FI62887B - GROV I-BALK - Google Patents

Description

1 62887 Sturdy I-beam

The invention relates to a robust I-beam. Sturdy wooden beams are now made by gluing to a sawn timber slab and together and the product is called glulam. The strength / weight ratio of glulam is quite advantageous. It is characterized, however, by the fact that, under different load situations, the dominant strength property varies, with the result that the wooden beam in question is oversized for other properties.

There are mainly three main properties in terms of strength. First, there is a deflection, which is generally about a span of the beam / 200-300, e.g. at a span of 15 m 50 mm.

The second is the bending stress caused by the load on the beam. It is at its maximum in the middle of the span in the case of a single-hole beam. The specific calculated bending stress of the material must not be exceeded, otherwise there is a risk that the beam will break across the middle.

The third feature is the shear stress caused by the load on the beam, which is applied to the ends of the beam with supports. At high loads, the shear force tends to split the glulam beam from its ends in the longitudinal direction so that the lower edge of the beam has to be stretched due to deflection and the upper surface resists this displacement, whereby the beam splits horizontally along its center line.

When starting from the other extreme edge of the glulam capacity range, the long voltage gap and the small load, the dimensioning factor is deflection (gap 1 in Figure 1). In the middle stages, the area is dimensioned by the bending stress (spacing 2 in Figure 1) and at the opposite extreme edge with a large 2,68887 load and a small span, the shear stress is the dimensioning factor (gap 3 in Figure 1).

As already stated above, when one property is determined, the glulam becomes otherwise oversized. To remedy this, glulam has also been glued to the shape of the I-profile (Figure 3).

The deflection and bending stress are thus optimized so that neither part becomes oversized, in which case the raw material savings would be considerable. However, this cannot be accomplished except in certain special situations, because the shear stress will, as the load increases, dimension the tapered web so that it should be widened. Thus, this profile does not benefit enough to make its economical manufacturing sensible. Such glulam is therefore not currently significantly produced.

As an alternative, the use of plywood as a web between wide chords has been studied. The shear strength of the cross plywood is sufficient, but buckling and buckling tendencies due to the very thin and narrow structure (Fig. 4A) have become a problem. By gluing the so-called. enclosure structures (Fig. 4B), these problems have been solved, but then expensive jointing solutions have been required, because if plywood boards are to be used economically, they must be made into beam-long boards. The fact that plywood-like heavy composite beams are generally not manufactured is probably, in addition to the above, apparently due to the cumbersome control of the moisture behavior of the beam in question and the non-existent fire resistance properties.

Kertopuu is an already well-known product, in which veneers thicker than 2 nm are first made of weather-resistant gluing, a 25-75 mm thick and up to 2 m wide continuous tile, up to 30 m 3 62887 long. The causes of veneers are largely longitudinal. By cutting the tile, glued wooden beams, planks or various small profiles are obtained. The product has been on the market since the beginning of 1978.

The advantage of multi-layer wood is its suitability for many clearly different applications, as its structure has been able to be modified to a large extent, if necessary. As a result, we deliberately set out to develop a sturdy I-tree beam by optimizing the multi-layer wood.

The goal was to have a robust, continuous and fire-resistant beam in which both deflection, bending stress and shear stress would all be equally dimensioning factors, thus achieving the greatest possible material savings. Surprisingly, this object was achieved when it was invented to apply a solution according to the features of the following claim using multiplication wood.

For example, I-beams with a web of at least 65 mm have been prescribed for use in fire classifications for public spaces. The fire resistance of the I-beam according to the invention is at least 1/2 hour.

The I-beam according to the invention achieves long spans so that the cross-section is clearly smaller than that of a glulam beam dimensioned for the corresponding span. A comparison table is attached. The table shows the maximum stress intervals of a multi-ply I-beam and the corresponding glulam when the effect of the three main design properties: bending stress, shear stress and deflection are considered separately. The final maximum span of the beam is the minimum of these three values.

The following advantages over glulam can be recorded in favor of the Kertopuu I-beam: 4 62887 - With a structure of the same height, a cross-section of 37-84% is achieved than with glulam, cf. table.

- Thanks to the crossed veneers of the web and the chords, the vertical living of the beam is almost completely prevented when it is about 4% of the completely dry to wet wood on the glulam.

- Thanks to the transverse veneers of the web, the joining technology becomes simpler at the ends of the I-beam.

- Thanks to the vertical adhesive seams of the transverse veneers and chords, stamping pressures do not become a problem. (The stamp pressure is the force with which the surfaces of the beam and the support below it press against each other. The end of the narrow beam goes loose when the stamp pressure is too high.) - The good fire resistance of the Kertopuu I-beam itself is easy to improve with fire-rated wool.

- With the same manufacturing technology, it is possible to produce very strong casing beams, and since the material of the web and the chords are largely the same, it is possible to control moisture distortions.

- In addition to the rigid beam, the profile in question can be used as a column, in which case it has very high stability values and makes the joining technique very simple, so that the joists in the column extend above the horizontal beam and the horizontal over the chords of the horizontal bar. In this way, the joists of the column can be easily connected to the web of the horizontal beam (Fig. 6).

The invention is illustrated below with reference to the accompanying drawings, in which Figure 1 graphically shows different load cases of glulam and Figure 2 graphically compares the strength properties of glulam and multi-ply I-beam. Figure 3 shows a known I-beam made of glulam and Figure 4 a known I-beam and a box beam made of plywood. Figure 5 shows an I-beam made of multi-layer wood according to the invention and Figure 6 shows a special use of an I-beam according to the invention.

5 62887

Figure 1 shows graphically the effect of the beam span L as a vertical axis and the load F as a horizontal axis on the effect of deflection lw, bending stress lb and shear stress lv on the dimensioning of ordinary glulam. The ratios are presented arbitrarily, so the bending stress may not have the bandwidth described. The deflection is a dimensioning factor between 1, the bending stress between 2 and the shear stress between 3. Figure 2 shows graphically the cross-sectional area of the glulam L (dashed lines) and the corresponding multiplicative I-beams K (solid lines) as a function of the product. and shear strength as well as deflection. The spacing of the brackets is 4.8, 6.0 and 7.2 m (see table). Three spans have been taken for each split, all of which have been optimized for both glulam and multi-ply I-beam, so the differences indicate overcapacity with one of the strength properties of the glulam.

Figure 3 shows a known adhesive beam in the form of an I-profile with a web u and chords p. Figure 4A shows a known I-beam in which the web u is made of plywood and arranged between wide chords p. Figure 4B, on the other hand, also shows a known box-like plywood beam.

Figure 5 shows an example of the dimensioning of a beam according to the invention.

Figure 6 shows how the I-beam according to the invention can be used as a column and connected to the horizontal beam in a simple manner so that the column chords pp extend by the height uv u of the horizontal beam over the web u u of the horizontal beam and the web u of the horizontal beam by more than the day of the horizontal bar chord.

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