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Structural Stability

Structural Steel Assembly

Since structural collapse is second only to falls as a cause of fatalities in this industry, stability is essential to the successful erection of any steel structure, including single- story, multi-story, bridges, etc. This section of the standard outlines the work practices that will prevent collapse due to lack of stability. In addition, it addresses slipping/tripping hazards and certain kinds of fall hazards encountered when working on steel structures.

Structural stability must be maintained at all times during the steel erection process. [29 CFR 1926.754(a)]

Structural Failure Leads to Worker Fatalities

Case Report:

  • A crew of steelworkers was connecting a steel beam to a steel column on the seventh level of an airport structure. The base of the column was secured to a sheer concrete wall by temporary welds to an embedded steel plate. When the crew encountered a problem connecting the beam to the column, a decision was made to pull the top of the column one inch to the north to facilitate the connection. The pull was performed by tensioning a guy wire, using a come-along, applying a fork at the column being connected, and using a sleeper. One worker was seated on the beam that was being connected, while another was standing at the base of the column, atop the concrete wall. When the force of the tensioning caused the temporary welds at the column base to fracture, the column collapsed, and the two workers fell to their death.
Safety Net
  • Permanent floors must be installed as the erection of structural members progresses, with no more than eight stories between the erection floor and the upper-most permanent floor. [29 CFR 1926.754(b)(1)]
  • Unfinished bolting or welding above the foundation (or the uppermost secured floor) is not permitted to exceed the lesser of [29 CFR 1926.754(b)(2)]:
    • Four floors
    • 48 feet (14.6 m)
  • Exceptions are allowed where structural integrity is accounted for in the design.
  • Safety nets or a fully planked or decked floor must be maintained directly under any erection work being performed, within the lesser of [29 CFR 1926.754(b)(3)]:
    • Two stories
    • 30 feet (9.1 m)
  • To prevent tripping hazards, the following components must not be attached so as to project from the top flanges of beams, joists, or beam attachments until after the metal decking, or other walking/working surface, has been installed [29 CFR 1926.754(c)(1)]:
    • Shear connectors (such as headed steel studs, steel bars, or steel lugs)
    • Reinforcing bars
    • Deformed anchors
    • Threaded studs
    • Exception: These may be factory installed if all workers, including connectors and deckers, use fall protection at all times. [CPL2-1.34, Q&A 25 (PDF*)]
  • Sheer Connector
  • When shear connectors are used in construction of composite floors, roofs and bridge decks, they must be laid out and installed after the metal decking has been installed, so the metal decking serves as a working platform. [29 CFR 1926.754(c)(1)]
  • Shear connectors may not be installed from within a controlled decking zone (CDZ). [29 CFR 1926.760(c)(7)]
  • Workers will not be permitted to walk the top surface of any structural steel member installed after July 18, 2006 that has been coated with paint or similar material, unless all of the following are met:
    • The coating has achieved a minimum average slip resistance of .50 in laboratory tests.
    • The tests were based on the appropriate ASTM standard test method and conducted by a qualified laboratory (Appendix B to this subpart references appropriate ASTM standard test methods).
    • Documentation of the test results is available at the site and to the steel erector.
  • When deemed necessary by a competent person, plumbing-up equipment must be installed during the steel erection process to ensure the stability of the structure. [29 CFR 1926.754(d)(1)]
  • Plumbing-UpWhen plumbing-up equipment is used, it must be in place and properly installed before the structure is loaded with construction material such as loads of joists, bundles of decking, or bundles of bridging. [29 CFR 1926.754(d)(2)]
  • Plumbing-up equipment may be removed only with the approval of a competent person. [29 CFR 1926.754(d)(3)]

Hoisting, Landing, and Placing of Metal Decking Bundles:

  • Bundle packaging and strapping may not be used for hoisting unless specifically designed for that purpose. [29 CFR 1926.754(e)(1)(i)]
  • If loose items such as dunnage, flashing, or other materials are placed on top of metal decking bundles intended to be hoisted, they must be secured to the bundles. [29 CFR 1926.754(e)(1)(ii)]
  • When bundles of metal decking are landed on joists, all bridging must be installed and anchored, and all joist-bearing ends attached. (See Open web steel joists for exceptions.) [29 CFR 1926.754(e)(1)(iii)]
  • Metal decking bundles must be landed on framing members so that enough support is provided to allow the bundles to be unbanded without dislodging the bundles from the supports. [29 CFR 1926.754(e)(1)(iv)]
  • At the end of the shift or when environmental or jobsite conditions require, metal decking must be secured against displacement. [29 CFR 1926.754(e)(1)(v)]

Roof and Floor Holes and Openings:

  • Metal decking at roof and floor holes and openings must be installed as follows: Metal Decking
    • Framed metal deck openings must have structural members turned down to allow continuous deck installation, except where prevented by structural design constraints or constructability. [29 CFR 1926.754(e)(2)(i)]
    • Openings such as roof and floor holes must be decked over.
    • Where large size, configuration, or other structural constraints do not allow openings to be decked over (e.g. elevator shafts, stair wells, etc.), employees must be protected in accordance with the fall protection provisions of this standard. [29 CFR 1926.754(e)(2)(ii)]
  • When metal decking holes and openings are cut, they must [29 CFR 1926.754(e)(2)(iii)]:
    • Immediately and permanently be filled with the intended equipment or structure.
    • Or immediately be covered.

Covering Roof and Floor Openings:

  • Covers for roof and floor openings shall be capable of supporting, without failure, twice the weight of the employees, equipment, and materials that may be imposed on them at any one time. [29 CFR 1926.754(e)(3)(i)]
  • Marked Covering
  • All covers must be:
    • Secured when installed to prevent accidental displacement by the wind, equipment or employees. [29 CFR 1926.754(e)(3)(ii)]
    • Painted with high-visibility paint, or
    • Marked with the word "HOLE" or "COVER" to provide warning of the hazard. [29 CFR 1926.754(e)(3)(iii)]
  • Installed smoke dome or skylight fixtures are not considered covers, unless they meet the appropriate strength requirements. [29 CFR 1926.754(e)(3)(iv)]
  • Where planks or metal decking around columns do not fit tightly, wire mesh, exterior plywood, or equivalent material must be installed, and must be of sufficient strength to:

Installation of Metal Decking:

Derrick Floors:

  • To support the intended floor loading, a derrick floor must be fully decked and/or planked, and the steel member connections completed. [29 CFR 1926.754(e)(6)(i)]
  • Temporary loads placed on a derrick floor must be distributed over the underlying support members so as to prevent local overloading of the deck material. [29 CFR 1926.754(e)(6)(ii)]
Workers Killed in Falls Through Decking Holes

Case Reports:

  • An employee fell from about the 60-foot level of a manufacturing facility where he was doing steel erection. He had just completed bolting up a vertical beam, and was attempting to disconnect the hoisting line, when he apparently backed into a floor opening in the metal decking on which he was standing. Guardrails had been manufactured for the opening but would not fit, and had been taken down to the ground for modification. The employee died of his injuries.
  • At around 10:00 a.m. on January 31, a steelworker was involved in metal decking installation. He fell approximately 20 feet through a roof opening to the ground floor, sustained multiple body injuries, and died the following day.
  • An employee for a steel erection company was helping to build an elevated automobile ramp. He was covering an opening on the ramp with metal decking when he fell about 42 feet through the opening and was killed. He was not using fall protection.
Unsecured Decking Causes Eighty-Foot Fall

Case Report:

  • While erecting a bridge, a worker placed metal decking onto the stringers of the bridge to be welded. When the first decking was placed, the employee apparently stepped onto that section in order to put down the next section. Because the decking he stepped onto was not secured in place, it slipped and the employee fell approximately 80 feet into the river.
Column

This section addresses the hazards associated with column stability and, specifically, the proper use of anchor rods (anchor bolts) to ensure column stability. Inadequate anchor rod/bolt installation has been identified as a primary contributing factor to structural collapses.

  • All columns must be anchored by a minimum of 4 anchor rods (anchor bolts). [29 CFR 1926.755(a)(1)]
  • Each column anchor rod (anchor bolt) assembly, including the column-to-base plate weld and the column foundation, must be designed to [29 CFR 1926.755(a)(2)]:
    • Resist a minimum eccentric gravity load of 300 pounds located 18 inches from the extreme outer face of the column in each direction at the top of the column shaft.
  • Columns must be set on elements that adequately transfer the construction loads [29 CFR 1926.755(a)(3)]:
    • Level finished floors
    • Pre-grouted leveling plates
    • Leveling nuts
    • Shim packs
  • All columns must be evaluated by a competent person to determine whether guying or bracing is needed; if guying or bracing is needed, it must be installed. [29 CFR 1926.755(a)(4)]
One Worker Killed, Three Injured as Columns Collapse

Case Report:

  • Four employees were sitting on steel roof beams. Two employees were bolting beams to columns and the other two employees were sitting on the beams connecting roof purlins. A gust of wind caused the columns to topple in a domino fashion. One of the employees connecting roof purlins fell 25 feet to his death, and the other three employees were hospitalized for injuries. Compliance with the new steel erection standard could have prevented this accident.
  • Approval by the project structural engineer of record is required before anchor rods (anchor bolts) can be [29 CFR 1926.755(b)(1)]:
    • Repaired
    • Replaced
    • Field-modified
  • Before the erection of a column, the controlling contractor must provide written notification to the steel erector if there has been any [29 CFR 1926.755(b)(2)]:
    • Repair
    • Replacement
    • Modification of the anchor rods of that column
Beams and Columns

Inappropriate or inadequate connections of beams and columns is hazardous and can lead to collapses and worker fatalities. This section sets forth performance and specification requirements for connecting beams and columns, in order to minimize the hazard of structural collapse during the early stages of the steel erection process.

  • During the final placing of solid web structural members, the load must not be released from the hoisting line until [29 CFR 1926.756(a)(1)]:
    • The members are secured with at least two bolts per connection, of the same size and strength as shown in the erection drawings.
    • These bolts are drawn up wrench-tight.
    • The equivalent, as specified by the project structural engineer of record, except as specified in 29 CFR 1926.756(b) of this section.
  • A competent person must determine if more than two bolts are necessary to ensure the stability of cantilevered members if additional bolts are needed, they must be installed. [29 CFR 1926.756(a)(2)]
  • Solid web structural members used as diagonal bracing must be secured by [29 CFR 1926.756(b)]:
    • At least one bolt per connection drawn up wrench-tight.
    • The equivalent, as specified by the project structural engineer of record.
  • When two structural members on opposite sides of a column web, or a beam web over a column, are connected sharing common connection holes:
    • At least one bolt with its wrench-tight nut must remain connected to the first member; unless
    • A shop-attached, or field-attached seat or equivalent connection device is supplied with the member in order to (See Appendix H to this subpart for examples of equivalent connection devices.) [29 CFR 1926.756(c)(1)]:
      • Secure the first member.
      • Prevent the column from being displaced.
  • If a seat or equivalent device is used:
    • The seat (or device) must be designed to support the load during the double connection process.
    • Before the nuts on the shared bolts are removed to make the double connection, it must be adequately bolted or welded to both [29 CFR 1926.756(c)(2)]:
      • A supporting member
      • The first member

Each column splice must be:

  • Designed to resist a minimum eccentric gravity load of 300 pounds.
  • Located 18 inches from the extreme outer face of the column in each direction.
  • Located at the top of the column shaft. [29 CFR 1926.756(d)]

Perimeter columns must not be erected unless:

  • They extend a minimum of 48 inches above the finished floor, to permit installation of perimeter safety cables prior to erection of the next story. [29 CFR 1926.756(e)(1)]
  • They have two sets of holes, or other devices that:
    • Are 42-45 inches above the finished floor, and also at the midpoint between the finished floor and the top cable.
    • Permit installation of perimeter safety cables as required by 29 CFR 1926.760(a)(2). [29 CFR 1926.756(e)(2)]

EXCEPTION: Where constructability does not allow, the above requirements can be waived. (See Appendix F to this Subpart.)

Workers Hospitalized After Inadequately Secured Beams Fail

Case Reports:

  • Two employees were ordered by their foreman to take down a two-ton I-beam about 20 feet long, which they had themselves bolted to shear lugs the day before. The employees stood at opposite ends of the beam, one worker removing the bolts, while his co-worker released a strap, commonly known as a "come-along," that was supporting the other end of the beam. As the "come-along" was released, the shear lugs ripped from the column and the beam dropped, sending both workers to the floor 16 feet below. They were each hospitalized; one worker suffered injuries to his right foot that required surgery. Investigation showed that on the night prior to the accident, a welding crew was assigned to help relocate the beam to a different elevation. They started by securing the beam with the "come-along," then partially cut the beam's shear lugs. This was unknown to the workers the next day, because the foreman did not inspect the shear lugs, even though he admitted he saw the "come-along."
  • Three ironworkers were laying metal decking when the deck they were standing on let go from the support beam. The three workers fell some 13 feet, and were sent to the hospital with injuries. Investigation revealed that the support beam only had a single loose bolt at each connection, instead of two wrench-tight bolts as required by OSHA standards. The support beam rolled, and since the metal decking was not yet welded or secured to the beam, it slid off and carried the workers with it.
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.

  • Where steel joists are used and columns are not framed in at least two directions with solid web structural steel members, the columns must be made laterally stable during erection by field-bolting the steel joist at the column. (See exception below) [29 CFR 1926.757(a)(1)]
  • When installing the stabilizing joist:
  • A vertical stabilizer plate for steel joists must be provided 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 1316-inch hole to provide an attachment point for guying or plumbing cables. [29 CFR 1926.757(a)(1)(i)]
  • The bottom chords must be stabilized to prevent rotation during erection. [29 CFR 1926.757(a)(1)(ii)]
  • Hoist Cable
  • Hoisting cables must not be released 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. [29 CFR 1926.757(a)(1)(iii)]
  • EXCEPTION: Where constructability does not allow a steel joist to be installed at the column:
  • Hoisting cables must not be released until the seat at each end of the steel joist is field-bolted and the joist is stabilized. [29 CFR 1926.757(a)(2)(ii)]
  • 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. [29 CFR 1926.757(a)(3)]
    • Alternatively, procedures described in the Compliance Directive may be used instead until July 18, 2003. [CPL 2-1.34, Q&A 32]
  • Where steel joists at or near columns span more than 60 feet:
    • The joists need to be set in tandem with all bridging installed. [29 CFR 1926.757(a)(4)]
    • An alternative method of erection may be used, which [29 CFR 1926.757(a)(4)]:
      • 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. [29 CFR 1926.757(a)(5)]
  • When steel joists are landed on a structure, they must be secured to prevent unintentional displacement prior to installation. [29 CFR 1926.757(a)(6)]
  • 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. [29 CFR 1926.757(a)(7)]
  • When connecting individual steel joists to steel structures in bays 40 feet or longer (see exception below):
  • 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. [29 CFR 1926.757(a)(9)]
  • A bridging terminus point must be established before bridging is installed. [29 CFR 1926.757(a)(10)]
Unstable Columns Cause Joists to Collapse; One Dead, Three Injured

Case Reports:

  • Five ironworkers were distributing 90-foot-long open web bar joists on a building under construction. The bar joists were supported by vertical columns spaced 30 feet apart. The steel columns were not framed in at least two directions, and the bar joists were not field-bolted to the vertical columns to prevent collapse. The bar joists shifted, causing the vertical columns to lean. This resulted in the entire section of columns and open web bar joists to collapse. Two employees rode the iron down. One was killed and one received serious injuries.
  • Two employees had just finished setting and bolting a 60-foot steel truss atop two 30-foot steel columns. As the crane load line was disconnected, a high gust of wind blew over the truss and columns. One employee rode the truss to within approximately 12 feet of ground level when he fell off, striking his face and nose on the ground. The other employee rode the truss all the way to the ground and was thrown into the webbing when the truss bounced on impact. He suffered a sprained right ankle. The whole truss and column configuration then fell into another erected truss/column set, knocking it down as well. As allowed by the steel erection standards in place at the time, neither employee was tied off to a safety device.
  • Each end of "K" series steel joists must be finally attached to the support structure with a minimum of [29 CFR 1926.757(b)(1)]:
    • 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 [29 CFR 1926.757(b)(2)]:
    • 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 [29 CFR 1926.757(b)(3)]:
    • 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. [29 CFR 1926.757(b)(4)]
  • Where the span of the steel joist is equal to or greater than the span shown in 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. [29 CFR 1926.757(d)(1)(i)]
    • Hoisting cables must not be released until this bolted diagonal erection bridging is installed and anchored. [29 CFR 1926.757(d)(1)(ii)]
    • No more than one employee is allowed on these spans until all other bridging is installed and anchored. [29 CFR 1926.757(d)(1)(iii)]
  • 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. [29 CFR 1926.757(d)(2)(i)]
    • 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. [29 CFR 1926.757(d)(2)(ii)]
    • Hoisting cables must not be released until this bolted diagonal erection bridging is installed and anchored. [29 CFR 1926.757(d)(2)(iii)]
    • No more than two employees are allowed on these spans until all other bridging is installed and anchored. [29 CFR 1926.757(d)(2)(iv)]
  • Where the span of the steel joist is 100 feet through 144 feet, the following applies:
  • For steel members spanning over 144 feet, the erection methods used must be in accordance with 29 CFR 1926.756. [29 CFR 1926.757(d)(4)]
  • Where any steel joist that requires bridging is a bottom chord bearing joist [29 CFR 1926.757(d)(5)]:
    • 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. [29 CFR 1926.757(d)(6)(i)]
    • Bridge Clip
    • The erection drawing must be the exclusive indicator of the proper placement of this bridging. [29 CFR 1926.757(d)(6)(ii)]
    • Shop-installed bridging clips, or functional equivalents, must be used where the bridging bolts to the steel joists. [29 CFR 1926.757(d)(6)(iii)]
    • 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. [29 CFR 1926.757(d)(6)(iv)]
    • Bridging attachments must not protrude above the top chord of the steel joist. [29 CFR 1926.757(d)(6)(v)]
Hoisting Cables Released Too Soon, Fatal Fall Results

Case Report:

  • An employee was sitting on a 40-foot-long bar joist, welded at one end, while he attempted to connect X-bracing to it at the other end. The hoisting cable was already released, and the joist was insufficiently bridged to support the load it was bearing. When it slipped, the employee rode the joist down 25 feet and died of massive head injuries.
  • During the construction period, the employer placing a load on steel joists must ensure that the load is distributed so as not to exceed the carrying capacity of any steel joist. [29 CFR 1926.757(e)(1)]
  • 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. [29 CFR 1926.757(e)(2)]
  • The weight of a bundle of joist bridging must not exceed a total of 1,000 pounds, and [29 CFR 1926.757(e)(3)]:
    • 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 [29 CFR 1926.757(e)(4)]:
  • The edge of any construction load must be placed within 1 foot of the bearing surface of the joist end. [29 CFR 1926.757(e)(5)]
Overloaded Joists Fail, Fatal Fall Results

Case Report:

  • Two employees had unloaded two bundles of metal decking, two bundles of bridging and two bundles of roof frames onto six open web steel joists 25 above ground level. The joists were at 5½-foot centers, and welded on the end to the I-beam. The employees had just unhooked the second bundle of frames when one joist rolled, causing the employees to fall. All six joists broke from their welds and collapsed, landing on one of the employees. He died of his injuries. His co-worker was hospitalized but survived.
Decking Placed on Unsecured Joists Leads to Worker Injury

Case Report:

  • A bundle of 25 steel deck sheets was sitting on three open web joists, approximately 40 feet in length and about 25 feet above ground level. A worker was standing on the deck sheets as a second bundle was being landed on the other end of the same joists. The three joists rolled and collapsed, along with two additional joists. The worker began falling and attempted to jump away from the deck bundle, but his legs became entangled within the joist webbing. He landed on soft mud and sustained two broken legs. According to the project superintendent, none of the joists was secured or bridged at the time of load placement.
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