1
AISC Night SchoolNovember 23, 2015
Application of the AISC Seismic Design ManualSession 8: Buckling Restrained Braced Frames
and Quality Requirements
Copyright © 2015American Institute of Steel Construction
AISC Night School – Seismic Design Manual
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AISC Night School – Seismic Design Manual
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2
AISC Night SchoolNovember 23, 2015
Application of the AISC Seismic Design ManualSession 8: Buckling Restrained Braced Frames
and Quality Requirements
Copyright © 2015American Institute of Steel Construction
AISC Night School – Seismic Design Manual
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AISC Night School – Seismic Design Manual
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3
AISC Night SchoolNovember 23, 2015
Application of the AISC Seismic Design ManualSession 8: Buckling Restrained Braced Frames
and Quality Requirements
Copyright © 2015American Institute of Steel Construction
AISC Night School – Seismic Design Manual
Copyright Materials
This presentation is protected by US and International Copyright laws. Reproduction, distribution,display and use of the presentation without written permission of AISC is prohibited.
© The American Institute of Steel Construction 2015
The information presented herein is based on recognized engineering principles and is for generalinformation only. While it is believed to be accurate, this information should not be applied to anyspecific application without competent professional examination and verification by a licensedprofessional engineer. Anyone making use of this information assumes all liability arising fromsuch use.
AISC Night School – Seismic Design Manual
Session 8: Buckling Restrained Braced Frames and Quality RequirementsNovember 23, 2015
Course Description
This session will define buckling-restrained braced frames and provide an overview of the design and test requirements per the AISC Seismic Provisions. A design example will be presented as part of the lecture. The session will then discuss Quality Control and Quality Assurance requirements per the Seismic Provisions.
4
AISC Night SchoolNovember 23, 2015
Application of the AISC Seismic Design ManualSession 8: Buckling Restrained Braced Frames
and Quality Requirements
Copyright © 2015American Institute of Steel Construction
AISC Night School – Seismic Design Manual
• Become familiar with the basis of buckling restrained brace frame(BRBF) design.• Gain an understanding of the differences between BRBF and typical concentrically
braced frames.• Gain an understanding of the BRBF system and connection requirements per the
AISC Seismic Provisions.• Become familiar with the Quality Control and Quality Assurance requirements per
chapter J of the AISC Seismic Provisions.
Learning Objectives
AISC Night School – Seismic Design Manual8
Presented by Thomas A. Sabol, Ph.D., S.E.Principal at Englekirk InstitutionalLos Angeles, CA
Application of the AISC Seismic Design ManualSession 8: Buckling Restrained Braced Braced Frames and Quality Requirements
5
AISC Night SchoolNovember 23, 2015
Application of the AISC Seismic Design ManualSession 8: Buckling Restrained Braced Frames
and Quality Requirements
Copyright © 2015American Institute of Steel Construction
AISC Night School – Seismic Design Manual
Chapter E
9
Application of the
AISC Seismic Design Manual
Session 8
AISC Night School – Seismic Design Manual10
Last Session• Special Concentrically Braced Frames
• Examples from the Seismic Design Manual
6
AISC Night SchoolNovember 23, 2015
Application of the AISC Seismic Design ManualSession 8: Buckling Restrained Braced Frames
and Quality Requirements
Copyright © 2015American Institute of Steel Construction
AISC Night School – Seismic Design Manual11
F4 Buckling-Restrained Braced Frame (BRBF)
Basis of Design
Specially fabricated braces connected concentrically to beams and columns
Eccentricities less than beam depth OK if considered in design and do not change source of inelastic deformation
AISC Night School – Seismic Design Manual
Chapter F
12
F4.2 BRBF – Basis of Design
BRBF are expected to withstand significant inelastic deformation (R = 8) in the links when subjected to the design earthquake.
Bracing members shall be composed of a structural core and a system that retrains steel core from buckling
7
AISC Night SchoolNovember 23, 2015
Application of the AISC Seismic Design ManualSession 8: Buckling Restrained Braced Frames
and Quality Requirements
Copyright © 2015American Institute of Steel Construction
AISC Night School – Seismic Design Manual13
F4.2 BRBF – Basis of Design
Braces shall be designed, tested and detailed to accommodate expected deformations
Expected deformations are minimum 2% story drift or 2 x (design story drift), whichever is larger, in addition to brace deformations
BRBF to be designed so that inelastic deformations under design earthquake occur as brace yielding in compression or tension
AISC Night School – Seismic Design Manual14
F4.2 BRBF – Basis of Design
Typical brace behavior is asymmetric with respect to tension and compression and is subject to strength and stiffness degradation
Tension
CompressionPcr
Ry Ag Fy
P
Conventional brace behavior
8
AISC Night SchoolNovember 23, 2015
Application of the AISC Seismic Design ManualSession 8: Buckling Restrained Braced Frames
and Quality Requirements
Copyright © 2015American Institute of Steel Construction
AISC Night School – Seismic Design Manual15
F4.2 BRBF – Basis of Design
Balanced Hysteresis(Performance Definition)
Compression buckling of limited capacity tension member is resisted by “sleeve”
“Sleeve”
Compression and tension performance are nearly identical
P
Δ
β Ag Fy
Ag Fy
AISC Night School – Seismic Design Manual16
F4.2 BRBF – Basis of Design
Advantages of BRBFBalanced Hysteresis
Slightly Stronger in Compression
Hysteretic Energy Dissipation
Hysteretic Stability Strength
Stiffness
Long Fracture Life
Ag Fy
β Ag Fy
9
AISC Night SchoolNovember 23, 2015
Application of the AISC Seismic Design ManualSession 8: Buckling Restrained Braced Frames
and Quality Requirements
Copyright © 2015American Institute of Steel Construction
AISC Night School – Seismic Design Manual
Chapter F
17
F4.2 BRBF – Basis of Design
Performance Advantages of BRBFStory Mechanisms Uncommon Fine-Tuning of Sizes
No Story Degradation
Distributed Yielding
Reduced Drift
No Chevron Problems
AISC Night School – Seismic Design Manual
Chapter F
18
F4.2 BRBF – Basis of Design
Steel core shall be designed to resist entire axial force in the brace
Buckling-Restrained Brace Assembly
Core
Sleeve
+
=
10
AISC Night SchoolNovember 23, 2015
Application of the AISC Seismic Design ManualSession 8: Buckling Restrained Braced Frames
and Quality Requirements
Copyright © 2015American Institute of Steel Construction
AISC Night School – Seismic Design Manual
Chapter F
19
F4.2 BRBF – Basis of Design
Unbonded Brace Type
Decoupling
Yielding steel core
Unbonding material between steel core and mortar
BucklingRestraint
Encasing mortar
Steel tube
AISC Night School – Seismic Design Manual20
F4.2 BRBF – Basis of Design – Brace Design
Adjusted brace strength in compression: βωRyPysc
Where: β = compression adjustment factor
ω = strain hardening adjustment factor
Pysc = axial yield strength of steel core
Adjusted brace strength in tension: ωRyPysc
Note: Ry need not be applied if Pysc established using coupon tests
11
AISC Night SchoolNovember 23, 2015
Application of the AISC Seismic Design ManualSession 8: Buckling Restrained Braced Frames
and Quality Requirements
Copyright © 2015American Institute of Steel Construction
AISC Night School – Seismic Design Manual
Chapter F
21
F4.2 BRBF – Basis of Design – Brace DesignCompression stress adjustment factor, β, shall be
calculated as ratio of maximum compression force to maximum tension force of test specimen per Section K3.4c
In no case shall β < 1.0
AISC Night School – Seismic Design Manual
Chapter F
22
F4.2 BRBF – Basis of Design – Brace DesignStrain hardening adjustment factor, ω, shall be
calculated as ratio of maximum tension force per Section K3.4c (for expected deformations) to measured yield force RyPysc
Where core material does not match prototype, ωshall be based on coupon test
12
AISC Night SchoolNovember 23, 2015
Application of the AISC Seismic Design ManualSession 8: Buckling Restrained Braced Frames
and Quality Requirements
Copyright © 2015American Institute of Steel Construction
AISC Night School – Seismic Design Manual
Chapter F
23
F4.3 BRBF – AnalysisBRBF braces shall not be considered to resist
gravity forces
Required strength of columns based on load combinations including amplified seismic load
For amplified seismic load: effect of horizontal forces including overstrength Emh shall assume all braces achieve adjusted tension or compression strength
AISC Night School – Seismic Design Manual
Chapter F
24
F4.3 BRBF – AnalysisBraces shall be classified as in either tension or
compression ignoring gravity loads
Analyses shall consider both directions of seismic loading
13
AISC Night SchoolNovember 23, 2015
Application of the AISC Seismic Design ManualSession 8: Buckling Restrained Braced Frames
and Quality Requirements
Copyright © 2015American Institute of Steel Construction
AISC Night School – Seismic Design Manual25
F4.3 BRBF – AnalysisExceptions:
May neglect flexural forces from seismic drift, but moment from load applied to the column between points of lateral support must be considered
Required strength of columns need not exceed lesser of
• Forces from foundation uplift
• Forces from nonlinear analysis per Section C3.
AISC Night School – Seismic Design Manual
Chapter F
26
F4.4 BRBF – System RequirementsV- and Inverted V-Braced Frames
Required strength of beams, connections and supporting members shall be determined assuming braces support no gravity loads
Vertical load effect on beam shall be determined using adjusted brace strength
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AISC Night SchoolNovember 23, 2015
Application of the AISC Seismic Design ManualSession 8: Buckling Restrained Braced Frames
and Quality Requirements
Copyright © 2015American Institute of Steel Construction
AISC Night School – Seismic Design Manual
Chapter F
27
F4.4 BRBF – System RequirementsV- and Inverted V-Braced Frames
Beams shall be continuous between columns and braced per moderately ductile requirements in Section D1.2(a)
See discussion of SCBF bracing requirements
For purposes of brace design, calculated maximum deformation of braces shall be increased to account for beam vertical deflection
AISC Night School – Seismic Design Manual
Chapter F
28
F4.4 BRBF – System RequirementsK-Braced Frames
Not permitted
15
AISC Night SchoolNovember 23, 2015
Application of the AISC Seismic Design ManualSession 8: Buckling Restrained Braced Frames
and Quality Requirements
Copyright © 2015American Institute of Steel Construction
AISC Night School – Seismic Design Manual
Chapter F
29
F4.5 BRBF – Members – Basic RequirementsDiagonal Braces
Steel Core Plates used in steel core 2 in. thick or greater shall
satisfy minimum CVN requirements of Section A3.3
Splices in steel core are not permitted
Buckling-restraining system shall consist of casing of steel core
In stability calculations, beams, columns and gussets connecting the core shall be considered parts of the system
AISC Night School – Seismic Design Manual30
Typically, Fysc (min) = 38 ksi
F4.5 BRBF – Members – Basic RequirementsAvailable Strength
Steel core designed to resist entire axial force in the brace
The brace design axial force, φPysc, and brace allowable axial strength, Pysc/Ω, in tension and compression, according to limit state of yielding shall be:
Pysc = Fysc Asc
φ = 0.9 (LRFD) Ω = 1.67 (ASD)
whereAsc = cross-sectional area of yielding segment of steel coreFysc = specified minimum yield strength of steel core or actual yield stress of core as determined by coupon test
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AISC Night SchoolNovember 23, 2015
Application of the AISC Seismic Design ManualSession 8: Buckling Restrained Braced Frames
and Quality Requirements
Copyright © 2015American Institute of Steel Construction
AISC Night School – Seismic Design Manual31
F4.5 BRBF – Members – Basic RequirementsProtected Zones
Protected zones include steel core of braces and elements connecting core to beams and columns.
AISC Night School – Seismic Design Manual32
F4.6 BRBF – Members – ConnectionsDemand Critical Welds
Groove welds at column splices
Welds at the column-to-base plate connection unless column hinging at base can be shown to be precluded by conditions of restraint and absence of net tension (including amplified seismic loads)
Welds at beam-to-column connections per Section F4.6b(b)
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AISC Night SchoolNovember 23, 2015
Application of the AISC Seismic Design ManualSession 8: Buckling Restrained Braced Frames
and Quality Requirements
Copyright © 2015American Institute of Steel Construction
AISC Night School – Seismic Design Manual33
F4.6 BRBF – Members – ConnectionsBeam-to-Column Connections
Where brace or gusset connects to both members at beam-to-column connection:
Connection shall be “simple” per Specification Section B3.6a with required rotation of 0.025 rad…or…
AISC Night School – Seismic Design Manual34
F4.6 BRBF – Members – ConnectionsBeam-to-Column Connections
Where brace or gusset connects to both members at beam-to-column connection:
…or…Designed for moment to resist lesser of:
• 1.1 x (beam expected flexural strength = RyMp)
• Sum of 1.1 x (column expected flexural strength = Σ (RyFyZ)
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AISC Night SchoolNovember 23, 2015
Application of the AISC Seismic Design ManualSession 8: Buckling Restrained Braced Frames
and Quality Requirements
Copyright © 2015American Institute of Steel Construction
AISC Night School – Seismic Design Manual35
F4.6 BRBF – Members – ConnectionsDiagonal Brace Connections
Required strength of brace connections in tension and compression (including beam-to-column connections, if part of braced frame) shall be 1.1 x (adjusted brace strength in compression)
When oversized holes are used, required strength for bolt slip limit state need not exceed that from required load combinations, including amplified seismic load
AISC Night School – Seismic Design Manual36
F4.6 BRBF – Members – ConnectionsDiagonal Brace Connections
Connection design shall consider local and overall buckling. Provide lateral bracing consistent with applicable testing.
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AISC Night SchoolNovember 23, 2015
Application of the AISC Seismic Design ManualSession 8: Buckling Restrained Braced Frames
and Quality Requirements
Copyright © 2015American Institute of Steel Construction
AISC Night School – Seismic Design Manual37
F4.6 BRBF – Members – ConnectionsColumn Splices
Comply with Section D2.5
When groove welds are used, they shall be CJP
Column splice shall develop at least 50% of the flexural strength of smaller member
Required shear strength shall be ΣMpc/Hc where Mpc = FycZc of spliced columns and Hc is clear height of column (including slab)
AISC Night School – Seismic Design Manual38
SDM Example 5.5.1Example 5.5.1: BRBF Brace Design
This example shows the information needed by and
produced by the engineer of record
working with a brace manufacturer
20
AISC Night SchoolNovember 23, 2015
Application of the AISC Seismic Design ManualSession 8: Buckling Restrained Braced Frames
and Quality Requirements
Copyright © 2015American Institute of Steel Construction
AISC Night School – Seismic Design Manual
Given:
Refer to Brace BRB-1 in Figure 5-70. Design a buckling-restrained brace to resist the resulting axial loading, PQE = 113 kips.
SDM Example 5.5.1
39
Note: There are two of these frames in the direction under consideration
BRB-1
AISC Night School – Seismic Design Manual
Note: Some printings of the SDM text incorrectly have
“1.5” on page 5-419
Frame configurations and preliminary loads have been sent to a BRB manufacturer
Elastic stiffness of the braces have been found to be 1.28 times higher than the stiffness of the yielding core area alone, if it were extended from work-point to work-point (KF = Kactual/Kcore= 1.28) .
40
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AISC Night SchoolNovember 23, 2015
Application of the AISC Seismic Design ManualSession 8: Buckling Restrained Braced Frames
and Quality Requirements
Copyright © 2015American Institute of Steel Construction
AISC Night School – Seismic Design Manual
These stiffness factors may be used to determine the horizontal load distribution on each story.
The applicable building code specifies the use of ASCE 7 for calculation of loads. According to AISC Seismic Provisions Section F4.3, buckling-restrained braces should not be considered as resisting gravity forces.
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AISC Night School – Seismic Design Manual
Allow for material variability of 42 ksi ± 4 ksi.
From an elastic analysis, the first-order interstorydrift is ΔH = 0.223 in.
Assume that the ends of the brace are pinned and braced against translation for both the x-x and y-y axes.
38 ksiyscF =min 46 ksiyscF =max
SDM Example 5.5.1
42
22
AISC Night SchoolNovember 23, 2015
Application of the AISC Seismic Design ManualSession 8: Buckling Restrained Braced Frames
and Quality Requirements
Copyright © 2015American Institute of Steel Construction
AISC Night School – Seismic Design Manual
Solution:The governing load combinations in ASCE 7
including seismic effects are:LRFD ASD
LRFD Load Combinations 5 and 6 from ASCE 7 Section 12.4.2.3 (including the 0.5 factor on L permitted in Section 12.4.2.3)
ASD Load Combinations 5 and 8 from ASCE 7 Section 12.4.2.3
( )1.2 0.2 ρ 0.5 0.2EDSS D Q L S+ + + +
( )0.9 0.2 ρ 1.6EDSS D Q H− + +
( )1.0 0.14 0.7ρDS ES D H F Q+ + + +
( )0.6 0.14 0.7ρ EDSS D Q H− + +
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AISC Night School – Seismic Design Manual
The required compressive and tensile strengths of the brace are:
LRFD ASD
ρ
1.3(113 kips)
147 kips
E
u u
Q
P T
P
====
( )0.7ρ
0.7 1.3 (113 kips)
103 kips
E
a a
Q
P T
P
===
=
44
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AISC Night SchoolNovember 23, 2015
Application of the AISC Seismic Design ManualSession 8: Buckling Restrained Braced Frames
and Quality Requirements
Copyright © 2015American Institute of Steel Construction
AISC Night School – Seismic Design Manual
Required Strength
Consider second-order effects
AISC Specification Appendix 8 is used to addresssecond-order effects. The required second-orderaxial strength is:
2r nt ltP P B P= + (Spec. Eq. A-8-2)
SDM Example 5.5.1
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AISC Night School – Seismic Design Manual
For the calculation of B2:
To determine Pstory, use an area of 9,000 ft2 on each floor and the surface gravity loads given in the BRBF Design Example Plan and Elevation section. Use load combinations that include seismic effects.
2
11 ( . Eq. A-8-6)
α1 story
e story
B SpecP
P
= ≥−
46
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AISC Night SchoolNovember 23, 2015
Application of the AISC Seismic Design ManualSession 8: Buckling Restrained Braced Frames
and Quality Requirements
Copyright © 2015American Institute of Steel Construction
AISC Night School – Seismic Design Manual
LRFD ASD[ ]
( )( )( )
( )
[ ]( )( )
2
1.2 0.2(1.0)
68 psf 3 85 psf9,000 ft
0 psf 0.5 3 50 psf
0.2 20 psf
(1 kip/1,000 lb)
1.2 0.2(1.0)
+ 175 lb/ft 4 390 ft
(1 kip/1,000 lb)
5,160 kips
storyP
+
× + = + +
+ ×
+
× ×
=
[ ]( )
[ ]( )( )
2
1.0 0.14(1.0)
9,000 ft 68 psf 3 85 psf
0 psf 0 psf 0 psf
(1 kip/1,000 lb)
1.0 0.14(1.0)
+ 175 lb/ft 4 390 ft
(1 kip/1,000 lb)
3,630 kips
storyP
+
= × + + + +
×
+
× ×
=
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AISC Night School – Seismic Design Manual
The total story shear, H, with two bays of bracing in the direction under consideration where each braced frame is designed to resist the seismic loads shown in Figure 5-70.
SDM Example 5.5.1
2(54.0 kips 49.0 kips 32.0 kips 16.0 kips)
302 kips
14.0 ft
1.0 for braced framesM
H
L
R
= + + +===
48
54k x 2
49k x 2
32k x 2
16k x 2Note: There are two of these frames in the
direction under consideration
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AISC Night SchoolNovember 23, 2015
Application of the AISC Seismic Design ManualSession 8: Buckling Restrained Braced Frames
and Quality Requirements
Copyright © 2015American Institute of Steel Construction
AISC Night School – Seismic Design Manual
Δe story M
H
HLP R= (Spec. Eq. A-8-7)
( )( )
302 kips 14.0 ft1.0
0.223 in. 1 ft/12 in.
228,000 kips
=
=
49
From an elastic analysis, the first-order interstorydrift is ΔH = 0.223 in.
AISC Night School – Seismic Design Manual
Using AISC Specification Equation A-8-6:
LRFD ASD
2
α 1.00
11
α1
11.00(5,160 kips)
1228,000 kips
1.02
story
e story
BP
P
=
= ≥−
=−
=
2
α 1.60
11
α1
11.60(3,630 kips)
1228,000 kips
1.03
story
e story
BP
P
=
= ≥−
=−
=
50
26
AISC Night SchoolNovember 23, 2015
Application of the AISC Seismic Design ManualSession 8: Buckling Restrained Braced Frames
and Quality Requirements
Copyright © 2015American Institute of Steel Construction
AISC Night School – Seismic Design Manual
Considering second-order effects, the required compressive and tensile strengths of the brace are:
Determination of the brace area required to resist the required brace strength must use the minimum yield of the core material, Fysc min.
LRFD ASD
( )1.02 147 kips
150 kips
u uP T===
( )1.03 103 kips
106 kips
a aP T===
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AISC Night School – Seismic Design Manual
LRFD ASD
( )2
150 kips0.90 38 ksi
4.39 in.
usc
ysc
PA
F=
=
=
minminφ
( )
2
Ω
1.67 106 kips
38 ksi 4.66 in.
asc
ysc
PA
F=
=
=
minmin
For the limit state of tensile or compressive yielding, set the required strength equal to AISC Seismic Provisions Equation F4-1 and solve for Asc min:
52
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AISC Night SchoolNovember 23, 2015
Application of the AISC Seismic Design ManualSession 8: Buckling Restrained Braced Frames
and Quality Requirements
Copyright © 2015American Institute of Steel Construction
AISC Night School – Seismic Design Manual
In design practice, either LRFD or ASD design should be used consistently. The two methods give slightly different results here.
In order not to show two separate designs, the LRFD result will be used.
Try a BRB with a core area, Asc, of 4.50 in.2
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AISC Night School – Seismic Design Manual
Note that while BRB manufacturers can fabricate a BRB with the accuracy to which the core can be cut (generally ± 1/8 in. in width) it is common to round the required core area up to standard increments.
Generally, it is good practice to specify core areas in:
• 0.25 in.² increments for 0 in.² < Asc ≤ 5.00 in.²
• 0.50 in.² increments for 5.00 in.² < Asc ≤ 10.0 in.²
• 1.00 in.² increments for 10.0 in.² < Asc ≤ 20.0 in.²,
• 2.00 in.² increments for Asc > 20.0 in.²
• (or maintaining increment amounts in the range of 5% to 10% of the total amount).
SDM Example 5.5.1
54
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AISC Night SchoolNovember 23, 2015
Application of the AISC Seismic Design ManualSession 8: Buckling Restrained Braced Frames
and Quality Requirements
Copyright © 2015American Institute of Steel Construction
AISC Night School – Seismic Design Manual
When specifying BRB area greater than required, the EOR must account for the increased demand that the specified area will place on the structure, because the beams and columns are designed to be stronger than the adjusted brace strength.
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AISC Night School – Seismic Design Manual
For LRFD, the available axial strength for the limit state of tensile or compression yielding is:
n ysc scP F A=min minφ φ
( )( )20.90 38 ksi 4.50 in.
154 kips >150 kips o.k.
=
=
(Spec. Eq. D2-1)
56
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AISC Night SchoolNovember 23, 2015
Application of the AISC Seismic Design ManualSession 8: Buckling Restrained Braced Frames
and Quality Requirements
Copyright © 2015American Institute of Steel Construction
AISC Night School – Seismic Design Manual
Verify with the brace manufacturer that the stiffness factor KF = 1.28 is acceptable for a 4.50 in.2 brace of this length.
The remainder of the brace design is performed by the BRB manufacturer.
Overstrength factors, β and ω, along with available stroke, the maximum deformation capability of the brace, must be provided by the brace manufacturer in order to design the columns and beams of the BRBF and to determine the BRB applicability to the design.
57
AISC Night School – Seismic Design Manual
The final part of the brace design is establishing the expected deformation of the brace and using this deformation to determine forces that the brace imposes on the columns, beams and connections.
AISC Seismic Provisions Section F4.2 requires consideration of deformations at the greater of 2% drift or two times the design story drift.
58
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AISC Night SchoolNovember 23, 2015
Application of the AISC Seismic Design ManualSession 8: Buckling Restrained Braced Frames
and Quality Requirements
Copyright © 2015American Institute of Steel Construction
AISC Night School – Seismic Design Manual
The design story drift is defined in the AISC Seismic Provisions Glossary as the calculated story drift including the effect of expected inelastic action.
As given, the first-order interstory drift is ΔH = 0.223 in. This drift does not include the redundancy factor, ρ.
Note that ASCE 7 Section 12.3.4.1 permits ρ to be taken equal to 1 for drift calculations.
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AISC Night School – Seismic Design Manual
The design story drift including inelastic action is:
Twice the story drift including inelastic action is:
( )
ΔΔ
5.0 0.223 in.
1.01.12 in.
d H
e
CI
=
=
=
(ASCE 7 Eq. 12.8-15)
( )2Δ 2 1.12 in.
2.24 in.
=
=
60
31
AISC Night SchoolNovember 23, 2015
Application of the AISC Seismic Design ManualSession 8: Buckling Restrained Braced Frames
and Quality Requirements
Copyright © 2015American Institute of Steel Construction
AISC Night School – Seismic Design Manual
2% drift corresponds to a deflection of:
( )
Δ 0.02
0.02(14.0 ft)
0.280 ft
Δ 0.280 ft 12 in./1 ft
3.36 in.
H====
=
61
AISC Night School – Seismic Design Manual
In this case, 2% drift governs. The brace spans 14.0 ft vertically and 12.5 ft horizontally. The brace deformation can be calculated to be:
( ) ( )
( ) ( )( )
2 2
2 2
14.0 ft 12.5 ft 0.280 ftΔ 12 in./1 ft
14.0 ft 12.5 ft
2.25 in.
br
+ + − = +
=
62
32
AISC Night SchoolNovember 23, 2015
Application of the AISC Seismic Design ManualSession 8: Buckling Restrained Braced Frames
and Quality Requirements
Copyright © 2015American Institute of Steel Construction
AISC Night School – Seismic Design Manual
Consulting with the brace manufacturer, the yield length for this brace is determined to be 70% of the work-point length.
The yield length is the length over which the core is expected to yield, and is typically equal to the length of casing.
( ) ( ) ( )2 2
0.7
0.7 14.0 ft 12.5 ft 12 in./1 ft
=158 in.
yL L≥
= +
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AISC Night School – Seismic Design Manual
The strain is therefore:
Determination of the strain and the yield length is typically performed by the brace manufacturer and is shown here for illustrative purposes only.
Δ 2.25 in.ε
158 in.
1.42%
br
yL= =
=
64
33
AISC Night SchoolNovember 23, 2015
Application of the AISC Seismic Design ManualSession 8: Buckling Restrained Braced Frames
and Quality Requirements
Copyright © 2015American Institute of Steel Construction
AISC Night School – Seismic Design Manual
Consulting with the brace manufacturer, the ω andβ factors corresponding to this level of strain aredetermined to be: ω = 1.36 and β = 1.1
Alternatively, according to AISC SeismicProvisions Section F4.3 and ASCE 7 Chapter 16,brace deformation is permitted to be determinedfrom a nonlinear analysis in lieu of the expecteddeformation requirements in AISC SeismicProvisions Section F4.2 illustrated here.
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End of SDM Example 5.5.1
End of Example
Example 5.5.1: BRBF Brace Design
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AISC Night SchoolNovember 23, 2015
Application of the AISC Seismic Design ManualSession 8: Buckling Restrained Braced Frames
and Quality Requirements
Copyright © 2015American Institute of Steel Construction
AISC Night School – Seismic Design Manual67
J1 Scope
Quality Control and Quality Assurance
AISC emphasizes reliance on visual inspection rather than an over-reliance on nondestructive testing (NDT)
There are no QA/QC examples in the SDM, but if the built structure doesn’t
follow the design requirements, all the examples in the world won’t make any
difference
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J1 Scope
Quality Control
Provided by the fabricator/erector
Quality assurance
Provided by others (e.g., third-party deputy inspectors)
NDT shall be provided by QA agency except as permitted by Specification Section N7.
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AISC Night SchoolNovember 23, 2015
Application of the AISC Seismic Design ManualSession 8: Buckling Restrained Braced Frames
and Quality Requirements
Copyright © 2015American Institute of Steel Construction
AISC Night School – Seismic Design Manual69
J1 Scope
Specification Chapter N (new for AISC 360-10) contains universal QA/QC requirements
Seismic Provisions Chapter J contains “seismic only” QA/QC requirements
The expectation is that will result in more appropriate inspection programs (e.g., engineers won’t invoke Seismic Provisions Chapter J requirements for gravity systems)
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J5 Inspection Tasks
Tasks identified as:
• Observe (O): observe on a random, daily basis
• Perform (P): inspection shall be performed prior to final acceptance of the item
• Document (D): prepare reports indicating work has been performed in accordance with contract documents
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AISC Night SchoolNovember 23, 2015
Application of the AISC Seismic Design ManualSession 8: Buckling Restrained Braced Frames
and Quality Requirements
Copyright © 2015American Institute of Steel Construction
AISC Night School – Seismic Design Manual71
J6 (J7) Welding (Bolting) Inspection and NDT
Seismic Provisions Chapter J contains tables listing inspection/NDT tasks for welding and bolting for different stages of construction:
Prior to welding (bolting)
During welding (bolting)
After welding (bolting)
Distinguishes inspection work by QA and QC personnel
Also has a list of other inspection tasks (e.g., contour and finish on the RBS cut)
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J6 (J7) Welding (Bolting) Inspection and NDT
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AISC Night SchoolNovember 23, 2015
Application of the AISC Seismic Design ManualSession 8: Buckling Restrained Braced Frames
and Quality Requirements
Copyright © 2015American Institute of Steel Construction
AISC Night School – Seismic Design Manual73
J6 (J7) Welding (Bolting) Inspection and NDT
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J6 (J7) Welding (Bolting) Inspection and NDT
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AISC Night SchoolNovember 23, 2015
Application of the AISC Seismic Design ManualSession 8: Buckling Restrained Braced Frames
and Quality Requirements
Copyright © 2015American Institute of Steel Construction
AISC Night School – Seismic Design Manual75
Questions?
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AISC Night School – Seismic Design Manual
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CEU/PDH Certificates
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AISC Night SchoolNovember 23, 2015
Application of the AISC Seismic Design ManualSession 8: Buckling Restrained Braced Frames
and Quality Requirements
Copyright © 2015American Institute of Steel Construction
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AISC Night School – Seismic Design Manual
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Application of the AISC Seismic Design ManualSession 8: Buckling Restrained Braced Frames
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Copyright © 2015American Institute of Steel Construction
AISC Night School – Seismic Design Manual
The final exam will be issued on Tuesday, December 1. Final exam must be submitted by December 11.
8-Session RegistrantsFINAL EXAM
AISC Night School – Seismic Design Manual
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AISC Night SchoolNovember 23, 2015
Application of the AISC Seismic Design ManualSession 8: Buckling Restrained Braced Frames
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Copyright © 2015American Institute of Steel Construction
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