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Structural Engineering Report No. 191
University of AlbertaDepartment of Civil &Environmental Engineering
Cyclic Behavior of SteeGusset Plate Connections
by
Jeffrey S. Rabinovitch
and
J.J. Roger Cheng
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Structural Engineering Report No 191
CYCLIC
BEHAVIOR OF
STEEL GUSSET PLATE
CONNECTIONS
by
Jeffrey
S
Rabinoviteh
and
J J Roger Cheng
Department of Civil Engineering
University
of Alberta
Edmonton Alberta
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connections appear capable absorbing significant amounts ener
proposed strong braced weak gusset concentric braced frame model.
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KNOWLEDGEMENTS
This report is a reprint
o
a thesis by the same name written by the ftrst aut
supervision o the second author
Financial support for the project was provided
by
the Natural Sciences and
Research Council
o
Canada to Dr J J Cheng under grant No 4727 and
Research Fund o the University o Alberta Financial support was provide
author by the Natural Sciences and Engineering Research Council
o
Canad
Walter
Johns Graduate Fellowship
The assistance o the technical staff o the I F Morrison Structural Labo
University
o
Alberta is acknowledged
A special gratitude o thanks goes to Michael Yam for his helpful advice and s
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T LE OF CONTENTS
hapter
INTRODUCTION
General
1 2 Seismic Design Considerations
1 3 Energy Absorption in Braced Frames
1 4 Current Gusset Plate Design
1 5 Objectives and Scope
2 LITERATURE REVIEW
2 1 Introduction
2 2 Early Gusset Plate Research
2 3 Monotonic Gusset Plate Behavior
2 4 Cyclic Gusset Plate Behavior
3 EXPERIMENTAL PROGRAM
3 1 Introduction
3 2 Preliminary Considerations
3 3 Specimen Description
3 4 Test Set up
3 5 Instrumentation
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4 3 2 Specimen A 2
4 3 3 Specimen A 3
4 3 4 Specimen A 4
4 3 5 Specimen A 5
5 DISCUSSION OF TEST RESULTS
5 1 Introduction
5 2 Parameters Affecting Energy Absorption
5 2 1 Gusset Plate Thickness
5 2 2 Plate Edge Stiffeners
5 2 3 Gusset Plate Geometry
5 2 4 Connection Bolt Slip
5 3 Comparison Test Results
5 3 1 Monotonic Tension
5 3 2 Monotonic Compression
5 3 3 Cyclic Load Behavior
5 4 Finite Element Analysis
6 SUMMARY AND DESIGN GUIDELINE
6 1 Summary
6 2 Design Guideline for Gusset Plates Under Cyclic Loads
6 3 Recommendations for Future Research
REFERENCES
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LIST OF TABLES
able
3 Specimen Description
3 2 Slip Resistance of Gusset Plate to Splice Member Connection
4 1 Material Properties
4 2 Ultimate Specimen Capacities
5 1 Comparison ofTest Results Tension
5 2 Comparison of Test Results Compression
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LIST
O
IGUR S
igure
Basic Configurations of Concentric
Braced
Frames
1.2
Hysteresis
Loops
- Concentric Braced
Frame
Wakabayashi, et al. 1974
1.3
Eccentric Braced Frame - Link Segment
1.4
Typical Experimental
Frame
Behavior
under
Cyclic Lateral Load
Popov
and
Engelhardt,
1988
2.1
Whitmore Gusset Plate Prototype
2.2 Whitmore Effective Width
2.3 Thornton Equivalent Column Method
2.4
Block Shear Tear-outModel
2.5
Gusset Plate Studied
by
Astaneh-Asl, et
al.
1981
3.1
Typical Test SpecimenGeometry - Specimen A-I to A-4
3.2
Geometry of Specimen
A-5
3.3 Simulation of Boundary Conditions
3.4 Schematic of Test Set-up
3.5 Test Set-up Reactions
3.6
Tension Reaction Frame
3.7 Test Set-up - Tension Reaction
Frame
Removed
3.8 Typical Strain Gage Locations - Specimen A-I to A-4
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igure
3 13
Test Frame Instrumentation
3 14
LVDT Support Frame
4 1
Typical Material Response
4 2
Load
vs
Axial Displacement Response of the Gusset Plate
Assembly Specimen A I
4 3
Final Specimen Yield Line Pattern Specimen A I
4 4
Load vs Axial Displacement
Response
Specimen A I
4 5
Plate Fracture in
Bolted
Connection Specimen A I
4 6
Out of plane Displacements Specimen A I
4 7 Buckled Long Free Edge Specimen A I
4 8 Strain Distribution Specimen A I
4 9 Load vs Axial Displacement Response of the Gusset Plate
Assembly Specimen
A 2
4 10 Final Specimen Yield
Line
Pattern Specimen
A 2
4 11
Load
vs
Axial Displacement Response Specimen A 2
4 12 Out of plane Displacements Specimen
A 2
4 13 Buckled Plate Free Edges Specimen A 2
4 14 Strain Distribution Specimen A 2
4 15 Load vs
Axial
Displacement Response of the Gusset Plate
Assembly Specimen
A 3
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INTRO U TION
General
Concentric braced frames are one
of
the most common lateral load-resistin
steel buildings. n a concentric braced frame the lateral loads applied to the
resisted by a network of inclined bracing members. Depending on the config
braced frame, either tensile
or
compressive loads can be accommodated b
members. These loads are commonly transferred to the beam and column m
frame by gusset plate connections. The gusset plate receives the load from
bracing member and transfers it to the main framing members. The delivery
and
out
of
the gusset plate
will
produce bending, shear, and normal forces
plate. Some common configurations of concentric braced frames are shown
When a structure is subjected to reverse lateral load conditions, the bracing
the gusset plate connections can be subject to both tensile and comp
conditions.
1.2 Seismic Design onsiderations
When a steel structure is required to resist seismic load conditions, the d
concentric braced frame is governed in Canada y the National Building Cod
1990 NRCC, 1990 and the provisions ofCAN/CSA-SI6.1 - Limit States De
Structures CSA, 1989 . The National Building Code outlines the p
determining the minimum lateral seismic force that is to applied to the str
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test behavior the frame specimen heavy dotted line and an analytical pre
frame response light dotted line .
Eccentric braced frames absorb energy
in
an entirely different manner th
braced frames. The distinguishing characteristic an eccentric braced fra
least one end every brace is connected so that the brace force
is
transmi
another brace or
to
a column through shear and bending
in
a beam segmen
Figure 1.3 . Inelastic activity under severe cyclic loading is restricted pri
links, which are designed and detailed
to
sustain large inelastic deformations
strength. n contrast to concentric braced frames, the braces are des
buckle, regardless the severity lateral loading on the frame. Because b
is
prevented and because the
link
can sustain large deformations without stre
and stable hysteretic loops similar
to
those moment resisting frames
Popov and Engelhardt, 1988 .
Figure 1.4, reprinted from Popov and Engelhardt 1988 , provides a crude
between the hysteresis behavior
a moment resisting frame MRF . a conc
frame CBF , and an eccentric braced frame EBF . The observed difference
behavior
is
recognized
by
the National Building Code
Canada NRCC,
favorable energy absorption behavior
ductile moment resisting frames
force reduction factor R =4.0. Eccentric braced frames are designed usin
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can be confmed to an element designed and detailed to sustain large ine
without significant loss
strength. The current research attempts to
frame model to be examined considers a concentric braced frame wher
is designed not to buckle. The energy of the system s designed to
gusset plate connection. The gusset plate
s
designed to yield n tensi
compression. n compression, a stable post-buckling behavior s des
plate
an improved energy absorption behavior
s
to be obtained. It
s
gusset plate element under severe cyclic loads that s the focus
this in
4 Current Gusset Plate Design
Design specifications n North America currently provide very little
design
steel gusset plates. Generally, only design philosophy s
specific formulas for evaluating the dimension and thickness
a guss
the design
gusset plates often draws upon the experience
the struc
When gusset plates are designed to resist strictly monotonic tensio
CAN/CSA-S6-88 - Design
Highway Bridges CSA, 1988 states onl
shall be
ample thickness to resist shear, direct load, and flexure, act
r
critical section. A simple design equation
s
provided to determine
resistance
the gross area of the gusset plate.
n
addition, a provis
avoid local buckling
the unsupported edge
a gusset plate. CAN
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their gravity axes intersect at one point, otherwise, provisions shall be made
and shearing stresses due to the eccentricity. Design strength for gusset pl
considered for tension loading conditions. It is stated that the design strength
lower value obtained according to the limit states of yielding, fracture of the
element, and block shear rupture of the connection. Provisions relating specif
design
of
gusset plates under seismic conditions are provided in the Seismic Pr
Structural Steel Buildings AISC, 1992 . A distinction
is
made between gusse
are connected to brace members that buckle in-plane or out-of-plane of the g
When the brace member buckles out-of-plane it is required that the brace term
gusset a minimum
of
two times the gusset thickness from the theoretical line
which is unrestrained y the column or beam joints. This detail is provided to
formation of a hinge line in the gusset plate.
Under seismic loading conditions, CAN/CSA-SI6.I-M89 - Limit States Desi
Structures CSA, 1989 provides detailed provisions for the design of braced
required factored resistance for the design of bracing connections is prov
resistance of the bolted gusset plate connection
is
based on the ultimate tens
u to block shear considerations.
addition, it
is
suggested that gusset pla
detailed to avoid brittle failures due to rotation
of
the brace when
it
buckles. T
design recommendation, and its origins, will be considered in detail in Chapter 5
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element undergoing large inelastic deformations no design guidelines x
5 Objectives andScope
order for the proposed strong brace weak gusset concentric br
effective under seismic loading conditions the gusset plate must be cap
large inelastic deformations without significant loss o load. There
research project was initiated to investigate the behavior o steel gusset p
loads. The main objectives o the project are s follows:
Observe the general behavior of gusset plates under cyclic loading
2. Provide experimental data for the various design parameters
3. Improve the compressive behavior o gusset plates under cyclic c
4. Determine the ultimate gusset plate capacity under tension
is
a
compressive inelastic deformations and vice versa
5. Determine the feasibility
o
having the gusset plate s the
absorption element in a concentric braced frame
6. Establish preliminary design rules possible
7. Identify areas requiring further investigation
Because o the complexity o the problem the research program develop
purposes was primarily experimental
in
nature. The test results are com
the current design practices and the results o tests performed on gu
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a Diagonal Bracing
b X-bracing
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8 9
3
' : . . ~ , 1 . '
: : i :
.
4
-50
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Detail
UnkSegment
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l
~
LATERAL OI PLACEMENT lN)
bl
,
S T - - - ~ · _ · _ - _ · _ - . - - - - - - r - - - - O - O - S - H
so
0
0
·
-
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2 LITERATURE REVIEW
2.1
ntroduction
The current design method for gusset plates
is
mainly the result
of
practice, and the engineer s intuition. Recent research has attempt
knowledge
of
the behavior
of
gusset plates
in
an effort to provide
approach. However, the focus has been only on the behavior unde
tension or compression. Research into the behavior of steel gusset
loads
is
severely lacking.
n
this chapter, past work done on gusset plate connections is revie
examines gusset plate research
from an
historical perspective, while S
recent research into the ultimate load behavior
of
gusset plates und
tensile and compressive loads. The limited investigations of the behav
under cyclic loads
is
considered
in
Section 2.4.
2.2
arly
Gusset Plate Research
Early research focused on determining the general elastic stress dis
plates. One
of
the early gusset plate studies that was to prove signific
by
Whitmore 1952). Whitmore tested a one-quarter scale model
connection from the lower chord of
a Warren Truss. A schematic dra
plate prototype
is
shown
in
Figure 2.1. Experimental tests were perfo
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diagonals does not accurately reflect the stress condition in gusset plates. B
observations, Whitmore found that the maximum tensile and compressive st
be approximated quite closely by assuming the force in each diagonal to b
distributed over an area obtained
by
multiplying the plate thickness by an eff
normal to the axis
o
the diagonal. This effective length
is
obtained by draw
from the outside bolts o the first row, to intersect with a line perpendicular to
through the bottom row o bolts. This concept compares quite well to test res
since been used as one o the primary tools
in
gusset plate design.
An
est
gusset plate yield load can be determined by multiplying the yield stress by th
t the effective width section. The method o determining the effectiv
illustrated in Figure 2.2.
Subsequent investigations attempted to confirm Whitmore s fmdings. Ir
investigated the primary stress in the double gusset plates o a Pratt truss. T
o
the maximum stresses were similar to Whitmore s. However, his method
o
the maximum stress was slightly different than Whitmore s. A further study
(1958) o a gusset connection o a Pratt truss confirmed lrvan s [mdings. Fi
studies were first performed by Davis (1967) and Vasarhelyi (1971) to de
elastic stress distribution in gusset plates. Davis performed s study
on
the
model used by Whitmore and confirmed his results. Vasarhelyi performed test
[mite element analyses on a scale model o a Warren truss. He found that th
stress determined by various simplified analytical methods are only slightly d
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problem of ultimate gusset plate capacity under monotonic loads,
compressive.
Tho rn ton 1984) presented an approach to the design of vertical br
based on satisfying the dual requirement of equilibrium and yield, with s
given to stiffness to preclude buckling and failure. Thornton considered
a typical bracing connection.
To
determine the gusset plate ultima
tension, he considered the tear-out of the gusset plate. The capacity is re
shear requirements of the 1978 AISC Specification. The tear-out capac
net section with hole size taken as bolt diameter plus 1/16 inch. n comp
considered gusset plate buckling by establishing the capacity
of
an e
section. This method considers an imaginary fixed-fIXed column strip
coefficient, k=O.65) of unit width below the Whiunore section. The len
strip may be taken as the largest
of l LZ
and
L3
as defmed in Figure
used to determine an equivalent slenderness ratio. Alternately, Thornto
shorter length, such as the average
of
L1 LZ and L3 may give a
approximation of the buckling strength. Thornton originally presented h
allowable stress method. From an ultimate strength perspective, the com
resistance
of
the gusset plate can be evaluated according to the colu
CAN/CSA S16 1 M89
standard CSA, 1989) using the Whiunore
Whiunore, 95Z as the column area and the equivalent slenderness fro
column strip. Thornton states that this approach is conservative becau
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were performed. with three tests each at two different plate thicknesses and t
bracing member angles. For the type
of
bracing connection examined, the p
mode
of
the gusset plate was a t ear across the boltom bolt holes
of
the splic
It was also determined that the type and location
of
the gusset
p ~
boundari
with the load transfer mechanism into the plate. have important secondary eff
buckling and associated out-of-plane bending.
Hardash and Bjorhovde 1985) continued the study
of
gusset plate capacity
loads. In o rd er to develop an ultimate strength approach t o the design
of
g
test results from the University
of
Arizona, the.University
of
Illinois, and the
Alberta were incorporated into the evaluation. For
all
42 gusset plate specim
te ar across the last r ow
of
bolts was observed, regardless
of
the strength para
size,
or
plate material. It was concluded that the governing block shear m
incorporating the tensile ultimate strength. F
u
on the net area between the
bolts. and a uniform effective shear stress, Feff. acting on the gross area alon
bolt holes Figure 2.4). The set
of
equations developed to give the nom
resistance, R
n
•
of
a gusset plate loaded in tension are as follows:
R
n
FuSnett
1.15F
e
ff
Lt
Feff
=
1-Cl F
y +
CIF
u
CI =0.95 - 0.047 L L in inches)
It was discovered that the shear stress distribution is
not
uniform, but rather
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design procedures for steel gusset plates
in
diagonally braced fra
considered both the tensile and compressive behavior
gusset pla
included the nonlinear behavior the fasteners and the frame to which
attached. Finite element results demonstrated that the additional stiffne
gusset plate cause the beam to develop end moments equivalent to a h
beam. To determine the tensile capacity, Richard developed a block sh
it is assumed that the plate will fail along the gross section of the bo
diagonal connections. The strength the gusset plate
in
tension may
combining the tensile stress resultant acting at the end the bolt patt
stress resultants acting along the sides
the bolts. the case b
with less than six rows
bolts, it
is
suggested that it may be appropr
shear area, as opposed to the gross shear area,
in
the block shear model.
were also generated to predict the gusset-to-frame fastener force dis
determined that fastener forces do not act in pure shear as is commonly
design procedures.
compression, the ftnite element analysis was
elastic behavior.
Full-scale diagonal bracing members were tested by Cheng and H
University Alberta. The compressive behavior and elastic buckl
examined. The gusset plate parameters considered
in
the investi
thickness, geometric conftguration, boundary condition, and out-of-plan
concentrically loaded tests failed
in
plate buckling. The eccentrically
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Additional analysis of the test results was performed by Cheng, et
al
199
element analysis by the program ANSYS gave reasonable predictions
of
buckling strength of the gusset plate test specimens. Furthermore, the sp
connection length and the thickness of the splice member were found to affe
buckling strength of the specimens. Increasing the length of the spl
connection, or the thickness of the splice member, results in an increase in
buckling strength.
An experimental program was undertaken by Gross 1990 to determine
1
t
of the members framing into the connection
on
the behavior and stren
connection, 2 the effect
of
connection eccenuicity on gusset plate capac
distribution
of
forces to the framing members, and 3 the difference
in
p
between a connection made to the column flange and one made to the colum
behavior of three nearly full-scale braced steel subassemblies were studied exp
It was determined that computing gusset plate buckling using the equival
method with a value of k=O 5 appears to be conservative. Additionally, gus
capacity is predicted very closely using the block shear approach. t was fou
eccentric connection, which had a compact gusset plate, had a higher buckli
than larger concentric gusset plates, and that the gusset plates produced a
condition for the beam to column connection.
Additional gusset plate research was performed at the University of Alberta by
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moving out-of-plane. The paper presents the results o the inelastic s
Cheng and Yam and reviews the test results o the elastic specimens t
Hu 1987 . It was determined that the plate thickness and plate size
strength o the gusset plate significantly. The failure mode for the
sway buckling o the gusset plate connection, while the failure mode fo
local buckling o the free edges o the plate. The out-of-plane restrain
on the inelastic buckling strength o the specimens while the elastic bu
greatly affected by the restraint. The test results show that the Whitm
concept overestimates the strength o the specimens that failed in e
underestimates the inelastic buckling strength. addition, the T
column method produced a large margin o safety for the gusset p
failed in inelastic buckling.
Cheng and Yam are considering the effect o the framing members
eccentric loading conditions
on
the compressive behavior
o
gusset pla
the research
is
currently
in
progress at the University o Alberta.
4 Cyclic Gusset Plate Behavior
Research into the cyclic behavior o steel gusset plates in concentrical
severely lacking. One of the most relevant studies
in
this area
is
a ser
investigations conducted at the University o Michigan. Astaneh-
conducted an experimental study to investigate the cyclic behavior
o
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simulate the effects of strong earthquakes. Although the study focused o
member behavior, gusset plate behavior was also monitored. Observations
plane specimen tests revealed that no major plastification occurred in the guss
they behaved mostly elastic until the end
of
the test. Observations from the
specimen tests showed that during post-buckling deformations the rotation
o
hinges in the gusset plate is about an axis normal to the axis
of
the brace mem
the study, i t was discovered that the portion of the gusset plate connected t
must be allowed to rotate freely about the axis of the hinge. Any restric
freedom would cause early fractures in the gusset plate.
s
such, it was con
the tests that an optimum free length of 2t, where t is the thickness of the guss
necessary for the free space in the gusset to prevent its premature fracture.
shows the type of gusset plate employed in this study and the recommended fr
gusset plate required t allow free rotation about the plastic hinge.
A further research paper by Astaneh-AsI,
et
al. 1985 focuses on the o
specimen tests. The results of both the welded and bolted specimens are inc
report.
t
was observed that three plastic hinges formed in all test specimens.
formed at midspan
of
the brace and one in each end gusset plate. The formatio
hinges in the end gusset plates was due to the relatively small strength and stif
gusset plate in out-of-plane bending, compared to that
of
the double-angle me
combined effect
of
bending and
x l
load in the post-buckling region caused
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he cyclic behavior of gusset plate connections in V-braced fram
Astaneh 1992 . o improve the behavior of V-braced frames, this
shear inelasticity of the gusset plate connection be utilized as a reliab
of
ductility and energy dissipation. The experimental part
of
the re
subjecting three gusset plate connections to cyclic loading. t wa
specimen with the largest eccentricity of point of intersection of mem
most desirable manner, while the behavior of the typical concentric co
braced frames was relatively brittle and undesirable.
n
the specim
eccentricity, the governing failure mode was the shear yielding
of
the
was a very ductile and stable energy dissipating mechanism. Add
design approach is proposed. The main component of the design ph
the shear yielding of the gusset plate the weakest link in the system. It
gusset plate will yield before the buckling of the bracing member an
shear deformation of the gusset will result in a more ductile bracing sys
Research into the behavior of
connections for seismic-resistant eccentr
EBFs is described by Engelhardt and Popov 1989 . Although b
EBFs may be subject to a significantly different stress environment tha
in concentrically braced frames, the observed gusset plate behavior is
was observed that large compressive stresses were produced along the
plate nearest the
l nk
region. n order to preclude gusset plate buckl
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inelastic compressive behavior he current study
o
the cyclic behavior o
plates draws upon the experienced gained in these previous investigations
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russ utline
o
o
o
onnection
o o
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Whitmore Eff
Width
Figure 2 2 Whitmore Effective Width
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Whitm
W
Imaginary Fixed Fixed
Column Strip:
k
65
Equivalent slenderness kL
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U1tmate Tear-out Resistance, R
n
:
Hardash and Bjorhovde, 1985
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Figure 2.5. Gusset Plate Studied y Astaneh-Asl, t al.
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3 EXPERIMENTAL PROGRAM
3.1
ntroduction
The purpose of the experimental program was to investigate the general
gusset plate connections
in
a braced steel frame under cyclic loading con
bracing system subjected to cyclic loads may
fail
either in the bracing membe
the gusset plate which connects the bracing member to the beam and co
proposed strong brace, weak gusset model to be examined in this investigatio
a concentric braced frame where the brace member
is
designed not to buckle
case, the bracing member acts
as
a restraining member to provide rotational
the gusset plate. The assumption was made in designing the present experimen
that the gusset plate would fail prior to the bracing member and that th
restraint provided by the bracing member
is
effectively infmite.
3.2
reliminary
Considerations
The experimental program was designed to represent the conditions of actual
connections. Thus, full-scale single gusset plate connections of a diago
member a t the joint of a beam and column were used. The variables of t
connection include plate thickness, plate size and configuration, plate boundary
angle of bracing, type of connection welded or bolted), cross-section of braci
length of splice member. order to simplify the problem, the test parameters
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designed to best represent the conditions
of
actual gusset plate conne
common bracing angles in practice range from 30 to 60 degrees.
As
bracing angle was used in this program. It was
chosen to connect the b
gusset plate through the use
of
a splice member. A bolted connection w
the splice member to the gusset plate
and
the gusset plate itself was dir
beam and column members in the braced frame assembly. All gusset
concentrically through the brace member.
3.3 Specimen Description
A series
of
five specimens was tested in the experimental program.
thickness
of
the test specimens are listed in Table
3.1
and a typical gusse
shown in Figure 3.1. All specimens were fabricated from CSA
structural quality steel. Two different thicknesses
of
gusset plate, 9.32
were used in the test program. The test specimens were rectangular
exception
of
Specimen A-5, which was designed to allow the free for
hinge under compressive buckling deformations. Based on the reco
previous research investigation Astaneh-Asl, et al., 1985 , a plastic hin
of
2t, where t is the thickness
of
the test specimen, was provided for
splice member connection. The modified geometry
of
Specimen
A
Figure 3.2.
order to investigate the effect
of
the stiffness
of
the free edge
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energy absorbing capacity of these specimens.
nall cases, two Tee-sections WTl25x22.5) and two
nun thick plates w
splice member to ensure that
the
gusset plate
failed
prior to the splice assemb
nun
specimens were connected to the splice member with five rows of 7
ASTM A325 high strength bolts designed for bearing. Due to the loads antic
connection, all 9.32 nun thick specimens were expected to experience bo
gusset plate to splice member connection during the cyclic loading history. T
thick specimens utilized 7/8 diameter ASTM A490 bolts in order to achieve
connection.
All
bolts were pretensioned using turn-of-nut tightening as
CAN/CSA-S16.1-M89, Clause 23.5 CSA, 1989). The calculated slip-resi
gusset plate to splice member connections are recorded
in
Table 3.2.
All
spe
designed to be loaded at
45
degrees
by
the bracing member and all spe
directly welded to the beam
and
column members. n the design of the weld
the force distribution between the gusset plate and the beam and column m
based on a model proposed
by
Williams
and Richard 1986).
n
connectin
plate specimens to the frame members, a mm ftilet weld was used for t
specimens and an 8 mm ftllet weld was used for the 6.18 mm specimens.
3.4 st Set-up
A gusset plate connection under cyclic loading conditions might deform out-
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allowed to move out-of-plane along with the frame assembly. To simp
the simulation Figure 3.3 b
w s
used. To further simplify the tes
that would normally exist in the framing members under lateral loadin
neglected in the testing program.
The test set-up is shown schematically n Figure 3.4. The cyclic test loa
the MTS 6000 testing machine. Two W31Oxl29 steel sections were us
column members in the test frame assembly. The frame assembly wa
WWF400x202 distributing beam
in
order
to
transfer the specimen loads
up reactions. The diagonal bracing member W250x67 was res
displacements in the plane
the test specimen
by
the restraint provi
bracing roller assemblies. The roller assemblies were fixed to the f
testing machine and restrained the brace member at the contact point
3.4. The test frame, with the specimen in place, was then sandwiched
rollers at each end of the set-up to allow it to sway laterally out-of
compressive and tensile loading Figure 3.5 . The compressive reaction
directly to the strong floor
the test lab, while the tensile reactions
tension reaction frame s shown in Figure 3.6. To prevent a sudden kic
frame a guided rod mechanism was affixed to each end
the distrib
movement the guided rod mechanism was monitored throughout th
unrestrained sway
the test
fr me
Figure 3.7 is a photograph
the a
up, with the tension reaction frames removed.
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the gusset plate. The location
the strain gages was decided on the basis
gusset plate test experience. addition, a pair rosette strain gages wer
either side the test specimens at the possible location the maximum no
The strain gage locations were the same for Specimens A-I through A-4, wh
locations were modified for Specimen
A 5
due to the unique geometry
tha
The locations
the specimen strain gages are shown in Figures 3.8 and 3.9.
LVDTs were used to monitor both the out-of-plane and in-plane displacem
gusset plate specimens and the test frame assembly. The out-of-plane buckl
the specimen plates were monitored by three sets of LVDTs which recorded th
shapes
the two free edges
the gusset plates and the center line of the l
Figure 3.10 and 3.11 .
the in-plane direction, a pair
LVDTs were use
the axial displacement the gusset plate itself. An additional pair LVDTs
.to monitor the axial displacement of the splice member and to observe the beh
proposed fixed boundary condition. By monitoring the axial displacement
gusset plate and the splice member, the deformation and bolt slip
in
the splice
gusset plate connection could be isolated. addition, an LVDT was used to
axial displacement the brace member relative
to
the distributing beam to c
the brace member
to
splice member connection was performing adequately. Th
the axial displacement LVDTs are shown
in
Figure 3.12. All axial displacem
were referenced
to
the distributing beam.
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lateral and longitudinal twist that might develop in the test frame. F
deflection
the distributing beam was recorded using a cable transdu
the test frame instrumentation is detailed in Figure 3.13. ll in-plan
out-of-plane LVOTs were placed on a support frame affixed
to
the
the point load application s shown
Figure 3.14. The rema
affixed to the frame of the MTS testing machine.
The cyclic load applied
to
the test specimens was monitored by the int
MTS 6000. Furthermore load cells were incorporated into the tens
ends
the test set-up. Under tension loading the MTS load was com
the loads recorded at the tension reactions. The MTS load was
str
the loads recorded at the reactions. Therefore the statics
the sy
and all loads are accounted for. The specimen load s recorded by th
machine was used the test results. Load cells were not inc
compression reactions due
to
stability considerations.
The electronic readings generated from the strain gages LVOTs load
testing machine were continuously monitored by the Fluke data acqu
gage readings were monitored manually at regular intervals through
addition a whitewash coating was applied to ll specimens
order to
yielding process.
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properties Fy=300 MPa). The procedure for calculating the Whitmore yield c
gusset plate
is
outlined
Section 2.2. During each cycle, the specimen w
loaded
n
tension to the desired
maximum
cycle load level. The specimen
unloaded from tension and cycled. through zero
to
the same load level
n
co
wo
cycles were conducted at each elastic load level. The first cycle was
start-stop fashion with the testing stopped at regular intervals for elect
acquisition. The second cycle at each load level was tested under continuo
conditions; the loading was only stopped at the peak tensile load, zero load, an
compressive load during each cycle so that qualitative specimen observation
gage readings could
be
recorded.
The inelastic loading sequence for all specimens began with a set o yield leve
100 o the expected nominal tensile
yield
load. The loading procedure in t
range varied slightly between the specimens tested.
n
general, subsequent inel
were conducted under increasing levels
o
specimen axial deformation. The
axial deformation was monitored using the LVDTs attached to the splice me
that the bolt slip in the connection, any, would be included the determina
cycle axial deformation level.
During each cycle, a specimen
was
initially loaded
in
tension to a predetermin
axial deformation. The specimen
was
unloaded from tension and then de
compression to the same axial deformation level, as referenced to the
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made to a nominal yield level defonnation.
As
such the cycle axia
was increased
in
roughly evenly spaced intervals over the course
of
th
he
level of axial defonnation was increased
in
subsequent cycles unt
of the specimen was achieved. Failure in tension was signified by a de
load carrying capacity under increasing MTS machine stroke. The tes
loading the specimen in compression until
an
excessive level
of
defonnation was obtained. The test loading was limited by the lev
defonnation that was able to be accommodated by the test set up.
All inelastic cycles were tested under continuous loading conditions wi
the testing of Specimen A I. It was originally thought that the effect of
stop start loading on the specimen behavior could be investigated in the
such the loading scheme for Specimen A I involved a set
of
three c
defonnation level in the inelastic range. The fIrst cycle was loaded in a
with the testing stopped at regular intervals for electronic data acquisiti
cycles of the set were loaded continuously. However when the axial d
held constant for successive inelastic cycles there is inadvertently an ob
load carrying capacity due to inelastic straining and residual defonnatio
no significant infonnation could be obtained from this cycle loading sc
inelastic loading cycles
of
increasing axial defonnation with no cy
employed in the testing of all remaining specimens.
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behavior
o
steel structures
is
relatively unaffected
by
moderate variations
i
rate within the range o loading rates employed this investigation Davis,
Therefore, the loading rates chosen reflects values that enabled careful an
observation o the specimen throughout the testing process.
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Table 3.1. Specimen Description
Test
Plate Size Thickness Speci
Specimen
mmxmm
mm
Test Par
A I
550 x 450 9.32
Basic
A 550x 450 6.18
Basic
A 3 550x
450
9.32 Stiffened F
A
550 x 450
6.18 Stiffened F
A 5
550x
450
9.32 Free Formatio
Hinge Fa
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Table 3 2 Slip Resistance Gusset Plate to
Splice Member Connection
Slip Resistance kN)
Test Connection
5 Probability of Slip
Specimen
Details
Class
A Surface
Class B S
Clean
mill
scale
Blast cl
9 32mm
10
ASTM
A325
918 151
Specimens
8
n
Bolts
6.18
mm
10
ASTM A490 1096 181
Specimens
8 n
Bolts
As
per
CAN/CSA SI6 I M89
Clause
13.12
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45
5
33
55
igur
3 1 Typical Test Specimen Geometry
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Distributing
Beam
WWF400x202
•
if
Brace Member
o 0
Splice Member1 :
W250X67
WT125x22.5
0 0
o 0
o 0
Gusset Plate
Lateral Brace
o
0
/ Specimen
Location
Fram
/
/
Asse
W31O
t
r r l
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Legend
Strain
k Rosett
50
50
r
5
~ f i
50
5
25
25
Figure 3 8 Typical Strain Gage Locations
Specimens A I to A 4
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:
:
Figure 3 10 Out or plane LVDT Locations
Specimens A I to A 4
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Figure 3 11 Out of plane LVDT Locations for Specime
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o
o
o
o
o
o
V
on both sides
of splice mem er
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4 EXPERIMENTAL RESULTS
4 Introduction
The results
the experimental program are presented
in
this chapte
properties
the test specimen are discussed in Section 4.2. The resu
plate tests are presented in Section 4.3. The
full
test behavior each
presented. This chapter will focus on the physical behavior
the spec
cyclic loading
as
well
as
consider the load versus defonnation respo
configuration, and the observed strain distribution the specimens. Fur
the test results in relations
to
the test parameters will be covered in Chap
4 2 Material Properties
Table 4 1 lists the values the elastic modulus, the static and dynamic
the dynamic ultimate strength
as
detennined
from
tensile tests on coupo
material used
in
the test specimens. Four coupons were fabricated from
thicknesses utilized. A 2 mm gage length was used for all material tes
from each plate were tested in the direction parallel to the sheet steel rol
while the remaining two coupons were tested
in
the perpendicular direct
values from each plate direction and the average values from the four co
reported. As expected, higher strengths were observed from the coupo
to the rolled direction
the steel plate. However, the response
the
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4 3 Test Results
The ultimate tensile and compressive loads attained during testing are record
4.2. The ultimate load
is
defmed as the maximum load level reached by
throughout its cyclic loading history. The test results each specimen are p
tum in Section 4.3.1 through Section 4.3.5. The discussion of each specime
focus on the physical response the specimen during testing and will then c
load versus deformation response, the buckled configuration, and the obse
distribution
within
the specimen. Additional test data, including the gusset
versus deformation response and the load versus out-of-plane displacement
frame, is provided in Appendix
4 3 Specimen ·
Specimen A-I
is
a basic, unreinforced gusset plate specimen
9.32
rom
thick
7/8 diameter ASTM A325 high strength bolts designed for bearing were used
the splice member to the gusset plate.
The load versus axial displacement response Specimen A-I throughout
history is shown in Figure 4.2. The area under the load-deformation curve is a
the energy absorbed by the gusset plate throughout the cyclic loading. Plotted
average axial displacement the gusset plate assembly. The displacement wa
by the LVDTs attached to the splice member and referenced to the distributing
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By examining the tension portion
o
the loading
in
Figure 4.2, it is
specimen response under tension
is
relatively stable; as the axial de
increased the load carrying capacity o the specimen
is
maintained
compression, the overall plate buckling
o
the specimen is accompa
increase in axial defonnation and a significant drop in load carrying ca
the cyclic specimen loading was not continued very far into the post-bu
still be observed that there is a deterioration
o
the compressive load c
the cyclic axial defonnation level and the specimen out-of-plane defonn
photograph
o
the failed specimen and the final yield line pattern is show
Figure 4.4 a) shows the specimen load versus defonnation response
o
assembly during the elastic portion o loading, Cycle 1-7. sexpec
were observed on the specimen during the elastic cycles. During the
Cycle 5,
t
a load o approximately 1000 kN, boIt slip occurred in t
splice member to gusset plate bolted connection. Due to the slack cre
system, the observed load dropped during the slip process. Upon comp
bolt slip, the specimen once again began
to
pick up load.
s
the testing progressed, the splice member to gusset plate conn
slippage twice during every test cycle, once during tension loading, and
the specimen was cycled through into compression. The connection
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Figure 4.4 b) shows the load versus deformation response the specimen
inelastic loading cycles up to the onset plate buckling. Cycle 8-13. The
signs yielding were recorded on the specimen along the welded boundary
gusset plate and the frame assembly. Yielding was indicated by the flak
whitewash coating on the specimen. Yielding
in
this region appeared to be
restraint provided by the welded boundary s the specimen began to deform o
the cycle axial deformation level increased. yield lines developed on the g
about the sides the splice member at the mid-height the connection. Th
the yielding plate material
in
the connection under both tensile and comp
bearing deformations. Yield lines about the base the splice member r
beginning a plate buckle stretching from the bottom comer one free edge
beneath the splice member. to the bottom corner the other free edge.
During the compressive loading of Cycle 13. overall plate buckling occurred
free edge
the gusset plate buckled. allowing the specimen to deform signil
of-plane. The load carrying capacity the specimen dropped signillcantly a
plate buckling occurred. a result, the maximum load 1682 kN reached d
11 is the compressive capacity this specimen.
Once overall plate buckling h d occurred, the remaining loading cycles for Spe
involved only an increase in the axial deformation level for the tension loading
each cycle. Since the specimen had already buckled
in
compression, it was
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Cycle 17). The specimen underwent significant tensile axial defonna
failure was reached at a load
1794 kN.
The gusset plate specimen was examined after the completion the test.
that the specimen failed
in
tension due a fracture
the plate material
holes in the bottom row the connection. Figure 4.5
is
a photograph
material. 11ris tensile failure mode was characteristic
all the specim
remaining bolt holes in the connection had been defonned in both tension
due to the bearing of the bolts under load, with the greatest defonnation
fIrst and last row the connection.
The linear variable displacement transducers recorded the out-of-plane d
the specimen free edges and the center line deflection. Figure
displacements that existed
in
the specimen after overall plate buckling o
13. It
is
observed that the deflected shape
the specimen center line
that a fIxed-fIxed but guided column. The long free edge has buckled
shape indicates that the restraint provided to the top the specimen by t
appears to be localized, and does not provide f ity
to
the free edges
Figure 4.7
is
a photograph
the long free edge
the specimen a
buckling occurred.
plotting the deflected shape of the specimen center line, an interpolati
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the splice member was assumed to be rougWy equal to the out-of-plane disp
the top
the gusset plate free edges. Since the splice member is relatively rigi
to the gusset plate, this assumption appears to be valid.
Specimen strain gage readings were recorded throughout the loading history.
only strain levels obtained from the elastic portion loading are relevant in an
the strain distribution in the specimen. Once local yielding occurs and the stres
redistribute in the plate, the strain readings are difficult to interpret. Strain
were investigated at the cycle maximum loads at both the 50 and
iClO
Whitmore load levels, 530 kN and 1060 kN respectively. From this anal
observed that the
p k
strain levels in the specimen were recorded at the roset
beneath the splice member. Figure 4.8 shows both the tensile and compressive
distributions at the 530 kN and 1060 kN levels. At the 530 kN load level th
significant difference between the strain levels and pattern distribution b
tension and compression stress states.
This
indicates that the elastic loading
the specimen is generally the same under both tension and compression loading
When the specimen load is increased to the I060 kN level, strain levels ar
twice those recorded at the 530 kN load level. The linearity strain s
assumption that the material response is generally elastic at this load level.
strain readings at the -1060 kN load level are analyzed, the strain levels ar
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For the purpose of comparison, the maximum strain levels
in
the specim
Whitmore critical stress theory, should be approximately ±1500 m
Whitmore section at the 100% nominal yield load level (1060 kN). The
runs through the bottom row of bolts
in
the splice member connection,
rosette gage locations.
4 3 Specimen A·
Specimen A-2 is a basic, unreinforced gusset plate specimen of 6.18 rom
7/8 diameter ASTM A490 high strength bolts were used to connect the
the gusset plate in order to achieve a slip-resistant connection. No bolt
to occur during the testing of this specimen.
Figure 4.9 shows the load versus the axial displacement response of
assembly throughout the loading of Specimen A-2. By examining the t
the loading, it is observed that the specimen response under tensio
compression, the buckling behavior of the specimen is revealed. The occ
plate buckling
is
well defmed
by
the compressive peak load plotted in
observed during testing, the compressive capacity immediately drops
post-buckling load capacity level. The figure confirms that the post-buc
relatively stable; the post-buckling load capacity is seen to deteriorate v
axial
plate deformations increase significantly. A photograph of the fail
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long free edge of the plate. Yielding was likely due to the restraint prov
welded boundary condition.
Figure 4.11 b) shows the load versus deformation response of the specimen
inelastic loading cycles
up
to the onset of plate buckling, Cycle 7-8.
th
deformation level increased, a significant increase in compressive plate y
observed about the base of the splice member. The fIrst signs of tension y
observed during Cycle 8 ±2.0l1
y
), when yield lines were noted about the
splice member as the material in the connection region was beginning to yield
loading was cycled through to compression, overall plate buckling occurred
1128
le
Immediately upon buckling, the load carried by the specimen dro
le
The plate buckle extended from the midpoint of both free edges down to
the splice member. Both plate free edges buckled in order to enable the
undergo signifIcant out-of-plane deformation.
Figure 4.11 c) shows the specimen load versus deformation response for the r
the test loading.
the test proceeded under sequentially increasing levels of
plate deformation, the tensile yield lines about the splice member connectio
h maximum tensile loads reached continued to increase as the cycle axial
level increased.
compression, only minor deterioration was observed i
buckling behavior of the specimen. The compressive loads attained only decrea
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Figure 4.10).
The tensile failure of the specimen occurred during Cycle 16 ±16.0d
carrying capacity reached 1340 le then quickly began to drop as the
axial deformation continued to increase. The test was concluded by load
in
compression until an excessive level
of
deformation was achieved. Eve
deformation level that was imposed during this [mal cycle, the compress
still 630
le
only 100 le less than the initial post-buckling capacity. Th
shape of the specimen Figure 4.10) reveals the complex pattern of plate
associated plastic hinge locations. It
is
believed that the complex pa
allowed the specimen to redistribute the compressive load through a ser
load paths, resulting in a relatively stable post-buckling capacity.
The failure
of
the specimen
in
tension was a fracture
of
the plate mate
bolts in the bottom row
of
the connection. Only the bottom row
of
bolt h
be significantly deformed. Since no major connection slip occu
deformations observed were due
to
overall connection material yielding,
deformations.
addition, tensile yielding caused the plate to spread out
upwards at the top
of
the splice member connection region.
The out-of-plane deflected shape
of
the plate free edges and the center l
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plane deformations increased, the fIxity
of
the free edges decreased as pl
developed at the bottom comers of the free edges· at the location
of
the weld
to the frame assembly. Photographs
of
the free edges (Figure 4.13) show th
shapes, including the location
of
the plastic hinge lines that developed as th
buckled.
Strain gage values were investigated at the maximum cycle loads at both th
100 cycle levels. For Specimen A-2, this corresponds to 353 kN an
respectively.
general for Specimen A-2, the strains are highest at the roset
at the base
of the splice member, and the edge strains are higher along the lon
The recorded plate strain distributions at both the 353 kN and 707 kN load
shown in Figure 4.14. At the +707 kN load level, the distribution
of
strains
unchanged from the +353 kN level. addition, strains have approximate
indicating an elastic linearity
of strains
in
tension. Under compressive loading
have more than doubled at the rosette locations when the loading increased fro
kN to the -707 kN level. The strains at the rosette locations are approaching
levels, which
is
in agreement with the whitewash flaking observed on the speci
load level.
4.3.3 Specimen A·3
Specimen A-3
is
a 9.32 mm thick specimen with reinforced plate free edges.
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Specimen A-I
in
that
as
the axial deformation level is cyclically inc
carrying capacity of the specimen
is
stable.
n
compression, the enha
Specimen A-3 is revealed. Not only is the ultimate compressive capaci
that of Specimen A I but the onset of overall plate buckling was not a
sudden increase
in
axial plate deformation nor a significant decrease
capacity. Since Figure 4.2 and Figure 4.15 are both plotted to the
increased energy absorption capacity
of
the reinforced plate, Specimen A
to the basic plate, Specimen A-I,
is
evident. A photograph of the failed
fmal yield line pattern
is
shown
in
Figure 4.16.
Figure 4.17 a) shows the specimen load versus deformation response
of
assembly during the elastic portion
of
loading, Cycle 1-6.
As
expecte
were observed
on
the specimen during the elastic cycles. Figure 4.17 b
versus deformation response during the inelastic loading cycles up to th
buckling, Cycle 7-14. Connection bolt slip
in
Specimen A-3 first occ
tension loading
of
Cycle 7 at a load
of
1290
kN As
in the testing
of
Sp
splice member to gusset plate connection experiences slippage twic
subsequent test cycle. The bolt
slip
experienced during each cycle of loa
the load versus axial deformation response of Figure 4.15. The saw-tooth
slip on the load versus deformation curve
is
a function of the discrete na
observations.
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tensile yielding was first noticed on the specimen along the sides the splice
the plate material in the connection region began
to
yield. Yielding about the
splice member connection was likely due to both tension and compressive lo
testing progressed, plate yielding spread out from the regions previously indica
During the compressive loading portion Cycle 14, a maximum compres
1990 kN was reached, accompanied by the first signs
yielding on the outsid
plate edge stiffeners. 1bis was a slight decrease from the maximum comp
reached during the previous cycle. The slight decrease in maximum load and
yielding
in
the stiffeners indicated that plate buckling or local plate cripp
specimen had begun. The maximum load of 2004 kN reached during Cycle
compressive capacity of this specimen.
The test proceeded under sequentially increasing levels
cyclic axial plate
until tensile failure of the specimen was observed. Figure 4.l7 c) shows the sp
versus deformation response for the remainder the test loading. The fa
specimen in tension occurred during Cycle 15 just prior to reaching the d
axial deformation level. The maximum tensile load reached prior to failure
1bis was slightly less than the ultimate specimen tensile capacity 1884 k
during the previous cycle. The test was concluded by loading the s
compression until
an
excessive level compressive deformation was achiev
this
fmal
loading a
peak
compressive load
1910 kN was reached prior t
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to spread outwards and to bulge upwards at the top o the connection.
the high compressive loads realized the compressive bolt hole deforma
severe resulting in some piling-up of material on the compressive side o
holes.
Figure 4.18 shows the out-of-plane deflected shape
o
the stiffened plat
center line deflection
o
the specimen after the onset
o
overall plate b
14. The deflected shape of the center line again resembles that
o
a
guided column. However the presence of the edge stiffeners restricts
from experiencing any signillcant out-of-plane deformation t this load le
severe compressive axial deformations were imposed during the fmal
significant deformations become visible along the stiffened edges. As seen
the stiffener displacements are predominately confIned to rotational defo
stiffener to frame weld locations while the rest of the stiffener remains relat
Gusset plate strain distributions for Specimen
A
were investigated at th
Specimen A-I. Figure 4.20 shows the strain distributions at both the 530 k
load levels for Specimen A-3. The general distribution
o
strains re
unchanged between the tensile and compressive load states. The peak s
are recorded
t
the rosette locations beneath the splice plate while the e
strains are higher along the long edge side
o
the specimen. Along each
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stiffeners onto the specimens, the plate stresses and strains are distributed ov
area
of
material. addition, at the -1060 leN load level, no significant
indicated by the strain readings in Specimen A-3.
is
observation sup
conclusion that the addition of stiffeners to Specimen A-3 delays the onset of yi
out-of-plane buckling deformation in
the gusset plate.
4 3 4 Specimen A 4
Specimen A-4 is a 6.18
rnm
thick specimen with reinforced plate free edges.
6
8
rnm
stiffeners, of the same material as the specimen, were welded alon
length
of
each plate free edge. Ten 7/8 diameter ASTM A490 high strength
used to connect the splice member to the gusset plate
in
order to achieve a sli
connection. No bolt slip was expected
to
occur during the testing
of
this specim
Figure 4.21 shows the load versus axial displacement response
of
Specimen
tensile portion of the cyclic loading curve shows the stable response of the speci
tension loading. compression, the effect of the edge stiffeners is observed.
the compressive capacity of Specimen A-4
is
not significantly higher than Spec
the presence
of
the plate edge stiffeners greatly affected the post-buckling behav
specimen. The attainment of the specimen compressive capacity was not follo
sudden drop in load carrying capacity, but instead, a steady deterioration is obse
comparing Figure 4.9 and Figure 4.21, the increased energy absorption capac
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observed during Cycle 5, at the 100 nominal Whitmore yield load lev
lines were noted running parallel to the long free edge at the base
of
the
onset of yielding was supported by the presence of residual plate strains a
of the cycle.
The testing proceeded with cycles
of
increasing axial plate deformation.
shows the load versus deformation response of the specimen during the
up to the onset of plate buckling, Cycle 7-10. During Cycle 9, at an a
level of
5d
y
, the fIrst signs of tensile yield lines were observed on the
sides
of
the splice member connection.
n
compression, yield lines inc
base
of
the splice member as a localized buckle began to form at the base
plate. The onset
of
yielding was also observed on the outsides
of
the pla
at the bottom corner of each edge.
During Cycle 10 (±3.0d
y
) the compressive capacity
of
the specimen w
compressive load of 1149
l
was attained, accompanied by an incre
activity about the base of the splice member and on the plate edge stiffener
compressive capacity had been reached, the plate appeared to have only b
overall plate buckling was being restrained
by
the plate edge stiffeners. U
A-2, the buckling
of
the
spe imen
was not immediately followed by a sig
the specimen load carrying capacity.
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steady pace as the testing cycles continued. There was an increase
in
yielding
the specimen as the plate continued to buckle under constraint
from
the
stiffeners. Yield lines developed along the long edge of the gusset plate just
edge stiffener. Eventually the buckled shape became more defined s t r e t ~ h i n
bottom comers the splice member out towards the comers of the plate ed
lines on the plate stiffeners increased significantly under cycles increasing
defonnation. Ultimately the plate edge stiffeners themselves defonned both in
out-of-plane allowing the outside edges of the specimen plate to buckle.
The tensile capacity of the specimen was reached during Cycle 17 ± 2 I . O ~
maximum load
1265
leN
was reached. However the tensile failure of th
occurred during Cycle 18 when the tensile load carrying capacity began to
increasing axial plate defonnation. During Cycle 18 a
new
region
yi
observed along the gusset plate to frame assembly boundary due to the cyclic o
defonnations
in
the specimen. The test
was
concluded
by
loading the sp
compression. The test was stopped when the compressive capacity
the spe
deteriorated
to
680
leN
The tensile failure mode of the specimen was a fracture of the plate material b
bolts in the bottom row the connection. There was no sign bolt
connection region. Tensile yielding defonnations were the most severe in the b
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connection region after the completion
of
testing.
Figure 4.26 shows the out-of-plane deflected shape
of
the stiffened pla
center line deflection of the specimen during the compressive loading
Initially, the deflected shape
of
the center line resembles the buckled shap
but guided column. The deflected shapes of the reinforced edges revea
themselves had not buckled at this load cycle level.
the co
deformations increased, the deflected shape of the specimen center line b
that of a fixed-pinned but guided column.
the stiffened edges began t
plate buckling was facilitated. This created a plastic hinge region beneat
splice member, thereby reducing the fixity provided by the relatively rigid
Photographs of the [mal deformed shape of the plate edge stiffeners Fi
that the stiffeners have buckled.
Gusset plate strain distributions for Specimen A-4 were investigated a
levels as Specimen A-2. Figure 4.27 shows the tensile and compressive str
at both the 353 kN and 707 kN level for Specimen A-4.
n
general, the
highest
at
the rosette locations beneath the splice member. The strai
generally the same along both stiffened edges of the specimen, with slight
observed
at
the top
comer
of
the long free edge. When the strain di
tensile and compressive loading
s
compared, the compressive loading sta
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edges and within the interior of the plate, but are at similar levels at the rosett
By providing stiffeners to the plate edges, the stresses
and
strains in the edge
the plate are distributed over a greater area material, thereby reducing the s
in
those locations.
4 3 5 Specimen A 5
Specimen A-5 is a 9.32 mrn thick specimen. The plate geometry was m
accommodate the free formation of a plastic hinge under compressiv
deformations. Ten 7/8 diameter ASTM A325 high strength bolts designed
were used to connect the splice member to the gusset plate.
The load versus axial displacement response of Specimen
A 5
is plotted
in
F
Although the specimen geometry
was
significantly altered, the tensile re
Specimen A-5
is
similar to the other test specimens. contrast, the d
compressive behavior
is
evident. The compressive capacity
Specimen A-5
fraction of the compressive capacity of the other specimens the same plate
(Table 4.2). By comparing the load deformation response Specimen A-5
response of Specimens A-I and A-3, the decreased energy absorption capac
specimen geometry is evident. A photograph of the [mal yield line pattern
specimen is shown
in
Figure 4.29.
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compression revealed the onset of yield lines along the specimen plate
welded boundary.
addition, strain gage readings also indicated
occurring in the plate in the region beneath the splice member. Ther
yielding had begun prior to reaching the expected nominal yield level. H
actual measured material yield level was significantly higher than the no
MPa, the 100 or nominal Whitmore yiel level cycles were actual
elastic range. Therefore, compressive yielding
h
begun well below
level based on the Whitmore critical stress theory.
Cycle 6 was loaded to the same
xi l
deformation level
s
Cycle 5. O
t
the maximum compressive load
o
905 kN revealed that the plat
visibly deformed out-of-plane and the strain gage readings in the 'pl
indicated significant plate bending. During compressive loading o Cyc
load o only 860 kN was reached. Specimen observations revealed t
buckle extending from the bottom comer
o
each free edge. The
themselves buckled
in
a region near the frame boundary, allowing the s
out-of-plane.
The testing was continued with cycles o increasing axial plate deformat
post-buckling behavior
o the gusset plate and to reach the tensil
specimen. Figure 4.30(b) shows the specimen load versus deformation
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plot Figure 4.30 b).
As
the testing progressed, the maximum tensile loads reached increased as the
deformation level increased. The fIrst signs tension yielding on the gusset
observed about the sides
the splice member as the bolt holes yielded un
bearing deformations. As the cycle axial deformation levels increased, the te
lines about the connection region began extending outwards towards the free ed
specimen. Under compression, the capacity the buckled specimen deteriora
but steadily from the peak capacity attained during Cycle 5. As the co
deformations increased, yield lines indicated the presence a secondary pl
extending from the base
the splice member out towards the middle
the
edges. n addition, the increase in cyclic out-of-plane deformations resulted
the weld along the gusset plate to frame weld boundary, at the extreme outsi
the long welded side. Initially, a fracture length about I cm was visible. A p
the weld fracture under tension loading is shown in Figure 4.3
The tensile failure the specimen occurred during Cycle 14. However,
capacity the specimen was reached during the previous cycle when a maximu
1887 kN was attained. The test was concluded by loading the specimen in co
until an excessive level compressive deformation was achieved. As
deformations increased, the length the weld fracture grew as the plate was b
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Figure 4.32 shows the out-of-plane deflected shape of the plate free ed
line deflection
the specimen recorded during Cycle 7 once
deformations
had
become significant The deflected shape the cen
that
a fixed-pinned but guided column. A hinge
is
evident on the gu
the base
the splice member.
At
this load level, the deformed shape
resembles the buckled shape a fixed-pinned but guided column, w
shape
the short free edge
is
closer to the buckled shape
fixed
column. The difference in deformation between the free edges is
increased
ftxity
provided to the top the short free edge
by
the close
splice member to that edge, as shown
in
the specimen geometry (Figure
is
a photograph the deformed plate free edges at the completion
observed that further deformation the specimen caused hinges
to
form
plate edges along the frame member boundary.
An
analysis
the specimen strain distribution during the assumed elastic
confirms the poor response of Specimen A-5. Figure 4.34 illustrates the
Specimen A-5 at both the 530 k N and +1060/-907 k N load level.
level, plate strains are highest under the splice member at the rosette loc
distribution
is
similar along both free edges with slightly higher strain
middle
the edges.
In
compression, the magnitude and distribution
s
unchanged from the +530 k N load level. However, the strain readings
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rosette region.
n
addition strain readings at the middle the free edges n
hinge region and at the rosette locations are at or beyond yield levels. Gag
appear distorted due the effects significant plate bending.
-
J
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r \
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Plate Assembly mm)
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•
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Displacement
or
Gusset
Plate
Assembly
mm )
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Cycle :13-:17
1000
0
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