KNEE JOINT OF THREE-HINGED GLUED TIMBER PORTAL FRAME EXECUTED AS JOINT ON GLUED-IN RODS

Abstract

 In  the  modern  construction  of  buildings  and  structures  there  are  many  constructive 
solutions for connecting the rafter with the column of wooden three-hinged portal frames. One of 
these constructive solutions is the use of knee joints executed as joint on glued-in rods. Despite the 
accumulated experience in the construction of buildings using timber structures with joints on glued-
in rods, there are still urgent tasks to improve the technology of their manufacture and calculation 
models. The purpose of this work was to conduct experimental and theoretical studies of the knee 
joint  executed  as  joint  on  glued-in  rods  to  determine  the  stress-strain  state  of  the  timber  in  the 
connection region. To develop of proposals for improving knee joint executed as joint on glued-in 
rods. The study of the stress-strain state of the knee joint was carried out by solving a plane problem 
of the theory of elasticity using a software package based on the finite element method. In the software 
package used, procedures are implemented to take into account the anisotropy of the mechanical 
properties of wood, the violation of contact between the surfaces of the elements connected in the 
knee joint. Experimental studies were carried out by the method of static loading of a prototype of a 
knee joint made in full size, which in its geometric parameters and material properties corresponded 
to the CE model. As a result of the conducted studies, it was found that in the stretched zone of the 
knee joint, the glued rods of the rafter and the column are characterized by  a significant uneven 
distribution of forces, in addition, the rods are subjected to compression, tension and bending. The 
most loaded are the rods located at the maximum distance from the joint of the rafter and the column. 
The  distribution  of  forces  in  the  rods  of  the  compressed  zone  is  close  to  uniform.  The  stress 
distribution along the length of the inclined rods of the embedded parts is characterized by a large 
unevenness. Based on the analysis of the stress-strain state of the knee joint of the frame, a new design 
solution is proposed in terms of the number of glued-in rods and their spacing.