HYDRAULIC TIE ROD FOR CONSTRUCTION PROJECTS
The present invention relates to a hydraulic tie rod for construction projects ensuring the protection of the construction structures against damage caused by earthquakes and hurricanes.
Background of the invention
The prior art scientific endeavours have focused on the anti-seismic and anti-wind protection of construction works. To deal with these natural phenomena successfully, efforts have mainly focused on improving the ground, the construction materials as well as on improving the German and the American static regulations. All these improvements produced good results, however, increased significantly the construction costs as regards the use of cement and steel and did not eliminate currently existing problems. There are still construction structures sustaining damage and losses, or even destroyed, by earthquakes and hurricanes and all that despite the improvements made. It is therefore necessary to redefine how the earthquake and wind forces are exerted onto the building structures and to re-examine whether the existing construction materials work together as expected for there must be some mistake made somewhere contributing to damage and destruction. To start with, regardless of how strong a building structure is, it will collapse if the ground on which it rests is unstable. To this date, ground improvement is achieved by ground compacting using end-bearing piles and friction piles or the vibration technique in order to prevent its fluidization during an earthquake. Considering that this kind of ground improvement which moreover requires soil sampling prior to its compaction is very expensive, it is not carried out in minor construction works and therefore such works are left exposed to serious risk should the ground subside. There is therefore a need to devise a mechanism that prevents a building structure from sliding on either soft soil or rocky ground during an earthquake. Another issue to be considered is whether the German or the American static regulations are adequate not so much as regards the strength of materials - the mechanical strength of materials is well known - but as regards the additional forces that are being generated during an earthquake, forces unknown in the prior art and once these additional forces are identified, an appropriate mechanism can be worked out to eliminate them and prevent damage to the structure. Figure 3 presents an analysis of the known static mechanics forces wherein a tensile force (42) is generated by two forces acting along the same axis but in opposite directions. It is a known fact that concrete (43) does not stand up to tensile forces and fractures. Steel (44) however stands up well to tensile forces and for this reason it is used together with concrete in appropriate locations to help concrete withstand the tensile forces generated. Compression (45) is another force generated when two forces are acting along the same axis but in opposite directions. Concrete (43) exhibits nearly the same behaviour as steel (44) in compressive loads. Shear force (46) is another force which occurs when two forces are applied on parallel axes but in opposite directions. Τhis force is exerted between steel (44) and concrete (43) at their point of contact. Buckling forces (48) occur when opposite forces are acting along the same axis but the distance (height) of the material on which they are applied is six times greater than the smallest dimension of its base. When such forces are exerted, the material tends to buckle like α razor blade (49) instead of taking the shape of a barrel (43) as in compression. Finally, there is the torsional force (50), which is generated when materials are subjected to twisting stress.
We will now consider the way these types of forces analysed above act on the building structure during an earthquake or under exceptionally high wind conditions. In situations involving an earthquake or very high winds (hurricanes), lateral forces are generated (see Figure 4 (40)). The building frame column (34) sways left and right as a result of the oscillations produced by the earthquake. During the swaying motion of the column, as seen in Figure 4, when the column tilts left, tension forces are generated (42) on its right side and compressive forces (45) on its left side. It is for this reason that steel is laid externally to "absorb" tensional forces from both sides alternately. When the column tilts to the right, the exact opposite occurs to what was just previously described and goes on throughout the duration of an earthquake. At this point, though, we are called to answer the question why columns break at point (55) although our static calculations on these forces are correct, the answer is simple. We know that steel withstands tensile stress (42) and our calculations are carried out on the basis of that knowledge. We do not, however, take into account the rest of the forces being generated. The first of these unknown forces, not taken into account usually, is that of buckling (48) generated in both concrete and steel and none of these materials can withstand buckling effectively. When column (34) tilts, the concrete in the column produces a steel displacing force (forcing steel to bend over backwards, so to speak) at point (60) and up to point (59). This happens because concrete that's on the inner side of the steel (44) withstands the compressive force generated between the two materials and this leads to an outward displacement of steel tending to push it out of the column. This being the case, steel cannot carry out the task of standing up to tension, this being the reason it was originally placed in the column. Another omission, that is not statically calculated, will now be shown using a simple illustration. If we take a candle (Figure 3 (52)) and break it near its base (53) we notice that its candlewick (51) will come out the bottom part of the candle, which provides less resistance in comparison to the top part of the candle, which is longer. This happens because the tensile force (42) generated on the candlewick (51) during breaking will create a shear force between the candle and the candlewick, which [shear force] is smaller in the bottom part of the candle compared to the other opposite shear force generated in the top part of the candle and this is because whenever tension occurs, there will always be shearing in response. This is exactly what happens to column (34) in Figure 4. Steel section (44) from point (58) to point (60) is less in length than steel section (44) from point (57) to point (59), thus concrete resistance to shear (46) in section from (58) to (60) is lower resulting in the steel being pushed out of the concrete in that section and leading to the collapse of the structure. Nearly always in building structures which collapse during an earthquake, column fracture occurs approximately at the same height as shown in Figure 4 with the steel being pushed out – not fractured, in other words, while steel can withstand much greater tensional forces, these forces are cancelled out due to concrete failure to resist the shear forces generated in the column section from point (58) to point (60). It follows from the foregoing description that a new method of laying steel within the column is required that would only allow the generation of shear forces (42) that steel (44) can withstand and compression forces (45) that concrete (43) can withstand. In other words, reinforcement should be laid in a way that prevents the generation of shear forces (46), between steel and concrete, which concrete cannot withstand.
All building load-bearing elements are constructed in a vertical and horizontal and rarely in a slanting manner, i.e. vertical columns, monolithic horizontal slabs, trusses, which collapse because, in columns (34), their vertical axis bends beyond the fracture point as stated earlier. Trusses collapse due to the buckling of their horizontal axis at the points of their contact with the columns owing to the wavy motion that, during an earthquake, is transmitted through the ground and which turns individual column bases and the columns themselves into column fracturing pistons. Trusses will also collapse due to the compressive (45), tensional (42), shear (46) and torsional forces exerted at the points of their support as a result of the "left and right" swaying of the building’s framework caused by an earthquake or very high winds.
Brief description of the invention
The principal object of the hydraulic tie rod for construction projects of the present invention as well as of the method for constructing building structures utilizing the hydraulic tie rod of the present invention is to minimise the aforesaid problems associated with the safety of construction structures in the event of natural phenomena such as earthquakes, hurricanes and very high lateral winds. According to the present invention, this can be achieved by a continuous pre-stressing (pulling) of both the building structure towards the ground and of the ground towards the structure, making these two parts one body like a sandwich. Said pre-stressing is applied by means of the mechanism of the hydraulic tie rod for construction projects. Said mechanism comprises a steel cable crossing freely in the centre the structure's vertical