Experimental and finite element analysis of protected composite cellular beams of different span length

Abstract

Cellular beams are widely spread structural elements in the modern construction industry having as main characteristic the web openings. Cellular beams are produced through a fabrication process from solid beams and have bigger section depth than the parent beam. In buildings design with need of open large spaces cellular beams can be used in long span, up to 20 metres, without the necessity of including columns. The most common protection material applied in cellular beams is intumescent coating, giving the advantages of allowing the passage for technical services through the web openings and adding an aesthetic look to the beams.

This PhD research investigates the behaviour of short-span and long-span composite protected with intumescent coating cellular beams in fire conditions, performing experimentally and analytical studies. The experimental process performed in FireSERT laboratory, tested under ISO-834 standard fire curve three composite protected with water based intumescent coating for 60 minutes cellular beams with different geometries but same 4.5 metres span. The furnace fire tests showed that the temperature distribution on protected cellular beams in non-uniform and the failure modes are web post buckling and Vierendeel bending. The collected results were compared with other furnace tests, which were previously emulated in the same conditions, although using unprotected beams. These comparative analyses showed that on the protected beams the temperature increase is slower and maximum deflections lower.

The recorded results were used for calibrating finite element models based on the geometryand properties of tested composite cellular beams using TNO-Diana software. The finiteelement modelling results showed high correlation with the experimental results givingconfidence to be used for further studies as part of the research. Following, has beenconducted a validation of the Eurocode 3 formula for calculating the temperature increaseon protected steel members. The finite element analysis performed based on thetemperature results given by the formula showed that further improvements should bemade in Eurocode 3 equation in order to be safely used by structural fire engineers in thecase of cellular beams. Furthermore, the same three cellular beams were modelled considering three cases of partial protections applied on the beams section demonstratingthe progressive collapse of the structural element when the protection layer decreases dueto the increase of temperature.

Finite element analysis is performed for the behaviour of long –span composite cellularbeams under 2-point mechanical and standard fire curve load. Finally, this study isintroducing a finite element method for modelling long span protected and unprotectedcomposite cellular beams. The finite element model is representing one of the secondaryunprotected long-span cellular beams and half concrete slab area, from the large-scalenatural fire compartment test, designed and performed by FireSERT, at University of Ulster(Nadjai et al., 2011). A detailed investigation on the long-span cellular beams failuremechanism when exposed at elevated temperatures is presented. The main failure modeson long-span cellular beams are lateral and torsional buckling of the bottom tee.

Thesis is embargoed until 30th June 2016

Date of Award	May 2014
Original language	English
Sponsors	Vice Chancellor's Research Scholarship (VCRS)
Supervisor	Ali Nadjai (Supervisor) & Faris Ali (Supervisor)