Method for improving the structural stability of an existing building construction

Inactive Publication Date: 2016-09-01
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AI-Extracted Technical Summary

Problems solved by technology

It is believed that this safety for all, both new and existing, constructions of reinforced concrete (hereinafter r.c.) is a huge error as it does not take into consideration in a suitable way the structur...
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Benefits of technology

[0005]In a first aspect the present invention relates to a method for improving considerably the structural stability of a building construction of already existing rei...
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The present invention relates to a method for improving considerably the structural stability of a building construction of already existing reinforced concrete (for example building constructions, schools, hospitals, bridges, etc.).

Application Domain

StrutsBuilding repairs +3

Technology Topic

Structural stabilityReinforced concrete +2


  • Method for improving the structural stability of an existing building construction
  • Method for improving the structural stability of an existing building construction
  • Method for improving the structural stability of an existing building construction


  • Experimental program(1)


[0034]The present invention will be described in details hereinafter by making reference to the above-mentioned figures. As shown in the abstract, a first subject of the present invention relates to a method for improving considerably the structural stability of an already existing building construction of reinforced concrete (for example buildings, schools, hospitals, bridges, etc.) having one or more pillars 3 and one or more beams 4 insisting on said pillars.
[0035]According to an embodiment a first drilling could be performed in cross direction to the pillar 3 so as to involve the beam 4 insisting on said pillar. For example, a first drilling, a horizontal hole, is performed orthogonally to the face, penetrating the beam 4 preferably for a depth of about 1.5 m. at the central portion of the section of the high beam sustaining the last flooring and another hole at the low beam sustaining the penultimate flooring. Both holes have to cross the pillar and they have to enter the beams. Consequently it is possible even to control the precision of the subsequent vertical hole (second drilling) performed starting from the top of the pillar and, in case, put suitable guides to ease the precision in the continuation of the vertical drilling. In this sense one continues from the top downwards, floor by floor, at first with the horizontal drillings in the beams (first drilling) and then with the vertical drillings in the pillars (second drilling), which act even as control, in the pillar and beam. The corner peripheral pillars are drilled in the same way of the intermediate peripheral pillars with the addition of a further second horizontal drilling, orthogonal to the other face, still at the central portion of the beam (FIG. 5B).
[0036]According to an embodiment in a building construction of reinforced concrete, subjected to the herein described method, each pillar will have the second (vertical) drilling from the top till the irons of the foundation base; said second vertical drilling will be prolonged beyond the foundation, until reaching a more suitable substrate, for those pillars which do not rest on an optimum ground (FIG. 1—dotted portion). The intermediate pillars, apart from the full-height vertical drilling, will have even one or more first (horizontal) drilling, orthogonal to the face, at the central portion of the beam (FIG. 5A); the corner pillars, at last, apart from the second full-height vertical drilling, will have even two first horizontal drillings, each one orthogonal to one of the two corner faces, at the central portions of the two beams sustained by the same corner pillar (FIG. 5B). The diameters of the horizontal and vertical drillings preferably will be those described hereinafter.
[0037]As previously described in said second (vertical) drilling a reinforcement 1 will be inserted, arranged orthogonally with respect to the first reinforcements 5. According to an embodiment a “cross-like” structure will be implemented on the intermediate peripheral pillars (FIG. 5A) in one of the most delicate and precarious points of the structure, that is at the pillar-beam fastening; furthermore according to an additional embodiment a second horizontal reinforcement 1 could be inserted in the beams 4 resting on the corner peripheral pillars (FIG. 5B), thus implementing a “double-cross” structure in the most precarious point that is at the corner linkage of the pillar with the two beams 4.
[0038]According to an embodiment in the horizontal holes obtained with con said first drilling first reinforcements 5 will be inserted comprising iron bars or threaded bars or metal tubes, preferably with improved adherence. The iron or threaded bars preferably will have a diameter of at least 20 mm; each one will have means for example a “head” nut to be screwed against a metal plate, for example with thickness of 12 mm, arranged like a “L” on two outer sides of the pillar. Upon screwing the nuts, placed at the “head” of the two bars, against the “L”-like metal plate on the outer sides of the pillar, the beams 4 are drawn to the pillar, thus by acting a pre-compression, at first of passive type which will become of active type as soon as the second vertical drilling will be performed, after the cut of some irons in the beam. The drawing of the beams 4 to the pillar 3 is very important to the purpose of avoiding that the pillars (especially the corner ones) during the seism move from the original position thereof due to the lack of a sufficient connection between pillar and beams. The “L”-like plate could even have two plate-fastening bolts near each one of the two outer sides thereof. Said metal plate could be arranged below the filler by covering it with a metal grid whereon, then, the filler is placed. It is underlined that after a possible seism, producing a “releasing” in the pre-compression, the same can be “recorded” and brought again in action as in the initial state.
[0039]The embodiment of FIG. 5B shows two horizontal threaded bars for connecting the two beams 4 to the corner pillar 3. The bar arranged in the sense of the longest side of the pillar preferably will be placed so as to leave the second reinforcement 5 to the outside. Furthermore, it is slightly tilted so that the long portion enters the beam 4 and better penetrates the central portion of the beam itself.
[0040]In some existing constructions there could be beams 4 particularly deteriorated in the reinforcements thereof; in some cases all beams of the building construction could be deteriorated, therefore it is necessary implementing more radical interventions by inserting first multiple reinforcements: in this case one will intervene on some or on all beams 4 with first horizontal reinforcements 1 crossing the beams of reinforced concrete for the whole length thereof, from a face to the other one of the building construction, on the faces thereof, with a “head” nut”, metal plates with rectangular or “L”-like shape are tightened. Said first horizontal reinforcements 1, according to the case needs, could be irons with minimum diameter 20 mm. or metal pipes with suitable diameter and thickness. For example, in case of a beam 4 with section 30×50 cm four metal pipes with diameter 40 mm. could be used, with a pair of tubes arranged symmetrically in the high portion of the beam and with another pair of pipes arranged in the same way in the low portion of the beam. Each above-described pipe is inserted in a pre-arranged hole with a diameter of 80 mm, so as to have around the metal pipe expanding mortar with thickness of 2 cm. The horizontal metal pipes could be inserted very near (as far as skimming) the pipe or vertical metal reinforcement even obtaining the advantage that the expanding mortar wrapping the tube or vertical reinforcement mixes homogeneously with the mortar wrapping the horizontal pipes.
[0041]The method of the present invention according to a preferred embodiment is described hereinafter wherein the intervention on different pillars is implemented gradually: once completed the intervention on a pillar (by inserting for example the pipe or metal cage 5 preferably for the whole height thereof and by inserting the first reinforcements 1 in the beams 4 of all floors and with a final pouring of the expanding mortar for the whole height thereof), one waits for a time of about 24 hours so that the so-treated pillar starts its full static function before intervening on the subsequent pillar. The waiting time, having used an expanding, fluidified and quick-set mortar, could be very short, about 24-48 hours. By working in this sense, during the global treatment of the building construction, only the treated pillar has a reduced static functionality, as during treatment (however in whole safety as the r.c., by rule, “works” at about ⅓ of its total capability), whereas the same after 24-48 hours acquires almost its full static function, function strengthened by the subjected treatment.
[0042]Said second reinforcement in tubular form or metal cage could be inserted in the vertical hole (starting from the top of the building construction) at subsequent tracts, usually long 3 m, screwed or welded according to the following procedure. The first tract is let down into the hole by stopping the upper end with a scarf; the upper end of the first tract of pipe or cage is screwed or welded with the lower end of the second tract of reinforcement and therefore the second tract is let down too, by stopping the upper end with a scarf too; the third tract of pipe or cage is welded or screwed thereto and one proceeds in this sense until inserting the metal reinforcement for the whole weight of the pillar (as far as reaching the lower reinforcement of the foundation or beyond that).
[0043]The horizontal bar connecting the pillar to the beam (in case of intermediate peripheral pillar) or to the beams (in case of corner pillar) are inserted starting from the last floor and as far as the first flooring, and acting the precompression. Then, one proceeds in the same way by descending from an upper flooring to the lower one, as far as the first flooring.
[0044]Then one passes to the second vertical drilling, to the insertion of the metal reinforcement and of the expanding cementitious mortar.
[0045]By acting in this way, the cut of the irons of the beams on the pillar with the second vertical drilling to insert at the centre of the pillar the second reinforcement 1 in the whole height does not cause any damage to the structure, as pre-strengthened and pre-compressed in advance, whereas the insertion of the second reinforcement 1 allows it to acquire earthquake-resistant and collapse-resistant features at a level that otherwise could not be reached.
[0046]According to an embodiment and by making reference to the main drawing in FIG. 6, the second reinforcement 1 can be implemented in the form of a metal tube 5b with suitable thickness and diameter or metal cage for the insertion in the performed drilling in substantially central position and along the longitudinal axis of the pillar 3. By way of example, if the second vertical drilling 1 performed in the pillar has a diameter of 12 cm, the pipe or metal cage 1 will have a maximum diameter of 8 cm. so that, placed in the hole obtained from the drilling of the pillar, it can have around it an empty space, shaped like a circular crown with a thickness of 2 cm. The empty space around and inside the reinforcement will be entirely filled up with cementitious material, preferably with expanding mortar.
[0047]According to an embodiment the metal reinforcement 1 will have a greater thickness in the lowest portion thereof of the building construction, for example for a height of 70 cm above the foundation. For a building construction with considerable height it could be further provide that the several tracts of the metal reinforcement 1 have different thickness and diameter in the height. For example a thickness of 5 mm in the lowest portion; thickness 3 mm. in the intermediate one and a thickness of 2 mm. in the highest portion with telescopic insertion.
[0048]According to an embodiment the second reinforcement 1, tube or cage, will be inserted for the whole length of the pillar 3, by screwing or welding several tracts from top to bottom for the height of the construction, by paying attention to make the screwed or welded portion to reach the intermediate height between two floorings, that is where the moment is equal to zero.
[0049]According to an embodiment said second reinforcement 1 along its circumference, preferably at each inter-floor, comprises one or more openings 2, for example four holes with diameter of about 4 cm; said openings have the function of draining off the cementitious material, from the inside of the reinforcement to the outside of the reinforcement.
[0050]Making the cementitious material to drain off from the inside to the outside of the reinforcement has the purpose of making the cementitious material to compenetrate inside the tubular reinforcement with the one of the cylindrical gap between the pipe and the performed drilling and, therefore, even with the inner surface. The openings 2 along the circumference preferably will be arranged staggered in height one with respect to the other one.
[0051]By way of example if the drilling in the pillar is 12 cm and said second reinforcement 5b in form of metal tube inside thereof is 8 cm, the four openings 2 will be placed two at a diameter (AB) and the other two at the diameter orthogonal to the first one (CD), but at a height higher or lower than 20 cm with respect to the height of the inter-floor. The two openings on the diameter AB (horizontal with respect to who observes the figure) have to be higher (or lower) than 10 cm with respect to the intermediate height of the floor; the two openings on the diameter orthogonal to the first one (CD) have to be lower (or higher) than 10 cm of the intermediate height of the floor.
[0052]Therefore, if for example the height of the floor is about 3 m, the two openings on the diameter AB will be at the height of mt. 1.50+0.10=1.60 mt.; whereas the two openings on the diameter CD will be at the height of mt. 1.50−0.10 needed resistance=1.40 mt.
[0053]The horizontal and vertical drillings will have to be performed exclusively with continuous core boring in the beams and in the pillars, at the centre of their section, as such drilling technique does not damage the structures, especially the precarious ones, contrary to other techniques, such as, for example, the roto-percussion. The vertical drillings in the pillars start at the top and continue as far as the foundation base to insert therein said second reinforcement 5. In case the ground immediately below the foundation of the building construction does not have a sufficient consistency, the drilling (and consequently the insertion of the reinforcement 5 of FIG. 1) can continue below the foundation beam as far as the layer of ground (as designated with dotted lines in FIG. 1) having the resistance considered necessary, by obtaining in this way a better response of the ground-structure system under seismic event. According to an embodiment the diameter of the vertical drilling starts from 8 cm to 10, 12 14, 16 cm etc. according to the height of the building construction and to the sizes of the pillars, whereas the diameter of the horizontal drilling (for the insertion of the “cross-like” and/or “double-cross-like” threaded bars) stars from 4 cm. and over.
[0054]The pillars of the reinforced concrete constructions, whereon the vertical drillings will be performed, to insert therein said second reinforcements, could be inner or peripheral pillars. The peripheral pillars, in turn, could be corner pillars or intermediate pillars. In FIG. 4 the different types of pillars are designated respectively with: A intermediate pillar, B corner peripheral pillar and C inner peripheral pillar. The drillings will be performed with partially different modes based upon the different position of the pillars. The internal pillars will be drilled starting from the top and continuing, in continuous way, for the whole height as far as the lower irons of the foundation, or beyond that. The position of the irons of the reinforcements in the pillars (and even in the beams) will be controlled even with the pacometer and, consequently, the necessary precision of the vertical and horizontal drillings in the pillars and in the beams will be obtained. Since in the building construction subjected to intervention the pillars could be old and have a very poor stirrups, one will not exceed with the mortar expansion so as not to damage them. Furthermore, the fact of making the pipe wall very rough will be very advantageous to improve the adherence between concrete and tubular reinforcement, especially in case of restructuring of a pillar. The internal pillars are those which during the seismic stresses suffer from lower damages to the nodes.
[0055]At the current state of art the resistance to the earthquakes of the new building constructions in r.c. is given by the conventional reinforcement or even by an always equal “central structure-reinforcement at the crossing between pillars and beams”, as height and position. Therefore, there is not a reinforced central core in the pillars and in the beams in r.c., variable with their position in the body of the building construction, with the heights at the several floors and with the corresponding stresses.
[0056]Therefore, it is not possible having all possible reinforcements designated in FIG. 7 at the same time: conventional outer reinforcement, reinforcement of the central core—which can be at whole height or at limited height at the head and at the foot of the pillar at the crossing with the beams (structural node)—iron or barycentric reinforcement. All reinforcements allow the structures in r.c. which are being constructed to be able to adequate in organic way to the different possible horizontal stresses.
[0057]The pillar with the “VARIABLE REINFORCED CENTRAL CORE” has the following reinforcements as REPORTED in FIG. 7: [0058] the outer reinforcement: conventional reinforcement; [0059] the reinforcement of the central core; [0060] the iron or the barycentric reinforcement.
[0061]The reinforcement of the central core can have reduced height, about 70 cm. below the flooring (that is at the head of the pillar) and about 70 cm. above the flooring or above the foundation beam (that is at the foot of the pillar); or it can be at whole height.
[0062]In the first case it corresponds to the earthquake-resistant system already existing in the art (“small pillar-kernel”) and reported above; in the second case it corresponds to what even provided by the present industrial invention.
[0063]The barycentric reinforcement or the barycentric iron are not provided in the earthquake-resistant system reported above, but possible ones are provided in the present industrial invention.
[0064]The reinforcements of the reinforced central core in the pillars are variable with the position of the pillar themselves in the body of the building construction, with the heights at the several floors and with the corresponding stresses.
[0065]The possible position of the pillars in a building construction is designated in FIG. 10: [0066] corner peripheral pillars (1,3,7,9); [0067] not corner peripheral pillars (2,4,6,8); [0068] (central) internal pillars (5).
[0069]Based upon the above-mentioned position of the pillars in a building construction there are the following different stresses at the horizontal forces: [0070] the corner peripheral pillars are those more stressed by the horizontal forces; [0071] the not corner peripheral pillars are less stressed than the first ones; [0072] the (inner) central pillars are the less stressed ones.
[0073]And therefore, consequently and in conformity with the present industrial invention, with the variable reinforced central core the corner peripheral pillars will be those more reinforced; the not corner peripheral pillars will be less reinforced of the previous ones; the central pillars will be the less reinforced ones.
[0074]The reinforcements of the reinforced central core in the pillars are variable even with the heights at the several floors and, therefore, with the corresponding stresses which, obviously, are higher at the low floors and lower at the high floors, that is they decrease from the low floors to the high floors. FIG. 11 represents the “scheme of a frame of a multi-floor building construction”. In the figure the possible different thicknesses of the pillars based upon the height are designated wherein the reinforcements variable in the reinforced central core will be inserted based upon the heights at the several floors. The low floors can be reinforced with: [0075] conventional reinforcement; reinforced central core at whole height; reinforcement in the centre of gravity of the central core.
[0076]The medium floors can be reinforced with: [0077] conventional reinforcement; reinforced central core at whole height; iron in barycentric position.
[0078]The high floors can be reinforced with: [0079] conventional reinforcement; reinforced central core not at whole height but only at the head and foot of the pillars (about 70 cm. above is under the flooring); in case barycentric iron.
Pillars and Other Structures in r.c. with Several Reinforced Central Nuclei.
[0080]The “variable reinforced central core”, so as described above, is the base element of the present industrial invention, but it can be repeated proportionally to the sizes and the shapes of the structures in r.c. themselves.
[0081]FIG. 12 shows a reinforced central core having, in the barycentric area, a circular reinforcement constituted by vertical irons wrapped by a continuous coil. There could be: [0082] pillars in r.c. with two reinforced central nuclei (FIG. 12a); pillars or walls in r.c. with three or more reinforced central nuclei (FIG. 12b). FIG. 12c shows a mast for bridges or analogous structure with several reinforced central nuclei. The reinforced central nuclei are mainly positioned in the corners and they have a “L”-like configuration.
[0083]The shown examples are indicative, and not exhaustive, as the reinforced central nuclei which will be suitably positioned in the structures in r.c., will depend upon the size and the shapes of the several structures in r.c. themselves.
[0084]The Variable Reinforced Central Core Approaches the Neutral Axis to the Geometrical Centre of Gravity of the Section
[0085]Let's consider FIGS. 13a and 13b, without seismic stresses. FIG. 13a shows the section of a reinforced pillar of cm 30×30 reinforced according to the current seismic law (without reinforcement in the central core); FIG. 13b shows the section of the same pillar of pillar of cm 30×30 equipped with the earthquake-resistant device (with reinforcement in the central core). Both will be subjected to the theoretical last moment and to the theoretical last force reported above: [0086] the pillar cm 30×30 without earthquake-resistant system with theoretical last moment Mu=KN 101.00 and Fu=KN 67.33; [0087] the pillar cm 30×30 equipped with the earthquake-resistant device with theoretical last moment Mu=N 136.10 e Fu=kN 90.73.
[0088]As it can be seen from FIGS. 13c and 13d, during the seismic stress the position of the neutral axis in the section without the earthquake-resistant device is moved more towards the outside edge with respect to the position of the neutral axis in the section with the earthquake-resistant device.
[0089]More precisely, in the first section it is cm 6.9 from the edge; in the second section it is cm 9.1 from the edge and that is it is more shifted towards the centre by 2.2.
[0090]By calculating the two areas and by comparing them there is the fact that this involves the increase by 31% of the cross portion subjected to compression: that is with the earthquake-resistant device a reduction in the compression of the concrete per cmq is obtained. There are very serious consequences: cracks and detachment of the concrete cover with greater stresses; bending of the irons due to the peak load with greater stresses etc.; that is there is an increase in the resistance by 31%.
[0091]It is obvious that the presence of an additional iron (or reinforcement) in the centre of gravity (FIG. 7) would move even more the neutral axis towards the geometrical centre of gravity with an additional increase in the compressed area.
[0092]FIG. 13c also compares the two diagrams: the one related to the pillar without earthquake-resistant device and the one related to the pillar equipped with earthquake-resistant system.
[0093]From the comparison between the two diagrams it results very clear that the presence of the reinforced central core reduces the compression, above all on the edge wherein it is more dangerous, as the possible destruction of the concrete cover would bring the reinforcement bars to peak load.
[0094]The Reinforcement of the Central Core Reduces the Tension on the Peripheral Irons by Dissipating it in a not Destructive Way.
[0095]The conventional reinforcement, with the irons on the periphery of the section, has been provided in this way because the capability of the irons of resisting to traction can be exploited at most on the edges, with the greater distance between the irons arranged on the opposite sides and that is with the greater arm in case of resistant moment with tensioned area and compressed area of the section.
[0096]However in this way, it is believed, there is not obtained the best adapting to the horizontal stresses.
[0097]If one observes the shape of the trunks and the branches of the trees it can be seen, in a circular section of a trunk or a branch, that there are several concentric rings starting from the outer bark and ending into the central kernel, which is the innermost portion.
[0098]If the tree had concentrated its own entire resistance on the most external ring, with the more violent stresses of the wind it would happen, during collision, that the tree branch would win, with its outer ring strengthened at maximum (analogously to what happens with the current state of art) or the wind would win, by overcoming the resistance thereof and breaking it.
[0099]On the contrary, the trees, in the millions of years of adaptation on the earth, have shaped and structured with several subsequent defence lines: the concentric rings.
[0100]Therefore, under the strongest push of the wind, the most external ring absorbs most part of the stress, whereas the remaining stress is absorbed by the subsequent rings, as second, third, etc. defence line, as far as the most barycentric ring (ecological resilience).
[0101]In this way the most external ring is stressed less.
[0102]It is believed that with the “VARIABLE REINFORCED CENTRAL CORE” the structures in r.c. can be equipped with analogous adaptability to the horizontal stresses which have the trees to the wind pushes. An experience made by the inventors confirms this. By referring to FIG. 7 and to FIG. 14 a stiff rod has been put on balance, long about 35 cm., on a metal sheet at the neutral axis of FIGS. 13b and 13d. Equal springs have been put, by fastening the opposite ends to the rod and to a supporting base, at a portion of the irons as designated in FIG. 7: at the conventional outer reinforcement; at the reinforcement of the central core and at the barycentric iron.
[0103]Then, growing weights are put, that is metal washers inserted on a vertical iron placed on the balance rod beyond the neutral axis. Several times the following has happened: if the resistance to the balance rod lowering at the weight is left to the spring only at the conventional outer reinforcement, the lowering, and then the corresponding rotation, is much more marked; if to resist to the lowering tilting, even the springs at the reinforcement of the central core and of the barycentric iron are made to intervene, the lowering and the rotation reduce by more than 40%.
[0104]Therefore the most external spring (that is the outer iron of the conventional reinforcement) is relieved by 40% at least of the total stress; 40% absorbed by the spring at the reinforcement of the central core and by the spring at the barycentric iron. This happens in the same way in which the rings subsequent to the most external one of a tree's branch absorb a portion of the wind push.
[0105]This is visible even graphically in FIG. 14 with the diagram of the tensioned portion and of the compressed portion of the section. Even the portions of areas of the tensioned area of the diagram itself corresponding to the several reinforcement irons of the tensioned area (peripheral irons of the conventional reinforcement, irons of the central core and barycentric iron) are shown therein. They absorb the tensions represented by the diagram. By calculating the several areas and by comparing them it can be seen that: [0106] the area going from the irons of the central core up to the outer limit of the section (tensioning area considered absorbed by the irons of the conventional reinforcement) is about 60% of the total tension area of the tensioned portion; [0107] the tension area going from the irons of the central core up to the neutral axis (tension are considered absorbed by the irons of the central core and by the barycentric iron) is about 40% of the total tension area of the tensioned portion.
[0108]This calculation has been made by default as it is to be considered that a portion of the tension area going from the irons of the central core up to the outer limit of the section—precisely that very near to the irons of the central core—is absorbed by these irons themselves, whereas in the above calculation it has assigned to the outer irons.
[0109]This means that with the reinforcement of the central core and with the barycentric iron at least 40% of the total tensile stress is absorbed, by taking it away from the outer irons which are tension-stressed less by the same percentage.
[0110]The dissipation of this 40% of total tensile stress is made in not destructive way as it is much below the admitted one.
[0111]On the other hand, the experiments made by the applicants have demonstrated that the central core has remained always integer, with vertical irons and stirrups at their place and with the concrete which, during collision, reacted with a metal sound to demonstrate the inner compactness.
[0112]Hereinafter the lengthening of the duration of the structures in r.c. according to some embodiments of the present invention is described in details hereinafter.
[0113]At the current state of art there are not systems to lengthen globally and radically the duration (nominal life) of the structures in r.c., but in most cases local interventions are made for stopping up the already occurred most superficial damages, such as for example interventions with anti-rust paints, or deeper ones, such as interventions with bandages and/or encirclements of the damages, or deteriorated portions, or other.
[0114]According to the system of the present invention the damages or deteriorated portions can be replaced, in the irons and in the concrete (hereinafter cnr), so that the structure in r.c. can return to the level of initial resistance or even upper level.
[0115]For this reason the presence of a reinforced central core, in the pillars and in the beams, is required guaranteeing even a temporary resistance in absence of the outer reinforcement. Thus, there is the renewal of the outer portions as it happens in all living organisms.
[0116]The living organisms are able to renew the most external portions in direct contact with the outer environment, with its stimuli and stresses, with its aggressiveness etc. by keeping more protected and integral the central core allowing them to renew.
[0117]The replacement of the damaged and deteriorated portions in most cases can take place at the foot of a pillar in r.c. at the level of the foundations; at the head and at the foot of a pillar at the level of the several floorings; at the head of a pillar at the level of the covering floorings; in the beams it can take place at the crossing between beams and pillars (structural node).
Duration of the Reinforced Concrete
[0118]With the system for the r.c. renewal proposed with the present invention the duration of the same will lengthen very much. The rust, due to the water succeeding to reach the reinforcement irons of the pillars and of the beams, once the concrete cover with the thickness provided by the existing rule has deteriorated, shortens the duration of the current r.c. At the current state of art, in particular with the recent existing patent device (small pillar-kernel), there is a protecting concrete cover 3 to 5 times bigger than the usual one and therefore there is a corresponding lengthening in the duration of the structures in r.c.; furthermore, the presence of small pillar-kernel intervenes as resolution and as guarantee against planning and/or manufacturing errors. There is further the advantage of being able to replace (with a local intervention, without any damage as the resistance of the pillar and of the beams in r.c. is guaranteed by the reinforced central portion which has remained wholly integral) the tract of deteriorated outer peripheral irons, by redeveloping the pillar and the beam. Thus, by re-developing all deteriorated pillars and beams of a building construction, it is possible to recover the building construction itself by bringing it back to the initial, or even better, resistance conditions.
The Main Factors Threatening the Duration of the Structures in r.c.
[0119]The main factors threatening the duration of the structures in r.c. are the following ones: [0120] 1) environment aggressiveness; [0121] 2) little violent earthquakes determining in the bearing structures not visible and little visible cracks and microlesions, which constitute weakness points in the resistance of the structure itself for future earthquakes; [0122] 3) violent earthquakes; [0123] 4) action of electromagnetic fields.
[0124]Environment Aggressiveness
[0125]A cnr, under ideal conditions, correctly packaged and laid, must have a Ph (Ph measures the acidity) comprised between 13 and 14, it must not be porous and must be impermeable. A so-made cnr is able to maintain unaltered the reinforcement steel for a not defined time, that is without limits. These ideal conditions can be obtained, in the central portion of the pillars and of the beams, with the presence of a reinforced central core thereabout one will speak hereinafter. In the current reality the concrete is subjected to the environment aggressiveness.
[0126]The main causes contributing to create an aggressive environment for the reinforcement irons of the structures in r.c. are the following: [0127] a) humidity, rising by capillarity above all to the underground and basement floors; [0128] b) cracks, bringing directly in contact the reinforcements with oxygen of air and water; [0129] c) the heat of a confined environment, such as for example in a basement wherein the inner temperature is higher than the temperature outside the building construction and there are contemporarily humidity and water, which by evaporating deposits on the coldest areas that is the lowest portions of the pillars; [0130] d) the exposure to the atmospherical agents of the pillars and of the peripheral beams of a building construction, or the pillars and the beams of the arcades.
[0131]It is important underlying the phenomenon of the concrete “carbonation”. The steel, dipped in an alkaline solution (the concrete is slightly alkaline), with ph higher than 11.5, is covered with an oxide patina. Subsequently, in a moderately aggressive environment, such as the hot-humid one of a basement floor, a corrosive process begins which starts from the micro-cracks of the surface layer, it extends over the whole surface and continues even deeply with speed of about 0.6 mm/year. The peripheral pillars and beams of a building construction and the pillars and beams of the arcades can come more easily in contact with rain water, which carries several pathogenic agent for the concrete: oxygen (O2), carbon dioxide (CO2), chlorine, (Cl), etc.
[0132]These agents, especially the carbon dioxide, brought in solution by the water can change the Ph, by lowering it at about 9, and causing the phenomenon of the “carbonation”, with the formation of calcium carbonate. The water, with the presence of oxygen, attacks and destroys the surface patina and it starts the corrosive process: the steel desquamates, with decrease in the section and in the adherence capability, it increases in volume and expels the concrete cover, thus increasing even more its contact with air and water, by continuing in this way the degrading process.
[0133]Little Violent Earthquakes
[0134]The little violent earthquakes (and even the frequent earth tremors only detected by the instruments) can determine in the bearing structures in r.c. visible, little visible or invisible micro-cracks which constitute weakness points for the future earthquakes. Furthermore, these micro-cracks make easier the environment aggressiveness: contact with water, with carbon dioxide, etc.
[0135]Violent Earthquakes
[0136]It is known that, when there is a so strong earthquake to damage seriously or to destruct even the structures in r.c., it can be seen that a pillar is damaged above all at the head and at the foot (that is in its portions in contact or nearer to the beams of the floors and the foundation beams). When an earthquake of high intensity occurs, the pillars are damaged above all at the “head” and at the “foot” (that is in the portions nearer to the floorings), whereas they remain almost integral in the central portion. During the stresses of the building construction, determined by a seism, at the “head” of each pillar below each flooring and at the “foot” of each pillar above the foundation and above each flooring there is this destruction: the concrete cover breaks due to the excessive pressure on the edges; the exposed irons become “peak-loaded” and assume the characteristic corrugated aspect (the thickening of the stirrups, provided by the current rules, improves the resistance but it does not solve the problem radically). The irons of the beams are no more connected to the irons of the pillar as these have come out from their seats and the beams sustain in precarious way only as if they had rested on the pillar destructed on the edges. As the seismic oscillations continue, the beams detach from the pillar and the floorings fall down. It does not solve the problem and it cannot solve it for what underlined hereinafter. Let's analyse a pillar in a static situation (absence of seismic stresses) and in a dynamic situation determined by the horizontal seismic pushes; more precisely let's consider the section at the foot of the pillar at the fastening to the foundation beams. In the static situation, without horizontal seismic stresses, the section is all compressed and the neutral axis is at the infinite. When the seismic pushes and the corresponding oscillations of the building construction begin and increase from one side to the other one, the neutral axis starts to enter the section and therefore, when the building construction tilts on the right, the left side of the section, with respect to the neutral axis, is tensioned whereas the right one is compressed. In the subsequent tilting on the left of the building construction the situation inverts and therefore the right portion of the section with respect to the neutral axis is now tensioned whereas the left one is compressed. Upon still increasing the horizontal seismic pushes, the neutral axis moves more and more, alternatively, first of all towards the right edge of the section (by increasing the tensioned portion on the left with respect to the neutral axis and by reducing the compressed portion on the right) and then towards the left edge of the section (by increasing the tensioned portion on the right and reducing the compressed portion on the left). In one considers the instants, the second fractions, wherein the neutral axis, in a section of a pillar with side of cm. 30 with load of 75,000 (75 thousand) Kg., it is progressively at 2.5 cm.-0.5 cm.-1 mm. from the edge, equal to 75-15-3 square centimetres (that is cmq), respectively, of compressed concrete, there is a compression on the concrete of 1,000 Kg/cmq.-5,000 Kg/cmq.-25,000 Kg/cmq., respectively; these compressions cannot be supported whatever is the adopted resistance-increasing system. The section is destructed starting from outside towards inside, that is from the edges towards the centre, which is the one resisting more due a geometrical-physical fact in itself of the section. Therefore, there will be the fact that the concrete cover breaks and consequently the same loads, during stresses, will burden for a second fraction on an area corresponding to the thickness of the vertical irons with the stirrups wrapping them. No matter how thick the stirrups can be arranged, the high entity of these loads will move them and the irons will be bent due to the peak load. The destructive process will move from the edges towards the inside of the section. And this has been demonstrated even by the destruction mode observed during the performance of monotonic and cyclic experimental tests, on comparison models implemented according to the building rules existing in Italy, one thereof equipped with the patent device, at the Department of Structures for Engineering and Architecture of the University “Federico II” in Naples.
[0137]First of all, during the horizontal pushes here and there, due to traction one noted: [0138] in the model according to the current seismic law, parallel horizontal cracks, delimiting strips, larger ones on the edges with respect to the centre and low; [0139] in the model even equipped with the patent device, parallel horizontal cracks less marked and higher due to the presence of the reinforced central core.
[0140]With the following oscillations, the loads compressed these subsequent strips, already cracked in height, and the pressure on the edges at first made some scales of concrete on the outer faces to detach due to pressure which, for an instant, upon moving outside the neutral axis, burdened only on portion of the concrete cover. In the end, it resulted that the model according to the current seismic law remained destructed on the edges by losing its resistance capability whereas the one equipped with the patent system, even if it subjected the same peripheral destruction, but with an increase by about 30% of the stress, maintained perfectly integral the central core giving the possibility of reconstructing the destructed portion and recovering the structure. In conclusion, the thickening of the stirrups improves the situation but it can never solve the problem radically. On the contrary, the presence of the patent device solve such drawback as there is a concrete cover which is three to five times bigger, that is a concrete cover from 7.5 cm. to 12.5 cm.
[0141]Therefore, with a concrete cover, respectively of cm. 7.5 and cm. 12.5, the compressed area thereabout it is spoken in the mentioned example of a pillar of cm. 30×cm. 50, with the “small pillar-kernel”, it will be still cm. 30×cm. 7.5=225 cm2, and cm. 30×cm. 12.5=375 cm2, therefore much bigger than cm. 30×cm. 2.5=75 cm2 of the above-mentioned example. The resistance to compression of the concrete, in the seismic areas, usually is limited to ⅓ of what really inserted in the sizing structural calculation (as usually the results of squashing on small cubes of concrete show, enclosed to the structural test certificates). Therefore, the patent device is able to sustain by itself the total weight sustained before by the pillar, even if it is subjected to a compression approaching the squashing limit. Then, with the patent device there are, in words, also the following advantages: [0142] to prevent that the beams go out of the pillar and fall down from the floorings (by avoiding dangers to people, etc.); [0143] the safety is thus guaranteed even when the structure, due to the seism violence, has loosen its elastic state and it has entered the plastic one; [0144] the structure is further guaranteed from possible planning and manufacturing defects; [0145] after the earthquake (with the reinforced central core which has maintained the beams still on the pillar), the destructed portions of the pillar itself, that is foot and head, can be reconstructed; in this way the advantage of recovering the building construction is obtained, apart from having saved human lives.
[0146]Action of Electromagnetic Field
[0147]The electromagnetic fields contribute to make aggressive the environment against the structures in r.c. But the proposed earthquake-resistant system, with the reinforced central structure, has the advantage that the peripheral outer reinforcement (as provided by the rules), constituted by longitudinal irons and by stirrups wrapping them, behave like a Faraday cage wrapping the central reinforcement(s) and protecting it/them from the action of the electromagnetic fields.
[0148]Additional Advantages Acting on the Lengthening of the r.c.:
[0149]another great advantage of the central reinforcement, apart form that against the earthquakes, is given by the lengthening of the r.c. duration against the environment aggressiveness. It gives the possibility of renewing indefinitely the outer reinforcements whereas the central core remains integral both from the earthquakes and the environment aggressiveness: it then allows the “renewal” of the r.c. One of the questions which is currently asked, after about 150 years as from the advent of the r.c., is the duration in time of the r.c. itself. Usually a nominal life of about 50 years is assigned to the common structures, whereas about 100 years is designated as nominal life of the public and strategic civil structures.
[0150]With the present invention there is the possibility of lengthening the duration of r.c. for an indefinite period of time, as described hereinafter. As said above: [0151] a) the duration of the structures in r.c. is threatened by: violent earthquakes, few violent earthquakes and earth tremors (causing weakening points), environment aggressiveness and actions of the electromagnetic fields. [0152] b) A concrete, under ideal conditions, can maintain unaltered the reinforcement steel for an indefinite period of time. [0153] c) The reinforced central core is under these ideal conditions as it has a protection of the concrete cover from 3 to 5 times bigger.
[0154]The reinforced central core, apart from remaining integral, is sized so as to be able to sustain temporarily the total weight of the whole pillar and it allows, then, to be able to repair the outer reinforcements damaged or destructed by the earthquake or destructed in time by the aggressive action of the environment and even by the negative action produced by the electromagnetic fields.
[0155]This action of regeneration (renewal) can be obtained in imitation of what occurs in nature, for example in a tree trunk or in a living organism, wherein the most external portions, more in contact with the environment, renew and they do it until their central core remains integral and protected by the outer casing. The prerequisite to make this to occur is the presence of the reinforced central core in the pillars and beams of the structures in r.c.
[0156]The structures in r.c. can be: [0157] d) new structures to be implemented, wherein the reinforced central core is inserted during the implementation of the structure itself. [0158] e) already existing structures in r.c., with recent or farer implementation, wherein the reinforced central core can be inserted; [0159] f) already existing structures in r.c. which have subjected violent earthquake tremors, then already very damaged, but not yet fallen down even if to be demolished (as the existing rules provide the removal and the demolition after losing resistance by 20%), which can be repaired and recovered and subsequently equipped with the reinforced central core to be inserted compulsorily after the occurred repair of the damaged portions.
[0160]The repair of the portions damaged by the seism at the fastening of the foot of the pillar to the foundation is the one described hereinafter, which can be the same of the one to replace, in figure, the irons of the peripheral reinforcement, damaged both by the aggressiveness of the outer agents and by the negative action produced by the electromagnetic fields.
[0161]Repair of the Damaged Portions
[0162]The substantial difference between a normal repair and a repair make based upon the present invention lies in the fact that a normal repair can be only external as it cannot affect and further reduce the resistance of the already damaged and compromized structure, FIGS. 20a and 20b.
[0163]On the contrary, a repair according to the present invention starts from the fact that inside the structure there is a central core which has remained integral and able to replace temporarily the structure in its entirety and therefore the repair can be made as far as the depth considered necessary so as to be able to bring the destructed portion back to the initial resistance state and then to the radical renewal, to its “revival”.
[0164]The interventions for repairing the damaged portions can be performed in the following cases: [0165] 2) fastening of the pillar to the foundation beam. FIG. 15a (current situation) and FIG. 15b (repair). [0166] 3) fastening of the pillar to the beams at the level of the inter-floor floorings. FIG. 16a (current state) and FIG. 16b (repair). [0167] 4) fastening of the pillar to the beam at the level of the covering floor. FIG. 17a (current state) and FIG. 17b (repair). [0168] 5) fastening of the beams to the pillars. FIG. 18a (current state) and FIG. 18b (repair). [0169] 6) fastening of the pillar to the foundation beam in case of structure damaged by the earthquake not equipped with the small pillar-kernel. FIG. 19a (current state), FIG. 19b (repair) and FIG. 19c (insertion of the small pillar-kernel).
[0170]According to an embodiment wherein the building construction has the irreparable damages by corrosion of the structural reinforcements (beams and pillars), then the intervention system will be the following: the central structure-reinforcement is inserted inside the pillars as already described; previous suitable drillings, adequately pretensioned strands, are inserted in the beams, instead of the threaded bars, going to one face to the other one by englobing suitable contrast outer structures with self-tightening “heads” positioned on metal plates. Expanding mortar will be injected in the hole so that the pretensioning is uniform for the whole length of the beam. At the sides of the central structure-reinforcement a pair of suitably sized pretensioned strands will be inserted. They will be used eve to improve the stiffness of the floor. The so-implemented strands are suitable to absorb wholly the horizontal forces generated by the seism. In the present description and in some figures the vertical reinforcement 1 or second reinforcement is designated even with the terms reinforced central core or small pillar-kernel.


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