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CROSS Safety Report

Flaws with partial encasements around steel columns

Report ID: 517 Published: 1 January 2016 Region: CROSS-UK

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Overview

A structural assessment found that steel columns encased in concrete to mid-storey height were heavily corroded directly above the top of the encasements.

Key Learning Outcomes

For civil and structural design engineers:

  • Adequate corrosion protection for the given environment should be provided to all construction elements to ensure they perform as expected

  • Good detailing is also a prerequisite for longevity and the safety of a structure

For building owners and managers:

  • Regular inspections and maintenance can help keep a structure safe and to detect any obvious maintenance issues

Full Report

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A structural assessment was carried out on a 40 year old steel framed structure in a pharmaceutical plant. Concrete encasements, with flat tops, had been formed up to mid-storey height around steel columns. Heavy corrosion was apparent at mid-storey height i.e. directly above the top of the encasements.

The encasements were cracked below mid-story height and upon removal of the concrete, it was found that the thickness of the steel columns were substantially reduced. Vapours and liquids had gathered on the flat surface and corroded the steel overtime. The absence of maintenance and the humid atmosphere (high temperature process area) aided the rate of corrosion.

To avoid this problem, the reporter recommends the following:

  • Form a chamfer around the top of concrete encasements

  • Avoid stopping the encasements at mid-storey height

  • Galvanise steelwork in corrosive environments

  • Ensure that the steel to concrete joint is adequate to mitigate liquid/moisture ingress

Expert Panel Comments

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Corrosion on older assets in harsh industrial environments is commonplace, and potentially critical to stability and hence safe use. This is a legacy of an era when inadequate attention was given to life-long performance, often coupled with less than adequate inspections over its life. Good detailing is a prerequisite for longevity and the safety of a structure only exists at a point in time related to the as-built condition.

Good detailing is a prerequisite for longevity and the safety of a structure only exists at a point in time related to the as-built condition

In all refurbishment projects, a key part of the work should be to fully assess the structure’s state as far as is possible. Cracking should be investigated as previous repairs to the concrete may not have addressed any underlying section loss. Such investigations should also consider the possibility that the encasement is providing an unintended load path and therefore removal may impact the element capacity.

A building being used as a workplace should be capable of supporting all foreseeable loads imposed upon it (Workplace (Health, Safety and Welfare) Regulations 1992). Depending upon the nature of the workplace, a foreseeable load might include accidental impact from a forklift truck.

Whilst this might be the precise reason for encasing the columns, given the reporter’s findings, it may be appropriate to implement additional measures that remove or reduce the risk of accidental impact.

The reporter’s recommendations are very sensible and if adopted as a matter of course would improve the life of new constructions.

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