News From CROSS - Confidential Reporting of Structural Safety

Cross Newsletter 18 reports on lessons that can be learnt from failures and near misses in the construction industry. A selection of the issues are provided below.

Concern has been expressed at the level of professional fees being accepted by some clients. An example has been cited of an existing commercial building that it is proposed to converted to flats with an estimated contract value of £1.5m. The client has apparently appointed a sole proprietor business. The main concern is that the fees for a full investigation of existing structure, addition of an extra floor, and full design and drawing service was £4,300 i.e. about 0.3%. This is considered an order of magnitude far too low to permit a proper professional service, normal fees would be considered closer to 2% and ideally 3% inclusive of investigations and RC detailing. This is an oft repeated tale, particularly in current difficult times. However, strictly it is not fees per se which determine the legal position, if a professional takes on a job for nothing they still bear the duty of care in their work. Whilst the unscrupulous may think they have a bargain, the client has a legal duty to ensure that they appoint competent parties, adequately resourced. Failure to comply with this can lead to prosecution and fines or in worst cases prison (see http://www.hse.gov.uk/press/2010/coi-nw-027smithwallace.htm?ebul=cons/may10&cr=12 ) . Those appointing professionals so far below typical market rates should ensure that they have suitable qualifications, experience, resources and insurances. Fee quotations that are far below the average should always be treated with suspicion because there is no way that one person can be that more efficient that they can produce competent work in less than a quarter of the time of other reasonable engineers. The question should be asked what are they not doing that others are!

Gain in Strength of Mortar Slower Than Concrete
Concern has been expressed regarding the use of brickwork instead of padstones.
The report involves a project where 600mm long padstones were specified to support steel beams over a wall but four courses of Engineering grade B bricks were substituted (not by the designer). The change was made purely on cost and handling grounds. The programme was such that the next floor of precast units was installed after a week, causing the brickwork to settle and crack. Whilst multiple unit brick bearings may provide an attractive handling and cost solution, it must be noted that the gain in strength and stiffness will be nearer the 28 days for brickwork. Brickwork does not have the inherent robustness of an in-situ concrete component.
It is recommended that any wet placed material such as masonry mortars or indeed in-situ concrete has a period of curing to establish sufficient strength for loading. The full strength gain is normally expected to occur at 28 days, but loading of upper construction can take place earlier as usually only dead load is being added.

At high load positions under beams, in-situ or precast concrete spreaders are better options. Padstones need to be of the right proportions to distribute the concentrated loading and any bedding mortars need to be specified correctly with time given for them to reach a suitable strength to carry construction loads from above. Substitution of a component on site without reference to the designer is an unacceptable practice.

Full reports can be found at http://www.cross-structural-safety.org