DESCRIPTION TECHNICAL FIELD OF THE INVENTION

[001] The present invention relates to an anti-seismic joint for joining concrete quoins. This type of joint is used, in particular, for joining quoins to form walls and vaults of tunnels.

PRIOR ART TECHNIQUE

[002] From the prior art technique it is known to make concrete quoins, in particular those designed to form vaults of tunnels, which normally consist of a block having a trapezoidal section with a curvilinear development. Those quoins are built connecting them one to the other by means of joints whose ends are inserted or are embedded in the body of the respective blocks.

[003] The joints used basically consist of rigid rods or tension rods, preferably made of steel, and the concrete blocks are provided with bushings to accommodate the ends of the tension rods.

[004] Joints of this type are known, for example from the Chinese patent CN 102086677, for the construction of beams and columns for buildings. The anti-seismic resistance is demanded to the elasticity of the material, concrete and steel, which is pre- stressed.

[005] The problem posed by seismic phenomena anyway cannot be correctly solved using normal joints which, being rigid, adapt themselves with difficulty to moderate intensity shocks and do not withstand those of a higher intensity.

[006] Structures of anti-seismic joints studied in Japan are known, for example the joint described in the Japanese patent JP 2009209639, which employs a band of an elastic material to seal the groove between two adjacent concrete blocks so as to prevent water passage. Its purpose is that of forming an anti-seismic reinforcement with a flat inner surface of the joint structure, and thus facilitating the inspection and maintenance of the joint. They are specific solutions having limited anti-seismic capacity.

SUMMARY OF THE INVENTION

[007] The main task of the present invention is that of overcoming the drawbacks of the prior art providing an improved anti-seismic joint for concrete quoins having enhanced anti-seismic characteristics. [008] In view of the foregoing, an object of the present invention is that of devising an anti-seismic joint having enhanced deformability characteristics.

[009] Another object is that of realizing an anti-seismic joint which is easy to install inside the quoin and having the possibility of being able to insert the joint in the formworks currently used.

[0010] Still another object is that of realizing a joint capable of withstanding the loads involved in the best possible way and of ensuring reliability and durability with time.

[0011] The object of the invention is achieved through an anti-seismic joint for joining concrete quoins adapted for the formation of walls and vaults of tunnels as defined in claim 1 .

BRIEF DESCRIPTION OF FIGURES

[0012] Further characteristics and advantages of the present invention will become more apparent from the following description of some particulars, but not exclusive, embodiments disclosed as non-limiting examples with reference to the appended figures, wherein:

- figure 1 is a perspective view of the anti-seismic joint for concrete quoins according to the present invention;

- figure 2 is a front elevation view of the joint of figure 1 ;

- figure 3 is a section along the plane A-A of the joint of figure 2;

- figure 4 is a first embodiment of a component of the joint;

- figure 5 is a second embodiment of a component of the joint;

- figure 6 is a third embodiment of a component of the joint;

- figure 7 is a fourth embodiment of a component of the joint;

- figure 8 shows a different embodiment of the joint according to the present invention;

- figure 9 shows the joint of figure 8 with the component of figure 6:

- figure 10 shows the joint of figure 8 with the component of figure 7;

- figure 1 1 shows the installed joint in normal working conditions with springs preloaded;

- figures 12 and 13 show the installed joint undergoing a medium intensity earthquake;

- figures 14 and 15 show the installed joint undergoing a great intensity earthquake; - figure 16 shows the seats in the quoins adapted to accommodate the joint according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0013] With reference to the aforementioned figures, it has generally been referred as number 1 to an anti-seismic joint for concrete quoins comprising an elastically deformable unit 2 comprised between a closing plate 3 and a movable flange 4, respectively arranged at the opposite ends of the elastically deformable unit 2, comprising a plurality of elastically deformable members 5 arranged in parallel.

[0014] The elastically deformable members 5 advantageously consist of a plurality of springs, preloaded when installing in the quoin, which are more apt at withstanding the heaviness of the involved loads and at ensuring the reliability and durability with time. In fact, the design preload value in the installation phase is of about 30kN, while in the operative phases envisaged the compression value is of about 95kN in the presence of a medium intensity earthquake (hereinafter also referred to as "operative earthquake ODE", acronym of "Operative Design Earthquake') and of about 165kN in the presence of a great intensity earthquake (hereinafter also referred to as "maximum earthquake MCE", acronym of ("Maximum Credible Earthquake').

[0015] In fact, in the design phase it has been observed that an elastomeric joint is not suitable to withstand the great loads involved, in addition to ensuring little certainty regarding durability. Furthermore, it has been seen that it is mechanically disadvantageous to rely on the under bolt head for the load withstanding. Another drawback which would be posed by the use of an elastomeric joint lies in the fact that the quoin would require an accommodating seat of big dimensions in order to make the system work in case of an earthquake, resulting in the weakening of the same quoin.

[0016] In order to give a definition of ODE operative earthquake and of MCE maximum earthquake it has been referred to the following conditions:

ODE Operative Earthquake:

- a seismic event which may occur at least once in the life of the structure;

- structural ruptures do not occur and the water seepage is blocked;

- the use of the structure after the earthquake is ensured;

- prospective seismic displacement in correspondence of the fault 15cm.

MCE Maximum earthquake:

- extremely serious seismic scenario with a long recovery period;

- only structural ruptures are prevented; - the statics of the structure after the earthquake is ensured with the possible formation of not foreseeable localized ruptures;

- prospective seismic displacement in correspondence of the fault 25cm.

[0017] Coaxially and inside each spring there are arranged respective first rods 6 for anchoring the joint to the quoin; the first tension rods 6 are provided with a stem at least partially threaded and are inserted into suitable first holes provided on the closing plate 3, where they are fitted by means of suitable first fastening means 7, such as bolts, so as to pass through the springs 5 and extend beyond the movable flange 4 protruding from respective second holes provided on the same flange 4.

[0018] In the embodiment described in the appended figures for exemplification only, the springs are four in number, but it is obvious that they may be two or more, preferably an even number for the correct balance of the joint.

[0019] According to a first embodiment of the joint, described in figures from 1 to 4, the end of the first tension rods 6 extending beyond the flange 4 can be connected, by suitable second fastening means 9 such as bolts, to an anchoring plate 10 embedded into one of the quoins to be joined.

[0020] In correspondence of the central portion of the movable flange 4 there is connected an internally threaded bushing 1 1 and which extends in the direction of the closing plate 3; a second tension rod 12 which extends beyond the closing plate 3 passing through an opening 14provided at a central portion of the closing plate 3 engages inside the bushing 1 1 by means of a counter-threaded first portion 13.

[0021] The second tension rod 12, essentially consisting of an elongated body according to a longitudinal axis, is therefore arranged at the centre of the elastically deformable unit 2 being between two or more springs 5, one or more for each side provided that they are of an equal number (one each side, two each side etc.) for a correct balance.

[0022] The preload value of the springs 5 is essentially given by the compression provided by the flange 4 put under tension by the second tension rod 12 and by the closing plate 3 against which the springs 5 stop, as shown in figure 1 .

[0023] Advantageously, in order to better deal with the involved loads, there can be provided springs with a different spring constant k or with a different length, as shown in figures 2 and 3. In this case, in order to ensure a correct travel of all the springs, and prevent the longer springs, shown in figures 2 and 3 with the reference sign 5A, from being completely compressed before the shorter ones, referred to as 5B, spacers 8 are provided thereon, suitably dimensioned and internally threaded so as to be capable of engaging the respective threaded portions of the first tension rods 6; the spacers 8 are adapted to interact as a stop with the end of each spring 5B along the respective first tension rod 6 through the threaded coupling, and compensate the different length between the springs 5A and 5B so that all the springs compress completely simultaneously.

[0024] The free end of the second tension rod 12 is provided with a second threaded portion 15 and ends with an enlarged head 16, preferably having a hexagonal section, that allows to be anchored to the other of the two quoins to be joined as shown in figure 1 1 , preferably through the interposition of one or more floating washers 19 having a spherical cap lying on a base 25 provided with a counter-shaped cavity; when the joint is installed inside the quoin, the base 25 stops against a seat wall 24 provided in one of the two quoins. As they are free to swing, the floating washers 19 make it possible to reduce the flexural strains on the second tension rod 12.

[0025] The central portion 20 of the second tension rod 12 has mechanical characteristics of ductility such that they allow an elastic type flexure, when undergoing an ODE type seismic event, or a plastic type flexure with yield when undergoing an MCE type seismic event.

[0026] Advantageously the bushing 1 1 is formed by a hollow cylindrical portion 17 provided at an end of a disc 18; in this case the bushing 1 1 can be connected to the flange 4 by inserting the cylindrical portion 17 in a central opening formed in the flange 4 until the disc 18 stops against the lower surface of the flange 4.

[0027] Compared with the embodiment described in figure 4, constructively and cost effectively more advantageous, the second tension rod can have different embodiments, as shown in figures from 5 to 7.

[0028] For example, in figures 5 and 6 the second tension rod 1 12 has a ductile central portion 120 that allows its flexure under load, to which are connected, from opposite sides, a first stem 1 13 for the engagement with the bushing (not shown) and a second stem 1 15 having an enlarged head 1 16 for anchoring to the quoin, the connection of the first stem 1 13 and of the second stem 1 15 to the central portion 120 can be obtained by screwing or by means of suitable connecting pins 121 , 122.

[0029] In figure 7 there is shown a further embodiment of the second tension rod 212, wherein the ductile central portion is replaced by an articulated joint formed by a pair of forks 220A, 220B rotatably connected one to the other by means of a pin 221 ; in this case the flexure of the central portion occurs through the swinging under load of the two forks. The first stem 213 and the second stem 215 are connected to the respective forks 220A, 220B by means of suitable pins 222, as in the embodiment of figure 6, or through threading as in the embodiment of figure 5.

[0030] According to a further embodiment variant of the joint according to the present invention, shown in figures from 8 to 10, the anchoring of the first tension rods 6 to one of the two quoins to be joined can be achieved by means of suitable threaded bushings 310 embedded in the quoins inside which the first tension rods 6 are screwed.

[0031] As it is apparent from figures 9 and 10, a second tension rod can be equally associated to the elastically deformable unit 2 in accordance with any of the embodiments described in figures 4, 5, 6 or 7.

[0032] The installation of the anti-seismic joint requires the adjacent quoins to be provided with suitable seats 23, 24 adapted to receive, respectively, the elastically deformable unit 2 and the second tension rod 12, as well as the insertion of the anchoring plate 10 or of the threaded bushings 310 embedded in the concrete for fixing the first tension rods 6, as shown in figure 16.

[0033] To install the joint according to the present invention, in one of the adjacent quoins, in particular in the one wherein the seat 24 for the second tension rod 12 is formed, an opening 26 is provided having a suitable form in order to communicate, on one side, with the outside so as to allow the insertion of the anti-seismic joint and, on the other side, with the seat 24. In the embodiments shown for exemplification only in figures from 1 1 to 16 the opening has an essentially triangular section in order to reduce the quoin weakening to a minimum and as well as allow the installation of the joint, which is inserted from below with reference to the above said figures.

[0034] To prevent the possible rupture of the quoin, at least a portion of the surface of the opening 26 is advantageously reinforced with a suitably shaped metal plate 27 and embedded in the quoin.

[0035] Bearing in mind the constraints when installing the joint inside the quoin, because of which it is necessary to design the opening 26 possibly reinforced with the metal plate 27, the anti-seismic joint is installed inside the quoins inclined with respect to the axis orthogonal to the joining line of the same quoins; the inclination will be the most suitable according to specific requirements, generally but not necessarily in the order of 25 °, so as to allow the installation of the joint without weakening the quoin excessively. In fact an installation orthogonal to the joining line of the quoins would require an opening that, in order to be capable of communicating with the outside, should involve the whole longitudinal extension of the quoin, resulting in its excessive weakening. [0036] In figures from 1 1 to 15 there are shown different operating conditions to which the joint can be made undergo according to the present invention, in particular:

- figure 1 1 shows the condition at rest of the joint with preloaded springs in the absence of loads generated by earthquakes;

- figures 12 and 13 show the condition under load in the presence of an ODE earthquake wherein, following a gap of about 10mm and an offset of about 15mm between two adjacent quoins, the elastically deformable unit is compressed by the flange and the floating washer 19 allows a limited swinging to the second tension rod 12, over which the central portion of the second tension rod is elastically deformed by flexing if ductile, or it undergoes a small swinging, if articulated, so as to absorb the energy of the earthquake;

- figures 14 and 15 show the condition under load in the presence of an MCE earthquake wherein, following a gap of about 18.5mm and an offset of 30mm between two adjacent quoins, the elastically deformable unit is compressed by the flange with a greater load with respect to the previous one and the portion of the second tension rod embedded in one of the quoins is plastically deformed by flexing, in case after having reached the maximum swinging width allowed by the floating washer or in the case of articulated tension rod.

[0037] From the foregoing it is therefore apparent that the present invention achieves the expected objects and advantages: in fact it has been envisaged an improved anti- seismic joint for concrete quoins provided with enhanced anti-seismic characteristics.

[0038] In particular, the joint structure made in this way allows a greater protection of the second tension rod 12 from excessive loads which would lead to its rupture, having moved the elastic point from under the enlarged head 16 of the tension rod 12 to the anchoring base of the same, which is constituted by the elastically deformable unit 2. In fact, it is mainly the latter which gives the joint the necessary elasticity to absorb the earthquake effects.

[0039] Furthermore the installation of the joint in the quoin is very simple, making it possible to insert the joint into the formworks currently used, as well as to ensure an optimal resistance to loads generated by earthquakes of the ODE and MCE types with certainty of reliability and durability with time.

[0040] Of course the present invention is susceptible of a great number of applications, modifications or variants without departing from the protection field as defined in the independent claim 1 . [0041] Furthermore the materials and equipment used to realize the present invention, as well as the forms and dimensions of the single components, can be the most suitable depending on the specific requirements.