behavior o welded plate connections in precast concrete panels under simulated seismic loads
TRANSCRIPT
-
8/10/2019 Behavior o Welded Plate Connections in Precast Concrete Panels Under Simulated Seismic Loads
1/13
Christian L. Hofheins, P.E.Engineer
JM Williams and AssociatesSalt Lake City, Utah
Lawrence D. Reaveley,Ph.D., P.E.ProfessorDepartment of Civil &Environmental EngineeringUniversity of UtahSalt Lake City, Utah
Tests were performed on precast wall panelswith typical loose-plate connectors located inthe vertical joint between panels. The tests wereperformed to investigate the performance of theconnectors under simulated seismic loads. In-plane lateral cyclic loads were applied to thewall panels, which applied tension-shear andcompression-shear forces to the loose-plateconnectors. The paper describes the experimental
program and results for the welded plateconnections in ten precast concrete wall panelassemblies. Design assumptions and simplifieddesign models are also examined. The researchshows that the connection possesses little ductilecapacity and, therefore, is not suitable for use inhigh seismic regions (Zones 3 and 4). However,based on the observed failure modes, minormodifications to the connection are suggested thatwill increase the ductility of the connection.
This paper addresses the behavior of a specific loose-
plate welded connector under applied cyclic loading.
This type of connection is widely used in the United
States. Due to the limited number of tests performed, no
specific design parameters were considered in this study.
The objectives of this investigation were to:
(a) Quantify the performance of the connection in terms
of force-deflection and ductility.
(b) Check the validity of design values that are currently
used for loose-plate welded connections in hollow-core
precast concrete wall panel construction.
Behavior of Welded PlateConnections in Precast ConcretePanels Under SimulatedSeismic Loads
122 PCI JOURNAL
Chris P. Pantelides,Ph.D., P.E.
ProfessorDepartment of Civil &
Environmental EngineeringUniversity of Utah
Salt Lake City, Utah
-
8/10/2019 Behavior o Welded Plate Connections in Precast Concrete Panels Under Simulated Seismic Loads
2/13
-
8/10/2019 Behavior o Welded Plate Connections in Precast Concrete Panels Under Simulated Seismic Loads
3/13
124 PCI JOURNAL
precast walls.6The connections were
designed to be ductile, and to be the
major location of inelastic response
of the structure. Vertical joint con-
nections included different designs of
welded loose-plate and bolted ductile
connections. The connections took ad-
vantage of the interaction between the
embed and concrete by incorporating
flexural yield, tension/compression
yield, shear yield and friction sliding
concepts.
The behavior of a six-story precast
concrete office building under mod-
erate seismicity was investigated.7 It
was concluded that uneven shear dis-
tribution in a precast system causes
a high ductility demand in the panel-
to-panel joint connections. The un-
even distribution drives the connec-
tion elements into the inelastic range.
Therefore, connection details that can
be easily replaced should be used in
precast concrete structures.
As part of the PRESSS five-story
precast concrete building test, a struc-tural wall system consisting of pre-
cast concrete panels was tested under
simulated seismic loading.8 The pre-
cast concrete panels were connected to
each other and the foundation by un-
bonded vertical post-tensioning, using
threaded bars. A horizontal connection
across the vertical joint was provided
by stainless-steel energy-dissipating
U-shaped flexure plates, welded to
embed plates in both adjacent wall
panels. In addition to providing energy
dissipation, these plates provided addi-
tional resistance by shear coupling be-
tween the structural walls. The struc-
tural response of the building under
simulated seismic loads was extremely
satisfactory.
The ability of precast double tee
floor diaphragm and wall systems to
perform adequately under in-plane
seismic forces has been studied in
terms of:
(a) The behavior of connections be-
tween double tees.
(b) The analytical modeling of con-
nectors, diaphragm, and wall systems.
(c) The development of design
guidelines for double tee diaphragms
and wall systems.9
It was found that the interaction be-
tween shear and tension forces in a
flange connection between double tees
could be significant. The connectors
ductility should allow the diaphragm
to redistribute the force among indi-
vidual connectors; this ensures that all
connectors reach their full strength.9
In an experimental study of 3/8 in.
(9.52 mm) stud-welded deformed bar
anchors subject to tensile loads, it was
found that a number of specimens
fractured at the weld. Based on the test
results, quality control procedures and
revised settings were recommended
for stud welding of deformed bar an-
chors.10
The strength and ductility of sev-
eral tilt-up concrete wall panel con-
nections were investigated in a se-
ries of monotonic and cyclic tests.11
Most of the connectors tested did not
show sufficient ductility to be used in
areas of high seismicity. Even when a
connection possessed some ductility,
extensive damage to the surrounding
concrete was observed.
Presently, there is no adequate set of
seismic code requirements for the de-
sign of loose-plate connections in hol-low-core precast wall panels. Many of
the loose-plate connections currently
used in construction are proportioned
using design models that are seldom
backed up with test data.
The truss analogy, currently being
used to describe the performance of
the connection under consideration,
leads to a conservative design.
This paper addresses the behavior of
a specific loose-plate welded connec-
tor for hollow-core precast wall panelsunder cyclic loading; this type of con-
nection is widely used in high seismic
regions of the United States.
The primary objective of this re-
search was to quantify the performance
of the connections between precast
concrete panels using loose-plate con-
nectors and to assess the feasibility for
their use in regions of high seismicity.
Due to the limited number of tests
performed, no specific design parame-
ters have been considered in the study.
The assemblies had variations which
commonly occur in practice. These
included the width of the welded plate,
the length of the weld, the vertical
unevenness of the embedded angles
between adjacent panels, and the mis-
alignment of the three wall panels in
the out-of-plane direction. This paper
presents the experimental results, ana-
lytical models of the connections, and
the details of a proposed new welded
connection.
EXPERIMENTAL PROGRAM
Tests were performed by applying a
quasi-static cyclic load to three precast
hollow-core wall panels connected to-
gether with two loose-plate connectors
at each vertical joint. Ten wall panel
assemblies were tested, all using the
same loose-plate welded connection.
Description of Precast
Wall Panel Assemblies
Fig. 2. Embedded angle assembly for welded connection tested.
-
8/10/2019 Behavior o Welded Plate Connections in Precast Concrete Panels Under Simulated Seismic Loads
4/13
July-August 2002 125
Typically, hollow-core precast pan-
els are 8 ft wide, 12 to 24 ft high (2.44
x 3.66 to 7.32 m) and have six hollow
cores as shown in Fig. 1. The overall
thickness of the panels is 8 in. (203
mm). Panels 12 ft (3.66 m) high and 4
ft (1.22 m) wide were used for testing
due to space constraints in the load
frame. Panels 4 ft (1.22 m) wide were
fabricated by cutting an 8 ft (2.44 m)panel in half.
The two center hollow cores of the
8 ft (2.44 m) panels were filled with
concrete. These solid cores were re-
quired to form a pin connection at the
two outside panels at the supports of
the wall assembly. The average 28-day
compressive strength of the concrete
wall panels was found to be 7150 psi
(49 MPa) with a standard deviation of
190 psi (1.3 MPa).
Description ofWelded Connections
Two welded connections were lo-
cated between panel pairs in vertical
joints. Each welded connection com-
prises two embedded angle assem-
blies and a loose plate. Each embed-
ded angle assembly consists of a 11/2x 2 x 1/4in. (38 x 50.8 x 6.4 mm) x 6
in. (152 mm) long angle, with three 3/8
in. (9.5 mm) diameter weldable steel
deformed anchor bars. The bars are 12in. (305 mm) long, and are stud welded
to the back of the angle as shown in
Fig. 2. Fig. 3 shows the details of the
embedded angle assemblies.
Each wall panel assembly consists
of three hollow-core wall panels joined
together with four welded connections.
Two welded connections are placed 3
ft (914 mm) from the top and bottom
of the wall panels in each vertical joint
found in between the wall panels, as
shown in Fig. 4.The width of the loose plate var-
ied in some wall panel assemblies.
Eight assemblies used 3 in. (76 mm)
wide plates, and two assemblies used
2 in. (51 mm) wide plates. Test re-
sults showed that the plate width had
no effect on the maximum force or
displacement sustained by the wall as-
semblies.
The loose plate was 1/4 to3/8 in.
(6.4 to 9.5 mm) thick A36 steel, and
it was welded to the embedded angle
assembly with two 3/16 in. (4.8 mm)
fillet welds that ran along the 5 in.
(127 mm) vertical edge of the plate
as shown in Fig. 5. All welds were
performed by certified welders with an
E70 electrode and a 7018 rod.
Test Setup
A total of ten wall panel assem-
blies were tested in a load frame at
the Structures Laboratory at the Uni-
versity of Utah. A steel belt enclosed
the wall panel assembly and was con-
nected to a hydraulic actuator with a
force link. The panels were welded
together in the vertical position after
being placed in the load frame. The
entire wall assembly was pushed orpulled by a 150 kip (667 kN) hydrau-
lic actuator through the force link and
the steel belt. The steel belt transferred
the force from the hydraulic actuator
to the wall panel assembly without
restraining the panels.
The panels were supported by two
pin connections placed at the two bot-
tom corners of the wall panel assem-
bly as shown in Fig. 4. The pin used
in this connection was a 2 in. (51 mm)
diameter steel rod. The pin supports
Fig. 3. Details of embedded angle assembly.
supported the wall assembly 1.5 in.
(38 mm) above the bottom of the test
frame, making the pins the only sup-
port for the wall assembly. This al-
lowed the walls to rotate at the pins
and transfer the applied cyclical forcebetween the panels in a symmetrical
manner.
A 1.5 in. (38 mm) thick steel plate
was placed under each corner of the
center panel as shown in Fig. 4. These
plates raised the center panel up to
the same height as the outside panels.
This aligned the embedded angles to
facilitate the placement of the welded
plate. A more detailed description of
the loading system and the wall as-
sembly supports can be found in otherpublications from the University of
Utah.12,13
Test Procedure andInstrumentation
A force was applied to the top left
corner of the wall assembly with a
hydraulic actuator in a quasi-static
manner. The test was carried out in a
force-controlled mode at a rate of ap-
proximately 1 kip (4.5 kN) per second.
Loading steps began at 10 kips (44.5
Note: 1 in. = 25.4 mm.
-
8/10/2019 Behavior o Welded Plate Connections in Precast Concrete Panels Under Simulated Seismic Loads
5/13
126 PCI JOURNAL
kN) and increased by 5 kips (22.2 kN)
until the welded connections failed.
Each loading step consisted of three
cyclic load increments to simulate the
effects of an earthquake. Strain gauges
the wall panel assembly (see Fig. 4).
EXPERIMENTAL RESULTS
The tests revealed the following
characteristics for the connection stud-
ied in this research:
(a) The connection can resist rela-
tively high shear loads.
(b) The connection possesses little
ductile capacity.
(c) The connection should be de-
signed as elastic due to insufficient
ductility.
Failure Mechanism
Cracking around the connections
began near the 20 kip (89 kN) load
cycle. Cracking was initiated by the
embedded angle pushing into the sur-
face of the concrete. As soon as the
concrete crumbled away from around
the connection (see Fig. 6), the de-
formed anchor bars on the back of the
embedded angle assemblies quickly
tore away from their welds. Figs. 6(a)
Fig. 4. Setup and instrumentation of typical wall assembly. Note: 1 in. = 25.4 mm.
Fig. 5. Detailsof welded
loose-plateconnection.
Note: 1 in. =25.4 mm.
were placed on welded plates to form
a three-element rectangular rosette.
Displacement transducers were used
in all of the tests to measure the dis-
placements at various locations of
-
8/10/2019 Behavior o Welded Plate Connections in Precast Concrete Panels Under Simulated Seismic Loads
6/13
July-August 2002 127
and 6(b) illustrate the typical failed
connections.
The following is a description of the
typical mode of failure for this con-
nection:
(a) The concrete around the embed-
ded connections begins to crack.
(b) The bearing capacity of the de-
formed anchor bars and embedded
angle is severely decreased.
(c) The deformed anchor bars
quickly tear free from the embeddedangles as soon as the concrete crum-
bles around the embedded angle as-
semblies.
(d) The load carrying capacity of the
connection is lost.
The welds connecting the loose-
plate to the embedded angle assem-
blies for nine of the ten wall assem-
blies were not damaged. A weld in
one wall panel assembly failed due to
poor penetration of the weld onto the
connecting plate. In general, the welddid not contribute to the failure of the
connection.
Vertical displacement transducers
DT2 and DT3 (see Fig. 4) recorded
very small relative movement between
panels, until the connections failed.
Therefore, the wall assembly moved
as a relatively rigid body until the first
connection failed.
Force-Displacement Relationship of
Wall Panel Assemblies
The hysteretic behavior of Assem-
bly 8 is typical of all wall assemblies
and is shown in Fig. 7. The shape of
the hysteresis loops demonstrates that
they were stable and did not degrade
until sudden failure. The assembly al-
lowed a displacement drift of only 0.5
percent, and did not demonstrate any
appreciable ductile behavior.
The hysteresis envelope for every
wall assembly was approximated by
a general component behavior curveas described in FEMA 273.14The gen-
eral component behavior curve for the
Fig. 6. Welded connections for Assembly 4 at failure: (a) top right connection, and (b) bottom right connection.
Fig. 7. Hysteresis curve for Assembly 8. Note: 1 kip = 4.448 kN; 1 in. = 25.4 mm.
ten assemblies tested is shown in Fig.
8. The general component behavior
curve is able to define the hysteresis
curves into important design criteria.
As defined by FEMA 273, QCE is
the expected strength of the welded
connection of the wall section, and
QCLis the lower-bound estimate of the
strength. Table 1 contains a summary
of the test data that was used to create
the general component behavior curve
of every wall assembly.The mean elastic force, QCL, equals
28.4 kips (126.3 kN), and the mean
(a) (b)
-
8/10/2019 Behavior o Welded Plate Connections in Precast Concrete Panels Under Simulated Seismic Loads
7/13
128 PCI JOURNAL
Table 1. Summary of test results for wall assemblies.
Wall Elastic force,QCL Elastic displacement Ultimate force,QCE Ultimate displacement
assembly (kips) (kN) (in.) (mm) (kips) (kN) (in.) (mm)
1 26.3 117.0 0.44 11.2 28.1 125.0 0.53 13.5
2 24.8 110.3 0.52 13.2 28.8 128.1 0.71 18.0
3 27.1 120.5 0.51 12.9 30.2 134.3 0.62 15.7
4 31.0 137.9 0.63 16.0 35.0 155.7 0.74 18.8
5 32.3 143.7 0.57 14.5 35.0 155.7 0.79 20.1
6 30.2 134.3 0.54 13.7 33.1 147.2 0.71 18.0
7 30.5 135.7 0.55 14.0 34.5 153.5 0.62 15.7
8 23.2 103.2 0.57 14.8 28.2 125.4 0.70 17.8 9 29.9 133.0 0.69 17.5 33.2 147.7 0.80 20.3
10 28.3 125.9 0.40 10.2 30.7 136.6 0.56 14.2
ultimate force, QCE (mean value of
peak on all hysteresis), equals 31.7
kips (141.0 kN). The mean elastic dis-
placement is 0.54 in. (13.7 mm) and
the mean ultimate displacement is 0.68
in. (17.3 mm). Thus, the range for the
inelastic displacement was only 0.14
in. (3.6 mm). According to FEMA
273, the wall panel assembly would
be defined as a force-controlled action
due to the small plastic range.
Strain gauges oriented in a three-
element rosette pattern were applied
to several welded plates on the wall
panel assemblies as shown in Fig. 9.
This rosette pattern was chosen so that
the principal stresses and their direc-
tions could be determined. There was
insufficient instrumentation to deter-
mine the force in each plate directly
from the strain gauges.Fig. 10 shows the principal strains
recorded by the three-element rosette
on the plate of the bottom right con-
nection of Assembly 2. Although the
plate yielded in the last loading cycle,
the connection failed immediately
thereafter. As a result, the ductility of
the connection was not significantly
increased by the yielded plate.
ANALYTICAL RESULTS
Fig. 8. General component behavior of ten wall assemblies. Note: 1 kip = 4.448 kN;1 in. = 25.4 mm.
Fig. 9. Three-element strain gauge
rosette appliedon loose-plate
connector.
-
8/10/2019 Behavior o Welded Plate Connections in Precast Concrete Panels Under Simulated Seismic Loads
8/13
July-August 2002 129
A structural analysis of the wall as-
sembly was performed using the struc-
tural analysis program SAP 2000.15
The purpose of the analysis was to find
the forces across each welded connec-
tion of the wall panel assembly, and
compare them to the commonly used
design methodologies. The precast
concrete wall panels were modeled
as rigid frame elements with a dia-phragm constraint on each wall panel
(as shown in Fig. 11). The wall panel
connections were modeled as rigid
pins, which is a reasonable assumption
given their brittle mode of failure.
The nodes located at the supports of
the wall panel assembly were assigned
pin restraints. The shim supports under
the center panel (see Fig. 4) were
not considered in the model. Verti-
cal displacement transducers revealed
that the center panel rose vertically,whether the wall assembly was being
pushed or pulled. These displacements
were a result of vertical movement
occurring at the pin supports, and the
rigid body motion of the wall panel
assembly.
The holes in the panels for the pin
supports were oversized for ease of
erection in the load frame. The over-
sized holes allowed the entire assem-
bly to rise and move as a rigid body.
As a result, the bottom corners of the
middle panel never touched the shims
during loading cycles. Consequently,
the shim supports did not restrain the
panel assembly, and were not included
in the model.
The weight of each wall panel was
applied as a point load at four differ-
Fig. 10. Principal strains at bottom right plate connection of Assembly 2.
Fig. 11. Structuralanalysis modelof wall panelassembly. Note:1 kip = 4.448 kN.
-
8/10/2019 Behavior o Welded Plate Connections in Precast Concrete Panels Under Simulated Seismic Loads
9/13
130 PCI JOURNAL
ent nodes on each wall panel (see Fig.
11). The average maximum force at
failure, 31.7 kips (141.0 kN), was ap-
plied as the lateral load at the top left
corner of the wall panel assembly to
find the capacity of each welded con-
nection. The structural analysis results
are shown in Fig. 12.
For the above conditions, the shearforce at failure of the welded con-
nections was 15.0 kips (66.7 kN) on
the two left connectors, and 16.6 kips
(73.8 kN) on the two right connectors.
This is significant because the capac-
ity of this connection typically used
in design is equal to 8 kips (35.6 kN).
Structures built with these welded con-
nections were safely designed with an
approximate factor of safety of 1.9.Using this design value, the connection
will safely stay in the elastic range.
Force-Displacement Relationshipof Welded Connection
The force-displacement relation-
ship of each welded connection was
found by plotting the relative vertical
displacement of two adjoining wallpanels versus the shear force across
the welded connection. The relative
displacement of two adjoining wall
panels in the vertical direction was
found by subtracting data retrieved
from displacement transducers DT2
and DT3 (see Fig. 4).
The shear force across each connec-
tion was found as follows: the force
applied by the hydraulic actuator on
the wall assembly was multiplied by
the ratio of the average maximum
force at failure of the welded connec-
tion, or 16.6 kips (73.8 kN), to the
average maximum force at failure of
the wall panel assembly, or 31.7 kips
(141.0 kN). This assumption is reason-
able because the connections behave
in a linear elastic manner.
The hysteresis curve for the connec-
tors of eight wall panel assemblies,
was approximated by a general com-
ponent behavior curve as described in
the Guidelines for the Seismic Reha-
bilitation of Buildings, FEMA 273.14
Fig. 12. Resultsof structuralanalysis for
maximum lateralload applied
to the wallassembly.
Note: 1 kip =4.448 kN.
Fig. 13. General component behavior of the welded connectors of eight wallassemblies. Note: 1 kip = 4.448 kN; 1 in. = 25.4 mm.
-
8/10/2019 Behavior o Welded Plate Connections in Precast Concrete Panels Under Simulated Seismic Loads
10/13
July-August 2002 131
Fig. 13 shows the general component
behavior curve for the connectors of
eight wall assemblies. The average
elastic force on the connectors was
14.7 kips (65.4 kN), and the average
ultimate force was 17.1 kips (76.1
kN).
The force-displacement relationship
is linear until the connection fails in a
brittle manner. This connection shouldbe designed to remain elastic due to
its brittle mode of failure and limited
ductility.
Analytical Model ofWelded Connection
The probable resisting mechanisms
of the connector under consideration
are bearing and tension actions in the
deformed anchor bars, as well as bear-
ing of the angle section. Many de-
signers currently model this welded
connection with the truss analogy as
described in the PCI Design Hand-
book.16
Fig. 14 is an illustration of the truss
analogy. The following equations are
used to describe this model:
CU= TU= Asfy (1)
VRU= (CU+ TU)cos (2)
where
CU = compression force
TU = tensile force
= capacity reduction factor =
0.9
= angle of deformed anchor
bar = 45 degrees
As = area of 3/8 in. (9.5 mm) di-
ameter deformed anchor bar
= 0.13 sq in.(71 mm2)
fy = yield strength of mild steel
reinforcement [= 60 ksi (420
MPa)]
VRU = vertical shear force resisted
by connection
The equations from the truss anal-
ogy yield a vertical shear resistance
of 8.4 kips (37.4 kN) for each connec-
tion. The analysis indicates that the
average capacity of this connection is
between 15.0 and 16.6 kips (66.7 to
73.8 kN). The truss analogy is a con-
servative design methodology when
applied to this connection.
The following is a list of some of
the differences between the truss anal-
ogy and the connection under consid-
eration:
a. The angle for this connection
equals zero, not 45 degrees (see Fig.
2).
b. The deformed anchor bars are
bent 90 degrees into the back of the
angle (see Figs. 2 and 3). The bars
will not be able to develop the full
tensile capacity as described in the
truss analogy. The deformed anchor
bars act more as 3/8in. (9.5 mm) studs
with ineffective tails rather than bars
in tension.
c. The truss analogy does not ac-
count for the bearing of the angle as-
sembly into the concrete. Angle bear-
ing is one of the main force resisting
mechanisms of the connection.
Fig. 15 illustrates that the deformed
Fig. 14. Truss analogy model for welded connection.
Fig. 15. Statics ofdeformed anchorbar at failure forcurrent connection.Note: 1kip = 4.448kN, 1 in. = 25.4mm; 1 k-in. = 133
N-m.
-
8/10/2019 Behavior o Welded Plate Connections in Precast Concrete Panels Under Simulated Seismic Loads
11/13
132 PCI JOURNAL
anchor bar cannot fully develop in ten-
sion due to the eccentric load from the
bend in the bar. Assuming the force
taken by each vertical deformed an-
chor bar is 8.3 kips (36.9 kN) (half of
the total vertical shear force taken by
the connection), the maximum shear
and moment taken by each vertical de-
formed anchor bar is 8.3 kips and 10.4
kip-in. (36.9 kN and 1.17 kN-m), re-spectively. The eccentric load causes
the deformed anchor bars to quickly
tear free from their welds as soon as
the concrete crushes around the con-
nection.
PROPOSED NEW WELDEDCONNECTION
The most effective way to improve
this connection is to provide a larger
surface area for concrete bearing andto minimize eccentric loads from the
deformed anchor bars. Fig. 16 is a
drawing of a proposed new embedded
angle assembly. The angle is replaced
by a 6 in. (152 mm) long ST2x3.85
to create a greater bearing area in the
concrete.
One continuous deformed anchor
bar replaces the two vertical deformed
anchor bars of the previous connec-
tion. The vertical deformed anchor
bar is attached to the back of the em-
bedded angle assembly with a 4 in.
(102 mm) long, 3/16in. (4.8 mm) fillet
weld. The vertical deformed anchor
bar is bent at 5 degrees to minimize
eccentric loads and to ensure adequate
concrete cover.
The strength of this fillet weld
can be described by Eq. (3), and the
strength of the base metal can be de-
scribed by Eq. (4), as:17
Rn= 0.75te(0.6Fexx) (3)
Rn= 0.75t(0.6Fu) (4)
where
Rn = strength of fillet weld or base
material
Fexx = strength of electrode = 70 ksi
(483 MPa)
Fu = tensile strength of base mate-
rial = 60 ksi (420 MPa)
te = 0.707a
a = weld size = 3/16in. (4.8 mm)
t = thickness of base material =5/16in. (7.9 mm)
Eq. (3) yields the strength of the fil-
let weld as 4.2 kips per in. (0.74 kN/
mm), and Eq. (4) yields the strength
of the base material as 8.4 kips per in.
(1.47 kN/mm). A 4 in. (102 mm) long
weld gives a strength of 16.8 kips (74.7
kN), which is significantly higher than
the allowable shear resistance of the
welds in the tested connection. In addi-
tion, the concrete will not easily break
away from the connection due to the
increased bearing area with the web
of the structural tee embedded into the
wall.
DISCUSSION OF
TEST RESULTS
Engineers prefer the panel connec-tions, not the panels themselves, to
be the weak link in the system. This
investigation has shown that the con-
nections are in fact the weakest link.
Although the loose-plate connection
used in this research effectively trans-
ferred the applied shear forces, the
connection failed in a brittle manner.
The small displacement ductility
exhibited by the welded connections
is lost as soon as the deformed an-
chor bars on the back of the embeddedangle fracture from their welds. Fail-
ure occurs before shear yielding can
take place in the welded plate.
These tests reveal that hollow-core
precast concrete panels can be used in
seismic regions provided that the con-
nections can be improved. To this end,
a new welded connection is proposed;
ductility may be restored to the sys-
tem by increasing the surface area for
concrete bearing and by reducing the
eccentric load in the deformed anchor
bars.
If the connection is a location of
ductile inelastic deformation, the pre-
cast concrete panels will remain elastic
under seismic response. Damage to
the overall structure will be reduced
and repair of the structure will be less
costly. Ductility in shear will allow the
force to redistribute among individualconnectors. Ductility will enable all
connectors to reach their full strength,
thereby increasing the overall force re-
sisting capability of the structure.
For existing connections of the type
tested in this investigation, a seismic
retrofit option has been studied using
a carbon fiber composite connection,
which will be published shortly.
CONCLUSIONS
Simulated seismic load tests of
Fig. 16. Details of proposed new embedded angle assembly. Note: 1 in. = 25.4 mm.
-
8/10/2019 Behavior o Welded Plate Connections in Precast Concrete Panels Under Simulated Seismic Loads
12/13
July-August 2002 133
loose-plate vertical connections be-
tween precast concrete wall panels
were performed. Based on the results
of this investigation, the following
conclusions can be drawn:
1. The loose-plate connection com-
monly used in precast construction can
resist relatively high shear forces.
2. The connection fails in a brittle
manner when the deformed anchorbars tear free from the embedded an-
gles, which occurs as soon as the con-
crete crumbles around the embedded
angle assemblies; as a consequence,
the connection possesses little ductile
capacity.
3. The connection should be de-
signed to remain elastic; in its current
form, the connection is not suitable for
use in areas of high seismic regions
(Zones 3 and 4).
4.The design methodologies com-
monly used for this connection are
conservative.
5. The connection can be modified
to increase its ductile behavior by pro-
viding more surface area for concretebearing, and by minimizing eccentric
loads in the deformed anchor bars.
ACKNOWLEDGMENT
The authors would like to acknowl-
edge the funding provided by XXsys
Technologies, Inc., and the Center
for Composites in Construction at the
University of Utah.
The authors wish to express their
gratitude to Eagle Precast Company
(Monroc, Inc.), for providing the pre-
cast wall specimens.
The authors would like to thank
Vladimir Volnyy and Professor Janos
Gergely for their assistance with thetests. In addition, the authors are
grateful to Philip Richardson and Carl
Wright of Eagle Precast Company for
their suggestions.
Lastly, the authors want to express
their appreciation to the PCI JOUR-
NAL reviewers for their thoughtful
and constructive comments.1. Rostasy, F. S., Connections in Precast Concrete Structures
Continuity in Double-T Floor Construction, PCI JOURNAL,
V. 7, No. 4, 1962, pp. 18-48.
2. Scoggin, H. L., and Pfeiffer, D. W., Cast-in-Place Concrete
Residences with Insulated Walls-Influence of Shear Connec-
tors on Flexural Resistance,Journal of the PCA Research and
Development Laboratories, V. 9, No. 2, 1967, pp. 2-7.
3. Abdul-Wahab, H. M. S., Ultimate Shear Strength of Vertical
Joints in Panel Structures,ACI Structural Journal, V. 88, No.
2, March-April 1991, pp. 204-213.
4. Spencer, R. A., and Neille, D. S., Cyclic Tests of Welded
Headed Stud Connections, PCI JOURNAL, V. 21, No. 3,
May-June 1976, pp. 70-81.
5. Stanton, J. F., Hawkins, N. M., and Hicks, T. R., PRESSS
Project 1.3: Connection Classification and Evaluation, PCIJOURNAL, V. 36, No. 5, September-October 1991, pp. 62-71.
6. Schultz, A., Tadros, M. K., Juo, X. M., and Magana, R. A.,
Seismic Resistance of Vertical Joints in Precast Shear Walls,
Proceedings, XII FIP Congress, Washington, DC., May 29 -
June 2, 1994.
7. Low, S.-G., Behavior of a Six-Story Office Building Under
Moderate Seismicity, University of Nebraska, Lincoln, NE,
May 1995.
8. Priestley, M. J. N., Sritharan, S., Conley, J. R., and Pampanin,
S., Preliminary Results and Conclusions from the PRESSS
Five-Story Precast Concrete Test Building, PCI JOURNAL,
V. 44, No. 6, November-December 1999, pp. 42-67.
9. Pincheira, J. A., Oliva, M. G., and Kusumo-Rahardjo, F. I.,Tests on Double-Tee Flange Connectors Subjected to Mono-
tonic and Cyclic Loading, Research Report, University of
Wisconsin, Madison, WI, 1998.
10. Strigel, R. M., Pincheira, J. A., and Oliva, M. G., Reliability
of 3/8 in. Stud-Welded Deformed Bar Anchors Subject to Ten-
sile Loads, PCI JOURNAL, V. 45, No. 6, November-Decem-
ber 2000, pp. 72-82.
11. Lemieux, K., Sexsmith, R., and Weiler, G., Behavior of Em-
bedded Steel Connectors in Concrete Tilt-Up Panels, ACI
Structural Journal, V. 95, No. 4, July-August 1998, pp. 400-
413.
12. Pantelides, C. P., Reaveley, L. D., Gergely, I., Hofheins, C.,
and Volnyy, V., Testing of Precast Wall Connections, Uni-
versity of Utah, Department of Civil and Environmental En-
gineering, Report UUCVEEN 97-02, 97-03, 98-01, Salt Lake
City, UT, 1997-98.
13. Hofheins, C., Welded Loose-Plate Connections for Hollow-Core Precast Wall Panels, M.Sc. Thesis, Department of Civil
& Environmental Engineering, University of Utah, Salt Lake
City, UT, May 1999.
14. Building Seismic Safety Council, NEHRP Guidelines for the
Seismic Rehabilitation of Buildings, FEMA Publication 273,
Federal Emergency Management Agency, Washington, DC,
October 1997.
15. SAP2000 Analysis Reference, Computers and Structures, Inc.,
V. I, Berkeley, CA, 1997.
16. PCI Committee on Industry Handbook, PCI Design Hand-
book: Precast and Prestressed Concrete, Fifth Edition, Pre-
cast/Prestressed Concrete Institute, Chicago, IL, 1999.
17. Salmon, C. G., and Johnson, J. E., Steel Structures Design andBehavior, Fourth Edition, Harper Collins College Publishers
REFERENCES
APPENDIX A NOTATIONInc., New York, NY, 1996.
Ab = area of reinforcing bar
As = area of deformed anchor bar
CU = compression force
Fexx = strength of electrode
fs = steel stress
Fu = tensile strength of base material
fy
= yield stress of reinforcement
n = number of reinforcing bars
QCE= expected strength
QCL= lower-bound strength
Rn = strength of fillet weld or base material
t = thickness of base material
te = effective area of weld
TU = tensile force
VRU = vertical shear force resisted by connection
Vs = shear strength of connection = angle of deformed anchor bar
-
8/10/2019 Behavior o Welded Plate Connections in Precast Concrete Panels Under Simulated Seismic Loads
13/13
= capacity reduction factor