The calculation and design elements of wooden structures and buildings. Until recently, the calculation was made of wooden structures on the allowable stress. Under this method, the calculated stress in a wooden element of operating loads compared with the permitted, the latter is obtained by dividing the tensile strength on the safety factor. In this case the tensile strength was taken on the basis of routine laboratory tests on small wood samples. Influence of the duration of the load of wood defects and other factors on the strength of the wooden structures were estimated to be the safety factor, which had different meanings for the lax, compressed and curved wooden elements. This calculation method gives an indication of the wooden structures at the operational load, but did not give a correct idea of the wooden structures in the state close to destruction. The source of the method of allowable stress of a linear relationship between stress and strain are not applicable in practice for many materials, especially wood, even at low voltages. Ignoring the plastic properties of materials, lack of consideration of the actual conditions of the structure under load, the method of calculation of allowable stress, do not give a correct idea of the true margin of safety.
As a result of extensive research carried out by Soviet scientists had solved the problem of calculating the wooden structures in engineering limit states. This new method calculation takes into account the effect of various circumstances on the strength of the wooden structure. In the method of limit analysis, in contrast to the method of allowable stress, safety factor is divided into a number of individual coefficients, which take into account the probable change in the load (overload factor n), a possible change in material strength (quality factor k) and the peculiarities of the element in the design (Coefficients of working conditions m). This formula takes into account a number of adverse circumstances: a possible increase in operating loads up to the limit values (estimated coefficients of the introduction of congestion to computational effort of these loads), the possible decrease in the strength of the material to the limiting value (taking into account the introduction of the coefficients of uniformity to the regulatory resistance), the impact of working conditions in his element strength in design (stress concentration, changes in carrying capacity due to the form section and so on). The formula expresses the idea that during the operation of wooden constructions, wooden houses, for example, will not come none of the dangerous limit states. According to this formula is determined by the load-bearing capacity of wooden construction (strength, stability, endurance). Analysis of the formula shows that the method of calculation of limit state can take the form of calculation by the method permitted loads. Indeed, applying, for example, the central stretch, we get. Thus, the method of calculation of allowable stress is a special case method of calculating the limit state. In addition to determining the bearing capacity of wooden structures, which is calculated by first limiting state, wooden houses still calculated according to the second limit state, the condition that the operation of a wooden structure there should be no undue strain on the static or dynamic loads. Determination of strain (deflection and vibration amplitudes) wooden structures produced by the efforts of the operational load (no need to overload factor).
As a result of extensive research carried out by Soviet scientists had solved the problem of calculating the wooden structures in engineering limit states. This new method calculation takes into account the effect of various circumstances on the strength of the wooden structure. In the method of limit analysis, in contrast to the method of allowable stress, safety factor is divided into a number of individual coefficients, which take into account the probable change in the load (overload factor n), a possible change in material strength (quality factor k) and the peculiarities of the element in the design (Coefficients of working conditions m). This formula takes into account a number of adverse circumstances: a possible increase in operating loads up to the limit values (estimated coefficients of the introduction of congestion to computational effort of these loads), the possible decrease in the strength of the material to the limiting value (taking into account the introduction of the coefficients of uniformity to the regulatory resistance), the impact of working conditions in his element strength in design (stress concentration, changes in carrying capacity due to the form section and so on). The formula expresses the idea that during the operation of wooden constructions, wooden houses, for example, will not come none of the dangerous limit states. According to this formula is determined by the load-bearing capacity of wooden construction (strength, stability, endurance). Analysis of the formula shows that the method of calculation of limit state can take the form of calculation by the method permitted loads. Indeed, applying, for example, the central stretch, we get. Thus, the method of calculation of allowable stress is a special case method of calculating the limit state. In addition to determining the bearing capacity of wooden structures, which is calculated by first limiting state, wooden houses still calculated according to the second limit state, the condition that the operation of a wooden structure there should be no undue strain on the static or dynamic loads. Determination of strain (deflection and vibration amplitudes) wooden structures produced by the efforts of the operational load (no need to overload factor).
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