Blacksburg+VA+High+School+-+Gymnasium+Collapse

Blacksburg VA High School - Gymnasium Collapse //Samantha deVries, BAE/MAE, Penn State 2015 //
 * Blacksburg, VA - February 13, 2010 **

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Introduction
On February 13, 2010, the gym roof of the Blacksburg High School collapsed under a heavy snow load. Fortunately, no one was in the gym at the time of the collapse, and so no one was injured. Earlier that day, cracking in the masonry block wall was noticed near the supports during a sports practice, and the gym was evacuated prior to the collapse. Leading up to the collapse, there were several engineering reports which pointed out some structural issues related to settlement of the building which would require repair. This caused extensive questioning over whether or not school maintenance officials should have addressed those issues. However, it was found that the structural problems previously brought up were not a contributing cause of the gym roof collapse. Another report later determined that the staff were not at fault for the collapse.

The snow load was relatively heavy, although not higher than the design snow load, and therefore was not the main cause of the collapse, but merely a contributor. During the investigation of the collapse, the roof truss supports were examined and three structural deficiencies were found to be present, all of which were contributing factors in the buckling of the supports during the collapse. The supports were not gusseted, which allowed for side-to-side movement, the yield strength of the support was found to be below the minimum specified requirements, and the welds between the truss and the support were faulty. Because of these deficiencies, the gym collapsed under the February snow load even though it was less than the design loads.

**Key Words**
Roof Collapse, Snow, Blacksburg VA, Masonry Wall, Gusset Plate, Truss Support

==** Collapse **==

The collapse occurred during the winter of 2010. During the winter, the area had been receiving large amounts of snow. Prior to the collapse on February 13, 2010, cracks were noticed during the morning basketball practice in the sections of the masonry block walls supporting the roof trusses as shown in figure 2. The masonry block had shown fissures propagating downwards in the wall. Fortunately, because the cracks were noticed, the building was evacuated before the roof collapsed later the same day. (Tanzer, 2011).

The collapse occurred in the early afternoon, around 1:30pm on February 13, 2010. Immediately, the area was fenced off and dispatchers worked to bring power up in the building to keep the heat on and try to avoid having a collapse elsewhere in the building due to the same snow load. (Adams, 2010). At the time of collapse, it is estimated that the roof had 50 cm of snow on it, which, although relatively heavy, did not exceed the design snow loads (Tanzer, 2011).

** Investigation **
Leading up to the collapse, engineers determined that there were several issues related to settling of the foundations that should be examined more thoroughly and possibly fixed. There were three separate reports over the course of ten years prior to the collapse, resulting in questions about whether or not school officials should have had maintenance work completed. Ultimately, it was determined that the officials were not negligent, and that they properly handled the information provided to them in the reports. The investigation event ually determined that settlement was not a contributing cause to the collapse (Polanz, 2010). At the time of collapse, it is estimated that the 152 by 106 foot roof had 20 inches (50 cm) of snow on it, and based on National Weather Service data from the day of the collapse as seen in figure 3, there was 2-4 inches of ground snow water equivalent (NWS 2010), or between approximately 10 and 20 lbs/ft2. The design roof snow load at the time the gym was built in the 1974 was approximately 35 lbs/ft2 (Mallory, 2010), and therefore, the snow load at the time of collapse did not exceed the design snow loads. The collapse mechanism was the buckling of a truss support which then caused the total collapse of the roof around the location of the support. During the investigation of the collapse, the roof truss supports were examined and three structural deficiencies were found to be present, all of which were potential contributing factors in the buckling of the supports during the collapse. The supports were not gusseted, which allowed for side-to-side movement, the yield strength of the support was found to be below the minimum specified requirements, and the welds between the truss and the support were faulty (Tanzer, 2011).

There was also an investigation of many of the other structural elements in the rest of the school. At one point during the investigation, 200 beams had been tested, and 54% of those were found to be defective (Polanz, 2010). Several cracked columns, walls, and beams were found in one section of the school, many of which were thought to be caused by foundation settlement, although some were directly caused by the gym collapse (Mallory 2010.) The school board continued to have engineers test and examine the school in order to decide whether the school should be torn down and replaced at a cost of about $65 million, repaired at a cost of approximately $20 million, or renovated for other safety and code concerns in addition to the repairs at a cost of $50 million (Mallory and Polanz, 2010).

** Cause of Failure **
One of the three main contributing deficiencies found included the roof truss supports, which did not have gussets, resulting in a lack of lateral support for dynamic loads. Therefore a roof truss could, over the course of its lifetime, experience a displacement away from the support center. Figure 2 shows that the top chord of the truss did indeed move to the left of the support. This would have produced increased stresses in the supports if the support was no longer supported by the same column area as the original design intended. The displacement of the support would have also contributed to the the failure mechanism, which was the buckling and rolling over of the support (Laird, 2010).

Another of the main factors included the material properties. Steel material was taken from the site and tested in order to determine its properties and strength. The yield strength was 9% below the original specified value. Therefore, the material was already below the design standards and specifications at the time of construction. The yield strength was a factor in the collapse of the roof purely due to material weakness (Tanzer, 2011).

The final factor was the quality of some of the welds in the roof. There were some butt welds between a horizontal member and support plate which did not achieve full penetration. Therefore, the area carrying load was reduced, increasing the stress in the weld and decreasing the connection’s load-carrying capacity. An investigation of these welds found that improper preparation of the welding surfaces and poor surface geometry led to the lack of full penetration. Ultimately, the investigation was unable to determine whether the roof would have remained stable without these three deficiencies, but it considered all three as being serious structural deficiencies for a building constructed at that time in the 1970’s (Tanzer, 2011).

**Prevention**
The main contributing causes of the collapse were design, construction, and material flaws. Therefore, the collapse could have been prevented by taking care to address lateral movement concerns during the design, better quality welds and construction practices, and more thorough material inspection or testing prior to its use in the building. Additionally, although the staff were not considered to be negligent in how they handled the engineering reports, it is possible that further investigation of the early reports’ concerns may have found some of the structural flaws that eventually led to the collapse. A lesson that can be learned from this case study is to stay on top of facility management and maintenance. The Blacksburg High School Gym and many other collapses could have been prevented with a more active approach to building maintenance.

** Similar Cases **
The Blacksburg VA High School gym roof collapse is a representative case study of typical roof failures due to snow loads. Like many other cases, the Blacksburg collapse was triggered by a heavy snow load that did not exceed the design load, but there were additional causes related to the building’s design or construction that ultimately led to the collapse. The typical roof failure due to snow load also tends to be metal or steel construction, which is consistent with the Blacksburg HS case study. In roof collapses due to snow, age is not necessarily a typical feature as there have been cases in which relatively new metal buildings have collapsed during a winter storm. The Blacksburg gym was fairly old at the time of the collapse, however its age was not necessarily an important factor as the collapse was not due to maintenance issues, but rather it was due to initial design flaws. Another typical feature of the gym collapse was the crack in the wall showing signs of a potential collapse. In a study of roof collapses that occurred during 2010, it was found that in many cases, a building will show warning signs prior to collapse, allowing people to exit safety before the collapse. This characteristic is consistent with the observation of the crack below the truss support in the gym that allowed an evacuation of the building before the roof collapsed later that day.

A similar case study is the Knickerbocker Theater Collapse, w as a collapse of a theater roof that occurred in 1922 due to excess snow loading during a blizzard in Washington D.C. This was a much older event, and one main difference between the Blacksburg HS gym and the theater collapse was that the gym showed warning signs of potential failures, while the theater did not, causing loss of life and injuries.

Another similar case study shown in figure 4 is the Katowice, Poland - Trade Hall Roof Collapse which collapsed when there was a snow load that was almost two times the design snow load on the roof. Therefore the case is a bit different from the Blacksburg HS case because the snow was the main cause of the collapse rather than just a trigger.

One last related case study is the Bad Reichenhall, Germany Ice Rink in which water damage had weakened the roof trusses, causing a collapse one the roof was loaded with snow. This is similar to the Blacksburg HS Gym because both cases had snow acting as the trigger of the collapse, but both had underlying structural deficiencies and weaknesses as the root cause of the collapse.

**Conclusions**
The Blacksburg VA High School gym roof collapse was triggered by snow load on the roof. On a February day, a downward propagating crack was observed in the masonry block wall below a roof truss support. Fortunately, the building was evacuated and no one was injured when the gym roof collapsed later that same day. An investigation found that although snow load triggered the collapse, the load was not higher than the original design load, and the there were three structural deficiencies which may have contributed to the collapse. There was a lack of support against lateral movement of the truss support (a gusset plate providing lateral support would have been a better design), material strength was nine percent lower than required, and improper preparation and quality control of welds led to partial penetration welds where full penetration was required. A lesson that can be taken away from this case study is the importance of quality control and active facility management.