The authors carried out a research of the stress - strain state of the hinge unit of light spatial grid framings of regular structure. The solid model of the hinge unit was created previously and numerical simulation was performed. Calculation identified, that the weak point of the hinge unit is connecting disk. Plastic deformation can arise in the disk during loading. The experimental research was required for verification of results of a pilot study. The test of disk was executed with application of a specially designed installation on universal tensile testing machine in the laboratory of the University. Mechanical characteristics of steel, from which the disk was made, were identified by a certified laboratory destructive control methods in accordance with the GOST. The experimental results are compared with the simulation results. The authors give recommendations for optimizing the design of the hinge unit.