# Study on the Fire Resistance of Axially Restrained H-Shaped Steel Beams Under Real Fire
## 1 Introduction
[17; 18] utilized finite element models, analyzed refractory performance parameters of steel beam-steel column frames considering creep effect and studied parameter impacts on the fire resistance of restrained beams, including heating rate, slenderness ratio, restraint position, and high-temp creep. [PERSON] et al. conducted theoretical calculations of the flexural curve equations, axial forces, and bending moments of restrained steel beams and derived the corresponding calculation methods. [PERSON] et al. [19] also performed theoretical analysis to derive the flexural curve equation for restrained steel beams under large deformation. In summary, the research on the fire resistance of steel beams has been quite comprehensive, with various countries formulating corresponding design codes for fire-resistant restrained steel beams based on this research, and studies on restrained steel beams with different cross-sectional forms are gradually being deepened. However, previous studies on the fire resistance of steel beams have mostly been conducted by directly using ISO 834 (standard heating curve) [20], but in actual fire, the temperature change on the surface of the steel beams is more complicated. Standard fire curves assume uniform temperature throughout the fire-exposed space, while in real fires, temperature distribution within the space is non-uniform both vertically and at different positions of the same height. To investigate the fire resistance of steel beams in real fires, constructing more realistic heating curves is required. A real fire test is constrained by cost and safety factors; thus, fire simulation technology plays a crucial role in practical applications. With the development of fire science and computer technology, theoretical models such as zone models and field models that represent the development of and variation in fire fields can be implemented through computational software, providing efficient computational tools for the study of real fire temperature fields. [PERSON] [21] first proposed the basic equations of the zone model, and subsequently, a series of zone models based on this theory, such as RFIRES, ASET-B, and BRANZFIRE, were successively developed [22; 23]. In addition, the CFAST software [24], introduced by the National Institute of Standards and Technology (NIST) in the US in 1993, remains one of the most commonly used zone simulation software platforms to date. Fire test data from numerous scholars indicate that the simulation results of CFAST software are in good agreement with experimental values [25; 26], verifying its accuracy and reliability. But the zone model cannot accurately calculate the horizontal diffusion of temperature and hot smoke and can only describe temperature changes from a macroscopic perspective. For simulating a real temperature field, a more detailed model is required. With the continuous advancement of computer technology and the increasing refinement of fluid dynamics models, the fire research field has developed field model software with computational fluid dynamics (CFD) as its core foundation. The field model method divides the building space into a large number of tiny control volume units and assumes that the physical parameters inside each unit are consistent. Then, according to the principle of material conservation and energy conservation, the partial differential equations describing the physical state changes of each unit are derived for calculation. Currently, field models are the most widely applied fire models. Among them, the fire dynamics simulator (FDS) developed by NIST, the most common in fire simulations, is widely used in fields like shipping, transportation, and tunnels and more extensively in building fires. The main functions of FDS include the following: (1) Building a fire scene, FDS can be used to build a real fire environment and set the type of fire source for fire simulation; (2) parameter analysis research, exploring the impact of various parameter changes on the fire field, studies the variables with the greatest impact.