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 presents a study of the resistance of connections of load-bearing laminated wood structures using domestic melamine-urea-formaldehyde adhesives (MMFC) to cyclic temperature and humidity influences. The method of cyclic tests is described. An assessment is made of the resistance of MMFC to temperature and humidity influences and the compliance of the selected adhesive with the requirements established for the production of long-span load-bearing structures.

Keywords: melamine-urea-formaldehyde adhesives, wooden structures, resistance of adhesive joints to cyclic temperature and humidity influences, strength

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

The paper presents the study of the effect of multiple cyclic humidification on the compressive strength across the grain edgewise of laminated veneer lumber (LVL), long-term sustained in conditions with high humidity. A significant decrease in its strength properties during cyclic humidification (up to 18% in three cycles) has been proved. The dynamics of crack growth due to the influence of the humidity factor is given.

Keywords: laminated veneer lumber, timber structures, strength, cyclic dampening, drying cracks, hygrostalness

The paper presents a study of the water resistance of joints of load-bearing laminated timber structures using domestic melamine-urea-formaldehyde adhesives (MMFC). The high relative strength of samples dried after soaking and boiling above that established for the increased water resistance group is shown. An assessment of water resistance for three formulations is given, the dynamics of crack growth due to the influence of the moisture factor of MMFC.

Keywords: melamine-urea-formaldehyde adhesives, wooden structures, water resistance of adhesive joints, strength