One of the main structural elements used for the construction of floors of attics or rooms on the second floor, mainly in low-rise individual construction, is a wooden or metal beam, which simultaneously performs the functions of a floor log and a basis for fixing ceiling coverings. The low cost of initial building materials and the possibility of constructing ceilings without the use of lifting mechanisms contributed to the wide distribution of beam ceilings.
Deflection lag
Entering some, especially old, houses, even with the naked eye, you can notice the deflection of the ceilings of the second, or, less often, the floor of the first floor, which is the result of an incorrect calculation of the bearing capacity of the lag or exceeding the permissible load on the floors. As the practice of operating multi-storey buildings built in the first half of the 50s of the twentieth century, where wooden interfloor floors were used, calls for, by 2000, the deflection of the ceilings was from 70 to 100 mm, which led to the need for major repairs of the building with the strengthening of the load-bearing elements of the floors . And this is provided that an accurate engineering calculation of loads and lag sections is carried out at the design stage. And what can we say about individual buildings, when the calculation of the bearing capacity of the lag was carried out "by eye" on the advice of "competent" specialists.
Very often, the quality of the material used, the excessive moisture content of the wood, the insufficient thickness of the rolled metal from which the beam is made, and many other reasons leading to sagging, for example, the overlap of the second floor under load, also affect the amount of lag deflection. Incorrect calculation of the bearing capacity can lead not only to the occurrence of deflection of the log, but also to the complete destruction of the structure and the collapse of the floor down, and when no one expects it.
When is it necessary to strengthen the lags?
If the owner of the house noticed the sagging of the upper floor, then the first thing to do is to take simple measurements and assess the condition of the structures, the amount of static load in order to determine the amount of sagging of the ceiling or changes in the curvature of the floor in order to decide on the need to strengthen the log.
Any floors under the influence of their own weight, static load of the structures and objects installed on them sag over time. The allowable sagging value is taken as 1:300, that is, if a three-meter beam is bent by 10 mm, there is no reason for concern, but if this value is greater, then measures must be taken to eliminate deformation and strengthen the structure.
Strengthening of metal structures
Metal structures used as floor beams can be reinforced with additional rolled metal products by welding or bolting. To do this, the surface of the floor or ceiling is disassembled, if necessary, adjustable supports are placed under the floor beams to eliminate deformation, and the structure is reinforced with standard rolled metal products of the required section, the calculation of which is performed using special tables and methods.
Reinforcement of wooden elements
Existing structural elements of a wooden floor, depending on their condition, can be strengthened in several ways:
- With the help of overlays from a bar, by performing a simple mathematical calculation, when the width of the existing bar is subtracted from the tabular value of the section of the required floor beam. The beam and beam are fastened with bolts with metal plates that prevent the destruction of wood at the point of attachment and the weakening of the structure. The existing beam is lifted with jacks until a flat floor surface is obtained, after which the overlay and the beam are fastened together;
- Using metal strips 10 mm thick and 10-20% less than the height of the beam as overlays. To prevent deformation of the strip and reduce strength, the number of fastening bolts should be increased by 25% compared to wooden elements. Linings are installed on one or both sides of the beam, depending on the load on the load-bearing elements of the floor of the upper floor;
- Wooden floor beams damaged by insects or putrefactive bacteria can be reinforced with prostheses welded from a bar in the form of a spatial truss, or with the help of a channel of the required size. The channel, installed as a prosthesis, is selected from a standard range of rolled metal, and for the manufacture of a spatial bar truss, it is required to perform a rather complex strength calculation, which only a qualified specialist can do.
- Strengthening the bearing capacity of interfloor structures can be done by installing an additional number of beams, but these works require making holes in the load-bearing walls, which in some cases is difficult to perform.
When using metal elements to reinforce the load-bearing interfloor structures, especially for the destroyed parts to be removed, it is necessary to provide for the installation of elements on which the floorboards of the upper floor will be fixed. The fastening must be reliable and durable, excluding the possibility of loosening and the appearance of squeaks.
Logs reinforced in various ways make it possible to increase the carrying capacity of load-bearing interfloor structures and the overall safety of the operation of existing buildings without significant capital investments and a large amount of construction work.
