July 2014, Volume 8, No. 7 (Serial No. 80), pp. 833-845
Journal of Civil Engineering and Architecture, ISSN 1934-7359, USA
D
DAVID
PUBLISHING
Design of Monolithic Concrete Ground Floors
Alexandros D. Bantias, Ioannis A. Tegos, Theodoros A. Chrysanidis and Asimina M. Athanatopoulou
Department of Civil Engineering, School of Engineering, Aristotle University of Thessaloniki, Thessaloniki 54124, Greece
Abstract: It is known that the slabs on soil constitute one of the most difficult types of structures despite their apparent simplicity.
The objective of this paper is to give a general survey of the design of ground supported slabs with the interposition of a suitable
subbase. A solution is proposed with the following characteristics: (1) complete suppression of joints; (2) conventional reinforcement
with meshes in the upper and lower fiber of the slab in order to confront and distribute cracking that is caused by hindrance of free
contractions and expansions; (3) effective confrontation of problems of bulging. The proposal is in effect on one hand for industrial
floorings and on the other hand for concrete pavings with large durability requirement.
Key words: Ground slabs, restraints, durability, jointless, fatigue.
1. Introduction
The design and construction of concrete slabs on
soil constitutes a difficult task despite their apparent
simplicity. It is not accidental that there are still no
recommendations on their proper construction. As
main cause of their failure, someone could mention
the restraints expressed either as differential
settlements or, mainly, as hindrance of contractions
and expansions. For the confrontation of restraints,
solution can be given by the joints (contraction joints,
construction joints, isolation joints, etc.). Because of
the big density of joints, the slabs are manufactured as
non-reinforced or fiber reinforced with small
percentages of steel fibers because of the unfavorable
influence of big percentages in workability of fiber
reinforced concrete. Also, at the joint locations, the
suitable placement of dowels is required to guarantee
the collaboration of neighboring segments.
Joints, along with the absence of conventional
reinforcements, constitute the Achilles’ heel of these
structures since they require maintenance, they are
prone to local failures and for the slabs which are
manufactured in the countryside, they constitute the
entries of rain waters and of melted, via salt, ice.
Corresponding author: Theodoros A. Chrysanidis, Dr.,
research fields: concrete design and earthquake engineering.
E-mail: theodoros_gr@yahoo.com.
Failure of joints can happen also because of the
phenomenon of pumping, which can lead to extensive
cracking and detachment of segments of concrete
from the surface of slab at the region of joint.
There is no correlation between ground slabs and
those supported on beams. A notable fact, indicative
of our ignorance concerning this issue, is that there are
no precise instructions referring to ground slabs.
Furthermore, the multiple applications of ground slabs
force engineers to research thoroughly the
international bibliography for defining specific rules
concerning their construction and design.
The strains these slabs are subjected to are derived
from point loads, uniformly distributed loads and
restraints due to deformation hindrance. The causes of
restraints are the expansions and contractions that
concrete undergoes due to its drying, temperature
changes, temperature difference between the top and
bottom side of the slab and the differential settlements
due to local subsoil deformation.
As in the case of conventional slabs, the main
purpose is to calculate the thickness and reinforcement.
Slab thickness is supposed to be determined by the
flexural, shear and puncture loads. As far as the
reinforcement is concerned, the ground slabs case is
considerably different to the conventional slabs case.
Traditionally, ground slabs in real life are weakly
834
Design of Monolithic Concrete Ground Floors
reinforced using grids on the top and bottom of slabs
which operate as surface reinforcement rather than
bearing. Today, these slabs are either unreinforced,
therefore operating at stage I (uncracked concrete), or
reinforced with steel fiber (percentage of reinforcing
steel 25-30 kg/m3). By using such low reinforcement,
it is intended to accommodate two basic requirements:
concrete workability and load bearing mechanism
activation by the two sides of the slab. Steel fiber
reinforcement imparts ductility to concrete, so bottom
side failure activates the top side and that enables us
to use the yield line theory. Certainly, steel fiber
reinforcement does not affect considerably the
flexural capacity of the slab, compared to the
unreinforced concrete case.
Regarding the restraints, joints is the “remedy” used
for strain relief. Occasionally, in order to reduce the
slab thickness, dowels are used to connect the adjacent
parts of the slab which is divided in rectangular parts
of size 5 m × 5 m. However, it is no exaggeration to
say that sometimes the “remedy” proves to be worse
than the disease that it is supposed to cure, more
precisely, the profuse cracking of the slab. Currently,
it is known that we are on the verge of releasing
ourselves from the joints. Many large area buildings
and long-span bridges are constructed jointless.
According to the beliefs of the present article’s
supervisor, who has a long experience in analyzing
jointless solutions for bridges and buildings, it is time
to apply this philosophy in ground slabs, since joints,
as mentioned before, cause more troubles than
restraints do.
The abolition of joints was on the table of
discussion, the period when railways were constructed
with expansion joints in every 30 m, due to intensive
phenomena concerning thermal expansions and
contractions. However, it was noticed that the rails
displacements due to thermal changes were much
lower than expected and as a result, joints were
connected by welding. In today’s railways, welded
connections are used and in that way deformations are
confronted.
The study of the temperature changes’ influence on
the length—deformation relationship of several
elements and the abolition of joints in building and
bridge construction, is addressed in many scientific
papers. However, bridges outpace buildings in current
bibliography.
Both the construction and the abolition of
expansion and contraction joints in buildings include
disadvantages which have to be taken into account
during their design, operation and maintenance. More
specifically, the existence of joints increases the
construction cost and their maintenance implies many
difficulties. Moreover, the application of joints
increases the possibility of moisture appearance and
disrupts the building’s uniformity (e.g., dual walls). In
contrast, the abolition of joints intensifies strains due
to restraints and as a result more reinforcement is
required in areas where tensile forces are more likely
to take place. For that reason, reinforcement is used on
the top and bottom side of the slab. Additionally, in
jointless constructions, it is essential that cracking
control has to be performed, since constrained and
imposed deformations due to restraints (temperature,
creep, shrinkage, settlements) cause high stresses to
indeterminate systems. In conclusion, a significant
disadvantage of joints’ abolition is the problematic
application of precast methods, because of the
difficulties arising in assembling and transporting
precast members.
The objective of this paper is to give a general
survey of the design of ground supported slabs with
the interposition of a suitable subbase. Despite the fact
that the dimensioning of these slabs is seemingly easy,
there are many factors that affect their behavior or
functionality that should be taken into consideration.
A solution is proposed with the following
characteristics: (1) complete suppression of joints; (2)
conventional reinforcement with meshes in the upper
and lower fiber of the slab in order to confront and
distribute cracking that is caused by hindrance of free
Design of Monolithic Concrete Ground Floors
contractions
and
expansions;
(3)
effective
confrontation of problems of bulging. The proposal is
in effect on one hand for industrial floorings and on
the other hand for concrete pavings with large
durability requirement.
2. The Main Disadvantages of Current
Construction Methods
The seeming simplicity of dowels’ application
disorients us from their real behavior. For example, if
dowels are not exactly perpendicular to the joint, they
will hinder contraction of the slab, causing or
contributing to cracking. Corrosion is another issue
that impedes free movement of dowels in and out of
the slab and can also cause spalling.
It is of outmost importance that doweled joints
should be able to open and close as concrete expands
and contracts. For that reason, dowels should be
slippery and smooth in order to slide in and out of the
concrete without resistance. Smoothness alone does
not guarantee free movement of the joints, so a
bond-breaker is also needed at the dowel surface. In
order
to
improve
dowel
performance,
grease,
mortar-tight sleeve or noncorrosive sleeve could be
used.
Conventional round dowels must be parallel with
each other and with the sides and surface of the slab.
Dowels which are not aligned have to bend as the
joint opens. This can generate immense tensile
stresses in the concrete. As a result, cracking and
reduction in load carrying capacity occur. Proper
positioning of bars could be achieved by using
prefabricated alignment cages but even with these, the
problem persists. Fortunately, misalignment is usually
not obvious.
Whatever provision is made, several issues still
come up. For example, if the top or bottom of the bar
is heavily greased, one slab must deflect by an amount
equal to the grease thickness before load is transferred
to the adjacent slab. High stresses can occur long
before the load is transferred. A similar problem may
835
come up if there is any space between the bar and the
sleeve. Additionally, if corrosion occurs on the bars
and sleeves or mortar enters the sleeve, dowel
movement will be hindered.
Even though dowels and tie-bars may be perfectly
placed, movements perpendicular to the bars and
parallel to the joints are restrained, causing notable
stresses which lead to cracking or failure. However,
these stresses were not included in the analysis and
design of the slab.
Usually, large floor slabs or pavements are dealt
with by using the long-strip method. More specifically,
lanes are placed separately each day and the intervals
are filled later. When placing the lanes, workers saw
cut transverse contraction joints the same night or the
next day. After one or two days, cracks occur below
the saw cuts and thus the joints open. The main
problem of this method takes place several days after
the filling of the aforementioned intervals. The new
concrete tries to contract but the bars in the
longitudinal joints resist. Certainly, the new concrete
has not developed its full strength and cannot
withstand the tensile forces applied to it.
Consequently, cracks are formed.
Also most designers usually ignore the horizontal
shear force occurring parallel to the joint at about the
end of the bars. It is also essential to say that slabs,
when put into service, can be already cracked or
highly stressed. Especially at the intersection of
transverse and longitudinal joints, stresses accumulate
and thus cause corner cracking, as shown in
Fig. 1 [1, 2].
3. Description of a Jointless Solution
3.1 Floor Loadings
The loads, slabs-on-ground are subjected to, fall
into two categories: Gravity loads and restraints. The
first category includes forklift and heavy wheeled
vehicle traffic, block stacked pallet loads, racking
loads, loads from bearing masonry or partition walls
and loads from fixed machinery and equipment. The
836
Fig. 1
Design of Monolithic Concrete Ground Floors
Cracking caused by bars at the corner of a slab.
second category includes differential settlements,
uniform temperature changes ts, temperature
difference between the top and bottom side of the slab
Δt, concrete drying and concrete deformations.
Reliable load carrying capacity is of utmost
importance in ground slabs design. Self-weights and
service loads are determined by codes where point
loads (derived from forklifts) are given. These point
loads fall into six different categories. As far as the
wheel loads and the dynamic amplification factor of
machinery equipment are concerned, they have to be
estimated with the help of the owner’s contribution as
well.
All the above apply both to the self-weight loads
and service loads of racking systems, too. Attention
should be paid to manufacturer’s details. Furthermore,
as for the racking systems, measures must be taken
against their overturn caused by horizontal seismic
load applied to the center of gravity of stored material.
Regarding the racking systems and forklifts, it is
critical for the stress calculation of ground slabs to
consider their total load. Concerning the truck traffic
loads, they have to be determined with the help of the
owner’s contribution, likewise forklift loads.
Regarding indoor ground slabs, uniform
temperature changes ts equal to ±25 oC according to
EC-1 must be considered. Also, in order to estimate
the deformations due to concrete drying, primarily in
the incidence of large glass facades, it is possible even
for indoor conditions that an equivalent temperature
greater than 35 oC is required. In the case of indoor
slabs, application of temperature gradient is not
required, provided that: (1) the placement of the slab
is accomplished after the construction of the roof and
exterior walls; (2) the room is already heated.
For the sake of simplicity, live loads and restraints
are determined using a safety factor equal to γQ =1.5
and γQ =1, respectively. The application of ψ
combination factors would give the illusion of
computational accuracy but due to the multiple
elements that influence the ground slab behavior, such
an effort would be pointless. This fact characterizes as
well the concrete modulus of elasticity estimation. For
the design and construction of ground slabs, the
Design of Monolithic Concrete Ground Floors
modulus of elasticity of concrete is considered equal
to Ec = 30,000 N/mm2, which is quite accurate if it is
referred to usual classes of concrete (C25/30, C30/37).
The thermal expansion coefficient αt for concrete and
steel is assumed to be equal to 1.0 × 10-5 K-1
according to EC2 [3-7].
3.2 Restraints Consequences
3.2.1 Uniform Temperature Changes
Friction between the slab and the soil generates
compressive stresses at the bottom surface of the slab
with increasing temperature and tensile stresses with
decreasing temperature, as indicated in Fig. 2. Long
span slabs exhibit greater sensitivity.
A jointless slab lying on graded crushed aggregates,
despite the presence of a slip membrane that hinders
its movements, forms cracks under a temperature
reduction of 20 oC. Stresses resulting due to the above
temperature reduction are given by the relation:
t t t s Ect 1105 20
30,000
3 N/mm2 f ctm
2
(1)
where,
Ect = 0.5·Ec (Ect = modulus of elasticity under
tensile forces);
fctm = 2.9 N/mm2 for C30/37.
The above concrete flexural strength fctm is not
sufficient to prevent cracking. It should be noted that
expansion and contraction of concrete is an
Fig. 2
(a) Expansion
Forces developed at the slab with temperature changes.
837
asymmetric
phenomenon.
More
specifically,
contraction due to concrete drying (from 0.02% to
0.04%, giving an equivalent temperature reduction
from 20 oC to 40 oC) combined with contraction due
to temperature reduction, results in a restraint load
much greater than this of temperature increase.
Moreover, if the EC1 values ±25 oC for temperature
changes are considered, it is apparent that the
temperature increase’s influence is eliminated by the
equivalent contraction due to drying. At the same time,
the combination of the latter with the thermal
contraction creates an equivalent contraction which
corresponds to a 50 oC to 60 oC temperature reduction.
3.2.2 Uneven Temperature Changes
Temperature increase on the top surface of the slab
accompanied by its delay in reaching the bottom
surface, results in slab curling, as shown in Fig. 3.
In order to calculate the curling stresses in ground
slabs, a temperature gradient Δt is initiated. Δt reaches
a value of approximately 5 oC at indoor slabs. This
temperature difference between the top and bottom
surface of the slab generates curling in its middle area.
In response to this curling, self weight loads activate
flexural stresses on the bottom side of the slab which
are regarded as curling stresses. When the slab to be
designed has theoretically infinite length, its shape of
deformation is similar to this of a clamped slab on two
or all four sides [3, 6].
(b) Contraction
Design of Monolithic Concrete Ground Floors
838
Fig. 3
(a) Temperature distribution across the slab; (b) slab curling.
4. Description of the Jointless Solution
4.1 Introductory Elements
In order to design a ground slab, several
requirements should be taken into consideration.
Namely, the type of load applied (static loads,
restraints), the desirable working life and soil
conditions. Ground slabs require high quality concrete
for the following reasons: (1) The high strength that
characterizes high quality concrete, permits the
reduction of slab thickness and that fact has beneficial
effects on the elimination of the Δt restraint and on the
better behavior regarding differential settlements, since
the moment of inertia is drastically decreased and the
modulus of elasticity remains more or less the same; (2)
It is known that the impacts of contraction due to
drying and creep weaken on high quality concretes; (3)
By reducing slab thickness, self weight reduces as well
and as a result, friction between the slab and the
subbase lowers; (4) In the case that the slab is
reinforced conventionally or with steel fibers, the
controlled transition from uncracked to cracked phase
(in terms of acceptable crack width) requires lower
steel per concrete ratio, by virtue of concrete strength.
The issue of ground slabs reinforcement went
through many phases before settling on steel fiber at
low percentage of reinforcing steel (25 kg/m3). The
main purpose of this solution is to enhance concrete
ductility rather than to increase its tensile strength, to
which steel fiber reinforcement little has to offer.
Additionally, it would be unwise to increase steel
reinforcement, since concrete workability would be
impaired and its placement time would be
unprofitably elongated with few positive results on its
strength. However, steel fiber reinforcement has two
advantages. Firstly, the construction time is shortened
and secondly, it does not influence the
electromagnetic field that automated vehicles need to
operate. In contrast, conventional reinforcement does
affect the electromagnetic field and for that reason, is
placed below the zone that concrete coverage
requirements dictate. As a result, the static height of
Design of Monolithic Concrete Ground Floors
the reinforced slab shortens [8].
4.2 Philosophy of Recommended Solution
The description of the proposed jointless solution
for indoor ground slabs are given in the following.
Concerning the joints, only the isolation joints of
vertical bearing elements are included in this solution,
either being within the slab plan or on its perimeter.
Around the perimeter of the slab, two construction
methods could be applied.
In the first method, slab boundaries are not
connected to the foundation walls which enclose the
slab foundation (subbase and subgrade). In the second
method, slab boundaries are monolithically connected
to the foundation walls which partially impede the
slab deformation towards the center of its plan. The
upper edge of the foundation wall is subjected to a
restraint load which must be taken into account. So
measures should be taken to confront this problem.
One of these measures could be the improvement of
passive forces resulting from the subbase and
subgrade (which constitute the slab foundation)
resistance to the inward movement of the foundation
wall. Another measure (that mostly helps the
structural system to adapt to the problem rather than
to solve it), is the expansion of the foundation wall
footing in order to prevent high rotational movements.
The thickness and reinforcement of the foundation
wall in its base should be calculated regarding the
aforementioned restraint load. The increase in passive
forces of slab foundation could be achieved by
impregnating the graded crushed aggregates with a
cement mixture within a zone of 1 m width.
It is obvious that the method described in the
beginning permits free movement of the slab with the
exception of friction forces which oppose that
movement. Friction forces are limited due to the low
thickness, hence the low self weight of the slab,
despite the increased value of the friction factor which
varies from 1.5 to 1.8. In the second method, slab
movement is impeded and friction forces are very low,
839
provided that the deflection of the upper edge of the
foundation wall is practically zero.
In the case of jointless slabs, their minimum
thickness which is approximately 150 mm suffices to
accommodate all requirements. The reason is that in
jointed slabs, the maximum tensional stress when the
load is applied to their perimeter is almost twice the
value of the tensional stress when the load is applied
to the middle area. The minimum thickness is
estimated with regard to minimum concrete covers
and the requirement of fitting two grid reinforcements
inside the slab. Apart from the absence of joints, high
quality concrete contributes significantly to the
adequacy of slabs load bearing capacity. Another
reason leading to smaller slab thickness, is the
minimization of reinforcement against restraints,
which is expressed as a percentage of slab section
area.
It is no exaggeration to say that the combination of
high quality concrete, the absence of joints and the
minimum slab thickness (15 cm) ensures a reliable
load bearing capacity to uncracked concrete and
without the reinforcement’s contribution. However,
absence of joints implies restraint forces which
provoke tensional and flexural stresses which will
definitely result in cracking. This crack width could
be limited by grid reinforcement which is calculated
by the following formula:
A
As k f ctm ct
(2)
s
where,
Act is the tension zone of uncracked concrete;
fctm is the average tensile concrete strength;
k is the coefficient determined considering the
stress condition of the structural element, for pure
tension and rectangular section k values depend on the
thickness of the structural element according to Fig. 4;
σs is the reinforcement tension (cracked concrete),
determined considering the selected diameter and the
maximum tolerable crack width which is equal to 0.3
mm or 0.2 mm.
Design of Monolithic Concrete Ground Floors
840
150 mm
100 mm
Fig. 4
Ø8/100
k coefficient values for pure tension.
Based on this formula, the reinforcement
percentage in both directions equals to ρ = 0.85 ×
2.9/350 = 0.007.
Consequently, the per meter steel reinforcement
area is As = 0.007 × 15 × 100 = 10.5 → 2Ø8/100 mm
(meaning that one bar is placed in the top and the
other in the bottom of the slab).
Fig. 5 shows the response of ground slab during
winter, in terms of applied force vs. width of
developed cracks. In the ground slab under tension,
the stresses of the longitudinal reinforcement
equilibrate the tensile stresses that are developed in
the element.
Fig. 6 presents the idealized behavior of a
reinforced concrete tie. According to this figure, the
contribution of the concrete may be considered to
increase the stiffness of the tensile reinforcement
(tension stiffening effect).
Fig. 7a shows the distribution of strains after the
appearance of the first crack, while Fig. 7b depicts the
distribution of strains after the element has been fully
cracked. In the areas between cracks, the tensile forces
Design of Monolithic Concrete Ground Floors
Tensile force
841
0
0.1
0.2
0.3
0.4
Crack width (mm)
Fig. 5
The response of slabs under changing tension.
Fig. 6
The idealized behavior of a concrete tie.
are transferred from steel to concrete by the friction
(bonding)
forces.
Concrete
contributes
to
reinforcement’s axial stiffness increase. The aim is to
reduce the width of the cracks induced and to keep
them within acceptable limits according to the
Eurocode 2-Part 1 (2004).
The restraint load per meter, in the extreme scenario
of immovable top edge of the foundation wall, is
calculated as follows: Fs = As × σs = 10 × 35 = 350 kN.
It is important to outline that the limited rigidity of the
foundation wall contributes drastically in decreasing
the restraints of the slab, since its movements are not
842
Design of Monolithic Concrete Ground Floors
(a) Single crack
(b) Final stage
Fig. 7 (a) The distribution of strains after the appearance of the first crack; (b) the distribution of strains after the element
has been fully cracked.
Fig. 8
Stress-strain diagrams of ties for several reinforcement percentages.
totally hindered. The response of slabs subjected to
restraints, is displayed in Fig. 8. According to Fig. 8,
after the uncracked phase of the slab (until a strain of
0.015% which initiates cracking), the cracked phase
follows during which reinforcement’s tension remains
almost stable up to a strain limit and eventually the
restraint load does not increase. It is implied that due
to the hindrance of slab contractions, its behavior
resembles that of a reinforced concrete tie rod. In the
case that the combination of temperature reduction
and drying contraction (which is regarded as
equivalent to a temperature reduction of 30 oC
because of high quality concrete) is considered as the
critical restraint load, then the total temperature
reduction would be T = 30 oC + 25 oC = 55 oC,
resulting in a strain of ε = αt × T = 10-5 × 55 = 0.00055.
According to Fig. 8, the strain value lies within the
sawblade-like section of the diagram, meaning that the
stresses of the slab reinforcement will not reach the
maximum tolerable value of σs = 350 MPa. That being
said, the crack width will be lower than the acceptable
value. Moreover, the restraint load, which has been
estimated equal to 350 kN, is actually smaller because
of reinforcement stress reduction. Fig. 8 displays the
stress-strain diagrams of ties for several reinforcement
percentages [9, 10].
Design of Monolithic Concrete Ground Floors
Creep effect is an additional factor that increases
significantly the movements at the top edge of the
foundation wall. Creep introduces a lasting force
which probably contributes to the most part of the
foundation wall deflection. As mentioned before, this
deflection permits the stress relief of the slab from
restraints.
Fatigue is the Achilles’ heel of unreinforced jointed
slabs, whose durability becomes extremely low due to
this fact. The recommended solution burdens the
reinforcement with this problem, so slabs employing
this solution hold a considerable advantage over
fatigue.
The aforementioned curling issue and generally the
elevational displacements of a slab, which does not
Fig. 9
Fig. 10
843
have the relieving effects of joints, constitute a
problem not to be ignored. However, in this particular
instance, there are two favorable facts: The first is the
small thickness of the slab and the second the
favorable
indoor
conditions.
Furthermore,
reinforcement confronts the combination of stresses
due to curling and those due to gravity loads
effectively, in comparison with unreinforced slabs.
Nevertheless, the present work recommends a
mechanism
which
restrains
the
transverse
displacements of the slab, at the intersection points of
a rectangular grid whose size varies from 5 m × 5 m to
7 m × 7 m. It is essential to clarify that the slab plane
is parallel to the grid plane. In the following paragraph,
a typical restraining point is described.
Curling prevention mechanism.
Jointless slab which connects the interior retaining wall with the perimeter foundation wall.
844
Design of Monolithic Concrete Ground Floors
Before the layers under the slab are compressed, a
special “foundation-slab” measuring 1 m ×1 m area
and 30 cm thickness is concreted and slightly
reinforced with a grid at its top surface. To the center
of the foundation-slabs, a plastic or stainless tube is
clamped which extends almost up to the lower level of
the slab. The diameter of the tube could be of the
order of 10-15 cm and its interior is partially filled
with concrete, clamped to the foundation-slab via slim
reinforcement bars. A 6/10-inch steel rope is
embedded in the tube’s concrete and its upper end is
to be anchored in the slab. The installation of this
mechanism is followed by the compression of the
supporting layers of the slab and its concreting. The
steel rope resistance to the vertical displacements of
the slab is assisted by the weight of the layers lying
between the slab and the foundation-slab. Toward this
end, the reason using steel rope instead of
conventional reinforcement bar, is that the first can
easily accommodate the displacements (due to
expansions and contractions) parallel to the slab plane,
in contradiction to the latter which no matter how slim
or flexible is, cannot meet the requirements. Fig. 9
displays this mechanism.
5. Application
The procedures described before were tested in one
of the warehouses of the supermarket chain
“MASOUTIS” located in Thessaloniki. The technique
was applied to a part of the warehouse slab (15 m ×
120 m area) which bears stored material loads and
material handling equipment loads. The slab in
question is located inside the warehouse and connects
the top edge of the interior retaining wall with the top
edge of the foundation wall of the elevated floor. This
connection is intended to support the retaining wall
which was designed as supported at both ends (the
one end fixed, the other simply supported) and not as
cantilever. After two years, no cracking has occurred
in the slab which absolutely meets all serviceability
demands. Fig. 10 shows the method of application.
6. Conclusions
Recent years have shown that conditions for
complete suppression of joints in large length and area
constructions are now mature. Inspired by this fact,
the authors of this paper present a solution for ground
slabs that takes us one step forward concerning the
monolithicity of these sensitive structures for which
joints imply many problems. Finally the following
conclusions are summarized.
The recommended solution constitutes a global
approach to the problem, since it provides measures
for all possible strains and especially those deriving
from restraints.
The recommended solution could be characterized
as economical in terms of concrete consumption, as
the slab thickness is significantly reduced.
As for the construction time, the present proposition
loses the edge due to the time consuming
reinforcement placement, however it does not employ
dowels and joints which also require time for their
proper application.
The present proposition prevails in terms of
maintenance cost which is diminished.
The recommended structure holds a considerable
advantage against fatigue and lasts longer than the
jointed one.
A large-scale application, which could be
considered as experimental confirmation, is proved
successful after the lapse of two years from the
construction date.
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[1]
[2]
[3]
[4]
E.K. Schrader, A solution to cracking and stresses caused
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ACI Committee 360, ACI 360R-06, Design of
Slabs-on-Ground, Farmington Hills, MI, 2004.
European Committee for Standardization, EN
1991-5:2003, Eurocode 1: Actions on Structures—Part
1-5: General Actions—Thermal Actions, Brussels,
Belgium, 2003.
European Committee for Standardization, EN
1992-1:2004, Eurocode 2: Design of Concrete
Design of Monolithic Concrete Ground Floors
[5]
[6]
[7]
Structures—Part 1: General Rules and Rules for
Buildings, Brussels, Belgium, 2004.
European Committee for Standardization, EN
1992-1:2004, Eurocode 2: Design of Concrete
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