Incident 

The tragic incident resulted in over 100 deaths and hundreds of injured people. Below are some rare photographs that does not include victims and graphic content.

The Crane

The crane that tilted that day was "LIEBHERR LR-11350 crawler crane". This is a mobile heavy-duty crane that uses counter-weights for balance. The specs and dimensions of the crane are accessed by the manufacturer's manual for this work.

Conditions 

Mecca was under unusually heavy weather conditions that day.  There were Strong winds with a sandstorm, 80-105 km/h wind speed, sudden 20 degree temperature drop, and the crane had a 190 m boom length.

Manufacturer's Investigation

Manufacturer Liebherr released a investigation report that states that, the crane was faultless. After this report, a question has risen up. What was the cause then? With some "journalism" it is answered easily below.

According to the manufacturer's 35 km/h max wind speed allowance statement, it is crystal clear that the crane was above the limits even with 2x safety factor.

So what should an engineer or operator should've done to prevent this from happening?

The question is answered in the crane's operator manual (see below).

Those operator manual screenshots make it very clear what to do. The crane must be completely taken down under those extreme conditions. This could be prevented if necessary measures are taken on time. The reasons for not taking preventative actions on time may vary, but our scope here is on the technical side. 

Let's explain the collapse mathematically.

To do that, calculations were made on the actual sketches of the collapsed crane step by step.

Acting Forces Force Directions

▪Gravitational force of boom  -cw (clockwise)

▪Tension force of derrick ballast -ccw (counter-clockwise)

▪Gravitational force of central ballast  -cw

▪Wind force  -ccw

▪Gravitational force of crawler  -cw

▪Counterweight  -ccw

▪Pin supports’s reaction forces 

As a result of these couple "moments", the crawler Crane tilted counter-clockwise (ccw) direction.  Now that we know the direction of the forces, we can try to calculate how much force was actually applied to the crane by the wind. To do that, we need some assumptions for the sake of easy calculation without compromising the realistic approach.

Assumptions 

▪Weight of 190m Crane jib is neglected.

▪All the weight and dimension and angle information are taken from Crane’s manufacturer or calculated from given values.

▪The wind effect calculation of Crane is based on the cylinder structure drag coefficient  (C =0.82).

▪Air density is assumed to be at sea level (rho=1.225 kg/m^3)

▪Air drag force has been calculated for the perpendicular cylinder structure with the same dimensions as the Crane.

▪Crane is not on the load.

As a result of over 220 KN wind force, the 190 m height crawler crane tilted backwards. 

What could have been done to save the day at the minimum? The below calculation gives the bare minimum solution to prevent the accident. The calculation has some major flaws, however, gives some notion of what are the resultant forces that day. 

Note: To achieve more realistic air drag force, the calculation must include smaller cylinders, the numbers and sizes of which are determined by more closely inspecting the crane structure.

All in all, in spite of some exaggerated assumptions for the sake of calculation, it is clear that some major actions should've taken to avoid disaster.  I hope that the calculation gives engineers some notion of what forces are we dealing with when designing similar structures.