## 1 Introduction
The team from the Warsaw University of Technology, headed by Professor [PERSON], conducted a detailed post fire inspection, which included materials tests, verification of the construction geometry and Finite Element Method (FEM) strength analysis [15]. Experts found numerous additional defects, including dilatation damage, failure of the steel structure of the access walkway, damages to the road surface, protective barriers, paint coatings, and utilities. It was concluded that the main cause of damage was thermal shrinkage of steel. Due to various boundary conditions for individual elementsof the bridge, a number of residual deformations occurred as the structure cooled. That resulted in selected elements being put out of operation. Finally, a decision was made to replace the steel structure of the spans using a modified incremental launching method. The bridge was opened on October 28, 2015. The reported cases of fires that have occurred in recent years clearly indicate the need to improve the methods and means of increasing the fire safety of structures. The concept of fire safety is an extremely extensive issue. Ensuring an appropriate level of fire safety has been implemented in research and activities in several fields, especially mathematical, physical, and numerical modeling of fire phenomena. Another issue is the design of all types of fire protection, such as types of alarm systems or sprinkler systems, and the design of roads and evacuation systems in a manner ensuring maximum safety for building users. Fire protection covers all types of structures, due to the nature of the work, as well as the material used. Currently popular composite materials, such as concrete filled steel tube (CFST) columns, papers [16; 17; 18], and polypropylene fibers [19] are used in the area of the structures themselves. In contrast, the connections of load-bearing elements are modeled with the participation of a high-performance fiber reinforced cement composite (HPFRCC) [13]. The HPFRCC high performance fiber-reinforced cementitious composite is a mixture of the correct proportions of Portland cement, fly ash, quartz sand, water, and polyvinyl alcohol (PVA) fibers. It is PVA fibers that have a decisive influence on improving the mechanical efficiency, elasticity, and durability of concrete structures [20; 21] due to fire conditions. According to [PERSON], [PERSON], [PERSON], and [PERSON] [22], PVA fibers under the influence of high temperatures melt to form channels to alleviate internal vapor pressure and thus explosive spalling. Therefore, the mechanical properties after a fire are higher compared to those of conventional concrete. In [22], the authors performed experimental studies of four two-story and two-nave frames, two made of typical concrete (S1 and S2) and two in which the beam-column joint was made of high-performance cement composite reinforced with HPFRCC fibers (S3 and S4). The frames S2, S3, S4 were subjected to fire. The results of the tests carried out in the fire chambers showed that the application of HPFRCC increased the initial stiffness by 30%, the resistance and ultimate displacement by 6% and 3%, and the energy dissipation by 21%. In addition, only small surface flakes appeared at the HPFRCC joints, without the participation of explosive spalling on the HPFRCC. In works [23] and [24], as thermal insulation, polystyrene foam was used and in [25], a portable compressed air foam system was used (regardless of its material of construction). An extremely important problem is the analysis of the static-strength response of structures in fire conditions [26]. This paper focuses on this field and narrows it down to steel trusses. In steel structures, fire insulation is used in the form of intumescent pains or fireproof spray materials. The properties of these materials are discussed in other scientific articles [1; 27; 28].