BLOCK 538 ANG MO KIO AVENUE 5 (Cause of crack of column)

Mr Low Thia Khiang asked the Acting Minister for National Development what is the root cause of the serious crack of the column at Block 538 Ang Mo Kio Avenue 5 and whether he will assure the public that similar incidents will not occur in other housing estates.

Mr Lim Hng Kiang: Mr Speaker, Sir, the root cause of the crack was the poor quality of the concrete in that particular column. As my Ministry has earlier announced, the column has since been repaired and reinforced to six times its design strength. HDB has also confirmed that the remaining columns in Block 538 are all structurally sound, and that the building as a whole can carry three times the normal load it is designed to bear.

I assure the public that this incident was an isolated case, and that all HDB buildings are structurally sound. HDB buildings are designed in such a way that even if one column is damaged, the overall stability of the building will not be affected, as the load on that column will be spread to the other columns.

Mr Low Thia Khiang: Sir, did the HDB specify the grade of concrete that should be used for the structure?

Mr Lim Hng Kiang: All the materials and all the designs in HDB flats are built according to the building code. So the quality of concrete was stipulated according to the building code.

Mr Low Thia Khiang: If the quality of material is specified, how could this particular column fail because of poor quality of concrete?

Mr Lim Hng Kiang: Mr Speaker, Sir, we are also a bit perplexed as to how that could happen, because HDB constructs millions of columns and this is one column that has failed. HDB has in place a very strict quality control system of examining the quality of the concrete before it is set in situ, especially for load-bearing columns. So we assess that this is a very isolated case. Out of the millions of columns we built, this is the only column that has cracked. We are not sure how it happened. It was probably due to poor workmanship at the point where the column was being cast.

Mr Low Thia Khiang: Mr Speaker, Sir, I understand from the Acting Minister that it was due to poor quality of concrete, but he mentioned about poor workmanship. My supplementary question is: if that happens once in this particular case, and he has mentioned that we have built millions of columns, would the same kind of incident happen in other blocks due probably to other factors?

Mr Lim Hng Kiang: Mr Speaker, Sir, HDB has a very stringent system of building inspections, done both by the Town Councils as well as by the structural teams in HDB. All HDB flats are inspected once every 10 years, as required under the law. In addition, if there are any cracks on load-bearing structures, HDB will immediately investigate. Our experience so far is that our buildings are built according to specifications and they are safe. In this particular case, the poor quality of the concrete could be due, as I said, to the mixing of the concrete when it was being constructed.

Mr Low Thia Khiang: Sir, does the HDB have an existing system of inspection of flats, especially structural loads, during a certain year to ensure safety or detection of possible concrete failure?

Mr Lim Hng Kiang: Mr Speaker, Sir, as I mentioned just now, under the Building Control Act, all residential buildings must be inspected at least once every 10 years. HDB has done so. In addition, HDB's structural engineers go round the flats all the time, especially if there are complaints about cracks or problems of defect. So HDB has a systematic programme to inspect all its buildings.

Let me also stress the point I made earlier. The buildings are designed in such a way that even if one column has cracked due to the poor grade of concrete in that column, the rest of the columns will be able to take the load. It is designed to take up to three times. So there is plenty of redundancy, a very high safety factor.

Mr Chiam See Tong: Sir, the Minister has said that the pillar of this particular block has been strengthened six times. Why is there a necessity? Normally, I believe, it is only three times. Has the HDB assumed that the others were also about to buckle up?

Mr Lim Hng Kiang: First of all, all the other columns have been inspected by HDB. As our press statement indicated earlier towards the end of last month, all the columns have been assessed to have a safety factor of at least 1.8, that means, all the columns in this block have a safety factor of at least 1.8. In this particular column which cracked, HDB put in the steel reinforcement. When you put in the steel reinforcement, and the encasement of concrete around it, you need a certain cover, and therefore it ends up six times.

Mr Chiam See Tong: In view of this incident, has the HDB stepped up its inspection of other blocks of flats built about that time?

Mr Lim Hng Kiang: HDB has an on-going programme of inspecting all its blocks regularly once every 10 years. In view of this, HDB is putting more resources to also conduct more inspections.

Mr Chiam See Tong: Can the Minister tell us, in view of this incident and that he has stepped up inspection, what is the result of the inspection so far?

Mr Lim Hng Kiang: HDB has been inspecting its blocks since 1991 after the introduction of the Building Control Act, and all the blocks have been safe. We are accelerating the inspection and we will know the results as inspections are under way. Let me assure him that all the blocks are safe.