Building Collapse at
University of Aberdeen
JURY FINDS BUILDERS
Progressive Collapse of the University of Aberdeen Zoology Building
November 1, 1966 - Aberdeen, Scotland
The University of Aberdeen Zoology Building collapse was a fairly unique incident in steel-frame building architecture and highlighted what can happen when adequate measures aren't taken in providing a building with sufficient support from lateral loads (force on a building from the sides).
The architectural firm chosen to build the University of Aberdeen Zoology Building chose a steel-frame design, with reinforced concrete floor sections across the girders.
To protect against lateral loads, the architectural firm relied on three variables:
1) The 1st floor girders being set deep enough in to the foundation to provide rigidity.
2) Strong welds where each girder formed a perpendicular "T" with another girder, forming a solid cubical matrix.
3) Strong perimeter and internal walls to tie the floors together. (The building collapsed before this phase).
The actual construction was to be carried out by another company. Neither company ever met face to face. All correspondence was done via telephone and via post.
There were no issues after the construction company had completed steelwork until the day of the collapse on November 1, 1966. Strong winds had been reported all throughout the day. Most of the construction crew was just returning from lunch at around 1:30PM when several of them witnessed the building begin to move from side to side. At that point, workers began to run out of the structure when the second floor seemed to fold over and pancake on to the roof of the first floor, which then collapsed to the ground along with the rest of the building in giant cloud of dust that obscured the construction site for several moments until the strong winds blew the dust cloud to the south.
5 men were killed in the collapse with another 3 being pulled out of the rubble in the hours that followed.
A jury inquiry was later ordered due to the loss of life. The question was whether or not the architectural firm or the construction company was negligent, either individually or as a whole, in their responsibility to ensure proper worker safety.
One of the first observations that technical experts made of the destroyed structure was the inadequacy of the welds used to hold the girders in place and that this was likely the cause of the failure and why the structure seemed to "blow over" as a result of the winds on November 1. The architectural firm argued that this vindicated them and laid the fault for the tragedy at the feet of the construction company. The construction company however argued that the buildings couldn’t have "blown over" as a result of their welds because, from October 24th to the 30th, far stronger winds had been reported in the area and the building withstood those just fine, so it had to have been a problem with the original design itself, which was the responsibility of the architectural firm.
Technical experts who gave testimony to the jury, argued that if the weld joints were insufficient to begin with, then they could have been weakened exponentially over a period of time by metal fatigue induced by winds, movement on the site, and other lateral loads.
This concept can be easily seen when bending a paper clip back and forth until it breaks. The paper clip will seem solid and rigid as you bend it back and forth until the last bend when it just falls apart like its made of paper. There is no gradual “ramp” up to the point of failure where it’s twice as easy to bend the paper clip every time you move it back and forth. It’s just hard to bend one moment and then it falls apart.
If the welds were not sufficient in tying the girders together so they could act as one solid unit, then the lateral forces exerted on the building would not have been transferred to the girders, but would instead have been transferred to the weakest structural links, which would have been the welds. Since the girders on the first floor were set deep in cement, they remained rigid. The girders on the second floor however were only held in place by virtue of their welds to the first floor girders. At the time, 6 of the 7 floors were completed. That meant the 6th floor girders had only to deal with the lateral forces of the 6th floor. The 5th floor girders had to deal with the lateral forces of both the 5th and the 6th floor. The 4th had to deal with the lateral forces of the 4th, 5th, and 6th floors, on down to the second floor, which had to deal with the combined lateral forces of floors 2-6.
The ground floor was actually the most stabile part of the structure since the girders were set in to the foundation, which would have explained why the failure seemed to occur on the second level where the stresses on the welds were the greatest.
Technical experts argued that the windstorms in the prior weeks would have provided the “back and forth” oscillating action that was required for the insufficient welds to be weakened. Therefore, the winds didn’t have to be as strong on November 1st as they were from October 24th through the 30th in order to initiate the final catastrophic failure. They only needed to be blowing strong enough to allow the building to oscillate until one weld began to fail, which would have transferred its lateral load to surrounding welds which would have accelerated their failure, and those welds would have then been more likely to fail and transfer their lateral loads to other welds, setting off a cascading domino effect, known in engineering as a “progressive collapse".
The jury ultimately found both parties at fault, stating that the architectural firm should have been working far more closely with the construction company, supervising every step of the building process. They also felt that the welds on the lateral beam connections were the responsibility of the contractor, and that this was the likely point of failure.
Today, in addition to proper welding techniques, steel-framed buildings carry far more protection from lateral loads by implementing crisscrossing girders called "diagonal braces" to lock the cubical matrix in place. An example can be seen here. When you try to collapse a cube, you have to bring the corners on two opposite sides together. By creating “box” wall formations and then locking them in place with crisscrossing girders, you can prevent the corners of the box from contracting in either direction and the lateral rigidity of a steel-framed building is enhanced several fold in that direction. This design ensures that all lateral stress is transferred to the diagonal braces and not to the perpendicular “T” sections, which are far more suited to handle vertical stresses rather than lateral ones. This is most beneficial during the construction phase when there is no elaborate matrix yet of internal and external walls to give the structure rigidity from lateral forces. Had Aberdeen been utilizing diagonal braces in the actual steel framework and had the welds on the beams themselves been thorough, the building would undoubtedly be standing today.
The accident also highlighted one of the most obvious weaknesses in all building design, which is that the lateral surfaces are only as strong as their connection points to the vertical surfaces and the vertical surfaces can’t stay vertical without the lateral surfaces keeping them upright. This highly interdependent relationship is a prime reason why, every time there’s a major earthquake, there are always various buildings around said region that become prime examples of progressive collapse.