosion-Resistant Coatings
Bi-Metal Fastener: Before coating, above. After coating, below.
Coating can be color matched as required.

102. PROOF
Steel and aluminum plates are connected by
fasteners and sprayed with saltwater, an
electrolyte.
HASCC-
resistant
fasteners
are not
affected
Standard
case-hardened
fasteners failed

103. PROOF
Conventional fasteners fail due to stress
concentration at screw heads that accelerates
embrittlement.
HASCC-
resistant
fasteners
are not
affected
Standard
case-hardened
fasteners failed

104. PROOF
Neither selectively-hardened nor bi-metal
fasteners fail.
HASCC-
resistant
fasteners
are not
affected
Standard
case-hardened
fasteners failed

105. PROOF

106. US Bank Building
Los Angeles, CA
Pei Cobb Freed Partners PROOF
HASCC-resistant
fasteners, securing roof-
top panels and building
envelope, have been
exposed to marine and
urban atmosphere and
earthquakes during two
decades of service.

107. Best Industry Practices
In applications where
dissimilar metals will be in
contact, specify
selectively-hardened self-
drilling fasteners to resist
HASCC.

108. Best Industry Practices
In aggressive environments
requiring stainless steel for
protection against visible
corrosion, specify bi-metal
self-drilling fasteners with a
selectively-hardened tip to
resist HASCC.

109. FASTENERS FOR
EXTREME LOADS
Fasteners exposed to extreme
loads also require special attention
to HASCC.

110. Extreme Loads
• During extreme loading, structures are
briefly subjected to loads far higher than
normal operating loads.
Determination Estimate Risk-Resistant
of Risk of Risk Loads Design

111. Extreme Loads
• Risks can include:
• Hurricane & Tornado, including windblown missile
impact
• Earthquakes
• Accidents (industrial accident, vehicular collision, etc.)
• Redistribution of load due to failure of other building
elements
• Explosion, including boiler, natural gas leaks, & attacks.
Determination Estimate Risk-Resistant
of Risk of Risk Loads Design

112. Extreme Loads
• If there is reason to suspect a risk, it should
be designed for.
Determination Estimate Risk-Resistant
of Risk of Risk Loads Design

113. Hurricane and Tornado Loads
Use building codes and regional history to predict
loads.

114. Hurricane and Tornado Loads
High-speed winds create
extreme atmospheric
pressure differentials
between the interior and
exterior of building
enclosures.
High-velocity, windblown
missiles create extreme
impact loads.

115. Blast (Explosion) Loads
Blast resistance should be
designed into structures:
•Containing volatile
materials.
•With high-security profile.
•With strategic importance The attack on Oklahoma City
Federal Building provoked rethinking
to an organization or of the need for blast-resistance.
mission.

116. Blast (Explosion) Loads
Blast resistance should be
designed into structures:
•That are or have occupants
considered targets for
attack.
•Located near possible The attack on Oklahoma City
targets. Federal Building provoked rethinking
of the need for blast-resistance.

117. Blast (Explosion) Loads
Blast resistance should be
designed into structures:
•That are “Essential
Facilities” that must remain
functional after disasters
due to importance to public The attack on Oklahoma City
health and safety: Federal Building provoked rethinking
of the need for blast-resistance.
• Hospitals
• Fire/rescue/police stations
• Toxic-material storage
• Air traffic control
• Critical defense installations.

118. Extreme Loading-Building Envelope
Hurricane, tornado and
exterior blast loads are
applied first to building
cladding and fenestration.
These elements either
absorb the load - by
deformation or failure - or
transfer load to other
structural elements.

119. Seismic Loading
Violent, cyclical
accelerations place
extreme loading on
all building
components, not just
structural members.
Failures of non-
structural elements
can injure or kill
people and make
buildings unusable.

120. Extreme Loading of Fasteners
Under extreme loading, if a
structural element does not fail, and
it does not deform sufficiently to
absorb all the load energy – that is,
if it is designed to withstand the
load – then the load is transferred
to the fasteners that hold it in place
and connect it to other structural
elements.

121. Extreme Loading of Fasteners
If the fasteners are ductile in
nature, they will deform, absorbing
some or all of the blast or impact
energy, but may still keep in place
the element they are attaching.
If fasteners are brittle, extreme
loading may cause them to fail.

122. Case-Hardened & Extreme
Loads
The outer layer of case- Hardened
hardened fasteners is brittle (brittle)
and less ductile. case
Core diameter <
fastener diameter
Under extreme loads, the
Soft
brittle outer case fails first, (ductile)
leaving the inner core to bear core
load.
Cross-section of case-hardened fastener.

123. Case-Hardened & Extreme
Loads
Even though the core may be Hardened
ductile, its smaller area can (brittle)
becomes overloaded and fail. case
Core diameter <
fastener diameter
Fasteners with incipient
Soft
HASCC are even more likely (ductile)
to fail during extreme loading. core
Cross-section of case-hardened fastener.

124. Case-Hardened & Extreme
Loads
Using ductile, HASCC- Hardened
resistant fasteners helps (brittle)
assure full design strength case
Core diameter <
of fasteners can be used to fastener diameter
resist extreme loads. Soft
(ductile)
core
Cross-section of case-hardened fastener.

125. Where to Specify
•Blast resist windows.
•Curtain wall framing.
•Building equipment.
•Critical life safety and
communications
equipment.

126. OTHER TYPES OF FASTENERS
HASCC-resistant fasteners can
be used to simplify a wide range
of special construction
applications.

127. Concrete and Masonry Screws
Specifying
concrete and Choice of
masonry anchors head
styles
also requires
consideration of
dissimilar metals
and corrosion
resistance. Hi-Lo
thread
taps into
masonry
Concrete Masonry

128. Concrete and Masonry Screws
A variety of special Choice of
head
designs are styles
available to satisfy
most construction
requirements.
Hi-Lo
thread
taps into
masonry
Concrete Masonry

129. Pressure-Relief Fasteners
In buildings with
potential for interior
explosions, special
panels can be
designed to blow off
and relieve
pressure, a built in
safety valve.

130. Pressure-Relief Fasteners
Examples include
places where highly
volatile liquids are in
use, or storage for
extremely fine, dry
materials subject to
dust-explosion.

131. Pressure-Relief Fasteners
Pressure-relief
panels are not
actually held in place
by fastener heads.
Panels have an
attachment-hole
larger than the
fastener-head, and
a special aluminum
washer retains the
panel in position.

132. Pressure-Relief Fasteners
Under explosive
pressure, washers
fail and allow panels
to blow off, venting
the pressure.
The panel is loosely
tethered to keep it
from becoming a
dangerous missile.

133. Pressure-Relief Fasteners
HASCC-resistant
fasteners can be
used in assembly.

134. Pressure-Relief Venting
Video at: http://www.dablackcompany.com/images/explosion.swf

135. Threaded Rod Anchors
Threaded rods are used to support fire sprinkler, HVAC, refrigeration,
general piping, electrical systems, and other essential building
services.
Self-tapping, self-drilling anchors simplify installation of these rods.

136. Sealing Washers
High performance
washers help
prevent leaks in the
building envelope.

137. SUMMARY

138. SUMMARY
• Fasteners are critical components of
buildings.
• Architects and Engineers must be aware
of their professional responsibility to
specify fasteners that fulfill design intent
and provide safe and durable connections.

139. HASCC-Resistance
• HASCC can cause sudden, catastrophic
failures when self-drilling or self-tapping
screws are used in conditions with dissimilar
metals and the potential for exposure to
moisture.
• It is not safe to assume that contractors will
be aware of this issue and will select anything
other than standard fasteners. Specify
accordingly.
• Selectively hardened and bi-metal self-drilling
fasteners mitigate risk because their load-
bearing sections remain ductile and less
vulnerable to HASCC.

140. Economy
• The lowest cost fastener may not be the most
economical when labor and service life are
considered.
• Specialty fasteners can sometimes save money
by providing lower installed cost.
• Fasteners are less than 2% of total building cost,
but specifying inadequate fasteners can cause
up to 100% of construction defect costs.

141. Sustainability
• Most metal fasteners have recycled-
material content and are recyclable.
• New corrosion-resistant finishes eliminate
toxic heavy metal plating.
• Durability over the life of a structure is the
most important measure of sustainability.

142. Thank you!
This concludes the American Institute of Architects
Continuing Education Systems Program.
Any Questions?
Gregg Melvin, Elco Construction Products
(815) 979-3249 - gmelvin@infastech.com