The FORCE that hit (Penang UMNO building)

At 7pm on 13 June 2013, a freak storm in Penang caused massive havoc - uprooting trees, blowing off the roof of the 25-story UMNO building, with deaths and injuries reported. This is the second tragedy Penang has faced in one week. 'Follow this story' for the latest updates from multiple sources. 

http://says.com/my/news/umno-penang-building-breaks-off-what-happened

A friend asked me how it was possible that the debris from the Menara UMNO tragedy could have punched so deep (>6m, i.e. two storeys) into the ground at Jalan Macalister. I will try and provide a purely technical explanation of this using the before-and-after photo of Menara UMNO below.

The structure that collapsed is the projecting top part of a 'wing wall' (the grey vertical fin that resembles a knife blade) designed to direct airflow into the building to promote natural ventilation. The wing wall is constructed of reinforced concrete. A steel antenna mast was attached to this wing wall.

From photographs of the incident and from the known dimensions of the building, I estimate that the height of the wing wall section that sheared (broke) off was at least 20m from top to bottom. Assuming an average width of 3m and thickness of 600mm... the mass of the collapsed concrete (density 2400 kg/m3) alone comes to nearly 100 metric tonnes. When you add in the steel reinforcement, steel antenna structures, aluminum cladding and other ancillary components... the total mass of debris was probably 110-120 metric tonnes, falling from an estimated height of 21 storeys (70-75m/230-250 ft).

The force on impact of a 100-tonne object falling from 70m can be approximately calculated as follows:

[ PE: potential energy (Joules); KE: kinetic energy (Joules); M: mass (kg); v: velocity (m/s - metres per second); h: height (m - metres); g: gravitational acceleration (metres per second squared - m/s2); 'Weight'-Force: (kg.m/s2 or Newtons - N) ]

KE at impact = PE of the object at rest
=> 1/2(m)(v)(v) = mgh = (100,000)(9.8)(70) 
= 68,600,000 J.

=> Impact velocity v = root of (2gh) = 37 m/s = 133 km/h

Assuming stopping distance = 6m (distance of penetration into the ground)

=> Force on impact = 1,143,333 N or 1,143 kN.

To put that into relatable perspective: if you place a 1 litre bottle of water on your hand, that exerts a downward force of approx 10N (9.8N) on your hand. The impact force of the debris was 114,333 times of that.

Alternatively, this is equivalent to a bundle of 7 fully-loaded RapidPenang buses impacting simultaneously at 133km/h.