CROSS Safety Report
Dangerous alterations to steel beam supports
This report is over 2 years old
A local authority building control officer went to site and witnessed on an upper floor that the columns had been removed out of sequence, before the new frame had been constructed.
Key Learning Outcomes
For construction professionals:
Quality control and competent supervision on site can help to ensure that the structure is built in accordance with the design
Effective communication of essential design information in an accessible form to tradespeople working on site can also ensure the works are in accordance with the design intent
Consider appointing a competent temporary works coordinator (TWC) on site who can ensure all temporary works are carefully considered and planned
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An existing building was being converted to another use, says a reporter. The structure is being replaced, but the facade retained. The construction method was to create a new frame within the existing, with columns punching through the existing slab. The facade was then to be tied into the new frame and the old structure removed. The local authority building control officer went to site and witnessed on an upper floor that the columns had been removed out of sequence, before the new frame had been constructed (Figure 1).
The existing beam over had been left simply supported, with no continuity over the columns. Upon removal of the columns, the beam tripled in length and with load reversal at the column points, the compression flange had no positive connection (Figure 2). It seemed that the floor over was spanning through membrane action, as there was luckily very good tying between members.
The building control officer asked for the beams to be propped immediately and no damage occurred. The reporter says that this highlights poor site control, an inadequate construction plan and a lack of understanding of the structure by the site operatives. Furthermore, they say, the structural engineer did not make any visits to the site.
Expert Panel Comments
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Judging by the number of failures that are reported to CROSS, the skills of assessing temporary stability during construction or alteration seem to be lacking. In any alteration there is no substitute for breaking down the planned changes into discrete steps and for then assessing strength and stability at each stage.
The CDM Regulations 2015 make clear that both phases be adequately planned, managed and monitored by the designers. It is good practice to refer the contractor to the Health and Safety Executive page Temporary Works (TW) FAQs which advises the appointment of a temporary works coordinator who then needs to direct the design and sequencing of the temporary works. It also requires that those involved have the right skills, knowledge, training and experience to carry out the tasks required of them.
Site monitoring is often neglected in terms of risk management, but it is a question that would arise in any formal proceedings in the event of failure. Insurers sometimes advise engineers to limit site visits unless specifically included in agreements and temporary works are generally additional services. CIRIA is currently (2015) undertaking a review of structural stability during alteration work and a series of recommendations will be published in due course.
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