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Case Study: Wind Design

posted Oct 16, 2016, 9:11 PM by jeffery jim   [ updated Jan 14, 2018, 3:42 PM ]

This is in Kuching, Sarawak. So engineers, what is the problem here? What will you suggest when you design awning in the future?


The problem with this is purely due to design problem and solely the fault of the designer (if the developer designated the civil engineer to design). Perhaps it would likely the addition to constructed building and installed by (uncertified) roofing specialist. The reason why i reckon this is due to the awning system where the bolting of the struts are irregular and did not embedded to the structural system but brick wall. Usually, engineers will tie these struts down to structural members with a dowel embedded to the steel reinforcements since the use of anchoring solution will not be as good as j-dowel in any pull-out test.


Was the wind too strong for overall design? No. There is one vertical signage which is standing robustly at the first photo. Malaysian Standard for Wind Load insist designs for roof, awning and signage to cater up to Typhoon/Cyclone Category I or II (depending on safety rating applied by designer), when this event only succumbed to the strongest wind speed from tropical depression.


The failure is not at the dowel point but the anchors linking to the aluminum frame to the strut. The strength of the wind was likely not considered during the design except for self imposed loading vertically. Bolts that hold and restrain the series of awning did not failed but the dynamic and amplitude of the aluminum structure when confronting the wind led to the shear force which tear off bolting holes and thus lead to larger hole. Larger holes (larger than the bolt and washer) significantly reduce allow the aluminum structure to slid off from the struts and failed.


Another reason which perhaps coupled to this free fall of awning is due to anchorage of the other end of the awning. These was loosely bolted to the concrete with small bolts, most likely using M8 size bolts.


The strong wind are funneled through the row of terrace houses on the left hand side of this building and thus increase the wind speed (remember your Bernoulli's Principle?) and coupled with vortex from the vertical sign boards. The movement of the awning behaved indifferently which formed wave-like due to the amplitude from the vortex.


Engineers should run wind load simulation when designing structures which are sensitive to wind load such as awning. Engineers should also consider the force and moment interacting on each node to ensure that the materials which the opted for are robust enough to function accordingly under stress.


** This is an educational article and should be use as it is


      

      


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