WO2018065911A1

WO2018065911A1 - Process for the antiseismic reinforcement and consolidation of existing structures in reinforced concrete

Info

Publication number: WO2018065911A1
Application number: PCT/IB2017/056110
Authority: WO
Inventors: Enzo MORELLI; Michele MICELI; Linda CARBONE
Original assignee: Morelli Enzo; Miceli Michele; Carbone Linda
Priority date: 2016-10-05
Filing date: 2017-10-04
Publication date: 2018-04-12
Also published as: IT201600099915A1

Abstract

The present invention relates to an antiseismic reinforcement and consolidation process of existing structures made of reinforced concrete.

Description

PROCESS FOR THE ANTISEISMIC REINFORCEMENT AND CONSOLIDATION OF EXISTING STRUCTURES IN REINFORCED CONCRETE

DESCRIPTION

In the current state of art in order to increase the structural resistance of the existing buildings made of reinforced concrete above all external interventions are implemented at the structural nodes and however not in the centre of pillars and beams. On the contrary, the present invention, allows, in a minimally invasive way and in an inexpensive way, to be able to place central armours with possible different shapes and materials, the greater effectiveness thereof has been already demonstrated, to make the existing buildings made of reinforced concrete more resistant to earthquakes, then by implementing a new quick and functional antiseismic retrofit. The formation of cavities, the related pre-reinforcements and the connected central armours, to be placed in the pillars and in the beams by means of continuous logging, or hydrodemolition, or other suitable technique, takes place by using even specific equipment, described in relevant paragraph, and it mainly depends upon the state shown by the existing structure made of reinforced concrete whereon one has to intervene.

For example, the structures made of reinforced concrete, implemented prior to Law Nr. 1086 of 5 November 1971 , show armours with partially different positions and quantities both for the longitudinal iron bars and for the stirrups with respect to those of the subsequent laws, until the one in force. The present patent application solves such problems even in quicker and cheaper way than the usual known arts.

l The cavities on the pillars, the implementation method thereof will be described in relevant paragraph, have to be implemented at the central portion of the pillar height, and that is wherein the stresses are smaller (main Figure).

From the inner base of said cavity one proceeds with continuous logging, or hydrodemolition, or other suitable technique, downwards as far as reaching and going beyond the corresponding beam by a distance nearly identical to the logged one on the upper side. In case of cavity implemented in pillars resting upon foundation beam the continuous logging should develop from the base of the cavity created as far as reaching almost the lower face of the foundation beam, except the cases wherein it is necessary to go beyond it to reach a more suitable laying ground.

Before making any intervention on pillars of existing buildings made of reinforced concrete it is necessary to carry out a series of preliminary activities to be implemented in order to be able subsequently to prearrange the most suitable interventions.

Before starting to implement the cavity sensors (made of optical fibre or other suitably type) are to be installed on the metal armours and on the concrete around the cavity to be realized so as to be able to perform a comparison monitoring of the stress state of the materials before and after implementing the cavity.

Hereinafter the main types of cavity are listed, depending upon the size of the pillar, the face of the same (long side or short side) whereon it is more appropriate to intervene, the related pre-reinforcements, and depending upon the state shown by the different buildings made of reinforced concrete to be subjected to the intervention and the connected central armours to be allocated. Existing structures made of reinforced concrete under very precarious conditions

Existing structures made of reinforced concrete under not precarious conditions The cavities to be implemented and the subsequent continuous logging, or hydrodemolition, or other suitable technique, should be proportioned to the different types of central armour which will be allocated therein: metal tube, or made of other material, solid or pre-drilled tube, metal cage, or made of other material, with continuous bracketing or coil, tubular combination plus cage or solid iron (or other material) armour, solid iron (or other material).

It is to be specified that, to the advantage of a minimum invasiveness, the cavity which should start about 40-50 cm as from the beam-pillar attachment, will have a maximum height of about 80 centimetres to be able to house the specific equipment apt to perform the continuous logging, or hydrodemolition, or other suitable technique; the total armour will be obtained by connecting (by screwing, welding or other) the several tracts therebetween. The base tract, the lower one to be inserted into the foundation beam, should have a size so as to be placed at about 10 cm from the lower face of the foundation and at about 20 centimetres from the upper one so as to obtain the attachment point of the first two tracts of the reinforcement armour in a less stressed area. Whenever necessary, such procedures for opening the cavities will be repeated even at the upper planes (such as for example in case of height offset of the pillars' section).

Preliminary Activities

In order to obtain a sufficient knowledge of the real state shown by the building to be subjected to antiseismic reinforcement and consolidation, before performing any intervention on the pillars of the existing buildings made of reinforced concrete it is necessary to perform the technical anamnesis, a series of preliminary activities to be implemented in order subsequently to prearrange and perform the most suitable interventions. Documental survey, relating to the acquisition of design printouts (drawings, calculations, checks, variants, tests, etc.)

Structural and instrument survey: it has to be performed both on the structure and on the site. Sclerometric, pacometric, and/or georadar examination, assays for local checks (thickness of foundations, thickness of concrete cover, etc.), checks of discharges in foundation of each pillar, installation of sensors (made of optical fibre or other suitable type) before and after opening the cavity for the comparison of the stress states, possible structural and bearing static checks, adequate surveys and in situ checks, etc.

Intervention design which will strictly depend upon the results of the two preceding steps and upon the real state shown by the building.

Hereinafter figures figures 1 a, 1 b and 1c are shown illustrating the pillars' areas which are most stressed and prone to ruptures and the right position of the cavity with respect to the stresses.

Figure 1a: Indication of the most stressed areas, at the "top" and at the "bottom", of the pillar.

Figure 1 b: Rupture of the most stressed areas, at the "top" and at the "bottom", of the pillar after the earthquake.

Figure 1c: Position of the cavity with respect to the most stressed areas, designated by the "butterfly- 1 ike" chart typical of the seismic stresses. Description Of The Intervention Cases ) Existing structures made of reinforced concrete under very precarious conditions

In such cases it is necessary to perform preliminarily as stated below: · Applying specific metal bandage, or made of other suitable material, with adequate thickness, all around the pillar whereon one has to intervene, starting from the floor level and up to a slightly greater height (about 10 cm) at the top of the cavity which should be realized. Said bandage, contoured according to the pillar geometry, should be perforated exactly corresponding to the cavity to be implemented. Figure 2 Obviously, the positioning of said sheet will request a suitable opening on the closing walls on the sides of the pillar.

• Together with the preceding bandage, or autonomously, the following pre- reinforcement system can be applied (before performing the opening of the cavity): on the opposite sides of the pillar, below and above the area wherein the cavity will be implemented, on the sides of the pillar, two or more pairs of brackets will be placed (relating to patent Nr. 0001408440 of 15.12.201 1 called "resistant cut plug") which will have the purpose, through the interposition of suitable jacks, placed between the lower bracket and the upper one of each pair, to mitigate or even cancelling the vertical load in the area of the cavity to be realized. This, once implemented the cavity, inserted the reinforcement central armour system and re-closed the cavity itself and removed the pairs of brackets, with the purpose of facilitating that the acting vertical load could be re-distributed correctly by involving even the area of the cavity Figure 2b.

• In order to solidify the bandage to the pillar some through-holes will be made at several heights which will connect the opposite sides to the opening one of the cavity through suitable threaded rods, or other material, connected and tightened by means of metal plate and nuts. With such pre- reinforcement activity a consolidation of the whole bandaged portion is obtained. Figure 2a.

Figure 2: Bandage with metal sheet, or other suitable material, and connection of the opposite faces with threaded rods and nut and safety washers (Figure 2a)

Possible additional pre-reinforcement to the beam-pillar attachment by means of "x-like seam" between the basal portion of the pillar and the lower beam, to be performed with previous continuous logging with suitable diameter and insertion of metal armour (threaded rod, harmonic cable, or other material) suitably fastened for a better beam-pillar solidification. Figure 3. Figure 3: "X"-like seams in the pillar with the beams.

The opening of the cavity could take place as described hereinafter. Starting from one of the two vertical edges of the bandage perforation one proceeds in a direction tilted towards the central portion of the cavity to be implemented. Then, one changes side and proceeds in the same way until implementing a triangular wedge made of concrete. At last, one proceeds with the horizontal cuts at the two ends of the short sides of the perforation and then the wedge made of concrete is extracted.

One proceeds with cutting by suitably varying the tilting on the two long sides and by performing the due horizontal cuts on the short sides of the cavity to be realized.

Once finished the cavity a pre-reinforcement is inserted inside thereof, made of perforated metal sheet, contoured metal grid, or other material, of adequate thickness on each inner face except the base one (whereon logging will be performed), in order to ease, by pouring adequate filling mortar, even coloured mortar for the subsequent checks, of the cavity, the best connecting adhesion between the pre-existing portion and the new one. Figure 4

• The specific equipment is inserted to perform the continuous logging, or hydrodemolition, or other suitable technique, at the base of the cavity.

Figure 5

• The logging, or hydrodemolition, or other suitable technique was performed. Figure 6

• The central armour is inserted. Figure 7a, 7b, 7c · Previously cut iron bars of armours (stirrups or vertical bars) are put back in order to allow housing the core barrel or other suitable equipment. Figure 8

• The filling casting with adequate, even pigmented (coloured), mortar is performed. Figure 9

2) Existing structures made of reinforced concrete under not precarious conditions

In these cases the activities of external pre-reinforcing of the pillar by means of the above-described bandage are not performed, whereas the cavity inside the pillar and the pre-reinforcement therein on each inner face except the base one (whereon the logging will be performed) are implemented.

Installation Of Sensors For Monitoring the Stress State

The installation of fibre optic sensors for monitoring the pillars is characterized as preventive moment in handling the structure quality in time as it provides immediate information about safety and conditions of the examined structure, that is it allows a long-term monitoring of the effectiveness and safety thereof. The "self-diagnosis" of the structure in real time is thus obtained.

Description of the method for implementing the cavities In order to interfere and alter the pre-existing state as less as possible it is appropriate using adequate tools, such as hydrojet, diamond wire, circular saw or other to implement the cuts according to a scheme described hereinafter. Once established the sizes of the cavity, in depth and width (preferably air gap, in order to avoid the cut of longitudinal iron bars), the contour of the cavity to be implemented is marked on the face of the pillar. The saw is then positioned at one of the side edges and the blade is directed vertically and one cuts towards half of the face opposite to the front one; the procedure is repeated on the opposite side edge. Then, the horizontal cut at the top and at the base of the cavity for whole width is performed; the triangular wedge is thus extracted. Then, one proceeds with cutting vertically in depth along the two side edges. Then the blade is oriented vertically starting from one of the outer edges and the blade is oriented towards the opposite angle on the inner face; the cut wedge is then extracted. The procedure is then repeated on the opposite edge (see figure). Thus, only two small triangular wedges remain attached only on the inner face of the cavity which will then be removed with additional analogous subsequent cuts.

Among all above-listed techniques for creating the cavity it is considered to be appropriate to prefer, whenever possible, the hydrojet for the hydrodemolition as it allows a series of advantages: · possibility of demolishing portions made of reinforced concrete without damaging armours (in particular at the structural nodes) absence of microfractures/micro cracks removal with result of a selective demolition absence of powders and vibrations action without damages to the armour iron bars and total cleaning thereof

• the surface which is obtained results to be wrinkled and very clamping for laying the new concrete lower noise than the traditional methods

Description Of The Intervention Types

First of all it is stated in advance as follows: · upon selecting the pillars' faces whereon the described cavities are to be implemented, whenever possible, the long side will be preferred as in this way, almost surely the cut of vertical armour iron bars will be avoided and only some horizontal stirrups will be cut so as to create the access to specific equipment; · if this is not possible, one will work on the short side and some vertical iron bar, as well as some horizontal stirrups, could be cut;

• however, it is clarified that, once implemented the cavity, inserted the pre- reinforcement inside thereof, performed the continuous logging, or hydrodemolition, or other suitable technique, at its base and inserted the suitable central armour, one will provide, before casting concrete, for restoring, with suitable welding, the previously cut armour tracts.

• whenever possible, one will prefer to perform the interventions of implementing the antiseismic reinforcement and consolidation only on each pillar of the outer faces of the building; • one will intervene even on the inner pillars which the preliminary analysis will have detected as most loaded.

The intervention types substantially are the following ones:

Implementation of the cavity preferably on the long side of the pillar, as illustrated in figures 4 to 8.

Figure 1 shows the pillar before the intervention. Figure 2 shows the application of the pre-reinforcement with bandage outside the pillar.

Figure 3 shows the pre-reinforcements by means of "x-like seams" Figure 4 shows the cavity to be implemented.

In subsequent figure 4 the implementation of the pre-reinforcement can be seen (pre-drilled metal sheet, contoured metal grid, or other suitable material) inside the cavity with the cutting of some horizontal stirrups and without cutting of vertical iron bars.

Figure 5 shows the vertical perforation by continuous logging, to be performed at the base of the cavity, for inserting the central antiseismic reinforcement. Figures 7a, 7b and 7c show the allocation of the central antiseismic reinforcement constituted by a cage of vertical armours, in adequate number and diameter, with horizontal stirrup or continuous coil. Figure 7a shows the allocation of the central antiseismic reinforcement constituted by a pre-drilled tube with associated barycentric iron bar, the latter could even be not necessary.

Figure 7b shows a type of central armour different from the previous one as constituted by the lower tract (placed in foundation) of pre-drilled tube whereon the upper tract connects constituted by a cage of stirred-up vertical iron bars with horizontal stirrups or continuous coil. Alternatively a type of central armour different from the previous one can be inserted as it is constituted by the lower tract (placed in foundation) of pre-drilled tube whereon the upper tract connects constituted by one single iron bar.

Figure 7c shows a type of central armour different from the previous one as it is constituted by one single armour with adequate diameter for the whole thickness.

Figure 8 highlights the restoration, by suitable welding, of the previously cut armours.

Figure 9 shows the closure of the cavity by specific casting with suitable mortar. and that the same diversify by activities depending upon the fact that the existing structures made of reinforced concrete are or are not under very precarious conditions.

Description of the Specific Equipment

The possibility of being able to perform the procedures of continuous logging in the implemented cavity is assigned to the use of particular specific equipment formed by a logging machine which, by means of a junction at 90°, a right-angle joint, allows to use the logging machine as unit outside the cavity (main Figure and Figure 5), wherein only the core barrel is positioned, by avoiding in this way to have to create a much larger passage in the pillar to house the perforation equipment, and then being able to engrave much less invasively in the pillar itself, without the need for shearing the vertical armours of the pillar.

Another possibility is that of using the known art of the hydrojet with the purpose of performing a controlled hydrodemolition of manufactured products made of reinforced concrete, by means of water jets at very high pressure, by removing systematically and selectively portions of concrete, without emission of powders, with a uniform final result, intervention speed, in absence of vibrations which avoid damages to the healthy structures and to the armour iron bars, with systematic removal of rust. In particular situations, all interventions can be performed by means of robotized machines.

Claims

1. An antiseismic reinforcement and consolidation process of existing pillars made of reinforced concrete, comprising the following steps:

Installation of suitable sensors all around the cavity to be realized to know the real stress state of materials (armour and concrete) before and after the intervention and for structural and effective monitoring during the time of the implemented system; external pre-reinforcing of the pillar by means of metal bandage or other suitable material, of adequate thickness, all around the pillar whereon one has to intervene, starting from the floor level and up to a slightly greater height (about 10 cm) at the top of the cavity to be realized and solidification bandage to the pillar through suitable threaded rods, or other, connected and tightened by means of metal plate and fixing nuts; opening of a cavity on a longitudinal side of the pillar; · use of specific, even known apparatuses, for opening the cavity (and the related holes thereabove and thereunder); internal pre-reinforcing of the cavity by means of perforated metal bandage, contoured metal grid, or other material, of adequate thickness on each inner face except that of the base or of other suitable material, of adequate thickness; external pre-reinforcing of the cavity by means of a system on the opposite sides of the pillar, below and above the area wherein the cavity will be implemented, at the pillar's sides, constituted by two or more pairs of brackets having the purpose, by interposing adequate jacks, placed between the lower bracket and the upper one of each pair, of mitigating and even cancelling the vertical load in the area of the cavity to be realized; providing specific equipment having a junction (joint) at 90° for performing a continuous logging into the cavity; performing a continuous logging on the base face of the cavity; insertion of antiseismic reinforcement in said logging; · reconstruction by welding of the previously cut portions of longitudinal bars and stirrups to implement said cavity; possible pre-reinforcement to the beam-pillar attachment by means of "X- like seam" between the basal portion of the pillar and the lower beam;

• filling the cavity with even pigmented (coloured) mortar, having suitable features, to allow the subsequent checks.