Calculation of wooden structures. Examples of calculations of wooden structures: Textbook for the discipline “Structures made of wood and plastics; Methodological manual for the design of wooden frame buildings

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1 Federal agency of Education Government agency higher vocational education Ukhta State Technical University Examples of calculations of wooden forest structures engineering structures Tutorial in the discipline "Forest Engineering Structures" Ukhta 008

2 UDC 634* 383 (075) Ch90 Chuprakov, A.M. Examples of calculation of wooden structures of forest engineering structures [Text]: textbook. manual for the discipline “Forest engineering structures” / A.M. Chuprakov. Ukhta: USTU, village: ill. ISBN The textbook is intended for students of the specialty “Forestry Engineering”. The textbook contains examples of the calculation of load-bearing elements and structures made of wood, which consistently outline the application of the basic design provisions to the solution practical problems. At the beginning of each paragraph there are brief information, explaining and justifying the calculation methods used. Toolkit reviewed and approved by the department of “Technologies and Logging Machines”, protocol 14 dated December 7, 007 and proposed for publication. Recommended for publication by the Editorial and Publishing Council of Ukhta State Technical University. Reviewers: V.N. Pantileenko, Ph.D., professor, head. Department of Industrial and Civil Engineering; E.A. Chernyshov, CEO LLC Companies "Northern Forest" Ukhta State Technical University, 008 Chuprakov A.M., 008 ISBN

3 INTRODUCTION This manual has a primarily educational and methodological goal of teaching students to apply the theoretical information presented in the course “Forest Engineering Structures” and the ability to apply SNiP to solve practical problems. The calculation examples in each section are preceded by brief information to explain and justify the calculation methods and design techniques used. This publication is intended as a guide when conducting practical classes during the study of engineering structures made of wood, when performing calculations coursework, as well as when developing the constructive part of diploma projects. Target this manual fill the gap in the calculation of elements of wooden structures, the ability to apply SNiP for the design of wooden structures in connection with the exclusion of the discipline “Fundamentals of Construction” from the curriculum in the specialty “Forestry Engineering”. It is necessary to design wooden structures in strict accordance with SNiPII.5.80 “Wooden structures. Design standards" and SNiPII.6.74 "Loads and impacts. Design standards". At the end of the manual, auxiliary and reference data necessary for structural calculations are provided in the form of appendices. 3

4 CHAPTER 1 CALCULATION OF ELEMENTS OF WOODEN STRUCTURES Wooden structures are calculated based on two limit states: bearing capacity(strength or stability) and by deformation (by deflection). When calculating according to the first limit state, it is necessary to know the design resistance, and according to the second, the modulus of elasticity of the wood. The main calculated resistances of pine and spruce wood in structures protected from moisture and heat are given in. The calculated resistances of wood of other species are obtained by multiplying the main calculated resistances by the transition coefficients given in. Unfavorable operating conditions of structures are taken into account by introducing coefficients for reducing design resistances, the values of which are given in [1, table. 10]. When determining the deformations of structures under normal operating conditions, the modulus of elasticity of wood, regardless of the species of the latter, is taken equal to E = kgf/cm. Under unfavorable operating conditions, correction factors are introduced according to. The moisture content of wood used for the manufacture of wooden structures should be no more than 15% for glued structures, no more than 0% for non-glued structures of industrial, public, residential and warehouse buildings and no more than 5% for livestock buildings, structures on outdoors and inventory structures of temporary buildings and structures. Here and further in the text, numbers in square brackets indicate the serial numbers of the list of references given at the end of the book. 4

5 1. CENTRALLY EXTENSION ELEMENTS Central extension elements are calculated using the formula where N is the design longitudinal force; ** net area of the cross-section under consideration; N R, (1.1) p 5 NT; N T b r o s l b gross cross-sectional area; osl weakening cross-sectional area; R p is the calculated tensile strength of wood along the fibers, Appendix 4. When determining the area of the LT, all weakening located in a section 0 cm long are taken as if combined in one section. Example 1.1. Check the strength of the wooden hanger of the rafters, weakened by two notches h bp = 3.5 cm, side cuts h st = 1 cm and a bolt hole d = 1.6 cm (Fig. 1.1). Calculated tensile force N = 7700 kgf, log diameter D = 16 cm. Solution. Gross cross-sectional area of the rod D 4 = 01 cm. Segment area at cutting depth h bp = 3.5 cm (Appendix 1), 1 = 3.5 cm. Segment area at cutting depth h st = 1 cm = 5.4 cm Since between the weakening by the notches and the weakening of the hole Fig. 1. Tensile element Here and in all subsequent formulas, unless a reservation is made, force factors are expressed in kgf, and geometric characteristics in cm

6 for bolt distance 8 cm< 0 см, то условно считаем эти ослабления совмещенными в одном сечении. Площадь ослабления отверстием для болта осл = d (D h ст) = 1,6 (1,6 1) =,4 см. Площадь сечения стержня нетто за вычетом всех ослаблений нт = бр осл = 01 3,5 5,4,4 = 103 см. Напряжение растяжения по формуле (1.1) кгс/см ЦЕНТРАЛЬНОСЖАТЫЕ ЭЛЕМЕНТЫ Центральносжатые деревянные стержни в расчетном отношении можно разделить на три группы: стержни малой гибкости (λ < 30), стержни средней гибкости (λ = 30 70) и стержни большой гибкости (λ >70). Low-flexibility rods are calculated only for strength using the formula N R. (1.) c High-flexibility rods are calculated only for stability using the HT formula N r a s h R s. (1.3) Rods of medium flexibility with weakening must be calculated for both strength according to formula (1.) and stability according to formula (1.3). The calculated area (calculation) of the rod for calculating stability in the absence of weakening and with weakening that does not extend to its edges (Fig. a), if the area of weakening does not exceed 0.5 br, is taken equal to 6

7 calculated = 6p, where 6p is the gross cross-sectional area; for weakening that does not extend to the edges, if the weakening area exceeds 0.5 6p, the calculation is taken equal to 4/3 NT; with symmetrical weakening extending to the edges (Fig. b), calculation = NT. The longitudinal bending coefficient is determined depending on the calculated flexibility of the element using the formulas: with element flexibility λ 70 1 a 100 ; (1.4) with element flexibility λ > 70 Fig. Weakening of compressed elements: a) not extending to the edge; b) facing edge A, (1.5) where: coefficient a = 0.8 for wood and a = 1 for plywood; coefficient A = 3000 for wood and A = 500 for plywood. The coefficient values calculated using these formulas are given in the Appendix. The flexibility λ of solid rods is determined by the formula l 0, (1.6) where l 0 is the design length of the element. To determine the design length of straight elements loaded with longitudinal forces at the ends, the coefficient μ 0 should be taken equal: with hinged ends, as well as with hinged connections at intermediate points of element 1 (Fig. 3.1); r 7

8 with one hinged and the other pinched ends 0.8 (Fig. 3.); with one pinched and the other free loaded end (Fig. 3.3); with both ends pinched 0.65 (Fig. 3.4). r radius of inertia of the element’s section. Rice. 3 Schemes for fastening the ends of the rods The radius of inertia r in the general case is determined by the formula r J br, (1.7) br where J br and 6p the moment of inertia and the gross cross-sectional area of the element. For a rectangular section with side dimensions b and h r x = 0.9 h; r y = 0.9 b. For a circular cross section (1.7a) r D 0.5 D. (1.7b) 4 8

9 The design flexibility of compressed elements should not exceed the following limit values: for the main compressed elements of the chords, support braces and support posts of trusses, columns 10; for secondary compressed elements, intermediate posts and truss braces, etc. 150; for link elements 00. The selection of sections of centrally compressed flexible rods is carried out in the following order: a) they are set by the flexibility of the rod (for the main elements λ =; for secondary elements λ =) and find the corresponding value of the coefficient; b) determine the required radius of gyration and set a smaller cross-sectional size; c) determine the required area and set the second cross-sectional size; d) check the accepted cross section using formula (1.3). Compressed elements made of logs while maintaining their conicity are calculated using a section in the middle of the length of the rod. The diameter of the log in the design section is determined by the formula D calculated = D 0 +0.008 x, (1.8) where D 0 is the diameter of the log at the thin end; x is the distance from the thin end to the section under consideration. Example 1. Check the strength and stability of a compressed rod weakened in the middle of the length by two holes for bolts d = 16 mm (Fig. 4, a). Rod cross-section b x h = 13 x 18 cm, length l =.5 m, ends are hinged. Design load N = kgf. Solution. Estimated free length of the rod l 0 = l =.5 m. Minimum radius of gyration of the section r = 0.9 b = 0.9 13 = 3.76 cm. 9

10 Fig. 4. Centrally compressed elements The greatest flexibility, 7 6 Therefore, the rod must be designed for both strength and stability. Net area of the rod nt = br osl = .6 13 = 19.4 cm. Compressive stress according to formula (1.) k g / s m. 1 9. 4 10

11 Buckling coefficient according to formula (1.4) 6 6, 6 1 0, 8 0, The weakening area is from the gross area of the slab 1, 8 5% Therefore, calculated area in this case, calculated = br = = 34 cm. Stress when calculating stability according to formula (1.3) to g s / s m R c 0, Example 1.3. Select the cross-section of the wooden block rack (Fig. 4, b) with the following data: design compressive force N = kgf; stand length l = 3.4 m, the ends are hinged. Solution. We set the flexibility of the rack to λ = 80. The coefficient corresponding to this flexibility is = 0.48 (Appendix). Find the required minimum radius of gyration (at λ = 80) l l 1 l cm; 0 0 r tr l, 5 cm 80 and the required cross-sectional area of the rack (at φ = 0.48) tr N cm R 0, c Then the required cross-sectional width of the beam according to formula (1.7a) b tr rtr 4, 5 1 4, 7 cm. 0, 9 0, 9 In accordance with the assortment of lumber, we accept b = 15 cm. The required height of the beam section. eleven

12 h tr tr 7 1 8.1 cm b 15 Take h = 18 cm; = = 70 cm. Flexibility of the rod of the accepted cross-section Stress l, 5 y r 0, m and n; u = 0.5. N k g s / s m 0, Example 1.4. A wooden post with a round cross-section, while maintaining a natural slope, carries the load N = (Fig. 4, c). The ends of the stand are hinged. Determine the diameter of the rack if its height is l = 4 m. Solution. We set the flexibility λ = 80 and find the coefficient corresponding to this flexibility = 0.48 (Appendix). We determine the required radius of gyration and the corresponding cross-section diameter: r tr l 400 r 0 tr 5 cm; D " 0 cm tr 80 0.5 We determine the required area and the corresponding cross-section diameter: hence tr N cm R 0, D "" tr Average required diameter c; tr 4 tr, 9 cm 3.1 4 D tr D " D " 1 9. 4 5 cm. D; 4. 1

13 We take the diameter of the log at the thin end D 0 = 18 cm. Then the diameter in the design section located in the middle of the length of the element is determined by formula (1.8): D = , = 19.6 cm; D 3, 6 30 cm. 4 4 Checking the accepted cross-section, 5 1 9, 6 ; 0, 4 6 ; k g s / s m 0, BENDING ELEMENTS Elements of wooden structures that work in bending (beams) are calculated for strength and deflection. Strength calculations are carried out using the formula M R, (1.9) u W where M is the bending moment from the design load; W HT the net moment of resistance of the section under consideration; R u is the calculated bending resistance of wood. The deflections of bending elements are calculated from the action of standard loads. The deflection values should not exceed the following values: for beams between floors 1 / 50 l; for beams attic floors, purlins and rafters 1 / 00 l; for lathing and flooring 1/150 l, where l is the design span of the beam. The values of bending moments and deflections of beams are calculated using general formulas structural mechanics. For a beam on two supports loaded with a uniformly distributed load, the moment and relative deflection are calculated using the formulas: HT 13

14 ql 8 M; (1.10) f 5 q l l H 3. (1.11) 384EJ The design span is taken equal to the distance between the centers of the beam supports. If the beam support width is preliminary calculations is unknown, then the design span of the beam is taken to be the clear span l 0, increased by 5%, i.e. l = 1.05 l 0. When calculating elements made of solid logs or logs sawn into one, two or four edges, take into account their natural slope (conicity). With a uniformly distributed load, the calculation is carried out along the section in the middle of the span. Example 1.5. Design and calculate the attic floor according to wooden beams, located through B = 1 m from one another. The width of the room (clear span) l 0 = 5 m. Solution. We accept this floor design (Fig. 5, a). Skull bars are nailed to the wooden beams l, resting on the walls of the building, on which are laid rolling boards 3, consisting of a solid plank flooring and four bars hemmed to it (Fig. 5, b). A dry gypsum plaster 4, covered on the inside with bitumen. On top of the board flooring, a vapor barrier 5 is first laid in the form of a cm thick layer of impregnated clay, and then insulation 6 is expanded perlite, vermiculite or other fireproof backfill materials, prepared from local raw materials and having a density (volumetric mass) γ = kg/m 3. Thickness layer of insulation 1 cm. A protective lime-sand crust 7 cm thick is placed on top of the insulation. Calculate loads. We determine the loads per 1 m of flooring (Table 1.1). 14

15 Fig. 5. To the calculation of attic floor beams Table 1.1 Elements and calculation of loads Lime-sand crust, 0, Insulation, 0.1 350 Clay lubricant, 0, Rolling boards (flooring + 50% on bars), 0.5 Dry plaster with bitumen, 0, 5 Payload Total... Standard load, kgf/m g, Load factor 1, 1, 1, 1.1 1.1 1.4 Design load, kgf/m 38.4 50.4 38.4 15.6 17, We do not take into account the own weight of the beams, since the loads from all other floor elements listed in the table were assumed to be distributed over the entire area without excluding the areas occupied by the beams. 15

16 Calculation of floor beams. When placing beams every 1 m, the linear load on the beam is: standard q H = 11 1 = 11 kgf/m; calculated q=65 1=65 kgf/m. Design span of the beam l = 1.05 l 0 = 1.05 5 = 5.5 m. Bending moment according to formula (1.10) M k gf / m. 8 Required moment of resistance of the beam W tr M cm. R and 130 Given the section width b = 10 cm, find h tr 6W tr, 6 cm. b 10 We take a beam with a cross section bxh = 10 x cm with W = 807 cm 3 and J = 8873 cm 4. Relative deflection according to formula (1.11) f l 3 5, Calculation of the shield roll forward. We calculate the panel deck for two loading cases: a) permanent and temporary load; b) assembly centered design load P = 10 kgf. In the first case, we calculate the flooring for a strip 1 m wide. Load per 1 linear line. m of design strip: q H = 11 kgf/m; q = 65 kgf/m. Design span of the flooring a 4 l B b cm. H Here B is the distance between the axes of the beams; b beam section width; and the cross-sectional width of the cranial block.. 16

17 Bending moment M 6 5 0.8 6 4.5 k gf / m. 8 The thickness of the flooring boards is taken equal to δ = 19 mm. The moments of resistance and inertia of the design strip of the flooring are equal to: W Bending stress J, cm; , cm, k g s / s m. 6 0, Relative deflection fl 3 5, Significant reserves of strength and rigidity of the flooring make it possible to use grade III semi-edged boards for its production. When the thickness of the flooring is reduced to 16 mm, its deflection will be more than the maximum. If there are distribution bars hemmed from below, the concentrated load is assumed to be distributed over a deck width of 0.5 m. We consider the load to be applied in the middle of the deck span. Bending moment M Pl H k g s / s m. 4 4 Moment of resistance of the design strip. W 5 0 1.1 cm. 6 17

18 Bending stress, g s / s m, 3 0.1 where 1 is a coefficient taking into account the short duration of action installation load. 4. TENSION-BENDING AND COMPRESSION-BENDING ELEMENTS Tension-bending and compression-bending elements are subject to the simultaneous action of axial forces and a bending moment resulting from transverse bending of the rod or eccentric application of longitudinal forces. Tensile bending rods are calculated using the formula N M R p R. (1.1) p W R H T H T and Compression bending rods in the bending plane are calculated using the formula N M R c R W R H T H T u c, (1.13) where the coefficient taking into account the additional moment from the longitudinal force during deformation of the rod, determined by the formula 1 N 3100 R with br. Compressed bending rods with lower cross-sectional rigidity in the plane perpendicular to the bending must be checked in this plane for general stability without taking into account the bending moment according to formula (1.3). 18

19 Example 1.6. Check the strength of a beam with a cross section of 13 x 18 cm (Fig. 6), stretched by a force N = kgf and bent by a concentrated load P = 380 kgf, applied in the middle of the span l = 3 m. The cross section of the rod in this place is weakened by two holes for bolts d = 16 mm. Rice. 6. Tensile bending element Solution. Maximum bending moment M Pl k g s / m. 4 4 Net cross-sectional area nt = b (h d) = 13 (18 1.6) = 19.4 cm Moment of inertia of weakened section bh J b d a cm HT 1 1 Moment of resistance W HT J 5750 HT see 0.5 h 9 19

20 Stress according to formula (1.1), k g s / s m. 1 9, Example 1.7. Check the strength and stability of the compressed-bending rod, hinged at the ends (Fig. 7). Section dimensions b x h = 13 x 18 cm, rod length l = 4 m. Design compressive force N = 6500 kgf, design concentrated force applied in the middle of the rod length, P = 400 kgf. Rice. 7. Compressed bending elements Solution. Let's check the strength of the rod in the bending plane. Design bending moment from transverse load M Pl k g s / m. 4 4 Section area = = 34 cm. Sectional moment of resistance W x = bh /6 = 70 cm 3. 0

21 Radius of inertia of the section relative to the X axis r к = 0.9 h = 0.9 18 = 5, cm Flexibility of the rod x 5, Coefficient according to formula (1.14), Stress according to formula (1.13) k g s / s m 3 4 0, Let's check the stability of the rod in a plane perpendicular to the bend. Radius of inertia of the section relative to the Y axis r y = 0.9 b = 0.9 13 = 3.76 cm. Flexibility of the rod relative to the Y axis y 3.7 6 Buckling coefficient (as applied) φ = 0.76. Stress according to formula (1.3) k g s / s m 0,

22 CHAPTER CALCULATION OF CONNECTIONS OF ELEMENTS OF WOODEN STRUCTURES 5. JOINTS ON NOTCHES Elements on notches are connected mainly in the form of frontal notches with one tooth (Fig. 8). Frontal notches are designed for crushing and spalling based on the condition that the design force acting on the connection does not exceed the design load-bearing capacity of the latter. Rice. 8. Frontal cut

23 Calculation of frontal notches for crushing is carried out according to the basic work plane crushing, located perpendicular to the axis of the adjacent compressed element, to the total force acting in this element. The calculated load-bearing capacity of the connection from the crushing condition is determined by the formula T R cm cm cm, (.1) where is the crushing area; R cm cm calculated resistance of wood to crushing at an angle to the direction of the fibers, determined by the formula R cm R cm R cm sin R cm 90. (.) The depth of notches in the support nodes of rod structures should be no more than 1 3 h, and in intermediate nodes not more than 1 4 h, where h is the cross-sectional size of the element in the cutting direction. The design load-bearing capacity of a connection based on the shearing condition is determined by the formula where is the shearing area; sk av, (.3) s k s k s k T R av R calculated average chipping resistance of wood over the sk cleaving area. The length of the shearing area l sk in frontal cuts must be at least 1.5 h. The average calculated chipping resistance over the shearing area with a platform length of no more than h and ten insertion depths in joints made of pine and spruce is taken equal to avg 1 /. R k gf s m For length l ck more than h, the calculated shear resistance is reduced and is taken according to Table 1. 3

24 sr l sk h Table.1,4,6,8 3 3, 3.33 R, k gf / s msk 1 11.4 10.9 10.4 10 9.5 9. 9 For intermediate values of the ratio l sk / h the values of the calculated resistances are determined by interpolation. Example.1. Check the load-bearing capacity of the truss support unit, solved by a frontal notch with one tooth (Fig. 8, a). Section of beams b x h = 15 x 0 cm; angle between belts " "(s in 0, 3 7 1; c o s 0, 9 8); cutting depth h = 5.5 cm; length of the shearing platform l ск = 10 h рр = 55 cm; calculated compressive force in the upper belt N c = 8900 kgf. Solution. Calculated resistance of wood to crushing at an angle according to the formula (.) Crushing area 130 R / 130 k gf s m cm, cm bhv 1 5 5. 5 8 8. 8 cm c o s 0. 9 8 Load-bearing capacity of the connection from the condition of bearing strength according to the formula (.1) T 8 8, N to gs. cm Design force acting on the shearing area, T N N c o s to gf. Shearing area p c c c c k l b cm c.. 4

25 Calculated average chipping resistance of wood at the ratio l sk / h = 55/0 =.75 avg 1 0.1 / (see Table 1). R k gf s m Load-bearing capacity of the connection from the condition of chipping strength according to formula (.3) T sk, k gf. Example.. Calculate the frontal notch of a triangular support unit roof truss(Fig. 8, b). The truss chords are made of logs with a design diameter at the node D = cm. The angle between the chords is a = 6 30" (sin a = 0.446; cos a = 0.895). The design compressive force in the upper chord is N c = kgf. Solution. Design resistance of wood crushing at a given angle cm / (Appendix 4). cm cm Using Appendix 1, we find that with D = cm, the nearest area seg = 93.9 cm corresponds to the cutting depth h bp = 6.5 cm. We accept h bp = 6.5 cm, which is less than the maximum cutting depth, which in this case, taking into account the necessary undercutting of the log of the lower belt to a depth of h CT = cm is 1 D h st h h 6, 6 7 cm wr Length of the cutting chord (width of the shearing plane) at h wr = 6.5 cm b = 0.1 cm (Appendix 15

26 Required length of the shearing plane at av R = 1 kgf/cm: sk l sk N c o s , c 3 7.1 cm av br 0.1 1 sk We accept l sk = 38 cm, which is more than 1.5 h = 1.5 () = 30 cm. Since the length of the shearing plane turned out to be less than h = () = 40 cm, cp, then the accepted value R = 1 kgf/cm corresponds to the standards. sk We arrange the support beam from plates with a diameter of cm. For the support cushion we take the same plate with a top edge of cm, which will provide a support width b 1 = 1.6 cm (Appendix 1). Bearing stress over the area of contact between the sub-beam and the support cushion N c sin, 4 k gf / s m 1. 6 cm where 4 kgf / cm is the calculated bearing resistance R CM90 across the fibers in the supporting planes of the structures.., 6. CONNECTIONS ON CYLINDRICAL DOGS Estimated load-bearing capacity the ability for one cut of a cylindrical dowel in joints of elements made of pine and spruce when the forces are directed along the fibers of the elements is determined by the formulas: according to the bending of the dowel T and = 180 d + a, but not more than 50 d; by collapse of the middle element with thickness T c = 50 cd; according to the collapse of the outermost element with thickness a T a = 80 ad. (.4a) (.4b) (.4c) The number of dowels n H that must be placed in the connection to transmit force N is found from expression 6

27 n H N, (.5) where T n is the smaller of the three values of the load-bearing capacity of the dowel, calculated using formulas (.4); p s number of dowel cuts. The calculated load-bearing capacity of the dowel T n can also be determined using Appendix 5. The distance between the axes of the dowels must be at least: along the fibers s 1 = 7 d; across the fibers s = 3.5 d and from the edge of the element s 3 = 3 d. The calculated load-bearing capacity of a cylindrical dowel T n when the force is directed at an angle a to the fibers of the elements is determined as the smaller of the three according to the formulas: H nt (1 8 0), but not more than T k d a c H T c = k α 50 cd; T a = k α 80 cd. k 50d ; (.6a) (.6b) (.6c) Angle α and degrees Table. Coefficient k a for steel dowels with a diameter in mm 1, 1.4 1.6 1.8, 0.95 0.95 0.9 0.9 0.9 0.9 0.75 0.75 0.7 0.675 0, 65 0.65 0.7 0.65 0.6 0.575 0.55 0.55 Note. The values of the coefficient ka for intermediate angles are determined by interpolation. Example.3. The joint of the lower stretched belt of the truss truss (Fig. 9, a) is made using plank overlays connected to the belt with dowels made of round steel. The belt is made of logs with a diameter at the joint of 19 cm. To ensure a tight fit of the overlays, the logs are hewn on both sides by 3 cm to a thickness of c = 13 cm. The overlays are made from boards with a cross section a x h = 6 x 18 cm. Design tensile force N = kgf. Calculate the connection. 7

28 Fig. 9. Connections on steel cylindrical dowels Solution. The diameter of the dowels is set approximately equal to (0.0.5) a, where a is the thickness of the lining. We accept d = 1.6 cm. We determine the calculated load-bearing capacity of the dowel per section using formulas (.4): H , ; T k gs k gs T c T a , k gs; , to Ms. 8

29 The smallest calculated load-bearing capacity Tn = 533 kgf. Double-cut dowels. Required number of dowels according to formula (.5): n H , 9 pcs We accept 1 dowels, of which 4 are bolts on each side of the joint. We place the dowels in two longitudinal rows. Distance between dowels along the fibers: s 1 = 7 d 7 1, 6 = 11, cm (assuming 1 cm). The distance from the axis of the dowels to the edge of the overlays is s 3 = 3 d 3 1, 6 = 4.8 cm (assuming 5 cm). The distance between the dowels across the fibers is s h s = 8 cm > 3.5 d = 5.6 cm. 3 Net cross-sectional area of the belt minus side stitches and weakening by holes for dowels. D 8 4 8, 8 1,. seg d c cm HT 4 Weakened cross-sectional area of the linings HT () 6 (1 8 1, 6) 1 7 7, 6. a h d cm Tensile stress in the linings N, k gf / s m. HT 1 7 7, 6 Example.4. In the crossbar of inclined rafters (Fig. 9, b) a tensile force of N = 500 kgf occurs. The crossbar is made of two plates with a diameter Dpl = 18 cm. The plates cover a rafter leg made of logs D = cm on both sides and are attached to it with two bolts d = 18 mm, working as double-cut dowels. Grinding depth 9

30 of the rafter leg at the junction of the crossbar h "ST = 3 cm. For a tight fit of the bolt washers, the plates are hewn to a depth of h ST = cm. The angle between the direction of the crossbar and the rafter leg is a = 30. Check the strength of the connection. Solution. Load-bearing capacity of a steel cylindrical dowel per cut with the direction of the force at an angle to the fibers is determined by the formulas (.6): H 0, 9 (, 8 7) , ; 9 coefficient k a, determined from the table.; c = D h st = 3 = 16 cm thickness of the middle element; a = 0.5 D pl h st = 0, = 7 cm thickness of the outer element. The smallest load-bearing capacity of the dowel T n = 647 kgf. Full load-bearing capacity of the connection p n p s T n = == 588 > 500 kgf. The distance from the axis of the dowel to the end of the crossbar is taken s 1 = 13 cm > 7 1, 8 = 1.6 cm. The distance between the axes of the dowels across to the axis of the crossbar we take s = 6 cm and across to the axis of the rafter leg. So, let's summarize: "s = 9 cm. The ability of a material to resist external force influences is called mechanical properties. TO mechanical properties wood include: strength, elasticity, ductility and hardness. The strength of wood is characterized by its ability to resist external forces (loads). thirty

31 Forces that resist external influences (loads) are called internal forces or stress. Thus, in the sections of wooden structures, compressive, tensile, bending, shearing (crushing) or chipping stresses arise. The considered methods for calculating wooden structures are focused on typical species structures studied in the discipline “Forest Engineering Structures”. . It is necessary to design wooden structures in strict accordance with SNiP and GOST. 31

32 Applications 3

33 Diameter in cm Indicators B B B B B B B B B B B B B B B B B B 4.8 1.6 5 1.68 5.3 1.75 5.37 1.8 5.57 1.87 5.76 1.93 5.91 1.98 6.08, 04 6.5.09 6.4.14 6.55, 6.7.4 6.85.3 Dimensions of chords b in cm and areas in cm of segments Cutting depth 0.5 1 1.5.5 3 3.5 4 4.5 5 7.34 7.14.39 7.7.45 7.41.49 7.55.5 7.67.57 6.6 4.5 6.9 4.7 7, 4.88 7.47 5.06 7.8 5.4 8 5.4 8, 5.56 7.94 8.18 8.3 8.65 8.67 8.85 9.0 9, 9.3 9.51 9.6 9.83 9.9 10.1 8.5 5.7 10, 10.4 8.7 5.87 8.9 6 9, 6.17 9.4 6.31 9.6 6.44 9.8 6.58 10.5 10.7 8.91 1.4 9.39 1.9 9.8 13.6 9.75 17, 10, 17.8 10.7 18.6 10, 14 11 ,1 19.7 10.6 14.5 10.4.1 10.9 3, 11.5 4, 11.6 0 1.5 6.1 10.3 15.4 11.7 15.9 10, 8 11 1.3 16.8 11.1 11.3 11.4 11.5 11.6 11.8 10 6.71 1.1 1, 10, 6.85 10.4 6.96 10.6 7 ,1 10.8 7.3 1.4 1.4 1.8.1 1 16.3 13.6 1.6 17.1.9 17.6 11.9 1 13.6 18.4 1.4 1.5 1.6 1.7 13.6 3.3 10.9 7.5 11.5 8.8 1.1 30.1 1 5.1 1.7 31.4 13.4 7.9 13 .8 8.8 14.3 9.6 14.7 30.4 14 3.9 15.1 31.1 14.3 4.4 15.5 31.9 13.7 5 15.9 3.6 13 ,8 18.8 14.1 19.1 14.4 19.5 1.7 19.9 13.1 13, 15 5.5 16, 33.4 13, 3.5 13.7 33.7 14, 34.8 14.7 35.9 15, 36.9 15.6 37.9 15.1 38.9 16.5 39.9 16.9 40.9 17.3 41.8 15.3 6 16, 7 4.6 15.7 6.6 16 1.7 16.3 7.6 15 0.4 16.6 8.7 18.1 43.6 17.3 35.4 17.7 36.1 18, 5 44.4 18.9 45.8 19.3 46.3 11.4 1.4 40.7 1.7 36.6 13.3 37.8 13.9 39.3 14.4 40.5 43 .7 13.1 4.8 13.8 44.7 14.4 46.6 49.7 16.51.4 16.7 5.9 16.54, 17.7 55.9 17.4 48.4 17.9 49.5 18.3 50.7 18.8 51.8 19.5.9 18.57.4 18.7 58.8 19.60.1 19.7 61.4 0.1 6, 7 Appendix 1 14.1 51.5 14.8 53.7 15.5 55.7 16.1 57.7 16.7 59.6 17.3 61.4 17.9 63, 18.4 64.6 19.5 68.3 0 69.9 0.5 71.6 54 0.6 64 1.4 74.4 58.1 1 65.5 1.9 76 1.4 66.5.4 77.4 33

34 34 End adj. 1 in round sections for different insertion depths h BP in cm 5.5 6 6.5 7 7.5 8 8.5 9 9.9 63.6 16.6 65.3 17, 68.1 17.7 76.8 17.9 70, 18.3 79.3 18.7 88.5 18.5 7.6 19.4 91, 19.1 74.3 19.6 84 0.1 93.9 0.6 76.3 0.86 , 0.7 96.5 1, 107 1, 78, 0.8 88.4 1.3 99 1.8 110, 11.6 13 0.7 80.1 1.4 90.5 1.9 101, 4 113.9 14 3, 81.9 1.9 9.7.7 84.5 94.7 3, 130 4.6 14 5.4 167, 85.4 3 96.7 3, 10 4, 171, 7 87.1 3.5 98.7 4, 111 4.8 13 5, 188 3, 88.9 19 8.3 06

35 35 Flexibility λ Appendix Value of coefficient φ Coefficient φ .99 0.99 0.988 0.986 0.984 0.98 0.98 0.977 0.974 0.968 0.965 0.961 0.958 0.954 0.95 0.946 0.94 0.937 0.98 0.93 0.918 0.913 0.907 0.891 0.884 0.87 0.866 0.859 0.85 0.845 0.838 0.831 0.84 0.810 0.8 0.79 0.784 0.776 0.768 0.758 0.749 0.74 0.731 0.71 0J0 0.69 0.68 0 .67 0.66 0.65 0.641 0.63 0.608 0.597 0.585 0.574 0.56 0.55 0.535 0.53 0.508 0.484 0.473 0.461 0.45 0.439 0.49 0.419 0.409 0.4 0.383 0.374 0.3 66 0.358 0.351 0.344 0.336 0.33 0.33 0.31 0.304 0.98 0.9 0.87 0.81 0.76 0.71 0.66 0.61

36 36 End adj. Flexibility λ Coefficient φ .56 0.5 0.47 0.43 0.39 0.34 0.3 0.6 0, 0.16 0.1 0.08 0.05 0.0 0.198 0.195 0.19 0.189 0.183 0.181 0.178 0.175 0.173 0.17 0.168 0.165 0.163 0.158 0.156 0.154 0.15 0.15 0.147 0.145 0.144 0.14 0.138 0.136 0.134 0.13 0.13 0.19 0.17 0.16 0.14 0.11 0.1 0.118 0.117 0.115 0.114 0.11 0.111 0.11 0.107 G, 106 0.105 0.104 0.10 0.101 0.1 0.099 0.098 0.096 0.095 0.094 0.093 0, 09 0.091 0.09 0.089 0.086 0.085 0.084 0.083 0.08 0.081 0.081 0.08 0.079 0.078

37 Appendix 3 Calculated data Height h=k 1 D 1 0.5 Sectional area =k D 0.785 0.393 Distance from the neutral axis to the outermost fibers: z 1 =k 3 D z =k 4 D 0.5 0.5 0.1 0.9 Moment of inertia: J x =k 5 D 4 J y =k 6 D 4 0.0491 0.0491 0.0069 0.045 Moment of resistance: W x =k 7 D 3 W y =k 8 D 3 0.098 0.098 0.038 0.0491 Maximum radius of gyration r min =k 9 D 0.5 0.13 37

38 End adj.971 0.933 0.943 0.866 0.393 0.779 0.763 0.773 0.740 0.5 0.475 0.447 0.471 0.433 0.5 0.496 0.486 0.471 0.433 0.04 5 0.0476 0.441 0.461 0.0395 0.0069 0.0491 0.0488 0.490 0.0485 0 .0491 0.0960 0.0908 0.0978 0.091 0.038 0.0981 0.0976 0.0980 0.097 0.13 0.47 0.41 0.44 0.031 38

39 Design characteristics of materials Appendix 4 Stress state and characteristics of elements Designation Design resistance MPa leniya, for kgf/cm graded wood Bending, compression and crushing of fibers: a) elements of rectangular cross-section (except for those specified in subparagraphs “b” and “c”) with height up to 50 cm b) elements of a rectangular section with a width of over 11 to 13 cm with a section height of over 11 to 50 cm c) elements of a rectangular section with a width of over 13 cm with a section height of over 13 to 50 cm d) elements made of round timber without inserts in the design section . Tension along the fibers: a) non-glued elements b) glued elements 3. Compression and crushing over the entire area across the fibers 4. Local crushing across the fibers: a) in the supporting parts of structures, frontal and nodal junctions of elements b) under washers at crushing angles of 90 to Chipping along the fibers: a) when bending non-glued elements b) when bending glued elements c) in frontal cuttings for maximum stress R and, R c, R cm R and, R c, R cm R and, R c, R cm R i, R c, R cm R p R p R c.90, R cm.90 R cm.90 R cm.90 R ck R ck R ck.8 18 1.6 16.6 16 1.5 15.6 16 1.5 15.1 1 39

40 Stress state and characteristics of elements Design characteristics of materials Designation End adj. 4 Calculated resistance MPa leniya, for kgf/cm graded wood 1 3 g) local in adhesive joints for maximum stress 6. Shearing across the grain: a) in joints of non-glued elements b) in joints of glued elements 7. Tension across the fibers of elements made of laminated wood R ck R ck.90 R ck.90 R p.90.7 7 0.35 3.5.1 1 0.8 8 0.7 7 0.3 3.1 1 0.6 6 0.6 6 0.35 3.5 NOTE: 1. The design resistance of wood to crushing at an angle to the direction of the fibers is determined by formula R cm R cm 3 1 (1) s in R R cm 90. The calculated resistance of wood to chipping at an angle to the direction of the fibers is determined by the formula R cm sk. R sk 3 1 (1) sin R R sk.90 sk.. 40

41 Bibliography 1. SNiP II Wooden structures. Design standards.. SNiP IIB. 36. Steel structures. Design standards. 3. SNiP II6.74. Loads and impacts. Design standards. 4. Ivanin, I.Ya. Examples of design and calculation of wooden structures [Text] / I.Ya. Ivanin. M.: Gosstroyizdat, Shishkin, V.E. Structures made of wood and plastic [Text] / V.E. Shishkin. M.: Stroyizdat, Forest engineering structures [Text]: guidelines for the implementation of the project wooden bridge for students of the specialty “Forestry Engineering” / A.M. Chuprakov. Ukhta: USTU,

42 Contents Introduction... 3 Chapter 1 Calculation of elements of wooden structures Centrally tensile elements... 5 Centrally compressed elements Bendable elements Tensile-bending and compression-bending elements Chapter Calculation of connections of elements of wooden structures... 5 Connections on notches... 6 Connections on cylindrical dowels.. 6 Applications... 3 Bibliography

43 Educational publication Chuprakov A.M. Examples of calculation of wooden structures of forest engineering structures Textbook Editor I.A. Bezrodnykh Corrector O.V. Moisenia Technical editor L.P. Korovkin Plan 008, position 57. Signed for printing. Computer typesetting. Times New Roman typeface. Format 60x84 1/16. Offset paper. Screen printing. Conditional oven l.,5. Uch. ed. l., 3. Circulation 150 copies. Order 17. Ukhta State Technical University, Ukhta, st. Pervomaiskaya, 13 Department of operational printing of USTU, Ukhta, st. Oktyabrskaya, 13.

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BUILDING STANDARDS AND RULES SNiP II-25-80 Wooden structures Date of introduction 1982-01-01 DEVELOPED BY TsNIISK im. Kucherenko of the USSR State Construction Committee with the participation of TsNIIPromzdanii of the USSR State Construction Committee, TsNIIEP complexes and buildings

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Ministry of Education of the Russian Federation

Yaroslavl State Technical University

Faculty of Architecture and Construction

examples of calculation of wooden structures

Tutorialin the discipline “Structures made of wood and plastics”

for specialty students

290300 “Industrial and civil construction”

correspondence courses

Yaroslavl 2007

UDC 624.15

MP ________. Structures made of wood and plastics: Methodological manual for correspondence students of specialty 290300 “Industrial and civil construction” / Compiled by: V.A. Bekenev, D.S. Dekhterev; YAGTU.- Yaroslavl, 2007.- __ p.

Calculations of the main types of wooden structures are given. The basics of design and manufacture of structures made of wood are outlined, taking into account the requirements of new regulatory documents. Described design features and the basics of calculation of solid, through wooden structures.

Recommended for students of 3-5 years of specialty 290300 “Industrial and Civil Engineering”, part-time courses, as well as other specialties studying the course “Structures made of wood and plastics”.

Il. 77. Table. 15. Bibliography 9 titles

Reviewers:

Technical University, 2007

INTRODUCTION

The present methodological instructions developed in accordance with SNiP II-25-80 “Wooden structures”. It provides theoretical information, as well as recommendations for the design and calculation of wooden structures, necessary for preparing for the exam for students of the specialty “Industrial and Civil Engineering”.

The purpose of studying the course “Structures made of wood and plastics” is for the future specialist to acquire knowledge in the field of application in the construction of wooden structures, the use of calculation methods, design and quality control of structures various types, knew how to examine the condition of structures, calculate and control load-bearing enclosing structures, taking into account the technology of their manufacture.

1. CALCULATION AND CONSTRUCTION OF ASBESTOS-CEMENT PLATE WITH WOODEN FRAME

An example of calculating an asbestos-cement covering slab.

It is required to design an asbestos-cement insulated roof slab for an agricultural building under roll roofing with a slope of 0.1. Step load-bearing structures the frame is 6 m. The building is located in the III snow region.

1. Choosing a design solution for the slab.

Asbestos-cement slabs with a wooden frame are produced in lengths of 3 - 6 m, widths of 1 - 1.5 m, respectively. They are intended for combined roofless roofs, mainly one-story industrial buildings with a roof made of roll materials with external water drainage.

We accept a slab measuring 1.5x6 m for the top and bottom skins, we take 5 sheets each measuring 1500x1200 mm. We accept the joining of the sheathing sheets end-to-end. The upper compressed skin is set to thickness δ 1 = 10 mm as the most loaded, the bottom stretched - thickness δ 2 =8 mm. The volumetric mass of the sheets is 1750 kg/m3.

As fasteners we use galvanized steel screws with a diameter d=5 mm and length 40 mm with countersunk head. The distances between their axes are at least 30 d(Where d- diameter of a screw, bolt or rivet), but not less than 120 mm, and not more than 30 δ (Where δ – thickness of asbestos-cement sheathing). The distance from the axis of the screw, bolt or rivet to the edge of the asbestos-cement sheathing must be at least 4 d and no more than 10 d.

The width of the slabs along the upper and lower surfaces is taken to be 1490 mm with a gap between the slabs of 10 mm. In the longitudinal direction, the gap between the slabs is 20 mm, which corresponds to the structural length of the slab of 5980 mm. The longitudinal joint between the slabs is made using quarter-shaped wooden blocks, nailed to the longitudinal edges of the slabs. Before laying the roofing felt carpet, the gap formed between the slabs is sealed with heat-insulating material (mipora, poroizol, polyethylene foam, etc.), and wooden blocks, forming the joint, are connected with nails with a diameter of 4 mm with a pitch of 300 mm.

The frame of the slabs is made of grade 2 pine wood, with a density of 500 kg/m3. The length of the supporting part of the slabs is determined by calculation, but at least 4 cm is provided.

Calculated bending resistance of asbestos cement R i.a=16MPa.

The elastic moduli of wood and asbestos cement, respectively, are E g=10000 MPa, E a=10000 MPa.

Design resistance of asbestos cement to compression R c.a=22.5 MPa.

Calculated bending resistance of asbestos cement across the sheet Rwt.A=14 MPa.

Calculated bending resistance of pine wood R i.d.=13 MPa.

For frame slabs, mineral wool or glass wool insulation with a synthetic binder, as well as other heat-insulating materials, are used. In this case we use hard mineral wool slabs on a synthetic binder in accordance with GOST 22950-95 with a density of 175 kg/m 3. Thermal insulation boards glued to the bottom trim asbestos-cement slabs on a layer of bitumen, which simultaneously acts as a vapor barrier. The thickness of the insulation is assumed to be structurally equal to 50 mm.

Calculation of wooden structures should be done:

on load-bearing capacity (strength, stability) for all structures;
on deformations for structures in which the magnitude of deformations may limit the possibility of their operation.

Calculation of bearing capacity should be carried out under the influence of design loads.

Calculation of deformations should be carried out under the influence of standard loads.

Deformations (deflections) of bending elements should not exceed the values given in table. 37.

Table 37. Limit deformations (deflections) of bending elements

Note. If there is plaster, the deflection of the floor elements is only from payload should not be more than 1/350 of the span.

Centrally stretched elements

Calculation of centrally stretched elements is carried out according to the formula:

where N is the calculated longitudinal force,

mр - coefficient of operating conditions of the element in tension, accepted: for elements that do not have weakening in the design section, mр = 1.0; for elements with weakening, mр = 0.8;

Rp is the calculated tensile strength of wood along the grain,

Fnt is the net area of the cross-section under consideration: when determining Fnt, weakenings located in a section 20 cm long are taken to be combined in one section. Centrally compressed elements. Calculation of centrally compressed elements is carried out according to the formulas: for strength

for sustainability

where mс is the coefficient of operating conditions of compression elements, taken equal to unity,

Rc is the calculated resistance of wood to compression along the grain,

The buckling coefficient, determined from the graph (Fig. 4),

Fnt - net cross-sectional area of the element, Fcalc - calculated cross-sectional area for stability calculations accepted:

1) in the absence of weakening: Fcalc=Fbr;

2) for weakening that does not extend to the edge - Fcalc = Fbr, if the area of the weakening does not exceed 25% of Fbr and Fcalc = 4/3Fnt, if their area exceeds 25% of Fbr;

3) with symmetrical weakening facing the edge: Fcalc=Fnt

Flexibility? solid elements is determined by the formula:

Note. For asymmetrical weakening extending to the ribs, the elements are calculated as eccentrically compressed.

Figure 4. Graph of buckling coefficients

where Io is the estimated length of the element,

r - radius of inertia of the element’s section, determined by the formula:

l6p and F6p are the moment of inertia and gross cross-sectional area of the element.

The estimated length of the element l0 is determined by multiplying its actual length by the coefficient:

with both hinged ends - 1.0; with one end pinched and the other freely loaded - 2.0;

with one end pinched and the other hinged - 0.8;

with both ends pinched - 0.65.

Bendable elements

Calculation of bending elements for strength is carried out according to the formula:

where M is the design bending moment;

mi - coefficient of operating conditions of the element for bending; Ri is the design bending resistance of wood,

Wnt is the net moment of resistance of the cross section under consideration.

The coefficient of operating conditions for bending elements mi is accepted: for boards, bars and beams with cross-sectional dimensions of less than 15 cm and glued elements of rectangular cross-section mi = 1.0; for beams with side dimensions of 15 cm or more, with the ratio of the height of the element’s section to its width h/b? 3.5 - mi = 1.15

Calculation of solid cross-section elements for strength during oblique bending is carried out according to the formula:

where Mx, My are the components of the design bending moment, respectively, for the main axes x and y

mi - coefficient of operating conditions of the element for bending;

Wx, Wy are the net moments of resistance of the cross section under consideration for the x and y axes. Eccentrically extended and extracentrically compressed elements. Calculation of eccentrically stretched elements is carried out according to the formula:

Calculation of eccentrically compressed elements is carried out according to the formula:

where? is a coefficient (valid in the range from 1 to 0), taking into account the additional moment from the longitudinal force N during deformation of the element, determined by the formula;

At low bending stresses M/Wbr, not exceeding 10% of the stress

stress N/Fbr, eccentrically compressed elements are calculated on

stability according to formula N

where Q is the calculated shear force;

mck=1 - coefficient of operating conditions of a solid element for chipping during bending;

Rck is the calculated resistance of wood to chipping along the grain;

Ibr is the gross moment of inertia of the section under consideration;

Sbr is the gross static moment of the shifted part of the section relative to the neutral axis;

b - section width.

Calculation of wooden floors

Calculating a wooden floor is one of the easiest tasks, and not only because wood is one of the lightest building materials. Why this is so, we will find out very soon. But I’ll say right away that if you are interested in classical calculation, in accordance with the requirements of regulatory documents, then you here .

When building or repairing a wooden house, using metal, and even more so reinforced concrete floor beams is somehow out of the question. If the house is wooden, then it is logical to make the floor beams wooden. It’s just that you can’t tell by eye what kind of timber can be used for floor beams and what kind of span should be made between the beams. To answer these questions, you need to know exactly the distance between the supporting walls and at least approximately the load on the floor.

It is clear that the distances between the walls are different, and the load on the floor can also be very different. It’s one thing to calculate the floor if there is a non-residential attic on top, and a completely different thing to calculate the floor for the room in which partitions will be built in the future. cast iron bathtub, bronze toilet and much more.

Wooden structures

The construction process of any scale involves not only the use of high-quality building materials, but also compliance with rules and regulations. Only strict adherence to the instructions and established standards will give the best result in the form of a strong, reliable and durable structure. A special place in the construction industry is occupied by such material as wood. In ancient times, the first settlements and cities were built from wood raw materials. In the modern construction industry, wood does not lose its relevance and is actively used for the construction of complex structures. Due to the fact that there are a colossal number of types of wood material, there are a number of requirements for the selection, calculation and protection of such structures. The most current edition of the set of norms and rules is (SNiP) 11 25 80.

Why a tree? The thing is that natural material is distinguished by natural aesthetics, high manufacturability and low specific gravity, which are its indisputable advantages. That is why many structures are made of wood. What is SNiP? Any design has certain characteristics, indicators of mechanical strength and resistance to various factors, which is the basis for design activities and technical calculations. All work is carried out in accordance with the requirements of SNiP.

Construction norms and rules (SNiP) are a set of strict regulatory requirements in legal, technical and economic aspects. With their help, construction activities, architectural and design surveys, and engineering activities are regulated.

A standardized system was created in 1929. The evolution of the adoption of rules and regulations is as follows:

in 1929 - the creation of a set of temporary rules and regulations to regulate design processes, construction of buildings and structures for various functional purposes;
in 1930 - development of rules and regulations for the development of populated areas, as well as the design and construction of buildings;
in 1958 - an updated set of rules for planning and urban development.

In the USSR, such standards represented not only consolidated technical requirements, but also legal norms separating the duties, rights and responsibilities of the main actors in a construction project: the engineer and the architect. After 2003, only some norms and requirements that are within the framework of the law “On the technical regulations of the set of rules” are subject to mandatory execution. With the help of SNiP, the most important standardization process is launched, which optimizes the efficiency and effectiveness of construction. The updated version of SNiP, which today is used in the construction industry for design work, calculations and construction of wooden structures, is SNiP 11 25 80. The contractors for this project were employees of the Institute “National Research Center Construction”. The set of requirements was officially approved on December 28, 2010 by the Ministry of Regional Development. It came into force only on May 20, 2011. All changes occurring in the rules and standardization are clearly illustrated by the updated edition, which is published annually in the specialized information publication “National Standards”.

Original wooden structure

General provisions

Like any consolidated regulatory document developed to regulate a particular activity, SNiP 11 25 80 contains basic provisions.

Installation of wooden elements

Here are some of them:

All requirements given in the SNiP document are subject to strict compliance during the construction of new buildings or reconstruction activities. The rules also apply to the design and construction of wooden support structures for power lines.

Important!

All rules and regulations do not apply to the construction of temporary structures, hydraulic structures or bridges.

When designing wooden structures, it is important to provide high-quality protection from all kinds of damage and negative influence from the outside. This is especially true for projects that are operated in unfavorable atmospheric conditions and high humidity. The updated edition provides protection against fire, biological damage, rotting and any possible “troubles” during future use.
According to the requirements of SNiP, structures made of various types of wood must meet design standards for the degree of their load-bearing properties and possible deformation. In this case, it is necessary to take into account the degree, nature and duration of operational loads.
All bases are designed with mandatory consideration of their production, transportation of individual parts, operational properties and installation specifics.
The required level of structural reliability is set using design measures, the quality of protective treatment, and increased fire safety.
In environments where there is intense heating of a constant or systematic nature, wooden structures are used within the permissible temperature range. For non-glued wood, the maximum permissible value cannot exceed 50 degrees, and for glued wood - no more than 35 degrees.
When developing a drawing, the following information is necessarily used: features and type of wood, glue and its specifics, individual requirements for the material.

These are just general provisions of the set of norms and rules of the updated edition, which should guide everyone, be it industrial or individual construction.

Spatial structure made of wood

Material selection

But not only the design and construction of a building is regulated by a set of rules and regulations. The current edition of SNiP describes in detail aspects of the selection of raw materials for certain purposes. Everything is important: the operating conditions of the wooden structure, the quality of the protective treatment, the aggressiveness of the environment, and the functional purpose of each component.

Dry edged boards

SNiP 11 25 80 describes in detail all possible situations and standards for the selection of materials. Let's consider the main points:

For wooden structures, as a rule, wood of various coniferous species is used. For elements that perform critical functions in the structure, such as dowels or cushions, hardwood is used.

Important!

To create power line supports, the edition of SNiP 11 25 80 implies the use of larch or pine. In some cases, spruce or fir wood is used.

Why conifers? It's not just their low cost. The presence of resins in large quantities provides wood bases with a reliable barrier against rotting no worse than specialized impregnations and antiseptics.

Edged board made of pine needles

Load-bearing elements of wooden structures must meet the standards of GOST 8486-66, 2695-71 and 9462-71.
The strength of the wood material complies with established standards; its resistance cannot be lower than the standard value.
The wood moisture content should not exceed 12%.
The raw materials cannot contain cross-layers, a large number of knots or other possible flaws.
If wood of species that are poorly resistant to decay (birch, beech and others) is used, it must be carefully treated with specialized impregnations and antiseptics.
If lumber with a round cross-section is used, the value of the slope in the technical calculations of a wooden structure according to SNiP 11 25 80 is equal to 0.8 per 1 meter of length. The exception is larch; it is calculated in the order of 1 centimeter per 1 meter in length.
The degree of density of wood or plywood sheet is regulated by the procedure set out in the set of rules 11 25 80. This helps to calculate the weight of the future structure.

The choice of synthetic adhesive depends on the operating conditions and the type of wood for the structures.

Building a house from large logs

In addition to general operational requirements, temperature and humidity are also important. The set of rules 11 25 80 clearly states the following standards for various operating conditions of wooden structures:

Temperature and humidity conditions	Characteristics of operating conditions	Wood moisture limit %
		Laminated wood	Unlaminated wood
	In rooms that are heated, t up to 35 degrees relative humidity
A 1	Less than 60%	9	20
A 2	More than 60 and up to 75%	12	20
A 2	More than 60 and up to 75%	12	20
A 3	More than 75 and up to 95%	15	20
	Inside unheated rooms
B 1	In the dry zone	9	20
B 2	In the normal zone	12	20
B 3	In a dry or normal area with constant humidity less than 75%	15	25
	On open air
IN 1	In dry areas	9	20
AT 2	In normal zones	12	20
AT 3	In wet areas	15	25
	In terms of buildings and structures
G 1	In contact with the ground or in the ground	-	25
G 2	Constantly moisturized	-	Not limited
G 3	In the water	-	Also

The totality of all provisions in the “Materials” section of edition 11 25 80 must be taken into account without fail. The correct choice of lumber, as well as auxiliary components, determines the durability and strength of the structure.

Aspen lumber

Design characteristics

The latest current edition of SNiP 11 25 80 is an effective and informative guide to creating strong and durable structures from various types of wood.

Beams from different types of wood

One of the main points of choice is the compliance of all kinds of wood species with the list of required resistance characteristics. The main indicators are as follows:

Characteristics of bending, crushing and compression of wood fibers. In technical calculations, both the size and the cross-sectional shape of a building element are important.
The degree of elongation along the fibers. The indicator, as a rule, differs for glued and non-glued elements.
Characteristics of compression and collapse along the wood fibers over the entire area.
Local indicator of fiber collapse. You should know that for supporting components of the structure, nodal and frontal, in places of collapse at an angle of more than 60 degrees, the indicator may be different.
Shearing along the grain. It can vary in the bends of non-glued or glued components of the structure, as well as in the end notches for ultimate stress.
Chipping across the grain. The characteristics are different in the connections of glued or non-glued elements.
The degree of tensile strength of laminated wood elements across the grain.

Main wood species

When choosing wood to create a structure, you should know the subgroups of species:

conifers – larch, fir, cedar;
hard deciduous - oak, ash, maple, hornbeam, elm, birch, beech;
soft deciduous - poplar, alder, linden, aspen.

Dry oak board

Important!

For each type of wood, the optimal performance is individual.

All calculations are performed at the design stage of the structure. To avoid a large error, and to ensure that the figures are as close as possible to the real ones, it is necessary to use the formulas provided by the updated edition of SNiP 11 25 80. To obtain the desired value, you need to multiply the individual wood indicator by the coefficient of operating conditions for the structure. The operating conditions coefficient depends on many factors: air temperature, humidity level, presence of aggressive environments, duration of variable and constant loads, installation specifics. The use of laminated construction plywood also requires compliance with established standards and regulations.

When calculating, the following indicators relative to the plane of the sheet are taken into account:

Stretching.
Compression.
Bend.
Chipping.
The cut is perpendicular.

All indicators depend on the type of wood that is the basis of the plywood sheet, as well as on the number of layers. In addition to the main indicators, there is one more that is important when designing a wooden structure. This is density. This value is very unstable and can change even on the scale of one tree species. Why is it important to measure density? It is this that will determine the weight of the resulting structure as a result of construction work. The density of wood is influenced by several factors, such as the age of the tree, moisture content. To achieve optimal density, a technique such as drying is used. Depending on the individual density, wood can be divided into light, medium and heavy. The lightest is considered to be pine, poplar and linden. Species with medium density include elm, beech, ash, and birch. The densest ones include oak, hornbeam or maple. As the density increases, its mechanical properties will change: the denser the material, the stronger it is in tension and compression.

Updated edition of SNiP II-25-80

Correct adhesive connection of structures

The choice of glue for a particular wood species is of decisive importance. The strength of the structure, reliability and durability of operation without the slightest sign of deformation depend on this.

Wood glue

According to the edition of SNiP 11 25 80, the following types of glue are used:

Phenolic resorcinol or resorcinol glue is used to join wood or plywood. Suitable for operating conditions where the humidity temperature is more than 70%. The secret lies in basic chemistry: the reaction of resorcinol and formaldehyde produces thermoactive resins. The more resorcinol in the glue, the higher its softening temperature. It is under high temperature and humidity conditions that the use of phenol-resorcinol glue is recommended. Its advantages are high levels of initial and operational strength, low cost and weather resistance. Minus - the glue is toxic, as free phenol is released.
Acrylic resorcinol adhesive is used for the same conditions as phenolic resorcinol adhesive. It has high characteristics of weather resistance and moisture resistance. The adhesive is stable, durable even in harsh operating conditions, and is characterized by high manufacturability.
Phenolic adhesives are actively used in the woodworking industry and are used for gluing plywood for outdoor use. The main advantageous characteristics are increased mechanical stability under shear loads, excellent elasticity, vibration resistance and good resistance to peeling loads.
Urea adhesives are used for surface treatment of wood. In such cases, a solution of cold-curing urea glue is used. The solution penetrates the wood, making it harder, forming a barrier against contamination, and increasing abrasion resistance. Urea-melanin glue is a derivative. Additives in the form of melanin can almost double the shelf life. The cost of urea glue is low, and low resistance to cyclic humidity is noted.

When choosing an adhesive for a wooden structure, you should rely on generally accepted standards and recommendations set out in the edition of SNiP 11 25 80.

Wood glue

Laminated wood or regular wood?

Adhesive bonding is one of the most progressive and reliable methods. This type of connection works well for chipping and allows you to easily cover spans of more than 100 m. Wooden structures glued together from many small elements have a number of advantages over solid timber. But in order to implement the project and achieve maximum strength and effectiveness, all technical conditions must be strictly observed. Today, such production is usually mechanized and automated.

Glued laminated timber

What are the advantages of laminated wood for creating reliable structures?

Conducting waste-free manufacturing of structures.
Rationalized use of different wood species in one package.
Increased design optimization due to targeted use of the anisotropic properties of wood.
Absolute elimination of any restrictions on the assortment, both in length and in cross-sectional size.
Tightness and high sound insulation properties.
Increased fire resistance compared to solid timber.
Excellent indicators of chemical inertness and biological resistance.

The choice of high-quality glue for making connections is the basis for the strength and durability of wooden structures in construction. Humidity is of decisive importance.

Laminated wood

Important!

The drier and thinner each adhesive structural element is, the less likely it is for cracks to form. Insufficiently dried wood can lead to divergence of the adhesive seam during operation.

Externally, laminated wood does not differ from solid wood, so the natural aesthetics are preserved. This type of structure is not only stronger and more durable. But it also creates a unique aura of warmth and comfort, which is so important in building a comfortable family nest.

Nodal connection of laminated timber

Protection from destruction and fire

Reliable protection of wooden structures from destruction is the key to a long service life. Today, many catastrophic situations can be prevented by promptly conducting high-quality and comprehensive “therapy.” The current edition of SNiP 11 25 80 implies the protection of wooden structures, as they say, “on all fronts,” since wood is a material gifted to us by nature, it is quite natural that aggressive external influences can lead to biological destruction and deformation. To install a reliable barrier, you need to be able to choose and use specialized tools correctly. There are many methods of protection: surface treatment, impregnation, diffuse coating and even chemical preservation.

Protecting wood from moisture

In addition to processing activities, attention should be paid to:

construction prevention, that is, use air-dried wood in the process, eliminate damaged areas;
monitor humidity and temperature during operation;
comply with all sanitary and technical conditions;
provide a functional ventilation system;
install waterproofing and vapor barrier.

The easiest to use and effective means that have proven their effectiveness in practice are antiseptics.

Protecting wood with antiseptic

The edition of SNiP 11 25 80 defines the following classification:

Antiseptic agents that are used in an aqueous solution. These include sodium fluoride, sodium fluoride, ammonium silicon fluoride, as well as other solutions. They are intended for processing for those structures that are maximally protected from moisture and direct contact with water.
Antiseptic pastes based on water-soluble antiseptics. The active ingredients of such products are bitumen, kuzbasslak or clay. They are practically not washed out by water, so they are applied to wood structures with any humidity. Such pastes can also be used to fill cracks, preventing rotting.
Oily antiseptics. The basis is shale, coke and coal oils. Antiseptics will protect those structures that come into contact with water or are in unfavorable conditions with high humidity.
Antiseptics that are used in organic solvents. Antiseptic agents are intended for reliable external treatment of wooden building elements.

Wood varnishing

The choice of antiseptic is determined by the main functional purpose of the wooden structure.According to the method of use, they are divided into two conditional groups:

The first group is those structures that are operated in unfavorable conditions or aggressive environments. These include elements used outdoors or those that require particularly effective protection.
The second group is those structures that are subject to periodic moisture (ceilings, joists, beams and much more).

Before carrying out antiseptic measures, experts recommend carrying out additional disinfection so that the protection of structures is carried out impeccably and meets all requirements.

How to choose an antiseptic for wood

Fire protection

As you know, wood is a material that, under certain conditions, is easily flammable. To improve the fire safety characteristics of wooden building elements, high-quality fire protection must be provided. There are several types of special coatings for this:

Weather resistant.
Moisture resistant.
Non-moisture resistant.

Fire protection of building structures

Chemicals in the form of pastes, impregnations, coatings are used, as a rule, for those wooden structures that are protected from the direct influence of the atmosphere. They are applied in two layers, maintaining an interval of 12 hours between them. Coating is used to cover structural elements that do not require painting: rafters, purlins and the like. The protection can be applied to the surface and deeply impregnate wooden elements, giving the structure fire-resistant properties.

Fire protection for wood

One of the most popular and effective means is flame retardant impregnation. Fire retardants are substances that prevent ignition and prevent flames from spreading over a surface.

In addition, protection is used in the form of special organosilicate paints or perchlorovinyl enamel. The most durable protection against fire is a combination of impregnation of the structure with subsequent painting.

Fire protection

Design Basics

The current information contained in the updated edition of SNiP 11 25 80 serves as a guide for both beginners in construction and experienced professionals.The basics of design and creation of wooden multi-component structures, which are set out in edition 11 25 80, are as follows:

The size of each wooden structural element must be selected taking into account transportation possibilities.
If the span of unsupported wooden foundations is 30 meters or more, one of the supports is made movable. This helps compensate for the lengthening of spans in conditions of unstable temperatures and humidity.
The spatial rigidity indicator is improved by installing vertical and horizontal binders. To enhance strength, the transverse connections of the structure are mounted on the tops of the load-bearing elements or in the plane of the vertical belt.
The supporting dimension of the board or plywood covering slab must be at least 5 centimeters. This protection will help prevent buckling before the necessary connecting elements are installed.
The number of connecting elements of composite beams should be three. It is more convenient to use plate dowels as connecting fasteners.
Design requires a lift of 1/2 span and hinged support. The same principle is used to design laminated beams in a structure.

Important!

Glued beams need to be assembled only in the vertical direction of the boards. Horizontal arrangement is allowed only when assembling box beams.

Plywood with increased water-resistant properties acts as the protective walls of the laminated beam. Moreover, its thickness should not be less than 8 millimeters.

Wooden structures

The requirements established by the current edition of the rules and regulations 11 25 80 must be strictly followed. Thus, a reliable and durable basis for the structure of any functional purpose is obtained.

Multi-component wooden structures

General requirements

The finished structure is subject to certain requirements, which are regulated by SNiP 11 25 80.

Wooden house made of timber

In accordance with established rules and regulations, the following must be ensured:

Durable protection of wood of any species from the effects of groundwater, precipitation and sewage.
Reliable protection of the material from freezing, condensation accumulation, possible saturation with water from the ground or any adjacent structures.
An impeccable ventilation system (continuous or periodic) to prevent the accumulation of logs, rot, mold or mildew on the surface of the structure.

Wooden house

Organizational, design and construction work must be carried out in a complex, strictly following the established standards and rules for the construction of wooden structures. There are many factors to consider. which will ultimately determine the service life of the structure, its strength and reliability. To obtain the optimal result, it is necessary to follow all established norms and rules, as well as follow updates in the edition of SNiP 11 25 80.

Multi-component wooden ceiling structure