Fire hazard in tunnels: review, assessment, and mitigation strategies Kodur V.K.R., Bhatt P. P.

Fire in a tunnel is a rare probability, but it represents a severe hazard to the tunnel structure and can lead to significant loss of life, property damage, and traffic disruptions. At present, tunnel design codes and standards, unlike building codes, do not provide specific fire resistance provisions for the design of tunnel structure. However, the fire incidents in the last few decades have opened a debate on the need for fire resistance provisions to structural members in tunnels. This paper presents an overview of fire hazard in tunnels. The magnitude of fire hazard in tunnels is highlighted through tunnel fire incidents in the past few decades. The fire scenario in tunnel is characterized and the factors influencing the performance of tunnels under fire conditions are presented. Various strategies for mitigating fire hazard in tunnels are outlined. Further, a strategy to undertake post-fire assessment of tunnels is outlined. Finally, Knowledge gaps relating to fire problem in tunnels, together with research needs for enhancing the fire safety in tunnels, are discussed.

Behavior of high-density polyethylene fiber reinforced concrete exposed to elevated temperatures of about 220°C Maheswara Marabathina Rao, Sanjaya K. Patro

Fiber-reinforced concrete has been popular in its use in the recent past. Limited authors have reported the influences of high-density polyethylene (HDPE) fiber in concrete. There is a possibility that the concrete may be exposed to higher temperatures. The mechanical and microstructure properties of high-density polyethylene fiber reinforced concrete (HDPE-FC) exposed to higher temperatures up to 220°C have been investigated in this study. Thus, this study shall add some helpful information on the behavior of HDPE-FC at elevated temperatures. Experiments disclosed the influences of temperature treatment on the mechanical properties of HDPE fiber reinforced concrete. Melting of fiber due to the application of temperatures up to 125°C promotes smaller channels in the concrete. Differential scanning calorimetric (DSC) and thermogravimetric (TG) disclosed the temperature ranges of the dissolution reactions in the HDPE fiber reinforced concrete. Scanning electron microscope (SEM) examination showed additional pores and smaller conduits formed in the concrete due to the melting of fiber.

A study on thermo-mechanical behavior of concrete subjected to thermal cycles B. Vidya, K. Srinivasa Rao

As the use of high-strength concrete becomes common, the risk of exposing it to high temperatures also increased. The behavior of high strength concrete under elevated temperatures differs from that of normal strength concrete. When concrete is exposed to elevated temperatures, it begins to experience dehydration reactions in the hydrated cement paste, possible thermal incompatibilities between paste and aggregate and eventual physico-chemical deterioration of the aggregate. Typically, such degradation is accompanied by a decrease in the strength and weight of the concrete. Moreover, repeated thermal cycling due to fluctuating temperatures reduces the peak strength and could loosen the bond between the cement and aggregate. The thermal gradients and induced thermal stresses could trigger micro cracking, crumbling and spalling of the concrete.

Hence, an investigation on the behavior of standard and high strength concrete, exposed to thermal cycles at elevated temperatures was carried out. They were carried out on concrete specimens of age 28 days and exposed to temperatures from 100 to 400°C for 8 hours duration and subsequent air cooling for the remaining period of a day. Therefore, one thermal cycle means 8 hours heating and 16 hours cooling. Thermogravimetric analysis (TGA) has been carried out to study thermal stability of standard concrete and high strength concrete and based on this study the critical temperature of concrete is found to be 400°C. The mechanical properties studied in this work are compressive strength, split tensile strength and flexural strength. The results obtained can be useful as guidelines for fire resistant design of the structures subjected to heating and cooling cycles at elevated temperatures.

Mechanical and micro structural studies of fiber reinforced high performance mortar mixtures at elevated temperature Shaswat Kumar Das, Sambita Sahoo, Sanjaya Kumar Patro, Syed M. Mustakim

The present study evaluates the effectiveness of two different fibers, i.e., steel and Polypropylene (PP), along with their hybridisation on the resistance properties of a mortar mix at elevated temperature. The used mortar mix has been made with a combination of silica fume and fly ash as mineral admixtures. To improve the temperature resistance property and sustainability of the fiber reinforced mortar (FRM), a combination of pumice and slag fines was used in place of natural sand aggregates. The FRM was reinforced with only steel, PP, and a mixture of steel and PP fibers. All FRM mixes were then evaluated for high-temperature performance at 300°C and 600°C inside a furnace for a duration of 1 hour. After the exposure to the elevated temperature of the FRM mixes, their performances were assessed through compressive strength tests, visual observation, and microstructural evaluations. The results revealed that the steel fiber was the most efficient one to prevent spalling and reduction in compressive strength at below and above 300°C as compared to the only PP and PP+steel fibers reinforced FRM. The improvement in the residual compressive strength values of the steel fiber reinforced FRM was 59.52 % and 19.05 % at 300°C and 600°C, respectively, as compared to the ambient temperature values.

Case study of fire damaged industrial structure and an experimental investigation on structural performance of fire damaged retrofitted RC beams J. D. Rathod, Pradip S. Chauhan, Vinay R. Anghan

Case study of fire damaged industrial structure is discussed which was investigated for the purpose of suggesting appropriate scheme of retrofitting. Experimental investigation was carried out to identify loss of structural performance in terms of flexural strength, ductility index and energy absorption in flexural members which were subjected to time-temperature controlled fire exposure. These fire damaged beams were retrofitted using the techniques of carbon fiber wrapping and steel plate jacketing using shear anchorage method in order to determine their ability to restore the structural performance. Fire damaged beams retrofitted with steel plate jacketing exhibit better structural performance compared to fiber wrapping technique.

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