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AISC Live Webinar July 12, 2018
Stiffeners and Doublers – Oh My!
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© The American Institute of Steel Construction 2018 The information presented herein is based on recognized engineering principles and is for general information only. While it is believed to be accurate, this information should not be applied to any specific application without competent professional examination and verification by a licensed professional engineer. Anyone making use of this information assumes all liability arising from such use.
Course Description Stiffeners and Doublers – Oh My! July 12, 2018 This webinar will present tips for avoiding costly doubler and stiffener detailing, along with good engineering practices that can make a big difference in the success of projects. The webinar will present a relative cost comparison between using stiffeners and doublers versus increasing member sizes. The latest requirements regarding doubler and stiffener design responsibilities will also be presented.
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Learning Objectives • • •
•
List locations within a building structure where stiffener and doubler plates are utilized. Describe the cost implications of using stiffener and doubler plate details versus using larger member sizes. Describe how the responsibility of stiffener and doubler detailing is assigned on the project using guidelines provided in the 2016 AISC Code of Standard Practice for Steel Buildings and Bridges. Explain how to communicate design responsibility in the contract documents. Explain how to properly design stiffener and doubler plates according to the 2016 AISC Specification for Structural Steel Buildings.
Stiffeners and Doublers Oh My! Carol Drucker, S.E., P.E., P.Eng. Drucker Zajdel Structural Engineers, Inc.
8
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Stiffeners and Doublers Summary • • • • • • •
What are doublers? When are they required? Doubler Cost COSP and Doublers Doubler Design Stiffener Applications Stiffener Design Stiffeners and Doublers
9
What is a Doubler? • A doubler is a plate at a member web used to reinforce a section for the required load
Courtesy of Lyndon Steel Company
Stiffeners and Doublers
10
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What is a Doubler? • A doubler plate is typically used to reinforce a column web panel zone B
B A
Stiffeners
A
Doublers Section A-A
Section B-B
Stiffeners and Doublers
11
Doublers • Other common applications – Coped beam web shear connections – Chevron connections – Truss Connections
a
a b
b
See Blodgett, Figure 41
Stiffeners and Doublers
12
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Why Doublers?
w
• Coped Beam to Girder – – – – –
Shear Yielding, Shear Rupture Block Shear Flexural Yielding, Flexural Rupture Flexural Buckling See Spec Part J and Manual Chapter 9
l
Capacity
V+ Doubler Force = Required Force – Strength of Section Stiffeners and Doublers
13
• Shear Flow at Top Edge of Doubler
C
C+dC
y2-y1
Shear Force and Stress v(t)(dz) dz
fv t t
V (Q ) I (t )
See Salmon and Johnson, Steel Structures Design and Behavior
Element Shear Stress
Stiffeners and Doublers
14
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Shear Force and Stress • Shear Flow at Top Edge of Doubler Average web shear used for design of steel beams
fv
V (Q ) I (t )
f avg
V ( d )(tw )
Stiffeners and Doublers
15
Shear In a Member • Shear Flow at Top Edge of Doubler
fv
Stiffeners and Doublers
V (Q ) I (t )
16
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Doubler Configurations • Doubler configurations commonly used: Prepped, Flush, and Offset • For flush doublers: use (1) doubler if thickness < 1/2” to 5/8”. • Doubler hierarchy (flush and prepped configurations): 1. Place on side without shear connection 2. Place on side with smaller beam framing into column web • Consider shear beam framing into doubler
Prep and Fillet Weld
Offset and Symmetric
Flush
Offset with Spacer Plate
Stiffeners and Doublers
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Doublers • Design Guide 13
N1
BEVEL, IF REQUIRED
Kdet
ENCROACHMENT OF WEB DOUBLER PLATE INTO COLUMN FILLET PER 15th ED MANUAL FIGURE 10-3 GROOVE WELD MAY BE A NON-PREQUALIFIED DETAIL (SEE DG13 SECTION 4.4.3)
(A) GROOVE-WELDED DETAIL N1. RIDING THE K CAUSES A GAP BETWEEN THE DOUBLER AND FACE OF WEB
Kdet
teff AT TOE OF FILLET
ENCROACHMENT OF WEB DOUBLER PLATE INTO COLUMN FILLET PER 15th ED MANUAL FIGURE 10-3
(B) FILLET-WELDED DETAIL WITH PLATE BEVEL EQUAL TO PLATE THICKNESS
Stiffeners and Doublers
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Doubler Prep • Design Guide 13 Dmin
0.6 Fy (treq ) 1.392
wmin t req 2 (t dp clip ) (tdp clip ) Dreq max( Dmin , wmin (16)) x
x t req (tdp clip ) 2
(tdp clip )
wmin
2 treq 2 2(tdp clip )
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Flush Doublers: DG13 • Not a prequalified CJP weld
kdet - tfc ENCR. 5/16" 1/8" 3/8" TO 1/2" 3/16" 9/16" TO 13/16" 1/4" 7/8" TO 1 1/4" 5/16" 1 5/16" TO 1 3/8" 3/8"
• Design Guide 13 – tdp =1/4” to 3/8” max: • C-L1a or C-L1a-GF with square cut edges (or beveled) – tdp > 1/4” to 3/8”: • TC-U4a with beveled plates edges
tfc kdet
DOUBLER MAY ENCROACH INTO COLUMN FILLET BY ENCR. ABOVE, FABRICATOR TO CONFIRM
DOUBLER PLATE
Stiffeners and Doublers
20° TO 30°
20
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Flush Doubler: Seismic Provisions • Prequalified doubler weld added to 2016 AWS D1.8/D1.8M Clause 4.3 • AISC 341-16 Seismic Provisions designate this weld as a “full strength” PJP Groove Weld (See Comm E3) – Routine ultrasonic testing is not required – 1/16-in. gap permitted between doubler and column web – Required strength of weld = available shear yielding strength of doubler
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Flush Doubler: AWS D1.8/D1.8M :2016
a
R
*AWS D1.8/D1.8M Clause 4.3: Decreased groove angle (a) and decreased root (R) require 3 macroetch test
Stiffeners and Doublers
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Flush Doubler Welds at Column Radius tfc kdet
tfc
DOUBLER MAY ENCROACH INTO COLUMN FILLET BY ENCR. BY AISC ACCEPTABLE AMOUNT
kdet
DOUBLER MAY ENCROACH INTO COLUMN FILLET BY ENCR. BY AISC ACCEPTABLE AMOUNT
a
20.0°
20.0° TO 30° PJP WELD NO TESTING REQUIRED
PJP WELD NO TESTING REQUIRED. PREPARE A WELD PROCEDURE SPECIFICATION (WPS) AND CONFIRM FULL PENETRATION
Rweld=(0.75)(0.6)(Fexx )(E)
WELD PER AWS D1.8 CLAUSE 4.3
Rweld= FULL SHEAR STRENGTH
PJP WELD NO TESTING REQUIRED PER D1.8 CLAUSE 4.3
Rweld= FULL SHEAR STRENGTH
Stiffeners and Doublers
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Shear In a Member • Exceptions at Chevron
y/2 MIN y Stiffeners and Doublers
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Shear In a Member • Exceptions at Chevron
Stiffeners and Doublers
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Doubler Extension
W-SHAPED BEAM
COLUMN
COLUMN
BOLTED FLANGE PLATE WIND AND LOW SEISMIC EXT = 2.5 kdes
(6" MAX)
COLUMN
DIRECTLY WELD CONNECTION WIND AND LOW SEISMIC EXT = 2.5 kdes
W-SHAPED BEAM
EXT
EXT
EXT
W-SHAPED BEAM
EXT
EXT
EXT
• Doubler Extension
(6" MAX)
Stiffeners and Doublers
END PLATE CONNECTION WIND AND LOW SEISMIC EXT = 3 kdes + t p
(6" MAX)
26
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Doubler Extension Seismic
W-SHAPED BEAM
COLUMN
EXT
W-SHAPED BEAM
EXT
W-SHAPED BEAM
EXT
EXT
EXT
EXT
• Doubler Extension
COLUMN
COLUMN
BOLTED FLANGE PLATE HIGH SEISMIC
WELDED FLANGE HIGH SEISMIC
END-PLATE CONNECTION HIGH SEISMIC
EXT = 6"
EXT = 6"
EXT = 6"
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Wind and Low Seismic • Doubler Termination
A
Size weld for 25% of stiffeners unbalanced force. See Design Guide 13
AISC minimum if no stiffeners
A Column Web Stiffener
Stiffener
Doubler Section A-A Stiffeners and Doublers
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High Seismic • Doubler Termination
A
Develop 75% of the shear yielding strength of doubler
Weld not required except if Eq E3-7 is not satisfied by both column web alone and doubler plate alone (to limit buckling of the doublers)
t
( d z wz ) 90
Eq. E3-7
A Column Web Stiffener
Stiffener
Doubler Section A-A Stiffeners and Doublers
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Continuous Doublers • Doubler Termination Size weld for 50% of the stiffeners unbalanced force A A
Column Web
E3.6f.2(c): Connect for lesser of: - Sum of stiffener tensile strength - Available shear strength of stiffener - Available shear strength of doubler Doubler
Stiffener AISC minimum if no stiffeners
Wind and Low Seismic
Stiffener Weld not required, Comm. E3, pg. 9.1-240
Section A-A High Seismic Stiffeners and Doublers
30
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Cost of Doublers • Rule of Thumb (Per Seismic Design Manual): Upsizing columns between 50 to 100 lb/ft might still be more cost effective than installing doubler plates and continuity plates. • Cost of Steel = $800/ton average (FOB mill) ($881 for plate) http://stld-cci.com/ • Platts S&P Global is also a good source for price of steel Size
Stiffeners and Doublers
WT/FT
Price/cwt*
*cwt=hundredweight:31 100 lbs Multiply by 20 for $/ton
Cost of Doublers – DG13 (1999)
Stiffeners and Doublers
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Cost of Doublers tST , TYP A
• • • •
LRFD, Grade 50 Plates W14x90 Column W24x55 Moment Connected Beams M = 350 kip-ft NOTES: – 1/2” stiffeners required – 1/2” doubler required
A
W24x55 BEAM
W24x55 BEAM
1. GR50 STEEL 2. 14 FT FLOOR-TO-FLOOR (#) tDB
• Upsize to W14x109 Column
COLUMN TYP. WW WW
– Stiffeners not required – 3/8” doubler required
COL. WEB
DOUBLER
TYP. WF WF
• Upsize to W14x193 – Stiffeners not required – Doubler not required
WW
STIFFENER
TYP
SECTION A
STIFFENERS
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Cost of Doublers Cost Comparison for Different Column Sizes
NOTES: 1. GR50 STEEL 2. 14 FT FLOOR-TO-FLOOR tST , TYP.
Stiffeners Column
A
Doublers
tST
Flange Weld WF
Web Weld WW
#
W14x90
1/2”
5/16”
5/16”
W14x90
1/2”
5/16”
W14x109
-
W14x109 W14x193
Cost Ratio
tDB
Doubler Weld WD
Weld Det.
1
1/2”
-
A
1.00
5/16”
1
1-1/2”
3/8”
B
0.75
-
-
1
3/8”
-
A
0.85
-
-
-
1
1-1/2”
5/16”
B
0.66
-
-
-
-
-
-
-
1.08
A
W24x55 BEAM
(#) tDB
W24x55 BEAM
COLUMN
OR
TYP.
20.0°
TYP.
DETAIL (A) GROOVE WELD
Stiffeners and Doublers
WD DETAIL (B) FILLET WELD
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Who Checks for Doublers? • Code of Standard Practice – 2005 and 2010 COSP Section 3.1.1 3.1.1 Permanent bracing, column stiffeners, column web doubler plates, bearing stiffeners in beams and girders, web reinforcement, openings for other trades and other special details, where required, shall be shown in sufficient detail in the Structural Design Drawings so that the quantity, detailing and fabrication requirements for these items can be readily understood.
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Who Checks for Doublers? • Code of Standard Practice – 2005 and 2010 COSP Section 1.1 1.1
In the absence of specific instructions to the contrary in the Contract Documents, the trade practices that are defined in this Code shall govern the fabrication and erection of the Structural Steel.
Stiffeners and Doublers
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Who Checks for Doublers?
TYP.
CJP
• Specific instructions to the contrary: – Contract documents can modify the COSP. For example, the Specification can indicate: “AISC’s COSP applies with the following modifications: Where reaction forces are given on the design drawings, Fabricator is responsible for designing stiffeners and/or doublers if necessary.”
CONTINUITY PLATES AS REQUIRED EACH SIDE OF COLUMN WEB TO MATCH THICKNESS OF BEAM FLANGES (SEE NOTE 1)
COLUMN
TYP.
PROVIDE WEB DOUBLER PLATES AS REQUIRED (SEE NOTE 1) NOTES: 1. PER THE PROVISIONS OF CHAPTER J OF THE AISC SPECIFICATIONS, PROVIDE COLUMN FLANGE STIFFENERS WHERE REQUIRED TO RESIST FORCES FROM MOMENT CONNECTIONS. PROVIDE COLUMN WEB DOUBLER PLATES AS REQUIRED FOR UNBALANCED MOMENT. ASSUME 20 KSI AXIAL STRESS IN COLUMNS FOR THE PANEL ZONE CHECKS
Stiffeners and Doublers
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Who Checks for Doublers? • Misleading Information: – Detail indicates stiffeners to be checked but not doubler – No loads given – No indication that Fabricator is to check for doublers on drawings or in Spec
Stiffeners and Doublers
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Who Checks for Doublers? • Current Code of Standard Practice – 2016 COSP (303-16) Section 3.1.2 » Option 3A: Member reinforcement (e.g. stiffeners, doubler, etc.) shall be designed by the owner’s designated representative and shown in the structural design documents issued for bid » Option 3B: Member reinforcement at connections is delegated design, but the quantities and conceptual configurations shall be provided and relied upon for bidding purposes. If no quantities or conceptual configurations are shown, member reinforcement at connections will not be included in the bid. Note: For Option 1 and 2, EOR designs stiffeners and doublers Stiffeners and Doublers
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Check for Doublers Determine Column Panel Zone Shear Strength • AISC Clean Column:
www.aisc.org/cleancolumn
Stiffeners and Doublers
40
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Doublers at Lateral Moment Connections - FBD Inflection point assumed at h/2
Pf1 = Mb1/db1
Pf1 +Pf2
Vc = ∑(Mb)/h Stiffeners if required
Vc
Pf2 = Mb2/db2
Mc Vp Mc
h
Panel Zone, Doublers if Required Vc
Vp = Panel Zone Shear = Pf1 + Pf2 - Vc
Vc
Shear
Moment
Stiffeners and Doublers
41
Forces from 3D Analysis
Vc Mc
Mc Vc
Shear Stiffeners and Doublers
Moment 42
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Check for Doublers Determine Column Panel Zone Shear Strength • Must Have
P
– Beam Moments
• Best to Have – Break Down of Beam DL, LL, and Lateral Moments – Column Axial Load
Stiffeners and Doublers
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Deflected Shape
Joint moments Typ.
Lateral
Gravity
Stiffeners and Doublers
44
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Deflected Shape
Joint moments Typ.
Lateral
Gravity
Stiffeners and Doublers
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Moment Connections – Doublers • ∑M = 0 ∑(Mb) < ∑(Mc) • Sum of beam moments can not exceed sum of column moment strengths Vp max = Panel Zone Shear = 2(Mc)/db - 2(Mc)/h
Stiffeners and Doublers
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Moment Connections – Doublers • ∑M = 0 ∑(Mb) < Mc
Top of Column
• At top of column, sum of beam moments can not exceed column moment strength Vc max = Panel Zone Shear = Mc/db
Stiffeners and Doublers
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Moment Connections – Doublers • Add dead and lateral loads on both sides • Add live load on one side MD2 MLAT2
MD1 ML1 MLAT1
Stiffeners and Doublers
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Moment Connections – Doublers
Column Web Doublers Loading Criteria
% Columns Requiring Doublers
Full Moment Beam, Limited to Strength of Column
100%
Actual Moments Given with No Break Down
79%
Actual Moments Given with Break Down
26%
Stiffeners and Doublers
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Give Actual Loads
1 ½” Stiffeners on a W14x90 Column
Courtesy of Larry Muir and Bill Thornton
Stiffeners and Doublers
50
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Check for Doublers Determine Column Panel Zone Shear Strength, J10.6 0.9 1.67
• Elastic Range:
aPr 0.4 Py : R n 0.6 Fy d c tw aP aPr 0.4 Py : R n 0.6 Fy d c tw 1.4 r Py
Pr (J10-9)
(J10-10)
• Plastic Range:
3bc f tcf2 aPr 0.75 Py : R n 0.6 Fy d c t w 1 ddt b c w
2 3b t 1.2a Pr aPr .75 Py : R n 0.6 Fy d ct w 1 c f cf 1.9 d d t Py b c w
(J10-11)
(J10-12)
• http://risa.com/news/code-requirements-for-panel-zone-shear-deformation/ Stiffeners and Doublers
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Check for Doublers Determine Column Panel Zone Shear Strength • Force in Doubler Vdoubler = SPf –Vc –Rn Vdoubler = SPf –Vc–Rn/
LRFD ASD
Pf
• Size of Doubler
d
Pf
– AISC Specification Eq. G2-1 Use ”d” of column
Vn (0.6 Fy AwCv1 )
Vn (0.6 Fy AwCv1 )
Stiffeners and Doublers
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Check for Doublers Determine Column Panel Zone Shear Strength • Consider beam shear when beam frames into doubler Pf=M/dm
H=Vg (x)/ dm Vg
Vg
V=Pf (dm)/x1
Vg V=Pf (dm)/x1
0.5Vg
0.5Vg
H=Vg (x)/ dm Alternate 1 Distribution
M
x
x1
Pf=M/dm
Alternate 2 Distribution, DG13
Stiffeners and Doublers
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Doubler Web Buckling • Wind and Low Seismic Doublers: Minimum thickness to prevent shear buckling (Spec Section G2): h 2.24 E / Fy t
t =
h Fy
W-SHAPED BEAM
381
h d c 2 kdes t = thickness of web doubler Alternatively, use plug welds and the total thickness (t= thickness column web + thickness doublers) can be used COLUMN
Stiffeners and Doublers
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Doubler Web Buckling • DG13 is per 1993 Spec which = 0.9 versus = 1.0 in 2016 Spec for Shear
t
t
h Fy 418 127 Fy
W-SHAPED BEAM
1993 LRFD, Section F2 Engineering for Steel Construction, 1984 Based on 1978 Spec Section 1.18.2.3 for Compression of COLUMN
Built-up Members Stiffeners and Doublers
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Doubler Web Buckling • High Seismic Doublers wz
( d z wz ) 90 d z d b 2 tbf t
dz
W-SHAPED BEAM
wz d c 2 tcf Where: t = thickness of column web or individual doubler
COLUMN
Stiffeners and Doublers
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Doubler Web Buckling • High Seismic Doublers with plug welds ( d z wz ) 90
W-SHAPED BEAM
dz
t
wz
Where: t = thickness of column web + thickness of individual doublers
Stiffeners and Doublers
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Moment Connections • Consider load path and equilibrium
Panel Zone Shear
• Same depth beams at cantilevers with equal and opposite moments do not need to be checked for doublers Stiffeners and Doublers
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Stiffeners • Stiffener Plates
B
B A
Stiffeners
A Doublers Section A-A
Section B-B
Stiffeners and Doublers
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Stiffeners • Other Common Applications
Column Bearing on Beam
Beam over Top of Column
Stiffeners and Doublers
Chevron Connections
60
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Stiffeners • Other Common Applications
Stability (J10.7)
To Direct Force Stiffeners and Doublers
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Stiffeners • Stiffeners, Spec J10.8 B
3
twc 2
b
bf
twc
b
– Minimum thickness, t:
t
B
bf
– Minimum width, b:
tf
Section B-B
2 b t 16 Where: tf (thickness) and bf (width) are for the element delivering the force
Stiffeners and Doublers
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Stiffeners • Limiting Stiffener Slenderness – Minimum width, t > b/16:
Simply Supported
• For plates with one free edge: 2
t cr 0.769 Dx D y 0.270( Dxy D yx ) 1.712Gt b
Dx 8, 000 ksi D y 31, 000 ksi
bs
Fixed
Dxy 16, 000 ksi Gt 2, 400 ksi
x
cr 33 ksi bs 15.2 16 ts
Free
y
Simply Supported
cr
Reference: Welded Interior Beam-to-Column Connections, AISC
Stiffeners and Doublers
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Stiffeners • Stiffeners, Seismic Provisions – Minimum width, b:
B
B
bf
t b wc 2 2
t
2 3t f 4
One sided connections Two sided connections
b
tf
twc
t
bf
– Minimum thickness, t:
Section B-B
Stiffeners and Doublers
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Stiffeners • Stiffeners – Minimum Length
ds
• AISC 360-16 Specification Section J10: – Transverse stiffeners shall extend a minimum of one-half the depth of the member except as required in Section J10.3 (WC)*, J10.5(WB), and J10.7(Unframed ends of beams not restrained against rotation about their longitudinal axis) *To satisfy web crippling strength, ½-depth stiffener increased to ¾-depth in the 15th Edition based on EJ 4th Qtr, 2015, Crippling of Webs with Partial-Depth Stiffeners under Patch Loading, by Salkar, et al
– Avoid welding stiffeners on 3-sides if possible, terminate at kdet for fabrication cost savings Stiffeners and Doublers
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Stiffeners • Stiffeners – Designing Partial Depth Stiffeners
b' • Reference EJ 4th Qtr, 2015, “Crippling of Webs with PartialDepth Stiffeners under Patch Loading” by Salkar, et al
a' 15th
• Reference for brackets
Manual Ed, Fig 15-2
Stiffeners and Doublers
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Stiffeners • Stiffener Clips – Gravity, Wind, and Seismic R=3 • Stiffeners should clear kdet and k1 • k-area (1-1/2” from k) is area of potentially lower notch toughness in rotarystraightened W-Shapes, see Commentary J10.8
Fig C-J10.8: Recommended placement of stiffener fillet welds to avoid contact with “k-area”
• Tests show a corner clip of 1-1/2” with fillets stopped short by (1) weld size can avoid this problem Fig C-J10.7:
Can reduce to ¾” at flanges for additional weld length
Representative “k-area” of wide-flange shape
67
Stiffeners • Seismic Stiffener clips – Seismic Provisions: • Reference AWS D1.8/D1.8M, Clause 4.1 – At web: Extend 1-1/2” min beyond kdet – At flange: Not to exceed 1/2” beyond k1 – Shall facilitate suitable weld termination – If curved, r = 1/2” min • Welding in the k-area should be avoided
Stiffeners and Doublers
AISC’s Seismic Provisions, Fig C-D2.3:
68
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Stiffeners/Continuity Plates • Flange Welds – AISC Specification Section J10.8 • Welds to be sized for the difference between the required strength and available strength.
FILLET
S (E)
– AISC’s Seismic Provision • Shall be CJP Welded per E3.6f2(c)
PJP
CJP
Stiffeners and Doublers
69
Stiffeners/Continuity Plates • Web Welds – Design Guide 13 • Weld for unbalanced stiffener force – AISC’s Seismic Provision • E3.6f.2(c): Connect for lesser of: - Sum of stiffener tensile strength at column flanges - Available shear strength of stiffener at column web - Available shear strength of column web (or doubler if doubler extended)
Stiffeners and Doublers
FILLET
S (E)
PJP
CJP
70
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Stiffeners/Continuity Plates • Stiffener Design – AISC Specification Chapter J Pstiffener = Pf – minimum Rn Pstiffener = Pf – minimum Rn/
LRFD ASD W-SHAPED BEAM
Rn is the minimum nominal strength for the applicable limit states – If kl/r < 25, yielding (k = 0.75) (J4.4) If kl/r > 25, see Spec Chapter E
COLUMN
Stiffeners and Doublers
71
Stiffener Design • Flange Local Bending – AISC Specification Section J10.1, Eq. J10-1
Load width
Rn 6.25 Fyf t 2f 0.90 (LRFD)
1.67 (ASD)
– Applicable to tension load only – Not applicable if load width is less than 0.15bf – Reduce Rn by 50% if force is applied less than 10tfc from end of column Stiffeners and Doublers
See Blodgett 5.7-8
72
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– AISC Specification Section J10.2
2.5
5kdes+lb
1
• Web Local Yielding Rn Fywtw 5kdes lb
lb
Stiffeners
Spec Equation J10-2 k des
Rn Fywtw 2.5kdes lb Spec Equation J10-3, Force d from end of column 1.50 (ASD)
lb = bearing length, in.
W14x90 COL
1.00 (LRFD)
W24x55 BEAM
d Stiffeners and Doublers
73
Stiffeners • Web Local Crippling – AISC Specification Section J10.3
l Rn 0.80t 1 3 b d
tw tf
l Rn 0.40t 1 3 b d 4l Rn 0.40t w2 1 b d 0.75 (LRFD)
tw tf
2 w
2 w
1.5
EF t yw f Qf tw
1.5
EF t yw f Qf tw 1.5 EF t t yw f 0.2 w Qf t t f w 2.00 (ASD)
Spec Equation J10-4, Force applied distance > d/2 from end of member Spec Equation J10-5a, Force applied distance < d/2 from end of member, lb/d<0.2 Spec Equation J10-5b, Force applied distance < d/2 from end of member, lb/d>0.2 See Section J10.3 for Qf definition
Stiffeners and Doublers
74
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Stiffeners • Web Compression Buckling – AISC Specification Section J10.5, Eq. J10-8
Rn
24tw3 EFyw
0.90 (LRFD)
h
Qf
1.67 (ASD)
– Reduce Rn by 50% if force is applied less than d/2 from end of column
W24x55 BEAM
Stiffeners and Doublers
W14x90 COL
– Applicable to double-concentrated forces at the same location
W24x55 BEAM
75
Stiffeners • Web Compression Buckling – Equation J10.8 developed from point loads and restrained flanges – If lb/d > approximately 1, Use Chapter E – See Chapter C and Appendix 6 for Stability
Test Set-up from Chen and Oppenheim 1970
Stiffeners and Doublers
See Spec Appendix Section 6.2.2 for point bracing (nodal bracing) required strength and stiffness
76
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Stiffeners/Continuity Plates • Stiffener Design – AISC’s Seismic Provision • Also Required if tcf < bbf/6
Eq (E3-8) W-SHAPED BEAM
COLUMN
Stiffeners and Doublers
77
Stiffener Eccentricity • DG13 which references testing by Graham, et al (1959), indicates stiffeners with 2” eccentricity, e, are 65% effective, reduced linearly: Rn_emax = 0.65 Rn
Stiffeners and Doublers
e
• Further research discussed for eccentric stiffeners
e
• Can slope stiffener if stiffener not needed for beam-to-column web moment connection
e = 2" MAX
78
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Web Sidesway Buckling – Beams • Web Sidesway Buckling (J10.4) – AISC Specification Eq. J10-6 and J10-7 3 Equation J10-6, h / tw Cr t w3 t f Compression Flange Rn 1 0.4 L /b h2 restrained, applicable if b f (h/tw)/(Lb/bf)<2.3
Cr t w3 t f h / t w 0.4 Rn h 2 Lb / b f
3
Equation J10-7, Compression Flange not restrained, applicable if (h/tw)/(Lb/bf)<1.7 AISC Commentary, Fig.C-J10.2 Web sidesway buckling
0.85 (LRFD) 1.76 (ASD) • Compression flange braced, tension flange unbraced • Lb = largest laterally unbraced section along either flange at the point of load. Stiffeners and Doublers
79
tst
Web Buckling - Girders tw
• Additional Stiffener Requirements for Beam and Girder Flange(s) – AISC Specification Section J10.8
beff =25tw AT
• Check web and stiffeners as column section with kl = 0.75h (see Spec Sections
E6.2, J4.4)
INTERIOR
tst
A
tw
A
• beff = 25 tw at interior 12 tw at ends of members
– For fabrication cost savings, fit one side of stiffener to bear at flange and transfer force at opposite end of stiffener by weld Stiffeners and Doublers
beff =12tw AT EXTERIOR Section A-A 80
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Stiffener & Doubler Example • Given: – Distance to end of column much larger than column depth – W Shapes ASTM A992, Fy = 50 ksi
-
Plates Grade 50, Fy = 50 ksi AISC Specification 360-16 AISC 15th Edition, LRFD ASCE 7-10 R= 3 Wind determined not to control
MD1 = 130 kip-ft
MD1 ML1 ME1 W27x94
W14x176
ML1 = 220 kip-ft ME1 = 690 kip-ft MD2 ML2 ME2 W27x94
MD2 = 130 kip-ft ML2 = 220 kip-ft ME2 = 690 kip-ft 81
Stiffeners and Doublers
Stiffener & Doubler Example • Find: – Check if stiffeners are required. If required, size the stiffeners. – Check if doublers are required. If required, size the doublers.
W14x176
Stiffeners if required
W27x94
W27x94
Panel Zone, Doubler if Required 82 Stiffeners and Doublers
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Stiffener & Doubler Example • Solution: – 1. ASCE 7-10, Load Combinations for Strength Design
1. 1.4D 2. 1.2D + 1.6L + 0.5(Lr or S or R)
= 182 kip-ft = 508 kip-ft
3. 1.2D + 1.6(Lr or S or R) + (L or 0.5W) 4. 1.2D + 1.0W + L + 0.5(Lr or S or R)
= 376 kip-ft = 376 kip-ft
5. 1.2D + 1.0E + L + 0.2S 6. 0.9D + 1.0W
= 1070 kip-ft = 117 kip-ft
7. 0.9D + 1.0E
= 807 kip-ft
MD1 = 130 kip-ft ML1 = 220 kip-ft ME1 = 690 kip-ft MD2 = 130 kip-ft ML2 = 220 kip-ft ME2 = 690 kip-ft
Governing Load Combination: 5. 1.2D + 1.0E + L + 0.2S M1 = M2 = 1.2(130 kip-ft) + 1.0 (690 kip-ft) + 1.0(220 kip-ft) = 1070 kip-ft 83 Stiffeners and Doublers
Stiffener & Doubler Example • Solution: – 2. Determine Each Beam’s Flange Force
Mu d t pl
Pfl
Mu d t fb
Pfl1
Pfl2
Flange Plate
Directly welded W27x94 BEAM
W14x176 COL
Pfl
W27x94 BEAM
84 Stiffeners and Doublers
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Stiffener & Doubler Example • Solution: – 2. Determine Each Beam’s Flange Force
M1 d b tf b 1070 kip-ft 26.9in. - 0.745 in. 491kips
W27x94 BEAM
Pfl2
W14x176 COL
Pfl1
Pfl Pfl 1 Pfl 2
W27x94 BEAM
85 Stiffeners and Doublers
Stiffener & Doubler Example • Solution: – 3. Check Stiffener Limit States • Web Local Yielding (J10.2)
1.00
– AISC Specification Eq. J10-2
Rwy Fywtwc 5kdesc lb 427 kips < Pfl 491kips n.g. Stiffeners Required
W27x94 BEAM
W14x176 COL
1.00 50 ksi 0.830 in. 5 1.91in. 0.745in. W27x94 BEAM
Note : lb t fb
86 Stiffeners and Doublers
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Stiffener & Doubler Example • Solution: – 3. Check Stiffener Limit States • Web Local Crippling (J10.3)
0.75
– AISC Specification Eq. J10-4
Rwc
1.5 lb t wc EFyc t fc 0.80t 1 3 t wc dc t fc 1.5 0.745in. 0.830 in. 2 0.75(0.80) 0.830 in. 1 3 15.2 in. 1.31 in. 2 wc
29000 ksi 50 ksi 1.31in. 0.830in.
672 kips Pfl 491kips o.k.
Note : lb t fb 87 Stiffeners and Doublers
Stiffener & Doubler Example • Solution: – 3. Check Stiffener Limit States • Web Compression Buckling (J10.5)
0.90
– AISC Specification Eq. J10-8
Rwb
24t w3 c EFyc
(0.90)
h
W14x176 COL
h dc 2kdesc 15.2in. 2 1.91in. 11.4 in. Qf
24 0.83in.
3
29000 ksi 50 ksi
11.4 in. 1305 kips Pfl 491kips o.k.
(1.0)
W27x94 BEAM
W27x94 BEAM
88 Stiffeners and Doublers
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Stiffener & Doubler Example • Solution: – 3. Check Stiffener Limit States • Flange Local Bending (J10.1)
0.90
– AISC Specification Eq. J10-1
R fb 6.25 Fyc t 2fc 0.90 6.25 50 ksi 1.31in.
2
483 kips < Pfl 491kips n.g. Stiffeners Required
See Blodgett 5.7-8
89 Stiffeners and Doublers
Use of Manual Tables • Web Local Yielding
1.00
– AISC 15th Edition Manual Eq. 4-2a
396 41.5 1310 483 Rn Pwo Pwilb kips 396 kips 41.5 0.745in. in. 427 kips Pfl 491kips n.g. Stiffeners Required
90 Stiffeners and Doublers
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Use of Manual Tables • Web Local Crippling
0.75
– AISC 15th Edition Manual Eq. 9-50a
Rn 2 R3 lb R4 kips 2 313kips 0.745in. 31.1 in. 672 kips Pfl 491kips o.k.
91 Stiffeners and Doublers
Use of Manual Tables 0.90
• Web Compression Buckling
– AISC 15th Edition Manual Eq. 4-3a
396 41.5 1310 483
Rn Pwb 1310 kips Pfl 491kips o.k.
92 Stiffeners and Doublers
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Use of Manual Tables • Flange Local Bending
0.90
– AISC 15th Edition Manual Eq. 4-4a
396 41.5 1310 483
Rn Pfb 483 kips Pfl 491kips n.g. Stiffeners Required
93 Stiffeners and Doublers
Stiffener & Doubler Example
lst
• Solution:
bst
– 4. Column Stiffener Design • Determine Force in the Stiffeners
Pst1tot Pst 2tot Pfl min(Rwy , Rwc , Rwb , Rfb) 491 kips 427 kips
Snip
= 64 kips • Determine Beam Force Per Each Stiffener
Pst 1 0.5( Pst1tot ) 0.5(64 kips) = 32 kips Pst 2 0.5( Pst 2tot ) 0.5(64 kips) = 32 kips
94 Stiffeners and Doublers
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Stiffener & Doubler Example • Solution:
bst
– 4. Column Stiffener Design • Determine Minimum Stiffener Width per AISC’s Specification, Section J10.8
Snip
bfb twc 10 in. 0.83 in. 2.92in. Min. (See Note below) 3 2 3 2 bfc twc 15.7 in. 0.830 in. bst max 7.44in. Max 2 2 bst min
Use bst = 7" Stiffener *Note: Use bpl in lieu of b fb if moment connection plate delivering the load 95 Stiffeners and Doublers
Stiffener & Doubler Example • Solution:
bst
– 4. Column Stiffener Design • Determine Minimum Stiffener Thickness per AISC’s Specification, Section J10.8
tst min
bst 7 in. 0.438in. 16 16
tst min
tfb 0.745 in. 0.373 in. 2 2
Snip
Controls (See Note below)
• Try a 1/2” Stiffener
*Note: Use t pl in lieu of t fb if moment connection plate delivering the load 96 Stiffeners and Doublers
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Stiffener & Doubler Example
lst
• Solution: • Check Minimum Thickness Due to Tension Yielding – AISC Specification Section J10.8
snip max(k det c tfc, k 1c
twc ,1.5 in.) 2
max(2.625 in. 1.31 in., 1.625 in.
bst
– 4. Column Stiffener Design Snip
0.83 in. ,1.5 in.) 2
1.5 in. Pst Fyp (bst snip ) 32 kips 0.90(50 ksi)(7 in. 1.5 in.) = 0.129 in. 0.5 in. o.k.
tst min
*Note: Can reduce snip at flange if needed. 97
Stiffeners and Doublers
Stiffener & Doubler Example – 4. Column Stiffener Design • Check Minimum Thickness Due to Compression Buckling – AISC Specification Section J10.8 and E3 0.90
bst
lst
• Solution:
lst dc 2tfc 15.2 in. 2(1.31 in.) = 12.6 in. k 0.75 kl klst 12 0.75(12.6 in.) 12 65.5 r tst (0.5 in.) Limit 4.71 Fe
2 E
r kl
2
E 29,000 ksi 4.71 113 Fyp 50 ksi π 2 (29,000 ksi)
65.5
2
66.6 ksi 98
Stiffeners and Doublers
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Stiffener & Doubler Example – 4. Column Stiffener Design • Check Minimum Thickness Due to Compression Buckling – AISC Specification Section E3 0.90 50 ksi Fyp Fcr 0.658 Fe Fyp 0.658 66.6 ksi 50 ksi 36.5 ksi Fcr 0.90(36.5 ksi) = 32.9 ksi
bst
lst
• Solution:
(E3-2)
Rearrange Pn FcrAg to Solve for tst min (E3-1) Pst tst min Fcr (bst ) *Note: Buckling limit state included for example purposes. 32 kips (32.9 ksi)(7 in.) = 0.139 in. 0.5 in. o.k. 99
Stiffeners and Doublers
Use of Manual Tables – AISC Manual Table 4-14: KL/r Table 65 22.0 33.0 66 21.8 32.7
Stiffeners and Doublers
100
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Stiffener & Doubler Example • Solution:
Lwf
– 4. Column Stiffener Design • Weld Design of Stiffener to Column – AISC Specification Section J2
Lww
Snip
Lww lst 2 snip 12.6 in. - (2)1.5 in. = 9.6 in. Lwf bst snip 7 in. - 1.5 in. = 5.5 in.
0.928 ASD 1.392 LRFD D min fl
Pst 32 kips = 1.39 (16th of an inch) (2) Lwf (1.5) 1.392(2)(5.5 in.)(1.5) 1/4” Fillet Weld o.k. 101 Stiffeners and Doublers
Stiffener & Doubler Example • Solution: – 4. Column Stiffener Design
Note : 0.928 D (0.6)( Fexx )(0.707)( w) /
w D (0.60)(70 ksi)(0.707) / 2 0.928 D 16 D 1.392 D (0.6)( Fexx )(0.707)( w) 16 w D (0.60)(70 ksi)(0.707) (0.75) 1.392 D 16 1.5 1.0 0.5(sin())1.5 1 0.5(sin(90))1.5 1.5
Reference Spec Eq (J2 - 5) 102
Stiffeners and Doublers
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Stiffener & Doubler Example • Solution: – 5. Determine Flange Forces for Column Doubler Checks • Based on ASCE 7 Load Cases • Determine sum of flange forces for each load load combination. Consider symmetric gravity moments and pattern loading if applicable
ASCE 7-10 1. 1.4D
MD1 = 130 kip-ft
2. 1.2D + 1.6L + 0.5(Lr or S or R)
ML1 = 220 kip-ft ME1 = 690 kip-ft
3. 1.2D + 1.6(Lr or S or R) + (L or 0.5W ) 4. 1.2D + 1.0W + L + 0.5(Lr or S or R )
MD2 = 130 kip-ft
5. 1.2D + 1.0E + L + 0.2S 6. 0.9D + 1.0W
ML2 = 220 kip-ft ME2 = 690 kip-ft
7. 0.9D + 1.0E 103 Stiffeners and Doublers
Stiffener & Doubler Example • Solution: – 5. Determine Flange Forces for Column Doubler Checks • Determine Critical Load Combination:
Governing Load Combination 5: M 1_ 5 = 1.2(130 k-ft) + 1.0 (690 k-ft) + 1.0(220 k-ft) = 1070 kip-ft M 2_ 5 = 1.2(-130 k-ft) + 1.0 (690 k-ft) = 534 kip-ft
MD1 = 130 kip-ft
Pfl1_ 5
M1 1070 kip-ft 491 kip db1 tfb1 26.9 in. - 0.745 in.
ML1 = 220 kip-ft ME1 = 690 kip-ft
Pfl 2 _ 5
M2 534 kip-ft 245 kip (Stiffener not required) db 2 tfb 2 26.9 in. - 0.745 in.
MD2 = 130 kip-ft
Pfd Pfl1_ 5 Pfl 2 _ 5 491 kips 245 kips 736 kips
ML2 = 220 kip-ft ME2 = 690 kip-ft 104
Stiffeners and Doublers
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Stiffener & Doubler Example • Solution: – 5. Determine Flange Forces for Column Doubler Checks • Confirm column strength does not control:
SM b = M 1_ 5 +M 2 _ 5 = 1070 kip-ft + 534 kip-ft = 1604 kip-ft 0.9(320 in.3 )(50 ksi) = 1200 kip - ft 12in. / ft = 1200 kip-ft + 1200 kip-ft = 2400 kip-ft
M nc ( Z xc )( Fyc ) SM c = M c _ t +M c _ b
SM b = 1604 kip-ft < SM c 2400 kip-ft
Beams Control
105 Stiffeners and Doublers
Stiffener & Doubler Example • Solution: – 6. Determine Panel Zone Shear Reduction Due to Column Shear
Pfd
Vc
hcol 15 ft M M2 Vc 1 hcol 1070 kip - ft + 534 kip - ft 15 ft 107 kips
Vc Pfd1 M1
M2
h
Vp Pfd Vc 736 kips 107 kips 629 kips
Pfd2
Vc
Vp
Vc Shear 106 Stiffeners and Doublers
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Stiffener & Doubler Example • Solution: – 7. Column Doubler Check
0.90
ᶲRn
• Web Panel Zone Shear Strength – AISC Specification Section J10.6
a 1.0 (LRFD); 1.6 (ASD) W27x94 BEAM
aPr (1.0)870 kips = 870 kips LRFD
W27x94 BEAM
Py Fyc Agc (50 ksi)(51.8 in.2 ) 2590 kips aPr (1.0)870 kips 0.336 0.4 Py 2590 kips
W14x176 COL
Since aPr 0.4 Py : R n 0.6 Fy d ct w
(J10-9) 107
Stiffeners and Doublers
Stiffener & Doubler Example • Solution: – 7. Column Doubler Check
0.90
ᶲRn
• Web Panel Zone Shear Strength – AISC Specification Section J10.6
Rn 0.6 Fywt wc dc W27x94 BEAM
0.90(0.6)(50 ksi)(0.830 in.)(15.2 in.)
W27x94 BEAM
341 kips W14x176 COL
Vp 629 kips > Rn 341 kips
n.g.
Doubler Required Stiffeners are not required
108 Stiffeners and Doublers
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Stiffener & Doubler Example • Solution: Vd
– 7. Determine Doubler Shear Force
Vd Vp Rn 629 kips 341 kips 288 kips Number of Doublers, nd = 1
W27x94 BEAM
Panel Zone, Doubler Required
W27x94 BEAM
W14x176 COL
109 Stiffeners and Doublers
Stiffener & Doubler Example • Solution: – 8. Column Doubler Design • Minimum Doubler Thickness to prevent Shear Buckling – AISC Specification Section G2.1
For, Cv = 1.0
td min 1
h 2.24
Fyp dc 2kd esc E 2.24
Fyp 15.2 in. 2(1.91in.) 50 ksi 0.211 in. E 2.24 29, 000 ksi
110 Stiffeners and Doublers
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Stiffener & Doubler Example • Solution: – 8. Column Doubler Design • Doubler Thickness Due to Panel Zone Shear – AISC Specification Equation G2-1
1.00
Vd (Cv ) (0.6)( Fyp )(dc )( nd ) 288 kips(1.0) (1.00)(0.6)(50 ksi )(15.2 in.)(1) 0.632 in.
td min 2
111 Stiffeners and Doublers
Stiffener & Doubler Example • Solution: – 8. Column Doubler Design • Doubler Vertical Edge Thickness Due to Beam-to-Column Web Shear Connection, Reference AISC’s Spec Equation J4-3
td min 3
1.00
0.5Vconn ' x (0.6)( Fyp )( Ld )
0.5(0 kips) 0.0 in. 1.00(0.6)(50 ksi)(26.9 in. - 0.745 in. - 0.5 in.) Where : Ld length of doubler db tfb ts
td min 3
td
min
Vconn’x
= max(td min 1, td min 2 td min 3) = max (0.211 in., 0.632 in. + 0 in.) = 0.632 in.
Use (1) PL 3/4" or (2) PL 3/8"
112
Stiffeners and Doublers
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Stiffener & Doubler Example • Solution: – 8. Column Doubler Design
1.00 Lwf
• Doubler Horizontal Edge Thickness Due to Unbalanced Stiffener Force
Pst 1 Pst 2 td min 4 (0.6)( Fyp )( Lww )(2)
Lww
Ref Spec Eq (J4-3) Snip Pst2
Pst1
32 kips + 0 kips (1.00)(0.6)(50 ksi)(9.6 in.)(2) 0.056 in. < 3/4" o.k.
113 Stiffeners and Doublers
Stiffener & Doubler Example – 8. Column Stiffener Thickness for Shear
1.00
• Check Minimum Thickness Due to Unbalanced Stiffener Force
bst
lst
• Solution:
Snip
Rearrange Rn 0.6 FypAgv to Solve for tst min
Ref (J4-3)
Pst 1 Pst 2 (0.6) Fyp (lst 2( snip)) 32 kips 0 kips 1.00(0.6)(50 ksi)(12.6 in. 2(1.5 in.)) = 0.111 in. 0.5 in. o.k.
tst min
114 Stiffeners and Doublers
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Stiffener & Doubler Example – 8. Column Stiffener Weld • Stiffener Weld to Doubler Horizontal Edge and Column Web for unbalanced stiffener force Snip
Lwf
• Solution:
Lww
Lww lst 2 snip 12.6 in. - (2)1.5 in. = 9.6 in. 0.928 ASD 1.392 LRFD
DOUBLER
Pst 1 Pst 2 (2)( Lww) 32 kips+ 0 kips 1.392(2)(9.6 in.) = 1.20 (16th of an inch)
COL. WEB
1/4
D min web
STIFFENER
1/4
TYP
< 4 (16th of an inch), use 1/4” Fillet Weld o.k. 115
Stiffeners and Doublers
Stiffener & Doubler Example • Solution:
Lwf
– 8. Column Stiffener Thickness – Weld Design of Stiffener to Column – AISC Specification Section J2
Lww
Snip
Check plate and column web thicknesses for weld size
0.75
tst min
(2)( D min) 1.392(2)(1.20) 0.114 in. (0.6) Fup 0.75(0.6)(65 ksi)
< tst = 0.5 in. o.k.
twc min
(2)( D min) 1.392(2)(1.20) 0.114 in. (0.6) Fuc 0.75(0.6)(65 ksi)
< twc = 0.83 in. o.k.
116 Stiffeners and Doublers
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Stiffener & Doubler Example • Solution: 1/4 TYP 1/4
– 9. Summary DOUBLER
DOUBLER MAY ENCROACH INTO COLUMN FILLET
COL. WEB
1/4 STIFFENER
1/4 SECTION A
TYP
SECTION B
a PL 3/4" DOUBLER B
B W27x94
1/2" STIFFENER PL NS/FS W27x94
A A W14x176 COLUMN
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Stiffeners and Doublers
Conclusion • Doublers are required to resist shear forces exceeding the panel zone shear strength • AWS D1.8/D1.8M: 2016 has a prequalified doubler weld configuration • Sufficient information is needed to check for web doublers • Increasing the column size to eliminate stiffeners and doublers can be cost effective • Stiffeners (also known as continuity plates) are required to resist applied loads greater than the local strength of the supporting member • Stiffener applicable limit states are in Specification Section J10
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Questions?
119
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PDH Certificates Within 2 business days… • Reporting site (URL will be provided in the forthcoming email). • Username: Same as AISC website username. • Password: Same as AISC website password.
Thank You Please give us your feedback! Survey at conclusion of webinar.
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© The American Institute of Steel Construction 2018 The information presented herein is based on recognized engineering principles and is for general information only. While it is believed to be accurate, this information should not be applied to any specific application without competent professional examination and verification by a licensed professional engineer. Anyone making use of this information assumes all liability arising from such use.
Course Description Stiffeners and Doublers – Oh My! July 12, 2018 This webinar will present tips for avoiding costly doubler and stiffener detailing, along with good engineering practices that can make a big difference in the success of projects. The webinar will present a relative cost comparison between using stiffeners and doublers versus increasing member sizes. The latest requirements regarding doubler and stiffener design responsibilities will also be presented.
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Learning Objectives • • •
•
List locations within a building structure where stiffener and doubler plates are utilized. Describe the cost implications of using stiffener and doubler plate details versus using larger member sizes. Describe how the responsibility of stiffener and doubler detailing is assigned on the project using guidelines provided in the 2016 AISC Code of Standard Practice for Steel Buildings and Bridges. Explain how to communicate design responsibility in the contract documents. Explain how to properly design stiffener and doubler plates according to the 2016 AISC Specification for Structural Steel Buildings.
Stiffeners and Doublers Oh My! Carol Drucker, S.E., P.E., P.Eng. Drucker Zajdel Structural Engineers, Inc.
8
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Stiffeners and Doublers Summary • • • • • • •
What are doublers? When are they required? Doubler Cost COSP and Doublers Doubler Design Stiffener Applications Stiffener Design Stiffeners and Doublers
9
What is a Doubler? • A doubler is a plate at a member web used to reinforce a section for the required load
Courtesy of Lyndon Steel Company
Stiffeners and Doublers
10
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What is a Doubler? • A doubler plate is typically used to reinforce a column web panel zone B
B A
Stiffeners
A
Doublers Section A-A
Section B-B
Stiffeners and Doublers
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Doublers • Other common applications – Coped beam web shear connections – Chevron connections – Truss Connections
a
a b
b
See Blodgett, Figure 41
Stiffeners and Doublers
12
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Why Doublers?
w
• Coped Beam to Girder – – – – –
Shear Yielding, Shear Rupture Block Shear Flexural Yielding, Flexural Rupture Flexural Buckling See Spec Part J and Manual Chapter 9
l
Capacity
V+ Doubler Force = Required Force – Strength of Section Stiffeners and Doublers
13
• Shear Flow at Top Edge of Doubler
C
C+dC
y2-y1
Shear Force and Stress v(t)(dz) dz
fv t t
V (Q ) I (t )
See Salmon and Johnson, Steel Structures Design and Behavior
Element Shear Stress
Stiffeners and Doublers
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Shear Force and Stress • Shear Flow at Top Edge of Doubler Average web shear used for design of steel beams
fv
V (Q ) I (t )
f avg
V ( d )(tw )
Stiffeners and Doublers
15
Shear In a Member • Shear Flow at Top Edge of Doubler
fv
Stiffeners and Doublers
V (Q ) I (t )
16
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Doubler Configurations • Doubler configurations commonly used: Prepped, Flush, and Offset • For flush doublers: use (1) doubler if thickness < 1/2” to 5/8”. • Doubler hierarchy (flush and prepped configurations): 1. Place on side without shear connection 2. Place on side with smaller beam framing into column web • Consider shear beam framing into doubler
Prep and Fillet Weld
Offset and Symmetric
Flush
Offset with Spacer Plate
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Doublers • Design Guide 13
N1
BEVEL, IF REQUIRED
Kdet
ENCROACHMENT OF WEB DOUBLER PLATE INTO COLUMN FILLET PER 15th ED MANUAL FIGURE 10-3 GROOVE WELD MAY BE A NON-PREQUALIFIED DETAIL (SEE DG13 SECTION 4.4.3)
(A) GROOVE-WELDED DETAIL N1. RIDING THE K CAUSES A GAP BETWEEN THE DOUBLER AND FACE OF WEB
Kdet
teff AT TOE OF FILLET
ENCROACHMENT OF WEB DOUBLER PLATE INTO COLUMN FILLET PER 15th ED MANUAL FIGURE 10-3
(B) FILLET-WELDED DETAIL WITH PLATE BEVEL EQUAL TO PLATE THICKNESS
Stiffeners and Doublers
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Doubler Prep • Design Guide 13 Dmin
0.6 Fy (treq ) 1.392
wmin t req 2 (t dp clip ) (tdp clip ) Dreq max( Dmin , wmin (16)) x
x t req (tdp clip ) 2
(tdp clip )
wmin
2 treq 2 2(tdp clip )
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Flush Doublers: DG13 • Not a prequalified CJP weld
kdet - tfc ENCR. 5/16" 1/8" 3/8" TO 1/2" 3/16" 9/16" TO 13/16" 1/4" 7/8" TO 1 1/4" 5/16" 1 5/16" TO 1 3/8" 3/8"
• Design Guide 13 – tdp =1/4” to 3/8” max: • C-L1a or C-L1a-GF with square cut edges (or beveled) – tdp > 1/4” to 3/8”: • TC-U4a with beveled plates edges
tfc kdet
DOUBLER MAY ENCROACH INTO COLUMN FILLET BY ENCR. ABOVE, FABRICATOR TO CONFIRM
DOUBLER PLATE
Stiffeners and Doublers
20° TO 30°
20
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Flush Doubler: Seismic Provisions • Prequalified doubler weld added to 2016 AWS D1.8/D1.8M Clause 4.3 • AISC 341-16 Seismic Provisions designate this weld as a “full strength” PJP Groove Weld (See Comm E3) – Routine ultrasonic testing is not required – 1/16-in. gap permitted between doubler and column web – Required strength of weld = available shear yielding strength of doubler
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Flush Doubler: AWS D1.8/D1.8M :2016
a
R
*AWS D1.8/D1.8M Clause 4.3: Decreased groove angle (a) and decreased root (R) require 3 macroetch test
Stiffeners and Doublers
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Flush Doubler Welds at Column Radius tfc kdet
tfc
DOUBLER MAY ENCROACH INTO COLUMN FILLET BY ENCR. BY AISC ACCEPTABLE AMOUNT
kdet
DOUBLER MAY ENCROACH INTO COLUMN FILLET BY ENCR. BY AISC ACCEPTABLE AMOUNT
a
20.0°
20.0° TO 30° PJP WELD NO TESTING REQUIRED
PJP WELD NO TESTING REQUIRED. PREPARE A WELD PROCEDURE SPECIFICATION (WPS) AND CONFIRM FULL PENETRATION
Rweld=(0.75)(0.6)(Fexx )(E)
WELD PER AWS D1.8 CLAUSE 4.3
Rweld= FULL SHEAR STRENGTH
PJP WELD NO TESTING REQUIRED PER D1.8 CLAUSE 4.3
Rweld= FULL SHEAR STRENGTH
Stiffeners and Doublers
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Shear In a Member • Exceptions at Chevron
y/2 MIN y Stiffeners and Doublers
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Shear In a Member • Exceptions at Chevron
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Doubler Extension
W-SHAPED BEAM
COLUMN
COLUMN
BOLTED FLANGE PLATE WIND AND LOW SEISMIC EXT = 2.5 kdes
(6" MAX)
COLUMN
DIRECTLY WELD CONNECTION WIND AND LOW SEISMIC EXT = 2.5 kdes
W-SHAPED BEAM
EXT
EXT
EXT
W-SHAPED BEAM
EXT
EXT
EXT
• Doubler Extension
(6" MAX)
Stiffeners and Doublers
END PLATE CONNECTION WIND AND LOW SEISMIC EXT = 3 kdes + t p
(6" MAX)
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Doubler Extension Seismic
W-SHAPED BEAM
COLUMN
EXT
W-SHAPED BEAM
EXT
W-SHAPED BEAM
EXT
EXT
EXT
EXT
• Doubler Extension
COLUMN
COLUMN
BOLTED FLANGE PLATE HIGH SEISMIC
WELDED FLANGE HIGH SEISMIC
END-PLATE CONNECTION HIGH SEISMIC
EXT = 6"
EXT = 6"
EXT = 6"
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Wind and Low Seismic • Doubler Termination
A
Size weld for 25% of stiffeners unbalanced force. See Design Guide 13
AISC minimum if no stiffeners
A Column Web Stiffener
Stiffener
Doubler Section A-A Stiffeners and Doublers
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High Seismic • Doubler Termination
A
Develop 75% of the shear yielding strength of doubler
Weld not required except if Eq E3-7 is not satisfied by both column web alone and doubler plate alone (to limit buckling of the doublers)
t
( d z wz ) 90
Eq. E3-7
A Column Web Stiffener
Stiffener
Doubler Section A-A Stiffeners and Doublers
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Continuous Doublers • Doubler Termination Size weld for 50% of the stiffeners unbalanced force A A
Column Web
E3.6f.2(c): Connect for lesser of: - Sum of stiffener tensile strength - Available shear strength of stiffener - Available shear strength of doubler Doubler
Stiffener AISC minimum if no stiffeners
Wind and Low Seismic
Stiffener Weld not required, Comm. E3, pg. 9.1-240
Section A-A High Seismic Stiffeners and Doublers
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Cost of Doublers • Rule of Thumb (Per Seismic Design Manual): Upsizing columns between 50 to 100 lb/ft might still be more cost effective than installing doubler plates and continuity plates. • Cost of Steel = $800/ton average (FOB mill) ($881 for plate) http://stld-cci.com/ • Platts S&P Global is also a good source for price of steel Size
Stiffeners and Doublers
WT/FT
Price/cwt*
*cwt=hundredweight:31 100 lbs Multiply by 20 for $/ton
Cost of Doublers – DG13 (1999)
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Cost of Doublers tST , TYP A
• • • •
LRFD, Grade 50 Plates W14x90 Column W24x55 Moment Connected Beams M = 350 kip-ft NOTES: – 1/2” stiffeners required – 1/2” doubler required
A
W24x55 BEAM
W24x55 BEAM
1. GR50 STEEL 2. 14 FT FLOOR-TO-FLOOR (#) tDB
• Upsize to W14x109 Column
COLUMN TYP. WW WW
– Stiffeners not required – 3/8” doubler required
COL. WEB
DOUBLER
TYP. WF WF
• Upsize to W14x193 – Stiffeners not required – Doubler not required
WW
STIFFENER
TYP
SECTION A
STIFFENERS
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Cost of Doublers Cost Comparison for Different Column Sizes
NOTES: 1. GR50 STEEL 2. 14 FT FLOOR-TO-FLOOR tST , TYP.
Stiffeners Column
A
Doublers
tST
Flange Weld WF
Web Weld WW
#
W14x90
1/2”
5/16”
5/16”
W14x90
1/2”
5/16”
W14x109
-
W14x109 W14x193
Cost Ratio
tDB
Doubler Weld WD
Weld Det.
1
1/2”
-
A
1.00
5/16”
1
1-1/2”
3/8”
B
0.75
-
-
1
3/8”
-
A
0.85
-
-
-
1
1-1/2”
5/16”
B
0.66
-
-
-
-
-
-
-
1.08
A
W24x55 BEAM
(#) tDB
W24x55 BEAM
COLUMN
OR
TYP.
20.0°
TYP.
DETAIL (A) GROOVE WELD
Stiffeners and Doublers
WD DETAIL (B) FILLET WELD
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Who Checks for Doublers? • Code of Standard Practice – 2005 and 2010 COSP Section 3.1.1 3.1.1 Permanent bracing, column stiffeners, column web doubler plates, bearing stiffeners in beams and girders, web reinforcement, openings for other trades and other special details, where required, shall be shown in sufficient detail in the Structural Design Drawings so that the quantity, detailing and fabrication requirements for these items can be readily understood.
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Who Checks for Doublers? • Code of Standard Practice – 2005 and 2010 COSP Section 1.1 1.1
In the absence of specific instructions to the contrary in the Contract Documents, the trade practices that are defined in this Code shall govern the fabrication and erection of the Structural Steel.
Stiffeners and Doublers
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Who Checks for Doublers?
TYP.
CJP
• Specific instructions to the contrary: – Contract documents can modify the COSP. For example, the Specification can indicate: “AISC’s COSP applies with the following modifications: Where reaction forces are given on the design drawings, Fabricator is responsible for designing stiffeners and/or doublers if necessary.”
CONTINUITY PLATES AS REQUIRED EACH SIDE OF COLUMN WEB TO MATCH THICKNESS OF BEAM FLANGES (SEE NOTE 1)
COLUMN
TYP.
PROVIDE WEB DOUBLER PLATES AS REQUIRED (SEE NOTE 1) NOTES: 1. PER THE PROVISIONS OF CHAPTER J OF THE AISC SPECIFICATIONS, PROVIDE COLUMN FLANGE STIFFENERS WHERE REQUIRED TO RESIST FORCES FROM MOMENT CONNECTIONS. PROVIDE COLUMN WEB DOUBLER PLATES AS REQUIRED FOR UNBALANCED MOMENT. ASSUME 20 KSI AXIAL STRESS IN COLUMNS FOR THE PANEL ZONE CHECKS
Stiffeners and Doublers
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Who Checks for Doublers? • Misleading Information: – Detail indicates stiffeners to be checked but not doubler – No loads given – No indication that Fabricator is to check for doublers on drawings or in Spec
Stiffeners and Doublers
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Who Checks for Doublers? • Current Code of Standard Practice – 2016 COSP (303-16) Section 3.1.2 » Option 3A: Member reinforcement (e.g. stiffeners, doubler, etc.) shall be designed by the owner’s designated representative and shown in the structural design documents issued for bid » Option 3B: Member reinforcement at connections is delegated design, but the quantities and conceptual configurations shall be provided and relied upon for bidding purposes. If no quantities or conceptual configurations are shown, member reinforcement at connections will not be included in the bid. Note: For Option 1 and 2, EOR designs stiffeners and doublers Stiffeners and Doublers
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Check for Doublers Determine Column Panel Zone Shear Strength • AISC Clean Column:
www.aisc.org/cleancolumn
Stiffeners and Doublers
40
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Doublers at Lateral Moment Connections - FBD Inflection point assumed at h/2
Pf1 = Mb1/db1
Pf1 +Pf2
Vc = ∑(Mb)/h Stiffeners if required
Vc
Pf2 = Mb2/db2
Mc Vp Mc
h
Panel Zone, Doublers if Required Vc
Vp = Panel Zone Shear = Pf1 + Pf2 - Vc
Vc
Shear
Moment
Stiffeners and Doublers
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Forces from 3D Analysis
Vc Mc
Mc Vc
Shear Stiffeners and Doublers
Moment 42
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Check for Doublers Determine Column Panel Zone Shear Strength • Must Have
P
– Beam Moments
• Best to Have – Break Down of Beam DL, LL, and Lateral Moments – Column Axial Load
Stiffeners and Doublers
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Deflected Shape
Joint moments Typ.
Lateral
Gravity
Stiffeners and Doublers
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Deflected Shape
Joint moments Typ.
Lateral
Gravity
Stiffeners and Doublers
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Moment Connections – Doublers • ∑M = 0 ∑(Mb) < ∑(Mc) • Sum of beam moments can not exceed sum of column moment strengths Vp max = Panel Zone Shear = 2(Mc)/db - 2(Mc)/h
Stiffeners and Doublers
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Moment Connections – Doublers • ∑M = 0 ∑(Mb) < Mc
Top of Column
• At top of column, sum of beam moments can not exceed column moment strength Vc max = Panel Zone Shear = Mc/db
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Moment Connections – Doublers • Add dead and lateral loads on both sides • Add live load on one side MD2 MLAT2
MD1 ML1 MLAT1
Stiffeners and Doublers
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Moment Connections – Doublers
Column Web Doublers Loading Criteria
% Columns Requiring Doublers
Full Moment Beam, Limited to Strength of Column
100%
Actual Moments Given with No Break Down
79%
Actual Moments Given with Break Down
26%
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Give Actual Loads
1 ½” Stiffeners on a W14x90 Column
Courtesy of Larry Muir and Bill Thornton
Stiffeners and Doublers
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Check for Doublers Determine Column Panel Zone Shear Strength, J10.6 0.9 1.67
• Elastic Range:
aPr 0.4 Py : R n 0.6 Fy d c tw aP aPr 0.4 Py : R n 0.6 Fy d c tw 1.4 r Py
Pr (J10-9)
(J10-10)
• Plastic Range:
3bc f tcf2 aPr 0.75 Py : R n 0.6 Fy d c t w 1 ddt b c w
2 3b t 1.2a Pr aPr .75 Py : R n 0.6 Fy d ct w 1 c f cf 1.9 d d t Py b c w
(J10-11)
(J10-12)
• http://risa.com/news/code-requirements-for-panel-zone-shear-deformation/ Stiffeners and Doublers
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Check for Doublers Determine Column Panel Zone Shear Strength • Force in Doubler Vdoubler = SPf –Vc –Rn Vdoubler = SPf –Vc–Rn/
LRFD ASD
Pf
• Size of Doubler
d
Pf
– AISC Specification Eq. G2-1 Use ”d” of column
Vn (0.6 Fy AwCv1 )
Vn (0.6 Fy AwCv1 )
Stiffeners and Doublers
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Check for Doublers Determine Column Panel Zone Shear Strength • Consider beam shear when beam frames into doubler Pf=M/dm
H=Vg (x)/ dm Vg
Vg
V=Pf (dm)/x1
Vg V=Pf (dm)/x1
0.5Vg
0.5Vg
H=Vg (x)/ dm Alternate 1 Distribution
M
x
x1
Pf=M/dm
Alternate 2 Distribution, DG13
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Doubler Web Buckling • Wind and Low Seismic Doublers: Minimum thickness to prevent shear buckling (Spec Section G2): h 2.24 E / Fy t
t =
h Fy
W-SHAPED BEAM
381
h d c 2 kdes t = thickness of web doubler Alternatively, use plug welds and the total thickness (t= thickness column web + thickness doublers) can be used COLUMN
Stiffeners and Doublers
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Doubler Web Buckling • DG13 is per 1993 Spec which = 0.9 versus = 1.0 in 2016 Spec for Shear
t
t
h Fy 418 127 Fy
W-SHAPED BEAM
1993 LRFD, Section F2 Engineering for Steel Construction, 1984 Based on 1978 Spec Section 1.18.2.3 for Compression of COLUMN
Built-up Members Stiffeners and Doublers
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Doubler Web Buckling • High Seismic Doublers wz
( d z wz ) 90 d z d b 2 tbf t
dz
W-SHAPED BEAM
wz d c 2 tcf Where: t = thickness of column web or individual doubler
COLUMN
Stiffeners and Doublers
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Doubler Web Buckling • High Seismic Doublers with plug welds ( d z wz ) 90
W-SHAPED BEAM
dz
t
wz
Where: t = thickness of column web + thickness of individual doublers
Stiffeners and Doublers
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Moment Connections • Consider load path and equilibrium
Panel Zone Shear
• Same depth beams at cantilevers with equal and opposite moments do not need to be checked for doublers Stiffeners and Doublers
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Stiffeners • Stiffener Plates
B
B A
Stiffeners
A Doublers Section A-A
Section B-B
Stiffeners and Doublers
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Stiffeners • Other Common Applications
Column Bearing on Beam
Beam over Top of Column
Stiffeners and Doublers
Chevron Connections
60
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Stiffeners • Other Common Applications
Stability (J10.7)
To Direct Force Stiffeners and Doublers
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Stiffeners • Stiffeners, Spec J10.8 B
3
twc 2
b
bf
twc
b
– Minimum thickness, t:
t
B
bf
– Minimum width, b:
tf
Section B-B
2 b t 16 Where: tf (thickness) and bf (width) are for the element delivering the force
Stiffeners and Doublers
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Stiffeners • Limiting Stiffener Slenderness – Minimum width, t > b/16:
Simply Supported
• For plates with one free edge: 2
t cr 0.769 Dx D y 0.270( Dxy D yx ) 1.712Gt b
Dx 8, 000 ksi D y 31, 000 ksi
bs
Fixed
Dxy 16, 000 ksi Gt 2, 400 ksi
x
cr 33 ksi bs 15.2 16 ts
Free
y
Simply Supported
cr
Reference: Welded Interior Beam-to-Column Connections, AISC
Stiffeners and Doublers
63
Stiffeners • Stiffeners, Seismic Provisions – Minimum width, b:
B
B
bf
t b wc 2 2
t
2 3t f 4
One sided connections Two sided connections
b
tf
twc
t
bf
– Minimum thickness, t:
Section B-B
Stiffeners and Doublers
64
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Stiffeners • Stiffeners – Minimum Length
ds
• AISC 360-16 Specification Section J10: – Transverse stiffeners shall extend a minimum of one-half the depth of the member except as required in Section J10.3 (WC)*, J10.5(WB), and J10.7(Unframed ends of beams not restrained against rotation about their longitudinal axis) *To satisfy web crippling strength, ½-depth stiffener increased to ¾-depth in the 15th Edition based on EJ 4th Qtr, 2015, Crippling of Webs with Partial-Depth Stiffeners under Patch Loading, by Salkar, et al
– Avoid welding stiffeners on 3-sides if possible, terminate at kdet for fabrication cost savings Stiffeners and Doublers
65
Stiffeners • Stiffeners – Designing Partial Depth Stiffeners
b' • Reference EJ 4th Qtr, 2015, “Crippling of Webs with PartialDepth Stiffeners under Patch Loading” by Salkar, et al
a' 15th
• Reference for brackets
Manual Ed, Fig 15-2
Stiffeners and Doublers
66
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Stiffeners • Stiffener Clips – Gravity, Wind, and Seismic R=3 • Stiffeners should clear kdet and k1 • k-area (1-1/2” from k) is area of potentially lower notch toughness in rotarystraightened W-Shapes, see Commentary J10.8
Fig C-J10.8: Recommended placement of stiffener fillet welds to avoid contact with “k-area”
• Tests show a corner clip of 1-1/2” with fillets stopped short by (1) weld size can avoid this problem Fig C-J10.7:
Can reduce to ¾” at flanges for additional weld length
Representative “k-area” of wide-flange shape
67
Stiffeners • Seismic Stiffener clips – Seismic Provisions: • Reference AWS D1.8/D1.8M, Clause 4.1 – At web: Extend 1-1/2” min beyond kdet – At flange: Not to exceed 1/2” beyond k1 – Shall facilitate suitable weld termination – If curved, r = 1/2” min • Welding in the k-area should be avoided
Stiffeners and Doublers
AISC’s Seismic Provisions, Fig C-D2.3:
68
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Stiffeners/Continuity Plates • Flange Welds – AISC Specification Section J10.8 • Welds to be sized for the difference between the required strength and available strength.
FILLET
S (E)
– AISC’s Seismic Provision • Shall be CJP Welded per E3.6f2(c)
PJP
CJP
Stiffeners and Doublers
69
Stiffeners/Continuity Plates • Web Welds – Design Guide 13 • Weld for unbalanced stiffener force – AISC’s Seismic Provision • E3.6f.2(c): Connect for lesser of: - Sum of stiffener tensile strength at column flanges - Available shear strength of stiffener at column web - Available shear strength of column web (or doubler if doubler extended)
Stiffeners and Doublers
FILLET
S (E)
PJP
CJP
70
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Stiffeners/Continuity Plates • Stiffener Design – AISC Specification Chapter J Pstiffener = Pf – minimum Rn Pstiffener = Pf – minimum Rn/
LRFD ASD W-SHAPED BEAM
Rn is the minimum nominal strength for the applicable limit states – If kl/r < 25, yielding (k = 0.75) (J4.4) If kl/r > 25, see Spec Chapter E
COLUMN
Stiffeners and Doublers
71
Stiffener Design • Flange Local Bending – AISC Specification Section J10.1, Eq. J10-1
Load width
Rn 6.25 Fyf t 2f 0.90 (LRFD)
1.67 (ASD)
– Applicable to tension load only – Not applicable if load width is less than 0.15bf – Reduce Rn by 50% if force is applied less than 10tfc from end of column Stiffeners and Doublers
See Blodgett 5.7-8
72
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– AISC Specification Section J10.2
2.5
5kdes+lb
1
• Web Local Yielding Rn Fywtw 5kdes lb
lb
Stiffeners
Spec Equation J10-2 k des
Rn Fywtw 2.5kdes lb Spec Equation J10-3, Force d from end of column 1.50 (ASD)
lb = bearing length, in.
W14x90 COL
1.00 (LRFD)
W24x55 BEAM
d Stiffeners and Doublers
73
Stiffeners • Web Local Crippling – AISC Specification Section J10.3
l Rn 0.80t 1 3 b d
tw tf
l Rn 0.40t 1 3 b d 4l Rn 0.40t w2 1 b d 0.75 (LRFD)
tw tf
2 w
2 w
1.5
EF t yw f Qf tw
1.5
EF t yw f Qf tw 1.5 EF t t yw f 0.2 w Qf t t f w 2.00 (ASD)
Spec Equation J10-4, Force applied distance > d/2 from end of member Spec Equation J10-5a, Force applied distance < d/2 from end of member, lb/d<0.2 Spec Equation J10-5b, Force applied distance < d/2 from end of member, lb/d>0.2 See Section J10.3 for Qf definition
Stiffeners and Doublers
74
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Stiffeners • Web Compression Buckling – AISC Specification Section J10.5, Eq. J10-8
Rn
24tw3 EFyw
0.90 (LRFD)
h
Qf
1.67 (ASD)
– Reduce Rn by 50% if force is applied less than d/2 from end of column
W24x55 BEAM
Stiffeners and Doublers
W14x90 COL
– Applicable to double-concentrated forces at the same location
W24x55 BEAM
75
Stiffeners • Web Compression Buckling – Equation J10.8 developed from point loads and restrained flanges – If lb/d > approximately 1, Use Chapter E – See Chapter C and Appendix 6 for Stability
Test Set-up from Chen and Oppenheim 1970
Stiffeners and Doublers
See Spec Appendix Section 6.2.2 for point bracing (nodal bracing) required strength and stiffness
76
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Stiffeners/Continuity Plates • Stiffener Design – AISC’s Seismic Provision • Also Required if tcf < bbf/6
Eq (E3-8) W-SHAPED BEAM
COLUMN
Stiffeners and Doublers
77
Stiffener Eccentricity • DG13 which references testing by Graham, et al (1959), indicates stiffeners with 2” eccentricity, e, are 65% effective, reduced linearly: Rn_emax = 0.65 Rn
Stiffeners and Doublers
e
• Further research discussed for eccentric stiffeners
e
• Can slope stiffener if stiffener not needed for beam-to-column web moment connection
e = 2" MAX
78
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Web Sidesway Buckling – Beams • Web Sidesway Buckling (J10.4) – AISC Specification Eq. J10-6 and J10-7 3 Equation J10-6, h / tw Cr t w3 t f Compression Flange Rn 1 0.4 L /b h2 restrained, applicable if b f (h/tw)/(Lb/bf)<2.3
Cr t w3 t f h / t w 0.4 Rn h 2 Lb / b f
3
Equation J10-7, Compression Flange not restrained, applicable if (h/tw)/(Lb/bf)<1.7 AISC Commentary, Fig.C-J10.2 Web sidesway buckling
0.85 (LRFD) 1.76 (ASD) • Compression flange braced, tension flange unbraced • Lb = largest laterally unbraced section along either flange at the point of load. Stiffeners and Doublers
79
tst
Web Buckling - Girders tw
• Additional Stiffener Requirements for Beam and Girder Flange(s) – AISC Specification Section J10.8
beff =25tw AT
• Check web and stiffeners as column section with kl = 0.75h (see Spec Sections
E6.2, J4.4)
INTERIOR
tst
A
tw
A
• beff = 25 tw at interior 12 tw at ends of members
– For fabrication cost savings, fit one side of stiffener to bear at flange and transfer force at opposite end of stiffener by weld Stiffeners and Doublers
beff =12tw AT EXTERIOR Section A-A 80
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Stiffener & Doubler Example • Given: – Distance to end of column much larger than column depth – W Shapes ASTM A992, Fy = 50 ksi
-
Plates Grade 50, Fy = 50 ksi AISC Specification 360-16 AISC 15th Edition, LRFD ASCE 7-10 R= 3 Wind determined not to control
MD1 = 130 kip-ft
MD1 ML1 ME1 W27x94
W14x176
ML1 = 220 kip-ft ME1 = 690 kip-ft MD2 ML2 ME2 W27x94
MD2 = 130 kip-ft ML2 = 220 kip-ft ME2 = 690 kip-ft 81
Stiffeners and Doublers
Stiffener & Doubler Example • Find: – Check if stiffeners are required. If required, size the stiffeners. – Check if doublers are required. If required, size the doublers.
W14x176
Stiffeners if required
W27x94
W27x94
Panel Zone, Doubler if Required 82 Stiffeners and Doublers
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Stiffener & Doubler Example • Solution: – 1. ASCE 7-10, Load Combinations for Strength Design
1. 1.4D 2. 1.2D + 1.6L + 0.5(Lr or S or R)
= 182 kip-ft = 508 kip-ft
3. 1.2D + 1.6(Lr or S or R) + (L or 0.5W) 4. 1.2D + 1.0W + L + 0.5(Lr or S or R)
= 376 kip-ft = 376 kip-ft
5. 1.2D + 1.0E + L + 0.2S 6. 0.9D + 1.0W
= 1070 kip-ft = 117 kip-ft
7. 0.9D + 1.0E
= 807 kip-ft
MD1 = 130 kip-ft ML1 = 220 kip-ft ME1 = 690 kip-ft MD2 = 130 kip-ft ML2 = 220 kip-ft ME2 = 690 kip-ft
Governing Load Combination: 5. 1.2D + 1.0E + L + 0.2S M1 = M2 = 1.2(130 kip-ft) + 1.0 (690 kip-ft) + 1.0(220 kip-ft) = 1070 kip-ft 83 Stiffeners and Doublers
Stiffener & Doubler Example • Solution: – 2. Determine Each Beam’s Flange Force
Mu d t pl
Pfl
Mu d t fb
Pfl1
Pfl2
Flange Plate
Directly welded W27x94 BEAM
W14x176 COL
Pfl
W27x94 BEAM
84 Stiffeners and Doublers
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Stiffener & Doubler Example • Solution: – 2. Determine Each Beam’s Flange Force
M1 d b tf b 1070 kip-ft 26.9in. - 0.745 in. 491kips
W27x94 BEAM
Pfl2
W14x176 COL
Pfl1
Pfl Pfl 1 Pfl 2
W27x94 BEAM
85 Stiffeners and Doublers
Stiffener & Doubler Example • Solution: – 3. Check Stiffener Limit States • Web Local Yielding (J10.2)
1.00
– AISC Specification Eq. J10-2
Rwy Fywtwc 5kdesc lb 427 kips < Pfl 491kips n.g. Stiffeners Required
W27x94 BEAM
W14x176 COL
1.00 50 ksi 0.830 in. 5 1.91in. 0.745in. W27x94 BEAM
Note : lb t fb
86 Stiffeners and Doublers
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Stiffener & Doubler Example • Solution: – 3. Check Stiffener Limit States • Web Local Crippling (J10.3)
0.75
– AISC Specification Eq. J10-4
Rwc
1.5 lb t wc EFyc t fc 0.80t 1 3 t wc dc t fc 1.5 0.745in. 0.830 in. 2 0.75(0.80) 0.830 in. 1 3 15.2 in. 1.31 in. 2 wc
29000 ksi 50 ksi 1.31in. 0.830in.
672 kips Pfl 491kips o.k.
Note : lb t fb 87 Stiffeners and Doublers
Stiffener & Doubler Example • Solution: – 3. Check Stiffener Limit States • Web Compression Buckling (J10.5)
0.90
– AISC Specification Eq. J10-8
Rwb
24t w3 c EFyc
(0.90)
h
W14x176 COL
h dc 2kdesc 15.2in. 2 1.91in. 11.4 in. Qf
24 0.83in.
3
29000 ksi 50 ksi
11.4 in. 1305 kips Pfl 491kips o.k.
(1.0)
W27x94 BEAM
W27x94 BEAM
88 Stiffeners and Doublers
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Stiffener & Doubler Example • Solution: – 3. Check Stiffener Limit States • Flange Local Bending (J10.1)
0.90
– AISC Specification Eq. J10-1
R fb 6.25 Fyc t 2fc 0.90 6.25 50 ksi 1.31in.
2
483 kips < Pfl 491kips n.g. Stiffeners Required
See Blodgett 5.7-8
89 Stiffeners and Doublers
Use of Manual Tables • Web Local Yielding
1.00
– AISC 15th Edition Manual Eq. 4-2a
396 41.5 1310 483 Rn Pwo Pwilb kips 396 kips 41.5 0.745in. in. 427 kips Pfl 491kips n.g. Stiffeners Required
90 Stiffeners and Doublers
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Use of Manual Tables • Web Local Crippling
0.75
– AISC 15th Edition Manual Eq. 9-50a
Rn 2 R3 lb R4 kips 2 313kips 0.745in. 31.1 in. 672 kips Pfl 491kips o.k.
91 Stiffeners and Doublers
Use of Manual Tables 0.90
• Web Compression Buckling
– AISC 15th Edition Manual Eq. 4-3a
396 41.5 1310 483
Rn Pwb 1310 kips Pfl 491kips o.k.
92 Stiffeners and Doublers
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Use of Manual Tables • Flange Local Bending
0.90
– AISC 15th Edition Manual Eq. 4-4a
396 41.5 1310 483
Rn Pfb 483 kips Pfl 491kips n.g. Stiffeners Required
93 Stiffeners and Doublers
Stiffener & Doubler Example
lst
• Solution:
bst
– 4. Column Stiffener Design • Determine Force in the Stiffeners
Pst1tot Pst 2tot Pfl min(Rwy , Rwc , Rwb , Rfb) 491 kips 427 kips
Snip
= 64 kips • Determine Beam Force Per Each Stiffener
Pst 1 0.5( Pst1tot ) 0.5(64 kips) = 32 kips Pst 2 0.5( Pst 2tot ) 0.5(64 kips) = 32 kips
94 Stiffeners and Doublers
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Stiffener & Doubler Example • Solution:
bst
– 4. Column Stiffener Design • Determine Minimum Stiffener Width per AISC’s Specification, Section J10.8
Snip
bfb twc 10 in. 0.83 in. 2.92in. Min. (See Note below) 3 2 3 2 bfc twc 15.7 in. 0.830 in. bst max 7.44in. Max 2 2 bst min
Use bst = 7" Stiffener *Note: Use bpl in lieu of b fb if moment connection plate delivering the load 95 Stiffeners and Doublers
Stiffener & Doubler Example • Solution:
bst
– 4. Column Stiffener Design • Determine Minimum Stiffener Thickness per AISC’s Specification, Section J10.8
tst min
bst 7 in. 0.438in. 16 16
tst min
tfb 0.745 in. 0.373 in. 2 2
Snip
Controls (See Note below)
• Try a 1/2” Stiffener
*Note: Use t pl in lieu of t fb if moment connection plate delivering the load 96 Stiffeners and Doublers
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Stiffener & Doubler Example
lst
• Solution: • Check Minimum Thickness Due to Tension Yielding – AISC Specification Section J10.8
snip max(k det c tfc, k 1c
twc ,1.5 in.) 2
max(2.625 in. 1.31 in., 1.625 in.
bst
– 4. Column Stiffener Design Snip
0.83 in. ,1.5 in.) 2
1.5 in. Pst Fyp (bst snip ) 32 kips 0.90(50 ksi)(7 in. 1.5 in.) = 0.129 in. 0.5 in. o.k.
tst min
*Note: Can reduce snip at flange if needed. 97
Stiffeners and Doublers
Stiffener & Doubler Example – 4. Column Stiffener Design • Check Minimum Thickness Due to Compression Buckling – AISC Specification Section J10.8 and E3 0.90
bst
lst
• Solution:
lst dc 2tfc 15.2 in. 2(1.31 in.) = 12.6 in. k 0.75 kl klst 12 0.75(12.6 in.) 12 65.5 r tst (0.5 in.) Limit 4.71 Fe
2 E
r kl
2
E 29,000 ksi 4.71 113 Fyp 50 ksi π 2 (29,000 ksi)
65.5
2
66.6 ksi 98
Stiffeners and Doublers
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Stiffener & Doubler Example – 4. Column Stiffener Design • Check Minimum Thickness Due to Compression Buckling – AISC Specification Section E3 0.90 50 ksi Fyp Fcr 0.658 Fe Fyp 0.658 66.6 ksi 50 ksi 36.5 ksi Fcr 0.90(36.5 ksi) = 32.9 ksi
bst
lst
• Solution:
(E3-2)
Rearrange Pn FcrAg to Solve for tst min (E3-1) Pst tst min Fcr (bst ) *Note: Buckling limit state included for example purposes. 32 kips (32.9 ksi)(7 in.) = 0.139 in. 0.5 in. o.k. 99
Stiffeners and Doublers
Use of Manual Tables – AISC Manual Table 4-14: KL/r Table 65 22.0 33.0 66 21.8 32.7
Stiffeners and Doublers
100
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Stiffener & Doubler Example • Solution:
Lwf
– 4. Column Stiffener Design • Weld Design of Stiffener to Column – AISC Specification Section J2
Lww
Snip
Lww lst 2 snip 12.6 in. - (2)1.5 in. = 9.6 in. Lwf bst snip 7 in. - 1.5 in. = 5.5 in.
0.928 ASD 1.392 LRFD D min fl
Pst 32 kips = 1.39 (16th of an inch) (2) Lwf (1.5) 1.392(2)(5.5 in.)(1.5) 1/4” Fillet Weld o.k. 101 Stiffeners and Doublers
Stiffener & Doubler Example • Solution: – 4. Column Stiffener Design
Note : 0.928 D (0.6)( Fexx )(0.707)( w) /
w D (0.60)(70 ksi)(0.707) / 2 0.928 D 16 D 1.392 D (0.6)( Fexx )(0.707)( w) 16 w D (0.60)(70 ksi)(0.707) (0.75) 1.392 D 16 1.5 1.0 0.5(sin())1.5 1 0.5(sin(90))1.5 1.5
Reference Spec Eq (J2 - 5) 102
Stiffeners and Doublers
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Stiffener & Doubler Example • Solution: – 5. Determine Flange Forces for Column Doubler Checks • Based on ASCE 7 Load Cases • Determine sum of flange forces for each load load combination. Consider symmetric gravity moments and pattern loading if applicable
ASCE 7-10 1. 1.4D
MD1 = 130 kip-ft
2. 1.2D + 1.6L + 0.5(Lr or S or R)
ML1 = 220 kip-ft ME1 = 690 kip-ft
3. 1.2D + 1.6(Lr or S or R) + (L or 0.5W ) 4. 1.2D + 1.0W + L + 0.5(Lr or S or R )
MD2 = 130 kip-ft
5. 1.2D + 1.0E + L + 0.2S 6. 0.9D + 1.0W
ML2 = 220 kip-ft ME2 = 690 kip-ft
7. 0.9D + 1.0E 103 Stiffeners and Doublers
Stiffener & Doubler Example • Solution: – 5. Determine Flange Forces for Column Doubler Checks • Determine Critical Load Combination:
Governing Load Combination 5: M 1_ 5 = 1.2(130 k-ft) + 1.0 (690 k-ft) + 1.0(220 k-ft) = 1070 kip-ft M 2_ 5 = 1.2(-130 k-ft) + 1.0 (690 k-ft) = 534 kip-ft
MD1 = 130 kip-ft
Pfl1_ 5
M1 1070 kip-ft 491 kip db1 tfb1 26.9 in. - 0.745 in.
ML1 = 220 kip-ft ME1 = 690 kip-ft
Pfl 2 _ 5
M2 534 kip-ft 245 kip (Stiffener not required) db 2 tfb 2 26.9 in. - 0.745 in.
MD2 = 130 kip-ft
Pfd Pfl1_ 5 Pfl 2 _ 5 491 kips 245 kips 736 kips
ML2 = 220 kip-ft ME2 = 690 kip-ft 104
Stiffeners and Doublers
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Stiffener & Doubler Example • Solution: – 5. Determine Flange Forces for Column Doubler Checks • Confirm column strength does not control:
SM b = M 1_ 5 +M 2 _ 5 = 1070 kip-ft + 534 kip-ft = 1604 kip-ft 0.9(320 in.3 )(50 ksi) = 1200 kip - ft 12in. / ft = 1200 kip-ft + 1200 kip-ft = 2400 kip-ft
M nc ( Z xc )( Fyc ) SM c = M c _ t +M c _ b
SM b = 1604 kip-ft < SM c 2400 kip-ft
Beams Control
105 Stiffeners and Doublers
Stiffener & Doubler Example • Solution: – 6. Determine Panel Zone Shear Reduction Due to Column Shear
Pfd
Vc
hcol 15 ft M M2 Vc 1 hcol 1070 kip - ft + 534 kip - ft 15 ft 107 kips
Vc Pfd1 M1
M2
h
Vp Pfd Vc 736 kips 107 kips 629 kips
Pfd2
Vc
Vp
Vc Shear 106 Stiffeners and Doublers
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Stiffener & Doubler Example • Solution: – 7. Column Doubler Check
0.90
ᶲRn
• Web Panel Zone Shear Strength – AISC Specification Section J10.6
a 1.0 (LRFD); 1.6 (ASD) W27x94 BEAM
aPr (1.0)870 kips = 870 kips LRFD
W27x94 BEAM
Py Fyc Agc (50 ksi)(51.8 in.2 ) 2590 kips aPr (1.0)870 kips 0.336 0.4 Py 2590 kips
W14x176 COL
Since aPr 0.4 Py : R n 0.6 Fy d ct w
(J10-9) 107
Stiffeners and Doublers
Stiffener & Doubler Example • Solution: – 7. Column Doubler Check
0.90
ᶲRn
• Web Panel Zone Shear Strength – AISC Specification Section J10.6
Rn 0.6 Fywt wc dc W27x94 BEAM
0.90(0.6)(50 ksi)(0.830 in.)(15.2 in.)
W27x94 BEAM
341 kips W14x176 COL
Vp 629 kips > Rn 341 kips
n.g.
Doubler Required Stiffeners are not required
108 Stiffeners and Doublers
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Stiffener & Doubler Example • Solution: Vd
– 7. Determine Doubler Shear Force
Vd Vp Rn 629 kips 341 kips 288 kips Number of Doublers, nd = 1
W27x94 BEAM
Panel Zone, Doubler Required
W27x94 BEAM
W14x176 COL
109 Stiffeners and Doublers
Stiffener & Doubler Example • Solution: – 8. Column Doubler Design • Minimum Doubler Thickness to prevent Shear Buckling – AISC Specification Section G2.1
For, Cv = 1.0
td min 1
h 2.24
Fyp dc 2kd esc E 2.24
Fyp 15.2 in. 2(1.91in.) 50 ksi 0.211 in. E 2.24 29, 000 ksi
110 Stiffeners and Doublers
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Stiffener & Doubler Example • Solution: – 8. Column Doubler Design • Doubler Thickness Due to Panel Zone Shear – AISC Specification Equation G2-1
1.00
Vd (Cv ) (0.6)( Fyp )(dc )( nd ) 288 kips(1.0) (1.00)(0.6)(50 ksi )(15.2 in.)(1) 0.632 in.
td min 2
111 Stiffeners and Doublers
Stiffener & Doubler Example • Solution: – 8. Column Doubler Design • Doubler Vertical Edge Thickness Due to Beam-to-Column Web Shear Connection, Reference AISC’s Spec Equation J4-3
td min 3
1.00
0.5Vconn ' x (0.6)( Fyp )( Ld )
0.5(0 kips) 0.0 in. 1.00(0.6)(50 ksi)(26.9 in. - 0.745 in. - 0.5 in.) Where : Ld length of doubler db tfb ts
td min 3
td
min
Vconn’x
= max(td min 1, td min 2 td min 3) = max (0.211 in., 0.632 in. + 0 in.) = 0.632 in.
Use (1) PL 3/4" or (2) PL 3/8"
112
Stiffeners and Doublers
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Stiffener & Doubler Example • Solution: – 8. Column Doubler Design
1.00 Lwf
• Doubler Horizontal Edge Thickness Due to Unbalanced Stiffener Force
Pst 1 Pst 2 td min 4 (0.6)( Fyp )( Lww )(2)
Lww
Ref Spec Eq (J4-3) Snip Pst2
Pst1
32 kips + 0 kips (1.00)(0.6)(50 ksi)(9.6 in.)(2) 0.056 in. < 3/4" o.k.
113 Stiffeners and Doublers
Stiffener & Doubler Example – 8. Column Stiffener Thickness for Shear
1.00
• Check Minimum Thickness Due to Unbalanced Stiffener Force
bst
lst
• Solution:
Snip
Rearrange Rn 0.6 FypAgv to Solve for tst min
Ref (J4-3)
Pst 1 Pst 2 (0.6) Fyp (lst 2( snip)) 32 kips 0 kips 1.00(0.6)(50 ksi)(12.6 in. 2(1.5 in.)) = 0.111 in. 0.5 in. o.k.
tst min
114 Stiffeners and Doublers
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Stiffener & Doubler Example – 8. Column Stiffener Weld • Stiffener Weld to Doubler Horizontal Edge and Column Web for unbalanced stiffener force Snip
Lwf
• Solution:
Lww
Lww lst 2 snip 12.6 in. - (2)1.5 in. = 9.6 in. 0.928 ASD 1.392 LRFD
DOUBLER
Pst 1 Pst 2 (2)( Lww) 32 kips+ 0 kips 1.392(2)(9.6 in.) = 1.20 (16th of an inch)
COL. WEB
1/4
D min web
STIFFENER
1/4
TYP
< 4 (16th of an inch), use 1/4” Fillet Weld o.k. 115
Stiffeners and Doublers
Stiffener & Doubler Example • Solution:
Lwf
– 8. Column Stiffener Thickness – Weld Design of Stiffener to Column – AISC Specification Section J2
Lww
Snip
Check plate and column web thicknesses for weld size
0.75
tst min
(2)( D min) 1.392(2)(1.20) 0.114 in. (0.6) Fup 0.75(0.6)(65 ksi)
< tst = 0.5 in. o.k.
twc min
(2)( D min) 1.392(2)(1.20) 0.114 in. (0.6) Fuc 0.75(0.6)(65 ksi)
< twc = 0.83 in. o.k.
116 Stiffeners and Doublers
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Stiffener & Doubler Example • Solution: 1/4 TYP 1/4
– 9. Summary DOUBLER
DOUBLER MAY ENCROACH INTO COLUMN FILLET
COL. WEB
1/4 STIFFENER
1/4 SECTION A
TYP
SECTION B
a PL 3/4" DOUBLER B
B W27x94
1/2" STIFFENER PL NS/FS W27x94
A A W14x176 COLUMN
117
Stiffeners and Doublers
Conclusion • Doublers are required to resist shear forces exceeding the panel zone shear strength • AWS D1.8/D1.8M: 2016 has a prequalified doubler weld configuration • Sufficient information is needed to check for web doublers • Increasing the column size to eliminate stiffeners and doublers can be cost effective • Stiffeners (also known as continuity plates) are required to resist applied loads greater than the local strength of the supporting member • Stiffener applicable limit states are in Specification Section J10
Stiffeners and Doublers
118
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Questions?
119
PDH Certificates Within 2 business days… • You will receive an email on how to report attendance from: [email protected]. • Be on the lookout: Check your spam filter! Check your junk folder! • Completely fill out online form. Don’t forget to check the boxes next to each attendee’s name!
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PDH Certificates Within 2 business days… • Reporting site (URL will be provided in the forthcoming email). • Username: Same as AISC website username. • Password: Same as AISC website password.
Thank You Please give us your feedback! Survey at conclusion of webinar.
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