The main provisions of the calculation of the first and second group of limit states

When calculating the 1st group of limit states (carrying capacity), the following condition must be met: F≤Fu

The left side of this equation is a calculated force equal to the possible maximum force in the cross section of an element with the most unfavorable combination of design loads; it depends on the forces F caused by the design loads q for f> 1, combination factors and reliability factors by design purpose P.

The calculated force F must not exceed the calculated bearing capacity of the Fu section, which is a function of the design resistances of the materials and the coefficients of the working conditions bi and si, taking into account adverse operating conditions of structures, as well as the shape and size of the section.

When calculating the 2nd group of limit states:

a) on displacements - it is required that the deflections from the standard load Ä do not exceed the limit values ​​of the deflections Ä u established by

standards for this structural element: L ≤ L u .

The values ​​of Ä u are taken according to SniP.

b) for the formation of cracks - the force from the design or regulatory load must be less than or equal to the force at which cracks arise in the section: F ≤ F with rc . (F - determined by calculation; Fcrc. - determined by SniP)

c) for the opening of cracks - the width of their opening at the level of tensile reinforcement should be less than the marginal opening limit established by the norms acrc, u.

a with rc ≤ a with rc , u = 0.1 - 04mm.

Questions for self-test.

1. Limit - this is the condition of the building structure -

2. Calculation for the first group of limit states -

3. Calculation for the second group of limit states -

four. f -

five. P -

6 b and s -

7 bi and si -

8. Constant loads -

9. Temporary loads -

10. Short-term loads -

11. Special loads -

12. Regulatory loads -

13. Design load -

14. Rb

15. Rs

16. Rsp

17. RBP

18. Rb

19. Rbt