What does this invention achieve which is not achieved with the current technology?
Current technology simply secures the structure to the ground. My invention unites it with the ground making these two as one (like a sandwich). For me, this uniting of the structure with the ground beneficially changes the direction and type of forces which act upon the structure dynamically during an earthquake.
Influences which cause failure in buildings:
a) Shearing stress
b) Moment of the nodes
How these are created:
A) SHEARING STRESS
a) Shearing stress is created mainly on the vertical supporting components during earthquake acceleration due to the inertia of the mass.
Question: Is the shearing stress the same in all of the supporting components?
Answer: No. The shearing is greater in force in the ground floor components
Answer: For two main reasons
- They have to handle (in movement) a greater mass which necessitates greater inertia, thereby creating greater shearing on the cross section plan.
- The ground floor components are more rigid.
All of the other supporting components (except for those of the ground floor) have a certain amount of elasticity in the nodes and supporting components which is beneficial in that they absorb the force of the earthquake due to transfer of this force into heat.
However, this beneficial absorption of energy is cancelled to a greater degree by the components of the ground floor for one main reason. Underneath the components (columns) on the ground floor the base is inflexible (because it is usually under the ground). It therefore transfers wholly the acceleration of the earthquake (and in this way shearing stress is also increased).
At the components (columns) of the upper floors the same does not occur because the components of the ground floor have already absorbed part of the force and less energy is transferred upwards to the more elastic components.
Because of this and due to the increased mass load which has to be handled we see greatly increased shearing stresses on the ground floor components. This explains why the majority of failures happen on the ground floor.
This issue can be resolved by increasing the cross section plan of the components of the ground floor. But if we do this then another problem occurs; we lose the elasticity in the components (and in this way we also lose the damping of the acceleration).
B) MOMENT OF THE NODES
Moment of the nodes also acts to create stress on the horizontal and vertical supporting components by shearing stress and occurs for the following reason.
During the acceleration of an earthquake we know that there is inertia of the load bearing elements but in addition inertia of the bearing mass has to be handled. These burden the vertical components with horizontal shearing stress.
In a high rise building, the vertical components are united from the first up to the top floor. The structural integrity of all the components of the load bearing elements (columns, girders, slabs) is improved when these are joined at the node points.
During the inertia of the bearing elements, these node points react with moment which taxes the vertical and horizontal supporting elements with shearing stresses. If the design is not correct, this results in failure of the vertical elements which are brittle but not the horizontal.
The reason for this is that the vertical elements (columns) have a smaller cross section by comparison to the girders. The girders mass along the length forms a structural unit with the slab so that it is considered a unified body stronger than the vertical element.
If we consider that each column bears at least two girders, we understand the difference in endurance (with regards to the shearing) between the column and the horizontal bearing element.
During oscillation of a tall building, there is the tendency for it to lift up off the ground on one side due to moment, creating a gap underneath the back foundations. That is, the front columns try to lift up the back ones due to the structural unity that they have. This unity is provided by the girders.
This gap cancels the resistance which is present between the ground and building base as the base which was securing the building is now in mid-air.
Of course, this event never really happens in reality because the static load of the structure during the lifting of one side immobilizes the column with the base to the ground creating moment of the nodes.
These moments create slanted shearing of the cross section of the vertical element which cannot withstand the load and we have cancelling of the structural unity of the building.
This explanation can be clearly seen during the first minute of the experiment which I have carried out:
In the first minutes of the experiment, we see a wooden structure (building skeleton) which, during inertia oscillates and lifts up on one side and then on the other alternately. This occurs because it is light and the nodes withstand the moment which is created from the static weight of the unsupported side of the structure.
As soon as we place the static load of the two bricks, it still oscillates but the base does not lift up on either side. In this situation the nodes can no longer withstand the additional load of the bricks.
Considering the analysis I have done above, we see why a structure fails when the limits of the design are surpassed.
There is no absolute anti-seismic design.
Current Greek anti-seismic systems have a certain amount of endurance but from this point onwards, the truth is that they are fragile. In my opinion the endurance here has particular limits due to my reasoning above. This phenomenon can be resolved by increasing the cross section plan of the ground floor components. If we do this though, another problem emerges; as stated before; we lose elasticity of the components (and the depreciation of the acceleration).
MY PROPOSED SOLUTION
The solution can be seen in the continuation of the experiment shown in the link above as well as in the explanation below.
There are three issues which need to be addressed in order to apply pre-stressing between the ground and the structure (the clamping of the ground with the structure)
b) durability of the materials
c) durability of the ground
For the pre-stressing or clamping of the structure with the ground to operate beneficially during an earthquake, a large cross section plan of the supporting components is necessary as well as very durable materials if it is to provide additional benefits.
Pre fabricated houses offer these two necessary components as they are constructed completely from fortified concrete.
The problem of loose ground (c) is resolved by using Radiere together with the specialised hydraulic traction mechanism. This improves the durability of the ground and provides additional support to the foundations.
See what happens to conventional houses:
Imagine PREFABRICATED houses which are made of fortified concrete and secured (screwed) at their four corners with this seismic base … even if they are turned upside down, nothing can happen to them.
When we do not screw down the base, what will happen?
If we have tall buildings completed constructed from fortified concrete, these will withstand the shearing stress but their nodes will have increased load due to the gap (discussed above) which is created under the base during second moment of the area as well as the greater static load which they bear. The combination of moment and static load creates slanting cracks in the walls.
Because of this prefabricated houses are suitable to be built only a few stories high. If we make the prefabricated house from fortified concrete ONE with the ground though:
…. It cannot lift up on one side during second moment of the area and in this way we avoid moment of the nodes.
THE FINANCIAL ASPECT
I believe that with this method, prefabricated houses can be placed in towns. Until now these houses have only been suitable for rural areas. The main reason for this is that the law does not allow them to be built more than two stories high.
If they become invulnerable during an earthquake and they can withstand the force with many stories then their construction will be permitted in towns.
At this moment, they are not permitted in towns because if, in a town ten story buildings are allowed and prefabricated ones can only be constructed up to two stories, financially it is not feasible to lose the possibility of another eight stories.
If I enable them to withstand earthquakes, then conventional methods of construction will be dispensed due to the fact that prefabricated structures are 30-50% cheaper because they are industrially produced. This way the manufacturers will profit from this change.
Apart from being for anti-seismic use, my invention can be used as a pre-stressing anchor for the improvement of the ground:
For example: http://postimage.org/image/29l3p1xpg/
That is, it can improve the density of loose ground as well as not allowing the structure to move upwards (during oscillation) or downwards (during subsidence of the ground).
I have already mentioned the placement methods in existing and buildings under construction as well as other types of structures such as dams and bridges etc.
The patent is also appropriate also for the protection of lightweight buildings during tornadoes which are seen mostly in the United States .