Tubular truss and column members with bolted connections widely used in construction. The object of this research was the flange joint of a truss bottom chord. The flange joint coaxially connects two cold-formed closed welded rectangular hollow section profiles. The flange connects with high-strength bolts of strength class 10.9. The stress-strain state of the joint was numerically and experimentally investigated. Experimental studies were performed on a full-size sample of a flange joint using strain gauges. Numerical calculations were performed at ANSYS. The bilinear isotropic hardening model simulated the metal elements performance of the joint. The “Frictional” model was chosen for the friction forces between the flanges. The microstructure of the bolt material was studied using an optical microscope. The study results showed that the model solution for a flanged provides a uniform distribution of stresses at the junction due to its spatial rigidity. The presence of stiffener ribs provides the absence of the clearance between the flanges and promotes the joint performance of welded units and high-strength bolts. The design of the flange joint using the developed finite element model indicates that the results of numerical and experimental studies are sufficient for practical application. The difference between finite element model calculations and experimental data in the most loaded elements of flange joints does not exceed 10 %. It is proposed for high-strength bolts of strength class 10.9 and higher to introduce regulatory restrictions on the number and size of non-metallic inclusions that affect the delayed brittle fracture of bolts. To improve the performance that bolts, it is proposed to use steel grades with a bainitic or bainitic-martensitic structure, which are formed by microalloying them with molybdenum, vanadium, niobium, titanium, boron and heat treatment.