PSI - Issue 81

Victor Datsiuk et al. / Procedia Structural Integrity 81 (2026) 73–77

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Zakic (1974); Pavluk et al. (2024); Hua et al. (2025); Gomon et al. (2024)). After long-term service, strengthening of load-bearing elements and structures may be required (Bula and Pelekh (2023); Rescalvo et al. (2020)). Modern measuring equipment enables long-term monitoring of timber elements and structures during service and allows changes occurring in the timber structure to be recorded (Lanata (2023)). The authors have also carried out experimental studies on timber that had been in service for several decades under different temperature and humidity conditions (Datsiuk et al. (2024)).

Nomenclature L beam span, mm a beam width, mm b beam height, mm T service life, years W moisture conten, % n

number of specimens, pcs ultimate bearing capacity, kN

F u

The aim of this study is to conduct experimental investigations of solid rectangular-section pine beams with different service lives and under various temperature and humidity conditions, as well as to assess their influence on the bearing capacity of the specimens. 2. Methods of experimental research To address the stated research objectives, solid rectangular- section pine beams with dimensions of 50 × 80 × 1650 mm were selected and cut from roof rafter structures that had been in long-term service and exposed to various temperature and humidity conditions. The rafters for testing were taken from the roofs of residential buildings. To compare mechanical properties, samples with relatively the same level of defects and damage were selected. They belong to the II grade of wood. The selection of structural elements was carried out in accordance with the requirements of DSTU EN 518:2003. The investigated timber elements had different service lives, approximately 25, 50, and 75 years, which corresponds to the provisions of the regulatory documents DBN V.2.6-161:2017, Eurocode 5:2004, and NDS:2018. At the time of testing, the moisture content of the bending elements was approximately 12% and 15%, which is typical for timber operating under dry and moderately humid environmental conditions. Moisture content was controlled using a certified moisture meter in accordance with the requirements of DSTU 4922:2008. For each age group of timber elements, two beams were selected, which ensured the possibility of a comparative analysis of the influence of service duration on the physical and mechanical properties of pine timber. The dimensions and characteristics of the beams are presented in Table 1.

Table 1. Characteristics of the test beams

Specimen No.

Timber species

Beam section a × b × l, mm

Service life T, years

Moisture content W, %

Loading type

Number of specimens n, pcs

1 2 3 4 5 6

Pine Pine Pine Pine Pine Pine

50x80x1650 50x80x1650 50x80x1650 50x80x1650 50x80x1650 50x80x1650

25 50 75 25 50 75

12 12 12 15 15 15

Single short-term Single short-term Single short-term Single short-term Single short-term Single short-term

2 2 2 2 2 2

Full-scale experimental tests of solid-section bending elements were performed using a specially designed test setup with the application of single short-term loading in accordance with the requirements of the applicable regulatory documents – DBN V.2.6 161:2017, Eurocode 5:2004, DSTU EN 380:2008, and NDS:2018 (Fig. 1). The test beams were loaded using a dynamometer. The load was applied according to a specified loading scheme with step-by-step control of its magnitude, which allowed the stress strain state of the timber elements to be evaluated during the testing process. w on e S r th e tr e m a i b e n e a m a s r u e i r n a e g s d u c r u a e s p m i a n c e g i n t h y t i s , g s w h t - i e f p r f r n e e e r c s e i s s c , i o o a r n n d d e d d e d f e u le f s o c in r ti m g o s n a t b g r i a a li i u t n y g g e o a s f u . t T g h h e e s i s b i n a e p s n t p d a r i l n o le g a d c e h a le t e m t n h s e e u n m r t e s i d . d I - t n s h p t e o a a t n c a s q l, e u 1 c i 2 t s i i o t s i n o o l o n id f o - t f s h r e e e c b l t i i e a o a b n m l e t s i e m , x w b p h e e i r r l i e b m d e e a e n m fl t e a s c l w t d io e a n r ta e s tested using the experimental setup (Fig. 1).