Damage to a column caused by external forces may have triggered the collapse of the building at 45J Ma Tau Wai Road on January 29, according to a Buildings Department investigation report.

Director of Buildings Au Choi-kai today said investigations are focused on three collapsed columns situated on the ground level of the building (C11, C12 and C13).

Under investigation: Director of Buildings Au Choi-kai says damage to column C13 caused by external forces may have triggered the collapse of the building at 45J Ma Tau Wai Road.

Assessments were made on the structural capacity of the building under different loading conditions, including additional loadings imposed by the sub-divided flats on the upper floors. The safety conditions were acceptable.

Although the 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 collapse.

Collapse causes

Based on the structurally asymmetrical design and respective estimated loading capacity of the three columns, as well as the information derived from further assessments, the department said column C13, which was affected and damaged by some external forces, may have caused the collapse. 

When column C13 was disturbed its loading capacity was reduced. As there was no provision of any precautionary measures at the site to share the load, the loading column C13 had to bear would have exceeded its capacity and the destructive effect spread to nearby columns C11 and C12, thereby increasing the loading on these two columns.

Once the three structurally asymmetrical columns 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.

The department concluded the collapse of the building at 45J was likely triggered by the disturbance of column C13 by external forces. Further investigations will be conducted to identify the origin of the forces. Click here for more investigation details.

Safety inspection results

The department also announced the results of its inspection of 4,011 buildings aged 50 or above. Two buildings require emergency remedial work, 1,030 have obvious defects, 1,270 have minor defects and 1,709 have no apparent defect.

The buildings are structurally safe in general, though the two buildings in Kowloon City require 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 has been 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 is safe.

The department will write to the owners of the 4,011 buildings to inform them of the findings and remind them of the importance of timely maintenance.

Repair and investigation orders will be issued to the buildings which require emergency remedial works or have obvious defects. Statutory orders have already been issued to 293 buildings in the course of the department's implementation of other enforcement programmes. The department will make sure the owners will properly repair their buildings. It has also begun issuing orders to the owners of the other 739 buildings.

Financial aid

Owners meeting the criteria can apply for financial assistance under the subsidy or loan schemes administered by the department, the Housing Society and Urban Renewal Authority.