CROSS Safety Report
Alteration to historic column bases causes settlement issues
This report is over 2 years old
Historic timber columns settled and tilted after unauthorised changes were made to their foundation bases.
Key Learning Outcomes
For clients and construction professionals:
Deviations from the construction drawings and specifications should never be made without approval from the design engineer
There is always a risk that safety will be compromised when allowances for competent site supervision are cut
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On this small project says a reporter, a structural engineer was commissioned by a contractor to recommend required works for the improvement of first floor living quarters over a shop. The fragile building was over 100 years old with the first floor projected over a pavement and supported by timber columns. These were on sandstone stub columns projecting above pavement line.
The contractor was instructed to ascertain the condition of a column base but to leave it undisturbed as it had been stable for many years and there was no additional load being applied as a result of the work. Without informing the structural engineer, the contractor, together with the building inspector, decided that the base should be investigated. Finding it bearing onto a sand layer they then decided to introduce a concrete pad beneath the stub columns at each end of the row.
The beams either side of the columns were propped and an in-situ pad was formed. As a result of this work, settlement occurred quite soon after removal of the props. This resulted in the column moving (tilting) horizontally so that an unstable condition was created. Remedial work was eventually undertaken but not before a major city road had been closed off due to a potentially dangerous public situation.
As a result of this work, settlement occurred quite soon after removal of the props. This resulted in the column moving (tilting) horizontally so that an unstable condition was created.
There was an informality about contractual arrangements which with hindsight is dangerous. However, on very small works this is a possibility. There was trust in the contractor carrying out instructions to the letter. It was also clear that in a bid to cut costs (corners) by the building owner, supervision was excluded from the contractor/engineer instruction. It may be that such arrangements should not be entered into and that is good sense.
In any event, it became clear that the instruction, by a note on the drawing, did not contain enough emphasis to compel the contractor not to pursue the activity he did without consulting the engineer. No legal liability on the part of the engineer resulted from this work.
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