Anchorage to Concrete per ACI 318-08 Appendix D and IBC 2006

ACI 318-08, Appendix DIBC 2006 Section 1912

Anchorage to Concrete

Mark Bartlett, PEField Engineer

Simpson Anchor Systems

Presentation Topics

Brief History of Anchor Design ACI 318-08, Appendix D

Design Equations Phi () Factors Interaction Equation Seismic Provisions Reinforcement to Prevent Breakout Other Issues Edge Distances, Thicknesses & Spacings

When to design per App. D IBC 2006 Adhesive Anchors and Concrete

Screws The Future of Anchor Design

Prior to ACI 318-02

Cast-In-Place anchors covered by: PCI / ACI 349 UBC / IBC codes listed allowable

stress capacities for CIP bolts

Prior to ACI 318-02

Design of Post-Installed anchors: Individual manufacturers supplied

load values based on testing

Values found in catalogs and ICBO/ICC reports

Methodology was allowable stressand assumed an uncracked and unreinforced section.

ACI 318-08, Appendix D

ACI 318, Appendix D

Strength design method for anchorage to concrete(i.e. Nua Nn or Vua Vn) Cast-In-Place (CIP) anchors Post-Installed (PI) anchors

Undercut anchors Torque-controlled anchors Deformation-controlled anchors

PI anchors must be prequalified per ACI 355.2

Appendix D Design Equations & Failure

Modes

Design equations check 5 different failure modes Steel capacity

Tension and Shear Concrete breakout capacity

Tension and Shear Pullout/Pull-through capacity

Tension only Concrete Pryout

Shear only Concrete side-face blowout

Tension and CIP only.

Appendix D Design Equations

Design Equations

Tension CapacitiesNsa = nAse,NfutaNcb = ANc/ANco(

Steel Strength In Tension D.5.1

Nsa = nAse,Nfuta(Eq. D-3) Nsa Nominal tensile

strength of an anchor group n Number of anchors Ase,N Effective cross

sectional area of anchor in tension

futa Specific ultimate tensile strength of anchor

Concrete Breakout Strengthin Tension

Concrete Breakout In Tension D.5.2

Ncb=ANc/ANco(

Concrete Breakout In Tension D.5.2

Ncbg=ANc/ANco(

Pullout Strength In Tension D.5.3

Npn =

Side-Face Blowout Strengthin Tension

Side-Face Blowout Strength D.5.4

Nsb = (160ca1Abrg)fc (Eq. D-17) Nsb Side-face blowout strength (headed

anchors only)

ca1 edge distance

Abrg Net bearing area of the head of anchor

Modification factor for lightweight concrete

Steel Strength in Shear

Steel Strength In Shear D.6.1

Vsa = n Ase,V futa (eq. D-19) CIP HSA Vsa = n 0.6 Ase,V futa (eq. D-20)

n number of anchors Ase,V effective cross sectional

area of a single anchor in shear futa specified tensile strength of

anchor steel

Steel Strength In Shear D.6.1

Vsa may also be based on the results of tests performed and evaluated according to ACI 355.2

Concrete Breakout Strengthin Shear

Concrete Breakout Strength In Shear

D.6.2

Vcbg = AVc/AVco(

Concrete Breakout In Shear D.6.2

Vcbg = AVc/AVco(

Concrete Breakout Strength In Shear

D.6.2

Vcbg = AVc/AVco(

Concrete Pryout Strength In Shear

D.6.3

Vcpg = kcpNcbg (Eq. D-30)

kcp = 1.0 for hef < 2.5 kcp = 2.0 for hef > 2.5

Ncbg Nominal concrete breakout strength in tension

Always do tension calcs first

Phi () Factors

Phi () factors

Nua Nn or Vua Vn

Phi () factors are applied to nominal capacities before comparing with factored forces

Based on: Supplemental reinforcement Failure mode Load type Anchor property

Phi () factors D.4.4

0.700.45Cat. 3

0.700.55Cat. 2

0.700.65Cat. 1

0.700.70

Use Condition B

CIP

Pryout

0.700.45Cat. 3

0.700.55Cat. 2

0.700.65Cat. 1

0.700.70

Use Condition B

CIP

Pullout

0.700.450.750.55Cat. 3

0.700.550.750.65Cat. 2

0.700.650.750.75Cat. 1

0.700.700.750.75CIP

Breakout

0.700.700.750.75CIPSide Face Blowout

0.600.65Brittle

0.650.75Use Condition B

DuctileSteel

ShearTension ShearTension

Condition BCondition A

FactorAnchor

PropertyFailure Mode

Supplemental Reinforcing D.4.4

Condition A Applies where supplementary

reinforcement is present except for pullout and pryout strengths.

Condition B Applies where supplementary

reinforcement is not present, and for pullout or pryout strength.

Supplemental Reinforcing

Supplemental Reinforcement Reinforcement that acts to restrain

the potential concrete breakout but is not designed to transfer the full design load from the anchors into the structural member.

Refer to sections D.5.2.9 and D.6.2.9 for full design load transfer requirements

Interaction of Tension and Shear

Interaction of Tension and Shear D.7

Interaction of Tension and Shear D.7

If Vua0.2Vn full tension allowed Ignore Shear

If Nua0.2Nn full shear allowed Ignore Tension

OtherwiseNua + Vua < 1.2Nn Vn

Appendix D Seismic Provisions

Seismic Provisions

D.3.3 When anchor design includes earthquake forces for structures assigned to Seismic Design Category C, D, E, or F, the additional requirements of D.3.3.1 through D.3.3.6 shall apply.

D.3.3.1 The provisions of Appendix D do not apply to the design of anchors in plastic hinge zones of concrete structures under earthquake forces.

D.3.3.2 Post-installed structural anchors shall be qualified for use in cracked concrete and shall have passed the Simulated Seismic Tests in accordance with ACI 355.2. Pullout strength Np and steel strength of the anchor in shear Vsa shall be based on the results of the ACI 355.2 Simulated Seismic Tests.

Seismic Provisions

D.3.3.3 The anchor design strength associated with concrete failure modes shall be taken as 0.75INnand 0.75IVn, where I is given in D.4.4 or D.4.5, and Nn and Vn are determined in accordance with D.5.2, D.5.3, D.5.4, D.6.2, and D.6.3, assuming the concrete is cracked unless it can be demonstrated that the concrete remains uncracked.

0.75 reduction to concrete capacity in Seismic Design Category C F

Impractical to prove concrete remains uncracked

Seismic Provisions

D.3.3.4 Anchors shall be designed to be governed by the steel strength of a ductile steel element as determined in accordance with D.5.1 and D.6.1, unless either D.3.3.5 or D.3.3.6 is satisfied.

D.3.3.5 Instead of D.3.3.4, the attachment that the anchor is connecting to the structure shall be designed so that the attachment will undergo ductile yielding at a force level corresponding to anchor forces no greater than the design strength of anchorsspecified in D.3.3.3.

D.3.3.6 As an alternative to D.3.3.4 and D.3.3.5, it shall be permitted to take the design strength of the anchors as 0.4 times the design strength determined in accordance with D.3.3.3. For the anchors of stud bearing walls, it shall be permitted to take the design strength of the anchors as 0.5 times the design strength determined in accordance with D.3.3.3.

Seismic Provisions

Summary Seismic Design Category C, D, E & F No anchors in plastic hinge PI anchors must pass Simulated

Seismic Test Design strength reduced by 25% Ductile steel failure of anchors shall

control, or... Ductile yielding of attachment, or... Anchor capacity reduced by 60%

Seismic Provisions

Seismic and edge effects At small edge distances, concrete

breakout (non ductile failure mode) will often control

If attachment will not experience ductile yielding before breakout occurs, then 40% anchor capacity reduction unless...

Reinforce section to prevent breakout from occurring

Reinforcement to Prevent Concrete Breakout

Reinforcement to Prevent

Concrete Breakout

D.4.2.1 The effect of reinforcement provided to restrain the concrete breakout shall be permitted to be included in the design models used to satisfy D.4.2. Where anchor reinforcement is provided in accor-dance with D.5.2.9 and D.6.2.9, calculation of the concrete breakout strength in accordance with D.5.2 and D.6.2 is not required.

D.5.2.9 Where anchor reinforcement is developed in accordance with Chapter 12 on both sides of the breakout surface, the design strength of the anchor reinforcement shall be permitted to be used instead of the concrete breakout strength in determining INn. Astrength reduction factor of 0.75 shall be used in the design of the anchor reinforcement.


Concrete Breakout

Refer to Commentary RD.5.2.9 for more information


Concrete Breakout

D.6.2.9 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 the concrete breakout strength in determining IVn. A strength reduction factor of 0.75 shall be used in the design of the anchor reinforcement.

Plan Section

Refer to Commentary RD.6.2.9 for more info


Concrete Breakout

Bars

effe

ctiv

e as

a

nch

or re

info

rcem

en

t

Plan

Edge Reinforcement

Anchor Reinforcement

Section

Refer to Commentary RD.6.2.9 for more info


Concrete Breakout

Per Commentary RD.5.2.9 and RD.6.2.9: As a practical matter, use of anchor

reinforcement is generally limited to cast-in-place anchors.

What about post-installed anchors? At small edge distances, anchor

capacity will be greatly reduced for seismic design.

Other Appendix D Issues

Capacity Adjustments

PI anchor pullout capacity Tested values of Np are done in 2500 psi

concrete Pullout capacities increase for higher fc Adjustment equations in ER

Grout pads 20% reduction in shear strength (D.6.1.3) App. D makes no mention to grout pad

thickness Shear load parallel to concrete edge

Breakout capacity doubled per D.6.2.1(c).

Triple Edge Conditions

D.5.2.3 Where anchors are located less than 1.5hef from three or more edges, the value of hef used in Eq. (D-4) through (D-11) shall be the greater of ca,max/1.5 and one-third of the maximum spacing between the anchors within the group.

D.6.2.4 Where anchors are influenced by three or more edges, the value of ca1 used in Eq. (D-23) through (D-29) shall be the greatest of ca2/1.5 in either direction, ha/1.5; and one-third of the maximum spacing between the anchors within the group.

Triple Edge Condition in Tension

Triple Edge Condition in Shear

Corner Condition D.6.2.1(d)

(d) For anchors located at a corner, the limiting nominal concrete breakout strength shall be deter-mined for each edge, and the minimum value shall be used.

V

ca1

ca2

V

ca2

ca1

Shear Near an Edge D.6.2.1

Where anchors are located at varying distances from the edge and the anchors are welded to the attach-ment so as to distribute the force to all anchors, it shall be permitted to evaluate the strength based on the distance to the farthest row of anchors from the edge. In this case, it shall be permitted to base the value of ca1 on the distance from the edge to the axis of the farthest anchor row that is selected as critical, and all of the shear shall be assumed to be carried by this critical anchor row alone.

V

ca1

0.5V

0.5V

ca1

Anchorswelded to

plate

Anchorsnot welded to plate

Shear Near an Edge D.6.2.1

Vca1

Increase ca1 without welding to plate Slot holes closest to edge

Required Edge Distances, Spacings, and Thicknesses

Section D.8

Minimum spacings and edge distances for anchors and minimum thicknesses of members shall conform to D.8.1 through D.8.6, unless supplementary reinforce-ment is provided to control splitting. Lesser values from product-specific tests performed in accordance with ACI 355.2 shall be permitted.D.8.1 Unless determined in accordance with D.8.4, minimum center-to-center spacing of anchors shall be 4da for untorqued cast-in anchors, and 6da for torquedcast-in anchors and post-installed anchors.D.8.2 Unless determined in accordance with D.8.4, minimum edge distances for cast-in headed anchors that will not be torqued shall be based on specified cover requirements for reinforcement in 7.7. For cast-in headed anchors that will be torqued, the minimum edge distances shall be 6da.

Section D.8

D.8.3 Unless determined in accordance with D.8.4, minimum edge distances for post-installed anchors shall be based on the greater of specified cover requirements for reinforcement in 7.7, or minimum edge distance requirements for the products as deter-mined by tests in accordance with ACI 355.2, and shall not be less than 2.0 times the maximum aggregate size. In the absence of product-specific ACI 355.2 test information, the minimum edge distance shall be taken as not less than:

Undercut anchors..................................................6daTorque-controlled anchors.....................................8daDisplacement-controlled anchors.........................10da

Section D.8

D.8.4 For anchors where installation does not produce a splitting force and that will remain untorqued, if the edge distance or spacing is less than those speci-fied in D.8.1 to D.8.3, calculations shall be performed by substituting for da a smaller value da that meets the requirements of D.8.1 to D.8.3. Calculated forces applied to the anchor shall be limited to the values corresponding to an anchor having a diameter of da.D.8.5 The value of hef for an expansion or undercut post-installed anchor shall not exceed the greater of 2/3 of the member thickness and the member thickness minus 4 in.

Section D.8

D.8.6 Unless determined from tension tests in accordance with ACI 355.2, the critical edge distance, cac, shall not be taken less than:

Undercut anchors...............................................2.5hefTorque-controlled anchors....................................4hefDisplacement-controlled anchors..........................4hef

Limitations of Appendix D

Applies for CIP and some Post-Installed anchors Specialty inserts, through bolts,

adhesive anchors, screw anchors, PAT fasteners outside scope of Appendix D

ACI Commentary: Adhesive anchors are widely used and can perform adequately. At this timeoutside the scope.


NW Concrete and LW Concrete only Reductions in capacity in LW

CMU and Concrete on metal deck outside scope of App. D

Grouted CMU will still use existing post-installed anchor products


Limits to: Diameter (2)

Embedment depth (25)

Concrete compressive strength (8000 psi PI;

When to use Appendix D

Per ACI 318-08, D.2.1 anchors in concrete used to

transmit structural loads by means of tension, shear, or a combination of tension and shear between (a) connected structural elements; or (b) safety-related attachments and structural elements.

What is a safety-related attachment?

When to use Appendix D

Per ACI 318-08, RD.2.1 Commentary lists examples for safety-

related attachments. safety-related attachments that are

not part of the structure (such as sprinkler systems, heavy suspended pipes, or barrier rails) are attached to structural elements.

Will sprinkler systems be attached with cracked concrete anchors?

When to Use Appendix DIBC 2006

IBC 2006, Section 1911

Anchorage To Concrete Allowable Stress Design

1911.1 Scope. The provisions of this section shall govern the

allowable stress design of headed bolts, and headed stud

anchors cast in normal-weight concrete for purposes of trans-

mitting structural loads from one connected element to the

other. These provisions do not apply to anchors installed in

hardened concrete or where load combinations include earth-

quake loads or effects. The bearing area of headed anchors

shall be not less than one and one-half times the shank area.

Where strength design is used, or where load combinations

include earthquake loads or effects, the design strength of

anchors shall be determined in accordance with Section 1912.

Bolts shall conform to ASTM A 307 or an approved

equivalent.


Anchorage To Concrete Strength Design1912.1 Scope. The provisions of this section shall govern the

strength design of anchors installed in concrete for purposes of

transmitting structural loads from one connected element to

the other. Headed bolts, headed studs and hooked (J- or L-)

bolts cast in concrete and expansion anchors and undercut

anchors installed in hardened concrete shall be designed in

accordance with Appendix D of ACI 318 as modified by

Section 1908.1.16, provided they are within the scope of

Appendix D.

The strength design of anchors that are not within the scope of

Appendix D of ACI 318, and as amended above, shall be in

accordance with an approved procedure.

Exception: Where the basic concrete breakout strength in

tension of a single anchor, Nb, is determined in accordance

with Equation (D-7), the concrete breakout strength

requirements of Section D.4.2.2 shall be considered

satisfied by the design procedures of Sections D.5.2 and

D.6.2 for anchors exceeding 2 inches (51mm) in diameter

or 25 inches (635mm) tensile embedment depth.


Modifications to ACI 318

1908.1.16 ACI 318, Section D.3.3. Modify ACI 318, section

D.3.3.2 through C.3.3.5, to read as follows:

D.3.3.2 In structures assigned to Seismic Design Category C,

D, E or F, post-installed anchors for use under D.2.3 shall have

passed the Simulated Seismic Tests of ACI 355.2.


D, E or F, the design strength of anchors shall be taken as

0.75Nn and 0.75Vn, where is given in D.4.4 or D.4.5, and Nn and Vn are determined in accordance with D.4.1.


D, E or F, anchors shall be designed to be governed by tensile

or shear strength of a ductile steel element, unless D.3.3.5 is

satisfied.

D.3.3.5 Instead of D.3.3.4, the attachment that the anchor is

connecting to the structure shall be designed so that the

attachment will undergo ductile yielding at a load level

corresponding to anchor forces no greater than the design

strength of anchors specified in D.3.3.3, or the minimum design

strength of the anchors shall be at least 2.5 times the factored

forces transmitted by the attachment.

Adhesive Anchors andConcrete Screws

Adhesives Anchors and Concrete

Screws

IBC 2006, Section 1912 The strength design of anchors that

do not within the scope of Appendix D of ACI 318shall be in accordance with an approved design procedure.

What design procedures are approved?

Who decides?


Screws

IBC 2006, Section 104.11104.11 Alternative materials, design and methods of

construction and equipment. The provisions of this code are not

intended to prevent the installation of any material or to prohibit

any design or method of construction not specifically prescribed by

this code, provided that any such alternative has been approved.

An alternative material, design or method of construction shall be

approved where the building official finds that the proposed design

is satisfactory and complies with the intent of the provisions of this

code, and that the material, method or work offered is, for the

purpose intended, at least the equivalent of that prescribed in this

code in quality, strength, effectiveness, fire resistance, durability

and safety.

104.11.1 Research reports. Supporting data, where necessary

to assist in the approval of materials or assemblies not

specifically provided for in this code, shall consist of valid

research reports from approved sources.


Screws

IBC 2006, Section 104.11 The building official has the ability to

approve a material if it is not specifically referenced in the code

Adhesive anchors and screw anchors fall into this category

Caution: Most building officials are still learning about strength design provisions of anchors


Screws

Many engineers are still designing adhesive anchors and screw anchors per ASD

Strength design code reports for adhesives and screws are just starting to come online


Screws

ICC ES AC 193 Expansion anchors Undercut anchors Screw anchors

ICC ES AC 308 Adhesive anchors

Code Reports

The Future of Anchors

Reliance on software for anchor design

Many new post-installed anchors

Confusion among engineers, contractors and building officials

Lengthy transition period

The Future of Anchors

What changes will the IBC 2009 and ACI 318-11, Appendix D bring?

Clearer provisions for adhesives and concrete screws?

Questions

Anchorage to Concrete per ACI 318-08 Appendix D and IBC 2006

Documents

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