PCI 6th Edition

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PCI 6th Edition

• Headed Concrete Anchors (HCA)

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Presentation Outine

• Research Background
• Steel Capacity
• Concrete Tension Capacity
• Tension Example
• Concrete Shear Capacity
• Shear Example
• Interaction Example

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Background for Headed Concrete Anchor Design

• Anchorage to concrete and the design of welded
  headed studs has undergone a significant
  transformation since the Fifth Edition of the
  Handbook.
• Concrete Capacity Design (CCD) approach has
  been incorporated into ACI 318-02 Appendix D

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Headed Concrete Anchor Design History

• The shear capacity equations are based on PCI
  sponsored research
• The Tension capacity equations are based on the
  ACI Appendix D equations only modified for
  cracking and common PCI variable names

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Background forHeaded Concrete Anchor Design

• PCI sponsored an extensive research project,
  conducted by Wiss, Janney, Elstner Associates,
  Inc., (WJE), to study design criteria of headed
  stud groups loaded in shear and the combined
  effects of shear and tension
• Section D.4.2 of ACI 318-02 specifically permits
  alternate procedures, providing the test results
  met a 5 fractile criteria

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Supplemental Reinforcement

• Appendix D, Commentary
• supplementary reinforcement in the direction
  of load, confining reinforcement, or both, can
  greatly enhance the strength and ductility of the
  anchor connection.
• Reinforcement oriented in the direction of load
  and proportioned to resist the total load within
  the breakout prism, and fully anchored on both
  side of the breakout planes, may be provided
  instead of calculating breakout capacity.

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HCA Design Principles

• Performance based on the location of the stud
  relative to the member edges
• Shear design capacity can be increased with
  confinement reinforcement
• In tension, ductility can be provided by
  reinforcement that crosses the potential failure
  surfaces

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HCA Design Principles

• Designed to resist
• Tension
• Shear
• Interaction of the two
• The design equations are applicable to studs
  which are welded to steel plates or other
  structural members and embedded in unconfined
  concrete

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HCA Design Principles

• Where feasible, connection failure should be
  defined as yielding of the stud material
• The groups strength is taken as the smaller of
  either the concrete or steel capacity
• The minimum plate thickness to which studs are
  attached should be ½ the diameter of the stud
• Thicker plates may be required for bending
  resistance or to ensure a more uniform load
  distribution to the attached studs

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Stainless Steel Studs

• Can be welded to either stainless steel or mild
  carbon steel
• Fully annealed stainless steel studs are
  recommended when welding stainless steel studs to
  a mild carbon steel base metal
• Annealed stud use has been shown to be imperative
  for stainless steel studs welded to carbon steel
  plates subject to repetitive or cyclic loads

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Stud Dimensions

• Table 6.5.1.2
• Page 6-12

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Steel Capacity

• Both Shear and Tension governed by same basic
  equation
• Strength reduction factor is a function of shear
  or tension
• The ultimate strength is based on Fut and not Fy

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Steel Capacity

• fVs fNs fnAsefut
• Where
• f steel strength reduction factor
• 0.65 (shear)
• 0.75 (tension)
• Vs nominal shear strength steel capacity
• Ns nominal tensile strength steel capacity
• n number of headed studs in group
• Ase nominal area of the headed stud shank
• fut ultimate tensile strength of the stud
  steel

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Material Properties

• Adapted from AWS D1.1-02
• Table 6.5.1.1 page 6-11

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Concrete Capacity

• ACI 318-02, Appendix D, Anchoring to Concrete
• Cover many types of anchors
• In general results in more conservative designs
  than those shown in previous editions of this
  handbook

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Cracked Concrete

• ACI assumes concrete is cracked
• PCI assumes concrete is cracked
• All equations contain adjustment factors for
  cracked and un-cracked concrete
• Typical un-cracked regions of members
• Flexural compression zone
• Column or other compression members
• Typical precast concrete
• Typical cracked regions of members
• Flexural tension zones
• Potential of cracks during handling

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The 5 fractile

• ACI 318-02, Section D.4.2 states, in part
• The nominal strength shall be based on the 5
  percent fractile of the basic individual anchor
  strength
• Statistical concept that, simply stated,
• if a design equation is based on tests, 5
  percent of the tests are allowed to fall below
  expected

Capacity
5 Failures
Test strength
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The 5 fractile

• This allows us to say with 90 percent confidence
  that 95 percent of the test actual strengths
  exceed the equation thus derived
• Determination of the coefficient ?, associated
  with the 5 percent fractile (?s)
• Based on sample population,n number of tests
• x the sample mean
• s is the standard deviation of the sample set

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The 5 fractile

• Example values of ? based on sample size are
• n 8 ? 1.645
• n 40 ? 2.010
• n 10 ? 2.568

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Strength Reduction Factor

• Function of supplied confinement reinforcement
• f 0.75 with reinforcement
• f 0.70 with out reinforcement

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Notation Definitions

• Edges
• de1, de2, de3, de4
• Stud Layout
• x1, x2,
• y1, y2,
• X, Y
• Critical Dimensions
• BED, SED

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Concrete Tension Failure Modes

• Design tensile strength is the minimum of the
  following modes
• Breakout
• fNcb usually the most critical failure mode
• Pullout
• fNph function of bearing on the head of the stud
• Side-Face blowout
• fNsb studs cannot be closer to an edge than 40
  the effective height of the studs

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Concrete Tension Strength

• fNcb Breakout
• fNph Pullout
• fNsb Side-Face blowout

fTn Minimum of
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Concrete Breakout Strength

• Where
• Ccrb Cracked concrete factor, 1 uncracked,
  0.8 Cracked
• AN Projected surface area for a stud or group
• Yed,N Modification for edge distance
• Cbs Breakout strength coefficient

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Effective Embedment Depth

• hef effective embedment depth
• For headed studs welded to a plate flush with the
  surface, it is the nominal length less the head
  thickness, plus the plate thickness (if fully
  recessed), deducting the stud burnoff lost during
  the welding process about 1/8 in.

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Projected Surface Area, An

• Based on 35o
• AN - calculated, or empirical equations are
  provided in the PCI handbook
• Critical edge distance is 1.5hef

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No Edge Distance Restrictions

• For a single stud, with de,min gt 1.5hef

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Side Edge Distance, Single Stud

• de1 lt 1.5hef

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Side Edge Distance, Two Studs

• de1 lt 1.5hef

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Side and Bottom Edge Distance, Multi Row and
Columns

• de1 lt 1.5hef
• de2lt 1.5hef

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Edge Distance Modification

• Yed,N modification for edge distance
• de,min minimum edge distance, top, bottom, and
  sides
• PCI also provides tables to directly calculate
  fNcb, but Cbs , Ccrb, and Yed,N must still be
  determined for the in situ condition

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Determine Breakout Strength, fNcb

• The PCI handbook provides a design guide to
  determine the breakout area

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Determine Breakout Strength, fNcb

• First find the edge condition that corresponds to
  the design condition

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Eccentrically Loaded

• When the load application cannot be logically
  assumed concentric.
• Where
• e'N eccentricity of the tensile force
  relative to the center of the stud group
• e'N s/2

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Pullout Strength

• Nominal pullout strength
• Where
• Abrg bearing area of the stud head
• area of the head area of the shank
• Ccrp cracking coefficient (pullout)
• 1.0 uncracked
• 0.7 cracked

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Side-Face Blowout Strength

• For a single headed stud located close to an edge
  (de1 lt 0.4hef)
• Where
• Nsb Nominal side-face blowout strength
• de1 Distance to closest edge
• Abrg Bearing area of head

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Side-Face Blowout Strength

• If the single headed stud is located at a
  perpendicular distance, de2, less then 3de1 from
  an edge, Nsb, is multiplied by
• Where

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Side-Face Blowout

• For multiple headed anchors located close to an
  edge (de1 lt 0.4hef)
• Where
• so spacing of the outer anchors along the
  edge in the group
• Nsb nominal side-face blowout strength for
  a single anchor previously defined

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Example Stud Group Tension

• Given
• A flush-mounted base plate with four headed
  studs embedded in a corner of a 24 in. thick
  foundation slab
• (4) ¾ in. f headed studs welded to ½ in thick
  plate
• Nominal stud length 8 in
• f'c 4000 psi (normal weight concrete)
• fy 60,000 psi

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Example Stud Group Tension

• Problem
• Determine the design tension strength of the
  stud group

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Solution Steps

• Step 1 Determine effective depth
• Step 2 Check for edge effect
• Step 3 Check concrete strength of stud group
• Step 4 Check steel strength of stud group
• Step 5 Determine tension capacity
• Step 6 Check confinement steel

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Step 1 Effective Depth
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Step 2 Check for Edge Effect

• Design aid, Case 4
• X 16 in.
• Y 8 in.
• de1 4 in.
• de3 6 in.
• de1 and de3 gt 1.5hef 12 in.
• Edge effects apply
• de,min 4 in.

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Step 2 Edge Factor
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Step 3 Breakout Strength
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Step 3 Pullout Strength
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Step 3 Side-Face Blowout Strength

• de,min 4 in. gt 0.4hef
• 4 in. gt 0.4(8) 3.2 in.
• Therefore, it is not critical

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Step 4 Steel Strength
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Step 5 Tension Capacity

• The controlling tension capacity for the stud
  group is Breakout Strength

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Step 6 Check Confinement Steel

• Crack plane area 4 in. x 8 in. 32 in.2

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Step 6 Confinement Steel

• Use 2 - 6 L-bar around stud group.
• These bars should extend ld past the breakout
  surface.

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Concrete Shear Strength

• The design shear strength governed by concrete
  failure is based on the testing
• The in-place strength should be taken as the
  minimum value based on computing both the
  concrete and steel

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Front Edge Shear Strength, Vc3
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Corner Edge Shear Strength, Modified Vc3
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Side Edge Shear Strength, Vc1
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Front Edge Shear Strength

• Where
• Vco3 Concrete breakout strength, single anchor
  
• Cx3 X spacing coefficient
• Ch3 Member thickness coefficient
• Cev3 Eccentric shear force coefficient
• Cvcr Member cracking coefficient

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Single Anchor Strength

• Where
• ? lightweight concrete factor
• BED distance from back row of studs to
• front edge

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X Spacing factor

• Where
• X Overall, out-to-out dimension of outermost
• studs in back row of anchorage
• nstuds-back Number of studs in back row

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Thickness Factor

• Where
• h Member thickness

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Eccentricity Factor

• Where
• e'v Eccentricity of shear force on a group of
  anchors

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Cracked Concrete Factor

• Uncracked concrete
• Cvcr 1.0
• For cracked concrete,
• Cvcr 0.70 no reinforcement
• or
• reinforcement lt No. 4 bar
• 0.85 reinforcement No. 4 bar
• 1.0 reinforcement. No. 4 bar and
  confined within stirrups with a spacing 4
  in.

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Corner Shear Strength

• A corner condition should
• be considered when
• where the Side Edge
• distance (SED) as
• shown

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Corner Shear Strength

• Where
• Ch3 Member thickness coefficient
• Cev3 Eccentric shear coefficient
• Cvcr Member cracking coefficient
• Cc3 Corner influence coefficient

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Corner factor

• For the special case of a large X-spacing stud
  anchorage located near a corner, such that
  SED/BED gt 3, a corner failure may still result,
  if de1 2.5BED

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Side Edge Shear Strength

• In this case, the shear force is applied parallel
  to the side edge, de1
• Research determined that the corner influence can
  be quite large, especially in thin panels
• If the above ratio is close to the 0.2 value, it
  is recommended that a corner breakout condition
  be investigated, as it may still control for
  large BED values

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Side Edge Shear Strength
Where Vco1 nominal concrete breakout strength
for a single stud CX1 X spacing coefficient
CY1 Y spacing coefficient Cev1 Eccentric
shear coefficient
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Single Anchor Strength

• Where
• de1 Distance from side stud to side edge (in.)
• do Stud diameter (in.)

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X Spacing Factor

• Where
• nx Number of X-rows
• x Individual X-row spacing (in.)
• nsides Number of edges or sides that influence
  the X direction

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X Spacing Factor

• For all multiple Y-row anchorages located
  adjacent to two parallel edges, such as a column
  corbel connection, the X-spacing for two or more
  studs in the row
• Cx1 nx

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Y Spacing Factor

• Where
• ny Number of Y-rows
• Y Out-to-out Y-row spacing (in) Sy (in)

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Eccentricity Factor

• Where
• ev1 Eccentricity form shear load to
  anchorage centroid

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Back Edge Shear Strength

• Under a condition of pure shear the back edge has
  been found through testing to have no influence
  on the group capacity
• Proper concrete clear cover from the studs to the
  edge must be maintained

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In the Field Shear Strength

• When a headed stud anchorage is sufficiently away
  from all edges, termed in-the-field of the
  member, the anchorage strength will normally be
  governed by the steel strength
• Pry-out failure is a concrete breakout failure
  that may occur when short, stocky studs are used

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In the Field Shear Strength

• For hef/de 4.5 (in normal weight concrete)
• Where
• Vcp nominal pry-out shear strength (lbs)

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Front Edge Failure Example

• Given
• Plate with headed studs as shown, placed in a
  position where cracking is unlikely. The 8 in.
  thick panel has a 28-day concrete strength of
  5000 psi. The plate is loaded with an
• eccentricity of
• 1 ½ in from the
• centerline. The
• panel has 5
• confinement bars.

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Example

• Problem
• Determine the design shear strength of the stud
  group.

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Solution Steps

• Step 1 Check corner condition
• Step 2 Calculate steel capacity
• Step 3 Front Edge Shear Strength
• Step 4 Calculate shear capacity coefficients
• Step 5 Calculate shear capacity

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Step 1 Check Corner Condition

• Not a Corner Condition

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Step 2 Calculate Steel Capacity

• fVns fnsAnfut
• 0.65(4)(0.20)(65) 33.8 kips

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Step 3 Front Edge Shear Strength

• Front Edge Shear Strength

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Step 4 Shear Capacity Coefficient

• Concrete Breakout Strength, Vco3

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Step 4 Shear Capacity Coefficient

• X Spacing Coefficient, Cx3

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Step 4 Shear Capacity Coefficient

• Member Thickness Coefficient, Ch3

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Step 4 Shear Capacity Coefficient

• Eccentric Shear Force Coefficient, Cev3

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Step 4 Shear Capacity Coefficient

• Member Cracking Coefficient, Cvcr
• Assume uncracked region of member
• 5 Perimeter Steel

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Step 5 Shear Design Strength

• fVcs fVco3Cx3Ch3Cev3Cvcr
• 0.75(47.0)(0.93)(0.53)(0.94)(1.0)
• 16.3 kips

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Interaction

• Trilinear Solution
• Unity curve with a 5/3 exponent

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Interaction Curves
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Combined Loading Example

• Given
• A ½ in thick plate with headed studs for
  attachment of a steel bracket to a column as
  shown at the right
• Problem
• Determine if the studs are adequate for the
  connection

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Example Parameters

• f'c 6000 psi normal weight concrete
• ? 1.0
• (8) 1/2 in diameter studs
• Ase 0.20 in.2
• Nominal stud length 6 in.
• fut 65,000 psi (Table 6.5.1.1)
• Vu 25 kips
• Nu 4 kips
• Column size 18 in. x 18 in.

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• Provide ties around vertical bars in the column
  to ensure confinement f 0.75
• Determine effective depth
• hef L tpl ths 1/8 in
• 6 0.5 0.3125 0.125 6.06 in

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Solution Steps

• Step 1 Determine applied loads
• Step 2 Determine tension design strength
• Step 3 Determine shear design strength
• Step 4 Interaction Equation

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Step 1 Determine applied loads

• Determine net Tension on Tension Stud Group
• Determine net Shear on Shear Stud Group

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Step 2 Concrete Tension Capacity
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Step 2 Steel Tension Capacity
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Step 2 Governing Tension
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Step 3 Concrete Shear Capacity
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Step 3 Steel Shear Capacity
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Step 3 Governing Shear
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Step 4 Interaction

• Check if Interaction is required

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Step 4 Interaction
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Questions?