Joints of wooden structures. Connections of timber structures: general information

The rafter system is the most complex and one of the most critical elements of the house, the comfort and operation time of the structure largely depends on the correctness of its construction. Calculation and design of the rafter system should be done only by experienced builders or engineers with special training.

It is much more difficult to design a wooden truss system than any metal structure. Why? In nature, there are no two boards with exactly the same strength indicators, this parameter is influenced by a lot of factors.

The metal has the same properties, which depend only on the grade of steel. The calculations will be accurate, the error is minimal. With a tree, everything is much more complicated. In order to minimize the risks of destruction of the system, it is necessary to provide a large margin of safety. Most decisions are made directly by the builders on site after assessing the condition of the lumber and taking into account the design features. Practical experience is very important.

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Construction boards

Why splicing rafters

There are several reasons why rafter splicing is required.

Roof length exceeds standard lumber length... The standard length of the boards does not exceed six meters. If the slope is large, then the boards will have to be lengthened.
During construction, there are many good boards with a length of 3-4 m... To lower the estimated cost of the building and reduce the amount of unproductive waste, you can use these pieces to make the rafters after splicing them together.

Important. It must be remembered that the strength of spliced rafters is always lower than that of whole ones. You need to try to place the splice as close to the vertical stops as possible.

Splicing methods

There are several ways of splicing, definitely no better or worse. Craftsmen make decisions based on their skills and the specific location of the joint.

Table. Methods for splicing rafters.

Splicing method	Brief description of technology
	It is used on boards with a thickness of at least 35 mm. Quite a complex method, it requires practical experience in performing carpentry work. In terms of strength, the connection is the weakest of all existing ones. The advantage is saving lumber. Practically at construction sites it is used very rarely.
	The length of the rafter legs is increased with a lining. The cover can be wood or metal. If the length of two pieces of boards is insufficient in terms of the parameters of the rafter system, then this method allows them to be increased. The butt joint has the highest flexural strength and is widely used during the construction of various structures.
	Overlap. Two boards are fixed with an overlap. The simplest method, in terms of strength, takes the middle position. The disadvantage is that the total length of the two boards must be greater than the design length of the rafter leg.

In this article, we will look at two of the simplest and most reliable splicing methods: butt and overlap. There is no point in touching the oblique cut, it is almost never used due to the large number of shortcomings.

Building code requirements for joining rafters

Inexperienced splicing of rafters along the length can not only sharply reduce their resistance to bending loads, but also cause the complete destruction of the structure. The consequences of this situation are very sad. Building rules provide for certain patterns when choosing the size of fasteners, places for their installation and the length of the plates. The data is taken taking into account many years of practical experience.

Spliced rafters will be much stronger if you use metal studs instead of nails to connect them. The instruction will help you make an independent calculation of the connection. The advantage of the method is its versatility, with its help it is possible to solve problems not only with lengthening the rafters, but also with building up other elements of the roof. Specialized companies performed rough calculations and collected data in a table, but only the minimum allowable parameters are indicated in it.

Diameter and length of studs... In all cases, the diameter of the studs must be ≥ 8 mm. Thinner ones do not have sufficient strength, it is not recommended to use them. Why? In metal joints, the diameter of the studs is calculated for the tensile forces. During tightening, the metal surfaces are pressed against each other so strongly that they are held by friction. In wooden structures, the stud works in bending. Individual boards cannot be pulled together with great force; the pucks fall into the board. In addition, during the change in the relative humidity of the boards, the thickness is changed, due to this, the tightening force is reduced. Bending studs should be oversized. The specific diameter of the stud must be determined by the formula d w = 0.25 × S where S is the thickness of the board. For example, for a 40 mm thick board, the stud diameter should be 10 mm. Although this is all fairly relative, you need to keep in mind the specific loads, and they depend on many factors.
Overlap length of boards... This parameter should always be four times the width of the boards. If the width of the rafters is 30 cm, then the overlap length cannot be less than 1.2 m. We have already mentioned that a specific decision is made by the master, taking into account the condition of the lumber, the angle of inclination of the rafters, the distance between them, the weight of the roofing materials and the climatic zone of the location of the building. All these parameters have a great impact on the stability of the rafter system.
Stud hole spacing... It is recommended to fix the fasteners at a distance of at least seven diameters of the studs; the distance from the edge of the board should be at least three diameters. These are the minimum indicators, in practice it is recommended to increase them. But it all depends on the width of the board. It is impossible, by increasing the distance from the edge, to reduce the distance between the rows of studs too much.
Number of tie rods... There are quite complex formulas, but in practice they are not used. Masters install two rows of studs, taking into account the distance between them, the holes are staggered.

Practical advice. To increase the bending strength of the spliced rafters, the holes of the studs should not be located on the same line, they must be displaced by at least one diameter.

Board splicing

It is much more convenient to do the work on the ground, prepare a flat area. Place bars on the ground - the rafters will have to be cut, you need a clearance for the circular saw. Know the exact length of the rafters before splicing. You need to measure it on the building, use any thin long boards, rope or construction tape. If an error of a few centimeters appears, no problem. When connecting the rafter legs on the roof, this error is eliminated without problems.

Step 1. Lay one board on the blocks, cut the butt off exactly at a right angle. It is better to cut with a hand-held electric circular saw.

Important. Follow the safety instructions, this is a high-speed and very traumatic tool. Never remove the factory guards on the saw blade or disable the electrical overload relays.

The rafter boards are quite heavy, position them during cutting so that they do not pinch the saw blade or break prematurely during cutting. Prepare the second board in the same way. Pay attention that the cut is only at right angles. The ends of the spliced boards should fit snugly against each other over the entire surface, this is necessary to increase the strength of the spliced rafters. The fact is that even if the connection of the studs is loosened, the ends during bending will abut against each other along the entire length of the cut and hold the load. Studs and overhead boards will only keep the structure from creeping along the length.

Step 2. Install two prepared rafter boards next to each other. Prepare the board for the overlay. We have already mentioned that its length should be about four times the width of the board. If the roof slopes have a slight slope, the distance between the rafters is large, and the roof will be insulated with mineral wool, then the bending loads increase significantly. Accordingly, the length of the splicing board must be increased.

Step 3. Place the patch over two side-by-side splice boards. Quite often, the thickness and width of the boards, even from the same batch, differ by several millimeters. If you have such a case, then level the boards from the side to which the crate will be nailed.

Practical advice. The science of resistance of materials says that the thinner the material, the greater its resistance to bending along a thin plane. This means that, for example, five boards placed side by side on an edge with a thickness of 1 cm each can withstand a significantly greater load than one board with a thickness of 5 cm. Conclusion - for splicing it is not at all necessary to cut thick expensive materials, you can use several thin pieces of the required length. There are enough such pieces at any construction site.

Step 4. In a checkerboard pattern and at the specified distances, drill holes for the studs. In order for the individual elements not to move during the drilling of the holes, they must be temporarily fixed to each other. Use long and thin self-tapping screws for this purpose; it is not recommended to hammer nails together. They cut or tear the grain of the wood; the strength of the board decreases slightly. Self-tapping screws do not cut the fibers, but push them apart; after unscrewing the boards, they almost completely restore their original strength characteristics.

Step 5. Drill holes, do not line them up, or the boards may crack during use.

You can find recommendations, after drilling holes, to separate the boards and lay jute between them to prevent the appearance of cold bridges. This is not only wasted work, but also harmful. Why? Firstly, no cold bridges appear at the splice points; on the contrary, they have the greatest thickness and, accordingly, the lowest thermal conductivity. But even if they appear, then there will be no negative consequences, this is the roof rafter system, and not a room window or door. Secondly, jute reduces the frictional force between the splicing elements, and this has a very negative effect on their strength. Thirdly, if condensate gets on the material, which is very likely, then moisture will be removed from it for a very long time. There is no need to tell what are the consequences of prolonged contact of wooden structures with moisture.

Step 6. Insert the studs into the prepared holes, put on washers on both sides and tighten them firmly with nuts. It is recommended to tighten until the washers are pressed into the wood. The excess length of the studs can be cut off with a circular grinder with a disc for metal.

All other rafters are spliced in the same way.

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Electric drills

Overlap splicing

This connection is easier to do, but on one condition - the total length of the two boards allows, it must be greater than the length of the rafter leg by the amount of overlap.

If you have low quality sawn timber, then before starting work, it is recommended to spread them out on a flat surface and make an audit. For long sections of spliced rafters, choose straight ones, and use curves for segments. Although it is highly recommended to buy only quality materials for the rafter system, this is not an architectural element of the building that can be saved on.

Step 1. Select the planks and place them on a raised block of beams. If you want, you can align the ends with a circular saw, if you don't want to - do not align. The condition of the ends does not in any way affect the strength of the overlap splice.

Step 2. Lay the boards on top of each other, adjust the length of the joint and the overall size of the rafters.

Practical advice. The boards should lie on top of each other strictly parallel. Due to the fact that the top rises above the bottom by the thickness of the material, under it and the bars, you should put supports from the segments. The thickness of the segments should be equal to the thickness of the bottom board.

Step 3. Align the boards along one of the edges and temporarily fasten them with self-tapping screws. Drill holes, install studs, washers and tighten nuts.

Plywood butt splicing

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Clamps

One of the ways of splicing rafters helps to save boards and rationally use waste of various lumber. In this case, one centimeter thick scraps of sheet plywood are used.

Step 1. Lay the rafter boards evenly on the site, close the ends, pay attention to the parallelism of the side edges. The boards should be extremely uniform in thickness, the ends are cut exactly at right angles.

Step 2. Apply a generous amount of PVA glue to the surface with a brush.

Step 3. Place the prepared piece of plywood on the splice, press it firmly with the clamps. When fixing, make sure that the plywood does not move from its original place.

Step 4. Using long strong self-tapping screws, screw the plywood to the boards in a checkerboard pattern. The length of the self-tapping screws should be 1–2 shorter than the total thickness of the boards and plywood, their ends cannot protrude from the back side. Be sure to place large washers under the self-tapping screws. Before tightening the screws, drill holes in the rafter. Their diameter should be 2-3 mm less than the diameter of the threaded part of the hardware.

Step 5. Turn the board upside down, place it under the ends of the stand, they should not hang in the air. Remove all installed clamps carefully one by one.

Step 6. Cover the surfaces with glue and place a second piece of plywood on top of them. Clamp it again with clamps.

Step 7. Tighten the screws with great effort.

Important. When tightening the self-tapping screws, pay attention so that they do not run against each other. The offset must be at least three centimeters.

Step 8. Remove the clamps. To strengthen the splice assembly, tighten it with through pins. They should be placed in the same way as for ordinary butt-splice.

Practical advice. The holes for the studs should be 0.5–1.0 mm smaller than the stud diameter. There are times when it is impossible to accurately select the diameter of the drill for wood. Then it is recommended to use a drill with a slightly smaller diameter, let the stud enter with a sufficiently large force.

During its hammering, the first few threads are crumpled from strong hammer blows, which makes it very difficult to tighten the nut. To avoid problems, before driving the stud, tighten the nuts, now let the thread on the end be jammed, it is no longer needed. Check if the glue is dry before reinstalling the rafters. In good weather, it takes about 24 hours to completely solidify.

The final touch is the application of glue

Important. If, during the splicing of the rafters along the length of the boards, the nuts were tightened until the washer was sunk into the wood, then this cannot be done with plywood. Carefully control the pressing force, do not damage the plywood veneer.

How to properly hammer nails into the rafters when splicing

It is not always possible and necessary to splicate individual elements of the rafters with pins, sometimes it is easier to do it with ordinary smooth nails. But you need to be able to hammer them correctly, otherwise, over time, the compression force of the boards will significantly decrease. The length of the nail should be 2.5–3 cm longer than the thickness of the rafters at the junction.

How to drive in nails correctly to connect loaded or critical timber structures?

Step 1. Drive the nail into the planks at a slight angle, but not completely. It is necessary that the tip protrude from the back side by about one centimeter.

Step 2. On the back of the rafter, bend the nail at a right angle with a hammer.

Step 3. Drive the nail in about one more centimeter. Bend the end again, the bend angle should already be much less than 90 °. The more you bend it, the more secure the final fixation will be.

Step 4. Now you can drive in the nail head to the very end. Bend the overhang on the back side until the sharp end is fully inserted into the board. Remember that the point where the body of the nail comes out and the point where the point is driven in should not lie in one line.

This technology completely excludes an independent weakening of the pressing force.

Prices for various types of fasteners for rafters

Fasteners for rafters

It has already been mentioned that the bending strength of the rafters at the splice is always less than that of the whole element. If possible try to place this knot as close as possible to the ridge, Mauerlat or various struts... Such precautions minimize the risks of mechanical destruction of the rafter leg. If for one reason or another there is no such possibility, then it is not recommended to place the stop under the splice at a distance of more than 15% of the leg length from either end.

Never use black self-tapping screws for the connection.... This metal has two significant disadvantages. First, it quickly oxidizes and loses its original strength. The second - the technology of manufacturing such self-tapping screws involves hardening. Hardened self-tapping screws do not stretch when the permissible load is exceeded, but burst. During the operation of the roof, the relative humidity of wooden structures changes, respectively, the thickness of the boards also fluctuates. And this can significantly increase the tensile force of the self-tapping screw, it will not withstand and will crack.

Do not overdo it with the amount of hardware... If there are too many of them, then the holes will significantly reduce the strength of the parts to be joined, as a result, you will get the opposite effect, the build-up will not increase, but will weaken.

Video - Splicing rafters along the length

The coolest joiners and carpenters are said to be able to build a house without a single nail. Japanese artisans, even amateurs, are just that.

A few years ago, a young and passionate automotive industry worker came across a book describing traditional Japanese woodworking techniques. He was very fascinated by the descriptions of the connections of parts without the use of nails, screws and glue. He wanted to learn how to do the same. But there were no diagrams for the manufacture of fasteners in the book. Then the guy decided to draw them himself.

He used the free service Fusion-360 to model and animate the parts. The Japanese translated the resulting result into GIFs and posted it on a Twitter account called The joinery... In almost a year, the young carpenter visualized 85 different types of detachable connections.

The variety of mounts is truly amazing. With their help, you can make basically anything - a stool, a sofa, a table, and so on. The main thing is to have straight arms and a good, preferably electric tool.

But even if the manual labor doesn't inspire you at all, you will probably enjoy watching GIFs. The grace with which the details mesh with each other is mesmerizing.

All photos from the article

In this article, we will provide an overview of the possible options for connecting wood products. And there are a great many such methods, from a simple butt joint to the most complex dovetail joint. It is important to remember that not all of them can be done independently, but the information below will definitely not be superfluous.

Reliable coupling is a guarantee of strength and reliability for any structure

We list the acceptable options

All of them are distinguished by their strength and complexity, for example, the cabinet body is assembled with a seam or butt joint, less often they use a "groove" or "mustache" alignment. But for the manufacture of a door frame or panel, the skill of the spike joint is useful.

The following are the methods for joining wooden parts.

Butt joint of parts

Butt registration is called edge pinning. For this, fasteners and glue are usually used. But the butt joint is not very reliable, so it should be strengthened, which is not so difficult to do.

It is advisable to strengthen the "butt-end" fastening with a metal fastener: corners and self-tapping screws

This method is commonly used when assembling a cabinet front frame, where strength is not important since the frame parts are securely attached to the cabinet itself. The butt joint of wooden structures is usually reinforced with lamellas or dowels, which are able to combine separate parts during gluing.

Fastening of parts "in a mustache"

This combination has some differences from the previous one. When gluing the surface, the parts are beveled at an angle of 45 ° with respect to the axis. The connection of wooden parts "in a mustache" must also be strengthened with additional fasteners.

For your information! Usually, this method of joining is used when it is necessary to join two pieces of molding in a corner.

Strengthening the connection of wood parts

As mentioned above, you can strengthen it with ordinary wooden dowels. Nagelny fortifications are usually made with the help of two pegs, glued into one and the other end of the crossbar, into vertical posts, into the nests corresponding to them. There is a specific instruction for making such connections:

We mark the nests for the dowels:

For clear marking, it is necessary to attach the parts to be fastened to each other.
Draw a line with a pencil, marking the places for the dowels.

Joints of timber elements have the task of tying mating building materials, such as edging beams, so that they do not move relative to each other. According to the position and direction of the connected wooden elements, longitudinal joints and corner joints, as well as joints at branches and crossings, are distinguished. Spatial sheet steel connectors and pre-drilled sheet steel cover plates often replace carpentry joints.

Joints that must transmit forces of a certain magnitude and direction, for example compressive forces, are also called joints of the connected wooden elements as rods, for example, compressed rods. Compressed rods, connected at an acute angle, can be connected at notches. Other joints of wooden structures are made by joining wooden elements using connecting means.

By the type of connecting means, such connections are called nail or bolted, dowel or dowel connections. In wood construction, glued building structures are also used. As they have particular advantages, the use of glued timber structures is of increasing importance.

Longitudinal connections

There are longitudinal connections on supports and longitudinal connections in the span. Above the supports, perpendicular pins are used, a joint "in a paw" and a partially trunnion joint "in a paw" (Fig. 1). To reinforce these joints, flat or round steel construction brackets can be driven in from the top or from the side. Often, wooden elements are joined to the forehead and secured only with construction brackets. If, however, large tensile forces act at the joint, for example at the girders on the roof rafters, then both elements are joined head-on on the support and are connected by side planks or perforated strips of corrosion-protected steel.

Rice. 1. Longitudinal connections

The runs can also be made in the form cantilever-suspended(Gerber runs) or articulated girders... In them, the joint is located in the place determined by the calculation, not far from the support, in which the bending moments are equal to zero and where there are no bending forces (Fig. 2). There the girders are connected with a straight or oblique overlay. The incoming girder is held in place by a screw bolt, also called a hinge bolt. The hinge bolt with washers must take the load from the suspended purlin.

Rice. 2. Longitudinal connections of Gerber girders

Gerber runs with a joint lying on top are impractical, since there is a danger that the runs at the edge of the joint will come off. With a suspended joint, on the contrary, there is no danger of separation.

To connect Gerber girders, spatial elements made of steel sheet are also used, which are also called Gerber connecting elements. They are attached with nails along the frontal abutting ends of the purlins (see Fig. 2).

Corner connections

Corner joints are necessary when two logs or beams in a corner are joined at a right or approximately right angle in the same plane. The most commonly used types of joints are notched trunnions, smooth angled foot and compressed foot (Fig. 3). With the help of cut pins and smooth corner legs, the ends of the thresholds, girders and rafter legs lying on the supports or protruding cantilever are connected. Nails or screw bolts can be used to secure the connections. The compressed paw has planes obliquely entering each other. It is especially suitable for joining loaded, fully supported sills.

Rice. 3. Corner connections

Branches

When branching off, a beam suitable at a right or oblique angle in most cases superficially butts with another beam. In normal cases, a joint on the trunnions is used, and in secondary structures also a joint "in the paw" is used. In addition, timber beams can be joined using metal connecting space elements. In trunnion joints, the trunnion thickness is approximately one third of the bar thickness. The trunnions have a length in most cases from 4 to 5 cm. The groove for the trunnion is made 1 cm deeper so that the compression force is transmitted not through the section of the trunnion, but through a large area of the remaining section of the beams.

When the trunnions are arranged, normal trunnions are distinguished, passing through the entire width of the bar, and protruding(hemp) pins, which are used for connections at the ends of the bars (Fig. 4). If the beams in the connection do not fit at right angles to each other, for example at corner braces, then the trunnion at the brace must be made at right angles to the horizontal (or vertical) structural element (see Fig. 4).

Rice. 4. Connections with trunnions

When installing trunnions in wooden beams and purlins, the trunnion must carry the entire load. It is more advantageous to carry out such compounds using girder shoes made of corrosion-resistant steel (fig. 9). These shoes are secured with special nails in such a way as to prevent them from skewing and turning relative to the docking point. In addition, the cross-section of the beam is not weakened by the trunnion holes.

Cross connections

Wooden beams can intersect in the same plane or with offset planes and be overhead or support. Bars intersecting in one plane can intersect "IN THE PAW" if the weakening of the section does not play any role (Fig. 5). It is advisable to tie intersecting overhead thresholds on the support beams with round dowels (pins) made of solid wood or steel from 10 to 12 cm long (Fig. 6).

Rice. 5. Connection "in the paw"

Rice. 6. Connection with round keys (pins)

The bars joining on the side get good support on the post, if their connection is made "IN PAZ" (Fig. 7). For this, the planes of intersection of both elements are cut to a depth of 1.5 to 2.0 cm. In this case, a non-displaceable connection is obtained, which is fixed with a screw bolt.

Rice. 7. Groove connection

When joining inclined and horizontal beams, as is usually the case when joining rafter legs with girders - thresholds, a cut is made in the rafter leg corresponding to the slope, which is called inset(fig. 8).

Rice. 8. Inset of the rafter leg

The depth of the inset in the rafter legs at a normal section height of 16 to 20 cm is from 2.5 to 3.5 cm. For fastening, one nail is used, penetrating the threshold for a length of at least 12 cm, or a special anchor for attaching the rafters to the girders.

Rice. 9. Steel shoe connection

Cuttings

In the case of notches, a compressed rod entering at an acute angle is connected to another bar using one or more force-transmitting planes on its frontal side. According to the number and position of the force-transmitting planes, a frontal cut, a cut with a tooth and a double frontal cut with a tooth are distinguished.

At frontal cut(also called a frontal stop) the receiving bar has a wedge-shaped notch that matches the shape of the end of the compressed rod (Fig. 10). The frontal plane should run at an angle dividing the obtuse outer angle of the cut in half. The fastening bolt must have the same direction, guaranteeing the joint against lateral displacement. To mark the cuts, parallels are drawn at the same distance from the sides of the corner, which must be halved. The connecting line between the point of their intersection and the apex of the obtuse angle will be the bisector of this angle (see Fig. 10). The position of the fastening bolt is obtained if the distance between the bisector and the end of the cut is divided into three parts parallel to the bisector (see Fig. 10).

Rice. 10. Frontal notch

Under the action of the compressive force, the wood lying in front of the frontal part of the compressed rod works on slice(see fig. 10). Since the permissible stress on a cut of wood along the grain is relatively small (0.9 MN / m 2), the plane of the wood in front of the cut edge (cut plane) should be large enough. Since, in addition, cracking due to shrinkage should be taken into account, then, with rare exceptions, the length of the cut plane should not be less than 20 cm.

At reverse or toothed cut the plane of the notch is cut at right angles to the underside of the compressed rod (fig. 11). Due to the fact that due to the eccentric connection in the toothed groove there can be a risk of splitting of the compressed rod, it is necessary that the free end of the groove does not fit snugly against the support rod and a seam is provided between them.

Rice. 11. Serrated notch

Double cut consists, as a rule, of a frontal cut in combination with a toothed cut (Fig. 12). The direction of the cut planes is the same as for each of the cuttings of this combination. However, the toothed cut in this case must be at least 1 cm deeper in order for its cut plane to be below the cut plane of the frontal cut. The fastening bolt should run parallel to the frontal part of the notch approximately halfway between the bisector and the top of the sharp corner of the joint.

Rice. 12. Double cut

Cutting depth t v is limited according to DIN 1052. For this, the abutment angle (a) and the height h of the bar to be cut out (Table 1) are decisive.

Pin and bolt connections

In the case of pin and bolt connections, wooden beams or boards, touching the sides, are connected by cylindrical connecting elements, such as rod dowels, bolts with countersunk heads and nuts, ordinary bolts with nuts. These rod dowels and bolts must prevent the timber elements from sliding in the joint plane, also called the shear plane. In this case, forces act perpendicular to the axis of the rod dowel or bolt. The dowels and bolts are bending at the same time. In the jointed timber elements, all efforts are concentrated on the inner surface of the dowel or bolt holes.

The number of rod dowels and bolts installed at the junction depends on the magnitude of the transmitted force. In this case, as a rule, at least two such elements should be installed (Fig. 13).

Rice. 13. Connection with rod dowels

In one connection, many shear planes can be located next to each other. According to the number of shear planes, which are connected by the same connecting elements, one can distinguish between single-shear, double-shear and multi-shear dowel and bolt connections (Fig. 14). According to DIN 1052, single-shear load-bearing connections with rod dowels must have at least four rod dowels.

Rice. 14. Bolted connections

For bolted connections, bolts with nuts made of steel with a standard diameter of 12, 16, 20 and 24 mm are mainly used. To prevent the head and nut of the bolt from cutting into the wood, strong steel washers should be placed under them. The minimum dimensions of these washers are given for the different bolt diameters in DIN 1052 (table 2).

In order to prevent splitting of the timber elements to be connected by rod dowels and bolts, these connecting means must be installed minimum distances between themselves, as well as from the loaded and unloaded ends. The minimum distances depend on the direction of force, on the direction of the wood grain and on the diameter of the dowel or bolt db and do (fig. 15 and 16). Bearing bolts with nuts must maintain greater distances between themselves and from the loaded end than in the case of rod dowels and bolts with hidden heads. On the other hand, rod dowels or bolts with hidden heads that are close to each other in the direction of the wood grain should be spaced apart relative to the cut line so that the joints do not crack (see Fig. 15).

Rice. 15. Minimum distances in the case of rod dowels and concealed head bolts

Rice. 16. Minimum distances in the case of bearing bolts

Holes for pins and bolts are pre-drilled perpendicular to the shear plane. For this, electric drills with a parallel movement bed are used. For pins when drilling holes in wood, as well as when drilling holes in wood and metal connectors at the same time, the hole diameter must match the diameter of the pin.

Also, the bolt holes should match the bolt diameter well. The hole diameter must not be increased by more than 1 mm compared to the bolt diameter. With bolted connections, it is bad when the bolt sits loosely in the hole. It is also bad if, due to the shrinkage of the wood, the bolt clamp in the hole gradually weakens. In this case, a backlash occurs in the shear plane, which leads to even greater pressure of the bolt rod on the boundary planes of the walls of the holes (Fig. 17). Due to the associated flexibility, bolted connections cannot be applied indefinitely. For simple structures such as sheds and sheds, as well as forests, they can, however, be used. In any case, in the finished structure, the bolts must be tightened repeatedly during operation.

Rice. 17. Backlash when bolted

Dowel connections

Dowels are hardwood or metal fasteners that are used together with bolts to connect smooth-jointed wooden elements (fig. 18). They are positioned in such a way that they act evenly on the surface of the elements to be joined. In this case, the transfer of forces is carried out only through the dowels, while the bolts provide a clamping effect in the connection so that the dowels cannot tip over. The slats made of flat or profile steel are also attached to the wooden elements using dowels. To do this, use one-sided dowels or flat steel dowels. Dowels come in various shapes and types.

Rice. 18. Connection of wooden elements using dowels and bolts

When installing dowel joints with pressed dowels, first, holes for bolts are drilled in the connected elements. After that, the wooden elements are separated again and, if necessary, a groove is cut out for the main plate. Depending on the construction technology, the dowel is fully or partially driven into the groove of one of the connected elements using a mallet. For the final clamping of the precisely aligned connection, special clamping bolts with a large washer are used. Connections with many or large press-in dowels are clamped using a hydraulic press. When connecting with a large number of dowels, as is the case when making corner joints in frames made of glued board elements, it is more preferable to use round plug-in dowels, since with pressed dowels, the pressing pressure may be too high (Fig. 19).

Rice. 19. Dowel connection in the corner of the frame

Each dowel, as a rule, must correspond to one bolt with nut, the diameter of which depends on the size of the dowel (Table 3). The size of the washer is the same as for bolted connections. Larger or smaller dowels can be used depending on the amount of force acting on the connection. The most common diameters are from 50 to 165 mm. In the drawings, the size of the dowels is indicated by symbols (Table 4).

Table 3. Minimum dimensions in dowel connections
Outside diameter d d in mm	Bolt diameter d b in mm	Distance between dowels / distance from the dowel to the end of the element, e db, in mm
50	M12	120
65	М16	140
85	M20	170
95	M24	200
115	M24	230
The values are valid for the D-type round press-in dowel family.

Table 4. Drawing symbols for special dowels
Symbol	Dowel size
	from 40 to 55 mm
	from 56 to 70 mm
	from 71 to 85 mm
	from 86 to 100 mm
	Nominal dimensions> 100 mm

At placement of dowels it is necessary to adhere to certain distances of the dowels between themselves and from the edges of the wooden elements. These minimum distances according to DIN 1052 depend on the type of plug and on its diameter (see table 3).

Bolts with dowel nuts are almost always guided through the center of the dowel. Only with rectangular and flat steel dowels do they lie outside the plane of the dowel. When tightening the nuts on the bolts, the washers should cut about 1 mm into the wood. For dowel connections, the bolted nuts must be re-tightened a few months after installation in order for their tightening effect to remain even after the wood has shrunk. They talk about a connection with a constant transmission of force.

Load bearing stud connections

Bearing dowel (nail) connections have the task of transmitting tensile and compressive forces. With the help of dowel joints, load-bearing parts can be fastened, for example, for freely supported trusses, as well as structures made of boards and beams. Stud connections can be made with single-shear, double-shear and multi-shear. In this case, the size of the nails must correspond to the thickness of the lumber and the depth of driving. In addition, when placing the nails, certain distances between them must be maintained. Holes must be drilled in the bearing dowel joints in advance. The drilled hole should be slightly smaller than the diameter of the nail. Since the wood does not crack so much, the nails can be placed closer to each other in this way. In addition, the bearing capacity of the nail joint will increase and the thickness of the wood can be reduced.

Single shear dowel connections used when compressed and stretched rods from boards or beams must be attached to the beams (Fig. 20). In this case, the nails pass only through one connecting seam. They are loaded there perpendicular to the bore shaft and can bend if too much force is applied. Since shear forces also arise in the connecting seam in the body of the nail, this section plane is called the cut plane. In the case of paired connection of plank rods on the planes of the main beam, there are two single-shear dowel joints opposite each other.

Rice. 20. Single shear stud connection

At double shear dowel joints the nails pass through three pieces of wood to be joined (fig. 21). Nails have two shear planes, since they are loaded in both connecting seams with an equally directed force. Therefore, the bearing capacity of a double-shear-loaded nail is twice that of a single-shear one. In order for the double-shear dowel joints to not disperse, half of the nails are hammered on one side, and the other half on the other. Double-shear dowel joints are mainly used if the free-standing trusses consist entirely or predominantly of planks or beams.

Rice. 21. Double shear stud connection

Minimum thicknesses of timber and minimum nailing depth

Since thin wooden elements break easily when hammering in nails, boards for load-bearing rods, belts and planks must be at least 24 mm thick. When using nails from size 42/110, use even larger minimum thicknessesbut(fig. 22). They depend on the diameter of the nail. With pre-drilled dowel joints, the minimum wood thicknesses can be reduced than with simple nailing, as there is less risk of cracking.

Rice. 22. Minimum thickness and depth of driving

Removing the tip of the nail from the closest cutting plane is called the driving depth. s(see fig. 22). It depends on the diameter of the nail dn and has a different value for single-cut and double-cut nail connections. Single shear loaded nails must have a driving depth of at least 12d n. However, for certain special nails, a driving depth of 8d n is sufficient due to the higher holding force due to the special profiling. With double shear connections, a driving depth of 8d n is also sufficient. At a shallower driving depth, the bearing capacity of the nails decreases. If the nails have a driving depth of less than half the required, then they cannot be taken into account for the transfer of forces.

Minimum distance between nails

Fastening of formwork, battens and filly, as well as rafters, battens, etc. acceptable with less than four nails. However, in general, at least four nails are required for each seam or multi-cut nail joint designed to transmit forces.

The uniform arrangement of these nails on the plane of the connection is made using nail marks(fig. 23). So that two nails located one behind the other do not sit on the same fiber, they are shifted relative to the point of intersection of mutually perpendicular nail marks by the thickness of the nail in both directions. In addition, the minimum distances must be observed. They depend on whether the direction of force is parallel or across the fibers. Next, you need to monitor whether the ends of the rods or the edges of the wood will be loaded by the force acting in the joint or not. Since there is a risk of cracking with loaded rod ends or edges, large distances from the edges to the nails must be maintained.

Rice. 23. The minimum distance between nails with a single shear connection

At single shear nail connection vertical or diagonal tensioned bar with nails with a diameter of d n ≤ 4.2 mm, the minimum distances shown in fig. 23. When using nails with a diameter d n> 4.2 mm, these distances should be slightly increased. If the nail holes are pre-drilled, then in most cases smaller distances are required.

At double shear nail connections nails are arranged in steps. Between the risks of a single-shear nail connection, additional risks are drawn with a minimum distance of 10d n (Fig. 24).

Rice. 24. The minimum distance between nails with a double shear connection

Device of nail connections

When making nail connections, nails must be driven vertically into the wood. In this case, the head of the nail should only be slightly pressed into the wood so that the wood fibers at the junction are not damaged. For the same reason, the protruding ends of the nails can only be bent in a special way. This should only happen perpendicular to the fibers. To apply the location of the nails, as a rule, appropriately drilled templates made of thin plywood or tin are used. In the case of plywood templates, the holes are made of such a diameter that the heads of the nails can pass through them. In the case of templates made of tin, the locations of the nails are marked with a brush and paint.

Nail connections with steel plates

Nail connections with steel strips can be divided into three types, namely, joints with embedded or outside lying plates with a thickness of at least 2 mm and connections with embedded plates less than 2 mm thick.

Outside overlays usually have pre-drilled holes (fig. 25). They are applied over the joint of the beams or boards at the end and nailed with the appropriate number of wire or special nails. At embedded linings with a thickness of at least 2 mm nail holes must be drilled simultaneously in the wood elements and in the lining. In this case, the diameter of the holes must correspond to the diameter of the nail. Embedded linings less than 2 mm, of which there can be several at the joint, can be punched with nails without preliminary drilling (Fig. 26). Such connections may only be made with specially designed spline tools and only with special approval from the authorities.

Rice. 25. Connection by means of a perforated steel plate-lining

Rice. 26. Nail connection with embedded steel linings (Greim)

Connections with nail gussets

Nail gussets are used for the rational manufacture of wooden half-timbered trusses from single-row sections of wood (Fig. 27). For this, wooden rods of the same thickness are cut to length, impregnated and fitted exactly to each other.

Rice. 27. Connection with a nail gusset

In this case, the moisture content of the wood should not exceed 20%, and the difference in thickness should not be more than 1 mm. In addition, the rods should not have any cuts or edges.

The nail gussets must be positioned symmetrically on both sides and, using a suitable press, press into the wood so that the nails sit in the wood for their entire length. Hammering the nail gusset with a hammer or the like is not permitted.

The fastening with the help of nail gussets creates at the nodal points a connection or joints that are strong in compression, tension and shear without weakening the load-bearing section of the wood. For the transfer of forces, the working area of the connection of the nail gusset is of prime importance (Fig. 28). It corresponds to the contact area of the nail gusset with the wood, with the exception of the edge strip with a minimum width of 10 mm.

Rice. 28. Working area of the connection at the nail gusset

Trusses with connecting rods by gussets are industrially manufactured only by licensed enterprises, delivered ready-made to the construction site and installed there.

All photos from the article

Sometimes, when carrying out construction and other work using wood, it is required to make the elements longer or wider, and very few know how to do this correctly. That is why we will consider how to splicate the board yourself and what methods and techniques exist. It is important to choose the option that best suits a given situation and requires a minimum investment of time and money.

Basic workflow requirements

Before we begin to consider specific options for carrying out work, it is necessary to understand what factors are observed to ensure that the result is expected to be obtained:

Material quality	Everything is simple here: it is impossible to make durable structures from low-quality wood, especially when it comes to joints, if they have knots, damage by woodworms, mold and other problems, then there can be no question of any reliability and durability. Choose the best items so as not to waste energy and money in vain
Humidity	Another overriding parameter that should always be considered. Only dry elements are suitable for work, since high humidity, firstly, reduces the strength, secondly, reduces the adhesion of the adhesive composition when using it, and thirdly, after the end of the work, no one will give a guarantee that in a week or a month the structure will not lead or it will not crack
Connection loads	It is on this indicator that the choice of one or another connection option largely depends, the greater the load, the higher the requirements for the quality of the pairing and the more complicated the process. Therefore, decide in advance which option will be used in order to guarantee a high result.
Using a quality tool	A lot also depends on this, especially when it comes to complex options, when the connection is cut with special devices. They must provide maximum cut quality and maximum joining accuracy, since reliability largely depends on this.

Important!
Remember one simple rule that experts always use: to obtain the best result, it is necessary that the parameters of the elements to be connected be the same, in other words, one type of wood should be used.

Work options

All events of this kind can be divided into two large groups - joining boards in width and length, we will consider them separately and tell you which techniques are the most popular and how to implement them correctly.

Width splice

Of course, the simplest solution would be the shield splice option, so we will start with it, first present a diagram of the main options, and below we will describe them in detail:

The first method involves cutting a cavity with a milling machine, which has a trapezoidal shape and allows you to use the key as a retainer... The plus of this solution can be called reliability, and the minus is the need for a milling machine or the presence of a hand milling cutter for work, you cannot do with a hand tool;
Joining using an end bar, which is connected to the ends of the board using the groove-comb method, is used for elements of short length, since this option provides high reliability of small structures. Again, you will need it for work. With his help, it will be carried out quickly and efficiently;
You can make a cutout along the end, fit a rail under it and put it on carpentry glue., it is also quite an interesting option, which is suitable for small structures;
The last two options involve gluing a triangular strip, only one of them cuts into the end, and the second option involves cutting the end at an angle, you need to choose what is best suited in a given situation.

But if you want to connect the board more securely, then one of the following methods will do:

The second solution is a connection into a so-called mini-thorn, this is a very durable and reliable option, but for work you will need a special cutter, the price of which is high, so this method is chosen by those who have to splicate elements frequently;

If the elements are connected in length not in one, but in two or more layers, then you can use the end-to-end option, such a connection of boards along the length is well suited for multilayer systems, in the figure it is under the letter A;

The traditional version of the groove-comb is often used, here it is important to ensure the optimal configuration of the connection, so the width of the groove and, accordingly, the tongue should not be more than a third of the total thickness of the board, it is important to cut very accurately so that the elements match perfectly, this will significantly increase the strength of the connection;

Important!
When working, a milling cutter is most often used, but the cutters can have a different configuration, you should monitor the condition of their cutting edges and sharpen them or replace them in a timely manner, since the quality of the connection largely depends on the cleanliness of the processing.

You can use the option of cutting at an angle, it is well suited where special strength is not required, but you need to well connect elements that can be used for finishing, etc.;
The triangular spike-groove is in many ways similar to the usual one, only the configuration of the ends differs. It is also important here that the elements are ideally combined with each other, as this will ensure both the accuracy of the pairing and its maximum reliability;
The quarter connection is simple - cutouts are made in half the thickness, the length of the protrusions should not greatly exceed the thickness, the elements are lubricated with glue and compressed until the composition dries, this is a standard procedure for almost all options;
The last type is keyed rallying, it does not differ from the above-described option when carrying out work in width, the requirements are the same.

Conclusion

Connecting the board correctly and reliably means ensuring its maximum strength, it is important to follow all recommendations and use only high-quality materials. The video in this article will show some of the options for carrying out the work visually, and if you have questions or additions - unsubscribe in the comments.