Easy Blok Technical Guide

Technical guide for Easyblok EPS formwork

ZavattiShop provides you with the technical guide for the Easyblok EPS formwork, for the construction of swimming pools.

In this guide you will find:

• Technical-structural report for poolside walls with EASYBLOK elements;
• Guidelines for structural sizing;
• Guidelines for correct installation: blocks, reinforcement and pouring.

NB = Technical-Structural Report published by the Zavatti Shop Technical Office

Updated in its entirety following the entry into force of the Ministerial Decree of 14 January 2008, it is intended to provide valid technical support for the supply and construction of "polystyrene swimming pools". It is not a complete design tool, nor does it replace one, as it is required by law.

Technical-structural report for poolside walls with Easyblok elements

Product Description: Polystyrene Pool?

Material

EASYBLOK elements are made of EPS, or sintered expanded polystyrene, using an industrialized process that ensures the element's uniformity of material and dimensions, essential characteristics for the applications this product finds on the market. Although it's commonly called "swimming pool polystyrene," it's actually a truly durable material, suitable for the construction of these structures.

The strength of the product lies in its strength-to-weight ratio.

Sintered expanded polystyrene generally has a density between 10 and 40 kg/m3, and is therefore on average composed of 98% air and only 2% pure hydrocarbon structural material. In addition to water vapor, only pentane is used to produce expanded polystyrene, which evaporates at the end of the expansion process.
Chlorofluorocarbons (CFCs), which are harmful to the ozone layer surrounding our atmosphere, are not used, nor have they ever been used. Therefore, the weight of each individual element is negligible. However, this does not apply to rigidity (and, indirectly, resistance). In fact, the internal ribs provide excellent rigidity and compactness to the product. This allows for ease of handling and quick installation, and a low risk of damage and warping of the elements.

Internal ribs - Straight EASYBLOK element.

Internal node - Straight EASYBLOK element.

Sizes and cuts

The company currently has the following EASYBLOK elements for skimmer pools:

• STRAIGHT ELEMENT 1250 X 250 X h300 mm;
• STRAIGHT ELEMENT 1250 X 250 X h250 mm;
• BENDABLE ELEMENT (radius h300: 0 ・ 1.5 ・ 2 ・ 2.5 ・ 3 - radii h250: 0 ・ 1.5 ・ 2 ・ 2.5).

As is clear to see, swimming pools with a straight edge are easily modular, especially if the dimensions are multiples of 1250 mm.
This not only saves a lot of time but also results in a more uniform wall, with all the blocks fitting together perfectly.
The elements are assembled using tongue-and-groove joints, carefully crafted on both the horizontal and vertical walls. Horizontal joints provide greater stability to the element against horizontal loads, while the vertical protrusions allow the formwork to withstand shear forces both during pouring and during the concrete's curing phase.
An H-shaped section was created inside, allowing the concrete to flow within the formwork and between the reinforcing bars, creating a reinforced concrete lattice composed of uprights and crosspieces. With the curved formwork, the lattice does not undergo any dimensional variation and is projected onto a curved surface that can be concave or convex. In the latter two cases, the rigidity of the structure is significantly increased due to the shape effect.
The lateral faces parallel to the long side are perfectly smooth in order to allow perfect adhesion of the waterproof sheet, which is subsequently laid.

Application as a lost formwork

The poolside walls are constructed using EASYBLOK elements as formwork to contain the concrete during pouring. Once cured, they no longer perform any static function, being much less rigid and in any case not connected to the concrete.
Having said that, it is worth remembering that the poolside walls created with the method proposed here use the EASYBLOK elements as permanent formwork and the structural body is to all intents and purposes a reinforced concrete structure.
The choice to use disposable formwork stems primarily from the increasingly shorter timeframes available today; in fact, it is no longer necessary to wait the traditional 28 days for the concrete to cure before proceeding with the stripping operations.
Equally important is the cleanliness of the construction site and the equipment used. By choosing disposable formwork, the required tools are reduced to a few units, resulting in significantly reduced management costs and significantly lower risks for operators.
Finally, the use of EPS formwork provides insulation for the concrete, which, as it cures inside the formwork, produces hydration heat. Good insulation minimizes the thermal gradient between the core of the wall and the exterior, thus reducing thermal cracking.

Huge and measurable benefits

Having presented the product from a technical perspective, it is now worth recalling the main points that distinguish its use.

LIGHTNESS - EASE OF HANDLING - MODULARITY

The EASYBLOK formwork allows for the construction of reinforced concrete walls in complete safety, without risking the health of workers. The loads transmitted to the foundation are relatively low, allowing for smaller dimensions and smaller reinforcement. Less material does not mean less strength, but rather better utilization of its mechanical properties.
Poolside pools made with EASYBLOK elements are quick and easy to build, and economical because they reduce time, labor, and equipment.
The standardization of measurements allows us to refer to a few construction elements and at the same time, if combined correctly, to create an infinite number of shapes and designs.
Zavatti Shop's offering is cutting-edge in this regard because it takes advantage of affordability and timeliness while complying with workplace safety regulations.

SPEED OF EXECUTION – ECONOMY

With EASYBLOK elements, you can build pools of any depth in a fraction of the time. The lightweight formwork is easily assembled, effectively resists the effects of pouring, and provides an excellent surface for installing the waterproof liner.
Comparing these operations to a cast-in-place pool, it's necessary to take into account the concrete curing time before stripping, the inspection and smoothing of the rough concrete wall, and all the equipment needed to construct the formwork to contain the pour. Ultimately, poolside walls with EASYBLOK elements reduce construction time by more than 50% and completely eliminate the need for boards, panels, spacers, and anything else needed to construct a reinforced concrete wall.

The new Technical Standards for Construction

Nominal life and use classes

According to the NTC, “The nominal life of a structural work VN is understood as the number of years in which the structure, provided it is subject to ordinary maintenance, must be able to be used for the purpose for which it is intended.”

Regarding building use, the technical building regulations provide four different classes based on the building's intended use. The classification is in ascending order, from the least important building in use class I to the strategic building requiring the greatest attention, placed in use class IV.
The above, in addition to being a useful way to classify the building we are about to design, is particularly useful for calculating the reference period VR when evaluating the seismic action on the building. In fact:

VR = VN ・ CU

In this regard, it is considered interesting to report a calculation table of the VR reference period, keeping in mind that if VR < 35 years, VR = 35 years is still assumed.

For structures with a nominal life of 10 years, regardless of the usage class, the reference period is taken as 35 years. However, the NTC specifies that, in seismic zones, if the building in question has a nominal life of less than two years, then structural checks can be waived.

Structural Design at Limit States

Current structural design is based on the semi-probabilistic Limit State calculation method. According to the Ministerial Decree of January 14, 2008 (hereinafter referred to as the Technical Standards for Construction NTC), "a limit state is defined as the condition beyond which the structure no longer meets the requirements for which it was designed."
The Technical Standards for Construction, harmonized with the Eurocodes, propose two types of Limit States which, in a very simplistic way, monitor the structure at two different moments in its life: a common limit state for every day and called the Serviceability Limit State (SLS), while a second, rarer and decidedly more important one is called the Ultimate Limit State (SLU).
The main objective that the structural designer must pursue is that the works must be able to possess the following requirements:

• Ultimate limit state safety: that is, the ability to avoid collapses and serious damage that could compromise human safety. Exceeding an ULS is irreversible.
• Safety with respect to serviceability limit states: that is, the ability to guarantee the performance expected for serviceability conditions. Exceeding an SLS can be reversible or irreversible.
• Robustness against exceptional actions: that is, the ability to avoid damage disproportionate to the importance of the triggering causes, such as fires, explosions, impacts, etc.

Italy is an earthquake zone

The NTC (National Technical Regulations) provide a new seismic classification for our country. The first major change is that all of Italy has become a seismic zone. The country has been divided into four zones of decreasing seismic hazard. Designers also have access to a fairly fine-meshed grid from which to obtain the key values ​​for performing a modal analysis. A spreadsheet, developed by the Central Technical Service, also provides response spectra representing the components (horizontal and vertical) of the design seismic actions for a specific site in the country.

Thin, lightly reinforced wall

Transition from mixed wall to reinforced concrete partition

By cross-sectioning the pool edge wall in the upright area, a “sandwich” can be observed consisting of two EPS walls and a concrete core with a thickness equal to the remaining 165 mm.
For example, in the case of an in-ground pool, the situation is as follows:

In the area between one upright and the next, the EASYBLOK element features a connection between the two external walls, thus reducing the thickness of the concrete and creating an H-shaped section.
Having said this, it is clear to understand that there is a local variation in the thickness of the concrete that constitutes the load-bearing partition.
For the purposes of studying the structural behavior of the poolside wall, it is best to move on to the equivalent reinforced concrete partition under the following two hypotheses:

• The cross-members provide two-dimensional behavior to the structural organism
• the recess at the ends and the running reinforcement provide continuity between the EASYBLOK formworks

That said, it's clear to see how there's a local variation in the thickness of the concrete forming the load-bearing partition. The dimension ranges from a minimum of 120 mm in the H-section to a maximum of 165 mm in the upright cross-section. To study the structural behavior of the pool wall, it's best to consider the equivalent reinforced concrete partition under the following two assumptions:

• the cross-members provide two-dimensional behavior to the structural organism;
• the recess at the ends and the running reinforcement provide continuity between the EASYBLOK formworks.
  

By virtue of what has been said, it is possible to calculate the thickness of the equivalent partition to be used in the structural sizing by operating as follows: 5 uprights 165 x 165 mm = 1 partition 125 x S mm

where S is the thickness of the equivalent septum we obtain
s = ( 5 x 165 x 165 ) / 125 = 109 mm

In both the Ultimate Limit State and Serviceability Limit State structural checks, the equivalent partition will be used, considering its global behavior obtained from a three-dimensional Finite Element model.

Armor: Where, How, and Why

As the notation itself, reported in the "Technical Construction Standards" detailed below, states, the structural body is a thin, weakly reinforced wall. This implies that the amount of reinforcement present within must be calculated using a rigorous calculation process that takes into account all relevant factors. The result is a correct use of reinforcing bars, commensurate with the characteristics of the steel, both in terms of quantity and quality.
With the introduction of the New Technical Standards for Construction, the reinforcing steels for reinforced concrete structures are B450A and B450C. The former is obtained through a cold rolling process and is typical of lattice girders and electro-welded mesh.
B450C steel is the classic reinforcing bar commonly known to all and produced through a hot rolling process. The acronym still contains two elements: the letter B, which stands for "Beton" (concrete, hence reinforcing steel), and a number indicating the characteristic yield strength. The European Union has established that this value, based on appropriate tolerances (which are omitted here), is equal to 500 N/mm2, but for countries with high seismic risk, such as Italy or Greece, it was preferred to reduce the resistance value in favor of increasing the material's ductility.
Regarding the placement of reinforcement, it's well known that it should be placed where tensile stresses are generated in the concrete. Therefore, it's necessary to identify the stress state within the structure and position the reinforcement. The fact that the wall is "thin" and "weakly" reinforced shouldn't be a sign of distrust. In fact, for structures like poolside walls, the stresses involved are almost always low, and this type of solution proves to be effective, safe, and economical.

Concrete: quality and durability

In this case too, the New Technical Standards for construction provide detailed and comprehensive indications regarding the mechanical properties, requirements and acceptance control of concrete.
For structural calculation purposes, according to the Technical Standards for Construction, concrete is classified according to the resistance class CX/Y where:
C = concrete
X = characteristic cylindrical compressive strength [ N / mm2 ]
Y = characteristic cubic compressive strength [ N / mm2 ]

There are two main types of concrete: engineered mix and guaranteed performance. The latter is the most common type, and for this type, the following items must be specified when ordering:

• Resistance class
• Consistency class
• Environmental exposure class
• Maximum aggregate diameter

It's highly anachronistic and incorrect to require concrete with a specific cement content, as the strength of the mix depends not only on the amount of binder. This strength is, in fact, a function of the mix design, which in turn must meet construction site requirements, such as workability, and the durability of the workpiece through its environmental exposure class.
For poolside walls with EASYBLOK elements, it will be very important to prescribe a concrete with an adequate consistency class to allow it to completely and homogeneously fill the cavities of the formwork without segregating.
One could even consider using a concrete mix with a finer grain size, which enhances workability. The strength class should be chosen primarily based on the resistance required to withstand the stresses encountered during operation. In this case, the environmental exposure class is significantly reduced due to the complete protection of the concrete within the EASYBLOK elements.

Structural behavior

Poolside walls made with cast-in-place EASYBLOK elements are similar to reinforced concrete partitions. As described in the previous pages, from a structural standpoint, they are a thin, weakly reinforced wall.
The wall is a two-dimensional structural element because its two dimensions are significantly larger than the third. This results in a two-dimensional behavior that allows for better distribution of stresses during operation. Furthermore, the wall is a structural element with two very different stiffness values; the one perpendicular to the midplane fluctuates around discrete values ​​depending on the length of the external wall and the influence of the interlocking at the ends. The stiffness measured parallel to the midplane, on the other hand, is characterized by significant values ​​that allow for excellent management of horizontal forces.

Static loads

In the case in question, the static loads derive from the self-weight of the structure, the weight of the soil wedge identified by the internal friction angle and the weight of the water contained within, when considered in static conditions.
In the case of an in-ground pool, the dominant action will be the push of the ground, especially when the pool is empty for maintenance operations.
In the case of an above-ground pool, however, the predominant action is hydrostatic thrust. In this case, a careful study of the pressure curve is required to determine the tensile and compressive zones, as well as the balance and stability of the wall.

Dynamic loads

The dynamic actions that may be of interest in this case are mainly the earthquake and the water present inside the tank.
Regarding seismic action, in light of what was previously reported (in the chapter "Italy and Seismic Zones"), the magnitude of the action is determined by the seismic zone within which the structure falls, the topographical conditions, the type of building, and its intended use. The study must be conducted through a dynamic modal analysis, taking into account the entire structural organism. If the structure presents regularities in plan and elevation, a fairly rare case, it is permissible to conduct an equivalent static analysis. Again, according to the Technical Building Standards, following the structural analysis, a careful evaluation of the construction details is mandatory. The construction of the structure must scrupulously follow the indications reported in the design documents without oversizing individual elements. This would lead to an imbalance in the resistance hierarchy principle, resulting in the structural components' malfunctioning during an earthquake. The study of fluid-structure interaction is also very important for evaluating the stresses produced by the water contained in the pool.

The study of fluid-structure dynamics is highly complex and requires in-depth analysis. Indeed, when the walls of tanks, subjected to seismic excitation, undergo displacements, a certain amount of liquid participates in this motion, moving along with the walls, while the free surface of the liquid oscillates freely within the tanks.
The oscillation of the free surface of the liquid is a phenomenon closely related to the significant geometric relationships of the tank, particularly the ratio between the height of the liquid and the length of the tank (in the direction of the earthquake). The first portion of the mass is called the impulsive mass: it moves rigidly with the walls of the tank. The second portion is called the convective mass: it moves independently of the walls of the tank, generating the so-called "sloshing" phenomenon, i.e., the oscillation of the free surface of the liquid.
A rigorous study requires a rational method based on the solution of the hydrodynamic equations with appropriate boundary conditions [EC8]. Alternatively, a simplified model based on a mechanical analogy can be adopted, as proposed by G.H.Housner [The dynamic behavior of water tanks, contained in Bulletin of the Seismological Society of America, Vol. 53, No. 2, pp. 381-387, February 1963].
The salient passages of the article in question are reported: if a tank containing a liquid has a free surface and is subjected to a horizontal acceleration of the ground, the forces exerted by the liquid on the structures of the tanks are of two types:

• First, when the wall of the tank accelerates, a certain portion of the liquid is forced to participate in the motion, and exerts an inertial force (impulsive component) on the wall. This force is the same that would produce a mass M0 rigidly connected to the walls of the tank at a height h0, as shown in the figure.
• Second, the acceleration of the tank wall causes oscillations in the free surface of the liquid, thus exerting a certain force on the walls themselves (convective component). This force, according to the Housner model, is the same as that produced by a mass M1 connected to the walls with a spring of stiffness kc placed at a height hc from the tank bottom.

For the calculation and definition of the above quantities, reference was made to the American standard ACI 350-3 “Seismic design of liquid-containing concrete structures” issued by the American Concrete Institute - Committee 350.
For a circular pool of diameter D (the case of curved edge pools) and a water height equal to HL, the above quantities can be calculated as follows:

For a rectangular tank of length L (in the direction of the earthquake considered) and water height HL

The modal analysis is then performed using this mechanical model, taking into account a sufficient number of vibration modes to ensure the excitation of at least 85% of the structure's total mass. The resulting quantities (nodal displacements) for each vibration mode are composed using the SRSS (Square Root or Sum of the Squares) method.

Structural Design Guidelines

Environmental exposure class according to EN 206-1

To ensure this condition, the concept of structural durability must be taken into consideration.

According to EN 206 – 1 and UNI 11104, the environmental exposure classes adopted are the following:

FOUNDATION STAND
XC2 Wet, rarely dry. Concrete surfaces in contact with water for extended periods.

TUB EDGE WALL
XC1 Dry or permanently wet. Concrete surfaces with low relative humidity.

Iron cover

Looking at the attached drawings, it is clear that the concrete cover of the metal reinforcement is of interest only as regards the foundation, as the concrete forming the pool edge wall is completely protected by the EASYBLOK elements and the waterproof sheet used on the surface of the pool.
That said, it should be noted that with regards to the foundation slab, in light of the qualities of the concrete reported below, the concrete cover of the metal structures is as follows:

Cnom = Cmin + Δtoll = 30 + 10 = 40 mm

Where:

• Cnom nominal concrete cover value;
• Cmin minimum value of the concrete cover to be achieved;
• Δtoll geometric and construction tolerance to be taken into account to compensate for any inaccuracies during the execution phase.

The structural organism

According to Presidential Decree 380/2001 – Art. 53-comma1, the swimming pool is to all intents and purposes a structure as it is subject to loads that require it to have a load-bearing function.
Therefore, its construction must be carried out according to an executive plan drawn up by a qualified technician. The resulting structural body is made up of the elements illustrated below.

Foundations

Foundations are designed to transfer loads to the ground upon which the structure is built. The choice of type and their sizing must be based on the mechanical characteristics of the ground itself and the magnitude of the loads involved.
Generally, a foundation slab is required, which is immediately finished using special equipment (helicopter) to create a smooth, level base ready for the waterproofing membrane to be laid. Because this type of foundation distributes loads very well to the underlying soil, it is used in the vast majority of cases.

If the foundation slab is not sufficient to guarantee the safety and stability of the building, it is possible to switch to special foundations such as piles.
Clearly, this solution is rarely used in the world of swimming pools, especially because the amount of load to be transmitted to the ground is so small that even good mechanical characteristics of the ground are still sufficient to guarantee stability.

Once the structure enters service, for example, with the addition of the walls and/or filling the pool, these walls are subject to compressive bending. In fact, compression along the vertical plane is minimal because it is due solely to the self-weight; furthermore, it proves to be a stabilizing factor with respect to the overall equilibrium, so during the design phase, it is neglected in favor of safety. Bending causes partialization of the cross-section, which must certainly be reinforced where tensile zones exist. The position and quantity of the reinforcement is therefore a function of the loading conditions and the type of pool being built. It is important to distinguish between straight and curved walls. In the latter case, the two-dimensional behavior is much more pronounced, with the activation of resistance due to the shape effect and the increase in thrust when the curvature favors thrust. In these cases, it is advisable to conduct a local study of the structural behavior and the required reinforcement, as tensile stress occurs not only in the vertical cross-section, but also in the transverse direction.

Calculation model and constraint conditions

In itself, the analysis of any structural organism should be conducted at a global level and only later at a local level to better understand particular structural mechanisms or, for example, to manage high concentrated loads.
Therefore, for straight-sided pools, and even more so for curved-sided pools, it's a good idea to create a mathematical model that simulates the structure's behavior under load. It should be noted that complex discretizations and refined geometric models are unnecessary; a simple and accurate model that accurately captures the pool's response is sufficient.

However, simplified methods exist in the literature for calculating the main stress characteristics. Below are two useful procedures for this purpose, valid only for straight walls.

If a single rectilinear wall is less than approximately twice its height, it is affected by the interlocking effect caused by the corners. This results in rigid wall behavior, with a bending moment that changes sign near the base. By studying the wall's cross-section, it is possible to model the structure as a shelf interlocked at the base with support at the top.

Edge influence – interlocking effect – Model with interlocking at the base and support at the top.

If a single rectilinear wall has a length greater than twice its height, the influence of the edge is no longer significant. As the wall grows in length, its deformability increases, reaching its maximum at the midpoint. By studying the wall's cross-section, it is possible to model the structure as a cantilever fixed at the base. As is easy to imagine, the deformations will be significantly greater, also because they all have the same sign; the bending moment at the fixed point will also have higher values ​​than in the previous case, as there is no longer any constraint at the top.

Loss of interlocking effect - Model with interlocking at the base

Load analysis

A fundamental step in structural design is defining the loads and magnitude of the forces acting on the structure. The structure must be placed within the context in which it will perform its intended functions and derived from there. For a swimming pool, in addition to the water and any ground pressure if it is in-ground, it is necessary to consider the accidental overload at the poolside. The value of this load must be determined based on the structure's intended use.

Load conditions

Empty underground tank

The first load condition that is examined is the case of an underground tank.
By evaluating the situation, it is immediately clear that the main condition is the case of an empty tank for which the thrust of the upstream ground and the acting surcharge are taken into consideration.
This thrust is considered passive thrust at rest because the potential failures would not justify the development of active thrust. The coefficient of passive thrust, according to the literature, is:

The pressure exerted on the walls is therefore:

The thrust of the earth thus calculated is added to the action of the aquifer, which creates a hydrostatic thrust (linear and increasing with depth) against the walls of the basin.
As regards groundwater, it produces a hydraulic thrust on the bottom of the tanks proportional to the depth of the tank bottom.
It is also assumed that an accidental overload applied to the wall according to the above coefficient is of an entity equal to that indicated by the current legislation.

Full underground tank

The opposite of the previous load condition is the case where the underground tank is full of water. It's clear to see how in this situation, hydrostatic thrust is added (obviously, a normal operating condition) from the inside out.
For safety's sake, however, the thrust due to overloading is not considered in this case, and the ground thrust is assumed to be 30% of the actual value to account for the fact that the material is moved for work and only later repositioned against the walls. Indeed, to rely on the ground's resistance, in this situation, passive thrust would need to be mobilized, which, however, only comes into play for large displacements, when the ground is compacted. This condition would never be reached without first breaking the material constituting the pool edge due to the large displacements.

Full extrados basin

In the case of an above-ground pool, the most unfavorable condition occurs when the pool is full.
Always remaining in static conditions, the edge of the pool must face the hydrostatic thrust of the internal liquid.

Empty extradosed tank

In this situation there are practically no stresses within the structural organism.
From an engineering perspective, this condition requires the structure to be almost completely unloaded except for its own weight.

Ultimate Limit State Checks

They are necessary to verify the resistance of structural elements to ensure the safety of the structure. Based on the wall geometry (remember the transition to the equivalent lightly reinforced partition), the mechanical characteristics of the structural materials (concrete and reinforcing steel), and the acting stresses, the resisting forces are calculated according to the canonical formulas of structural science.

The goal is to ensure the following inequality:

ER / EE ≥ 1

Where:

• ER resistant action (bending moment MRd, shear VRd, etc.)
• EE stress action (bending moment MEd, shear VEd, etc.)
• d = design, i.e. design value of the action calculated with the partial safety factors applied to the characteristic values.

Serviceability Limit State Checks

Given the simplicity of the structure and the limited forces involved, Serviceability Limit State (SLS) checks are mostly a meticulous analysis aimed at confirming design choices. While the sizing of structures is performed through a pre-design procedure and verified using relationships that take into account the ULS stresses, it is equally true that the structural complex must comply with the SLS limitations. These limitations are based on the possibility, provided for by EC2 and NTC '08, of verifying the behavior of structures through empirical procedures related to construction and reinforcement details.

VOLTAGE LIMITATION EC2 SECTION 7 – point 7.2
The compressive stress in concrete must be limited in order to avoid cracking
longitudinally perpendicular to the tensile direction. Microcracks and high viscosity values ​​must also be avoided to avoid compromising the functionality of the structure (in our case, tearing of the waterproof coating with consequent water loss) and to prevent preferential paths for attack of the reinforced concrete elements. In-service stresses generally reach values ​​of around 4-5 N/mm2 in the most stressed wall area, significantly lower than the limit imposed by the regulations and equal to 60% of the characteristic cylindrical compressive strength fck = 25 N/mm2 for class C 25/30 concrete.

EC2 CRACK CONTROL SECTION 7 – point 7.3
As mentioned above, high stresses in the reinforcing steel cause high stresses in the concrete, which are transferred through bonding. This causes the material to stress, which cracks and corrodes more easily. A nonlinear calculation of the crack opening is omitted here, as the correlation proposed by EC2 in Table 7.2 is more than sufficient. Indeed, if we wish to limit the crack opening to the most restrictive limit of WK = 0.2 mm, the maximum usable diameter can be deduced based on the stress in the steel bars (e.g., the connection between the foundation slab and the pool edge wall).

EC2 DEFLECTION CONTROL SECTION 7 – point 7.4
The control of deflection, understood as relating to the supports, is aimed at avoiding compromising or even damaging the functionality and aesthetic appearance.
Appropriate deflection limit values, which take into account the nature of the structure, secondary and non-structural elements, are contained in ISO 4356. It is in fact written that in order not to compromise the functionality of the work, the limit of 1/250 h must be respected, or for a height of 1500 mm, a limit value of 6 mm.
Generally, the greatest deformations are found in the middle of the longest wall where the two-dimensional behavior is minimal, there the interlocking effect at the corners with the walls is little affected and a cantilever-like behavior prevails.

Guidelines for correct installation: Blocks, Reinforcement and Pouring

Easyblok Elements - On-site Storage

The manufacturer must take appropriate precautions regarding storage, as given the particle structure of the elements and their vulnerability, they could suffer permanent damage, with consequences for their future use.
The panels must be stored in a dry place, if possible, to avoid continuous exposure to humidity which could cause warping, which could affect their subsequent installation, and in particular the level of tolerance of flatness and verticality.
Wooden planks must be placed in the designated storage area and then stacked on top of the EASYBLOK panels, allowing air to circulate through them via convection, thus maintaining a certain level of ventilation. A tarp must be provided to protect against the elements, and wooden planks must be placed near the stacked edges to protect against impacts.

Correct installation

To facilitate the installation of the EASYBLOK, it is important to have a clean, smooth and level concrete base; it must be free of roughness and holes and must be "tightened" according to the rules of the art. Therefore, a mechanical surface finishing is recommended.
On the edge of the bottom base, use a blue-impregnated string to draw a polyline corresponding to the internal dimensions of the pool.
Next, you need to carefully check the squareness, and make sure that the internal diagonals match the design diagonals.
The next step is to place the vertical rods and tie them with the recurve ones, therefore, on the obtained path, arrange the modules of the first row starting from a corner, in this way:

• Respect the assembly direction, teeth facing downwards;
• Place the upper and lower end keys at the ends of the relevant modules to ensure closure when casting the concrete;
• Proceed with the help of a cutter to make a localized cut in the EASYBLOK part, in each of the 4 corners so as to allow the continuity and homogeneity of the concrete cast in the structure;
• Place the second row starting from a corner and staggering the elements by 0.25 m at each course, by an amount equal to the thickness of the wall;
• Position the head keys as before and make the cuts in the corners.

Next, you need to lay the horizontal reinforcement. Once the modules have been laid, pass the corresponding reinforcement inside them.
For walls less than or equal to 1.50 m high, the structure can be filled in a single pour. Depending on the concrete consistency, it's important to monitor the hydrostatic pressure acting on the formwork to avoid bulging and unevenness once the concrete has hardened. This recommendation becomes more necessary the longer the wall, or the more the interlocking effect is lost. In this case, adequate shoring is recommended, with spacing no greater than 4 meters.
It is recommended to use a pump with a vertical discharge pipe to ensure even distribution of the pour. Pour the concrete starting from one corner and moving the pipe along the perimeter of the tank, working in layers to avoid segregation of the concrete and the formation of gravel nests. It is good practice to vibrate the concrete repeatedly, for short periods of time, in different areas.
After pouring the concrete and before curing, perform a final check to ensure the verticality of the edges, the flatness of the walls, and the levelness of the top. This check must be carried out meticulously, especially for pools with curved walls.
In fact, when the curvature is in favor of the load, the wall could enter into crisis since the concrete is still fluid, and the reinforcement does not find the necessary anchoring.

Joints between elements

Proper overlapping of the courses plays a fundamental role in the successful execution of the wall. During pouring, the concrete exerts pressure on the formwork walls, and if the formwork doesn't provide a proper seal (cracks, holes, overlaps, etc. resulting from improper installation), there's a risk of the grout leaking. If this were the case, the concrete would lose a significant amount of its binder, resulting in a significant reduction in its mechanical properties.

Armor - Foundation Armor

The foundation slab has a dual function:

• Transmit loads to the ground;
• Serve as a smooth, flat pool bottom ready for the application of the waterproof sheet.

The thickness of the foundation depends on the load (and therefore largely on the pool's depth), the type of soil, and its mechanical properties. Equally important is the foundation's size, which must be carefully considered to allow for both timely pouring and the curing of the concrete. To properly manage shrinkage cracking, it is good practice to create expansion joints and to pour in stages, starting from the point furthest from the fixed constraint (the wall).
The slab is generally 15-20 cm thick, and the reinforcement is almost always made of a double electro-welded mesh spaced by trestles. Diameters range from 06 to 012, and the mesh is usually one of three sizes: 10x10, 15x15, or 20x20.

Recovery irons

Since the foundation slab needs to be finished immediately after pouring, it's not possible to embed the reinforcing bars in the concrete. They are therefore positioned later using chemical anchoring, which involves drilling a hole and blowing two-component epoxy resin into it, in contact with the reinforcing bars themselves.
The anchorage length must be carefully calculated as it is the connecting element between the foundation slab and the pool wall. It is through the anchorage length that the interlocking moment and shear force are transmitted, which are greatest precisely at the connection section.
The chemical anchor must be made of two-component epoxy resin, injected into the previously drilled and thoroughly cleaned hole, after which the steel bar, or other element, is inserted to secure the part to be anchored to the foundation structure.
For successful anchoring, perfect execution is of great importance, as is careful consideration of the material and structures in which the holes will be drilled during the pre-design phase.

The wall at the edge of the pool must be reinforced in such a way as to contain the stresses and maintain the stresses within the limit state range considered.
The wall reinforcement must be inserted correctly inside the formwork.
Given the limited space available in each rib, the specifications provided in the drawings must be adhered to. The concrete cover is of little importance in this case, as the particular shape of the formwork means the reinforcement is completely protected by the PSE. What requires careful attention is the position of the reinforcement with respect to the formwork; in fact, the transmission of stress from the steel to the concrete is ensured only if the concrete completely envelops the entire bar. The minimum overlap of the vertical bars is suggested in the schedules for preliminary sizing. The minimum overlap of the horizontal reinforcement must be no less than 50 µm (bar diameter), while the welded mesh must have a minimum overlap of 4 meshes.
Near the edge of the platform, the nets are folded at 90° for 14 cm, to allow the anchoring and closing of the framework.
The reinforcement of the pool edge walls is made up of vertical bars and wall stringers.

Case 1: Simply reinforced wall
If the stresses involved are modest and the horizontal forces are insignificant, a single reinforcement layer can be used, obviously placed in the tensile zone of the concrete. The compressive forces will be transferred entirely to the concrete.

Case 2: Doubly reinforced wall
If the structural analysis provides high values ​​of the acting stresses, it is best to use double reinforcement. The section will have both tensile and compressive reinforcement, while the concrete will contribute its contribution only in the compressed zone, cracking in the tension zone.

Special pieces and accompanying armour
Having defined the classic reinforcement to be used in the various structural elements, it is worth presenting a further overview of all those special pieces, sometimes unfortunately overlooked, necessary for the transmission of forces where the wall presents a change in direction.

Right angle
When changing direction, it is a good idea to arrange the EASYBLOK elements at intervals between each course with an L-shaped reinforcement of no less than 50 cm in length. This should be placed on the side that is most heavily loaded so that the resulting empty thrust does not crack the
concrete. Each course of EASYBLOK elements must feature this type of reinforcement; the quantity and diameter must match those of the wall subjected to the greatest stress.

Intersection of walls of any orientation
Based on what is written above, the connection between the walls is made by means of “L” shaped irons,
with appropriately sized sides. These reinforcements, arriving from the secondary wall, are anchored to the main wall along the opposite side, crossing the existing transverse reinforcement to close it. This type of reinforcement must be provided for each course of EASYBLOK elements; the quantity and diameter must follow those of the wall subjected to the greatest stress.

Top of the wall
If the horizontal loads are significant, to stiffen the wall and contain the reinforcement (double in these cases), it is advisable to provide U-shaped steel locking forks. The pitch and diameter are recommended in the schedules for preliminary sizing.

Armor Hierarchy
To ensure the reinforcement's compactness, the horizontal bars must be placed outside the vertical ones. In turn, if forks are required at the top, they must close the horizontal bars.

Concrete - Requirements and performance

The Technical Standards for Construction based on the Ministerial Decree of 14 January 2008 are harmonized with the European standard UNI EN 206-1 through the national application of UNI 11104, the performance of concrete in relation to the following specifications:

• The strength class of hardened concrete, C fck/Rck, where fck represents the characteristic strength determined on cylindrical specimens with height/diameter = 2, and Rck represents the characteristic strength determined on cubic specimens;
• The environmental exposure class that identifies the aggressive conditions in which the concrete will have to operate;
• The consistency class, SN, where N, between 1 and 5, identifies the workability of the fresh concrete;
• The maximum diameter of the aggregate useful for determining the inter-gap as well as for the composition of the mix-design.

In this case, the concrete cover becomes less significant, as the concrete is protected by the EPS and the waterproof membrane. The only critical area is the underside of the foundation slab, for which the concrete cover will be determined based on the environmental exposure class and the type of concrete.

In addition to the four characteristics mentioned above, one or more additional performances can be prescribed, all on hardened concrete, such as:

• maximum withdrawal value;
• water permeability determined by penetration of water under pressure;
• flexural strength (Rf) or tensile strength (Rt) usually at 28 days;
• short-term compressive strength (Rci), where “i” indicates the time in days usually between 1 and 7 days.

Structural materials proposal

In their structural design, structural steelworkers always include a table indicating the mechanical characteristics of the materials. An excerpt from this table is provided below as an example.