design comparison of ordinary concentric brace frames and special concentric brace frames for ...

192 Pages·2012·1.44 MB·English

DESIGN COMPARISON OF ORDINARY CONCENTRIC BRACE FRAMES AND SPECIAL
CONCENTRIC BRACE FRAMES FOR SEISMIC LATERAL FORCE RESISTANCE FOR
LOW RISE BUILDINGS

by

ERIC GRUSENMEYER

B.S., Kansas State University, 2012

A REPORT

submitted in partial fulfillment of the requirements for the degree

MASTER OF SCIENCE

Department of Architectural Engineering
College of Engineering

KANSAS STATE UNIVERSITY
Manhattan, Kansas

2012

Approved by:

Major Professor
Kimberly Waggle Kramer, P.E., S.E.
Copyright
ERIC GRUSENMEYER
2012

ii
Abstract
Braced frames are a common seismic lateral force resisting system used in steel
structures. Ordinary concentric braced frames (OCBFs) and special concentric braced frames
(SCBFs) are two major types of frames. Brace layouts vary for both OCBFs and SCBFs. T`his
report examines the inverted-V brace layout which is one common arrangement. OCBFs are
designed to remain in the elastic range during the design extreme seismic event. As a result,
OCBFs have relatively few special requirements for design. SCBFs are designed to enter the
inelastic range during the design extreme seismic event while remaining elastic during minor
earthquakes and in resisting wind loads. To achieve this, SCBFs must meet a variety of stringent
design and detailing requirements to ensure robust seismic performance characterized by high
levels of ductility.
The design of steel seismic force resisting systems must comply with the requirements of
the American Institute of Steel Construction’s (AISC) Seismic Provisions for Structural Steel
Buildings. Seismic loads are determined in accordance with the American Society of Engineers
Minimum Design Loads for Buildings and Other Structures. Seismic loads are very difficult to
predict as is the behavior of structures during a large seismic event. However, a properly
designed and detailed steel structure can safely withstand the effects of an earthquake.
This report examines a two-story office building in a region of moderately high seismic
activity. The building is designed using OCBFs and SCBFs. This report presents the designs of
both systems including the calculation of loads, the design of frame members, and the design and
detailing of the connections. The purpose of this report is to examine the differences in design
and detailing for the two braced frame systems.

iii
Table of Contents
List of Figures ............................................................................................................................... vii 
List of Tables ............................................................................................................................... viii 
List of Notations ............................................................................................................................ ix 
Acknowledgements ........................................................................................................................ xi 
Dedication ..................................................................................................................................... xii 
Chapter 1 - Introduction .................................................................................................................. 1 
Chapter 2 - Scope of Research ........................................................................................................ 2 
Chapter 3 - Building Loads ............................................................................................................. 5 
Gravity Loads ............................................................................................................................. 5 
Dead Loads ............................................................................................................................. 5 
Live Loads .............................................................................................................................. 6 
Snow Loads ................................................................................................................................. 6 
Wind Loads ................................................................................................................................. 7 
Seismic Loads ............................................................................................................................. 7 
Seismic Ground Motion .......................................................................................................... 7 
Site Classification ............................................................................................................... 8 
Seismic Design Category .................................................................................................... 8 
Design Coefficients and Factors ............................................................................................. 9 
Response Modification Coefficient .................................................................................. 10 
Deflection Amplification Factor ....................................................................................... 11 
Overstrength Factor .......................................................................................................... 11 
Seismic Design Force ........................................................................................................... 12 
Effective Seismic Weight ................................................................................................. 12 
Seismic Response Coefficient ........................................................................................... 12 
Building Period ..................................................................................................................... 13 
Distribution of Seismic Forces.......................................................................................... 13 
Torsion Forces .................................................................................................................. 14 
Chapter 4 - Ordinary Concentrically Braced Frame Member Design .......................................... 15 
iv
Analysis .................................................................................................................................... 17 
Brace Design ............................................................................................................................. 17 
Slenderness ........................................................................................................................... 17 
Local Buckling ...................................................................................................................... 19 
Brace Strength ....................................................................................................................... 20 
Column Design ......................................................................................................................... 20 
Beam Design ............................................................................................................................. 21 
Chapter 5 - Ordinary Concentric Brace Frame Connections ........................................................ 23 
Design Forces ........................................................................................................................... 23 
Brace-to Gusset Design ............................................................................................................ 23 
Brace-to-Gusset Connection ................................................................................................. 24 
Tensile Rupture of Brace ...................................................................................................... 24 
Gusset Plate Design .................................................................................................................. 25 
Shear Rupture ........................................................................................................................ 25 
Compression Buckling .......................................................................................................... 25 
Whitmore Section ................................................................................................................. 26 
Gusset-to-Beam Connection ..................................................................................................... 26 
Gusset-to-Beam Weld ........................................................................................................... 27 
Gusset Shear Rupture and Yielding ...................................................................................... 27 
Web Local Yielding and Beam Web Crippling .................................................................... 27 
Gusset-to-Column Connection ................................................................................................. 28 
Beam-to-Column Connection ................................................................................................... 28 
Chapter 6 - Special Concentric Brace Frame Member Design ..................................................... 29 
SCBF Analysis .......................................................................................................................... 29 
Brace Design ............................................................................................................................. 30 
Column Design ......................................................................................................................... 31 
Beam Design ............................................................................................................................. 32 
Chapter 7 - Special Concentric Brace Frame Connection Design ................................................ 34 
Brace Connection Design Forces .............................................................................................. 34 
Tension .................................................................................................................................. 34 
Compression ......................................................................................................................... 35 
v
Flexure .................................................................................................................................. 35 
Shear Lag and Brace Section Rupture at Gusset ...................................................................... 37 
Protected Zones ......................................................................................................................... 39 
Free-Edge Buckling .................................................................................................................. 40 
Demand Critical Welds ............................................................................................................. 40 
Beam-to-Column Connections ................................................................................................. 41 
Chapter 8 - Conclusions ................................................................................................................ 43 
Governing Lateral Load ............................................................................................................ 43 
Brace Slenderness Limits .......................................................................................................... 44 
Member Sizes ........................................................................................................................... 44 
Inverted-V Brace Layout .......................................................................................................... 45 
Story Drift ................................................................................................................................. 46 
General Conclusions ................................................................................................................. 46 
References ..................................................................................................................................... 48 
Appendix A - Building Plans and Elevations ............................................................................... 49 
Appendix B - Load Calculations ................................................................................................... 75 
Appendix C - OCBF Member Designs ......................................................................................... 92 
Appendix D - OCBF Connection Designs .................................................................................... 92 
Appendix E - SCBF Member Designs ........................................................................................ 115 
Appendix F - SCBF Connection Designs ................................................................................... 136 

vi
List of Figures
Figure 2-1: Building Framing Plan ................................................................................................. 2 
Figure 2-2: Longitudinal Building Elevation .................................................................................. 3 
Figure 2-3: Transverse Building Elevation ..................................................................................... 3 
Figure 3-1: Inelastic Force-Deformation Curve ........................................................................... 10 
Figure 4-1: Intersection of Member Centerlines ........................................................................... 15 
Figure 4-2: Brace Frame Layouts ................................................................................................. 16 
Figure 4-3: Unbalanced Load Due to Inverted-V Brace Layout .................................................. 18 
Figure 5-1: Net Area of HSS Brace at Gusset Connection ........................................................... 24 
Figure 5-2: Whitmore Section ...................................................................................................... 26 
Figure 7-1: Brace End Clear Distance .......................................................................................... 37 
Figure 7-2: Reinforced Brace Connection .................................................................................... 39 
Figure 7-3: Protected Zone ........................................................................................................... 40 
Figure A-1: Building Plan………………………………………………………………………..48
Figure A-2: OCBF Elevation…………………………………………………………………….49
Figure A-3: SCBF Elevation……………………………………………………………………..50

vii
List of Tables
Table 3-1: Dead Loads .................................................................................................................... 6 
Table 3-2: Live Loads ..................................................................................................................... 6 
Table 3-3: Design Coefficients and Factors .................................................................................. 10 
Table 8-1: Comparison of Building Base Shears .......................................................................... 43 
Table 8-2: Comparison of Braced Frame Member Selection ....................................................... 45 
Table 8-3: Comparison of Braced Frame Steel Tonnage .............................................................. 45 
Table 8-4: Summary of Building Story Drifts .............................................................................. 46 

viii
List of Notations
A – Gross area
g
C – Ratio of required strength to available strength
a
C – Deflection amplification factor
d
C – Seismic response coefficient
s
C – Approximate period parameter
t
C – Vertical distribution factor
vx
D – Dead load
D – Diameter of brace
D – Elastic story drift at elastic seismic force, V
s e
D – Ultimate story drift
u
H – Required shear force on beam to gusset connection
ub
H – Required axial force on column to gusset connection
uc
h, h – Height of level i, x
i x
h – Approximate period parameter
n
E – Modulus of elasticity
F – Short period site coefficient
a
F – Critical buckling stress
cr
F – Expected critical buckling stress
cre
F – Elastic critical buckling stress
e
F – Long period site coefficient
v
F – Specified minimum yield stress
y
F – Portion of seismic base shear acting at level x
x
I – Importance factor for seismic design
e
K – Effective length factor
k – Distribution exponent
L – Live load
L – Member length
M – Plastic bending moment
P
P – Expected post-buckling strength
c
ix
P – Expected tensile yield strength
t
Q – Seismic load
E
R – Response modification coefficient
R – Material overstrength factor, ratio of expected yield stress to specified minimum yield stress
y
r – Radius of gyration
S – Snow load
S – Design spectral response acceleration parameter for short periods
DS
S – Design spectral response acceleration parameter for periods of 1 second
D1
S – Site class adjusted spectral response coefficient for short periods
MS
S – Site class adjusted spectral response coefficient at a period of 1 second
M1
S – Mapped spectral response acceleration parameter for short periods
s
S – Mapped spectral response acceleration parameter for periods of 1 second
1
T – Fundamental building period
T – Approximate fundamental building period
a
T – Long-period transition period
L
t – Wall thickness of HSS
V – Base Shear
V - Elastic seismic force
e
V – Design seismic force
s
V – Required axial force on beam to gusset connection
ub
V – Required shear force on column to gusset connection
uc
V – Actual seismic force
y
W – Effective seismic weight
w, w – Portion of effective seismic weight at level i, x
i x
Z – Plastic section modulus about the axis of bending
λ – Slenderness parameter

λ  – Limiting slenderness parameter for moderately ductile compactness
md
λ  – Limiting slenderness parameter for highly ductile compactness
hd
ρ – Redundancy factor
Ω – System overstrength factor
o
x