[seismic]

Anti-seismic system placed in a shaft of a load-bearing structure http://www.youtube.com/watch?v=KPaNZcHBKRI
The main object of the hydraulic tie rod for construction projects of our invention along with its application method in the construction field for structural projects is to minimise the problems associated with the safety of structural projects such as buildings in the case of natural phenomena such as earthquakes, tornados and very powerful winds in general. According to the present invention, this can be achieved by a continuous pre-stressing (pulling) of both the roof of a large, geometrical part of the building structure which independent of the load-bearing structure towards the ground and of the ground towards the structure, making these two parts one body like a sandwich.

This pre-stressing force is applied by the mechanism of the hydraulic tie rod for construction projects, said mechanism mainly consisting of a steel cable penetrating free in the centre the vertical support elements of the structure, as well as the drilling length, beneath them. Said steel cable's lower end is tied to an anchor-type mechanism that is embedded into the banks (walls) of the drilling to prevent it from being uplifted. This embedding is attained due to the drilling hole being somewhat smaller than the exterior diameter of the completely opened anchor mechanism. Said steel cable's top end is also tied to a hydraulic pulling mechanism exerting a continuous uplifting force. This pulling mechanism comprises a piston, said piston reciprocating within a piston sleeve, connected to a pressure chamber beneath it. This pulling force, exerted on the top-end of the steel cable, by the hydraulic mechanism due to the hydraulic pressure originating from the rise of the chamber towards the piston, and the reaction in this pulling force originating from the embedded anchor at its other end generate the desirable compression in the construction project which in turn is tied to the ground and thus rendered resistant to the horizontal forces of an earthquake.

Utility analysis of the anti-seismic system titled: “Hydraulic Tie Rod for Construction Projects”.

Innovative step of the invention:
The forces of an earthquake (horizontal and vertical) start being transported from the bottom (base) towards the top (load-bearing structure). The horizontal and vertical (tectonic) transfer of the earthquake forces to the load-bearing structure is executed necessarily by the ground floor columns via the bases, and by means of the nodes, to the first floor and from then on from the first to the second, and so on.
.,
However the following paradox emerges:
The first (bottom), intermediate and top plates, when oscillating each have different amplitudes, and different directions. This is due to the inertia of each one of the multiple plates, as well as the additive elasticity of the columns of each floor, in different time-space, from the bottom to the top.

This delayed transfer of the acceleration forces results in the multiple plates moving in different lateral directions, (due to the inertia exhibited by each individual plate, in different time-space). Thus, additional torques are created, as well as shearing stresses form different directions in the column nodes, said columns due to their elasticity tending to deform along the vertical axis of the structure framework, in the form of an S.

CONCLUSION
For the above reasons, it is imperative to stop this irregular vertical axial development of additional torques and shearing stresses, originating from the horizontal forces developing on the plates which in most cases are in phase difference between them depending on the floor (height). This irregular development therefore creates additional problems in the column nodes.

The above problems to be resolved, i.e. of the shearing stresses and the torques generated in the nodes due to the horizontal (lateral) acceleration of an earthquake, and of the irregular displacement of the vertical axis of the load-bearing structure, are much accentuated in the nodes of the ground floor columns.

This is because of an additional problem occurring only in the nodes of the base with the columns. These nodes are not at all elastic so as to be able to transfer smoothly the violent shearing forces imposed on them by the base embedded to the ground.

The result is that these first load-transfer nodes developing by the dynamics of an earthquake, additionally bearing increased compressive components, and in combination with the acceleration of the earthquake, are the first to fail in the event of an earthquake. For these reasons, said nodes are placed under seismic insulation by creating a double “one-piece” base, and placing elastic supports in-between.

Another major problem to be solved is the great tendency of the load-bearing structure sides to rise alternately, said tendency originating from the increase in the structure oscillation. This tendency of the load-bearing structure to rise induces additional torque on all the nodes, forcing them to develop the tendency to change their existing, until now, angle in order to receive the additional bending loads of the load-bearing structure.

The proposed solution in order to address the above reported problems induced on the load-bearing structure by the earthquake is summarised in the following three points:
1) Create the conditions for controlled axial oscillation of the load-bearing structure.
2) Help the columns in transferring the horizontal forces of the earthquake, to the plates, not only from the bottom to the top in different time-spaces (phase difference from plate to plate depending on the height of placement), as occurs in the current conventional structures, but also laterally in relation to the vertical axis to all the plates simultaneously from a pre-stressed rigid structure (e.g. shaft).
3) Strengthen the nodes dimensionally along with additional reinforcement (or pre-stressing) in order to resist shearing.

The above is achieved by placing right at the centre of the load-bearing structure, architecturally exploitable in an effort to lower the cost, pre-stressed with the ground but independent from the load-bearing structure, rigid shaft, or dimensionally large cross-shaped column, or even a big room. The essential condition for the above rigid geometrical forms is for them to have axial vertical continuity, along the whole height of the building, and to be constructed entirely from reinforced pre-stressed with the ground concrete.

This pre-stressing applied by the hydraulic tie rod on the shaft and on the ground, is mainly imposed in order for these two parts to become one body, such that at the horizontal acceleration of the earthquake, the ground, the base, and the loft of the shaft are found in the same acceleration phase (in the same time-space as one body in the three dimensions).

The larger the geometric dimensions of the base (cross-section area), relative to the height, the larger is the resistance in the foot block, as well as in the emerging shearing.

An increase in the pre-stressing placed on the shaft, means a corresponding increase in its resistance to shearing, an increase in the compaction of the drilling banks, and consequently a better embedding of the anchor mechanism.

In order to achieve the independence of the rigid shaft from the load-bearing structure, we leave a gap between them. This gap is useful for the following reasons:
a) earthquake dynamics is not transferred from the shaft to the load-bearing structure,
b) the load-bearing structure remains independent in the seismic insulation offered to it by the double “one-piece” base-plate away from the oscillating shaft,
c) the load-bearing structure exhausts the mechanical resistance properties of the existing reinforcement, (so that it does not transfer large impact forces to the shaft), and just before it breaks, there occurs damping and retaining of the load-bearing structure on hydraulic systems placed in the lift gap, (rubber, or dampers),
d) to prevent the load-bearing structure from leaning on the lift shaft and transferring the additional compressive forces of its weight, thereby making the application of further pre-stressing forces on the shaft possible, thus rendering it more rigid.
e) to help the columns in transferring the earthquake forces, not only vertically, but also laterally in same time-space, by means of the pre-stressed rigid shaft and the dampers.

All this elasticity of the vertical axis of the load-bearing structure may be put under control in such a fashion as to achieve the smooth transfer of its vertical axis torques to the shaft.

When it is intended for the upper floors to oscillate more than the lower ones, the gap on the upper floors is made larger, setting a lower pressure on their hydraulics, in relation to the lower floors. Operating in such a manner, and in order to keep the bending action of the vertical axis under control to avoid the destructive transfer of torque towards the lower floors, the transfer of torque is computed statically during the plate impact from each and every floor onto the shaft and following that the proper gap between each floor plate and the rigid structure is computed and the proper hydraulic pressure is applied on the dampers.

In order to further strengthen the rigidity of the rigid structure (shaft), to decrease the oscillation amplitude, to prevent the overthrow, and to increase the shaft resistance to the shearing stress that is generated by the lateral impact of the plates due to their inertia, it is necessary to render the rigid structure “one-body” with the ground.

This can be achieved by means of the hydraulic tie rod for construction projects mechanism, applying pre-stressing between the loft (top floor) and the ground, making these two parts “one-body”.

CONCLUSION
It is wrong to let the columns transfer all alone the horizontal forces of an earthquake from the bottom to the top in the load-bearing structure, as is currently the case in the majority of the building construction methods.

The horizontal forces of an earthquake are not transferred effortlessly from the columns to the structure framework, this being due to the existence of other forces acting contrary to the direction of the earthquake horizontal forces, said forces originating from the inertia of the plates and resulting in the plates not responding readily to the direction of the earthquake horizontal forces. This opposition of forces on the horizontal axis of the building structure, creates shearing stresses, as well as non-uniform bending in the shape of an S (for the reasons reported above) deforming the vertical axis of the structure, with the known results.

It is at this point that the invention provides for the columns to transfer the earthquake forces uniformly and smoothly, not only vertically towards the top, but also horizontally to the floor plates, by means of the hydraulic tie rod, the pre-stressed shaft, and the hydraulic dampers placed in the gap.

Deductively in this way, the framework vertical axis maintains its initial form, not deforming into an S shape, due to the uniform movement of the mass of the multiple plates in the same time-space imposed on them by the pre-stressed shaft, relieving and helping this way the columns to transfer the destructive earthquake forces to the plates. That is to say, the invention creates controlled flexibility on the load-bearing structure vertical axis, helps the columns transfer laterally the earthquake forces to the plates, at the same time achieving the seismic insulation of the load-bearing structure horizontal axis (with double “one-piece” base-plates carrying elastic inserts between them). Moreover it also stops the tendency of the building to rise unilaterally, said tendency originating from the increase of the oscillation co-ordination, which oscillation co-ordination depends on the height of the building, the time duration of the earthquake as well as the wavelength of the earthquake and the amplitude of its oscillation.

Ground fluidization (subsidence) as well as the cracks, caused by an earthquake, are a major problem, which, however, in part has been resolved by the invention.

Stopping the video http://www.youtube.com/watch?v=KPaNZcHBKRI at the point ( 55 sec. ) showing under the ground surface, a pipe can be observed starting from the anchor and reaching up to the bottom part of the base.

This is called resistance pipe, and is useful for the following reasons:
1) it constitutes the passage of the steel cable applying the pre-stressing,
2) should the ground recede under the base, then this resistance pipe undertakes the weight of the base and transfers it to the banks (side-walls) of the drilling (this is a very important reason),
3) should the banks of the drilling recede (due to oscillations), the steel cable does not sag because the hydraulic pressure (under the piston in the upper part of the system) causes the tightening of the steel cable which in turn generates resistance on the bottom anchor piston the movement of which activates the anchor pins to move towards the solid ground around them restoring the desirable embedding in the banks (side-walls) of the drilling.


This video, http://www.youtube.com/watch?v=C2Z1zmrJhsc towards the end, in the 52nd minute, presents an earthquake simulation, and shows very distinctly that the building structure is not tied (embedded) to the ground contrary to what was common belief to date. Clearly the object of this invention is to counterbalance (and not only that) these uplifting forces generated by the oscillation of the building.



The anti-seismic system installed inside the shaft of a load-bearing structure: http://www.youtube.com/watch?v=KPaNZcHBKRI
Invention webpage: http://www.antiseismic-systems.com/index.php?lang=el