STI_Webinar_Dos_and_Donts_HSS_1Slide.pdf

Steel Tube Institute Hollow Structural Sections ® 2022 Steel Tube Institute. All Rights Reserved
STEEL TUBE INSTITUTE
1
YOUR TRUSTED RESOURCE FOR ALL STEEL TUBE AND PIPE PRODUCTS

DO’S AND DON’TS
OF HSS
THE STEEL TUBE INSTITUTE’S WEBINAR SERIES
AUGUST 2022– BETH SUMINSKI, PE, SE

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STEEL TUBE INSTITUTE
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www.steeltubeinstitute.org
• Resource Library
• Capability Tool
• Limit State Tables
• HSS Design Manuals
• HSS Excel Design Tools
• HSS Connex
• Webinars and eNews
• Professional Membership

DO’s and DON’Ts of HSS
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7

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AND MUCH MORE AND MUCH MORE
CHECK AVAILABILITY
END DISTANCE REDUCTION
MATERIAL SPECIFICATIONS
DO’s
OVERTIGHTEN BOLTS
MINIMIZE WALL THICKNESS
FULL WELD LENGTH
DON’Ts
Learning Objectives
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Agenda
• Practical / Technical DO’s and DON’Ts
• Big Picture DO’s and DON’Ts
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PRACTICAL /
TECHNICAL
DO’S AND DON’TS
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Material Grades – A500
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• Do specify Grade C
• Dual certification
• All domestically produced
materials have met Grade C
for about the last 20 years
• Be aware of ASTM 500
updates
• Don’t specify Grade A
• Eliminated in 2021
• Don’t specify Grade B
• You’re getting Grade C anyway!

Update to ASTM A500
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• ASTM A500 Yield Strengths
• Yield and tensile strengths same
for rounds and rect
• Grade C rounds = 50 ksi yield
• Increase max wall
thickness to 1”
• Increase max periphery
to 88”

Material Grades – A53 / A513 / A1085
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• Do specify A500 round
• Do check for minimum
yield if asked to
substitute for A500 for
smaller shapes
• Do check availability for
A1085 before specifying
• Don’t specify A53 or A513
• Lower or no minimum yield
strength
• More expensive
• Intended for mechanical and
pressure applications (steam,
water, air, gas)

Wall Thicknesses for Design
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• Do reduce A500
wall thickness to
0.93 tnom
• Do be aware that the
AISC manual assumes
A500 and already uses
0.93 tnom in its section
property tables
• Don’t reduce wall
thickness for A1085
• Tighter spec tolerance
doesn’t require this
• STI Design Manual Volume 1
includes section property
calculations for both A500
and A1085
0.93 x tnom
tnom

Choosing Wall Thicknesses
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• Do consider connections
during member design!
• Local strength at
flexible HSS walls
may control
• Fabrication costs
factor heavily into
finished structure
cost
• Don’t assume lightest =
cheapest with HSS!
• Don’t be fooled by
tension-only designs
• High slenderness ratios will
likely result in reinforced
connections

HSS Limit States
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• Do become familiar with
HSS limit states
• Punching, local yielding, local
buckling, plastification…
• Do use the STI limit
state tables!
• “Cheat sheet”
• Don’t use outdated
Chapter K tables
• AISC 360-2016 removed
many prescriptive connection
design tables that were in
2010 Chapter K
• Don’t assume your
connection software is
checking all limit states

STI Limit State Tables
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• AISC 360-10, Chapter K
• Going from:
• Tables
• Prescriptive
• Unique to the Spec
• Content is repetitive
• Limits of Applicability
• AISC 360-16, Chapter K
• Going to:
• Adds on to Chapter J
• Additional requirements
• Consistent
• No duplication
• Removed many Limits of
Applicability
Per AISC 360-16 K2.3 – The available
strength of connections to rectangular HSS
with concentrated loads shall be determined
based on the applicable limit states from
Chapter J.

Review of Limit States
Limit States
for such a combined failure mechanism but it was too complex for routine design and design
endations have opted instead for discrete individual limit state checks. Importantly though,
nd Packer (1982) showed that the formulation to capture Local yielding of the branch plate, Eqn.
epresented a lower bound to both their combined plastification-and-punching mechanism as well
imental results, further substantiating the discussion above regarding these three failure modes.
4: A tension-loaded, transverse branch plate connection exhibiting three failure mechanisms: (i)
ication of the HSS face; (ii) Punching shear of the HSS connecting face; (iii) Local yielding of HSS
side walls
yielding of HSS side walls.
This limit state, shown in Figure 4, can occur with the branch plate loaded in either tension or
ssion when β is close to 1.0. It is manifested by yielding of the two HSS side walls, or webs, along
• Shear Yielding (punching) • Plastification
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Review of Limit States
nnection, the available strength differs from international HSS connection recommendations and is
apted by AISC from the web local crippling expression for a W-section web:
Rn = 1.6t2
[1 + 3tp/(H – 3t)] [EFy ]0.5
Qf (K1-10) and (J10-4)
milarly, for a pair of concentrated forces, corresponding to a plate-to-HSS Cross- (or X-) connection (see
ure 5), the available strength differs from international HSS connection recommendations and is
apted by AISC from the web local buckling expression for a W-section web:
Rn = [48t3
/(H – 3t)] [EFy ]0.5
Qf (K1-11) and (J10-8)
Figure 5: Buckling of HSS side walls under transverse compression
mits of Applicability
Table K1.2A of AISC 360-10 gives a range of validity for a number of geometric and mechanical
perties for which all of Table K1.2 would be valid. All limits would not apply to all the limit states in
ble K1.2. For transverse plate connections, Eqns. (K1-7) and (K1-8), corresponding to Limit States 2 and
• Sidewall Failure
• Yielding, Crippling, Buckling
• Local Yielding
• Due to uneven load distribution
Limit States (continued)
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Limits of Applicability
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• Do become familiar with
limits of applicability
(LOA)
• Govern the use of
prescriptive AISC equations
• Do check LOA as a first
step in designing HSS
connections
• Don’t apply prescriptive
equations if the
connection falls outside
of the LOA

End Distance Provisions
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• Do be aware that
connection available
strengths in Chapter K
must meet end distance
LOA
• 𝑙!"# ≥ 𝐷 1.25 −
$
%
[Table K3.1]
• 𝑙!"# ≥ 𝐵 1 − 𝛽 [Table K3.2]
• Do apply a reduction
where end distance LOA
is not met
• A conservative reduction of
50% is typical
• Do use a cap/end plate to
waive the end distance
LOA

End Distance Provisions
23
• This connection does
not meet the end
distance requirements
Photo credit: Dr. Jeffrey Packer, STI Article: Rect HSS Connections Close to a Chord End

Effective Width for Rectangular HSS
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• Do be aware that
flexible HSS walls
cause non-uniform
distribution of
forces
• Do use effective
weld lengths per
Table K5.1
• 𝑙! = 2𝐵! [K5-4]
• Don’t rely on full width of
plates or branches
perpendicular to
longitudinal HSS axis
• Calculate effective width
• 𝐵! =
&'(
)
*!(
*!"("
𝐵+ ≤ 𝐵+ [K1-1]

Welding to HSS
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• Do apply directionality
factor correctly for HSS
• Do be aware of rule of
thumb that a fillet weld =
1.1tb (rounds) or
1.3tb (rects) develops
yield strength of branch
member
• Don’t use the 1.5
increase for most HSS
applications!
• Don’t apply limitation of
max fillet = t - 1/16” per
J2.2b to HSS at base
plate

Directional Strength Increase Factor
• AISC 360-16 Section J2.4(b) permits the use of
directional strength increase factor, kds, “for fillet welds…
if strain compatibility of the various weld elements is
considered.”
• Based on research on lap splice connections loaded in
shear
1.5
1.00 0.50sin
ds
n nw we ds
k
R F A k
q
= +
=
26

• Single-sided welds to a HSS wall in
tension are partially unrestrained and are
prone to bending about the local axis
leading to an opening of the weld root
• Actual failure plane is closer to the HSS
fusion face and has a longer failure line.
Conservative to use the weld effective
throat thickness as defined by Spec (min
distance between root of the fillet welds
and the face of the triangular weld
profile).
Packer, 2015
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• The restraint provided to the fillet weld depends on the
HSS wall thickness and shape, weld size and penetration
• Effect is much more severe on rectangles than rounds
• 1.5 increase should not be used for rectangular HSS in
tension to base or cap plates; ok for round HSS
• 1.5 increase should not be used for transverse plate to
HSS connections
• Permitted for double sided fillet welds (i.e. plates)
Do Use 1.5!
Round HSS
in tension
Don’t Use 1.5!
Rectangular HSS
in tension
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J2.2b and D1.1 Clause 2.4.2.9
• Limitation on size of weld applied
to edges
• Possible to melt away the top edge of
a member
• Max fillet = t – 1/16”
• HSS to base plate – not an edge
– does not apply
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Don’t apply
limitation to HSS
at base plate

Bolting to HSS
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• Do recognize bolting is
difficult due to closed
shape
• Do reinforce HSS if
using tensioned
through-bolts
• Do use alternatives
• Nelson studs
• Blind bolts
• Don’t forget access holes
• Don’t through bolt if
possible
• Difficult to install
• Req’d length may exceed stock
• Don’t overtighten through-
bolts, only snug tight!

Through Bolts
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Designating Truss-Type Connections
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• Do designate your truss
connection based on
force transfer
• Don’t designate your
truss connection based
solely on what it looks
like!

Designating Truss-Type Connections
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• “Letter” connection types
• K (also includes N) - load essentially equilibrated by other branch
members on the same side
• Y (also includes T) - load equilibrated by beam shear in chord member
• X or cross - load transferred through chord member & equilibrated on
other side
• Based on method of force transfer in the connection –
not on the physical appearance of the connection

STI Resources
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• Do use STI resources!
• HSS Design Manuals
• Limit State Tables
• Capability Tool
• HSS Connex
• eNews
• Resource Library
• Webinars on Demand
• Library of articles
• Don’t use
• Old general notes
• Old specifications
• “We’ve always done it this
way”

STI HSS Design Manuals
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STI Limit State Tables
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STI Capability Tool
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STI HSS Connex
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BIG PICTURE DO’S
AND DON’TS
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HSS Big Picture
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• Do recognize all the big
picture benefits!
• Columns
• Bi-axial strength
• Torsional superiority
• Curved members
• AESS
• Unique and non-building
structures
• Don’t default to the idea
that HSS is expensive!
• Efficient weight-to-strength
• Look at overall fabricated
project cost, not just $/ton

HSS Big Picture - Columns
42
• Do use HSS columns
• More efficient than WF
columns - no weak axis
• For 12’-0” W12x58 vs.
HSS12x12x3/8, HSS has 12%
more capacity at the same
weight per foot
• HSS can be concrete-filled for
extra capacity
• Do use Jumbo HSS
• Further increase capacity
• Squares up to 22”
• Rounds up to 28”
• Rects up to 34” x 10”
• Walls up to 1”

HSS Big Picture - Columns
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Target store. Photo credit: Mary Ingram-Schatz
• Do use HSS columns for big box / warehouses

HSS Big Picture – Bi-Axial
44
• Do use HSS to reduce
bracing
• No weak axis
• Truss case study found
tonnage reduction from
WF option – 174k, 81 pieces
HSS option – 114k, 49 pieces
HSS vs WF – 34% weight
savings

HSS Big Picture – Curved & AESS
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• Do expose HSS
• Smooth appearance is very
pleasing
• Varied shapes available
between rectangular and round
sections
• Not all exposed HSS needs to
be spec’d as AESS
• Do curve HSS
• Round HSS are especially
adaptable to almost anything
a designer can image

HSS Big Picture – Curved
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Allianz Field. Photo credit: MA Mortenson Company

HSS Big Picture – Curved
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Allianz Field. Photo credit: Justin Barton

HSS Big Picture – AESS Exteriors
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Seattle-Tacoma International Airport. Photo credit: exploresea.org

HSS Big Picture – AESS Exteriors
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Salvador Dali Museum

HSS Big Picture – Canopies
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Wight Acquino Student Center at Lewis University. Photo credit: Paul Schlismann Photography.

HSS Big Picture – Canopies
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Allianz Field. Photo credit: Justin Barton

HSS Big Picture – Atriums
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Transbay Transit Center. Photo credit: STC Photography Jason O’Rear

HSS Big Picture – Non-Bldg Structures
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Ballston Quarter Pedestrian Walkway. Photo credit: AISC

HSS Big Picture – AESS Interiors
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Brookfield Place Entry Pavilion. Photo credit: Plaza Construction

DO’s and DON’Ts SUMMARY
When using ASTM A500, specify Grade C as opposed to Grade B.
Check availability of HSS sections that you specify.
Reduce design wall thicknesses of ASTM A500 sections.
Consider impact of connections at the time you perform your member design. In
most instances, upsizing the member will be cheaper and more cost-effective than
reinforcing the connection.
Become familiar with HSS limit states.
Become familiar with HSS limits of applicability for Chapter K.
Utilize the STI limit state tables for a "cheat sheet" of the applicable limit states for
typical connections.
Check all applicable limit states for each connection.
Reduce connection capacities that don't meet end distance requirements; or
reinforce them.
Be aware of effective width phenomenon in rectangular HSS shapes. Use effective
width and effective weld length where applicable.
Traditional bolting, which requires access to both sides of the bolt, is difficult in HSS
and may require access holes.
If you must through-bolt HSS, do not overtighten, only snug tight.
If you must through-bolt HSS and tension the bolts, internally reinforce the section.
Alternative bolting options to HSS include Nelson studs and blind bolts.
For truss-type connections, designate your connection type (K, T, X, etc.) based on
the load transfer.
Use the STI resources available on www.steeltubeinstitute.org.
Do use HSS for its advantages!
Don't use non-structural material specifications, like
ASTM A53 or A513.
Don't reduce design wall thicknesses of ASTM A1085
sections.
Don't assume lightest = cheapest with HSS!
Don’t apply prescriptive equations if the connection falls
outside of the limits of applicability.
Don't assume that your HSS connection design software
is checking all the applicable limit states.
Don't use the 1.5 weld increase for many HSS
applications, especially one-sided welds and welds in
tension to rectangular HSS.
Don't apply limitation of reduced max fillet weld per
J2.2b at base plates.
Don't through-bolt HSS if possible.
For truss-type connections, don't designate your
connection type (K, T, X, etc.) based solely on the
geometry of the connected members.
Don't assume that HSS = expensive!
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UPCOMING WEBINARS
58
Site Registrations
Available
HSS CONNECTION EXAMPLES OUTSIDE THE TUBE
October 5, 2022 11:00 a.m. – 12:00 p.m. CDT
Let’s dive into HSS connections that might be commonly used but are tough to find an example for
reference. We will offer detailing options, review limit states and calculations, and guide engineers
through applying AISC code provisions for a number of HSS examples.
HSS SHEAR CONNECTIONS
November 9, 2022 11:00 a.m. – 12:00 p.m. CDT
The ubiquitous HSS shear connection can be wonderfully versatile. From a simple shear tab to a
more robust arrangement of angles or tees, the variety of shear connections available inspired this
session. The presentation will cover the importance and diversity of shear connections while working
with HSS members, including hand calculations and software options.
UNIQUE CONSIDERATIONS FOR HSS DESIGN
December 7, 2022 11:00 a.m. – 12:00 p.m. CDT
Building one’s expertise in HSS design broadens the options in one’s design toolkit. For those looking
to increase their HSS knowledge, this webinar will highlight several of the unique aspects of HSS
design. These include yield-line application, fire rating, the Qf factor and HSS-specific connection
checks.

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