Designing and testing façade access equipment

by Katie Daniel | May 2, 2017 2:17 pm

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All images courtesy Wiss, Janney, Elstner Associates Inc.

by Richard A. Dethlefs, PE, SE, Howard J. Hill, PhD, PE, SE, Leonard M. Joseph, PE, SE, Jonathan E. Lewis, SE, Karl J. Rubenacker, PE, SE, and Gwenyth R. Searer, PE, SE

Buildings taller than a few stories often include façade access equipment for washing windows, performing routine building maintenance, or engaging in construction activities on the building exterior. Building-mounted support elements for the façade access system may include davits, outriggers, and fall-arrest/lifeline anchorages. Proper design and load-testing of these components is a topic of considerable confusion and potentially dangerous misinformation. Having seen erroneous advice shared on several key technical aspects of this type of work on numerous projects, this article’s authors seek to provide a more comprehensive and rational summary of the design and testing requirements for façade access equipment.

Shown in Figure 1, façade access equipment is regulated by the Occupational Safety and Health Administration (OSHA), as well as other national and local codes and standards. It is important that engineers, architects, and owners, as well as the contractors who use the equipment, understand the regulations governing its design, inspection, and testing.

Design regulations
Codes and standards that address the design of façade access equipment include:

The design requirements for façade access equipment in these codes and standards are briefly summarized below.

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Figure 1: Typical window-washing equipment.

OSHA
The key to understanding the OSHA design requirements is having a clear comprehension of ‘rated load’ and ‘stall load,’ as these terms pertain to hoisting equipment for powered platforms.

‘Rated load’ is the safe working load that the hoist on a particular suspended window-washing platform is intended to lift. OSHA requires davits, outriggers, and connections to the building that support and/or provide backup for these elements be designed for a minimum of four times the rated load of the supported hoist. Why a safety factor of 4.0? Suspended platform starting and stopping loads are dynamic, resulting in forces that may be substantially larger than the static weight of the platform and its occupants. Additionally, hoists are machines capable of generating tension in the support lines far in excess of their rated load.

‘Stall load’ is the load at which a hoist stops operating. Since OSHA allows hoist stall loads to be as high as three times the hoist’s rated load, a platform moving up the side of a building that snags under a projection will continue to increase tension in the suspension cable until the platform breaks free of the obstruction, the hoist stalls, or an element of the suspension system fails. As a result, equipment designed to support four times the hoist rated load may only have an anticipated operating factor of safety of about 2.0 with respect to starting and stopping impact loads and 1.33 if a stall were to occur.

When façade access equipment is used for “construction” activities—defined by OSHA as almost any activity other than window-washing, including such mundane activities as painting and hanging of signage or holiday lights—the equipment must also be designed to resist 1.5 times the demands imparted by the stall load of the hoists they support. Absent knowledge of actual stall loads for all potential hoists that may be used with the equipment, façade access equipment for construction activities should be designed for 1.5 times the maximum permissible stall load, which is 3.0 times the rated load, resulting in a multiplier of 1.5 x 3.0 = 4.5 times the rated load(s) of the hoist(s).

OSHA fall-arrest/lifeline anchorages typically must be designed to withstand, without failure, 22.2 kN (5000 lb) per attached person. This might seem large for a worker who only weighs about 115 kg (250 lb), but dynamic behavior must be considered. To arrest a worker falling 1.8 m (6 ft), harnesses and lanyards are permitted by OSHA to generate up to 11.2 kN (2520 lb) of force. Thus, the 22.2-kN pound design load represents a fall-arrest factor of safety of about 2.0, which is not unreasonable for a fall-arrest/lifeline—especially considering that falls greater than 1.8 m are possible in some instances and workers may weigh more than 115 kg.

While the aforementioned load requirements for façade access equipment are generally clear, less clear is how to incorporate those load requirements into structural design and test loads for this type of equipment. OSHA requirements use terminology inconsistent with common structural engineering design methodologies, which has led to confusion in this regard. A clear and comprehensive discussion of the key structural requirements for design, assessment, and testing of façade access and building maintenance equipment can be found in ASCE’s 2015 publication, Façade Access Equipment: Structural Design, Evaluation, and Testing.

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Load-testing of an anchorage. A tube steel sleeve welded to a cantilever beam is placed over the anchorage. By jacking up against the roof at the end of the beam, an equivalent moment is created in the anchorage.

ASCE 7-16 and the 2015 IBC
ASCE 7-16 and the 2015 IBC incorporate design loads for façade access equipment that are consistent with OSHA strength requirements and comply with accepted structural engineering design procedures. Both ASCE 7-16 and the 2015 IBC require structural elements supporting façade access equipment (including both davits and outriggers, their connections to the structure, as well as the beams and columns supporting these elements) be designed to resist an unfactored service live load equal to the larger of:

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When combined with the applicable live load
factor of 1.6, the factored design live load equals the larger of:

Unlike OSHA, the ASCE 7-16 and 2015 IBC design approach eliminates the need to distinguish between window-washing/maintenance activities and construction activities. Where the stall load of a hoist is unknown, it should be assumed to be 3.0 times the rated load of the hoist (the maximum allowed by OSHA), resulting in an equipment design load of 1.6 x 3.0 = 4.8 times hoist’s rated load.

For fall-arrest/lifeline anchorages, ASCE 7-16 and the 2015 IBC adopted an unfactored live load of 13.8 kN (3100 lb) for each attached person. Applying a 1.6 live-load factor, the resultant factored live load is 22.1 kN (4960 lb), essentially matching OSHA’s requirement of 22.24 kN (5000 lb) for each attached person.

Testing requirements
OSHA requires building owners provide users of façade access equipment with assurances that all equipment meets OSHA’s requirements, including the minimum strength requirements. OSHA further requires the assurance be based on a “field test” prior to initial use and following any major modifications. OSHA provides no guidelines for what constitutes an acceptable “field test.” It is typically interpreted to mean an in-situ load test, with the test method and magnitude left up to the judgment of the engineer in charge of the testing and certification program. Regardless of how the field test is performed, it must demonstrate that the tested equipment and its connections to the building meet the minimum capacity requirements of OSHA 1910.66. Otherwise, it is an invalid test and cannot be used as a basis for an assurance to the user.

Complicating the matter, OSHA published an interpretation in 1993 that conflicts with their published assurance and testing requirements. The 1993 interpretation by OSHA illogically indicates that test loading to the minimum capacity requirements is not required by the assurance/testing requirements in OSHA 1910.66.

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Load-testing of a permanent outrigger beam and its support rails.

To satisfy the testing and assurance requirements of OSHA 1910.66, some engineers advocate for load-testing façade access equipment to only 50 percent of the minimum required strength. Use of this 50-percent test load limit was advocated in an article that appeared in the September 2016 issue of [5]The Construction Specifier. Other engineers, including the authors of this article, believe that valid tests loads must be 100 percent of the required strength to verify whether façade access equipment complies with a particular strength requirement. Determining a logical test procedure to ensure the equipment is tested in the appropriate direction, and ensuring excessive deflections do not occur, requires consideration of well-established principles of mechanics, material science, and statistics.

Testing to only 50 percent of the minimum required strength
Advocates in favor of limiting testing to only 50 percent of the required strength (or ‘50-percent tests’) have often tested davits and outriggers to only twice the rated load of the supported hoists, and fall-arrest anchorages to only 11.1 kN (2500 lb). These test loads are only half of the minimum required strength for these components (and less than half the required strength for hoists used for construction purposes). Additionally, many proponents of this approach recommend only testing a sampling of the equipment and not every element. Advocates of this level of testing claim it is standard in the industry, but this is false; further, the 50-percent approach has absolutely no scientific or structural engineering justification.

Arbitrary limits on test loads and sampling rates may result in missing design or construction defects, deterioration, or damage that could result in failure—either when loaded between 50 and 100 percent of the minimum required capacity or at untested locations. This level of testing prevents owners from providing a valid OSHA-required assurance the equipment has the required capacity. Engineers who certify compliance with applicable capacity requirements based on test loads at 50 percent of the minimum required capacity are providing false certifications.

The following examples show the potential irrationality of this approach. In one case reviewed by the authors, an engineer tested a group of apparently identical fall-arrest anchorages to only 11.1 kN (2500 lb). While several of the anchorages failed and were unable to resist even the 50-percent test load, the engineer certified that the remaining anchorages could all support the full minimum required design load of 22.2 kN (5000 lb). Despite the blatant red flag that a significant number of the anchorages were not able to resist even half of the design load, the engineer took the leap of faith that the remaining anchorages—also tested to only 11.1 kN (2500 lb)—would be able to resist 22.2 kN (5000 lb).

In another case, an engineer certified a group of davit bases based on testing to only half the minimum required capacity. Subsequent testing to higher loads revealed several bases did not have the strength needed to carry the minimum OSHA-specified loading. In the time between the two tests, workers had unknowingly placed their lives at risk by using the defective equipment.

In their arguments against 100-percent testing, proponents of 50-percent testing often confuse the term “minimum required strength” with “ultimate strength.” By definition, the “ultimate” strength of an element is the load at which that element fails. As structural engineers know, the ultimate strength of a properly designed, constructed, and maintained element is always greater than the minimum required strength. When ultimate strength is less than the minimum required capacity, only load-testing to 100 percent of the required load will reliably identify this unacceptable situation.

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Multiple suspended construction platforms are being used in order to perform façade repairs on this building.

Testing to 100 percent of the minimum required strength
If load-testing is performed to 100 percent of the minimum required strength and the equipment successfully holds the minimum required loads, the tester (and users) can be confident the equipment has the minimum required strength. Successfully passing the test load includes confirming the tested element did not suffer damage during the test (e.g. significant yielding, cracking, or fracture).

Unfortunately, not all equipment can be load-tested; some equipment is designed such that it must develop significant inelastic deformations in order to resist the minimum required loads. In these instances, load-testing may not be an option, and other methods may need to be employed if the capacity of the equipment is
to be verified—however, even in this situation, load testing to only half the required capacity is clearly not an acceptable means of verifying the capacity of the element.

IBC load test requirements
Where the 2015 IBC has been adopted, Section 1708 governs in-situ load tests. Where load-testing requirements are not specified by the appropriate materials standard (e.g. components constructed of wood, which employ a design standard that does not include provisions for in-situ testing), Section 1708.3.2 requires the minimum load applied during the test to be the factored design load. For davits, outriggers, and their supports, the factored design loads—and therefore the minimum test loads—are the greater of the two loads shown below:

For fall-arrest anchorages, the factored design load—and therefore the minimum test load—is 1.6 x 13.8 kN (3100 lb), or 22.1 kN (4960 lb).

Where load tests are specified by an IBC-referenced material standard (e.g. components constructed of steel or concrete), Section 1708.3.1 requires load testing be conducted according to the provisions of that standard, as described below.

AISC load test requirements
Load-test requirements for steel structures are provided in Section 5.4 of Appendix 5 of American Institute of Steel Construction (AISC) 360-10, Specification for Structural Steel Buildings. Like IBC, the load test provisions require the factored load be applied. As the load factor for live loads is 1.6, the net result is identical to IBC.

ACI load test requirements
Load-test requirements for concrete structures are provided in Chapter 27 of American Concrete Institute (ACI) 318-14, Building Code Requirements for Structural Concrete. ACI requires the magnitude of the load test be determined using a live load factor of 1.5. In the case of davits, outriggers, and their supports, the minimum test load can be calculated as the greater of the following:

For reinforced concrete components of fall-arrest anchorages and their supports, the minimum test load can be computed by multiplying the live load factor of 1.5 times 13.8 kN (3100 lb), which equals 20.7 kN (4650 lb).

These values are within six percent of the test loads required by AISC and IBC, which is a negligible difference.

Voluntary standards
International Window Cleaning Association (IWCA) I14.1, Window Cleaning Safety, and American Society of Mechanical Engineers (ASME) A120.1, Safety Requirements for Powered Platforms and Traveling Ladders and Gantries for Building Maintenance, are two voluntary standards often cited by engineers justifying testing to only 50 percent of the minimum required strength. However, neither of these two voluntary standards can supersede the requirements of mandatory standards. More importantly, both documents have significant technical flaws.

The IWCA I14.1 standard was published only once, in 2001. Concerns about technical issues in the standard were pointed out numerous times by this article’s authors, as well as other engineers and the National Council of Structural Engineering Associations (NCSEA), but the committee never addressed and incorporated the comments into an updated standard.

As the standard had not been maintained or updated for more than a decade, the American National Standards Institute (ANSI) administratively withdrew it in 2011. Further, ANSI suspended IWCA’s accreditation for cause in 2012, then took the unusual step of permanently withdrawing IWCA’s accreditation in 2016, citing “repeated serious procedural and administrative concerns… including but not limited to unreasonable restrictions on consensus body membership and failure to properly process public review comments, substantive changes, and appeals.” For these reasons, this document should not be relied on for technical information.

Many of the members of the de-accredited IWCA committee are also members of the ASME A120 committee. In 2010, that committee proposed restrictions on load testing of façade access support elements to no more than 50 percent of the minimum required capacity—restrictions essentially identical to those in IWCA I14.1. Like the IWCA committee, the A120 committee is dominated by individuals without engineering degrees or licenses. Although a large number of public comments were provided objecting to the proposed changes, the test limits were adopted into the 2014 edition. Fortunately, A120.1 is only a voluntary, advisory standard. Unfortunately, some engineers do not appreciate or understand its various shortcomings, including contradicting codes and standards that are legally required to be used.

Examples of proper testing
Often, load tests can only approximate the actual loads a structure may experience. Still, with comprehensive planning along with careful implementation, proper load-testing of façade access equipment can often be performed.

Figure 2 shows a davit base being load tested by a hydraulic ram pushing upward off the roof structure against a long inward-pointing beam provided for this purpose. By creating a moment toward the side of the building, it mimics the overturning demand that would be caused by a work platform suspended over the side of the building. Deflections of the equipment were carefully monitored during the load test, and the load test ensured the results were repeatable.

Figure 3 shows the load-testing of a fall-arrest/tie-down anchorage. In this case, the load is being applied toward the edge of the roof to match one of the potential directions for a fall-arrest load. Since fall-arrest loads could come from a number of directions, this anchorage was also pulled toward the adjacent edge of the building just out of view on the left side of the photo. Loads were applied several times to verify the results were repeatable.

Figure 4 shows a davit being load-tested. The load is applied downward at the tip of the davit, simulating the demand from a suspended work platform. Load-testing of the carriage and the rails supporting the davit was accomplished separately via a cantilever loading beam similar to that shown in Figure 2.

Conclusion
Although the aforementioned September 2016 article from The Construction Specifier may have been intended to highlight the importance of properly load-testing façade access equipment, these authors feel a number of technical inaccuracies and other misinformation undermined its stated purpose. Engineers conducting or specifying load tests of this type of equipment must fully understand both fundamental engineering principles and the requirements governing such testing. Failing to understand the requirements, or basing certifications on inappropriate testing, may result in equipment users experiencing excessive risks.

OSHA regulations form the basis for numerous code requirements related to the design of this type of equipment contained in the 2015 IBC and ASCE 7-16. In addition, AISC 360 and ACI 318 govern key issues related to design and testing of elements constructed of steel and concrete. By the IBC and ASCE 7-16 restating some design requirements in more familiar form, they can bring clarity to engineers who may struggle with the unorthodox wording of the various OSHA regulations.

For design professionals specifying new or replacement equipment, this article’s authors recommend the following:

  1. Require hoist-supporting elements (e.g. davits, outriggers, rooftop carriages, and tiebacks and their structural supports) be designed elastically or essentially elastically to support the loads provided in Section 1607.9.3 of the 2015 IBC when multiplied by the required live load factor of 1.6.
  2. Require fall-arrest/lifeline anchorages and their supports be designed elastically or essentially elastically to support the loads provided in Section 1607.9.4 of the 2015 IBC when multiplied by the required live load factor of 1.6.
  3. Require all façade access equipment be load-tested to satisfy OSHA requirements prior to initial use. Testing should be performed according to Section 1708 of the 2015 IBC, Section 5.4 of Appendix 5 of AISC 360-10, and Section 27.4 of ACI 318-2014, using the full factored loads required by the 2015 IBC and ASCE 7-16. Equipment should be required to show no evidence of significant deformation or failure during the test or upon removal of the test load.

Although the recommendation that façade access equipment remain elastic (or essentially elastic) may exceed the minimum requirements of IBC and OSHA, it should result in a design that facilitates any load-testing that may be required, particularly in the event that the equipment’s ability to sustain the required loads is ever in question.

While this article highlights key aspects of façade access design and testing, the topic is too complicated to fully cover here. Interested readers can find a comprehensive discussion of this topic in ASCE’s Façade Access Equipment: Structural Design, Evaluation, and Testing.

Richard A. Dethlefs, PE, SE, is a principal at Wiss, Janney, Elstner Associates (WJE), with 22 years of experience. Dethlefs has designed, tested, and certified façade access systems for over 100 buildings. He can be reached at rdethlefs@wje.com[10].

Howard J. Hill, PhD, PE, SE, is a senior principal and director of project operations at WJE, with more than 34 years of experience in the evaluation and design of structural elements and systems. He can be contacted via e-mail at
hhill@wje.com[11].

Leonard M. Joseph, PE, SE, is a principal at Thornton Tomasetti Inc., with 42 years of experience designing structures for varied buildings around the world, from sports facilities to skyscrapers, using steel, concrete, masonry, and timber. He can be reached at ljoseph@thorntontomasetti.com[12].

Jonathan E. Lewis, SE, is an associate principal at WJE. He has evaluated fall protection issues and façade access equipment at dozens of buildings in multiple states. Lewis can be e-mailed at jlewis@wje.com[13].

Karl J. Rubenacker, PE, SE, is a partner at Gilsanz Murray Steficek LLP. Having designed structures on both the East and West Coast, he is the lead engineer for a diverse portfolio including new construction and restoration projects. Rubenacker can be reached at karl.rubenacker@gmsllp.com[14].

Gwenyth R, Searer, PE, SE, is an associate principal at WJE. She has 23 years of experience, and has evaluated, designed, and tested numerous façade access installations. Searer can be e-mailed at gsearer@wje.com[15].

Endnotes:
  1. [Image]: https://www.constructionspecifier.com/wp-content/uploads/2017/05/Photo-8-facade-e1493741690123.jpg
  2. [Image]: https://www.constructionspecifier.com/wp-content/uploads/2017/05/Figure-1-P8290012-with-labels2.jpg
  3. [Image]: https://www.constructionspecifier.com/wp-content/uploads/2017/05/Photo-5-facade.jpg
  4. [Image]: https://www.constructionspecifier.com/wp-content/uploads/2017/05/Photo-6-facade.jpg
  5. September 2016 issue of : https://www.constructionspecifier.com/life-safety-testing-to-failure-2
  6. [Image]: https://www.constructionspecifier.com/wp-content/uploads/2017/05/Photo-7-facade.jpg
  7. [Image]: https://www.constructionspecifier.com/wp-content/uploads/2017/05/Figure-2-P7140101.jpg
  8. [Image]: https://www.constructionspecifier.com/wp-content/uploads/2017/05/Figure-3-DSCN0030.jpg
  9. [Image]: https://www.constructionspecifier.com/wp-content/uploads/2017/05/Figure-4-P1270157.jpg
  10. rdethlefs@wje.com: mailto:rdethlefs@wje.com
  11. hhill@wje.com: mailto:hhill@wje.com
  12. ljoseph@thorntontomasetti.com: mailto:ljoseph@thorntontomasetti.com
  13. jlewis@wje.com: mailto:jlewis@wje.com
  14. karl.rubenacker@gmsllp.com: mailto:karl.rubenacker@gmsllp.com
  15. gsearer@wje.com: mailto:gsearer@wje.com

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