HERA has been working with Dimond since 2014 on their new Hibond 80 deck product, with one of our work packages being the optimization of composite slabs using this deck in fire conditions.

From the know-how developed previously in assisting a Singaporean client, through advanced finite element analyses our Finite Element Analyst Nandor Mago was able to demonstrate that the bottom reinforcement bars traditionally included within the ribs of the composite slab could be eliminated by taking account of the deck in fire conditions to provide the main tension reinforcement (a practice that has been used in the UK since the 1980’s).

Furthermore, rather than adopting the code-defined minimum slab thicknesses for insulation that are given in Eurocode 4 and BS 5950-8, we were able to show that these could be reduced by 6% for this particular deck.

Loaded fire test close to being discontinued at Exova Warringtonfire with time in the background shown in hours, minutes and seconds

To validate the finite element analyses predictions, a loaded fire test on a composite slab using the Hibond 80 deck was undertaken in October 2016 at the world-renowned fire test lab Exova Warringtonfire in the UK. Apart from its prestige, the reason for selecting Exova Warringtonfire was that the larger furnace size provided compared to local laboratories meant that the heated span was equal to the maximum that would occur in practice.

However, apart from the location of the fire test being in the UK, the test specimen complied with the new Australasian composite design standard AS/NZS 2327. Moreover, unlike competitor products, the decking, reinforcing bars and shear studs were all sourced from New Zealand using local materials and the load level complied exactly with AS/NZS 1170.0.

The three functions of structural adequacy (R), Integrity (E) and Insulation (I) are universally recognised to define fire resistance rating (FRR) of structural elements in the standard test. Even with the shallower slab, the target FRR was set the onerous period of 120 minutes.

Our General Manager Structural Systems Dr Stephen Hicks, managed the fire test in person with the test specimen performing exceptionally well in fire conditions – where he was able to instruct the fire test be discontinued after it exceeded the target FRR by some margin.