BRICKS, BLOCKS & LINTELS 37
Superlintels with Duragalv 70 post-galvanising, for spans up to 6m, were specified by lead consultants and architect, HKS, to meet minimum 65 years PFI design life for the external envelope at the University Hospital of North Staffordshire, Stoke.
The maths is quite simple. For instance, a steel lintel destined for an area of average (category 3) corrosivity will be subject to a zinc erosion rate of 1.5µ per annum. This means it needs a minimum 90 microns zinc coating to meet a minimum 60 year design life.
But there are other variables to factor into the equation, to maximise the reliability of
lintel service life figures and minimize the risk of durability failure.
Post-galvanising allows the control and totality of zinc coverage essential to achieving required service life.
The lintel is ‘hot dipped’ in molten zinc after fabrication to ensure a continuous,
metallurgically bonded coating, including corners, edges and hidden surfaces. Pre- galvanised lintels are prone to cuts and damage during fabrication that create areas of reduced protection that cannot be fully restored with supplementary paint.
The thickness of the coating developed during post-galvanising can be adjusted for a more accurate and cost-effective match with lifespan and location needs. But thicker steel will be needed to bond thicker coatings. For example, a minimum 4mm thick steel plate is needed to develop higher specifications of zinc coating (70+ microns).
All this provides a rigorous formula for specifying lintels with dependable and measurable longevity. Sound durability figures will reduce the costs of over-specification and the risk of durability failure, help budget control, and facilitate sustainable construction by minimising under and over-specification.
TOM WILSON, ASSOCIATE WITH JENKINS & POTTER, COMMENTS:
Calculated protection: Superlintels are made of minimum 4mm thick steel and hot dip post-galvanised with a choice of Duragalv zinc coatings for a cost-effective fit with project design life and location.
“As structural engineers, it is important that we consider and validate the longevity of individual structural components during the early stages of projects to enable us to ensure that the functionality and design life requirements established by our clients will be met. In addition, and particularly in relation to the more demanding criteria of public sector projects, we must fully appreciate the impact on the functionality of a building should intermediate maintenance be required to structural elements during its design life. By validating a component’s durability we can be confident of achieving modern and sustainable construction.”
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