concrete capacity of cazaly hangers in shallow members

8/3/2019 Concrete Capacity of Cazaly Hangers in Shallow Members

1/26Fal l 2010 |PCI Journal0

Editors quick points

n The PCI design guidelines for the Cazaly hanger connection are

based on a series of tests conducted by the Canadian Precast/

Prestressed Concrete Institute (CPCI) in 1965.

n Little research or review of the test results and failure models

has been performed since the CPCI reports were published.

n This research and reporting of test results focuses on updating

the PCI design guidelines for the Cazaly hanger connection.

Concrete

capacity

design

of Cazaly

hangers

in shallow

membersWestin T. Joy,Charles W. Dolan,and Donald F. Meinheit

Connections play an important role in building construc-

tion for all materials. Field-installed connections used

in precast concrete systems are often much simpler than

those required in steel, timber, or even some cast-in-place

concrete systems. This simplicity gives precast concrete

an important advantage over other building systems by

allowing shorter building assembly and, ultimately, early

completion of the building project.

However, the simplicity and history of use may lead the

engineer to assume that connections are as robust as the

rest of the structural system. Thus, connection design

becomes routine. If the underlying design theory is based

on incomplete assumptions, the boundaries of application

of the design method may be exceeded, which could lead

to unexpected performance.

One connection that gained popularity in the 1960s and

has been in continuous use in the precast concrete indus-

try since is the Cazaly hanger. Developed by Laurence

Cazaly, the Cazaly hanger was first used in 1957 in theconstruction of a precast concrete warehouse building. The

Cazaly hangers were used as purlin-to-girder connections

and allowed the members to be erected much more quickly

and economically.1

The three main components of the Cazaly hanger are a

cantilevered top bar, a strap, and dowel anchorage in the

top and bottom of the member (Fig. 1). In the original

design, the cantilevered bar serves as the main supporting

element for the member, while the strap transfers the verti-

cal load to the member web. The bottom dowel provides

anchorage for the strap to avoid rotational pullout of the


2/26 10PCI Journal|Fal l 2010

1965 research program on hanger connections. Little

research or review of the test results and failure models

has been performed since these reports were published.1,2

Beginning with the third edition of the PCI Design Hand-

book: Precast and Prestressed Concrete,3 a shear-friction

calculation for the bottom-dowel anchorage of the hanger

has been included as one of the design checks to establish

the connection strength.

Concrete capacity design (CCD) for concrete inserts was

introduced in the 1990s and has solidified the procedures

for design and evaluation of anchorage in concrete. In the

current study, the CCD models of ACI 318-08 appendix

D4 and the PCI design method5 are applied to the original

1965 research-program specimens as well as recentlytested specimens, reported herein, to evaluate the Cazaly

hanger for both shear friction and CCD failure modes.

This research and reporting of test results focuses on

updating the PCI design guidelines for the Cazaly hanger

connection. Proposed revisions to the current design guide-

lines include removing unnecessary or noncritical design

checks and unifying deep- and shallow-section design

methodologies to provide consistent, safe strength predic-

tions.

Background

strap, and the top dowel aids in transferring any horizontal

force to the rest of the member.2 Note that the sketches in

Fig. 1 and 2 are simplified because the top dowel is shownwithout cover. In the usual case, the top bar is embedded in

concrete.

The Cazaly hanger is cast into a concrete member, leaving

the cantilevered top bar extended beyond the member end.

The precast concrete piece is then placed so that the pro-

truding bar rests on the supporting member. Figure 1 is a

sketch of a typical system in which the hanger is placed on

a transverse member. Typically, a Cazaly hanger is a grav-

ity connection; however, the exposed portion of the top bar

may be connected to the supporting member either through

bolting or welding to embedded steel plates in the support-ing concrete girder or to a steel support member to make it

function as a bracing element. One advantage of the Cazaly

hanger is its ability to minimize the overall structural

depth, leading to a decrease in floor-to-floor height. By de-

creasing the floor-to-floor height, less material is used both

inside and outside the structure and an economical savings

for the building project may result, or more floors can be

placed within the code building-height restrictions.

The PCI design guidelines for the Cazaly hanger con-

nection are based on a series of tests conducted for the

Canadian Precast/Prestressed Concrete Institutes (CPCIs)

Figure 1. This diagram shows the main components o a Cazaly hanger. Source: PCI Industry Handbook Committee 2004. Note:Vu = ultimate actored shear load.


3/26Fal l 2010 |PCI Journal2 10

Of these seven hanger variables, one variable stood out

as needing further attention. The unstudied variable was

the beam and corresponding hanger depth, and therefore,research on shallow sections remained an open issue.

Those test specimens with hanger depths of 10 in. (250

mm) or less failed to reach the ultimate load calculated us-

ing the CPCI handbook first-edition recommendations.1 To

account for this shortcoming, a strength-reduction factor,

based on hanger depth, was proposed to be included in the

design procedure.

The steel area required for the bottom-dowel anchor

depended on the concrete key (the area of concrete within

the enclosed U-shaped strap) and the tension force in the

strap at failure of the concrete key. A shallow hanger depthmeans a smaller concrete key, so the researchers devel-

oped a so-called key factor. The key factor was to address

designing shallow hangers by adjusting the strength of the

concrete key downward when designing the bottom-dowel

anchor.

Ife, Uzumeri, and Huggins2 presented the results of tests

performed at the University of Toronto for the CPCI 1965

research program on hanger connections. The University of

Toronto tested a total of 52 hangers, 8 of which were part of

a pilot test series to gather insight on possible failure modes

and variables potentially affecting the hanger capacity.

In 1965, CPCI funded a research program to study hanger

connections.1 CPCI chose to focus this research program

on hanger connections because at the time the Cazalyhanger was widely used throughout Canada. Tests for the

CPCI research program were carried out at the University

of Alberta in Calgary, the University of Manitoba in Win-

nipeg, and the University of Toronto in Ontario. CPCI sug-

gested that the following variables be studied throughout

the testing process:

shear spantodepth ratio

web reinforcement along the top bar

beam depth

fabrication tolerances

concrete strength

prestressing

horizontal forces

Figure 2. This schematic sketch shows how a Cazaly hanger is placed on a support girder.



All 52 hangers used a closed, U-shaped strap, as shown in

Fig. 1. The top bar and strap were overdesigned and were

not the critical components of the hanger system. Tests

performed on hangers without a bottom dowel resulted in

failure by shearing of the concrete key on a plane flush

with the back of the strap (Fig. 3). This failure further sup-

ported the thesis that the strength of the concrete key plays

an important role in the overall capacity of the hanger.

When the bottom dowel was included in the test speci-

men, all of the tests resulted in ultimate failure only when

the bottom-dowel anchorage of the strap failed.2 Failure

of the strap anchorage was characterized by the failure of

the bottom dowel welded to the strap, allowing the hanger

to rotate away from the member. The hanger capacity

was attributed to the combination of shear strength of the

concrete key infill within the strap and the strength of the

bottom dowel in shear.

In cases where the specimens used two dowels for the bot-

tom anchorage (one on each leg of the strap), the hanger

capacity was reportedly controlled not only by the concrete

key and the dowels but also the bearing capacity of the

concrete above the dowels.2

Observations by the University of Toronto research team

reinforced the importance of hanger depth on the hanger

capacity. A series of 14 hanger specimens in the test pro-

gram were identical except for the variation of strap depth,

which varied from 10 in. to 16 in. (250 mm to 400 mm).

These 14 specimens were all in beams 20 in. (500 mm)

in depth. The decrease in strap depth from 16 in. to 10 in.

(400 mm to 250 mm) caused a reduction in hanger capac-ity of 38%, despite a 6% increase in concrete strength.

Figure 4. Assumed loads are given or the Cazaly hanger components. Note: V= shear orce on insert.

Figure 3. Shown is what Ie et al. described as a shear-riction ailure. Source: Ie,

Uzumeri, and Huggins 1968. Note: V= shear orce on insert.



The conclusion drawn from these test results was that the

hanger capacity depends more on the hanger depth than on

the strength of the concrete, and the relationship between

hanger depth and capacity is not linear.2 The Canadian

research team concluded that the decrease in capacity for

the shallow hangers is partly due to the decrease in the

concrete shear-key area.

The sixth edition of the PCI Design Handbook: Precast

and Prestressed Concrete5 (the edition to which we are

henceforth referring as the PCI Design Handbook) relieson various simplifying and presumably conservative as-

sumptions about the hanger and incorporated shear-friction

behavior for the design of the Cazaly hanger. The PCI De-

sign Handbookstates that the cantilevered top bar is typi-

cally proportioned such that the hanger strap is subjected

to, and thus designed for, 1.33 times the ultimate shear

force on the hanger. The 1.33 factor results from the statics

of the bearing reaction on the hanger and proportioning the

top bar such that the bearing load at the interior end of the

top bar is 33% of the applied load (Fig. 4).

The PCI Design Handbookdesign procedure assumes thatthe ultimate shear force acts at the middle of the bearing

length on the supporting member, an assumption that af-

fects the moment in the cantilevered bar. The PCI Design

Handbookallows the cantilevered bar to be designed in

one of two manners:

for the moment combined with axial and shear forces

for the moment at yield by using elastic section prop-

erties, ignoring the shear and axial force contributions

The bearing pressure on the interior portion of the cantile-

ver bar can be conservatively based on the hanger width.

The top dowel is sized to carry axial force (that is, the ten-

sion usually associated with time-dependent deformations

of the beam member), while the bottom dowel is designed

using shear-friction concepts.

Cazaly hanger failure modes

The Cazaly hanger consists of multiple parts, leading to

two global failure modes: steel failure of the hanger andconcrete failure of the connection unit. Each of the condi-

tions is evaluated, and the lowest capacity establishes the

strength of the connection. This is consistent with the ACI

318-08 appendix D4 design method.

The steel failure modes include yielding of the cantile-

vered top bar due to bending (Fig. 5), yielding of the strap

in tension, failure of the bottom anchorage, or failure of

the weld between the strap and the cantilevered top bar.

Because the design approach requires the hanger to be

stronger than the concrete capacity, the PCI Design Hand-

bookdesign method is adequate for bending of the top barabout the centerline of the strap as well as strap yielding.

In all connection designs, the weld strength should be

stronger than the rest of the connection components. This

ensures that the connection will not fail due to a brittle

weld fracture.

Failure of the concrete may be reached through one of

several different failure modes:

shear across the entire concrete section

Figure 5. This sketch shows possible ailure modes or a Cazaly hanger.



shear friction

concrete breakout

Shear across the full concrete cross section is gener-

ally addressed with the inclusion of shear stirrups, and

the cross-section shear strength is based on ACI 318-08.

Shear-friction failure is controlled by the capacity of the

concrete in shear in the key area and the bottom dowel, as

proposed by Ife, Uzumeri, and Huggins.2 Figure 3 shows

an example of what the original researchers described as a

shear-friction failure. In the 1965 CPCI research program,

test specimens without bottom dowels failed by shear-fric-

tion failure where the capacity was limited to the strength

of just the concrete key. Without dowels, the shearing of

the concrete key occurred on a vertical plane flush with the

back of the strap. Sketches of the concrete failure modes

are shown in Fig. 5.

ACI 318-08 appendix D4 describes CCD for headed studs

cast in concrete. Appendix D uses a 35 deg failure plane

for the concrete-breakout prism for both tension and shear

loading of the anchors. The concrete tension breakout

capacity is dependent on the area of the failure plane,

Figure 6. These photographs show side and end views o the ailure o a shallow member with modied Cazaly hangers.



which is highly dependent on the depth of the embedment.

Correction factors are included to account for anchors

near edges or corners and also for eccentricity in loading.

While the CCD methods are prescribed for headed studs

and expansion anchors, Fig.6 suggests that the behavior

of the shallow Cazaly hanger follows one of the concrete-

breakout behavior modes instead of a shear-friction failure

mode.

CCD breakout failure, when applied to this case, is either

a tension or shear mode. Tension and shear failures appear

similar but occur for two distinct reasons. ACI 318-08

appendix D4 contains pictorial examples of the concrete

breakout of headed studs due to tension and shear, as well

as design strength models for the prediction of the two fail-

ure modes. Tension breakout and shear breakout are shown

pictorially in Fig. 7.

In the Cazaly hanger, concrete breakout due to tension

would be caused by pulling on the hanger strap (Fig. 8).

The mechanical anchorage of the strap to the concrete

would lead a section of the concrete to break out from the

parent member. For the CCD methodology, the strap acts

similarly to a cast-in headed anchor in tension. The ACI

318-08 prediction of concrete-breakout strength, based

on headed cast-in-place anchors, should be conservative

for the strap because the strap contact area in the bottom

bend is larger than the bearing area of the typical head of a

headed anchor.

Breakout due to shear can be viewed as the strap transfer-

ring tension to the bottom of the strap and loading the bot-

tom dowel in shear (Fig. 9). The shear on the bottom dowelthus causes a failure plane at about 35 deg and appears

identical to the failure plane caused by tension breakout.

For the CCD analogy, the bottom dowel acts similarly to a

cast-in headed anchor in shear.

Anderson and Meinheit6 conducted numerous tests on

headed studs in shear to determine capacity and develop

design methods. Anderson and Meinheit compared dif-

ferent behavior models to predict their test results, one

of which was the ACI 318-08 appendix D method. The

results obtained demonstrate the variation in test-to-

prediction ratios for different tests when using the ACI

318-08 appendix D shear-prediction method void of the

reduction to get a 5% fractile characteristic equation. A

histogram of the variation of the ACI prediction of capac-

ity in uncracked concrete was adapted from Anderson and

Meinheits work (Fig. 10).

The ACI 318-08 appendix D approach resulted in an aver-

age test-to-predicted failure load in uncracked concrete of1.25 with a standard deviation of 0.245. A test-to-predicted

Figure 7. These sketches show the concrete breakout o headed anchors in ten-

sion and shear. Note: N= tensile orce on insert; V= shear orce on insert.

Figure 8. This sketch shows the tension breakout model applied to the Cazaly hanger and the concrete capacity design equivalent. Note: N= tensile orce on insert.



ACI 318-08 appendix D CCD model to remove the conser-

vative nature of the ACI 318-08 model to make the design

model more consistent with test data.

ratio of 1.25 implies that the ACI 318-08 shear model,

without phi factors, when applied to headed-stud concrete-

breakout failures in uncracked concrete, is conservative.

The design procedure for headed studs loaded in shear in

the sixth edition of the PCI Design Handbookmodified the

Figure 9. This sketch shows the shear-breakout model applied to the Cazaly hanger and the concrete capacity design equivalent. Note: V= shear orce on insert.

Figure 10. This histogram shows shear test results on headed studs loaded toward a ree edge compared with ACI 318-08 appendix D equations. Note: Avg. = average;CCD = concrete capacity design; SD = standard deviation.



breakout strength for the 1965 CPCI specimens, a value of

c,N= 1.25 was used based on the assumption of no crack-ing in the connection under service-level loads.

For embedment less than 11 in. (280 mm),Nb is calculated

by Eq. (3) (Eq. D-7 in ACI 318-08):

h N k f .

efb c c

1 5m= la k (3)

where

kc = 24 for cast-in-place anchors

hef = embedment depth of the anchor

= a modification factor addressing lightweight concrete

fcl = concrete strength in psi

For hefbetween 11 in. and 25 in. (280 mm to 635 mm)

the 5% fractile design strength of a single anchor can be

expressed as Eq. (4) (Eq. D-8 in ACI 318-08):

N f h16b c ef 5

3m= l^ h (4)

These equations are based on the cracked-concrete tension

breakout frustum developed by either the head of a headed

anchor or the expansion force from a post-installed anchor.

Both of these equations include a reduction in strength to

get a 5% fractile load. The average capacities are about 4/3of the fractile values.

These models do not account for the size of the head on

the headed anchor or plate washers. Further research is

needed to confirm the actual effective load-bearing capac-

ity of the anchor straps acting as headed bearing if the

behavior model is one of tension.

PCI method for tension breakout

The PCI tensile breakout capacity is given as

.h

f N A C 3 33

,ef

ccb n crb ed N

m }=l

(5)

where

An = projected surface area of insert or group of inserts

Ccrb= cracking factor = 1.0 for uncracked section

The PCI formulation assumes that a precast concrete sec-

tion is uncracked. Hence, Ccrb is 1.0 and Ccrb decreases for

Concrete-breakout strength:tension

ACI 318-08 appendix D method

ACI 318-08 appendix D provides the 5% fractile design

equations to use when predicting the concrete-breakout

strength of headed studs in shear or tension. These equa-tions can be applied directly to the traditional Cazaly

hanger with some minor redefinitions of parameters as

summarized here. The nominal concrete-breakout strength

for tension of a single Cazaly hanger is predicted by Eq.

(1) (Eq. D-4 in ACI 318-08).

NA

AN

, , ,cbNco

Nc

ed N c N cp N b} } }= (1)

where

ANc = projected area of failure surface for an anchor or

group of anchors considering limitations due to

size of member in which anchor is located

ed,N = a modification factor for edge effects

c,N = a modification factor addressing concrete cracking

at service loads

cp,N = a modification factor addressing splitting of post-installed anchor, which does not occur here, thus

cp,N= 1.0

Nb = basic concrete 5% fractile breakout design strength

of a single anchor in tension in cracked concrete

The calculation forANco is similar toANc except that it is not

limited by edge or corner influences, spacing, or member

thickness. In other words, it assumes full development of

the concrete capacity based on a single anchor, as is calcu-

lated in Eq. (2) (Eq. D-6 in ACI 318-08).

A h9 Nco ef 2

= a k (2)

where

hef = equivalent to the depth to the bottom anchor of the

Cazaly hanger in the present context

The ratio ofANc/ANco therefore gives the influence of edges,

corners, spacing, and number of anchors in a group in a

relatively straightforward manner.

When analysis indicates no cracking at service loads, as

would be the case for a Cazaly hanger at the end of a beam

without shear cracking, c,N= 1.25. In calculating the



C3 = PCI correction for edge effects

Ch = PCI correction for thickness

Cev = PCI correction for eccentric load

Cvcr= PCI correction if the section is cracked

For a Cazaly hanger Ch, Cev, andCvcr= 1.0. The PCI un-

cracked average strength equation Vco3 from the Anderson

and Meinheit research is:

fV BED22. .

cco3

0 5 1 33= la k

where

BED = the basic embedment depth of the Cazaly hanger

If the 5% fractile value is used, which is what the ACI

318-08 design equation represents, then the coefficient 22

reduces to 16.5, as used in the design example. Last, the

edge correction factor C3 is given by:

. .BED

SEDC 0 7 1 0

3

3#=

where

SED = the side-edge distance to the first anchor plus half

the center-to-center spacing of inserts

Anchor reinforcement

Reinforcement immediately adjacent to the anchor af-

fects the connection strength. ACI 318-08 appendix D4

addresses anchor reinforcement in a straightforward

manner. Section D.6.2.9 of ACI 318-08 states the follow-

ing: Where anchor reinforcement is either developed in

accordance with Chapter 12 on both sides of the breakout

surface, or encloses the anchor and is developed beyond

the breakout surface, the design strength of the anchor

reinforcement shall be permitted to be used instead of theconcrete-breakout strength in determining Vn. A strength

reduction factor of 0.75 shall be used in the design of the

anchor reinforcement.

ACI 318-08 allows anchor reinforcement to be designed

for a capacity greater than concrete breakout. When the

member cracks in a manner that looks like a concrete-

breakout crack, anchor reinforcement provides an alterna-

tive load path and assumes the entire load that the anchor

was carrying before cracking. To ensure strength and

ductile behavior, it is recommended that the minimum

anchorage reinforcement capacity equal the CCD capacity.

a cracked section. ACI 318-08 assumes a cracked section

and increases capacity if the section is uncracked. The

difference is reflected in the initial coefficient in Eq. (5).

Equations (1) and (5) provide identical strength predictions

when the appropriate correction factors are applied.

Concrete-breakout strength:

shearACI 318-08 appendix D method

The shear-breakout model is similar to the tension model,

as shown in Fig. 8 and 9. The cracked concrete, single

anchor ACI 318-08 appendix D basic shear-strength cal-

culation model is partially dependent on the bottom-dowel

embedment length e as depicted in Eq. (6) (ACI 318-08

Eq. D-25).

d

V d f c8

.

.

a

e

b a c a

0 2

1

1 5,m= l

f ap kR

T

SS

SS

V

X

WW

WW(6)

where

da = outside diameter of anchor

ca1 = distance from center of anchor shaft to edge of

concrete in one direction, taken in the direction of

the applied shear

For the calculations within this research, the maximum

limit on the e/da ratio of 8 was used for the bottom dowel.Because the shear-breakout capacity depends on the dowel

length, the calculated strength can be changed by modifying

the dowel embedment. Equation (6) is also the 5% fractile de-

sign strength for an anchor in cracked concrete. The average

cracked strength is about 4/3 times the 5% fractile strength.

PCI method for shear

The PCI shear-strength-prediction equation does not

have the anchor embedment eterm included because the

research found that embedment did not have a significant

effect on strength. Diameter, likewise, was not found to bevery influential for the test results reviewed on diameter of

headed anchors.

The PCI formulation for shear capacity, as presented in the

PCI Design Handbook, is:

Vc3 = Vco3 C3 Ch Cev Cvcr

where

Vco3 = PCI basic shear-breakout strength of an insert



CPCI researchand shear friction

The results of the 1965 CPCI research program on hanger

connections show that in all cases the ultimate load of the

connection was reached when the bottom-dowel anchor

failed and allowed the hanger strap to rotate away from the

member.

2

However, the researchers described a slightlydifferent behavior for test specimens with differing bottom-

dowel configurations. Hangers with a single bottom dowel

attached to the bottom of the strap failed due to combined

shear on the concrete key and the bottom dowel. Those test

specimens with two bottom dowels attached to the bot-

tom of the strap failed when the concrete bearing capacity

above the bottom dowels was exceeded, in addition to the

shear capacity of the concrete key. The inclusion of two

bottom dowels on the vertical sides of the strap, as opposed

to a single bottom dowel at the bottom of the strap, resulted

in a much more complex cracking pattern throughout the

tests, as shown in Fig. 11. Last, three hangers without

bottom-dowel anchors were tested and failed due to shear

on the concrete key alone. The vertical failure plane for the

hangers without bottom anchorage was flush with the back

of the hanger strap (Fig. 3).

While shear friction as a possible behavior-prediction

mode for the Cazaly hanger, the hangers from the 1965

CPCI research program violate important requirements

of shear-friction behavior. In Fig. 3, it appears that when

the weld between the strap and the bottom dowel failed,

the hanger strap rotated away from the member face. For

shear friction to occur, the cracked concrete must remain

in full contact with the rest of the member to generatefriction across the crack interface. This condition is not the

observed behavior for the hanger in Fig. 3.

Furthermore, the researchers reported that hanger depth

greatly affected the hanger capacity. Shear-friction theory

is independent of depth and relies only on the area of steel

crossing an assumed crack to create the normal force for

shear friction. While shear friction is a convenient tool,

the observed failure mechanism does not meet the basic

assumptions of shear-friction theory.

Assessment of CPCI researchprogram failure modes

An assessment of the possible failure modes, including

steel failure, can demonstrate which failure mode controls

the capacity of the Cazaly hanger. Ratios of test-to-pre-

dicted failure loads were tabulated to provide a means for

comparison of the various failure modes. Table 1 presents

the summary results.

The test specimens used throughout the 1965 CPCI re-

search program on hanger connections included stirrups,

some of which can be considered anchorage reinforcement.

The shear stirrup/anchorage reinforcement began 3 in. (75

mm) from the ends of the beams. This spacing effectively

qualifies as anchor reinforcement placement according to

Fig. RD.6.2.9 in ACI 318-08 appendix D.4 The longitudinal

flexural reinforcement for the majority of the CPCI test

specimens consisted of four no. 9 (29 mm) reinforcing bars.

Failure modes, assuming the steel components of the hang-

er control the ultimate load on the test specimen, produced

test-to-predicted values less than one. This indicates thatthe strap and the top bar are stronger than the concrete-

breakout capacity. That is, predicted concrete capacity

greatly underestimates the test load. The test results are

consistent with the approach of designing the bar and strap

to have capacity greater than the concrete capacity.

The remaining failure calculations in Table 1 consider

the failure modes of the original shear-friction concept,

concrete breakout due to shear, concrete breakout due to

tension, and yielding or ultimate strength of the anchor

reinforcement. The shear stirrups in the vicinity of the

connection meet the requirements of ACI 318-08 appendix

Figure 11. Concrete ailure is shown or a Canadian PCI specimen with two bottomdowels.



The authors considered this second stirrup close enough to

contribute to the anchor-reinforcement capacity. Therefore,

the calculations use a minimum of two shear stirrups, each

with two legs, for the anchor reinforcement. The CPCIreport does not record the stirrup yield stress or ultimate,

so the prediction calculations are based on an assumed 60

ksi (420 MPa) yield stress. At the time of the CPCI tests,

it is equally possible that a 40 ksi (275 MPa) yield stress

could have been used. The original paper does not provide

this information.

Figure 12 plots the test-to-predicted ratios for the CPCI

test data. Any data that fall below the horizontal line of

1.0 mean that the prediction of capacity is unconserva-

tive; any data that plot above the 1.0 line imply that the

prediction is conservative. The closer to the 1.0 line,

D4 for anchor reinforcement, which allows the strength of

the anchor reinforcement to be used in the analysis of the

strength of this failure mode. The anchor reinforcement

strength also exceeds the concrete-breakout strengths inshear or tension so that if cracking occurs the anchor steel

is activated.

Consistent with ACI 318-08, the shear reinforcement

used for this calculation was the number of stirrups within

a distance of half the strap depth from the centerline of

the strap. For most of the test specimens, this provision

permits at least two stirrups to be used for the anchor-

reinforcement-capacity calculation. For seven of the

specimens, one stirrup falls completely within the specified

range and the second stirrup falls just beyond half of the

strap-depth limit.

Table 1. Test-to-predicted ailure loads or selected Canadian PCI specimens

Specimenf'c,

psi

Vtest,

kip

Concrete

breakout:

tension

Concrete

breakout: shear

Anchor

reinforcementShear friction

Bending of top

barStrap failure

Vpredict,

kip

Vtest

Vpredict

Vpredict,

kip

Vtest

Vpredict

Vpredict,

kip

Vtest

Vpredict

Vpredict,

kip

Vtest

Vpredict

Vpredict,

kip

Vtest

Vpredict

Vpre-

dict,

kip

Vtest

Vpredict

P-1-B 8040 18.2 5.66 3.22 5.99 3.04 17.60 1.03 12.61 1.44 26.67 0.68 30.00 0.61

P-2-A 8040 17.3 5.66 3.06 5.99 2.89 17.60 0.98 12.61 1.37 26.67 0.65 30.00 0.58

P-3-A 8040 14.4 5.66 2.55 5.99 2.40 17.60 0.82 12.61 1.14 26.67 0.54 30.00 0.48

P-4-A 8040 16.7 5.66 2.95 5.99 2.79 17.60 0.95 12.61 1.32 26.67 0.63 30.00 0.56

T-1-1 4910 33.5 8.44 3.97 9.41 3.56 32.00 1.05 29.17 1.15 47.62 0.70 62.50 0.54

T-1-2 4910 33.8 8.44 4.00 9.41 3.59 32.00 1.06 29.17 1.16 47.62 0.71 62.50 0.54

T-3-5 5430 39.3 8.88 4.43 9.89 3.97 32.00 1.23 29.17 1.35 47.62 0.83 62.50 0.63

T-5-9 5630 43.4 9.04 4.80 10.07 4.31 32.00 1.36 29.17 1.49 47.62 0.91 62.50 0.69

T-5-10 5630 36.5 9.04 4.04 10.07 3.62 32.00 1.14 29.17 1.25 47.62 0.77 62.50 0.58

T-7-14 7160 44.3 10.19 4.35 11.83 3.75 32.00 1.38 35.06 1.26 47.62 0.93 62.50 0.71

T-9-17 6375 46.7 9.62 4.86 8.54 5.47 32.00 1.46 29.56 1.58 47.62 0.98 62.50 0.75

T-11-22 7280 47.5 10.50 4.52 11.46 4.15 32.00 1.48 29.21 1.63 47.62 1.00 65.00 0.73

T-12-23 7220 39.9 10.46 3.82 11.41 3.50 32.00 1.25 29.21 1.37 30.30 1.32 65.00 0.61

A-2-3 5820 35.3 8.68 4.06 9.67 3.65 32.00 1.10 27.57 1.28 47.62 0.74 62.50 0.56

T-13-26 5240 50.3 8.72 5.77 9.72 5.18 32.00 1.57 29.17 1.72 47.62 1.06 62.50 0.80

Average 4.78 4.64 1.35 1.48 0.78 0.65

Standard deviation 2.46 2.27 0.51 0.55 0.25 0.21

Coecient o variation 0.51 0.49 0.37 0.37 0.32 0.32

Note: f 'c = compressive strength o concrete; Vpredict= shear orce predicted rom theory; Vtest= shear orce obtained in experimental program.

1 psi = 6.895 kPa; 1 kip = 4.448 kN.



anchor reinforcement is the best of the conservative

prediction models.

the better the prediction equation. However, the results

in Table 1 and Fig. 12 suggest that the strength of the

Figure 12. Test-to-predicted ratios are given or the Canadian PCI Cazaly hanger test program. Note: 1 psi = 6.895 kPa.

Figure 13. This modied Cazaly hanger was used in University o Wyoming tests.



University of Wyomingtest series

To supplement the 1965 CPCI research program, several

new tests were conducted on shallow members using mod-

ified Cazaly hangers (Fig. 13). These hangers differ from

the original Cazaly hanger in that the strap is not a closed

loop and a hollow steel tube is used for the top bar instead

of solid bar stock. This design precludes the need to thread

prestressing strand through a closed loop, allowing easier

member fabrication.

The modified design used two separate steel straps, which

curve away from the centerline of the hanger at their bottom

The anchor reinforcement model has an average test-to-

predicted ratio of 1.35, a standard deviation of 0.51, and

coefficient of variation of 0.37. If the ultimate strength of

the anchor steel were known, the authors believe that the

average test-to-prediction ratio would be very close to 1.

Therefore, the anchor reinforcement model is a reasonable

predictor of strength for the 1965 CPCI Cazaly hanger

test specimens. With the anchor reinforcement capacity

exceeding the concrete-breakout capacity, the concrete-

breakout crack serves as the means of activation of the

anchor steel. The crack pattern observed in Fig. 11 is con-

sistent with the anchor reinforcement transferring the end

shear load to the Cazaly hanger after the concrete cracks.

Table 2. Test-to-predicted ailure loads or University o Wyoming test specimens

Specimen f'c, psi Vtest, kip

Concrete breakout: tension Concrete breakout: shear

Vpredict, kipVtest

VpredictVpredict, kip

Vtest

Vpredict

BS 17 N-L 6500 21.8 18.71 1.16 15.14 1.44

BS 17 N-R 6500 21.8 21.84 1.00 19.30 1.13

BS 17 S-L 6500 24.8 21.84 1.13 19.30 1.28

BS 17 S-R 6500 24.8 18.71 1.32 15.14 1.63

BS 34 N-L 6500 20.6 13.17 1.56 10.40 1.98

BS 34 N-R 6500 20.6 13.17 1.56 10.40 1.98

BS 34 S-L 6500 28.0 23.32 1.20 20.31 1.38

BS 34 S-R 6500 28.0 19.88 1.41 16.05 1.75

FS-143 N 6000 25.3 12.95 1.95 10.53 2.40

Average 1.37 1.66

Standard deviation 0.29 0.41

Coecient o variation 0.21 0.24

Note: f 'c = compressive strength o concrete; Vpredict = shear orce predicted rom theory; Vtest = shear orce obtained in experimental program.

1 psi = 6.895 kPa; 1 kip = 4.448 kN.

Figure 14. These photographs show the test specimens and loading system or the University o Wyoming specimens. Note: 1 kip = 4.448 kN.



Evaluation ofPCI Design Handbook

shear friction method for CPCIspecimens

The PCI Design Handbookdesign equations were ap-

plied to the 1965 CPCI research specimens to calculate the

capacity of the Cazaly hanger (Table 6). The phi factors

were all taken as 1.0 for these calculations to allow a directcomparison of predicted and test results. The results are

in the form of test-to-predicted failure-load ratios for the

same specimens reviewed in Table 1. Figure 15 plots the

ratio of the test failure loadtopredicted failure load for the

each specimen based on the three PCI Design Handbook

design checks of section 6.10.1. The solid line in the plot

represents a unity ratio of test-to-predicted failure loads.

Points lying above the line indicate that the predictor is

conservative, whereas points below the line indicate an

unconservative predictor.

The plot in Fig. 15 shows that when the least-squares line

is drawn through the test-to-predicted data for each failure

mode, all prediction equations are unconservative, some by

30%. This indicates that the PCI Design Handbookcapaci-

ties overpredicted the hanger capacity based on the 1965

CPCI research program test database. The points in Fig.

15 representing the shear-friction design capacity indicate

that this computation is the least-conservative predictor of

Cazaly hanger capacity. The PCI Industry Handbook Com-

mittee is addressing this situation.

Evaluation of CPCI specimenconcrete-breakout strength

The strength of each test specimen from the 1965 CPCI

research program database is also compared with the

concrete-breakout predictions of ACI 318-08 appendix

D4 in Table 1. The predictions are based on an uncracked

concrete condition. Figure 12 shows the test-to-predicted

ratios for the concrete-breakout models in shear and ten-

sion. Figure 12 also compares the capacity of the anchor

reinforcement with the tested failure load for the 1965

CPCI specimens.

As illustrated in Fig. 12, concrete breakout determined

from tension or shear alone significantly underpredictedthe strength for the hangers in all cases. Because all

specimens considered in this 1965 CPCI database included

anchorage reinforcement, test-to-predicted failure-load

ratios for an anchorage-reinforcement-failure model were

also calculated for all test specimens. The data plotted in

Fig. 12 for the anchorage-reinforcement predictions lead

to the conclusion that anchor reinforcement governs the

capacity of these specimens and must be included in the

PCI Design Handbookdesign procedure. A comparison of

the results presented in Fig. 12 and 15 demonstrates that

the shear-friction model is not a reliable predictor of the

capacity of the shallow Cazaly hanger. Reevaluation of

ends. These are referred to as J-straps. The bottom-dowel

bar may be welded to the bottom of the J-strap or just before

the strap bend starts. The bottom-dowel bar welded to the

strap adds additional anchorage to the J-strap and prevents

the strap from rotating out of the concrete (Fig. 3).

The University of Wyoming (UW) tests were designed to

study the behavior and failure of wide, shallow sectionswith Cazaly hangers. Five full-scale test specimens (BS-

17, BS-34, FS-143, FS-143A, FS-143B) were fabricated

and tested at the Rocky Mountain Prestress facility in

Denver, Colo. The test procedure placed fixed weights on

the specimens and used the cranes internal-load sensors

as instrumentation for partial loads during testing. The test

member was placed in such a manner that the cantilevered

top bar of the Cazaly hanger rested on a large hollow

structural section (HSS) tube, with steel shims used to level

the test members. The clearance between the bottom of the

member and the ground varied from 4 in. to 6 in. (100 mm

to 150 mm). The test setup is illustrated in Fig. 14 with

the photo on the right showing one of the fixed-weight test

blocks being placed.

Load application was achieved using 9-ton (18 kip or 80 kN)

concrete blocks. A crane picked up the blocks and set them

down on nominal 6 in. 6 in. (150 mm 150 mm) timber

cribbing. The timber cribbing was used to avoid placing the

test weights directly on the Cazaly hanger hardware or the

projecting lifting devices.

The first loading block was set on the test end of the

member with the cribbing beneath the block. Then a second

block was set at the same level at the opposite end of thespecimen. The process was repeated until four total blocks

were placed on the specimen. A fifth block, as well as the

sixth block if needed, was slowly lowered onto the test

end of the specimen in 1 kip or 2 kip (4.5 kN or 9.0 kN)

increments until failure. Shear loads on the connectors

were computed from the final static loading of the concrete

blocks and the self-weight of the test specimen. Table 2 con-

tains the test results and predictions, while Tables 3 through

5 contain the source information for the UW specimens.7

Tests conducted by UW with modified open straps demon-

strated that the crack begins at the bottom of the strap evenfor the case where the bottom-dowel anchors were above the

bottom of the strap. Therefore, if the bottom dowels were

placed slightly above the bottom of the strap, the distance to

the bottom of the strap was used as the embedment distance

for calculations.

Analysis of test results

The following sections examine the test database results

from the perspective of the PCI Design Handbookand the

ACI 318-08 CCD.



second part, N-L for example, refers to the north end of

the member and the left hanger. In some cases, the hangers

are not completely symmetrical in the member, hence thedual identification. The difference in capacity between the

left and right anchors reflects the asymmetric placement.

In actuality, the lowest-strength hanger would fail first, but

the individual values are provided for comparison. Table 2

presents the results of concrete-breakout-testtopredicted

capacities due to tension and due to shear on the UW speci-

mens using uncracked concrete-breakout capacities calcu-

lated using Eq. (1) and (5). Note that these are the calculated

5% fractile loads accounting for edge and spacing effects.

The results in Table 2 and Fig. 16 suggest that the strength

can be estimated for the Cazaly hanger using either the

all of the design equations in the PCI Design Handbookis

suggested because Fig. 15 shows the trend of all predic-

tion models to be unconservative. The inclusion of anchorreinforcement as a design check predicts a conservative

strength for most of the specimens.

Evaluation of UW specimen

concrete-breakout strength

Initial UW tests were conducted without the inclusion

of anchor reinforcement, allowing assessment of a pure

concrete-breakout failure. The UW test specimens each

contained four Cazaly hangers, two at each end of a beam.

The first part of the test-specimen identification, BS 17,

for example, refers to the test specimen itself, while the

Table 3. Summary o hanger properties or University o Wyoming test specimens

Specimenf'c

Top bar Strap

L L1 L2 e b d f t h' h h" s

psi in. in. in. in. in. in. in. in. in. in. in. in.

BS 17 N-L 6500 22 13.25 5.75 2.875 6 3 0.75 0.313 11 8.5 7.25 3

BS 17 N-R 6500 22 13.25 5.75 2.875 6 3 0.75 0.313 11 8.5 7.25 3

BS 17 S-L 6500 22 13.25 5.75 2.875 6 3 0.75 0.313 11 8.5 7.25 3

BS 17 S-R 6500 22 13.25 5.75 2.875 6 3 0.75 0.313 11 8.5 7.25 3

BS 34 N-L 6500 22 13.25 5.75 2.875 6 3 0.75 0.313 13 10.5 9.25 3

BS 34 N-R 6500 22 13.25 5.75 2.875 6 3 0.75 0.313 13 10.5 9.25 3

BS 34 S-L 6500 22 13.25 5.75 2.875 6 3 0.75 0.313 13 10.5 9.25 3

BS 34 S-R 6500 22 13.25 5.75 2.875 6 3 0.75 0.313 13 10.5 9.25 3

FS-143 N 6000 22 13.25 5.75 2.875 6 3 0.75 0.313 11 8.5 7.25 3

Note: ab= embedment length o bottom dowel; b= width o top bar in Cazaly hanger; bd= width o beam in University o Wyoming test; d= dis-

tance rom extreme compression ber to centroid o longitudinal tension reinorcement or depth o top bar in Cazaly hanger; db= reinorcement bar

diameter; dp= depth o prestress strand in University o Wyoming tests; e= eccentricity to applied load in University o Wyoming test hanger; f=

concrete cover in ront o hanger strap; f 'c = compressive strength o concrete; h= depth rom bottom o top bar to bottom o strap in Cazaly hangeror Canadian PCI specimens, depth rom top o beam to center o bottom anchor or use in PCI equations; h'= depth o embedment o J-strap; h"=

depth o embedment o dowel reinorcement rom top o concrete; L= length o top bar in University o Wyoming tests; L'= length o beams in Uni-

versity o Wyoming tests; L1 = distance rom centerline o strap to end o top bar in University o Wyoming tests; L2 = distance rom centerline o strap

to cantilever end o top bar in University o Wyoming tests; n.a. = not applicable; s= width o strap in Cazaly hanger; s1 = center-to-center spacing o

J-straps in University o Wyoming hanger specimens; se = hal the distance o center-to-center spacing o interior J-straps o two individual hangers in

University o Wyoming specimens; sc = edge spacing rom centerline o J-strap in University o Wyoming hanger specimens. 1 in. = 25.4 mm;

1 psi = 6.895 kPa; 1 kip = 4.448 kN.



breakout capacity.

If concrete-breakout capacity is

insufficient to resist design loads,

add anchor reinforcement for the

required strength per ACI 318-08

section D.5.2.9.

If space is not adequate for anchor

reinforcement, increase the section

size.

5. Design the top bar for bending caused by

the ultimate load with = 0.9.

6. Design the strap(s) to yield at 133% of

the ultimate load with = 0.9.

7. Design the bottom dowel(s) to prevent

strap rotation in the event that the cantile-

ver bar bends at the top weld.

Once the concrete-breakout capacity in shear

is found, the components of the hanger can

be sized. The design procedure for the top bar

and the hanger strap(s) is already included in

the PCI Design Handbooksixth edition.5 The

bottom dowel(s) shall be designed to prevent

strap rotation in the event that the cantilever

bar bends at the top weld.

hf

VA

a

y

udowel

= (7)

where

a = distance from ultimate beamshear

load to centerline of strap

Adowel = area of bottom dowels in Cazaly

hanger

h = depth to bottom dowel from the cen-terline of cantilever bar

fy = yield strength of bottom dowel

Vu = ultimate factored shear load

Strap rotation can only occur if the bottom

dowel fails and the plastic moment capacity

of the top bar is exceeded. The calculation

assumes that the total restraining force will

be carried by the bottom dowel. Because the

cantilever retains its plastic moment capac-

concrete breakout in tension or shear when no anchor reinforcement is

present. The statistical mean and coefficient of variation for these code

equations are comparable to the Anderson-Meinheit6 data, further argu-

ing that this is similar behavior.

The tension breakout capacity used the recommendations of ACI 318-08

appendix D4 without any adjustment for the area of the base of the J- or

U-strap. Without calibration-test data, the authors did not apply ACI 318-08 recommended corrections for the larger head area. Inclusion of a larger

bearing-area correction should increase the tensile breakout capacity,

making the calculation more conservative. The shear-breakout capacity

depends on the embedment of the shear stud e. The only guidance in

ACI 318-08 on the maximum length ofe is that e/da must be less than

8. Therefore, the PCI Design Handbookformulation for shear-breakout

capacity is recommended for design. The bottom dowel does, however,

prevent the tension strap from rotating outward and is, therefore, a neces-

sary part of the design.

The UW test specimens identified an additional case to consider in the

Cazaly hanger design. Specimens were made with the hanger straps

terminating just above the prestressing strand. In those instances, the

end of the member experienced a premature failure when a splitting

crack appeared due to the prestress transfer to the concrete. The test

was aggravated by a splitting tension at the member end along the line

of the prestressing strands (Fig. 17). A lateral, bursting tension stress is

induced in the concrete as a result of prestressing-force transfer into the

concrete in the beam. The bursting tension initiated premature cracking

along the plane of the strand. Without the Cazaly hanger strap confin-

ing the strand, the cracks propagated through the width of the member.

Members that failed in that fashion suggest that a provision requiring

the hanger strap to be extended below the prestressing strand or to in-

clude the splitting tensile zone be included in the design provisions.

Recommendeddesign guidelines

This study suggests updates to the PCI Design Handbookfor the Cazaly

hanger. The principal revision is the inclusion of a CCD check for the

hanger based on the concrete-breakout strength of an anchor in shear

using the PCI Design Handbookheaded-stud shear-breakout design.5

The top bar, strap(s), and bottom dowel(s) of the Cazaly hanger would

then be designed based on the ultimate design load. The recommended

design process is the following:

1. Assume hanger depth consistent with the member depth and a barlength such that the statics results in a force of 1.33Tu in the hanger.

2. Verify that the termination of the hanger strap is not in the splitting

tension zone of the beam web.

3. Compute the concrete-breakout capacity in shear as the nominal

capacity of the connection with = 0.75.

4. Add anchor reinforcement.

If concrete-breakout capacity is sufficient to resist design

loads, add anchor reinforcement for 100% of the concrete-



As previously stated, the welds in connections should be

stronger than the joined components of the connection to

ity to augment the dowel restraint, no is needed on thebottom-dowel capacity.

Table 4. ACI 318-08 appendix D calculations or concrete breakout due to tension on University o Wyoming specimens

SpecimenConcrete-breakout strength of anchor in tension

hef 1.5hef ca, min ca, max ANco ANc Nb ed,N c,N Ncb

in. in. in. in. in.2 in.2 kip n.a. n.a. kip

BS 17 end 1 let 8.5 12.8 2.25 5.6 650.3 269.63 48.0 0.75 1.25 18.71

BS 17 end 1 right 8.5 12.8 2.25 5.6 650.3 314.63 48.0 0.75 1.25 21.84

BS 17 end 2 let 8.5 12.8 2.25 5.6 650.3 314.63 48.0 0.75 1.25 21.84

BS 17 end 2 right 8.5 12.8 2.25 5.6 650.3 269.63 48.0 0.75 1.25 18.71

BS 34 end 1 let 10.5 15.8 2.25 2.25 992.3 213.75 65.8 0.74 1.25 13.17

BS 34 end 1 right 10.5 15.8 2.25 2.25 992.3 213.75 65.8 0.74 1.25 13.17

BS 34 end 2 let 10.5 15.8 2.25 5.7 992.3 378.45 65.8 0.74 1.25 23.32

BS 34 end 2 right 10.5 15.8 2.25 2.6 992.3 322.65 65.8 0.74 1.25 19.88

FS-143 8.5 12.8 2.25 2.75 650.3 194.25 46.1 0.75 1.25 12.95

Note:ANc = projected concrete ailure area o a single anchor or group o anchors;ANco= projected concrete ailure area o a single anchor i not limited

by corner or edge infuences; ca,max = maximum distance rom center o an anchor strap to edge o concrete; ca,min = minimum distance rom center

o an anchor strap to edge o concrete; hef = eective embedment depth o anchor; n.a. = not applicable; Nb = basic concrete-breakout strength in

tension o a single anchor in cracked concrete; Ncb = nominal concrete-breakout strength in tension o a single anchor; c,N= actor used to modiy

tensile strength o anchors based on presence or absence o cracks in concrete; ed,N= actor used to modiy tensile strength o anchors based on

proximity to edges o concrete member. 1 in. = 25.4 mm; 1 kip = 4.448 kN.

Table 5. ACI 318-08 appendix D calculations or concrete breakout due to shear on University o Wyoming specimens

SpecimenConcrete-breakout strength of anchor in shear

ca1 ca2 da e c,V AVco AVc Vb ed,V Vcb

in. in. in. in. n.a. in.2 in.2 kip n.a. kip

BS 17 end 1 let 8.5 2.6 0.5 20 1.4 325.1 269.6 20.68 0.76 18.28

BS 17 end 1 right 8.5 5.6 0.5 20 1.4 325.1 314.6 20.68 0.83 23.31

BS 17 end 2 let 8.5 5.6 0.5 20 1.4 325.1 314.6 20.68 0.83 23.31

BS 17 end 2 right 8.5 2.6 0.5 20 1.4 325.1 269.6 20.68 0.76 18.28

BS 34 end 1 let 10.5 1.75 0.5 20 1.4 496.1 213.8 28.39 0.73 12.56

BS 34 end 1 right 10.5 1.75 0.5 20 1.4 496.1 213.8 28.39 0.73 12.56

BS 34 end 2 let 10.5 5.7 0.5 20 1.4 496.1 378.5 28.39 0.81 24.52

BS 34 end 2 right 10.5 2.6 0.5 20 1.4 496.1 322.7 28.39 0.75 19.38

FS-143 8.5 2.75 0.5 20 1.4 325.1 194.3 19.87 0.76 12.71

AVc = projected concrete ailure area or an anchor or group o anchors considering limitations due to size o the member in which anchor is located;

AVco = projected concrete ailure area o a single anchor i not limited by corner or edge infuences; ca1 = distance rom center o anchor shat to edge

o concrete in one direction, taken in the direction o the applied shear; ca2 = distance rom the center o the anchor to the edge perpendicular to ca1;

da= outside diameter o anchor; Vb = basic concrete-breakout strength in shear o a single anchor in cracked concrete; Vcb = predicted shear capacity

using PCI ormulation (Eq. [5]); e = load-bearing length o interior cantilever or use in PCI equations; c,V= actor used to modiy shear strength o

anchors based on presence or absence o cracks in concrete; ed,V= actor used to modiy shear strength o anchors based on proximity to edges o

concrete member. 1 in. = 25.4 mm; 1 kip = 4.448 kN.



fy = 36 ksi (250 MPa) (strap)

fy = 46 ksi (320 MPa) (HSS tube)

futa = 90 ksi (620 MPa)

Zyy = 5.56 in.3 (91,000 mm3)

Vu = 6.7 kip (29.8 kN)

= 0.75 (for concrete breakout)

Solution

From statics, the tensile force on the strap is Tu = 1.33Vu

= 1.33(6.7 kip) = 8.91 kip (39.7 kN).

avoid a brittle fracture of the weld. Therefore, at a mini-

mum, the weld between the strap and the bar should be

designed to resist the maximum possible load that the strap

can transfer to the weld. This will ensure that the hanger

will never be critical at the weld.

Example

The proposed design methodology is demonstrated here

through a design example using a modified J-strap Cazaly

hanger in a 12-in.-wide (300 mm) shallow beam (Fig. 18).

Given

fcl = 6500 psi (44.8 MPa)

fy = 60 ksi (420 MPa) (reinforcing bars)

Table 6. Test-to-predicted ailure loads o Canadian PCI specimens using PCI design checks

Specimen f'c, psi Vtest, kip

Concrete breakout:

tension

Concrete breakout:

shearAnchor reinforcement

Vpredict, kipVtest


Vtest


Vtest

Vpredict

P-1-B 8040 18.2 20.30 0.90 26.67 0.68 28.23 0.64

P-2-A 8040 17.3 20.30 0.85 26.67 0.65 28.23 0.61

P-3-A 8040 14.4 20.30 0.71 26.67 0.54 28.23 0.51

P-4-A 8040 16.7 20.30 0.82 26.67 0.63 28.23 0.59

T-1-1 4910 33.5 42.29 0.79 47.62 0.70 55.34 0.61

T-1-2 4910 33.8 42.29 0.80 47.62 0.71 55.34 0.61

T-3-5 5430 39.3 42.29 0.93 47.62 0.83 55.34 0.71

T-5-9 5630 43.4 42.29 1.03 47.62 0.91 55.34 0.78

T-5-10 5630 36.5 42.29 0.86 47.62 0.77 55.34 0.66

T-7-14 7160 44.3 42.29 1.05 47.62 0.93 72.28 0.61

T-9-17 6375 46.7 42.29 1.10 47.62 0.98 56.47 0.83

T-11-22 7280 47.5 43.98 1.08 47.62 1.00 55.34 0.86

T-12-23 7220 39.9 43.98 0.91 30.30 1.32 55.34 0.72

A-2-3 5820 35.3 42.29 0.83 47.62 0.74 55.34 0.64

T-13-26 5240 50.3 42.29 1.19 47.62 1.06 55.34 0.91

Average 0.96 0.78 0.76

Standard deviation 0.31 0.25 0.41

Coecient o variation 0.32 0.32 0.53

Note: The hanger strap provides the lowest predicted strength capacity and is thereore the most critical element. The moment in the top bar and the

dowel are over strength and hence have the lower Vtest/Vpredict. f 'c = compressive strength o concrete; Vpredict = shear orce predicted rom theory;

Vtest = shear orce obtained in experimental program. 1 psi = 6.895 kPa; 1 kip = 4.448 kN.



Figure 16. Test-to-predicted ailure-load ratios are given or concrete breakout on the University o Wyoming tests. Note: 1 kip = 4.448 kN.

Figure 15. Test-to-predicted ailure-load ratios are given or PCI Design Handbookequations. Note: 1 psi = 6.895 kPa.



2. Check the capacity of the top bar.

Mu = 6.7 kip(5.25 in.) = 35.2 kip-in. (3.97 kN-m)

Mn = fy(Zyy) = 0.9(46 ksi)(5.56 in.2) = 230 kip-in.

(26 kN-m) >Mu OK

3. Check the capacity of the straps.

Tu = 1.33Vu= 1.33(9.0 kip) = 12.0 kip (53.4 kN)

Tn = fyAst= 0.9(2)(36 ksi)(3 in. 5/16 in.)

= 60.8 kip (270 kN) > Tu OK

4. Check the capacity of the lower dowels.

Areq =.

.

hf

V a

7.25 in 60 ksi

9.0 kip 5.25 in

y

u =a

akk

(70 mm2)

Adowel = 2 (0.2 in.2) = 0.4 in.2 (258 mm2) > 0.11 in.2 OK

5. Design anchor reinforcement.

Anchor reinforcement strength should be equal to the

shear capacity required within hef/2 of the end of the

beam. Thus, the anchor reinforcement for hef= 11 in.

is

Av = 1.33 Vu/fy = 1.33 6.7/(0.75 60) = 0.20 in.2

(129 mm2)

1. Calculate the concrete-breakout strength in shear using

the PCI Design Handbookshear equations and nota-

tion and assumed hanger embedment depthBED.

The depth to the bottom of the inside of the strap is

used as the effective depth, while any edge distances

are taken from the centerline of the strap:

BED = 11 in.(280 mm)

SED =2

12 616

5-

= 2.84 in.(72.2 mm)

Vco3 = . f BED16 5. .

c

0 5 1 33la k = 32.3 kip (144 kN)

C3 = .BED

SED0 7

3 = 0.446

Ch = Ceva = Cvcr= 1.0

Vc3 = Vco3C3ChCev3Cvcr= (32.3)(0.446)(1)(1)(1)

= 14.4 kip (64.1 kN)

Vc3 = 0.75(14.4) = 10.8 kip(48 kN)

Based on the given concrete properties and dimensions

of the hanger components, the breakout capacity is

10.8 kip (41.4 kN), which is greater than the ultimate

load of 8.9 kip (39.7 kN). Therefore, the hanger break-

out is satisfactory.

Figure 17. The location o the splitting tension zone is shown in the University o Wyoming test specimens.



are analogous to the strap of the Cazaly hanger, though ad-

ditional modeling of the anchor is needed for direct com-

parison. The equations for concrete-breakout capacity in

ACI 318-08, or the PCI Design Handbook, can be applied

directly to the Cazaly hanger, except that the embedment

depth is taken to the bottom of the hanger plate. Thus, the

bottom of the strap is used for determining the embedment

depth and the bottom-dowel anchor prevents the rotation

of the hanger after the concrete has failed. Calculation

using the PCI Design Handbookequations for shear issimpler than using the ACI 318-08 equations for shear.

Evaluation of the test results from the CPCI 1965 research

program on hanger connections established that anchor

reinforcement resisted the end shear load after the concrete

cracked in a concrete-breakout mode. If the yield strength

of the anchor reinforcement is used for design, the anchor

reinforcement is an accurate and conservative approach to

finding the capacity of the 1965 CPCI Cazaly hanger test

specimens. The UW tests demonstrated the application

of a concrete-breakout model to accurately and conser-

vatively predict the capacity of the connection in shallow,unreinforced members. This is in contrast to the shear-friction

design currently included within the PCI Design Handbook,5

which overpredicts the capacity of the hanger. A statistical

analysis of the test data for concrete breakout was similar to

the results of the tension breakout strength as conducted by

Anderson and Meinheit6 and further suggests that a strength-

reduction factor of = 0.75 is appropriate for the design. This

is consistent with the methods of ACI 318-08 appendix D.4

Recommendationsfor future work

One no. 4 stirrup (Av = 2 0.20 in.2 = 0.40 in.2 [260

mm2]) is sufficient for anchor reinforcement. The stir-

rup should be located within 51/2 in. (140 mm) of the

center of the strap.

Deep sectionsand strengtheningexisting hangers

This research focused on shallow sections. As the sec-tions become deeper, the breakout strength increases to the

point that the hanger bar or the strap becomes the critical

limiting capacity. Thus, each possible failure mechanism

must be checked for a valid design; however, no key depth

correction is required.

In most applications, the anchor reinforcement comple-

ments the concrete-breakout capacity, which means that

older installations would be safe. If evaluation of an exist-

ing installation results in insufficient capacity, a Cazaly

hanger can be strengthened by through-bolting a plate

above and below the hanger such that the bolts provide theanchor reinforcement.

Conclusion

Testing on full-scale Cazaly hangers revealed that concrete

breakout is the predominant failure mode of the shallow Ca-

zaly hanger under vertical load and that this behavior does not

conform to the originally postulated shear-friction behavior

forming the basis of the longstanding design methodology.

ACI 318-08 appendix D4 specifies methods for CCD of

headed studs in concrete. Headed studs in tension or shear

Figure 18. This sketch shows the Cazaly hanger used in the example problem. Note: HSS = hollow structural section; Vu= ultimate, actored shear load.

1 = 1 in. = 25.4 mm; 1' = 1 t = 0.305 m; #4 = no. 4 = 25 mm.



Department of Civil and Architectural Engineering,

Laramie, Wyoming.

Notation

a = distance from location of application of load to

location of support reaction for use in Canadian

PCI test setup or distance from support reaction tocenterline of strap for use in PCI equations

ab = embedment length of bottom dowel

Adowel = area of bottom dowels in Cazaly hanger

An = area of upper dowel in Cazaly hanger for use in

PCI Design Handbookequations or projected area

of an insert or group of inserts

ANc = projected concrete failure area of a single anchor

or group of anchors

ANco = projected concrete failure area of a single anchor

if not limited by corner or edge influences

Areq = required area of bottom dowels in Cazaly hanger

to prevent pryout

Ast = area of strap cross section

Av = area of anchor reinforcement

AVc = projected concrete failure area for an anchor or

group of anchors considering limitations due tosize of the member in which anchor is located

AVco = projected concrete failure area of a single anchor

if not limited by corner or edge influences

b = width of top bar in Cazaly hanger

b1 = width of beam containing Cazaly hanger, for use

in PCI equations

bd = width of beam in University of Wyoming test

BED = depth of embedment of the Cazaly hanger

c = clear cover of strap in Cazaly hanger

ca1 = distance from center of anchor shaft to edge of

concrete in one direction, taken in the direction of

the applied shear

ca2 = distance from the center of the anchor to the edge

perpendicular to ca1

ca,max = maximum distance from center of anchor strap to

The calculations, assessments, and recommended design

guidelines presented in this research were calibrated on

work conducted in 1965. The UW test specimens demon-

strated the ability of the CCD approach from ACI 318-08

appendix D4 to predict the capacity of the connection.

However, current test-specimen data are limited and ad-

ditional testing on numerous specimens with a wider range

of hanger depths, as well as different variations of anchorreinforcement, would provide confirmation and better

statistical reliability for todays practice. Additional testing

and calibration would provide greater assurance for the

precast concrete industry and would possibly adjust the phi

factor used for these connections.

Acknowledgments

The UW specimens for this research, as well as assistance

with testing, were provided by Rocky Mountain Prestress

of Denver, Colo., and their input on specimen design and

testing are greatly appreciated. The views and opinions

expressed in this paper are those of the authors and do not

necessarily reflect those of Rocky Mountain Prestress. The

authors also extend their appreciation to John Hanlon, the

members of the PCI Industry Handbook Committee, and

the PCI Technical Activities Council, whose review and

comments improved this paper.

References

1. Slater, W. M. 1966. Canadian Prestressed Concrete

Institutes 1965 Research Program on Hanger Connec-

tions. PCI Journal, V. 11, No. 3 (June): pp. 7282.

2. Ife, J. S., S. M. Uzumeri, and M. W. Huggins. 1968.

Behavior of the Cazaly Hanger Subjected to Vertical

Loading. PCI Journal, V. 13, No. 6 (December): pp.

4866.

3. PCI Industry Handbook Committee. 1985. PCI Design

Handbook: Precast and Prestressed Concrete. MNL-

120. 3rd ed. Chicago, IL: PCI.

4. ACI Committee 318. 2008.Building Code Require-

ments for Structural Concrete (ACI 318-08) and

Commentary (ACI 318R-08). Farmington Hills, MI:American Concrete Institute (ACI).

5. PCI Industry Handbook Committee. 2004. PCI Design

Handbook: Precast and Prestressed Concrete. MNL-

120. 6th ed. Chicago, IL: PCI.

6. Anderson, N. S., and D. F. Meinheit. 2006. Design

Criteria for Headed Stud Groups in Shear. Final report.

Chicago, IL: PCI.

7. Joy, W. T. 2008. Concrete Capacity Design of the

Cazaly Hanger. MS thesis. University of Wyoming,



kc = coefficient for basic concrete-breakout strength in

tension

b = load-bearing length of interior cantilever for use

in PCI equations

e = load-bearing length of anchor for shear

p = bearing length of exterior cantilever for use in PCI

equations

L = length of top bar in University of Wyoming tests

L' = length of beams in University of Wyoming tests

L1 = distance from centerline of strap to end of top bar

in University of Wyoming tests

L2 = distance from centerline of strap to cantilever end

of top bar in University of Wyoming tests

Mn = nominal flexural strength

Mu = ultimate factored moment at section

N = tensile force on insert

Nb = basic concrete-breakout strength in tension of a

single anchor in cracked concrete

Ncb = nominal concrete-breakout strength in tension of a

single anchor

s = width of strap in Cazaly hanger

s1 = center-to-center spacing of J-straps in University

of Wyoming hanger specimens

sc = edge spacing from centerline of J-strap in Univer-

sity of Wyoming hanger specimens

se = half the distance of center-to-center spacing of

interior J-straps of two individual hangers in Uni-

versity of Wyoming specimens

SED = side edge distance to centerline of insert

Tn = nominal tensile strength of hanger strap

Tu = ultimate factored tensile force on hanger strap

V = shear force on insert

Vb = basic concrete-breakout strength in shear of a

single anchor in cracked concrete

Vc3 = PCI shear breakout capacity

edge of concrete

ca,min = minimum distance from center of anchor strap to

edge of concrete

C3 = PCI correction for edge effects

Ccrb = coefficient for cracked section in PCI formulationof tensile capacity of insert

Cev = PCI correction for eccentric load

Ch = PCI correction for thickness

Cvcr = PCI correction if the section is cracked

d = distance from extreme compression fiber to

centroid of longitudinal tension reinforcement or

depth of top bar in Cazaly hanger

da = outside diameter of anchor

db = reinforcing-bar diameter

dp = depth of prestress strand in University of Wyo-

ming tests

e = eccentricity to applied load in University of Wyo-

ming test hanger

f = concrete cover in front of hanger strap

fbu = bearing pressure created by interior cantilever foruse in PCI equations

fcl = compressive strength of concrete

futa = specified tensile strength of anchor steel

fy = yield strength of steel, varies for reinforcement,

strap, top bar

g = gap between member and support, for use in PCI

equations

h = depth from bottom of top bar to bottom of strap

in Cazaly hanger for Canadian PCI specimens or

depth from top of beam to center of bottom anchor

for use in PCI equations

h' = depth of embedment of J-strap

h" = depth of embedment of dowel reinforcement from

top of concrete

hef = effective embedment depth of anchor



Vcb = predicted shear capacity using PCI formulation

(Eq. [5])

Vco3 = PCI basic shear breakout strength of an insert

Vn = nominal shear strength

Vpredict = shear force predicted from theory

Vtest = shear force obtained in experimental program

Vu = ultimate factored shear load

Zyy = plastic section modulus

= strength-reduction factor

= modification factor reflecting reduced mechanicalproperties of lightweight concrete relative to nor-

malweight concrete of same compressive strength

c,N = factor used to modify tensile strength of anchorsbased on presence or absence of cracks in concrete

c,V = factor used to modify shear strength of anchors

based on presence or absence of cracks in concrete

cp,N = factor used to modify tensile strength of post-installed anchors intended for use in uncracked

concrete without supplementary reinforcement

ed,N = factor used to modify tensile strength of anchors

based on proximity to edges of concrete member

ed,V = factor used to modify shear strength of anchors

based on proximity to edges of concrete member


26/26

About the authors

Westin T. Joy is a civil engineer

with the Materials Engineeringand Research Laboratory of the

U.S. Bureau of Reclamation in

Lakewood, Colo.

Charles W. Dolan, FPCI, is the H.

T. Person Professor of Engineer-

ing at the University of Wyoming

in Laramie.

Donald F. Meinheit, FPCI, is an

affiliated consultant with Wiss,

Janney, Elstner Associates Inc. in

Chicago, Ill.

Synopsis

This paper evaluates the behavior of the Cazaly hanger

under vertical load and proposes an additional design

requirement for the connection. In 1965, Canadian PCIinstigated a research program to evaluate the behavior

of the hanger, which led to the shear-friction design

basis for the hanger in the third edition of the PCI

Design Handbook: Precast and Prestressed Concrete.

Current tests show that in shallow sections the hanger

does not follow shear-friction behavior but instead

behaves more closely to a concrete-breakout model.Reassessment of the 1965 specimens revealed shear-

friction to be a poor predictor of capacity in shallow

sections, while the concrete-breakout models provide

conservative predictions. A proposed revision to the

sixth edition of the PCI Design Handbookbased on

concrete-breakout capacity is recommended for Cazaly

hanger design method.

Keywords

Cazaly hanger, design, vertical load.

Review policy

This paper was reviewed in accordance with the

Precast/Prestressed Concrete Institutes peer-review

process.

Reader comments

Please address any reader comments to journal@pci

.org or Precast/Prestressed Concrete Institute, c/o PCI

Journal, 200 W. Adams St., Suite 2100, Chicago, IL

60606. J

concrete capacity of cazaly hangers in shallow members

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