- The essence of buildings on a steel frame
- Range of materials
- Building base
- Insulation and filling systems
- External and internal finishing
- About layout and partitions
Steel-framed buildings are commonly used as warehouses and manufacturing facilities, but the same technology can be applied to residential construction as well. Yes, such a house will have a number of disadvantages, but we will tell you how to level them out, while receiving additional benefits..
The essence of buildings on a steel frame
LSTK stands for “lightweight thin-walled steel structures” and this definition quite accurately reflects the basic technological concept. Few know that the concept of LSTK includes two types of building materials:
- Less than 0.7 mm thick, used for roughing and finishing, i.e. profiled or smooth sheet.
- Thickness from 0.7 to 3 mm – steel profiles designed to form the supporting frame.
Today we will focus on profile systems, they are the most specific and are characterized by high manufacturability of use. Materials for the construction of the frame are not just moldings of galvanized steel. Each part is made individually as a separate part of the structure, that is, cutting and fitting of the frame elements in place is not performed. The customer simply sorts the provided set of products and uses them according to the construction project and assembly scheme.
The advantages and disadvantages of buildings constructed using the LSTK technology are for the most part the same as those of other types of frame structures. This is high accuracy, a significant reduction in the load on the foundation, the ability to do without the use of heavy equipment on the site and complete the construction of the box as soon as possible. An impressive number of utilities can be placed in the cavities of the frame, the walls can contain up to 400 mm of insulation, while the configuration and layout of the building are modified in a variety of ways without compromising the strength and ease of use of the building.
And yet, when getting acquainted with the LSTC technology, it is not so much the construction process itself that is of interest, but the nuances of designing a house kit and the manufacturer’s policy regarding the quality of raw materials and finished products. The material base is extremely important: equipment for bending and cutting metal must carry out the production cycle in an automatic mode without the influence of the human factor. We must not forget about logistics: only careful delivery and completeness of the set of parts can guarantee the absence of complaints and the successful completion of the project..
Range of materials
The so-called thermoprofile is considered to be the main structural element of LSTC buildings. It received such a specific name due to special perforations – notches shifted in a checkerboard pattern, which significantly complicate the transfer of heat in the transverse direction. The rest of the thermoprofile is no different from a conventional steel frame, which is also widely used where there is no need to artificially increase the resistance to heat transfer, for example, at the base of internal load-bearing walls.
All profiles are classified according to a number of characteristics:
- the form;
- metal thickness;
- galvanized layer thickness.
Typically, the profile size is determined by the heat engineering calculation, the maximum possible thickness of the insulation, which is used to fill the cavity of the frame, depends on it. If necessary, the thermal insulation properties of the walls can be enhanced by the outer belt of thermal protection, but this will radically change the thermal mechanics of the walls and the composition of the cake. The shape of the profile determines its purpose: like most frame systems, LSTK includes guides and rack profiles, as well as reinforced purlins and special elements such as gussets and lintels.
Galvanizing class and metal thickness are the main indicators that determine the durability of the structure. This is one of the main disadvantages of the LSTK technology, because neither the buildings themselves, nor the materials used in their construction, are standardized by domestic standards. This trick is readily used by unscrupulous manufacturers, who do not provide sufficient resistance to stress and corrosion..
The thickness of the metal also provides the structure with the necessary strength, which raises the question: how to determine the appropriate type of rolled metal? Independently – no way, for these purposes they use specialized CAD tools. In addition to the design part, such programs have the ability to simulate physical processes for the correct prediction of operational loads..
One of the main arguments in favor of LSTK is a significant reduction in the weight of the building. In this regard, it is assumed that the costs of excavation and foundation construction are lower, but there are a number of reservations.
Firstly, this is mainly typical for almost all frame buildings, as well as for buildings made of sandwich panels. In terms of weight, a steel frame is comparable to a wooden one, although it is characterized by a long service life, providing high stability of geometry. But what is really important is the ability to start assembly work almost immediately, without waiting for the initial settlement of the foundation into the ground.
Secondly, recommendations for the construction of a strip or pile-grillage foundation are not always relevant. If the house needs an exploited basement floor, the construction of the MZLF cannot be avoided, this is the only type of foundation that can cope with lateral soil pressure and frost heaving forces.
In general, a LSTC building can be erected on almost any type of foundation, including pile-screw and slab foundations. One of the benefits of a lightweight steel frame is that it does not require anchoring for anchoring. However, in this case, it is necessary to provide a central zone free of reinforcement, in which the fastening of the guide profiles will be performed..
Insulation and filling systems
The most important disadvantage of buildings on a steel frame is their extremely low degree of thermal protection. On the one hand, this is due to the numerous cold bridges, represented by rack profiles, following through the entire section of the walls, on the other hand, by the limited thickness of the enclosing structures. Also, there is a problem that is typical for all frame houses – ventilation.
In order for a house from LSTK to have high energy efficiency, its construction must be carried out strictly according to technology. There are two options for heat and wind protection, the first and the most popular of which is filling the space between the frame elements with mineral wool with a density of 80-100 kg / m3 in several layers with overlapping joints between mats. This method of warming is called basic, its characteristic feature is that it does not completely solve the problem of cold bridges and airflow.
Another option is to fill free cavities in the walls with foam concrete without reinforcement. This option is optimal when constructing floors: a layer of concrete is poured over profiled sheets, fixed to the beams and serving as a permanent formwork. Also, pouring with concrete is successfully used for walls, due to which all elements of the frame are reliably connected to each other. A significant drawback of concrete filling is an increase in the mass of the building, which can be neglected when building on a MZLF or a monolithic slab of sufficient power.
Although the LSTK formulation reflects the essence of only the load-bearing part of the structure, the technology itself has advanced much further. In particular, it provides for a system of protection against blowing and heat loss due to the use of additional external and internal cladding. As a rule, for these purposes LSU and DSP are used outside, as well as gypsum board or gypsum plasterboard inside the building. Any other rough sheet materials with a sufficiently high strength, low weight and a minimum value of linear deformations can be used. Sheathing is carried out both from the outer and inner sides, while steam and windproof membranes are preliminarily fixed on the frame.
In the case of filling the cavities of the wall frame with concrete, the sheathing can act as a permanent formwork, but at the same time the pouring of the mixture should be strictly dosed to avoid bulging. The surfaces formed by the rough sheathing are quite even, which increases the convenience and speed of finishing work, and in the case of external walls, it allows the installation of an external insulation belt made of expanded polystyrene plates.
External and internal finishing
Steel-frame buildings practically do not limit the developer in the choice of finishing materials. Moreover, due to the high accuracy of the assembly of the structure and the presence of rough surfaces, the tedious work of leveling the planes, correcting the geometry and converting the abutments is not required. The fact that at a 10×10 meters building the diagonal discrepancy fits within 10-15 mm is quite indicative.
On the inner surfaces of the walls, in order to reduce the consumption of materials and the time of builders, it is allowed to replace the rough finishing materials with two layers of moisture-resistant gypsum board, sewn intermittently with overlapping joints. As a result, each room acquires perfectly flat walls and right angles, subsequently it is possible to use any decorative materials: from painting to tiles..
The presence of rough sheet sheathing on the outer walls is required. It performs a combined function, providing insulation protection and acting as a rigid connection for the frame elements. Also, an interlayer of LSU or DSP acts as a kind of damper, smoothing out seasonal and temperature fluctuations in the structure and not allowing them to affect the appearance of the facade. Technologies of both wet and ventilated facades can be used directly for finishing; in this regard, LSTK does not limit the choice.
About layout and partitions
The process of assembling building structures can be briefly described as follows: first, trusses and panels are assembled at the installation site, which are then installed in the installation site and fastened to neighboring modules. Blocks of various configurations can be assembled from LSTK, which makes it tempting to build only a frame box, while ensuring complete planning freedom. However, such a decision in most cases will be wrong..
The fact is that, despite the high strength of the profiles themselves, the rigidity of the entire structure in the assembly remains insufficient. With a relatively small size of the building, this can be neglected by performing diagonal fastening of the walls with a special tape or reinforcing the structure with slopes. However, when it comes to the construction of a multi-storey building, the influence of wind and operational loads can be critical..
It is much more correct to use LSTK also for the formation of internal partitions. Due to the additional ties, the outer frame acquires a sufficiently high strength and rigidity, while there is no need to use complex-shaped trusses designed for a long span in the base of the floors. There are no drawbacks in the idea of assembling at least part of the internal partitions from LSTC, because the assortment of the profile starts with a width of 100 mm, that is, taking into account the cladding, the final wall thickness allows for the correct installation of door blocks.
Of course, it is not easy to decide to build a house using a fairly young technology, because hard earned and accumulated money will be invested in this event. However, LSTK cannot be called a pig in a poke, because today there are already quite a lot of successfully operated facilities, including municipal housing..
Dispelling doubts will be helped by the fact that the LSTC project is always complex, that is, the designer and manufacturer of the frame system is one person who is responsible for the final result. In order not to be disappointed in the lightweight frame, you should strictly follow the assembly technology, use high-quality hardware and not seek to save money by buying profiles of dubious origin.