Termisk analys av brandutsatta tunnelkonstruktioner med olika ytegenskaper
Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Tunnels are constructed to withstand a fire during a designed time period.In Sweden tunnels are dimensioned according to the Hydrocarbon (HC)temperature curve during 180 minutes. Fires in tunnels are different fromfires in compartments; the temperatures in a tunnel are more severe. Thegas temperatures may be higher than fires in compartments, which mayaffect the tunnel construction. A worst case scenario is that it may collapse.This will have a devastating outcome both for the tunnel owners and thefuture traffic situation. There are different ways of protecting tunnelstructures. One is to use insulation called Promatect-T boards. The productis used worldwide and used for analysis in the present study.The aim of the study is to gain knowledge about thermal impact on tunnelstructures. A finite element program called TASEF (Temperature Analysisin Structures Exposed to Fire) has been used throughout this study. InTASEF, tunnels have been dimensioned and different thermal loads hasbeen used as an input to see what temperatures are obtained in thereinforcement bars inside the concrete in the tunnel construction. Averification of a part in TASEF called TASEF-tube has been made, and ananalysis of the most optimal element size in TASEF-tube was also carriedout.During the verification of TASEF-tube, a comparison between thetemperatures at the end of the tunnel obtained from TASEF-tube and thetemperatures at the end of the tunnel obtained from an equation made fromDeWitt and Incropera was made. The length of the tunnel, the radius of thetunnel, the ventilation velocity and the heat transfer coefficient werechanged to see when the temperatures would correlate with each other.That occurred when a long tunnel and a high value of the heat transfercoefficient was used. Overall, TASEF and TASEF-tube is a quite goodprogram for dimensioning simple tubes to see the temperature flow insidethem.The optimal element size was analysed and calculated to three m, whichgave a relative error of 0.2%. Since the calculation times in TASEF are veryshort, and due to a limitation in TASEF regarding the number of nodes andthe number of elements, a longer element size could be used. For example,an element size of six m gave an absolute error at 5 degrees Celcius.A comparison between gas temperatures calculated by TASEF-tube and amodel developed by Jonatan Gehandler was made. Focus was only on thegas temperatures downstream a fire in a tunnel. Two different types oftunnel surfaces was used; concrete and calcium silicate (Promatect boards).The temperatures obtained from TASEF-tube and Gehandlers model didcorrelate well after approximately 200 seconds when using concrete as asurface in the tunnel structure. When calcium silicate was used, thetemperatures from Gehandler's model were higher than for TASEF-tubeduring the first 200 seconds.To study the thermal impact on concrete and the reinforcement bars inconcrete, different standardized temperature curves and experimental temperature curves obtained from full scale tests were compared. Thetemperature curves from the full scale test simulate a heavy good vehiclefire. The temperature curve from the full scale test also showed the samebehaviour as the temperature curve HC during a 60 minutes fire. Asuggestion is then to compare these results obtained in this study andcompare them to Swedish regulations, and see if a change could be made.Instead of dimensioning tunnels to withstand a HC fire during 180 minutes,a HC fire during 60 minutes could be enough. This is because if a fire wouldlast during 180 minutes, a spreading of the fire is needed.A last case during this study was to analyse if a spreading fire is moredangerous than a fire in one position. Input data from a model scale testwas used in TASEF, where one, two and three burning wood pilescorresponded to a burning heavy good vehicle. The obtained results showedthat a similar temperature development inside the reinforcement bar insidethe concrete could be seen when the temperatures were measured directlyabove the first burning wood pile. Further away from the first burning woodpile, the temperature evolution was different. The highest temperatureswere obtained approximately 50 m downstream the tunnel, and not directlyabove the fire source. The temperature evolution inside the concrete showedthat the differences between the burning wood piles are larger closer to thesurface of the concrete, but near the first reinforcement bars a similarbehaviour could be seen.
Place, publisher, year, edition, pages
2014. , 119 p.
Technology, Tunnel fires, Concrete, Reinforcement bars
IdentifiersURN: urn:nbn:se:ltu:diva-49329Local ID: 6b02944a-0479-4429-91e0-2ddebfa951b0OAI: oai:DiVA.org:ltu-49329DiVA: diva2:1022676
Subject / course
Student thesis, at least 30 credits
Fire Engineering, master's level
Validerat; 20141021 (global_studentproject_submitter)2016-10-042016-10-04Bibliographically approved