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Question 11
My brother and a few friends were killed in the collapse of the Rana Plaza in Bangladesh on 24 April 2013. Now my mother is very ill due to great grief and all the family members are in deep depression and need to be treated by the Psychiatrists. We want to do something to prevent something similar from happening, is there a simple way to check and prevent? (dated 26 May 2013)
The Answer:
When the aforesaid news were reported in Singapore, practically all the Singaporeans were so shock and everyone we know was talking about it. We felt very sad for you and we would like to offer our condolences to all the victims’ families and friends.
See My Paper dated 6 May 2013, page A3 extracted below.
The simplest way to prevent similar incidents from happening could be the following: When you see a Building being completed for a few years or after many years, and you see suddenly more stories (or even 1 storey) is going to erect above it, quickly report to the Building Authorities. The Building Authorities would then check whether the erection has been approved and they would do the necessary to help.
What would a Responsible Engineer normally do?
To increase the usage of a Building by erecting more floors above it is not a simple matter. Normally, a responsible Structural Engineer would perform the following steps before he / she decides whether it is feasible:
a) Retrieve all the Structural Drawings to check that all the structural members especially the beams (in the case when new columns are going to erect above any of them), all the columns and the foundations (likely to be piled foundation for a 6-storey Building with Basement) are able to carry the new loads of the stories to be erected above. There could be complications if the Structural Drawings could not be found due to the various reasons of the past, then the ascertaining of the structural details of each structural element becomes complicated or impossible even with the use of non-destructive testing.
b) To devise strengthening measures on the beams, columns or foundation to increase their strength / carrying capacities if any of the aforesaid is likely to fail under the increased loads. This could mean using strengthening measures such as the fibre wraps to increase the column capacity, install more beams to carry any new column loads above it (for any new column supporting by any of the transfer beam) and to install more piles to increase the foundation capacities.
c) Even the columns and the beams structural issues could be settled, to increase the foundation loading capacities remain to be the most challenging task for a completed building, as the piling might not be able to perform due to headroom constraints of the Basement or the 1st storey in this case. We have seen an example in UK how a Builder erected the 2nd storey after knowing that the existing 1 storey structural members are not able to carry the new loads. They erected new foundation system outside the existing structure and have the new structure bridge across the existing 1 storey structure, making the 2nd storey structure behaves as a “Separate Building” and not in any way relying on the original building below for supporting its loads. They had done it so beautifully that the new truss structure connecting the 2nd storey to the new foundation to integrate perfectly with the appearance of the 1st Storey Structure; making the whole entity aesthetically pleasing to look at.
d) The steps in (a) to (c) could be omitted if the original structure has been designed and built with the new erection in mind and have already catered for them in the original construction. This kind of situation is quite rare as the construction of a Building with Basement is quite costly and many a times, the owner is already being financially stressed with the basic construction cost.
e) A brand new analysis needs to be performed taking into considerations the pattern loadings and other new loads above (Dead Loads and Live Loads) including the gigantic electrical generators and basic horizontal loadings including wind loads and decide how it would affect the entire structure in this case.
What are the other Complications?
The original Rana Plaza was designed to be a commercial building, but part of it was eventually used for industrial purposes – this has great implications; as the designed loads that Structural Engineers use for the commercial purposes are much lower than that of Industrial use (as heavy machineries and equipment need to be considered), with the added 3-4 stories above it; making the entire matter worse. This is causing great distress to the original structure and its foundations and causing them to fail and collapse.
The 4 gigantic electrical generators had worsened the aforesaid situation by inducing vibrations to the already “distressed structure”. It was not mentioned whether these supporting bases had been installed with Dampers to lessen the vibrations acting on the structure. Good Dampers are in fact very efficient to reduce any kind of vibrations at the supports of these Generators.
You need to know that reinforced-concrete is not an “as good material” to be used in construction compared to steel. The moment it is cured after casting, micro-cracks would start to develop in the concrete due to shrinkages, causing its strength to weaken, this is an automatic process. In other construction, some have lessened its micro-cracking effects by introducing fibres to automatic bridge the micro-cracks but it has evidently jacked up the construction cost due to the related complications such as the reduced flow speed of concrete in casting operations and others. That is why the Design Codes have included factors to be used to counteract this reduction in strength over the years. For a normal commercial building, the design life is normally around 100 years.
What are the warning signs before a Reinforced Concrete Structure Collapse?
In All Reinforced Concrete Structure collapse cases, the Structure always shows signs of distress before it fails / collapses. This could happen in the matter of days or months prior to that; telling the people that “I am coming down”.
These signs would include some pattern cracking which increases in widths starting from around 1mm and widening continuously indefinitely, forming other cracks until the structure fails either locally or entirely. The speed of cracking would increase further when the structure is located in a moist / corrosive environment, where the moisture / corrosive vapors would corrode the steel bars in the reinforced concrete element, causing detachment and concrete to spall and expose part of these steel bars.
Thus you could watch for these signs and advise the people to avoid these places until the Building Authority has checked to be safe for occupation.
Conclusion
I hope that with the aforesaid, I have given you sufficient information concerning your query.
I hope that you and your family would slowly recover from your grief and pick up the courage to go on in life.
Through the dead victims, we have received a message: It is for every one of us, including myself to amend our lives. Yes, it is to do our work with love, no matter whether we are professionals or not; it is to view all others under our care as brothers and sisters whose lives God wants us to help & to protect. The person beside us is not just a stranger, he or she is our brother / our sister, and there is nothing more valuable than each human life - made in the image of God and capable of doing great things to make the world a better place with their valuable contributions… Drafted by: Er. Goh Cheow Leng Maria First drafted on 26 May 2013. |
