On October 20, 2018, a tragic event occurred at The Woodlands at Clemson. The clubhouse floor collapsed early on a Sunday morning, during an annual homecoming weekend party, resulting in injuries to several individuals. Initial reports and analyses from various engineers and media outlets pointed to rhythmic jumping and dancing by a large crowd as the primary cause of the collapse. However, a deeper investigation by two structural engineers revealed a different, more technical reason behind the failure.
The clubhouse, a two-level wood-framed structure, was classified as an A-3 Assembly on its Certificate of Occupancy. According to the 2000 International Building Code (IBC), dance halls are included under the A-3 Assembly category, with a prescribed design live load of 100 pounds per square foot (psf). This load was considered reasonable for a community building within an apartment complex, despite not specifically accounting for rhythmic jumping.
The local Fire Marshal had limited the maximum occupancy of the main floor to 135 people. The floor area that collapsed measured approximately 20 feet by 30 feet, suggesting it could accommodate up to 120 individuals based on the IBC's 5 square feet per person standard for standing space in an Assembly area.
The collapsed floor was supported by 24-inch-deep metal plate connected wood trusses, spaced 16 inches on center, with a span of about 20 feet-9 inches. The truss failures were predominantly at the end intersecting with the stair wall. Despite these failures, the truss bottom chords in the center span were intact, and the metal truss plates were fully embedded, indicating a failure not due to the trusses' inability to handle the design load.
The investigation used the 1995 Edition of the National Design Standard for Metal Plate Connected Wood Truss Construction (TPI), referenced in the 2000 IBC, to collect data and perform analyses. The wood truss design drawings were unavailable, so the analysis focused on the existing conditions.
The truss midspan bottom chord tension stress was calculated for a 115 psf total load (combining the 100 psf live load and a 15 psf dead load). This calculation showed that the truss chord was structurally sufficient for the load, and the metal connector plates were adequately sized for the 115 psf load, confirming the trusses were designed according to code.
No specific wood truss industry guidelines exist for evaluating dynamic loads from activities like rhythmic dancing. However, studies such as Stuart C. Kerr's 1998 research on staircases suggest a significant amplification factor for dynamic loads. Using these studies, the engineers evaluated the trusses' capacity under dynamic loads.
They found that the trusses could support a 255 psf maximum uniform static live load before failure, translating to a dynamic load capacity far exceeding the code-prescribed 100 psf. This suggested that the trusses, if properly designed, should not have failed under the dynamic loads experienced during the event.
The investigation then focused on the truss end bearing condition. It was discovered that the truss design failed at the interior stair wall due to improper bearing support. The 10-inch-wide double stud wall was misaligned, causing the primary truss support to rest on a less suitable 2x4 wall instead of the intended 2x6 wall. This misalignment led to a load path deviation, causing the truss bottom chord to bend and eventually fail under dynamic loading.
The absence of a truss web element above the 2x4 wall was a critical design flaw, reducing the truss capacity by 50%. This deficiency was exposed during the event, leading to the collapse.
The collapse of the clubhouse floor at The Woodlands at Clemson was not primarily due to rhythmic dancing, as initially reported. Instead, the failure was caused by a significant design error in the truss bearing. The improper alignment of the bearing walls reduced the load capacity, causing the truss to fail under dynamic loading conditions. Proper design and fabrication according to the code would have prevented this collapse, even under the dynamic loads experienced during the event.
Sources: structuremag.org, issuu.com
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