Column base plate design to AISC 360

Tekla Structural Designer
2021
Tekla Structural Designer

Column base plate design to AISC 360

Column Bases: only simple column bases are supported in the current release.

Unless explicitly stated all calculations will adopt either a load and resistance factor design (LRFD) or an allowable strength design (ASD) as consistent with the design parameters for column base connections as specified in the AISC Specification (Ref. 2) and its associated 'Commentary', the AISC Steel Design Guide 1: Base Plate and Anchor Rod Design (Ref. 4), and the ACI 318 Building Code Requirements (Ref. 1).

The following advice is written principally from the point of view of operating column base plate design from within Tekla Structural Designer.

Practical applications

In the current release of Tekla Structural Designer only simple column base plate design checks are supported, following primarily the design procedures given in AISC Design Guide 1: Base Plate and Anchor Rod Design (2nd Edition, 2nd printing, revised). (Ref. 4)

Tekla Structural Designer will check the base plate size and thickness, with the latter check displaying a bearing stress calculation. Shear and tension resistance of the rods, concrete and the welds are also checked. Base plate bending and/or shear lug bending is also checked.

The concrete foundation design is checked separately in accordance with ACI 318. (Ref. 1)

Graphics are used to display the base plate in its current state. You can therefore graphically see the base that you are defining and the results that the design process has achieved. This allows you to see the effects of any modifications that you make instantly on the screen. Reinforcement in the foundation is not represented in the graphics.

Limitations

For the current release of Tekla Structural Designer the following limitations apply:

  • Column sections - Only the following column sections will have their base plate design checked:
    • I section columns (W, M, S & HP shapes)
    • HSS
    • Pipe sections
  • Anchor rod layout - Anchor rod layouts are restricted as follows:
    • The rod layout must be symmetric about both axes
    • See the section on Base Plate Bending Strength for rod layout restrictions related to columns in uplift
  • Base plate position - The column base plate can only be concentrically placed about the major axes of the steel column, so that there is no eccentricity in the line of action of the vertical load with respect to the baseplate. In addition, the base plate can only be positioned symmetrically on the concrete base.
  • Concrete pedestal - No concrete pedestal will be defined.
  • Welds
    • Partial length welds are permitted only on the webs of I section columns.
    • For gravity loading the column is assumed to be prepared for direct contact in bearing.
    • Shear lug welds are not considered in the current release.

Theory and assumptions

This section describes the theory used in the development of column base plate design checks and the major assumptions that have been made, particularly with respect to interpretation of the AISC Specification (Ref. 2) and the AISC Steel Design Guide 1 (Ref. 4). A basic knowledge of the design methods for column bases is assumed.
Note: Column base plates designed to the AISC Specifications 360-05, -10 and -16 (Ref. 2) should all produce the same results as each other.

Checks Performed

The following table summarizes the main checks performed:

Note: Some checks are carried out depending on the shear transfer option selected.
Applied Load Calculations
Positive vertical load Base plate
  • Bearing strength of concrete foundation.
  • Base plate thickness.
(Major) shear load Shear
  • Friction Strength
  • Shear strength of rods
  • Concrete anchorage strength for shear forces on rods
  • Concrete pry-out strength of anchor rod in shear
  • Concrete bearing strength of shear lug
  • Concrete breakout strength of shear lug
  • Shear lug bending strength

Weld

  • Weld shear strength

Positive vertical + (major) shear load Base Plate
  • Bearing strength of concrete foundation.
  • Base plate thickness.

Shear

  • Friction Strength
  • Shear strength of rods
  • Concrete anchorage strength for shear forces on rods
  • Concrete pry-out strength of anchor rod in shear
  • Concrete bearing strength of shear lug
  • Concrete breakout strength of shear lug
  • Shear lug bending strength

Weld

  • Weld shear strength
Negative vertical load (Uplift)
  • Base Plate
    • Base plate bending strength.
  • Rods and Anchorage
    • Shear lug dimensional checks
    • Rods (in tension)
    • Concrete breakout (in tension)
    • Concrete pull out (in tension)
  • Weld
    • Weld tension strength
Negative vertical (uplift) + (major) shear load
  • Base Plate
    • Base plate bending strength.
  • Shear
    • Friction Strength
    • Shear strength of rods
    • Concrete anchorage strength for shear forces on rods
    • Concrete pry-out strength of anchor rod in shear
    • Concrete bearing strength of shear lug
    • Concrete breakout strength of shear lug
    • Shear lug bending strength
  • Rods and Anchorage
    • Shear lug dimensional checks
    • Rods (in tension)
    • Concrete breakout (in tension)
    • Concrete pull out (in tension)
    • Rods (in tension + shear)
    • Concrete (in tension + shear)
  • Weld
    • Weld shear strength
    • Weld strength with combined shear and tension

Base plate

There are potentially 3 base plate checks:

  1. Bearing strength of concrete foundation

  2. Base plate thickness

  3. Base Plate Bending Strength

  1. Bearing strength of concrete foundation

    This check is only performed under positive vertical load (i.e. axial compression).

    In the calculation of the nominal bearing strength of the concrete, Pp, the Area A2 is as defined in the AISC Design Guide 1 (Ref. 4), i.e. "the maximum area of the portion of the supporting surface that is geometrically similar to and concentric with the loaded area" with a maximum value of 4*A1, where A1 is the area of the base plate.

  2. Base plate thickness

    This check is only performed under positive vertical load (i.e. axial compression).

    The check requires tp ≥ tmin where tp = the base plate thickness, and tmin = the minimum thickness, according to LRFD or ASD as appropriate.

    The required bearing stress, fpu (LRFD) or fpa (ASD), is reported within the calculations for tmin.

  3. Base Plate Bending Strength

    This check is performed under negative vertical load (i.e. axial tension / uplift), with the bending strength determined according to LRFD or ASD, as appropriate.

    • I section columns (W, M, S & HP shapes)

      The plate bending model assumes a 45 degree dispersion from the end points of the column flanges (see diagram below) to a straight yield line across the width of the plate. The effective bending width is limited to the lesser of the actual plate width or the column flange width plus the difference between plate length and column section depth.

      Rods ‘outside’ the flanges are those between the ends of the plate and lines through the mid thickness of the column flanges (including the mid thickness lines). Rods ‘inside’ the flanges are those between lines through the mid thickness of the column flanges (excluding the mid thickness lines).

      No rods should be positioned within the shaded areas shown in the diagram below, between the two 45 degree dispersal lines emanating from each flange tip.

      • For rods outside the flanges, all rods should be contained within an area bounded by the plate edges, the flange and lines drawn at 45 degrees from the outside corners of the flange to the plate edge. If this is not the case, a Warning status is issued.

      • For rods inside the flanges, all rods should be contained within an area bounded by the plate edge, the flanges, the web and lines drawn at 45 deg from the inside corners of the flange to the plate edge. If this is not the case, a Warning status is issued.

        Plan view on base plate with I section column and 45 degree dispersal lines

      The number of effective rods contributing to the bending depends on the rod layout. Where 4 rows of rods are used and all 4 rows lie inside the flanges, then all rods in the outer 2 rows count but only the 4 rods adjacent to the web count from the inner 2 rows (see diagram below). In all other layouts all of the rods count as effective.

      The nominal tension force on each effective rod is the total uplift force divided by the total number of effective rods.

      For rods outside the flanges the full nominal tension force on each rod is used when deriving the required bending strength.

      For rods inside the flanges, when there are only 2 rows inside the flanges then for the 4 rods adjacent to the web the nominal tension force is proportioned between the flange and the web, in the ratio dw/(dw+df) to the flange and df/(dw+df) to the web, where dw is the distance from center of rod to centerline of web, and df is the distance from center of rod to centerline of flange; while all other rods in the row use the full nominal tension force. The proportioned tension force to the web does not contribute to plate bending but is taken into account for the required web weld tension strength. When there are 4 rows of rods inside the flanges, the outer 2 rows adopt the tension forces as described above for 2 rows only inside the flanges; while the other 4 effective rods (adjacent to the web) from the inner 2 rows assume the full nominal tension force to the web and so do not contribute to plate bending but are taken into account for the required web weld tension strength.
      Distribution of rod nominal tension force, Tn (rods in red are non-effective for tension)
      Note: Bending around lines parallel to the web is not considered and there is no local strength check on the web in the current release of the software.
    • HSS and pipe section columns

      The plate bending model assumes a 45 degree dispersion from the corner points of the column section (see diagram below) to straight yield lines across the width and length of the plate.

      Note, for circular HSS and pipe column sections an equivalent square section profile is assumed based on a side length equal to three quarters of the outside diameter of the HSS or pipe (which gives an approximately equal perimeter length).

      The general rule adopted for valid rod layouts is that no more than one line of rods is permitted in each zone, opposite and parallel to each face of the HSS section. For rod layouts which do not follow this rule a Beyond Scope status is issued.

      Plan view on base plate with HSS section column and 45 degree dispersal lines

      In all valid HSS rod layouts all of the rods count as effective towards plate bending.

      The nominal tension force on each effective rod is the total uplift force divided by the total number of effective rods.

Shear

There are five options to choose from for (major) shear transfer:

  1. Friction alone

  2. Shear on rods alone

  3. Friction and shear on rods

  4. Bearing on shear lug

  5. Friction and bearing on shear lug

  1. Friction Alone
    • Friction Strength

      This shear strength check is calculated in accordance with ACI 318 (Ref. 1) and considers the full (major) shear force. Since ACI 318 only takes account of LRFD requirements then this check is not performed for ASD load combinations.

      The default for μ, the coefficient of friction between the base plate and concrete, is taken as 0.4 per ACI 349-01 (section RB.6.1.4), 349-06 and -13 (section RD.6.1.4) (Ref. 8).

  2. Shear on Rods Alone

    Checks for Shear on Rods Alone are divided into 3 separate parts and consider the full (major) shear force:

    a. Shear strength of rods.

    b. Concrete anchorage strength for shear forces on rods.

    c. Concrete pry-out strength of anchor rod in shear.

    The anchor rod strength is calculated in accordance with AISC 360 Ref. 2 and AISC Design Guide 1 (Ref. 4) for both LRFD and ASD load combinations.

    The concrete strength checks are calculated in accordance with ACI 318 (Ref. 1). Since ACI 318 only takes account of LRFD requirements then these checks are not performed for ASD load combinations.

    1. Shear Strength of Rods

      AISC Design Guide 1 (Ref. 4) recommends taking a cautious approach when using anchor rods to transfer horizontal shear loads. Unless special provisions are made to equalize the load to all anchor bolts, such as using field welded setting plates or field welded washer plates, Design Guide 1 recommends using only 2 of the rods to resist the shear. If all rods are used to resist the shear, Design Guide 1 requires that the bending of the rods within the depth of the base plate should be checked which in turn requires that the washer plate/setting plate thickness is also checked. These rod bending and washer/setting plate thickness checks are not available in the current release. If the option to use either ‘Shear on rods’ or 'Friction and Shear on rods' to resist shear is selected then a Warning is displayed in the results viewer:

      "To transfer the shear equally to all anchor rods special provisions need to be made such as the use of field welded setting plates or field welded washers. These provisions are beyond the scope of this release and instead the recommendation given in Design Guide 1 to use only 2 rods to resist shear has been adopted."

      The nominal shear strength, Fnv, from AISC 360-10 and -16 is 0.45Fu and is back-fitted to AISC 360-05, and is also factored by 0.8 if a grout layer is used (per ACI 318-08 and -11 Appendix D and Chapter 17 of ACI 318-14 and -19).

    2. Concrete Anchorage Strength for Shear Forces on Rods

      This check is carried out in accordance with the provisions of ACI 318-11 Appendix D and Chapter 17 of ACI 318-14 and -19, which all have similar provisions, and back-fitted to ACI 318-08 (which has slightly different provision).

      For the purposes of resisting shear forces, an anchor rod may act as an individual or as part of an anchor rod group which is defined in ACI 318 as "a number of anchors spaced at less than 3*ca1 from one or more adjacent anchors when subject to shear".

      As only 2 rods are considered effective in resisting shear, it is assumed that the effective rods are those closest to the edge of the concrete foundation and, further, that these rods act as a group if spaced at less than 3*c’a1 where c’a1 is the limiting value of ca1 defined in ACI 318. This returns a conservative result.

      Only shear perpendicular to the concrete edge is considered in the current release.

      The concrete edge distances, ca1 and ca2, relative to the shear perpendicular to an edge are shown in ACI 318-14 Figure R17.5.2.1d, part of which is reproduced below. These distances are referred to in the design calculations as "Distance (parallel to shear) to concrete edge, ca1" and "Distance (perpendicular to shear) to concrete edge, ca2".

      Plan view on concrete foundation with edge distances ca1 and ca2 from an anchor.

      In the calculation of the nominal concrete breakout strength, Vcbg, the modification factor for eccentricity of shear load, Ψec,V, and the modification factor for cracked concrete, Ψc,V are both set to 1.0

    3. Concrete Pry-out Strength of Anchor Rod in Shear

      This check is carried out in accordance with the provisions of ACI 318-08 and -11 section D.6.3, ACI 318-14 section 17.5.3, and ACI 318-19 section 17.7.3

      Calculation of Vcp, the nominal concrete pry-out strength for rods in shear, involves calculation of N’cbg, the nominal concrete breakout strength for rods in shear, which is determined in accordance with the provisions of ACI 318-08 and -11 section D.6.2, ACI 318-14 section 17.5.2, and ACI 318-19 section 17.7.2

      In the calculation of N’cbg, the nominal concrete breakout strength, a limiting value of rod embedded depth, hef, is used and labeled as h’ef. The limiting value is determined in accordance with the provisions of ACI 318-08 and -11 section D.5.2.3, ACI 318-14 section 17.4.2.3, and ACI 318-19 section 17.6.2.1.2

      Also in the calculation of N’cbg, the nominal concrete breakout strength, a “total number of effective rods'' is referred to. Typically this will be equal to the total number of rods in the layout of rods, but for I section columns with 4 rows of rods, where all 4 rows are positioned inside the flanges of the column section, the internal 2 rows of rods are taken as having a total of 2 rods in each row - the 2 rods adjacent to either side of the column web. For example, in a rod layout of 4 rows of 4 rods in each row, with all 4 rows positioned inside the flanges of an I section column, the total number of effective rods = 2 * 4 + 2 * 2 = 12 (rather than the 16 rods in the total layout).

      Also in the calculation of N’cbg, the nominal concrete breakout strength, the modification factor eccentricity of shear load, Ψec,N, and the modification factor for cracked concrete, Ψc,N are both set to 1.0

  3. Friction and Shear on Rods

    When Friction and Shear on Rods is selected as the (major) shear transfer option, then the three Shear on Rods checks consider a net shear force i.e. the remaining (major) shear force not taken by frictional resistance alone.

    Checks for Friction and Shear on Rods are divided into the same 3 separate parts as for Shear on Rods Alone (as detailed above), with the addition of a Friction calculation (as detailed above), at the start of each of the three Shear on Rods parts, that derives the net (major) shear force.

  4. Bearing on Shear Lug

    Checks for Bearing on Shear Lug are divided into 3 separate parts and consider the full (major) shear force:

    1. Concrete bearing strength of shear lug.

    2. Concrete breakout strength of shear lug.

    3. Shear lug bending strength.

    All 3 separate parts vary in design approach according to the ACI 318 design code year selected in the model, with demarcation between pre-2019 (i.e. 2008, 2011 or 2014) and 2019.

    When ACI 318 pre-2019 is selected, the concrete strength checks are calculated in accordance with guidance from AISC Design Guide 1 (Ref. 4) and Gomez et al (Ref. 9), otherwise in accordance with ACI 318-19 (Ref. 1). Since concrete design only takes account of LRFD requirements then these concrete strength checks are not performed for ASD load combinations.

    The shear lug bending strength is calculated in accordance with AISC 360 (Ref. 2) and AISC Design Guide 1 (Ref. 4) for both LRFD and ASD load combinations. The choice of ACI 318 design code year determines only the lever arm distance for bending.

    1. Concrete Bearing Strength of Shear Lug

      When ACI 318 pre-2019 is selected this check is carried out under AISC DG1 guidance, which references ACI 349 Appendix Section D.4.6.2. The nominal concrete bearing strength is based on an embedded depth of shear lug equal to actual depth of lug less the grout pad thickness.

      When ACI 318 2019 is selected, this check is carried out in accordance with the provisions of ACI 318-19 Section 17.11.2, and the nominal concrete bearing strength is based on an effective embedded depth of shear lug equal to the lesser of the embedded depth of lug and twice the lug thickness. The 318-19 design method also includes a bearing factor, Ψbrg,sL, which varies between 1.0 and 2.0 for applied axial compression, and between zero and 1.0 for applied axial tension.

      For all ACI 318 code years, if the embedded depth of the shear lug is less than 2 inches (or 50 mm in metric design) then a Warning is displayed in the results viewer.

    2. Concrete Breakout Strength of Shear Lug

      When ACI 318 pre-2019 is selected this check is carried out to recommendations by Gomez et al (Ref. 9) whose research report was presented to AISC in 2009. The research report recommends the nominal concrete breakout strength of shear lug is based on the minimum of that found from a 35 degree fracture failure plane with a design equation adapted from a Concrete Capacity Design (CCD) method given by Fuchs et al (Ref. 10), and that found from a 45 degree tension failure plane, per ACI 349 Appendix Section D.11.2.

      Note that the effective area of the 35 degree failure plane is factored in Gomez et al by 0.7 to account for disturbance of symmetric stress distribution when close to a corner, but this factor is more refined in Fuchs et al (Ψ5 in Equation 13c). The more refined factor is adopted in Tekla Structural Designer.

      When ACI 318 2019 is selected, this check is carried out in accordance with the provisions of ACI 318-19 Section 17.11.3, and the nominal concrete breakout strength of shear lug is based on an effective area of shear lug and a 35 degree fracture failure plane. Note in the calculation of the nominal concrete breakout strength of shear lug, Vcb,sL, the modification factor for cracked concrete, Ψc,V is set to 1.0 and only shear perpendicular to the concrete edge is considered in the current release.

      The concrete edge distance, ca1, relative to the shear perpendicular to an edge is shown in ACI 318-19 Figure R11.3.1, part of which is reproduced below. This distance is referred to in the design calculations as "Distance (parallel to shear) to concrete edge, ca1" and its perpendicular equivalent, measured from the end face of the lug to the adjacent concrete edge, is referred to as "Distance (perpendicular to shear) to concrete edge, ca2".

      Plan view on concrete foundation with edge distance ca1 from a shear lug

    3. Shear Lug Bending Strength

      When ACI 318 pre-2019 is selected the lever arm for bending of the lug is taken as half the embedded depth of the lug plus the grout pad thickness.

      When ACI 318 2019 is selected the lever arm for bending of the lug is taken as half the effective embedded depth of the lug plus the grout pad thickness.

      For all ACI 318 code years, following the guidance of AISC DG1 Section 3.5.2, if the thickness of the shear lug is greater than the thickness of the base plate then a Warning is displayed in the results viewer.

  5. Friction and bearing on shear lug

    When Friction and Bearing on Shear Lug is selected as the (major) shear transfer option, then the three Bearing on Shear Lug checks consider a net shear force i.e. the remaining (major) shear force not taken by frictional resistance alone.

    Checks for Friction and Bearing on Shear Lug are divided into the same 3 separate parts as for Bearing on Shear Lug (see above), with the addition of a Friction calculation at the start of each of the three Bearing on Shear Lug parts, that derives the net (major) shear force.

Rods and Anchorage

Checks for Rods and Anchorage are divided into 6 separate parts and, where combined with shear, consider the full (major) shear force:

  1. Shear lug dimensional checks
  2. Rods in tension
  3. Concrete breakout (in tension)
  4. Concrete pull out (in tension)
  5. Rods (in tension + shear)
  6. Concrete (in tension + shear)

The anchor rod strength checks are calculated in accordance with AISC 360 (Ref. 2) and AISC Design Guide 1 (Ref. 4) for both LRFD and ASD load combinations.

The concrete strength checks are calculated in accordance with ACI 318 (Ref. 1). Since ACI 318 only takes account of LRFD requirements then these checks are not performed for ASD load combinations.

The shear lug dimensional checks are calculated in accordance with ACI 318 but only when a shear lug is present and the ACI 318 code year selected is 2019. Since the presence of a shear lug can influence anchor rod tension, the dimensional checks are performed for both LRFD and ASD load combinations.

In the current release of the software, no reinforcement is assumed in the concrete foundation.

  1. Shear Lug Dimensional Checks

    This pair of dimensional checks is performed whenever negative vertical load (i.e. axial tension / uplift) and a shear lug are both present and the ACI 318 code year selected is 2019.

    The checks are calculated using the provisions of ACI 318-19 Section 17.11.1.1.8

  2. Rods in Tension

    This check is performed whenever negative vertical load (i.e. axial tension / uplift) is present.

    Note: If a shear lug is also present and the ACI 318 code year selected is 2019 then there will be a calculation to determine additional tension load due to forces on the lug, per the requirement of ACI 318-19 Section 17.11.1.1.9 (Refer also to Section 3.5 of Cook and Michler (Ref. 11).)

    Anchor rod tension strength is calculated using the provisions of AISC 360 Section J3.6

  3. Concrete Breakout (in Tension)

    This check is performed whenever negative vertical load (i.e. axial tension / uplift) is present.

    Note: If a shear lug is also present and the ACI 318 code year selected is 2019 then there will be a calculation to determine additional tension load due to forces on the lug, per the requirement of ACI 318-19 Section 17.11.1.1.9 (Refer also to Section 3.5 of Cook and Michler (Ref. 11).)

    This check is carried out in accordance with the provisions of ACI 318-08 and -11 Appendix D and Chapter 17 of ACI 318-14 and -19.

    In the calculation of the nominal concrete breakout strength, Ncbg, the modification factor for eccentricity of shear load, Ψec,N, and the modification factor for cracked concrete, Ψc,N are both set to 1.0

    When the column is subject to uplift conditions, to avoid problems associated with side face breakout, Design Guide 1 (Ref. 4) recommends that the minimum concrete side cover to an anchor rod, cj,min, should be ≥ MAX [6*rod diameter, hef/2.5], where hef = the anchor rod embedded depth. If this is not the case then a Warning message is displayed in the check indicating that additional hand calculations may be required.

  4. Concrete Pull Out (in Tension)

    This check is performed whenever negative vertical load (i.e. axial tension / uplift) is present.

    Note: If a shear lug is also present and the ACI 318 code year selected is 2019 then there will be a calculation to determine additional tension load due to forces on the lug, per the requirement of ACI 318-19 Section 17.11.1.1.9 (Refer also to Section 3.5 of Cook and Michler (Ref. 11).)

    This check is carried out in accordance with the provisions of ACI 318-08 and -11 Appendix D and Chapter 17 of ACI 318-14 and -19.

    In the calculation of the nominal concrete pull out strength of an anchor rod in tension, Npn, the modification factor for cracked concrete, Ψc,P is set to 1.0.

  5. Rods (in Tension + Shear)

    This check is only performed under negative vertical load (i.e. axial tension / uplift) with (major) shear, and also only when the shear transfer option selected is either Shear on Rods Alone or Friction and Shear on Rods.

    Anchor rod strength in combined shear and tension is calculated using the provisions of AISC 360 Section J3.7

    The nominal shear strength, Fnv, from AISC 360-10 and -16 is 0.45Fu and is back-fitted to AISC 360-05, and is also factored by 0.8 if a grout layer is used (per ACI 318-08 and -11 Appendix D and Chapter 17 of ACI 318-14 and -19).

    As in the Shear Strength of Rods check, only 2 of the anchor rods are assumed to be resisting the shear.

  6. Concrete (in Tension + Shear)

    This check is only performed under negative vertical load (i.e. axial tension / uplift) with (major) shear, and also only when the shear transfer option selected is either Shear on Rods Alone or Friction and Shear on Rods.

    This check is carried out in accordance with the provisions of ACI 318-08 and -11 Appendix D and Chapter 17 of ACI 318-14 and -19.

Welds

The weld strengths are calculated in accordance with AISC 360 (Ref. 2) for both LRFD and ASD load combinations.

The welds are checked for the following design conditions: shear; tension; combined shear and tension. For gravity loading the column is assumed to be prepared for direct contact in bearing.

Shear lug weld is not considered in the current release.

For base plates with thickness ≤ 3/4 in (19 mm), the default weld leg length is 1/4 in (6mm) and for all other base plate thicknesses the default weld leg length is 5/16 in (8 mm). These defaults can be adjusted in the database [Materials > Welds > Defaults].

AISC 360-10 and -16 stipulates that when the length of the weld exceeds 300 times the leg size, w, the effective length shall be taken as 180w (section J.2b.(d).(3)), and this is similarly applied when AISC 360-05 has been selected for steel design.

  • Weld Shear Strength

    This check is performed whenever (major) shear load is present.

    Weld shear strength is calculated using the provisions of AISC 360 Section J2

  • Weld Tension Strength

    This check is performed whenever negative vertical load (i.e. axial tension / uplift) is present.

    Weld tension strength is calculated using the provisions of AISC 360 Section J2

    Tension forces are derived as above in the section on Base Plate Bending Strength.

  • Weld Strength with Combined Shear and Tension

    This check is only performed under negative vertical load (i.e. axial tension / uplift) with (major) shear.

    Weld tension strength is calculated using the provisions of AISC 360 Section J2

    Tension forces are derived as above in the section on Base Plate Bending Strength.

Analysis

Connection forces are established from a global analysis of the building as a whole. Column base plates in Tekla Structural Designer have a limited set of design forces for which they can be designed. Non-design forces are identified and, where their value is greater than a given limit, they are displayed to you in the results along with a Warning status. The given limits are defined on the Design Forces page of the Design Settings dialog available from the Design tab on the ribbon.

The forces from the global analysis are treated in the following manner:

  • Simple column bases are designed for the positive or negative axial force at the base of the column and the shear (foundation reaction) in the plane of the column web (column section minor axis). Bases are orientated to the column’s major and minor axes and hence there is no requirement to resolve the force when the column is rotated. Columns can only be sloped in the plane of the web and the bottom stack axial force and shear are resolved into vertical and horizontal forces in the base.

Where the global analysis includes second-order (P-Delta) effects the Ultimate Limit State design forces will include these effects also. However, for column bases the design forces for soil bearing pressure calculations are taken from an elastic global analysis of the unfactored loadcases without second-order effects. All seismic combinations appear in the results. However, those deriving from ELF are considered for design while those from RSA result in Beyond Scope status.

Sign Conventions

The following sign conventions apply.

Convention looking at the column with face A on the right:

  • Positive shear from face C to A,
  • Positive axial into the base.
Note: The column member direction arrow is placed on face A.
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