sleeve-type expansion anchor behavior in cracked and uncracked concrete

Nuclear Engineering and Design 228 (2004) 273–281

Sleeve-type expansion anchor behavior in crackedand uncracked concrete

Sang-Yun Kima,∗, Chul-Soo Yub, Young-Soo Yoonba Structural Systems and Site Evaluation Department, Korea Institute of Nuclear Safety, Taejon, South Korea

b Department of Civil and Environmental Engineering, Korea University, Seoul, South Korea

Received 25 February 2002; received in revised form 5 May 2003; accepted 17 June 2003

Abstract

A test was performed to investigate the effect of concrete cracks on the static behavior of sleeve-type expansion anchors, andto confirm the seismic and fatigue resistance capability in cracked concrete. The tensile and shear test was conducted on singleanchors with three different anchor diameters. Concrete test specimens are sufficiently large to prevent the effect of the concreteedges on the anchor behavior. The types of failure, the static strength and displacement behavior of the anchors in uncrackedand cracked concrete were compared to evaluate the effect of the cracks. The strength reduction rate of the anchors due to thecracks was exhibited almost less than the corresponding value specified in ACI 349-01, APP. B. Through the residual strengthtests, the seismic and fatigue resistance capability of the anchors was confirmed in cracked concrete. The characteristics of theanchor shear capacity significantly vary with how the displacement failure criteria are determined.© 2003 Elsevier B.V. All rights reserved.

1. Introduction

Expansion anchors are widely used in piping andequipment supports in nuclear power plants. Thecracks could be generated on concrete members suchas slabs and walls that are used mainly to fix the com-ponents on, due to not only the mechanical loads suchas seismic force but also the concrete shrinkage andtemperature variation. Therefore, the performance ofthe anchor to be installed in a nuclear power plantshould be qualified in cracked concrete. This papershows the static behavior, and the seismic and fatigueresistance capability of sleeve-type expansion anchorsin cracked concrete. Especially, using three kinds ofdisplacement failure criterion, the characteristics of

∗ Corresponding author. Tel.:+82-42-868-0178;fax: +82-42-868-0523.

E-mail address: [email protected] (S.-Y. Kim).

the anchor shear capacity were compared to each other.This was done considering that there are many piecesof electrical equipment in nuclear power plants thatare vulnerable to even small anchorage displacements.

2. Test program

2.1. Test specimens

Testing was conducted on the sleeve-type expansionanchors, M10, M16 and M24, which have 10, 16 and24 mm anchor bolt diameter and 69, 101 and 148 mmeffective embedment depth, respectively (Fig. 1).

The target concrete compressive strength was315 kg/cm2 (4500 psi) at 91 days. The concrete spec-imens were reinforced with steel reinforcement tocontrol the cracks in specific size, but not to affectthe concrete breakout failure cone. The dimensions of

0029-5493/$ – see front matter © 2003 Elsevier B.V. All rights reserved.doi:10.1016/j.nucengdes.2003.06.018

274 S.-Y. Kim et al. / Nuclear Engineering and Design 228 (2004) 273–281

Fig. 1. Sleeve-type expansion anchor.

concrete specimens were 1400 mm× 1400 mm× 300(250) mm, and the anchors were installed far fromthe concrete edges to preclude the edge effects. Testpopulation was decided according to ACI 355.2 (ACI355.2-00, 2000) and ASTM E488 (ASTM E488-96,1996) as shown inTable 1.

2.2. Crack inducement and anchor installation

The anchor holes were drilled with an electro-pneumatic drilling machine and a carbide tipped drillbit of the specified nominal diameter. The initial crack(about 0.1 mm) was induced by insertion of splittingtubes in the pre-drilled holes and tapping them asshown inFig. 2. Anchors were installed with a max-imum deviation of 6◦ from the perpendicular in theinitially cracked concrete block and tightened to theinstallation torque. These values were 50, 200 and500 N m for M10, M16 and M24 anchor, respectively.The installed anchors were loosened to 50% of the in-stallation torque to account for relaxation. The initial

Table 1Test number

Anchordiameter(mm)

Test number

Static test Seismic test SLRTa Fatigue test

Tension Shear Tension Shear Shear Tension Shear

Cracked Uncracked Cracked Uncracked Cracked Cracked Cracked Cracked Cracked

10 5 5 5 5 5 5 3 3 316 5 5 5 5 5 5 3 3 324 5 5 5 5 5 5 3 3 3

ACI 355.2 – ASTM E-488

a SLRT : Slip load resistance test.

Table 2Fm value for seismic and fatigue test input

Anchor Fma in tensile test (kN) Fmb in shear test (kN)

M10 36 22M16 80 77M24 133 163

a Fm: mean value of static ultimate strength.b Fm: mean value of displacement(1/4Φ) based strength.

crack was widened to 0.5 mm for the seismic test and0.3 mm for the fatigue test by tapping the splittingtube, and the crack width was measured with micro-scope video at two places which are 30 mm awayfrom both sides of loading plate. The anchor holesize in the loading plate is the anchor diameter plus1.6 mm, and the contact surface between the loadingplate and the concrete block was not coated for theshear and slip resistance test.

2.3. Test loads

Test loads were determined in accordance with thespecifications of ACI 355.2 and ASTM E488.

The anchors for the static test were loaded to failureand the mean value (Fm) of the ultimate failure loadswere used as the base of the seismic and fatigue testinput as shown in theTable 2.

According to ACI 355.2, the test loads for the seis-mic tension and shear were determined as shown inFigs. 3 and 4, and the loading frequency was 0.1–2 Hz.Since ACI 355.2 is the test specification of the an-chors related to the ACI, 318, Appendix D, draft (ACI318-02, Appendix D, 2002), which is not for the nu-clear facilities, ACI 355.2 is for the general industrialfacilities. USNRC SRP (NUREG-0800, 1981) sub-

S.-Y. Kim et al. / Nuclear Engineering and Design 228 (2004) 273–281 275

Fig. 2. Crack inducement.

Fig. 3. Seismic tensile test input.

Fig. 4. Seismic shear test input.

section 3.7.2 requires that ten loading cycles per oneseismic event shall be considered and five OBEs andone SSE shall be applied in designing the nuclearpower plant. Accordingly, a minimum 60 cycles couldbe applied for the seismic test of anchors used in nu-clear power plants. 100 cycles of 0.25 Fm load ampli-tude used in this test must be enough, and 0.25 Fm canbe used for the seismic design level in nuclear powerplants. In case where the OBE level could be assumedto be one half of the SSE level, 0.5 Fm can be usedfor the seismic design level. The mean value of failureload, Fm, was determined based on the maximum ca-pacity in tension, and the displacement (0.25 anchordiameter) based capacity in shear (Table 2).

The fatigue tension and shear loads are shown inFigs. 5 and 6, and have 7–9 Hz frequency. The mean

Fig. 5. Fatigue tensile test input.


Fig. 6. Fatigue shear test input.

value of failure load was the same as that used in theseismic test input.

For all dynamic tests, pulsating loads in tension andalternating loads in shear were applied.

2.4. Test method

The test setups for the tension and shear are shownin Figs. 7 and 8. The concrete blocks for the tensile testwere attached to the reaction wall in the testing facility

Fig. 7. Tensile test setup.

Fig. 8. Shear test setup.

by four high strength bolts. All tests were performedin accordance with ACI 355.2 and ASTM E488.

The static test lasted until failure occurred. For theshear test, the anchors were installed in the hole of theloading plate to allow the displacement in the loadingdirection, which is in the same direction as the crack.The loading pattern of the seismic and fatigue testsdescribed above was applied. After the completion ofcyclic loading, a static tensile test to failure was per-formed to verify the residual strength. The crack widthwas controlled to 0.5 mm for the static and seismictest according to ACI 355.2 and 0.3 mm for the fatiguetest considering that the fatigue loading takes place innormal operating conditions.

The compressive strength of concrete was designedfor 315 kg/cm2 at 91 days after casting. To verifythe concrete strength, the concrete cylinder specimenswere made and tested in accordance with ASTM C39.The magnitude of the loads was measured by load cell,which is installed between loading plate and actuator,and the displacement was measured from the head ofthe anchor bolt to the pre-assigned base point.

The slip load resistance test (SLRT) was performedto get the reference data for determining the level offatigue shear test input. For this test, the anchors wereloaded with a monotonically increasing shear load ata rate not exceeding 0.076 mm (0.003 in.) displace-ment per minute. The test was terminated when thedisplacement of 1.27 mm (0.05 in.) was recorded, andthe slip resistance load was determined at this point.This test procedure accords with the testing methodto determine the slip coefficient for coatings used inbolted joints (AISC, 1989). This SLRT was performedin cracked concrete to consider the preload loss dueto the widened cracks.

3. Analysis of test results

3.1. Failure mode of anchor and characteristic ofload–displacement curve

All single anchors showed that the pullout failuremodes in tension were independent of the presenceof cracks or the effective depths of anchor. The M16and M24 anchors showed the concrete pryout failuremodes in shear with no relation to the presence ofcracks (Fig. 9). However, for M10 anchors subjected


Fig. 9. Concrete pryout shear failure.

to shear, all of the failures in uncracked concrete werein the steel bolts; while for cracked concrete, fourof the failures were in the steel bolt and one was aconcrete pryout failure (Fig. 10). This showed the factthat M10 anchors could produce two kinds of shearfailure modes in cracked concrete.

The analysis of the load versus displacement curveobtained from the ultimate strength test showed thatthe displacement of the anchor in cracked concreteelements increased but the strength decreased.

3.2. Effect of concrete cracks on static capacity ofanchor

3.2.1. Tensile strengthCompared to the corresponding value in uncracked

concrete, the maximum tensile capacity under thestatic loading in cracked concrete decreased by 25%in M10 anchor, 14% in M16 anchor and 9% in M24anchor (Fig. 11). These decreases are less than thereduction value, about 29%, to account for cracksspecified in ACI 349, APP. B (ACI 349-01, 2001).

The effect of cracks on the decrease rate of the an-chor strength is proportional to the decrease of the

Fig. 10. Bolt steel shear failure.

anchor diameter. The smaller anchor diameter was af-fected more by cracks.

The displacement at ultimate strength is less than6 mm, and the displacement behavior was almost un-affected by cracks.

3.2.2. Shear strengthM10 anchors with steel failure modes showed the

shear strength in cracked concrete was up to 16% lessthan the value in uncracked concrete (Fig. 12). Thedisplacement at ultimate strength of an M10 anchorwas increased by 15% due to the crack. This increaseof the displacement made the anchor bolt bend more,which seems to decrease the bolt shear capacity. ACI349, APP. B gives no explicit consideration of theeffects of cracks on the shear strength of the bolt steel.Therefore, additional study is needed on this issue.

M16 and M24 anchors in cracked concrete showedconcrete pryout failure modes. The maximum shearcapacity in cracked concrete decreased by 9% in M16anchor and 7% in M24 anchor (Fig. 12). These de-

Fig. 11. Static tensile behavior in uncracked and cracked concrete.


Fig. 12. Static shear behavior in uncracked and cracked concrete.

crease rates are less than one third of the reductionvalue to account for cracks in ACI 349, APP. B. Thereare no significant differences of the shear capacity re-duction rate between M16 and M24 anchors.

3.3. Effect of concrete cracks on displacement basedshear capacity

The shear capacity was evaluated using the displace-ment based capacity concept, and the results are asfollows.

If 1/4Φ (Φ: anchor diameter) is selected as thedisplacement failure criteria, the anchor strength de-creases to 41% of the ultimate strength in M10 an-chors, 56% in M16 anchors and 66% in M24 anchorsin uncracked concrete, and 33% in M10 anchors, 44%in M16 anchors and 57% in M24 anchors in crackedconcrete.

As a result of analyzing the effects of cracks on1/4Φ displacement based strength, it was found thatthe anchor strength decreased by 33% in M10 anchors,28% in M16 anchors and 19% in M24 anchors. Theserates of the strength reduction are more than twicethe corresponding values obtained with the ultimatestrength. The strength reduction rate of the anchor wasincreased with the decrease of the anchor diameter.The smaller anchor was affected by cracks more thanthe larger one.

In adopting 6.35 mm (1/4 in.) as an displacementfailure criterion, the anchor strength decreases to 62%of the ultimate strength in M10 anchors, 67% in M16anchors and 66% in M24 anchors in uncracked con-

crete, and 59% in M10 anchors, 59% in M16 anchorand 57% in M24 anchor in cracked concrete. Com-pared to the corresponding values in 1/4Φ displace-ment based strength, the shear strength increases morethan 20% in maximum.

The analysis of the effect of cracks on 6.35 mmdisplacement based strength shows that the anchorstrength decreases by 20% in M10 and M16 anchors,19% in M24 anchors. Compared to the correspondingeffect on 1/4Φ displacement based strength, the ef-fect of cracks on the reduction of the anchor capacityis small. The rates of the strength reduction are simi-larly independent of the size of the anchor. This fact iscontrary to the results from 1/4Φ displacement basedstrength.

In a case that a 12.7 mm (1/2 in.) is selected as andisplacement failure criterion, the anchor strength de-creases to 79, 79 and 83% of the ultimate strengthin M10, M16 and M24 anchors, respectively in un-cracked concrete, and 75, 76 and 81% of the ultimatestrength in M10, M16 and M24 anchors, respectivelyin cracked concrete.

After analyzing the effects of cracks on 12.7 mmdisplacement based strength, it was found that the an-chor strength decreased by 20, 13 and 10% in M10,M16 and M24 anchors, respectively. The anchor ca-pacity reduction caused by cracks tends to decreasewith the increase of the anchor diameter.

As described above, the anchor shear capacity varieswith how the displacement failure criteria are deter-mined (Fig. 13). The evaluation results are summa-rized as follows.

Fig. 13. Displacement based shear strength in uncracked andcracked concrete.


Firstly, 12.7 mm displacement based shear strengthof the anchor reaches about 80% of the ultimatestrength independent of the presence of the cracksand the size of the anchor. The anchor capacity re-duces abruptly with the decrease of the amount of thedisplacement as failure criteria.

Secondly, in adopting 1/4Φ, 6.35 and 12.7 mm asdisplacement failure criteria, the effect of the crackon the shear strength reduction is less than 30% ex-cept 1/4Φ displacement based strength of M10 anchor,which shows 33% strength reduction. The larger thedisplacement as a failure criterion is, the smaller theeffect of the crack on the anchor strength reduction.

3.4. Seismic resistance capability of anchor incracked concrete

3.4.1. Tensile strengthThe residual strength of anchors after a seismic

test was found to be a little greater than the ulti-mate strength obtained through the static test with nopre-seismic test, and the displacement at the maximumresidual strength was changed little compared with thecorresponding value in the static test (Fig. 14). As aresult, it can be seen that the seismic load has lit-tle influence on the resisting capacity of the anchors,and the maximum displacement that occurred was lessthan 1 mm even with seismic load.

3.4.2. Shear strengthThe residual strength of anchors after a seismic test

was as large as the ultimate strength in the static test

Fig. 14. Comparison of static tensile behavior with residual tensilebehavior after seismic tensile tests in cracked concrete.

Fig. 15. Comparison of static shear behavior with residual shearbehavior after seismic shear tests in cracked concrete.

(Fig. 15). The displacement of M10 anchors at themaximum residual strength increased, which causedsteel failure modes. M16 and M24 anchors showedconcrete pryout failure modes. The maximum dis-placement under seismic load was found less than6 mm and the anchors were confirmed to survive suc-cessfully under the alternating seismic loads.

3.5. Fatigue resistance capability of anchor incracked concrete

3.5.1. Tensile strengthThe residual strength after a fatigue test exceeded

the ultimate strength obtained through the static test(Fig. 16). The displacement at the maximum residualstrength showed little difference from the correspond-

Fig. 16. Comparison of static tensile behavior with residual tensilebehavior after fatigue tensile tests in cracked concrete.


Fig. 17. Comparison of static shear behavior with residual shearbehavior after fatigue shear tests in cracked concrete.

ing value in the static test. The reasons why the resid-ual strength after fatigue test exceeded the ultimatestrength in the static test can be assumed as follows.The expanded crack width (0.3 mm) in the fatigue testis less than that (0.5 mm) in the static test. Further-more, the anchoring force of the sleeve part was in-creased under the fatigue loads.

3.5.2. Shear strengthThe maximum residual strength after a fatigue test

exceeded the ultimate strength obtained through thestatic test (Fig. 17).

Through the shear fatigue load test on M10, M16and M24 anchors, it was found that an appropriate

Fig. 18. Comparison of static displacement based shear strengthwith residual shear strength after fatigue shear tests in crackedconcrete.

magnitude of alternating loads could increase the max-imum strength of anchors. This strength increase canbe attributed to enhancement of the anchoring forceof the sleeve during the tests.

The residual strength was larger than the static shearstrength. Hence, the fatigue load tends to increasethe shear strength of anchors even when the residualstrength is decided on the displacement based strengthexcept 1/4Φ displacement based strength of M10 an-chors (Fig. 18). Consequently, whether based on theultimate strength of anchors or the displacement basedstrength, the resisting shear capacity of anchors afterfatigue test increased a little.

4. Conclusions

A test was performed to investigate the effect of con-crete cracks on the static behavior of the sleeve-typeexpansion anchors, and to confirm the seismic and fa-tigue resistance capability in cracked concrete. Thefollowing conclusions were drawn from the evaluationof test results.

Firstly, the effects of concrete cracks on the tensilecapacity reduction of a single anchor are mostly be-low 25% and decrease to below 10% with the increaseof the anchor diameter. The effects of concrete crackson the shear capacity reduction are also below 10%.These test results are considerably less than the reduc-tion value, about 29%, to account for cracks specifiedin ACI 349, APP. B.

Secondly, even though bolt steel shear failure oc-curred in the M10 anchor, there was some decreaseof shear strength due to the increase of bolt bendingcaused by the crack. In case of steel failure, shearcapacity reduction to account for the cracks is notconsidered in ACI 349, APP. B. Additional study isrecommended on this issue.

Thirdly, the characteristics of the anchor shear ca-pacity significantly vary with how the displacementfailure criteria are determined. The anchor capacityreduces abruptly with the decrease of the amount ofthe displacement as failure criteria. The larger the dis-placement as a failure criterion, the smaller the effectof the cracks on the anchor strength reduction.

Fourthly, the seismic and fatigue resistancecapacity of sleeve-type expansion anchor in crackedconcrete was confirmed under the alternating shear


load and pulsating tensile load. Some level of fatigueload tends to increase the anchor strength by build-ing the anchoring force additionally inside holes inconcrete.

References

ACI 355.2-00, 2000. Evaluating the Performance of Post-InstalledMechanical Anchors in Concrete and Commentary, An ACIProvisional Standard.

ASTM E488-96, 1996. Standard Test Methods for Strength ofAnchors in Concrete and Masonry Elements.

ACI 318-02, 2002. Building Code Requirements for StructuralConcrete.

NUREG-0800, 1981. Standard Review Plan for the Review ofSafety Analysis Reports for Nuclear Power Plants.

AISC, 1989. Manual of Steel Construction, Allowable StressDesign, Appendix A, Testing Method of Determine theSlip Coefficient for Coatings used in Bolted Joint, 9thedition.

ACI 349-01, 2001. Appendix B, Anchoring to Concrete.

sleeve-type expansion anchor behavior in cracked and uncracked concrete

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