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Shaftwall History


Q: Can you provide a historical background on gypsum panel shaft walls?



A: Vertical shafts are extremely important in the design of high-rise construction. They serve as a means to convey utilities such as electricity, water and conditioned air up to the upper floors. They also allow building occupants ingress to those same floors. In the event of a fire, vertical shafts offer access for fire services and a means for occupant egress from the upper reaches of high-rise buildings. These same shafts are typically housed in the core of the high-rise building. The core of the building also serves as the primary structural component to resist wind-induced forces.

   

Special attention must be made to both the design and construction of shaft enclosures. Over the years, these walls have gone through an evolution of building materials and design. Original building materials that were used for these walls included masonry, structural clay tile and gypsum blocks. In 1931, for example, the architectural firm of Shreve, Lamb and Harmon specified masonry walls for the Empire State Building. Many consider this iconic building to be the first modern high-rise. In that same year, Graham, Anderson, Probst and White selected gypsum block for the construction of the 4-million square-foot Merchandise Mart in Chicago.

   

However, as buildings reached greater heights, the need for a lighter, more elastic wall system became apparent. Traditional building materials such as masonry and gypsum block limited the design capabilities of shafts in modern high-rises and placed physical constraints on the finished spaces within those buildings. Walls that enclosed elevator shafts had to be designed as dynamic building elements. Those walls were subjected to cyclical and opposing forces as an elevator transits within the shaft. As the elevator cab climbs up the building, the wall experiences outward forces while the walls below the cab are impacted with inward forces.

   

The first-generation shaft walls comprised of gypsum panels were introduced in the 1960s. The first project was an office building in Los Angeles. This project was followed by a gypsum partition shaft wall application at the Central National Bank Building in Cleveland, and then at the U.S. Steel Building in Pittsburgh.

   

Designers today have much more flexibility in both cavity shaft wall material selection and system design. The term “cavity” is used to reflect that some of these walls have a stud cavity, and the walls are not solid. Modern shafts may be enclosed with cast-in-place concrete, masonry, gypsum plaster, steel stud drywall or specially designed gypsum panel shaft wall systems. Cast-in-place concrete walls provide resistance against horizontal building movement in high-rise structures. Masonry walls work well in the elevator pits within the shaft. Solid plaster gypsum partitions have been specially designed for shaft enclosures that require added security. The specially designed gypsum panel shaft system is the assembly of choice for many applications. Given the right design parameters for shafts and the end use of the structure, any of these may be appropriate for a given building.

   

The first definitive design parameters for shaftwall systems, which was prompted by a shaft wall failure in a prominent New York office building, were developed by the structural engineering firm of Skilling, Helle, Christiansen and Robertson, working in association with Minoru Yamasaki Associates and Emery Roth & Sons. The engineers discovered that the walls in the building had failed due to aforementioned cyclic loading. This led to the following system design requirements:

   

1. Shaftwall systems should be capable of being built from one side.

   

2. Assemblies must obtain a two-hour fire resistance rating.

   

3. Assemblies should have a minimum sound transmission classification of 40 STC.

   

4. The maximum dead load should be 15 pounds per square foot.

   

5. The shaft wall must withstand an instantaneous load of 25 psf without structural failure.

   

6. The assembly must be cycled through its maximum deflection without failure for 1 million cycles.

   

7. The system must be airtight.

   

In the aftermath of the attack on the World Trade Center in New York City, additional structural requirements were codified for buildings taller than 420 feet above grade. This is the result of the mandate for “hardening” these critical walls. The International Building Code essentially adopted the language that was first worked out with the New York Building Department.

   

The history of gypsum panel shaft walls is relatively short when compared to the history of construction. After approximately 50 years, the walls have a strong background based on solid design and physical testing. As building go to greater heights, these critically important gypsum panel shaft walls will evolve further to meet increasing demands.



Robert Grupe is AWCI’s director of technical services. Send your questions to grupe@awci.org, or call him directly at (703) 538.1611.

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