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  • 1

    Tips for Successful Delegation of

    Connection Design

    by Clifford Schwinger, P.E.The Harman Group, Structural Engineers

    King of Prussia, Pa.

    cschwinger@harmangroup.com

    Delaware Valley Association of Structural Engineers

    10/8/14 breakfast seminar

    2

    3

    Engineers can reduce the cost of the

    connections even when delegating

    connection design.

    A substantial percentage of structural

    steel cost is related to the connections.

    Why care? Why delegate?

    Less work for the engineer of record

    Connection design is becoming a specialty

    Fabricators have different preferences

    for preferred connection details

    4

    But there is a right way and a wrong

    way to delegate connection design.

    5The wrong way:

    ALL SHEAR CONNECTIONS SHALL BE

    DESIGNED TO DEVELOP THE FULL SHEAR

    STRENGTH OF THE MEMBER.

    ALL MOMENT CONNECTIONS SHALL BE

    DESIGNED TO DEVELOP THE FULL

    PLASTIC MOMENT CAPACITY OF THE

    MEMBER.

    6

  • 2

    The wrong way:

    ALL SHEAR CONNECTIONS SHALL BE

    DESIGNED TO DEVELOP A SHEAR

    STRENGTH EQUAL TO 0.6 x Fy x d x t

    ALL MOMENT CONNECTIONS SHALL BE

    DESIGNED TO DEVELOP THE FULL

    PLASTIC MOMENT CAPACITY 0.9 x Mp OF

    THE MEMBER.

    7 The wrong way: 8

    The right way=.

    9

    Follow the Code of

    Standard Practice

    10Rule #1

    11 12

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    13 14

    15 16

    17

    From the commentary of AISC 303A10,

    The EOR has ultimate ).responsibility for the

    adequacy and safety of the entire structure).

    Follow Code of Standard Practice18

    Section 3.1.1

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    19

    This is not connection design This is not connection design

    20

    21

    Design of stiffeners is the responsibility of the

    engineer of record

    Show the reactions

    22Rule #2

    23 24

  • 5

    25

    Wrong way #1

    ALL SHEAR CONNECTIONS SHALL BE

    DESIGNED TO DEVELOP THE FULL SHEAR

    STRENGTH OF THE MEMBER.

    ALL MOMENT CONNECTIONS SHALL BE

    DESIGNED TO DEVELOP THE FULL PLASTIC

    MOMENT CAPACITY OF THE MEMBER

    26

    Wrong way #2

    27

    Do not specify

    connections be

    designed using

    Table 3A6

    Wrong way #3

    28

    Relying on Table 3A6 will usually result in excessively

    conservative connection designs.

    29

    Relying on Table 3A6 will usually result in excessively

    conservative connection designs.

    30

    But, relying on Table 3A6 can also result in connections with

    insufficient strength

  • 6

    31

    Show member shear reactions on

    framing plans, moment connection

    design moments and axial loads in

    brace and truss members.

    (preferably factored)

    The right way.

    Do not make up

    connection design

    requirements

    32Rule #3

    Do not mandate connection design

    requirements more stringent than

    required by the Building Code and

    AISC 360

    33 34

    All bolts shall be slipAcritical

    All connections shall be designed for the

    full strength of the member

    All holes shall be standard sized holes

    SingleAsided shear connections are

    prohibited

    Examples of arbitrary (and usually

    unnecessary) requirements,

    Use R=3 (where

    permitted)

    35Rule #4

    Limit Strength Ratio of

    tension members

    36Rule #5

  • 7

    37Limit strength ratio

    ASAGS = Available strength at the gross section

    Strength ratio =ASAGS

    Required strength

    Members must have sufficient strength at both the gross

    and net sections

    38Limit strength ratio

    39Limit strength ratio

    40Limit strength ratio

    41Limit strength ratio

    42

    Following this rule will reduce the likelihood that

    sections will require reinforcement at the net section

    Limit strength ratio

  • 8

    43Limit strength ratio

    44Limit strength ratio

    Think about

    constructability and

    connection

    designability

    45Rule #6 46

    Designability

    The ease by which economical

    connections can be designed for a

    given framing configuration

    47

    How will the connections be designed and detailed?

    Are the connections designable?

    Designability

    Will the connections be easy to fabricate?

    Will they be easy to install in the field?

    Constructability

    48

    Engineers have options during design

    Engineers can configure the framing to

    improve the designability of connections

    Failure to consider designability during

    design reduces options for the fabricator

    during detailing

    Designability

  • 9

    49Designability

    50Designability

    51Designability

    Head off steeply skewed connections

    52Designability

    53

    Configure framing so that no more than one beam frames to

    any one side of a column

    Designability54

    Configure framing so that no more than one beam frames to

    any one side of a column

    Designability

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    55

    Be aware of connection interference where beams are

    slightly offset from columns.

    Designability

    Avoid skewed beamAtoAcolumn moment connections

    56Designability

    Issue complete, coordinated

    and wellAdetailed contract

    documents

    57Rule #7 58

    59 60

    Show details giving concept of design.

    Permit alternative details.

  • 11

    Permit consideration of

    alternative connection details

    61Rule #8Summary

    62

    1.Understand and follow the Code of Standard Practice

    2.Show the reactions

    3.Do not specify requirements in excess of the building code

    4.Use R = 3 for seismic design (if permitted)

    5.Limit strength ratio in tension members to 0.75

    6.Think about constructability and connection designability

    7.Issue complete & coordinated contract documents with

    designable concept connection details

    8.Permit alternative connection details

    Questions?

    Thank you!

    Clifford Schwinger, P.E.The Harman Group, Structural Engineers

    King of Prussia, Pa.

    601A337A3360

    cschwinger@harmangroup.com

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