Method for increasing shear strength of notches of connecting joints of rod elements of structure made of logs or beams

Abstract

FIELD: construction.SUBSTANCE: method for increasing the shear strength of the notch of connecting joints of rod elements of a structure made of logs or beams relates to load-bearing structures made of wood with connections on the end notch. The method consists of connecting two rod elements of the structure by means of a notch at an angle to each other and securing them relative to each other by means of a bolted connection, and then the rod element of the notch, which operates in tension and is located behind the notch, is covered with at least one metal clamp. The flanges of the metal strips of the clamp are spring-loaded relative to each other.EFFECT: increase in the strength and load-bearing capacity of the connection nodes made of logs or beams on the frontal notch.2 cl, 3 dwg

Description

[0001] The invention relates to the field of construction, in particular to load-bearing structures made of wood with joints on a frontal notch.

[0002] A well-known connection node for wooden rods on a frontal notch is one in which a tie bolt is installed for reinforcement (see Industrial Structures Designer's Handbook. Wooden Structures edited by G.F. Kuznetsov, Moscow-Leningrad, Main Editorial Board of Construction Literature, 1937, p. 54).

[0003] The disadvantage of this knot is the low resistance to shearing and crushing of the lower belt across the grain.

[0004] Reinforcement of the joint on the frontal notch is known (see ibid., p. 259). Reinforcement is achieved using a stop, metal ties, and wooden plates attached to the lower chord with bolted dowels.

[0005] The disadvantage of this solution is the weakening of the tension rod element by dowels, as well as the increased complexity of installing this type of connection on the frontal notch.

[0006] The closest to the invention in technical essence and the achieved result is a method for increasing the shear strength of the notch of connecting joints of rod elements of a structure made of logs or beams, which consists in connecting two rod elements of the structure by means of a notch at an angle to each other and fixing them relative to each other by means of a bolted connection (see the book by V.I. Linkov, Structures of Wood and Plastics (course notes), Moscow, Moscow State University of Civil Engineering, 1997, pp. 31-33).

[0007] The disadvantage of this unit, as well as the above-mentioned analogs, is the low strength to shearing and crushing of the rod element working in tension.

[0008] Furthermore, the disadvantages of the above-mentioned known technical solutions include the fragility of the support unit due to changes in the moisture content of the wood, hence the formation of cracks and a decrease in the load-bearing capacity of the dowel connection; the difficulty of operating a truss assembled from timber rod elements connected in the manner described above due to uneven tension by means of tie bolts during long-term operation, since there is a high probability of the rod element working in tension leaving both the vertical and horizontal planes, and also the lack of design solutions that take into account the change in the linear dimensions of the wood with changes in the temperature and humidity conditions of the external environment.

[0009] The technical problem that the present invention aims to solve is to overcome the above-identified disadvantages.

[0010] The technical result that the present invention is aimed at achieving is that it is possible to increase the strength (load-bearing capacity) and thereby extend the service life of the connecting nodes of rod structures on notches made of logs or beams and, as a consequence, of buildings and structures as a whole.

[0011] The said technical problem is solved and the technical result is achieved due to the fact that the method for increasing the shear strength of the notch of connecting units of rod elements of a structure made of logs or beams consists in connecting two rod elements of the structure by means of a notch at an angle to each other and fixing them relative to each other by means of a bolted connection (tie bolt), and then the rod element of the notch, working in tension, on the length of the shearing area located behind the notch, is covered by at least one clamp made of metal strips with flanges at their ends, and when forming each clamp on the above-mentioned rod element of the notch, a gap is left between the flanges of the metal strips forming the clamp, and the flanges of the metal strips located opposite each other are pulled together by means of a bolted connection,and between the head of the bolt and one of the nearest flanges or between the nut and one of the nearest flanges coaxially with the rod of the bolted connection, a spring is installed, by means of which the flanges of the metal strips that form parts of the clamp, pulled together, are spring-loaded relative to each other.

[0012] It is preferable to pre-determine the moisture content of the log or beam, as well as the transverse dimensions of the log or beam at a maximum moisture content of 30% and at zero moisture content, and, based on this, calculate the maximum compression force between the parts of the clamp made of metal strips with flanges.

[0013] The conducted research has established that when connecting two rod elements of a structure by means of a notch at an angle to each other and fixing them relative to each other by means of a bolted connection (tie bolt), the change in the linear dimensions of the wood due to changes in the temperature and humidity conditions of the external environment during the operation of the assembled structure made of wooden rod elements using their connection by means of a frontal notch is not taken into account (see, for example, the Code of Practice SP 64.13330.2011, Wooden Structures, updated version of SNiP II-25-80, Moscow, 2011). At the same time, the current method for calculating the frontal notch takes into account only the friction of the elements of the wooden structure under the condition of constant pressing of the elements of the structure in the absence of a dynamic load (see SP 64.13330.2011 p.43 Item 8.4) or if friction worsens the operating conditions of the structure and connections and compression and crushing over the entire area across the grain and local crushing across the grain are taken into account (see SP 64.13330.2011, p. 4, table 3).

[0014] The proposed method for increasing the shear strength of the notch joints of structural rod elements made of logs or beams eliminates this drawback by strengthening the end notch at the most sensitive point of the rod element connection. Specifically, in the area beyond the notch along the shearing area, this tensile rod element is reinforced by installing at least one clamp made of metal strips at this section of the tensile rod element. Importantly, the change in the transverse dimensions of this rod element during operation is taken into account, both in terms of an increase in its dimensions due to swelling of the rod element under conditions of high humidity, and a decrease in the cross-section of the rod element during wood shrinkage.The production of a clamp from several metal strips with flanges at their ends and the connection of these metal strips to each other by means of a bolted connection with spring loading at the place where the metal strips are connected to each other allows for increasing the strength of this rod element at the weakest point of the connection of the rod elements using the frontal notch method.

[0015] In this case, it is possible to take into account the average statistical data on weather conditions to determine the magnitude of the clamping force of the rod element or to use known literary information on the change in the transverse dimensions of specific types of wood depending on the humidity, taking into account the requirements for the humidity of the wood supplied for construction.

[0016] Thus, the stated technical result has been achieved - increased strength (load-bearing capacity), as well as an extension of the service life of the connecting nodes of rod structures on notches made of logs or beams and, as a result, of buildings and structures as a whole.

[0017] Fig. 1 shows a general view of the notch of connecting nodes of rod elements of a structure made of logs or beams.

[0018] Fig. 2 schematically shows a cross-section of a rod element made from a round log in cross-section with a clamp installed on it.

[0019] Figure 3 schematically shows a cross-section of a rod element made from a beam with a rectangular cross-section and a clamp installed on it.

[0020] A connecting unit using a frontal notch of rod elements of a structure made of logs or beams consists of two rod elements connected by notches at an angle to each other, namely, rod element 1 working in compression and forming the upper chord and rod element 2 working in tension, forming the lower chord. Rod element 1 is inserted into a notch 3 in rod element 2. Rod elements 1 and 2 are tightened together by means of a tie bolt (also known as an emergency bolt). On rod element 2 behind the notch 3 along the length of the shearing platform ск at least one, and preferably two clamps 5 are installed. Each clamp 5 is made of several metal strips 6 with flanges 7, which are pulled together by means of a bolted connection. In this case, the bolted connection is made spring-loaded, for which a spring 10 is installed between the head of the bolt 9 and one of the flanges 7 closest to it, or the latter can be installed between the nut 11 of the bolted connection and the flange 7 of the clamp 5 closest to it. The bolted connections are preferably made using washers 12, which are installed under the head of the bolt 9, under the nut 11, and also between the end of the spring 10 and the flange 7 closest to it.

[0021] The method for increasing the shear strength of the notch of connecting nodes of rod elements of a structure made of logs or beams is implemented as follows.

[0022] Two rod elements 1 and 2 of the structure are connected by means of a notch at an angle to each other and fixed relative to each other by means of a bolted connection using a tie bolt.

[0023] Tensile rod element 2 notches on the length located behind the notch ск the shearing areas are covered by at least one clamp 5 made of metal strips 6 with flanges 7 at their ends.

[0024] When forming each clamp 5 on the above-mentioned rod element 2, the notches between the flanges 7 of the metal strips 6 forming the clamp 5 leave a gap, and the flanges 7 of the metal strips 6 located opposite each other are pulled together by means of a bolted connection.

[0025] Between the head of the bolt 9 and the flange 7 closest to it, or between the nut 11 and the flange 7 closest to it, a spring 10 is installed coaxially with the rod of the bolt 9 of the bolted connection, by means of which the flanges 7 of the metal strips 6, which form parts of the clamp 5, pulled together, are spring-loaded relative to each other.

[0026] The moisture content of the logs or beams from which the rod elements 1 and 2 are made, as well as the transverse dimensions of these logs or beams at a maximum moisture content of 30% and at zero moisture content, are pre-determined.

[0027] To do this, we determine the actual dimensions of the section, for example, the log from which rod elements 1 and 2 are made, for which we use design documentation or the results of in-kind surveys - wood moisture (W ф ) and the diameter of the end of the log of the lower chord (D ф ) we determine the area (F ф ) and the circumference (L ф ).

[0028] Sets the cross-sectional dimensions at minimum wood moisture content:

[0029] - shrinkage coefficient γ w0% , i.e. the conversion factor from area F ф to area F w0%.

[0030] γ w0% ⋅ (W ф – W w0% ) / 100), (1)

[0031] where ( W ф – W wo% ) – shrinkage percentage;

[0032] - log area

[0033] F w9% = F Ф .⋅ γ w0% , (2)

[0034] where F Ф – actual area of ​​the log at moisture content W ф ;

[0035] - log diameter

[0036] D ус. = , (3)

[0037] - circumference

[0038] L w0% = π ⋅ D w0% , (4)

[0039] Determine the cross-sectional dimensions at maximum wood moisture content:

[0040] - swelling coefficient γ w30% , i.e. the area conversion coefficient) F ф to area F w30%

[0041] γ w30% = (W30% – W ф ) / 100 ) , (5)

[0042] where (W 30% – W ф ) – percentage of swelling;

[0043] - log area

[0044] F w30% = F Ф . ⋅ γ w30% , (6)

[0045] - log diameter

[0046] D w30% = , (7)

[0047] - circumference

[0048] L w30%б. = π ⋅ D w30% . (8)

[0049] Gap between flanges 7 of metal strips 6 of clamp 5 (Fig. 2 and 3)

[0050] δ = 0.5 ⋅ (L w30% – L w0% ). (9)

[0051] And then the compression forces of the log with clamp 5 are determined

[0052] We set the width of the metal strip 6 from which the clamp 5 is made – b хом . ).

[0053] Force per unit of circumference

[0054] q = b хом. G с90 , (10)

[0055] where G с90 ≤ R с90= 3 MPa – calculated compressive strength across the grain (SP 64.13330.2011, p. 4, table 3, item 3),

[0056] Based on this, the maximum compression force between the parts of each clamp 5 made of metal strips 6 with flanges 7 is calculated, namely, we determine:

[0057] Tensile force of clamp 5 at maximum humidity W 30%

[0058] R хw30% = 0.25 ⋅ L хw30%. ⋅ q, (11)

[0059] Compression force by bolted connection

[0060] R болт.30% = 0.5 R хом.30% = 0.125 L w30% ⋅ q, (12)

[0061] Tensile force of clamp 5 and bolts 9 at minimum wood moisture content W w0%

[0062]

[0063] where ɣ w0% = (0.65-0.75) reduction factor, assigned during design.

[0064] After this, the bearing capacity of the frontal notch is determined taking into account the friction forces.

[0065] Using a calibration wrench, tighten the nuts 11 of the bolted connection of the parts of the clamp 5 to a force corresponding to the actual moisture content of the wood (W факт. ) according to the formula

[0066] R ФАКТ = R W0% + ∆Р / 30, (15)

[0067] where R W0% – tensile force of the clamp at zero wood moisture content 0%;

[0068] ∆P = (P w30 % - R W факт.% ) – the difference in the tensile forces of the clamp at wood moisture content of 30% and 0%.

[0069] And then determine the full bearing capacity of the frontal notch for shearing:

[0070] T = T ск. + T тр. , (16)

[0071] where: T ск – the shear force is determined according to SP 64.13330.2011, p. 23, pp. 7.2 and 7.3, formulas (58) and (59);

[0072] – friction force at zero wood moisture content,

[0073] Where n is the number of clamps, f = 0.2 is the coefficient of friction of wood on wood of the side surfaces (SP 64.13330.2011, p. 43, clause 8.4 a);

[0074] Rхw0% – the compressive force of the ends of the log of the lower chord of the frontal notch at zero wood moisture content.

[0075] As a result, it is possible to increase the strength (load-bearing capacity), and thereby extend the service life of the connecting nodes of rod structures on notches made of logs or beams and, as a consequence, of buildings and structures in general.

Claims

1. A method for increasing the shear strength of the notch of connecting assemblies of rod elements of a structure made of logs or beams, which consists in connecting two rod elements of the structure by means of a notch at an angle to each other and fixing them relative to each other by means of a bolted connection, characterized in that the rod element of the notch, working in tension, on the length of the shearing area located behind the notch, is covered by at least one clamp made of metal strips with flanges at their ends, and when forming each clamp on the above-mentioned rod element of the notch, a gap is left between the flanges of the metal strips forming the clamp, and the flanges of the metal strips located opposite each other are pulled together by means of a bolted connection, and a spring is installed between the head of the bolt and one of the flanges or between the nut and one of the flanges coaxially with the rod of the bolted connection,by means of which the flanges of the metal strips, which form parts of the clamp, are pulled together, spring relative to each other.

2. The method according to paragraph 1, characterized in that the moisture content of the log or beam is preliminarily established, as well as the transverse dimensions of the log or beam at a maximum moisture content of 30% and at zero moisture content, and, based on this, the maximum compression force between the parts of each clamp made of metal strips with flanges is calculated.

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