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Old Posted Apr 3, 2021, 4:49 PM
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Truths and lies about the seismic shielding of structures.

The intensity of earthquake damage designed to withstand any construction depends on the acceleration of the ground that will reach under the construction and not on the magnitude of the Richter which measures the amount of intensity at the epicenter of seismic activity. The acceleration of the ground and the mass of the structure multiplying create the whole product of the intensity of inertia, which computationally determines the intersection of the base. The reinforced concrete structure stands on vertical support elements, which consist of columns, walls, and large elongated walls, which inertia causes them to overturn. To calculate the magnitude of the moments of the inversion forces, we multiply the magnitude of the inertia by the height at which the inertia force acts and divide the result by the width of the wall. The result of the mathematical operations will show us that the columns are overturned more easily than the elongated walls are overturned and this is because they have a large width.
The body of the vertical elements is designed to have elasticity and ductility and the elasticity depends on the size and shape of their cross section and the construction materials and the ductility from the placement configuration of the steel reinforcement.
Elastic is the displacement during which the construction returns to its original position and does not show failures. Inelastic displacement is that during which the construction shows leaks - failures and no longer has the ability to return to its original position.
The plasticity of structural elements and structures made of reinforced concrete is characterized by their ability to deform beyond the leakage limit, without significantly reducing their strength.
In the dynamics of structures we study the structures in dynamic stress as a consequence of seismic movement of the ground. The columns have high ductility and low dynamics, while elongated walls have low ductility and high dynamics. According to ยง 5.2.1 of EC8 there is a design option of the available plasticity of the building. Reinforced concrete buildings can be studied with two different design methods. a) To be designed with the necessary ductility, which means to have the required - necessary ability to consume seismic energy, but without losing their resistance to all loads during the rocking of the earthquake. b) To be designed with low ductility, (low energy consumption,) but have very great dynamics.
Columns that have a small and square cross section have greater elasticity than large elongated walls, but do not have the dynamics of large walls.
Basically in the design, the columns mainly undertake the static loads and the walls the static loads as well as the dynamic stress due to seismic movement of the ground.
The response of the structure to seismic displacement intensities depends on the dynamics of the sections and the damping measures of the structure. Another factor that contributes to the collapse of the structure is the duration of the earthquake. A construction can withstand high acceleration for a short time or small acceleration for a long time. Constructions in areas where statistically large and frequent earthquakes occur are designed to withstand an acceleration of 0.36g (1g is the acceleration of a body falling to the ground and equal to 9.81m / sec) In Greece, the largest earthquake recorded had an acceleration of 1g The largest earthquake recorded in the world had an acceleration of 2.9g Here we conclude that even the best constructions in the very large earthquake with duration are not safe. If there is coordination of ground construction, the collapse of the structures is certain. For the above reasons, it is a myth to claim that today's constructions are 100% safe from earthquakes. The reason that the structures collapse in the earthquake is that the tensions that are created are recycled and increase during the earthquake and because the cross-sectional strengths of the bearing elements are insufficient in large earthquakes with duration. If we increase the size and reinforcement of the cross-sections of the load-bearing elements, we also increase the intensities because the additional mass increases the inertia. If the constructions are high and rigid, they are in danger of total overturning. There are of course seismic energy damping mechanisms that help the construction cope better, such as horizontal seismic insulation, (bearings), hydraulic dampers that convert kinematic energy into thermal, viscous dampers, the plasticity of structures and more. These mechanisms help the construction a lot but there are also very large earthquakes with acceleration close to 3g that does not save any construction because they can not control the inelastic displacement above 0.5 g and this, for a short time. The structures that will survive in such a large earthquake will be those where they will be far away from the earthquake, or those whose soil composition will not allow the transfer of high seismic acceleration below the base. Even today's anti-seismic designs are very expensive and are only placed in projects of great importance. Even poor countries can not afford the current seismic regulations, and even more so in the installation of seismic damping systems. Question Is there a solution for cheap and seismically shielded constructions? Answer. Yes there is as long as the seismic design changes a bit. The solution is to remove the stresses above the construction and prevent their additional recycling within the seismic duration which increases the stresses in each seismic charge cycle. How do we do that? Answer Joining the construction with the ground shivering outside the construction the magnitudes of the earthquake. And where will we lead the seismic intensities? Answer ... in the ground. How do we do that? Answer With double pre-tensioning The first prestressing is applied before the construction of the project on the ground surface, in an anchoring mechanism which is placed in the depths of a bore under the base foot and which during the prestressing expands towards the slopes, compresses them creating a strong anchorage. The second pretension is applied after the completion of the bearing body, between the upper ends of the construction and the anchored anchorage. If we place at each end of the elongated walls by a mechanism then during rocking the tensions are transferred into the ground and not on the cross sections around the nodes to break them. And this happens in every seismic loading cycle so the duration of the earthquake does not bring additional loads to the construction. Even with this method there is no coordination. If the pre-tensioning of the elongated walls reduces the displacement of the structure, then the pre-tensioning of the ground also reduces the seismic displacements. The case of whether the proposed foundation soil eliminates or reduces soil oscillations is also being investigated. But it definitely compresses it because the pre compresses horizontally and vertically, improving its durability.
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