Never Under Estimate The Power of Wind
It was late Sunday afternoon and a powerfull gust of wind came ripping through the front section of two factory units, as the wind blew inside the building, the wind had no where to go but to the rear of the building, with no rear door open, the wind had to go somewhere, and it did, up and out, blowing out two sections of roof, purlins and roof sheets, the whole two bays.
One bay was flipped back onto the main roof on the factory, the other was just blown out and landed on the factory roof next door at least 10m away. Each roof section measured 7m x 6m (42 square meters) and weighed aprox 900 kgs.
When I arrived on the Monday morning and walked to the rear of the factory, I had never seen anything like it, standing on the ground and looking up, all I could see was blue sky, both bays were missing. The wind had blown out each roof section.
Upon closer inspection, I found that most of the C200 purlins had been ripped like they were made of paper and the purlin bolts were snaped in half, I could not believe the power of the wind and the damage it had done.
After looking at the purlin ends and the double brick wall at the end of the building, it was obvious that the purlins had only been bricked into the top course of the factory wall, there was nothing structual holding/tying the purlins down to the gable end of the building. This was obviously why each of the roof sections did not stay in position under wind load and remained vulnerable to up lift in a high wind.
When the assessor arrived from the insurance company, even he could not believe what he was looking at. After explaining to him my thoughts on how this happened, I suggested to the assessor that we get an engineer out here to recommend a way that we could properly tie in the purlins so that this would never happen again.
The engineer arrived that afternoon the first thing he said “this builder has cut corners when he built this factory” the engineer recommended that a length of 3/8 threaded rod be bolted to the end of each purlin and the rod placed down the cavity (between the bricks). Where the base of the rod ended up, bricks were removed so a ½ thick galvanised MS plate 200 x 200 with a 3/8 centred hole was fixed to the base of the rod and tensioned to lock the purlin ends down to the building. After inspection by the engineer the holes in the brick work were then bricked up. This is how it should have been done in the first place.
On completion of all recommended structual work and the installation of all purlins had been done, we fixed new box gutter brackets, flooring and box gutters. We then craned up new roof sheets, all flashings and insulation. The job was completed within a week with little inconvenience to the business owner. Since the completion of this job there have been winds even stronger than what caused this damage, the roof sections still remain there today.