SIMULATION OF WORK OF A REINFORCED PRE-STRESSED WOODEN ELEMENT

Abstract

An  undeniable  disadvantage  of  wood  when  using  it  in  construction  is  its 
excessive  flexibility.  One  of  the  ways  to  increase  the  stiffness  of  wooden  elements  is  to  use 
prestressing  and  reinforcement  with  stiffer  elements.  The  manufacturing  process  of  pre-stressed 
bending  elements  proposed  by  us  is  simple.  However,  determining  the  necessary  effort,  the 
necessary  bending  of  the  beam  to  ensure  reliable  operation,  preventing  the  destruction  of  the 
element is quite difficult. 
One  of  the  methods  of  prestressing  is  described,  namely,  the  method  by  which  the  beam 
receives internal stresses due to the release of the bending element after the action of the external 
load by gluing reinforced elements. The principle of such tension can be described in the following 
sequence: 1. We create a bend in the bending element by applying an external load to the element. 
2. We reinforce the lower zone of the bending element. At the same time, we need to know under 
which  stress-strained  state  the  reinforced  element  was  installed,  so  that  its  operation  can  be 
predicted. 3. We remove the applied force with which we created the bend in the flexible wooden 
element, while the element wants to acquire its  original shape, but this  will be prevented by the 
armature, which will absorb part of the load and leave a small bend. It was established that the level 
of prestressing, namely the curvature acquired by the bending element after prestressing, depends 
on the initial curvature of the wooden element, as well as on the area and physical and mechanical 
characteristics  of  the  materials  reinforcing  the  beam  zones.  To  determine  the  prestress,  it  is 
necessary to establish the stress-deformed states of the bending element, which occur after gluing 
and  release  of  the  external  force.  At  the  same  time,  3  levels  of  the  stress-strain  state  can  be 
distinguished.  1.  At  the  first  stage,  the  compressed  zone  is  more  than  the  stretched  zone.  The 
relative  deformations  of  the  compressed  lower  zone,  where  the  material  is  to  be  attached,  is  the 
initial  start  for  the  work  of  the  reinforced  element.  2.  At  the  second  stage,  the  external  bending 
moment  decreases,  the  internal  redistribution  of  forces  takes  place,  in  addition  to  the  moment 
perceived by the compressed and stretched zone, a moment also occurs in the stretched reinforced 
element. 3. The third stage is characterized by the absence of an external load, and this causes a 
balance between the internal forces of the bending prestressed element. The equilibrium equation 
for three stages was obtained. When using the element as a load-bearing structure, the cross-section 
in  the  element  can  be  with  both  positive  and  negative  curvature.  The  peculiarities  of  these  two 
stress-strain  states  are  manifested  in  the  change  in  the  position  of  the  compressed  and  stretched 
zones.  In the first case,  the compressed zone is  located in the lower part of the  element and the 
upper part is occupied by the stretched zone. After the curvature changes its sign from negative to 
positive, the upper part becomes compressed, and the lower part becomes stretched. As a result of 
the  simulation,  it  is  possible  to  conclude  that  the  cross-section  of  a  bending  wooden  element 
undergoes 3 main stress-deformed states during prestressing and two during its operation.