Method for verifying the horizontal metallic continuity of the reinforcing bars of structures made of reinforced concrete

Abstract

A method for verifying the horizontal metallic continuity of the reinforcing bars for reinforced concrete that are comprised in a building (1) comprises the following steps: measuring inductance by an inductometer (5) connected to upper ends of vertical elements (2) made of reinforced concrete of said building (1) at a roof or terrace (4) of said building (1), so as to obtain a measured inductance value; calculating an inductance value in a rectangular electrical circuit (6; 7) consisting of reinforcing bars, said reinforcing bars being comprised in a pair of said vertical elements (2) and in at least one horizontal element (3) made of reinforced concrete of said building (1), and of said inductometer (5) connected to said upper ends of said vertical elements (2 ), so as to obtain a calculated inductance value; comparing said measured inductance value with said calculated inductance value. The horizontal metallic continuity is verified when said measured inductance value is in agreement with said calculated inductance value; or the horizontal metallic continuity is not verified when said measured inductance value is not in agreement with said calculated inductance value.

Description

Method for verifying the horizontal metallic continuity of the reinforcing bars of structures made of reinforced concrete

[0001] The invention relates to a method for verifying the metallic continuity, in particular the horizontal metallic continuity, in reinforced concrete or prefabricated structures of buildings.

[0002] In order to verify the efficacy of a protection system from direct lightning (Lightning Protection System, LPS) installed in a building it is necessary to verify the metallic continuity, and thus the electrical connection continuity, of the reinforced concrete or prefabricated structures of the building. The known method for verifying the aforesaid metallic continuity provides for taking instrumental measurements of electrical resistance.

[0003] A drawback of the method for verifying the metallic continuity based on the measurement of the electrical resistance consists of the fact that measuring this parameter makes it significantly difficult to verify, in addition to the vertical continuity, also the horizontal continuity and subsequently the corresponding equipotentiality, given the complexity of the electrical circuits constituted by the reinforced concrete or prefabricated structures. This is particularly important in the case of buildings of a great height for which protection from lightnings is very important.

[0004] It should be noted that, in addition to the verification of vertical metallic continuity of the actual ground electrodes (metal bodies that are in contact with the ground directly or via concrete and are usually used for purposes that are different from earthing electrical systems), which verification enables the pillars conductive towards the ground (actual ground electrodes) to be distinguished from the pillars that are isolated from the ground, the verification of horizontal metallic continuity conducted in a zone near the last floor of a building enables it to be assessed whether equipotentiality exists at a given height between the reinforcing bars of the pillars.

[0005] In fact, if the actual ground electrodes constituted by the reinforcing bars are in metallic continuity (and thus in a galvanic electrical connection) at a given height, they will also be able to make all the conductive part equipotential at the aforesaid height of the building. The “atmospheric discharge” event, given the high currents and voltages involved, is harbinger of high gradients of voltage along the ground drainage path of the currents, so that the “equipotentialization” (minimization of the potential differences due to the lightning current) of the down conductors (electrical connections between the devices collecting thelightning current and the building’s earthing system) is recognized as a beneficial measure also by current regulations (see in in particular the CEI EN 62305-1, 2, 3, 4 rules).

[0006] In the light of what has been highlighted above, the need is clear to be able to verify the horizontal metallic continuity of the reinforcing bars for reinforced concrete easily and efficiently.

[0007] Objects of the invention

[0008] An object of the invention is to improve known methods for verifying the metallic continuity of the reinforced concrete or prefabricated structures of buildings.

[0009] Another object is to provide a method for verifying the horizontal metallic continuity of reinforced concrete or prefabricated structures of buildings easily and effectively.

[0010] Short description of the invention

[0011] According to the invention, a method is provided for verifying the horizontal metallic continuity of the reinforcing bars for reinforced concrete that are comprised in a building, as defined in claim 1.

[0012] Owing to the invention, a method is provided that enables a prior-art drawback to be overcome, namely the substantial unsuitability of electric resistance measurements for the purpose of evaluating correctly the horizontal metallic continuity in reinforced concrete or prefabricated structures of buildings.

[0013] The method according to the invention provides for carrying out an instrumental measurement of inductance of an electrical circuit consisting of actual ground electrodes, which ground electrodes consist of the reinforcing bars of the reinforced concrete structures of a building, in order to verify the horizontal metallic continuity (and thus the continuity of the galvanic electrical connection) of the aforesaid circuit. The reinforced concrete structures of the building include both the vertical pillars, and the horizontal floors and the corresponding beams.

[0014] Once carried out the instrumental measurement, the latter is validated by carrying out a calculation of the inductance of the aforesaid electrical circuit, by using an analytical formula (known from the scientific literature) that is applicable to rectangular electrical circuits of finite dimensions. The Inventors found that, owing to the material nature and geometry of the actual ground electrodes, the aforesaid analytical formula is suitable for being used for the purposes of the method according to the invention.

[0015] The validation of the instrumental measurement is based on the comparison between the measured inductance value and the calculated inductance value and on the outcomes of the aforesaid comparison. When the measured inductance value is in agreement with the calculated inductance value, the horizontal metallic continuity is verified. When, on the other hand, the measured inductance value is not in agreement with the calculated inductance value, the horizontal metallic continuity is not verified.

[0016] From the point of view of the safety and efficacy of the lightning protection systems (LPS), a significant advantage of the method according to the invention consists of the possibility of evaluating the horizontal metallic continuity of the actual ground electrodes constituted by the reinforced concrete or prefabricated structures by an instrumental measurement and of validating the instrumental measurement by a theoretical formula, based on the geometry of the aforesaid structures. This makes the method according to the invention significantly reliable, since the instrumental measurement can be validated by the calculation, and enables the use thereof in the design and manufacturing step of an LPS.

[0017] From the economic point of view, another significant advantage of the method according to the invention consists of the fact that verifying the equipotentiality of the ground electrodes at the greatest heights of a building may enable the development and / or the complexity - and thus the cost - of the lightning collection devices at the top of the building to be reduced, as well as the installation of additional devices along the vertical extent of the building to be reduced or avoided: this is especially useful in the case of particularly high buildings. Therefore, the method according to the invention can be used effectively in the sizing of lightning protection systems of buildings.

[0018] Short description of the drawings

[0019] The invention can be better understood and implemented with reference to the enclosed drawings that illustrate an embodiment thereof by way of non-limiting example, in which:

[0020] Figure 1 is a flow chart illustrating the steps of the method according to the invention.

[0021] Figure 2 is a prospective schematic drawing, showing a building in which the method according to the invention is applied.

[0022] Figure 3 is a prospective schematic drawing showing a rectangular electrical circuit comprising the reinforcing bars of pillars and beams of the building of Figure 2.

[0023] Figure 4 is a prospective schematic drawing showing a rectangular electrical circuit comprising the reinforcing bars of pillars and foundation plinths of the building of Figure 2.

[0024] Detailed description of the invention

[0025] Figure 2 shows schematically a building 1, comprising a plurality of vertical elements 2 made of reinforced concrete and horizontal elements 3 made of reinforced concrete, inside which the reinforcing bars (which are not shown) are contained. The vertical elements 2 comprise pillars 2a and the horizontal elements 3 comprise beams 3a, foundation plinths 3b and floors 3c. A roof or terrace 4 is positioned at the top of the building 1.

[0026] An operator positioned on the roof or terrace 4 can use an instrument of known type, in particular an LCR multimeter or inductometer (shown schematically by the symbol of an alternating current generator) 5, for measuring the inductance of a rectangular electrical circuit consisting of the reinforcing bars comprised in the vertical elements 2 and in the horizontal elements 3 of the building 1. Alternatively to the inductometer, the operator can use an LCR bridge.

[0027] By way of example, Figure 3 shows a rectangular circuit 6 (represented by a dashed line) comprising portions of a pair of pillars 2a, a beam 3a that is interposed between the pillars 2a and the inductometer 5 connected to the upper ends of the pillars 2a at the roof or terrace 4.

[0028] Again by way of example, Figure 4 shows a rectangular circuit 7 (represented by a dashed line) comprising a pair of pillars 2a (over the entire length thereof), a plurality of foundation plinths 3b and the inductometer 5 connected to the upper ends of the pillars 2a at roof or terrace 4.

[0029] It should be noted that the circuit 6 of Figure 3 is hypothetical and represents the (more favourable) case of horizontal electrical continuity of the floor 3c (namely of the beams 3a) below the roof or terrace 4. The circuit 7 of Figure 4 is also hypothetical and represents the (less favourable) case of horizontal electrical continuity of only the foundation plinths and the ground. On the basis of the inductance calculation formulas set out below, the calculated inductance will be minimal if the actual metallic continuity - and thus the electrical connection continuity - of the reinforced concrete or prefabricated structures of the building is appropriately described by the hypothetical circuit 6 of Figure 3 (horizontal electrical continuity of the floor 3c below the terrace 4). Vice versa, the calculated inductance will be maximum if the actual metallic continuity - and thus the electrical connection continuity - of the reinforced concrete or prefabricated structures of the building isappropriately described by the hypothetical circuit 7 of Figure 4 (electrical continuity of only the foundation plinths 3b and the ground). A measured inductance value that is intermediate between the minimum value and the maximum value calculated respectively on the basis of the hypothetical circuit 6 di Figure 3 and the hypothetical circuit 7 of Figure 4 will suggest that the actual metallic continuity - and thus the electrical connection continuity - of the reinforced concrete or prefabricated structures of the building is obtained at the floor facing the ground.

[0030] The inductance measurement carried out through the inductometer 5 provides a measured inductance value, which can be compared with the calculated inductance value on the basis of the hypothetical circuit 6 of Figure 3, of the hypothetical circuit 7 of Figure 4, or of other electrical circuits that are hypothesizable on the basis of the different possible configurations of metallic continuity of the reinforced concrete or prefabricated structures of the building under examination. The closer the measured inductance value is to the inductance value that is calculated on the basis of a given hypothetical circuit, the better the given hypothetical circuit describes the actual situation of metallic continuity of the reinforced concrete or prefabricated structures of the building under examination.

[0031] The inductance of the electrical circuit consisting of the reinforcing bars is calculated using the following analytical formula:in which:L(l,w,r) is the inductance value (expressed in Henry, [H]) of a rectangular coil; go is the magnetic permeability of the vacuum; w and I are the dimensions of the rectangular coil; r is the radius of the conductor (radius of the reinforcing bar).

[0033] The formula (1), proposed in the literature for calculating the inductance of rectangular electrical circuits of finite dimensions and used in the method according to the invention, is disclosed in: Clayton R. Paul “Inductance: loop and partial” ISBN: 978-0-470- 46188-4 December 2009, Wiley-IEEE Press, 400 Pages.

[0034] By comparing the measured inductance value with the inductance value that is calculated by hypothesising the horizontal metallic continuity at a given vertical position of the reinforced concrete or prefabricated structures of the building under examination (forexample at floor 3c under the roof or terrace 4, as hypothesized in the circuit 6 of Figure 3, or of only the foundation plinths 3b and of the ground, as hypothesized in circuit 7 of Figure 4) two cases can occur: a) the measured inductance value is in agreement with the calculated inductance value; b) the measured inductance value is not in agreement with the calculated inductance value.

[0035] The horizontal metallic continuity is verified when the measured inductance value is in agreement with the calculated inductance value, whereas the horizontal metallic continuity is not verified when the measured inductance value is not in agreement with the calculated inductance value. In particular, the measured inductance value is considered to be in agreement with the calculated inductance value when the difference between the measured inductance value and the calculated inductance value is < 50%.

[0036] The method according to the invention thus comprises the following steps:- measuring the inductance by the inductometer 5 connected to the upper ends of the pillars 2a at the roof or terrace 4 of a building 1 under examination, so as to obtain a measured inductance value;- calculating the inductance value in a rectangular electrical circuit, consisting of reinforcing bars comprised in vertical elements 2 made of reinforced concrete and in horizontal elements 3 made in reinforced concrete of the building 1 and obtained by hypothesizing the horizontal metallic continuity at a given vertical position of the reinforced concrete or prefabricated structures of the building 1 (for example the circuit 6 of Figure 3 or the circuit 7 of Figure 4), so as to obtain a calculated inductance value;- comparing the measured inductance value with the calculated inductance value; wherein- the horizontal metallic continuity hypothesized at a given vertical position of the reinforced concrete or prefabricated structures of the building 1 is verified when the measured inductance value is in agreement with the calculated inductance value; or- the horizontal metallic continuity hypothesized at a given vertical position of the reinforced concrete or prefabricated structures of the building 1 is not verified when the measured inductance value is not in agreement with the calculated inductance value.

[0037] The aforesaid steps of the method are summarized in the flow chart of Figure 1.

[0038] By way of non-limiting example of the invention, in the following Example 1, an example of applying the method according to the invention a reinforced concrete building is described.

[0039] Example 1 - Verification of the horizontal metallic continuity in a building

[0040] The method according to the invention was used for a building made of reinforced concrete, having a height of about 60 m. In a zone near the last floor of the building, the verification of horizontal continuity between the reinforcing bars of pairs of pillars was performed. The reinforcing bars of the pillars extend vertically for about 60 m and form at a certain height with the reinforcing bars in metallic connection (namely the reinforcing bars of the beams) a loop, the inductance of which can be calculated by the analytical formula (1). In particular, a closing of the loop has been hypothesized that is near to or far from the vertical ends of the pillars that are part of the circuit the metallic continuity of which it is intended to verify. The so calculated inductance can be compared with the measured inductance. The values in agreement prove the equipotentiality at a certain height between the bars of the pillars, whereas values that are not in agreement do not enable equipotentiality to be established.

[0041] In the following Table 1 the values are shown that were measured and calculated for near and far closings of four loops, i.e. four pairs of pillars:

[0042] Table 10043] Some applications of the method according to the invention are listed below:- Supporting instrument during LPS design stage, in particular in the case of very high buildings;- Verification of the horizontal continuity of the actual ground electrodes in newly built buildings;- Periodic verification of the horizontal continuity of the actual ground electrodes in buildings that were not built recently, in order to check the suitability and efficacy of LPS in buildings subject to aging of the structures;- Project testing and periodic verification of the functionality of the electrical systems, both in private buildings and above all in public buildings, such as for example hospitals, schools, universities, shopping malls, headquarters of organizations and public administrations.

[0044] From what has been disclosed and exemplified above, it can be stated that the method according to the invention enables the previously indicated objects to be achieved.

Claims

CLAIMS1. Method for verifying the horizontal metallic continuity of the reinforcing bars for reinforced concrete that are comprised in a building (1), said method comprising the following steps:- measuring the inductance by an inductometer (5) that is connected to upper ends of vertical elements (2) made of reinforced concrete of said building (1) at a roof or terrace (4) of said building (1), so as to obtain a measured inductance value;- calculating an inductance value in a rectangular electrical circuit (6; 7) consisting of said reinforcing irons, wherein said reinforcing irons are comprised in a pair of said vertical elements (2) and in at least one horizontal element (3) made of reinforced concrete of said building (1), and by said inductometer (5) connected to said upper ends of said vertical elements (2), so as to obtain a calculated inductance value;- comparing said measured inductance value with said calculated inductance value; wherein- said horizontal metallic continuity is verified when said measured inductance value is in agreement with said calculated inductance value; or- said horizontal metallic continuity is not verified when said measured inductance value is not in agreement with said calculated inductance value.

2. Method according to claim 1, wherein said vertical elements (2) comprise pillars (2a) of said building (1) and said at least one horizontal element (3) comprises beams (3a) or foundation plinths (3b) of said building (1).

3. Method according to claim 1, or 2, wherein said calculating is carried out by using the following formula (1):wherein:L(l,w,r) is the inductance value of a rectangular loop; go is the magnetic permeability of vacuum; w and I are the dimensions of the rectangular loop; r is the radius of the conductor.

4. Method according to claim 3, wherein said dimension w, said dimension I and said radius of the conductor r are expressed in cm.

5. Method according to any one of claims 1 to 4, wherein said measured inductance value is considered to be in agreement with said calculated inductance value when the difference between said measured inductance value and said calculated inductance value is < 50%.

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