Regarding the news reports yesterday that the investigation report will be made public soon, I would like to offer some of my views on what could have happened. Take note that these are all speculation and that I have no knowledge of what is contained in that report.
There are many factors that can contribute to a failure during the demolition process. These are:
1. Lacking in procedures and guidelines to carry out a safe demolition job.
2. Risk Assessment not completed before and during the demolition phase.
3. Site operatives not following laid down method statements on the sequence of work and procedures.
4. Inadequate temporary supports to the structure or the elements of the structure being demolished. Temporary support should be provided for any or combination of the following conditions:
a. When the whole or any part of the structure is subjected to excess loading derived from the demolition activities, movement of powered mechanical plants or debris accumulation. Overloading in term of impact of falling large debris and accumulated debris on the floor may cause the floor to give way and result in chain reaction effect to the lower floor. Extra loading from the machinery used on top of the building should also be considered to prevent excessive loading.
b. When any part of the structure or any element being demolished is not self-supporting; or
c. When the temporary stability of the structure or its elements could be impaired as a result of the demolition activities.
5. In case of prestessed concrete structure (constructed of either precast or cast-in-place concrete in which prestressing is introduced to the concrete by tensioning the steel reinforcement, or tendon, to counteract a desired degree of stress resulting from a given external loading – Hong Kong Code of Practice for Demolition) any accidental and unplanned cutting of tendons may cause the elements of building structure (Beams or Slabs) to rapture and become unstable. The prestressed concrete floor system shall be properly shored prior to detensioning to prevent the collapse of the system. The release of energy during the demolition of prestressed concrete could be extremely hazardous.
6. Lack of site supervision and inspection during the demolition job.
These are some of the general factors that can cause failure during demolition works. I am in no way referring to any specific cases here!
I'm interested in all aspects of demolition and bringing down old buildings, and this is my blog relating to the collapse of the old jaya supermarket. I find this case very interesting and am keeping track of developments as they happen.
About Me
- JMC Engineer
- Engineer by training! USed to work very closely with construction industry as subcon. Fascinated by the process of turning perfectly good buildings into rubble. call it a childhood obsession, I used to build then destroy lego towns and knock down other boys sandcastles on the beach!
