POSITION OF THE NEUTRAL LINE AND ITS EFFECT ON DETERMINING THE ACTUAL MECHANICAL CHARACTERISTICS OF WOOD UNDER TRANSVERSE BENDING

Abstract

The analysis of the work of elements made of solid and glued wood under direct and oblique transverse bending with an increase in the level of short-term load was carried out.

     Coniferous wood, used in engineering structures, is an elastic-plastic anisotropic material for work both along and across the fibers. An exception is work on longitudinal tension. Within the limits from the beginning of loading and up to (0.9...0.95)% of the destructive wood works elastically, but in the future, as the loads increase, it also goes into the stage of nonlinear deformation.

It has been established that many authors who conducted experimental and theoretical studies of the work of wooden beams indicate that the position of the neutral line of force in the cross section of the element under conditions of direct transverse bending at different levels of action of one-time loads changes its position.

     The destruction of long wooden beams ( ) during transverse bending, due to the lower strength of wood in longitudinal compression compared to tension, begins in the compressed zone of the cross section with the formation of folds, which are often difficult to visually notice and record due to their instantaneous appearance and disappearance. in experimental studies. The final destruction of such beams takes place precisely in the stretched zone by breaking of the extreme fibers.

     Disproved theses on which the calculations of wooden structures, both from solid and glued wood for transverse bending, are based, which are carried out according to the current design standards of various countries using the limit state method with the prediction of the elastic work of wood from the beginning of loading to failure.     It was established that the moment of resistance of the cross-section of a bending wooden element can be determined only in the case when the force neutral line (plane) will pass only through the center of gravity of this section and when it is located in the middle of the beam at the height .     The obtained results of the temporary resistance of wood in transverse bending, which are determined in the limit state using the moment of resistance of the cross section of the element , are unreliable.