RSSV 4 2013.indd - Stazione Sperimentale del Vetro

4-2013
studies
studi
Rivista della Stazione Sperimentale del Vetro
Shear resistance and shear modulus of adhesive are
important characteristics and have high influence on
the load carrying capacity and structural behaviour
of the hybrid steel glass beam. The stiffness of the
bonded connection depends on the stiffness of the
adhesive and geometry of the joint. Increasing thickness
of the adhesive will decrease the stiffness of
the joint [1]. Enlargement of the width of joint leads
to an enlargement of stiffness of whole connection,
therefore direct connection on the face of the glasssheets
have a low stiffness because of the small
bonding width. Other geometries of the joint offer
larger bonded surface and therefore higher effective
connection stiffness. Flexible composite hybridbeams
can be pre-designed according to Möhler’s
theory [2] (which is today known as the γ-method).
It can be applied to the hybrid steel glass beam considering
the different material properties of steel and
glass as well as the flexibility of the joint with an effective
moment of inertia with reduced contribution
of the flanges. Therefore it is qualified very well for
the pre-design of hybrid steel glass beams and experimentally
proved on the full-scale test of hybrid
beam with the span of 4m made by CTU Prague [3].
Composite beams with divided glass web
For longer span (more than ca. 6m) there is a need
to divide a web because of fabrication criteria of
the glass. Manufacturing of that beam is more difficult,
but on the other hand, this solution caries the
improvement of the robustness behaviour of whole
structure, because pertinent impact damage can be
isolated on separate part of the web. Static behaviour
of the hybrid beam subjected to bending moment
is completely different in comparison with
previously mentioned hybrid beam with continuous
glass web. Analytical model is based on the truss
analogy, because behaviour of hybrid beam evokes
truss with some peculiarities due to the elastic shear
connection and the special panel structure of the
web have to be taken into account. The structural
behaviour of the composite beam can be simplified
to the idealised elastic structure, see Fig. 3. According
to this model, glass panes begin to rotate due to
the increasing load. Shear flow, caused by external
load, produces a moment in each part of the glass
web. It results to a contra moment in the joint between
web and flange. This creates additional shear
stresses in adhesive layer on the edge of the glass
panes and compression at the corners of the pane.
This shear distortion makes rotation of glass panes
and every glass pane of composite beam behaves
like compressed diagonal in truss system. Than internal
forces of this structure can be calculated like
the internal forces of a truss system. This truss analogy
allows an easy determination of the internal
force distribution and reactions between the hybrid
beam components. The total shear flow action in the
adhesive layer can be computed by a vectorial addition
of both orthogonal shear flow values.
Experimental investigations
Described experiments (4 point bending tests) were
aimed to investigate the static behaviour of hybrid
beams with glass web divided to several panes. The
span of test specimens was chosen the same as for
the experiments of beams with the web made of one
glass pane, it was 4m. The same length, detail of the
connection, dimensions of the cross-section as well
as the same type of adhesive allow comparison of
all obtained results. 9 full-scale tests of beams with
divided glass web were performed. Behaviour under
loading was completely different in comparison
with the experiments of beam with glass web from
one panel. Failure of every test specimen started
near the support at the contact of adjoining glass
panes, see Fig. 3 and Fig. 4 for different types of
web-flange connection.
Figure 2. Analytical model based on the truss analogy
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