Name: DANIEL CARVALHO DE MOURA CANDIDO
Type: MSc dissertation
Publication date: 26/02/2021
Advisor:
Name |
Role |
|---|---|
| ADENILCIA FERNANDA GROBÉRIO CALENZANI | Advisor * |
Examining board:
| Name |
Role |
|---|---|
| ADENILCIA FERNANDA GROBÉRIO CALENZANI | Advisor * |
| RONALDO PILAR | Internal Examiner * |
Summary: The structural engineering market aims to solve a portion of infrastructure issues in
society. As such, structural solutions are constantly developed to meet an everincreasing
demand for controlling execution time, cost and environmental impact of
business endeavors. In order to fulfil said demand, solutions for efficient floor systems
that propose the use of intermittent steel formwork in the lower surface of a slab, which
consists of uniformly spaced ribs. The space between ribs is filled by superposition of
steel profiles or structurally inert elements, in similar fashion to reinforced concrete
unidirectional ribbed slabs. This research investigates the flexural behavior of a trussed
floor system called Trelifácil®, in which traditional precast reinforced concrete (RC)
lattice joists are replaced with trussed rebar fastened inside a cold formed steel
channel by uniformly distributed plastic spacers. The flexural strength was determined
by means of a series of laboratory tests on full-scale specimens, considering
constructions and serviceability phases. Two sets of four-point bending tests were
conducted on specimens that represent the system during construction, one of which
consisting of the isolated U channel profile and the other featured specimens with rebar
trusses fastened to the profiles to evaluate the contribution of this element to the
strength and flexural stiffness of the system during construction. The failure mode of
the specimens was dependent on the proportion between the length with constant
bending moment and the length of the specimens, as well as the relation between the
latter and the width of the widest cross-section element. Among profile specimens,
shorter lengths presented failure by distortion of the cross-section outside of the
bending moment length, and medium lengths presented distortions at midspan and at
the support, while longer specimens failed by cross-sectional distortions at midspan.
The specimens featuring the U profile and truss presented similar dependency of the
geometric properties, with shorter and medium lengths presenting different failure
modes for the profile without loss of bearing capacity, until the definitive collapse,
consisting of diagonal buckling of truss outside the length of constant bending moment.
Long specimens exhibited failure by instability of the upper chord, immediately followed
by distortion of the cross section at midspan. Furthermore, the bending moments
equivalent to the maximum experimental loads obtained were compared with the
characteristic resistance to bending moment obtained with the direct strength method
and presented significant divergence. A third set of four-point bending tests were
conducted on reinforced concrete slabs with incorporation of the Trelifácil® system to
evaluate the contribution of each component to the strength and stiffness of the system
during serviceability. Overall, all specimens presented failure by what could be
classified as a plastic hinge inside the constant bending moment length and the
registered slip between steel and concrete was not considerable. The maximum
experimental loads observed presented similar value to an analytical proposal that
considers the system as a reinforced concrete tee with the steel profile acting as
additional positive steel reinforcement.
Keywords: Trussed ribbed slab, Cold formed steel U channel formwork, Experimental
analysis of structures, Four-point bending test
