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Desktop Investigation on SK Jerangau "roof beam" failure

posted Feb 24, 2018, 11:18 PM by jeffery jim   [ updated Feb 24, 2018, 11:22 PM ]

1. The building was constructed between 2008 to 2010 using design and built concept. The construction adopted IBS system where JKR forensic highlights the issue of dowels that linked the existing beam to the non-homogeneous precast beam/slab which is designated as transfer beam/slab to carry rooftop water tank. This is the time when CIDB spearheads the use of IBS system in building construction and I believe the in-house consultant is not knowledgeable or competent in IBS system.

2. The issue here is almost like the shearing of reinforcement bars as dowels which are only 3 inches long. In this case if we look at the configuration, the fallen beam is actually an extended slab for the rooftop water tank. For that reason there is no evidence of connection at the end of the beam/slab, instead dowel bars at the side and on of the central gravity for the slab.

3. The heavy slab (700kg estimated) plus the water tank, say 1000kg for 1000 liter leads to development of large moment (force multiply by distance, rotation) where uniform load. 3 inch connection spells disaster where the concrete cover is around 1 inch each side which means the dowels effective strength is 1/2 inch at both side into the concrete. This causes tear-off at the original structure and not shearing of the dowel as clearly seen in the photo.

4. Other possible reason for aggravation to these dowels is the deflection of the beam/slab due to poor reinforcement. Apart from that, it is possible that the collapsed structure was sitting on the top floor and exposed to creep from heat expansion. Different concrete types have different thermal expansion coefficient and linking both with different materials leads to imbalance and cause cracking. Besides that it is probably the indirect result of high humidity which leads to corrosion where the exposed dowel between the additional piece and the original, and the loss of dowel friction capacity.

5. This failure of dowel or bolting is similar to the tragedy occurred at the Stock Exchange Jakarta.

6. This is the author's opinion and only for the purpose of structure forensic study.