BUTT E COE UNITED WOODEN STRUCTURES:

EVALUATION OF CARRYING CAPACITY

Ariskin M.V, Kislyakova E.S

Connection to ring washers glued wooden structures are relatively new, poorly understood, which limits the magnitude of their application in practice construction. In preliminary studies, the use of wood glued to the steel washers, even a relatively small diameter (D _w = 50 mm) allows you to pass from one element to another in the butt joint effort from 45 to 50 to H. This value is several times larger than a carrier with a similar ability to splice th performed only on washers (by analogy with the key) or only on the pivot bolt. Possibility of transfer efforts on a relatively small contact area is the main advantage of glued steel washers.

In this paper we attempt a theoretical evaluation of glued steel washers and plug inyaemyh elements, and the paper presents the results of experimental studies on the glued joints of steel washers.

Effect of increasing the carrying capacity and rigidity of the connection achieved monolithic glued to the nest wood element steel washer is not dependent on the availability of provisional no density between the socket and washer (precision manufacturing nest diameter washers). Moreover nest in wooden elements should be chosen with a diameter slightly larger than the diameter of the washer. This provides a reinforced disc (Disc plus adhesive) larger in diameter than the shaft itself. The essence of the increase before Yelnia second load connection is that the concentrated force is transmitted through the connecting bolt from one element to another, and although locally but on a fairly large area, washers and certain area next to her zones. Thanks solidity of the connection

Due to the increased rigidity washers maximum stress from the transmission bolt effort falls on the puck at the same wooden elements normal and tangential stresses are transmitted outside washers, ie in areas relatively distant from the point of application of a concentrated effort.

It should be noted that the washer is not glued to the entire thickness of the wooden element, and only a portion thereof. This creates strain d w concentration not only in the plane of the washer, but also the thickness of the wooden element. Given the difficult state of stress throughout the volume of the connected timber element with adhesive steel washer attempted solution of the spatial task of identifying all the components of the stress (σ _y, σ _y, σ _y, τ _xy, τ _{z y,} τ _{x z).} Each of these stresses can affect the size of the ultimate load. However, in our opinion decisive role will still have a bearing stress σ _y and tangential shear stress τ _xy along the fibers. Stress σ _x, directed across the grain may also have an impact on the value of the limit load. However, their action can be taken into account separately, taking into account the results of experimental tests of the samples and the real character of their destruction.

To assess the ability of the carrier, connecting glued on steel washers considering real wood element stress state below the results of theoretical research. The calculations are performed in the program ANSYS, based on the use of finite element method (FEM). Degree of accuracy of the solution of the problem depends on the shape and size of finite elements. For modeling metal washer was used finite element Solid 45 for modeling wood used finite element Aniso 64. Compounds of metal and wood plate occurs by combining the movements of relevant nodes of the two bodies.

To estimate the stress strain state of a wooden plate with adhesive element in the mix, the shear calculations were made with the following parameters of the sample:

- Metal E _x = 21 * 10 ¹⁰ Pa, μ = 0,3

- Wood E _x = 10 ¹⁰ Pa, μ = 0,05; E _y = 4 * August ¹⁰ Pa, μ = 0,02; ; E _z = 5 * August ¹⁰ Pa, μ = 0,02; G _x, G _y, G _z - program calculates itself.

Numerical computation diameter washers glued taking L to be equal to 60, 80 and 100 mm. Loading set the same for all samples with diameters accepted that the external load is transmitted through the N _w central bolt d = 16 mm, creating a uniform stress σ ₀ along the arc of a semicircle.

Calculations were performed on a typical cross section of the sample Which in our view should take place as normal stress concentration and tangents, and the level and change in stress, which will depend on ultimate bearing capacity of the sample.

In each section were counted at all stress components acting on the pasted steel washer diameter D _{w w} N load.

Characteristic stress distribution σ _x, σ _y, τ _xy, which, in our opinion, are crucial for the maximum load-bearing capacity of the sample, loft, where these stresses are maximum values. Buckling stress distribution along the line of contact with timber washers (line 5) is shown in the example of Fig. 2b.

Ultimate bearing capacity of the sample depends strongly on the nature and magnitude of the voltage collapse th (σ _y), which in turn depend on the thickness and diameter glued washers.

Maximum ordinate σ _y even regardless of their degree of concentration at certain points averaged values significantly less stress buckling calculated as σ ₀ = N _w / _cm A = N _w / t _{w w} D that compelling cost value equal to D _w = 60 mm σ _y = 5667 Pa, for D = 80 mm _{w-σ 0} = 4250 Pa; for D = 100 mm _w - σ ₀ = 3400 Pa. This is natural, since the voltage σ _y, as can be seen from the graphs in Fig. 3 and 4, are distributed on a much larger area than A _cm = t D _{w w.} This gives grounds for the appointment of ultimate load capacity of the compounds to the bonded steel washers or enter a larger value of the design resistance of wood Collapse (R cm) or enter the active area greater than A _cm = t _w D _w in the perception of stress collapse. In this and in another case, the limit load capacity washers will be more than [N _w] = R _{cm w} t D _w.

To evaluate the effect of stress on the limiting value chipping bearing capacity washer is enough to compare the ratio values and maximum values σ _y and τ _xy and design characteristics for wood _cm R and R _ck. Computations have shown that the maximum values of σ _y prevail over the maximum values τ _xy is almost an order of magnitude, ie 8 ÷ 10 times, while the ratio R _cm / R _sk according to SNIP II -25-80 pine (Grade 2) is 6.19. This suggests that the voltage value of cleaving R _ck. It should be noted that regardless of the above, the voltage spallation have still a role on the ultimate bearing capacity washers as crushing wood chipping with yet more dangerous type of work than just collapse.However, this assessment needs to know in more detail wood work the combined effect of voltage collapse and spalling.