Course 817 - Steel Erection Safety

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Structural Stability (Continued)

Open Web Steel Joists

Some of the most serious risks facing the ironworker are encountered during the erection of open web steel joists, particularly landing loads on unbridged joists and improperly placing loads on joists. Based on a recent analysis of OSHA data, more than half of ironworker fatalities due to collapse are related to the erection of steel joists. More information can be obtained by reading OSHA Standard 1926.757.

General Requirements

columns
Field-bolting Columns
(Click to enlarge)

Where steel joists are used and columns are not framed in at least two perpendicular directions with solid web structural steel members, a steel joist must be field-bolted at the column to provide lateral stability to the column during erection.

The purpose of this requirement is to prevent joists from collapsing due to insufficient stability of the columns that are supporting them. A field-bolted joist is required in order to provide stability at a column that is not framed in at least two directions with solid web structural steel members (see, for example, column A by clicking on the image to the right).

This requirement does not apply to a column in a line parallel to the joists that does not help bear the joists (such as columns B and C in the image above). Column support in this context means the column is supported in two axes so the column cannot fall (column D in the diagram above is framed in two directions with solid web members).

Installing Stabilizing Joists

Rebuilding Ground Zero – Discovery TV
(Click to play video)

When installing the stabilizing joist:

  • Provide a vertical stabilizer plate for steel joists on each column, which must:
    • Be at least 6 inches by 6 inches.
    • Extend at least 3 inches below the bottom chord of the joist.
    • Have a 13⁄16-inch hole to provide an attachment point for guying or plumbing cables.
  • Stabilize the bottom chords to prevent rotation during erection.
  • Do not release hoisting cables until:
    • The seat at each end of the steel joist is field-bolted.
    • Each end of the bottom chord is restrained by the column stabilizer plate.
    • EXCEPTION: Where constructability does not allow a steel joist to be installed at the column, install an alternate means of stabilizing joists on both sides near the column that must:
      • Provide equivalent stability to a steel joist field-bolted at the column.
      • Be designed by a qualified person.
      • Be shop-installed.
      • Be included in the erection drawings.
  • Do not release hoisting cables until the seat at each end of the steel joist is field-bolted and the joist is stabilized.
  • Where steel joists at or near columns span 60 feet or less, the joist must be designed with sufficient strength to allow one employee to release the hoisting cable without the need for erection bridging.
  • Where steel joists at or near columns span more than 60 feet:
    • The joists need to be set in tandem with all bridging installed.
    • An alternative method of erection may be used, which:
      • Provides equivalent stability to the steel joist.
      • Is designed by a qualified person.
      • Is included in the site-specific erection plan.
  • A steel joist or steel joist girder must not be placed on any support structure that is not stabilized.
  • When steel joists are landed on a structure, they must be secured to prevent unintentional displacement prior to installation.
  • Any modification that affects the strength of a steel joist or steel joist girder must be made with the approval of the project structural engineer of record.
  • When connecting individual steel joists to steel structures in bays 40 feet or longer (see exception below):
    • The connections must be fabricated to allow for field-bolting during erection.
    • The connections must be initially field-bolted unless constructability does not allow.
    • EXCEPTION: These requirements do not apply when steel joists are pre-assembled into panels.
  • Steel joists and steel joist girders must not be used as anchorage points for a fall-arrest system unless written approval to do so is obtained from a qualified person.
  • A bridging terminus point must be established before bridging is installed.

Steel Joists and Steel Joist Girders

There are three distinct series of joists, the K, LH/DLH and Joist Girders.

Joists and Girders - Red Engineering
  • K-Series Joists: K-series joists are open web steel joists that are simply supported uniformly loaded trusses that can support a floor or roof deck. These joists have a maximum length of 60 feet. The maximum uniform load for K-series joists is 550 pounds per linear foot (plf).
  • LH/DLH-Series Joists: The LH or “Long Span” and DLH or “Deep Long Span” joists are also simply supported uniformly loaded trusses. The LH series may support a floor or roof deck. The DLH series may support only a roof deck.
    • The LH series is 18” to 48” in depth, has a maximum span of 96 feet and the maximum uniform loading is up to 1000 plf.
    • The DLH series is 52” to 72” in depth, has a maximum span of 144 feet and maximum uniform loading of 700 plf.
  • Joist Girders: Joist girders are simply supported, primary load carrying members. Loads are applied through steel joists and evenly spaced along the joist girder top chord. They may span up to 60 feet.

Each end of "K" series steel joists must be finally attached to the support structure with a minimum of:

  • two ⅛-inch fillet welds 1 inch long
  • two ½-inch bolts
  • or an equivalent connection

Each end of "LH" and "DLH" series steel joists and steel joist girders must be finally attached to the support structure with a minimum of:

  • two ¼-inch fillet welds 2 inches long
  • two ¾-inch bolts
  • or an equivalent connection

Except for panelized joists, each steel joist must be attached to the support structure, with at least one end on both sides of the seat:

  • immediately upon placement in the final erection position
  • before additional joists are placed

Panels that have been pre-assembled from steel joists must be attached with bridging to the structure at each corner before the hoisting cables are released.

Erection of Steel Joists

steel joists

For steel joists in OSHA Standard 1926.757 Tables A and B that require bridging:

  • Attach both sides of the seat of one end of each steel joist to the support structure before hoisting cables are released.

For joists more than 60 feet:

  • Both ends of the joist must be attached as specified in steel joists and steel joist girders.
  • The provisions of erection bridging must be met before the hoisting cables are released.

Only one employee is allowed on steel joists that do not require erection bridging under OSHA Standard 1926.757 Tables A and B, until all bridging is installed and anchored.

Employees are not allowed on steel joists where the span of the steel joist is equal to or greater than the span shown in OSHA Standard 1926.757 Tables A and B except in accordance with erection bridging provisions.

When permanent bridging terminus points cannot be used during erection, additional temporary bridging terminus points are required to provide stability.

Erection Bridging

steel joists
Steel Joist Bridging

Where the span of the steel joist is equal to or greater than the span shown in OSHA Standard 1926.757 Tables A and B, the following applies:

  • A row of bolted diagonal erection bridging must be installed near the mid-span of the steel joist.
  • Hoisting cables must not be released until this bolted diagonal erection bridging is installed and anchored.
  • No more than one employee is allowed on these spans until all other bridging is installed and anchored.

Where the span of the steel joist is 60 feet through 100 feet, the following applies:

  • All rows of bridging must be bolted diagonal bridging.
  • Two rows of bolted diagonal erection bridging must be installed near the third points of the steel joist (e.g. ⅓ joist-length) from each end.
  • Hoisting cables must not be released until this bolted diagonal erection bridging is installed and anchored.
  • No more than two employees are allowed on these spans until all other bridging is installed and anchored.
erection bridging

Where the span of the steel joist is 100 feet through 144 feet, the following applies:

  • All rows of bridging must be bolted with diagonal bridging.
  • Hoisting cables must not be released until all bridging is installed and anchored.
  • No more than two employees are allowed on these spans until all bridging is installed and anchored.

For steel members spanning more than 144 feet, the erection methods used must be in accordance with 29 CFR 1926.756.

Where any steel joist that requires bridging is a bottom chord bearing joist:

  • A row of bolted diagonal bridging must be provided near the supports.
  • This bridging must be installed and anchored before the hoisting cables are released.

When bolted diagonal erection bridging is required, the following applies:

  • The bridging must be indicated on the erection drawing.
  • The erection drawing must be the exclusive indicator of the proper placement of this bridging.
  • Shop-installed bridging clips, or functional equivalents, must be used where the bridging bolts to the steel joists.
  • When two pieces of bridging are attached to the steel joist by a common bolt, the nut that secures the first piece of bridging must not be removed from the bolt in order to attach the second.
  • Bridging attachments must not protrude above the top chord of the steel joist.

Landing and Placing Loads

Cranes placing loads – Time lapse
(Click to play video)

During the construction period, the employer placing a load on steel joists must ensure the load is distributed so as not to exceed the carrying capacity of any steel joist.

Except as noted below, no construction loads are allowed on the steel joists until all bridging is installed and anchored and all joist-bearing ends are attached.

The weight of a bundle of joist bridging must not exceed a total of 1,000 pounds, and:

  • A bundle of joist bridging must be placed on a minimum of three steel joists that are secured at one end.
  • The edge of the bridging bundle must be within 1 foot of the secured end.

No bundle of decking may be placed on steel joists until:

  • All bridging has been installed and anchored.
  • All joist bearing ends are attached, unless a qualified person has first determined the structure or portion of the structure is capable of supporting the load and documented it in the site-specific erection plan.
  • The bundle of decking is placed on a minimum of three steel joists.
  • The joists supporting the bundle of decking are attached at both ends.
  • At least one row of bridging is installed and anchored.
  • The total weight of the bundle of decking does not exceed 4,000 pounds.
  • Placement of the bundle of decking is within 1 foot of the bearing surface of the joist end.

The edge of any construction load must be placed within 1 foot of the bearing surface of the joist end.

Real-World Accident

Three employees were using a crane to unload stacks of metal roof decking onto open web steel joists. The joists were not bridged, supported or restrained against movement. After the load was set down on the joists, the employees began to release the slings. After the first sling was released, the load shifted and one of the joists fell over. This caused the joist to collapse and fall 40 feet to the ground. One of the employees was tied off to this joist, and he was pulled off the roof. Two other joists rolled over and collapsed, landing on the employee. The employee suffered severe head injuries but survived.

Instructions

Before beginning this quiz, we highly recommend you review the module material. This quiz is designed to allow you to self-check your comprehension of the module content, but only focuses on key concepts and ideas.

Read each question carefully. Select the best answer, even if more than one answer seems possible. When done, click on the "Get Quiz Answers" button. If you do not answer all the questions, you will receive an error message.

Good luck!

1. Based on a recent analysis of OSHA data, what was the cause of more than half of ironworker all fatalities due to collapse?

2. When installing stabilizing joists, do not release hoisting cables until the seat at each end of the steel joist is_____.

3. Who must approve any modification that affects the strength of a steel joist or steel joist girder?

4. During the construction period, the employer placing a load on steel joists must ensure that the load is distributed so as not to exceed _____.

5. The edge of any construction load must be placed within ____ of the bearing surface of the joist end.


Have a great day!

Important! You will receive an "error" message unless all questions are answered.