Bridging1

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Bridging of Open Web Steel Joists and Joist
Girders
Perry S. Green, Ph.D. Technical Director, Steel
Joist Institute, Myrtle Beach, SC Tim Holtermann,
P.E. Corporate Engineering Manager, Canam Steel
Corp., Washington, MO
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Introduction

• Bridging is an integral component of the open-web
  steel joist system that braces the joists against
  unanticipated horizontal movements
• During joist erection ERECTION BRIDGING
• Placing of construction loads CONSTRUCTION
  BRIDGING
• Permanently restrain the joist chords from
  out-of-plane or lateral displacement when other
  means are NOT present PERMANENT BRIDGING.
• One of the mosts important aspects of safe
  erection of joist products is proper bridging.

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SJI 42nd Edition Steel Joist Catalog 2005

• Steel Joist Institute
• History, Policy, Membership, Publications,
  Introduction
• Accessories and Details
• K-Series Standard Specifications
• K-Series Load Tables
• KCS Joists
• LH- and DLH-Series Standard Specifications
• LH- and DLH-Series Load Tables
• Joist Girders Standard Specifications
• Joist Girder Weight Tables
• Referenced Specifications, Codes and Standards
• Code of Standard Practice for Steel Joists and
  Joist Girders
• Glossary
• Appendices
• A) Joist Substitutes, K-Series
• B) TCXs and Extended Ends, K-Series
• C) Economy Tables, K-Series
• D) Fire-Resistance Ratings with Steel Joists
• E) OSHA Safety Standards for Steel Erection

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SJI First Edition Composite Steel Joist Catalog
2007

• Steel Joist Institute
• History, Policy, Membership, Publications,
  Introduction
• Accessories and Details
• CJ-Series Standard Specifications
• Referenced Specifications, Codes and Standards
• Design Guide LRFD Weight Tables for Composite
  Steel Joists, CJ-Series
• Design Guide LRFD Bridging Tables for Composite
  Steel Joists, CJ-Series
• Design Examples 1 and 2
• Code of Standard Practice for Composite Steel
  Joists
• Composite Joist Floor Design Parameters Checklist
• Appendices
• A) Fire-Resistance Ratings with Composite Steel
  Joists
• B) OSHA Safety Standards for Steel Erection

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Definitions
Joist
Column Joist
Joist Girder
Column
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Types of Bridging
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OSHA

• Since 1984, representatives of the steel
  community have worked with the Department of
  Labor and the Occupational Safety and Health
  Administration (OSHA) to establish new rules for
  the safe erection of structural steel and as part
  of that rule, safe erection standards for Open
  Web Steel Joists.
• The OSHA Safety Standards supplement the SJI
  Specifications and Table 1 summarizes the
  Federal Regulations that are included in 29 CFR
  1926.757 - Open web steel joists related to the
  erection of joist products.

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Federal Regulations 29CFR1926.757 - OWSJ
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Federal Regulations 29CFR1926.757 - OWSJ
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ERECTION BRIDGING

• The SJI K-Series and LH- and DLH-Series Load
  Tables show the total safe uniformly distributed
  loads for standard products at various spans.
• As the span increases for a particular joist
  designation, the uniformly distributed
  load-carrying capacity decreases.
• The Load Tables indicate when the span becomes
  too great for a particular joist designation to
  be erected without ERECTION BRIDGING.

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ERECTION BRIDGING

• Standard K-Series joists that require ERECTION
  BRIDGING are indicated by the RED SHADED area in
  the Load Tables.
• Standard K-Series joists that require ERECTION
  BRIDGING are found in the OSHA Safety Standards
  1926.757 Table A Erection Bridging for Short
  Span Joists.
• ERECTION BRIDGING is the bolted diagonal bridging
  that is required to be installed prior to
  releasing the hoisting cables.
• The required bolted diagonal ERECTION BRIDGING
  for K-Series joists must be installed as the row
  of bridging nearest the mid-span of the joist.

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ERECTION BRIDGING

• Standard LH-Series joists that require ERECTION
  BRIDGING are indicated by the RED or BLUE SHADED
  areas in the Load Tables.
• Standard LH-Series joists that require ERECTION
  BRIDGING are found in the OSHA Safety Standards
  1926.757 Table B Erection Bridging for Long
  Span Joists.
• ERECTION BRIDGING is the bolted diagonal bridging
  that is required to be installed prior to
  releasing the hoisting cables.
• All standard DLH-Series joists require ERECTION
  BRIDGING as indicated by the BLUE or GRAY SHADED
  areas in the Load Tables.

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ERECTION BRIDGING

• The required bolted diagonal ERECTION BRIDGING
  for LH-or DLH-Series joists depends on its
  length.
• Where the span is less than 60 ft., the required
  bolted diagonal ERECTION BRIDGING must be
  installed as the row of bridging nearest the
  mid-span of the joist.
• Where the span is over 60 ft. through 100 ft.,
  the required bolted diagonal ERECTION BRIDGING
  must be installed as the two rows of bridging
  nearest the third points of the joist.
• Where the span is over 100 ft. through 144 ft.,
  all rows of bridging are considered ERECTION
  BRIDGING and must be completely installed.

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ERECTION BRIDGING
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ERECTION BRIDGING
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Column Joists

• SJI conducted an extensive research program from
  2001-2003 to develop design methods for column
  joists to be erected without bridging. The SJI
  determined that for some joist lengths there are
  no existing joist designs that would provide the
  necessary stability.
• Current OSHA Safety Standards require that where
  columns are not framed in at least two directions
  with solid structural steel members, joists at
  column lines shall be field bolted and the joist
  bottom chords must be restrained by a vertical
  stabilizer plate.

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Column Joists
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Joist Girders

• Joist Girders are primary structural members that
  are normally supported by structural steel
  columns, but they can also bear on steel plates
  on masonry or concrete supports.
• Joist Girders must be erected singly and since
  they are erected without ERECTION BRIDGING, a
  minimum stiffness relative to the overall length
  is required.
• The radius of gyration of the Joist Girder top
  chord about the vertical axis shall not be less
  than the girder span divided by 575.
• A vertical stabilizer plate is required to be
  furnished on each column as a means of laterally
  stabilizing the Joist Girder bottom chord.

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Joist Girders
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Joist Girders
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Bridging for Construction Loads

• After any required ERECTION BRIDGING is installed
  and the hoisting cables have been released, the
  remaining bridging rows (CONSTRUCTION BRIDGING)
  need to be installed before the application of
  additional construction loads.
• Under no circumstances are construction loads to
  be placed on unbridged joists.
• Construction loads are defined in the OSHA Safety
  Standards as any load other than the
  employee(s), the joists and the bridging bundles.

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Construction Loads

• Weight of metal deck bundles
• Individual sheets of metal deck being placed
• Weight of multiple Erectors placing the deck
• Equipment loads
• Welding machines
• Hand tools
• Bridging for adjacent bays

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Construction Loads on Unbridged Joists
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Construction Loads on Unbridged Joists
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Joist Bridging Theory

• The bracing force that a joist imparts to the
  bridging is based on three assumptions
• An initial out-of-straightness of L/920
• The resultant total nominal bracing force is
  0.0044P, where P is the chord axial force. Since
  horizontal bridging rows are continuous, i.e.
  each joist is braced from both sides, the total
  bracing force is assumed to be 0.0025P,
• An assumed construction stress in the top chord
  and the axial force P that it creates.
• For K-Series joists the bridging criteria are
  based on a top chord axial construction ultimate
  stress Fcr of 17 ksi and the resultant
  slenderness limit, l /ryy is 145 For LH- and
  DLH-Series joists Fcr 12 ksi and the resultant
  slenderness limit, l /ryy is 170.

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Bridging for Construction LoadsTABLE 5.4-1
Last digit(s) of joist designation shown in
Load Table See Section 5.11 for additional
bridging required for uplift design.
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Bridging for Construction LoadsTABLE 104.5-1
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Joist Bridging Theory

• The nominal compressive force that accumulates in
  a horizontal bridging row is
• Pbr 0.0025 n At Fconstruction
• where,
• Fconstruction is approximately 17 ksi for
  K-Series joists, and 12 ksi for LH- and
  DLH-Series joists, as noted above.
• At is the top chord area
• n the number of joists
• For horizontal bridging, n is taken as 8 joist
  spaces, whereas n is taken as 2 for diagonal
  bridging.

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Bridging for Construction LoadsCode Of Standard
Practice TABLE 2.6-1a
Refer to last digit(s) of Joist
Designation Connection to joist must resist a
nominal unfactored 700 pound force (3114 N)
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Bridging for Construction LoadsCode Of Standard
Practice TABLE 2.6-1b
Refer to last two digit(s) of Joist
Designation Connection to joist must resist
force listed in Table 104.5-1
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Composite Joist Bridging Theory

• The following equations were developed for the
  new SJI Standard Specifications for Composite
  Steel Joists, CJ-Series in which Fconstruction
  and the top chord slenderness limit vary
  depending on the depth and span length.

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Bridging for Permanent Loads

• Top chord bridging serves a role as PERMANENT
  BRIDGING in the absence of a deck diaphragm.
• Top chord bridging provides lateral support
• Standing seam roof (SSR)
• Deck opening or skylight
• New or retrofit joists that will not be welded to
  the existing metal deck
• Bottom chord bridging provides lateral support
• Uplift
• Compression in cantilevered ends

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Joist Bridging
Bolted Diagonal Erection Bridging (if necessary)
Horizontal Bridging (typ.)
Bridging Needed for Uplift typical at both ends
(if necessary)
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Bridging Considerations

• While it is common for top and bottom chord
  bridging rows to align vertically, this is not a
  requirement.
• There are situations where it is advantageous to
  offset the locations of bottom chord bridging
  rows from those of the top chord, including
  uplift design, or coordination with ESFR
  sprinklers.

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Bridging ConsiderationsJoist Girder Bottom Chord
Bracing
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Parting Bridging ShotsJoist Girder and Column
Joist
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Parting Bridging ShotsBolted Diagonal ERECTION
BRIDGING
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Parting Bridging Shots Bridging Bundles
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Parting Bridging ShotsHorizontal Bridging Being
Placed
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Conclusions

• The Steel Joist Institute and OSHA requirements
  for steel joist and Joist Girder bridging have
  been reviewed.
• Bridging has been described by three functional
  purposes Erection Bridging, Bridging for
  Construction Loads, and Bridging for Permanent
  Loads.
• The underlying theory used to develop the current
  bridging equations has been provided.
• Future SJI research is going to look at
  construction stress levels, unification of
  different specification requirements, and a
  better understanding of the accumulation of
  bridging forces due to net uplift.

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Any Questions?
SJI Website http//www.steeljoist.org/composite