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Buildings Department report on building collapse in Ma Tau Wai Road and inspection results of buildings aged 50 or above (with photos/video)
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     The Buildings Department today (April 26) released the investigation report on the building collapse at 45J Ma Tau Wai Road. A column damaged by some external forces may have caused the building to collapse.

     The building at 45J Ma Tau Wai Road was a five-storey tenement building (with a mezzanine floor) of reinforced concrete construction.  Its occupation permit was issued in September 1955.  After the collapse of the building on January 29, 2010, the Buildings Department carried out an investigation from three aspects with a view to establishing the cause of the collapse: first, review of the building records on repair, addition and alteration works; second, carrying out of site inspections, examination of evidence gathered and laboratory tests on samples collected from the site; and third, study of witness statements and interviews with the relevant parties.

     Based on the information gathered and analyses derived from the investigation under the aforementioned three aspects, the Buildings Department focused the investigation on the three collapsed columns situated on the ground level of the building, i.e., C11, C12 and C13 (shown in the diagram attached).

     During the investigation, assessments were made on the structural capacity of the building under the different scenarios of loading conditions, including additional loading imposed by the sub-divided flats on the upper floors, material ageing conditions, appraised deteriorated conditions and the lack of timely maintenance.  The factors of safety of the building structure under all of these different loading conditions were found to be acceptable.  Therefore the above factors were not the causes of the building collapse.

     One of the assessment results confirmed that even though the aforementioned columns may have been subjected to inadequate or improper repair with noticeable signs of deterioration, resulting in the reduction of the effective column sizes thus diminishing the structural capacity, the factors of safety were still acceptable and should not have caused the building to collapse.

     Based on the structurally asymmetrical design and respective estimated loading capacity of columns C11, C12 and C13, as well as the information derived from further assessments (including force analysis on the condition of the column remnants, distribution of debris on the site, and pattern of collapse of the building), the Buildings Department believes that column C13, which was affected and damaged by some external forces, may have caused the collapse of the building.  When column C13 was disturbed, its loading capacity would be reduced.  As there was no provision for any precautionary measures (such as the erection of steel props and bracing ties) at the site to share out the loading, the loading that column C13 had to bear would have exceeded its ultimate loading capacity and the destructive effect spread to the nearby columns C11 and C12, thereby increasing the loading on these two columns.

     Once the three structurally asymmetrical columns C11, C12 and C13 reached their ultimate failure state, they would have crushed progressively within a very short period of time, causing the lower portion of about two storeys of the building to collapse.  The pull-down force so produced would have then caused the remaining upper portion of the building to collapse afterwards.

     The Buildings Department concluded that the collapse of the building at 45J was likely triggered by the disturbance of column C13 by some external forces.  As for the identification of the origin of these forces, further investigation has to be conducted including building material testing and forensic study.

     The Buildings Department also announced the results of the Department's inspection of about 4,000 buildings aged 50 or above in Hong Kong.

     Following the collapse of a building at 45J Ma Tau Wai Road on January 29, 2010, the Buildings Department began territory-wide inspections of about 4,000 buildings aged 50 or above to ascertain the safety of these buildings.  The special inspection exercise was completed at the end of February as scheduled.  A total of 4,011 buildings aged 50 or above were inspected.  The Department divided these target buildings into four categories and provided the breakdown as below:

Cat.I íV Buildings requiring emergency remedial works (2 buildings)
Cat.II íV Buildings with obvious defects found (1,030 buildings)
Cat.III íV Buildings with minor defects found (1,270 buildings)
Cat.IV íV Buildings with no apparent defect (1,709 buildings)

     The department's spokesman said, "Based on the findings from the special inspection exercise targeting these old buildings, we conclude that the buildings are structurally safe in general, though the two Cat. I buildings located in Kowloon City required emergency remedial works by government contractors.  In the first case, a loose window and loose rendering from the exteriors of the building were removed.  In the second case, cracks were found at a cantilevered slab balcony of the building.  Emergency shoring was erected as a protective measure pending the appointment of an Authorised Person by the building owner to conduct a detailed examination.  The overall structure of the two buildings was safe."  

     The Buildings Department will follow up by writing to the owners of the 4,011 buildings concerned to inform them of the inspection findings and remind them of the importance of timely maintenance of their buildings. Repair/investigation orders will be issued under the Buildings Ordinance (Chapter 123) to the Cat. I and II buildings.  In fact, among the buildings in these two categories, statutory orders have already been issued to 293 buildings in the course of the department's implementation of other enforcement programmes.  The department will follow up these orders to make sure that the owners properly repair their buildings.  The department has also begun issuing repair/investigation orders to the owners of the other 739 buildings.

     "Owners meeting the criteria may apply for financial assistance under the subsidy or loan schemes administered by the Buildings Department, Hong Kong Housing Society (HKHS) and Urban Renewal Authority (URA).  We will also consider selecting some buildings whose owners are having difficulties in co-ordinating repair works themselves and also facing financial difficulties, to be included as Category II target buildings under the Operation Building Bright (OBB) programme," the spokesman added.

     The spokesman also emphasised that building owners were responsible to regularly inspect and maintain their own private properties and common parts of their buildings.  They should make sure that their own private properties and common parts of their buildings are safe and in good condition.

      The report on the collapse of the building at 45J Ma Tau Wai Road and the report on inspection of buildings aged 50 or above have been uploaded to the website of the Buildings Department: www.bd.gov.hk .

Ends/Monday, April 26, 2010
Issued at HKT 19:57

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