Page 25 - Riem-Vol6_nº3

377 IBRACON Structures and Materials Journal • 2013 • vol. 6 • nº 3
P. F. SCHWETZ | F. P. S. L. GASTAL | L. C. P. SILVA F°
The loading adopted in the original design was the structure’s own
weight of 4.8 kN/m2 with an additional dead load of 12 kN/m2, a live
load of 3.0 kN/m2 and a masonry load applied directly on the edge
beams. The high value of the additional dead load is due to the
several layers of the base filling material of the tennis court. Only
the additional dead load was used in the experimental program.
2.2 Instrumentation
The experimental program predicted measurement of strains and
vertical displacements.
In the concrete, strain gauges were placed in four slab locations,
at the top and bottom surfaces (Fig. 4a). In the reinforcement, two
strain gauges were placed at each instrumented location, protect-
ed with an epoxy based resin (Fig. 4b).
A precision optical level was used to measure the vertical displace-
ments (Fig. 5) at locations as shown in Fig. 6.
2.3 Testing
The test began 63 days after casting. The loading was to be car-
ried out in three stages and strain and vertical displacements were
to be measured at the end of each loading stage. However, the
load was distributed unevenly throughout the testing period. Some
areas of the slab were used to store other types of material gen-
erating a non-uniform load (Fig. 7a and b). Hence, readings were
made at different points in time and care was taken to register the
actual load applied at each reading. The process of loading the
structure lasted 87 days and readings were taken at 5 different
times. Cylinder tests were also carried out to determine the modu-
lus of longitudinal elasticity of the concrete (E) and the character-
istic concrete strength (fck). The average value of the modulus of
elasticity of the concrete E28measured experimentally was equal to
28,45 GPa, and the average concrete strength obtained at 28 days
was equal to 33,27 MPa, corresponding to a concrete characteris-
tic strength fck, estimated equal to 30 MPa.
and to verify whether their behavior is adequately simulated by
the design methods and mathematical models widely used today.
In order to achieve this aim, an experimental program was imple-
mented, measuring strains and deflections in a full-scale waffle
slab, designed to receive several layers of filling material neces-
sary for use as the floor of a tennis court. The experimental results
were compared with results obtained from numerical analyses per-
formed using two different approaches to represent the structure (a
grid matrix analysis and FEM analysis).
2. Experimental program
The floor analyzed was designed commercially by a structural en-
gineering design office located in the city of Porto Alegre, Brazil. It
is to be used as a tennis court floor.
The formwork was built with plastic formwork developed for waffle
slabs by Ulma Fôrmas e Escoramentos Ltda. This system is com-
posed by a two-way ribbed structure that serves as support for the
plastic molds. The ribbed structure is supported by a set of tubular
metallic braces that are easy to disassemble (Fig. 1).
The slab reinforcement was made with type CA-50. The weight of
positive reinforcement used was about 16,000 kg and the amount
of negative one was around 23,000 kg.
Fig. 2 shows the generic position of the steel in the ribs. Besides the
top and bottom reinforcements predicted in the numerical analysis,
the structural designer considered the possibility of tensile stress on
the bottom of the slab topping located between the ribs and placed a
welded CA-60 steel mesh on the bottom part of the top slab.
2.1 Geometry and loading
The geometry of the waffle slab floor is shown in Fig. 3. The de-
signer used semi-inverted edge beams to increase stiffness in
order to prevent excessive deformation. Around the internal col-
umns, a 37.5 cm solid slab was used due to punching shear and
high bending moments.
Figure 4 – Position of strain gauges: (a) concrete and (b) reinforcement
CS
CI
A B