Cranes, Structures under Construction, and Temporary Facilities: Are We Doing Enough to Ensure They Are Safe?

As of the date of preparation of this editorial in mid-November, the National Transportation Safety Board (NTSB) had just released their report on the collapse of the I-35W Bridge in Minneapolis. The report indicated that the most probable cause of the collapse was inadequate load capacity due to a design error that resulted in the undersizing of as many as 24 of the bridge’s gusset plates. The NTSB notes that failure of the U10 plates was in part due to substantial weight increases on the bridge from previous modifications and concentrated construction loads from equipment and materials stored on the bridge, along with traffic on the bridge on the day of the collapse.

Similar to many modern day structural failures, the lack of prevention of this collapse can be traced back to procedural flaws, but the fact remains that in this case, as with many other facilities under construction, the structure received its worst historical load case during the construction process. As a result of these findings, we are reminded once again that structures under construction are often more susceptible to collapse than at any other time during their lifespan.

Almost exactly two years ago, a $210\text{-}\text{foot}$ -tall tower crane collapsed at the site of a 20-story office tower in Bellevue, Washington, toppling onto an adjacent apartment building. The collapse was just one in a long line of crane accidents of various types that have occurred in the Seattle area, including one in 1994 that killed two construction workers who were working on emergency repairs in the Kingdome.

New York City experienced two crane collapses in 2008 within a three-month period. The first involved a 20-story tower crane that collapsed at East 50th Street, resulting in seven fatalities and a number of other injuries in addition to causing significant property damage. The second collapse involving a similar-sized crane occurred at 91st Street and First Avenue even as city officials were responding to problems in crane licensing and inspection procedures within the city that had been made painfully obvious by the first collapse.

Even in today’s slowing construction market, a number of cities have the booms of cranes for large construction projects looming over their city streets (Fig. 1). And while most of these cranes will operate safely and effectively, some will fail or collapse, resulting in injuries to workers and pedestrians, or worse, in addition to causing property losses and significant construction delays.

The Occupational and Safety Health Administration (OSHA)’s crane and derrick rules date back to standards developed in the 1960s and are no longer reflective of the equipment and operations of the industry. Though there was much talk in the industry about the need for new rules and standards over the years, it wasn’t until 2003 that OSHA finally formed a committee charged with developing a consensus set of rules through the use of a negotiated industry process. Even though this committee released a document in July of 2004, a new set of OSHA rules has yet to be adopted.

As a result, New York, Seattle, Miami, and other cities have begun to assemble their own regulations in response to various crane failures, accidents, and concerns for construction safety. While these efforts are commendable, they have met with some resistance and in a few cases are not viewed as a comprehensive response to the issue. Unfortunately, rules enacted by multiple jurisdictions are causing confusion for inspectors, construction companies, and crane operators, who must deal with different requirements and procedures in different locales. Cases also exist where some of the new local regulations are in conflict with older rules such as the OSHA regulations, causing confusion over enforcement even though the intended result is the same: to increase safety. Regardless of perspective, most in the industry agree that new regulations and cooperative agreements with OSHA on the topic of crane safety are long overdue.

Temporary structures represent another continuing concern for the industry. Each year numerous structures are constructed, including such items as temporary or emergency shelters, public art projects, lateral earth retaining structures in construction zones, temporary grandstands and bleachers, sound system and lighting support structures for parades and public events, and indoor and outdoor theatrical stages, to name just a few. In addition, each year a number of permanent structures are used to support temporary loads that may not have been considered in the original design, including additional mechanical equipment, staging areas for building expansions, entertainment loads imposed on roof structures in concert arenas, etc.

This is not to say that the industry has ignored these issues, but to simply point out that more needs to be done in this area, and refinements are required relative to existing efforts. For example, ASCE is involved in advancing the process by releasing and supporting SEI/ASCE 37, Design Loads on Structures during Construction. This is a good start, but there is much more to do, not only in regulations and standards development, but in providing education and awareness to those practicing in the industry. One lesson from studying past accidents, failures, and collapses that should not be forgotten is that just developing code requirements or rules related to cranes, temporary facilities, and structures under construction is only part of the solution. We often discover that such items such as lack of awareness, poor enforcement of existing regulations and standards, and a general lack of diligence in design and construction operations can also lead to collapses and other structural failures.

All of the examples and types of structures mentioned in this installment represent conditions that may contribute to collapse, injury, or structural performance failures. There is an ongoing need for additional guidelines for architects, engineers, and constructors to use in designing, erecting, and inspecting many of the structures described, as well as an educational thrust in this area to ensure that the industry is aware of the seriousness of the situation, as well as of the programs and resources available to help address them.

Few will argue that the industry has done enough to address these types of structures, despite the dangers associated with our current policies and regulations. The Journal of Architectural Engineering (JAE) would like to do its part by serving as a forum for industry discourse on this topic. Readers are invited to submit comments in the form of a guest editorial or forum to the JAE editor, using the contact information noted in the editor’s note section of this issue.