Design hanging trusses
The contents
The selection scheme of the roof is determined by the climate, rainfall, house construction and more construction experience. Based on the classic gable roof is the use of roof beams, connected at the top of the triangle, the crown or the ridge, and serve as the framework for the sheathing and the actual roof. Are the rafter beam, or rafter feet to form a closed rigid frame, very durable and resistant to precipitation and wind load.
Distinguish naslonnye and hanging the rafters. The main difference in the structure of the rafters is the way in which is transmitted the weight of the roof to the walls. For a simple home, not having the inside of the box bearing interior walls, baffles, there is no way to prop up the ceiling rack, so rafters are based only on the exterior walls. The rafters are called the suspension. Least two support rafters are always connected to each other by the third element – tightening. It is a powerful and strong beam, which allows you to remove the lion’s share of arching loads from the rafters. Hanging rafters are always applied with a puff.
Design of roofs with hanging rafter ↑
There are several basic designs of roofs with hanging rafter:
- A simple triangle without any additional reinforcements;
- Triangular arch design with internal reinforcing mechanisms – grandmother, struts and beams;
- Arched triangular design with a raised cross beam, mansard.
If the frame of the truss system has the additional support of the frame on the inside walls of the house, such call naslonnye rafters. In contrast to the hanging rafters, they are simpler and easier to use and manufacture, use less material but require «slicing» the internal space of the box at home with additional interior walls or nodes. Find application for light roofs of the small houses.
The specific arrangement and design of gable roof on the hanging rafters are largely dependent on the parameters of the building. In Northern latitudes with lots of snow and rain find use high gable roofs with hanging rafter having a small angle vertex of a triangular arch. As a consequence, the application of the steep slope of the roof. The application of the system hanging on the rafters will require a significant increase in the internal nodes of the beams due to significant loads due to the large sail structures.
At southern latitudes, on the contrary, homes have a roof slope of very gentle and light, so I find the use of the roof where the hanging truss legs alternate with naslonnye.
The vast majority of modern buildings finds use mainly the roof structure with roof rafters, it has established itself as the most convenient and practical:
- The interior space of the house not reduced because of the need to provide additional support, as in the case of naslonnye roof truss beams;
- The design turns out stronger, all the power elements of the frame are hidden in the attic space;
- Units of a design simpler and easier to maintain than other schemes.
Versions of the designs with hanging rafters, their schemes and units ↑
It should be noted that the use in the construction of the hanging of the truss bars allows you to apply as a sole for supporting the rafter on the upper part of the stone wall of the usual 50mm oak Board that simplifies and reduces the cost of work.
A simple arch structure without reinforcements ↑
Among the features of the framework it is worth noting two points. The first is the connection node supports with tightening must be performed in compliance with construction norms and rules, namely, the centerline of the beam tightening should take place in the center of the weakened section of the connection. This is well illustrated in the diagram.
The second is the requirement to support location, which is connected to the end rafter leg and tighten in the center of the substrate or mauerlat. More precisely, the imaginary point of intersection of the axes of the beams of the rafters and pull should be located above the longitudinal axis of the backing Board. The height of the crest in the normal version recommended is not above the sixth part of the length of the tightening.
Most often the connection node of the end rafter and end logs of the torque applied method of cutting a single tooth and «double» tooth. The principle of running grooves are well understood from the diagram. The strength of the connection node in both cases is satisfactory, the second variant is used, if the thickness of the beam torque is small, or is less resistant to crushing wood. Sealed the site by using bolting, sheathing boards and nails, or by metal sheets.
The connection nodes prepare and adjust to the lifting beams to the top of the house, followed by only tightening the screws and hammering nails. Most of the work is performed with a template of a pair of rafters on them, mark the holes and places notching.
Skating unit used the so-called pair of ends of roof beams with a small divergence of their axes in the plane of contact, which enhances the rigidity of their connection.
Arched scheme with internal reinforcing elements ↑
According to the above scheme is made, the vast majority of roofs with a span length of roof that exceeds six meters. As a rule, large and high spaces of hangar type. Structurally, it is possible to increase the thickness of the beams tightening to avoid deflection, it is expensive, inefficient and increases the weight of the entire structure. More rational is the use of nodes with additional strengthening beams, redistribute the load. The most common can be called Rigel, grandmother or suspension, and raised a puff. They’re all designed to increase the stability of the arch with hanging rafters.
Suspension often instead of one long beam torque to use two at half the length. Both pieces connect to the Central T-shaped hub. As a rule, at the connection node is added to the fixing – clamp for extra light stand, called a suspension, or grandmother. In fact, this design is identical to the previous, as it does not change the distribution of forces and loads in the hanging rafters. The use of the suspension allows to transfer part of the vertical load on the span to node a ridge connection of rafters hanging.
Large spans automatically entail an increase in the length of themselves hanging rafters. Possible deflection of beams hanging rafters kompensiruet application of the additional node of the struts. Strut braces are installed in pairs and absolutely symmetrical. The attachment point to the suspension is usually a cutout in the body of the beam suspension two identical grooves with the bearing pad. For attachment to the rafters is used, the node’s rigid attachment, similar to the connection of the ends of the tightening and hanging rafters.
Design with a raised puff ↑
Roof hanging on the rafters with a raised puff harder than the previous schemes. Often, these variants have increased the number of connections require more careful measurements and precise coupling elements. The circuit finds application in houses where the attic is scheduled to perform, as attic.
The basis of the scheme is a new use for tightening and attachment points. She raised two thirds of the height of the roof ridge and is rigidly connected by two oblique grooves. This attachment is called «poluskovorodnem» and is additionally enhanced with bolts or spikes. This site requires considerable skill and good practice.
Rigid clamping torque requires the use of special node supports hanging of the rafters. One of the points of support make the moving or «crawling» on mauerlat or reference beam. It is necessary to equalize the loads on the arch structure, if one of the roof slopes will be loaded more than the other. In some cases reference «slides» made with the removal of the end of the rafter over the outside wall plane. Asymmetric stress through hanging of the rafters and fixtures will lead to the alignment position of the second slope of the roof. Often this occurs on roofs with a slope angle higher than 30on in a strong wind.
If in the future the attic room planned insulation and waterproofing of the ceiling, which will carry I-beam torque, the latter increase to installation of the mount Assembly with clamps.