At present, the construction of modern three-dimensional transportation is in the stage of rapid development, in order to shorten the traffic distance and make reasonable use of traffic space, tunnels play an increasingly important role in the transportation system. The interior of the tunnel is relatively closed, and once a fire breaks out, the fire spreads rapidly, causing casualties and property losses that cannot be ignored. Therefore, it is of great significance to strengthen the research and application of tunnel fire prevention technology to improve the safety and reliability of tunnels.
As a part of traffic engineering, the research and application of fire protection technology is to ensure the safe operation of the tunnel, in order to do a good job in tunnel fire prevention, determining the best fire protection material is an important part of tunnel fire protection, not only tunnel fire retardant coatings, fire protection boards, etc., the fire resistance of the embedded channel is also one of the factors that need to be considered.
Because it is finally to be put into practical use, the research on the fire resistance of the embedded channel can not only stay at the theoretical level, but also obtain relevant data through the fire resistance test to evaluate whether its fire performance can meet the relevant technical requirements.
Fire Resistance Requirements·
The standard specification "Embedded Channel Section" (GB/T 37613-2019) stipulates that the embedded channel should not only meet the requirements of GB 50016, but also carry out relevant fire resistance tests according to the requirements, and give specific requirements for fire resistance bearing capacity and bearing time. In addition, it is mentioned in the "Embedded Channel in the Electrified Railway Catenary Tunnel" (Q/CR 1001-2023) that the bearing capacity of the channel, T-bolt and related fasteners in accordance with the engineering design requirements will not produce functional failure after the single-sided fire resistance test of 90min of the RABT-ZTV heating curve specified in GB/T 26784-2011. The "Embedded Channel in the Electrified Railway Catenary Tunnel" (TB/T 3329-2013) also requires that the embedded channel, T-bolt and related fasteners shall not fail after the fire resistance test is carried out in accordance with the specified method.
Fire Resistance Test·
Prepare the embedded channel, T-bolt and related fasteners required for the test, confirm that the sample meets the relevant requirements, and then pre-embed it in the concrete in the correct way, and cured it under suitable environmental conditions, and ensure that the strength of the concrete used is consistent with the actual engineering situation. Install the supporting fasteners at the reasonable position of the embedded channel, and the prepared specimen with the side of the embedded channel is placed downward, and be installed in the test furnace according to the test requirements.
The RABT-ZTV heating curve of tunnel fire can be used to evaluate the fire resistance of the embedded channel under the heating condition of tunnel fire RABT-ZTV. If it is necessary to evaluate the fire resistance of the embedded channel under other conditions, a different temperature rise curve can be used. Under the condition of RABT-ZTV heating in tunnel fire, the temperature-specimen relationship in the refractory test furnace is as follows:
During the ceremony:
t - the time when the test was carried out, in minutes;
T - the average temperature in the refractory test furnace at time t when the test is carried out, in degrees Celsius (°C);
T0 - the initial average temperature in the refractory test furnace before the start of the test, which is required to be 5°C~40°C;
N - the sum of the time of the heating and constant temperature phases, the unit is minutes (min), and the cooling time is specified as 110min.
When the value of T0 in equations (1) and equations (3) is 20°C, the RABT-ZTV heating curve of tunnel fire is as follows:
a - RABT-ZTV curve of tunnel fire when the N value is 90 in Eq. (2) and Eq. (3);
b - RABT-ZTV curve of tunnel fire when the N value in Eq. (2) and Eq. (3) is taken as 120.
During the test, the corresponding specified load can be hung vertically downward through the T-bolt, and whether the embedded channel and T-bolt lose the fire-resistant bearing capacity within the specified fire-resistant time can be evaluated. It can also be taken out to measure the ultimate pull-out force after the fire resistance test without hanging the load during the fire resistance test.
·Conclusion·
The embedded channel can not only effectively avoid the damage of the tunnel lining due to the force and vibration of the catenary, but also meet the fine installation requirements of the high-speed catenary. In the future, with the technology and intelligence of electrification facilities and equipment, the requirements for the fire resistance performance of the embedded channel will become more stringent, and we should also do a good job in the quality control of the embedded channel from many aspects to ensure the safe operation of various related projects.