According to modern regulations, the seismic design of buildings is based on the ability requirements of the correct design of the nodes and plasticity.

The (inevitable) inelastic behavior under strong seismic excitation is directed at selected elements and failure mechanisms.

In particular, the incorrect design of the nodes and the clearly limited plasticity of the components lead to major failures.

1) The philosophy of the correct design of the nodes of the regulations is characterized by the appropriate dimensioning of columns-beams so that we have plastic joints in the beams and not in the columns so that we do not have immediate collapse.

Question right or wrong?

Answer

Without the inelastic behavior the bearing would not show plastic joints in the beams.

I believe that displacement control is better than what they apply today which is nothing more than the management of inevitable inelastic displacement and failure.

Displacement control means no failure no plastic joint

It basically means controlling the deformation.

Deformation control also means control in failures since deformation and failures are directly connected.

If you do not have the ability to control the distortion then you manage it with the proper design of the nodes and that is good.

But being able to control the deformation of the construction is better.

2) 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

According to § 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, with low energy consumption, but with very high dynamics. The ductility or interoperability of the structural elements and nodes (exists) is achieved with the existence of the appropriate reinforcement, the construction devices, the proper dimensioning and the limitation of the axial loads to some limits.

Plasticity is a critical factor for seismic constructions for many reasons.

At the carrier level with inelastic analyzes you also find the levels of plasticity that the construction can develop.

Question right or wrong?

Answer

If the seismic energy (measured by ground acceleration) is too large, it will produce excessively large displacements that will cause a very high curvature in the vertical and horizontal elements.

If the curvature is too high, this means that the rotation of the sections of columns and beams will be well above the elastic area (Compressive concrete deformation over 0.35% and reinforcement fiber stresses over 0.2 %) beyond the leakage limit.

When the rotation exceeds this limit of elasticity, the structure begins to "dissolve the energy storage" through plastic displacement, which means that the parts will have a residual displacement that will not be able to be recovered (while in the elastic region all displacements are recovered).

Basically the design of the strength of a current building is limited to the limits of the elastic design range, and then passes to the default plastic leak areas, which are default areas of small and many leak failures, (usually designed to occur at the ends of the beams) so as not to collapse the structure.

This is the mechanism of plasticity that consumes seismic energy.

(Structure collapses when oblique / failed columns fail)

If the parts that experience the plastic deformations exceed the breaking point limit, and there are too many on the structure, the structure will collapse.

Basically, plasticity is achieved by placing a dense reinforcing connector at the ends of the elements because this helps to create many and small cracks, avoiding the creation of large catastrophic cracks.

Plasticity is directly related to the cooperation of concrete and steel (mechanism of relevance)

The most serious problem of relevance is created by the ultra-tensile strength of the steel, which turns the failure into a shear form, which is extremely brittle. When the shear stresses in the steel concrete interface reach their limit value, the correlation is destroyed in the form of concrete rupture.

Part of the reduction in stresses is achieved by increasing the overlap and reducing the diameter of the reinforcement bars. The increase of their limit value is achieved by increasing the strength of the concrete. The presence of transverse reinforcement acts favorably by restricting the opening of the developing cracks.

3) The columns or walls are rigid and flexible. It depends on the cross section in relation to the height and the beams that are connected etc. (Frames etc)

Question right or wrong?

Answer

Yes it is right ... the relationship between the height and the size of the cross section determines whether the elements are rigid or flexible.

But there are other factors such as the cross-sectional shape factor. A square column cross-section is more flexible than a cross-section of the same size which has the shape of a cross, angle or wall.

So we can design rigidly with walls if we want.

The walls may be located around the perimeter of the building (excluding shop facades) surrounding the stairwell and the elevator (strong cores) and may be internal walls (eg partition walls) throughout the height of the building. The installation of many strong walls implies, of course, due to their great rigidity, a significant reduction of the fundamental eigenperiod of construction. This, in combination with the view q = 1, leads to a correspondingly large increase in the seismic loads of the structure. However, it should not be overlooked that precisely because of the many and strong walls the strength increases more or conversely the cross-sectional loads decrease despite the increase of seismic loads.

Due to the fact that the wall has a double lever (that of height and that of width) the axial forces (kN) are smaller than they are in the column.

4) The diaphragm function ensures approximately the same movements of nodes in a plane (in a horizontal direction) which has the effect, among other things, to facilitate the analysis in space taking into account three degrees of freedom instead of six if you do not have a diaphragm. We should not confuse them with the walls. The coexistence of walls and columns is the most suitable formation for seismic structures made of reinforced concrete and especially for structures with many floors.

Question right or wrong?

Answer

Yes, correct for the diaphragm function of the plates.

The walls also have a diaphragm function under certain conditions. If the width and height do not have big differences then yes, and the walls are of diaphragm function. If they are both prestressed and anchored to the ground, then they are super diaphragmatic.

If you combine the diaphragm function of the slab and the compacted and prestressed walls, you have achieved complete rigidity, with zero same period and zero deformation which means zero failures.