Tag Archives: fire

LITS -The peculiar behaviour of heated concrete

Like most materials, when you heat a piece of concrete, it expands.  Unlike most materials, when you heat a piece of concrete with a load on it, it expands less, or not at all, or it may even contract, depending on how big the load is – diagram below.  This unusual behaviour goes by a number of names such transient thermal strain, transient thermal creep, or load-induced thermal strain (LITS).   Here I will use LITS.

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LITS – in simple terms.  Concrete thermal expansion is stress dependent.

My interest in LITS began about eight years ago when then PhD student, Angus Law, started investigating its role in concrete-framed structures under fire.  Angus implemented a LITS model in Abaqus and showed that LITS can affect the behaviour of certain types of structural element substantially.   He also demonstrated the importance of correctly representing the multi-axial behaviour of LITS.

More recently two more PhD students working with me have started looking at LITS from very different angles: Continue reading

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How Hot are Fires?

I have been working for several years now with Guillermo Rein, Angus Law, Jamie Stern-Gottfried and others on “travelling fires” for structural design – that is, design fires where it is not assumed that the temperature remains the same in all parts of a fire compartment.  This research has been highly successful and resulted in prizes and journal publications.  However, for me, there remains a problem – the temperature of the travelling design fire is too hot! Continue reading