The paper presents the results of the study of the condition of wooden structures of the attic floor of the St. Petersburg Theological Academy of the Russian Orthodox Church. The main defects and damages of the rafter system elements are indicated. Conclusions are given on the physical and mechanical characteristics of a beam over 200 years old. Conclusions are made on measures to maintain the operability of the structures.

Keywords: load-bearing capacity of wooden structures, biodestructors, strength reduction, rafter system

The article shows the importance of analyzing the state of strength properties of old wood during restoration work and monitoring the state of the structure. In particular, the physical and mechanical properties of wood during long-term use in an aquatic environment are analyzed. Changes in the chemical composition of wood as a result of use in the water of the Gulf of Finland are determined. Using the example of logs of the crib foundation of the Kronshlot fort, it is described how a change in the chemical composition of the material affects its strength properties.

Keywords: Mechanical properties of wood, long-term strength, chemical composition of wood, water-soluble extractive substances

The paper describes a model of behavior of the connection of wooden structures with glued rods when exposed to negative temperatures. The results of determining the resistance of wood to punching of a glued rod of reinforced joints of wooden structures at temperatures of -30°C, -70°C and +22°C are given. The characteristic features of the destruction of the reinforcing bar and the connection as a whole are revealed.

Keywords: wood, glued rods, extreme temperature and humidity conditions, indentation strength of adhesive bonding of metal rods