work under load [3]. Among them, a significant role is played by keyed connections
with increased shear resistance. The aim of the research, which is carried out in
PoltNTU [4], is to improve the joints of floor slabs between themselves, with a girder,
column or wall panel, vertical joints of wall panels, as well as proposals for calculating
the strength of such joints on an experimental and theoretical basis.
Improvement of joints in large-panel housing construction. Peikko (Finland)
[5] developed a technology for vertical monolithic keyed joints with loop transverse
reinforcement between wall elements, in which wire rope loops are used instead of
rigid loops. It uses a closed metal box made of thin tin, inside of which is a stainless
steel wire rope loop. The ends of the loop cable from its outer (rear) side are
interconnected and pressed in by a steel saucer. In the manufacture of the panel, closed
boxes with flexible loops nested in them are installed in the ends surface of the inner
bearing layer of the panel with the anchor inside (Fig. 1). The lids of the boxes are
removed after concreting, a set of concrete panels of sufficient strength, stripping the
panel and installing it in the design position and loops are expand. In this case, the box
forms a cavity that is not contaminated with dust and other debris to form by future key
of a vertical seam between the panels. After the release and unfolding of all the loops
in the joint, an anchor rod with a length equal to the height of the floor is passed through
them. Next concreting keyed seam occurs. The method allows you to use the formwork
wall panel repeatedly, individually change the keys step and their location, greatly
simplifies the installation of panels.
There are proposals [6] for the design of vertical joints of large-panel buildings
with flexible steel links (wire rope loops), which are installed by calculation with a step
of 250 ‒ 750 mm in the ends surface of adjacent panels. If necessary, provide additional
concrete keys. The class of concrete monolithing is accepted by calculation, but not
less than C20/25. The adopted design of vertical joints of wall panels ensures that the
keys perceive vertical and horizontal shear forces, steel wire rope loops ‒ horizontal
tensile forces, and monolithing concrete ‒ horizontal compressive forces.
Its theoretical and experimental studies are conducted at PoltNTU. The method
for calculating the strength of key joints on wire rope loops by a variational method in
the theory of concrete plasticity is proposed. This takes into account the proposals [7]
regarding the determination of the stresses rate that act in wire rope loops in the stage
of the joints destruction. The results of the calculation method for Eurocode 2, in which
these stresses are assumed to be equal to the conditional yield strength, do not agree
with the experimental data [8], which necessitates refining the loads in the loops.
Suggestions for resizing a tin box (key) are made. The existing dimensions
predetermine the destruction of keys from crushing, and the effect of constrained
deformation conditions is understudied. According to research results [9], the ratio of
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