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DUMPING OF STRUCTURES ON THE GROUND

• July 2024
• By Ioannis Lymperis

[Packing is the name given to the support that prevents all movement and rotation. In the construction of buildings and structures there are many settlements. The buttressing between the vertical walls and columns at the nodes, with the beams, foundation footings and connecting beams is common. The question is whether there is construction ground settlement. We assume that buildings do not only rest on the ground, but are embedded in it through foundations. The foundation process is critical to the stability and safety of a building. Foundations are structural elements that transfer the weight of the building to the ground and ensure that the building remains stable and safe in an earthquake. But is this correct? The foundation of the structure ensures that there will be no settlement in the structure from static and seismic loads, but does it ensure that there will be no wall buckling from the moments? No it does not ensure it so we cannot say that the structure is embedded in the foundation soil. E.g. The base of the wind turbine works gravitationally with a low centre of gravity preventing it from tipping over. It is not stuck and pressed into the ground. The same is the case with columns and walls, which have bases, which transfer static loads to the ground, but seismic loads are not received entirely, but partially, because the bending of the wall contains compressive loads ( downward ) that are received by the ground, but also tensile loads ( upward ) that are not received because there is no footing. This distinction is important and absolutely correct. Ground foundation footing implies that a wall is fixed in such a way that it does not allow any bending or movement. However, in most building structures, walls are not footed in this sense, but are supported to the ground in a different approach, allowing for wall rotation. The rotation of the walls and columns as well as their bending moment is prevented by the buttresses of the beams and the connecting beams to the walls. The post-tensioned walls at their sides increase their stiffness and their dynamic with respect to the base shear and other shear forces, and prevent inelastic displacements, so that failures due to large deformations are avoided. But stiff tensed walls at high accelerations transfer very large moments to the connecting beams and girders at the nodes, much larger than those carried by the columns, and break beams and connecting girders. In this case, it is necessary to pack the wall faces with the foundation soil with anchors placed at drilling depths, which will be able to take large moments, so that together with the connecting beams and girders they can prevent the walls from bending and bending, thus preventing the deformation and failure of the beams and walls throughout the whole load-bearing structure, due to the inability of their cross-sections to absorb the large moments, which, when the anchors are embedded in the ground, are deflected and diffused into the ground. Damage and deformation are closely related concepts, as the control of deformation also controls damage. Conclusion. By designing structures with longitudinal shear walls with post-tensioned and ground-retained ribs, we will not have failures in strong earthquakes.]

Dear Dr. Sundus F Hantoosh

Go To Article The Ultimate Anti-Seismic Design Method

Proposed mitigation measures:

These measures can help reduce the deformations and consequently, the damage to the reinforced concrete load-bearing structure.

https://caeassistant.com/product/bio-mechanical-abaqus-simulation-full-package/

Dear Alvin Molberg Thank you for the suggestion

I have done simulation and experiments.

Article The Ultimate Anti-Seismic Design Method

Presentation Seismic experiment.

The deformation causes failures in the columns in the walls and in the beams to which they are connected at the nodes.

If we stop the deformation we stop the failures. The deformation comes mainly from the bending moment of the columns and walls, which is also reflected in the beams in the nodes. The rotation of the walls and columns is also reflected in the beams and is the main cause of the deformation and failure of the beams together with the deformation from the bending moment. If we stop the bending moment and wall rotation we will also stop the deflection of deformation and failure of the cross sections around the nodes. To stop the bending moment we apply prestressing To stop the wall rotation we ensure the footing of the same tendons into the ground that we applied prestressing and thus divert the stresses that the tendons have accumulated from the bending moment and the wall rotation into the ground The diversion of the seismic stresses developed in the structure into the ground prevents the stress of the cross-sections around the nodes. In this way, we stop damage and collapse of structures by stopping deformation in both walls and beams and making the ground react as an external force to the earthquake tensions.

In seismic solutions for structures, post-tensioning at the edges of walls involves applying tension to steel tendons to enhance wall stiffness and reduce cracking. Embedding tendons in the foundation soil provides additional anchorage and stability, improving the overall seismic performance by increasing resistance to lateral forces and reducing movement during earthquakes.

Very well understood, dear Dr. Chuck A Arize

We need to stop the displacement of the top edge of the wall and the recall of its base.

These two causes create inelastic deformations in the trunks of the horizontal and vertical support elements, which are responsible for the collapse of the structures. Displacement of the top of the wall is stopped by post-tensioning, which adds stiffness and momentum to the wall, and recall of the wall base is stopped by using ground anchors.

When we say load-bearing capacity of the building we mean how much it can withstand.

1. There is the bearing capacity in terms of the static loads of the building.

2. There is the bearing capacity with respect to the non-linear loads of the earthquake.

From the other earthquakes are not all the same and each building reacts differently from another to each earthquake.

For this reason, the design of the load-bearing capacity of a building is not based on the Richter magnitude of an earthquake, but on the acceleration of ground displacement that reaches beneath the structure. ( e.g. a large but distant earthquake from the structure will give smaller accelerations to the structure than a small and nearby earthquake )

In an experimental finite element simulation I did for this seismic system which includes prestressing at the ends of the walls and simultaneous footing of the tendons in the foundation soil,the following was found.

Conclusion of the Simulation

From the analyses made, the following conclusions are generally drawn:

Ÿ Nonlinear static analyses were performed (pushover) in order to draw the diagram of the shear force of base—displacement of the control node and to find the bearing capacity of the structure in lateral loads.

Ÿ It has been found that the application of the system generally has beneficial effects on the bearing capacity of the construction, as in each case it increases it.

Ÿ It is generally desirable to apply the compressive load evenly throughout the structure and not to individual vertical elements.

Ÿ When the system is applied only to the central pillar of the structure the benefit is very small.

Ÿ When the system is applied to only the four corner pillars of the structure, the benefit is relatively limited.

Ÿ When the system is applied to all columns, then it achieves significantly increased load-bearing capacity values.

The simulation I did is correct as done mounted on columns but it has less performance than if mounted on walls with footings. Anchored footing only works on walls that are downloading large moments to the footing and need to receive the moments. The columns break before they download moments to the base, and the reason is that their cross section is small, powerless in momentum so they break at the first lateral force and the connecting beam is sufficient to take up any moments downloaded to the base before breaking in two.

So anchoring the columns to the ground, whether done or not, is of no use

The simulation only showed the good of prestressing The simulation with the columns had footing (0) but as I mentioned the reasons it was not useful.

Why the anchorage is needed in the walls?

Let's consider how the columns react to the earthquake and how the walls react to the earthquake.

The inelastic bending moment and base recall create failures.

To stop the base recoil today, they place connecting beams.

Two things are needed to break the connecting beams.

1.Large accelerations

2.Large wall cross-sections.

When the design earthquake is up to 0.36g acceleration the connecting beams work satisfactorily. Then they break.

The earthquake gives accelerations exceeding 0.36g and up to 3g The recent earthquake in Turkey exceeded 2g

The upper design acceleration with sufficient bearing capacity of structures today is 0.36g From 0.36g up to 3g there is a big problem of lack in the bearing capacity of structures.

At these large accelerations, recall of the footing of the wall base occurs and the connecting beam breaks because it is unable to receive the large moments that the wall is downloaded. Together with the connecting beam, the beams at the nodes also break.

Anchoring the walls to the ground with anchors helps the connecting beams to stop the recoil of their base, which breaks the beams, in high acceleration earthquakes.

We are referring to wall base recall, not recall of the area of the structure.

In addition to the base recall, damage is also caused by the inelastic deformation of the wall frame and column.

If we make strong walls they break beams and connecting girders.

If we make strong walls prestressed and embedded in the ground nothing breaks.

The simulation showed that even small columns increase their load bearing capacity, walls even more so.

Dear Samy Elhadi Oussadou

I'm glad you agree!