The first group concerns losses of general shape and stability, failure, and qualitative changes in configuration of the structure (i.e., ultimate limit states). Appearance of non-allowable residual deformations, displacements, yielding of materials or opening of cracks.
Analysis of structures for the first limit state is performed using the maximum (design) loads and actions, which can cause failure of structures.
The second group concerns states of the structure which worsen their service or reduce durability due to exceeding allowable deflections, deviations, settlements, vibrations, etc. (i.e., service conditions)
Analysis of structures for the second limit state is performed using service (normative) loads and actions. Relation between design and normative loads is referred to as coefficient of load reliability, which is defined in SNiP 2.01.07.- 85 Loads and Actions.
The coefficient of reliability for destination GAMA n according to SP 20.13330.2011 shall be taken in to account determining loads or their combinations.
According to the European standards, the strength of steel is represented by the characteristic value. To obtain the design value, the steel reliability coefficient GAMM is used. The default value of GAMM is 1.0.
Only members from rolled, tube, and roll-formed assortment sections, and compound sections (such as double angles of T-type sections, double channels) are may be designed in STAAD.Pro.
Economy of selected section is indicated by ratio the ration (which can be set using the RATIO parameter) σ/Ryyc presented in calculation results. A section is economical when said ratio equals to 0.9 – 0.95.