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Method of estimating load capacity of arch support steel sets based on the limit load capacity theor |
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Method of estimating load capacity of arch support steel sets based on the limit load capacity theory Author: D. Domańska
A new simplified method for estimating load capacity of steel arch support based on the limit load capacity theory was presented in the article. In particular, the article contains: - main formulas and definitions of the limit load capacity theory (form. 1-8), verifying the possibility of using this theory for determining load capacity of steel arches made of section V (form. 9-13) and assumptions for calculations (ch. 2), - input data for the analysis of the load capacity of steel arches with regard to the limit load capacity method (limiting curve equation for sections V; kind of the probability distribution and value of variation coefficient of yield point of steel using for arches' ŁP production) (p. 3.1), - determination of the theoretical dependences of bending moment on longitudinal force in steel arches in the state of limit equilibrium, procedure of estimating the load capacity construction being accepted with regard to the limit load capacity theory and verification of the calculation method on the basis of stand tests results (p. 3.2), - factors influencing the values of the internal forces appearing in steel arches (p. 3.3.2): modulus of ground compressibility; cross-sectional area of section V; the width of steel arches clear section, the variability of the mean value of the yield point of steel, the length of the loaded steel arch segment referred to the arch span, - the calculation experiments' design (Table 2), variants and calculations cases varying in approach to arch buckling effects and section's plane surface stability in bending with regard to the variability of the yield point of steel (p. 3.3.2), - the calculation model used to create the formulas binding the load capacity of a steel arch and the longitudinal force arising in it with the selected technical factors; method and results of estimating linear regression coefficients (p. 3.3.3), - the selection of dependences for practical usage for estimating the load capacity and the reduced load capacity of steel arch with regard to the strength of the section and the required load capacity of joints and determining a safe range of their application (p. 3.3.4). Determination of the regression coefficients of the functions describing the basic strength parameters of the steel sets of the arch support was done by their modelling in the stiffened state (i.e. without the slide down of joints), in the action conditions of vertical load uniformly distributed on the width being assumed: 0,2 s sub w; 0,6 s sub w and s sub w (s sub w ? width of the steel arch clear section). When taking into consideration the real working conditions of the steel arch, which are characterized by the possibility of the slide down of the arches to each other, the steel arch should be treated as a flexible structure. Therefore, the load capacity of steel arch was considered not only as the ability to carry the external loads by a section, but also as the required load capacity of joints. The load capacity of joints was determined by the characteristic value of the longitudinal force arising on the joint length at the moment of reaching the state of limit equilibrium by the section (form. 32). The values obtained with the use of the considered method are higher than the ones based upon the standard design principles cited in the article. Thus, when designing the steel arch support, taking into account the plastic properties of material makes the use of material more economical. Other features of the carried out method are: - the possibility of quick and easy estimating the load capacity of steel arch support ŁP in the range of the most common variability of the factors influenced it, - adaptation facility with respect to the steel arch sets with another geometry, made of another section and working under different conditions.
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2011