CEPIC 2.1.16 Prestressing steel reinforcements-A general call for steel bars,steel wires,and strands which are used in the prestressed concrete structural members. 2.1.17 Degree of reliability-It refers to the measurement for the probability of which the ability of a structure fulfils the expected functions within stipulated time-limil and stipulated conditions. 2.1.18 Safety class-The classes of structures and structural members which are classified according to the degre of severity for the destructive 2.1.19 Design working life-The design stipulation for the time-limit of working period of structures or structural mmbers,which can serve for the expected have no ned of 2.1.20 Load-effect-The reactivity of the structures and structural members are induced by loads. such as defomations and cracks etc. 2.1.21 Combination of load-effects-In the limit states design,it is the stipulated combination for de sign valucs of various load,tos the rliability of the stuctures. 2.1.22 Fundamental combination-It refers to the combination of permanent loads and variable loads in the calculation of utimate limit states. 2.1.23 Characteristic combinntion-In the checking calculation of serviceability limit states,that the characteristic values and combination values of variable loads are used as the represenive values of variable loads in combination. 2.1.24 Quasi-permanent combination-In the checking calculation of serviceability limit states,that theuas-pemanent values of variable oadsareused as the represenative values of the variable loads in combination. 2.2 Symbols 2.2.1 Material properties -modulus of clasticity of concrete; E modulus of fatigue deformation of concrete; E. C20 strength grade with characteristic value of cube/mm fa -compressive strength of 150mm side length concrete cube during period of construc tion; characteristic value side fcharacteristic value,design value of axial compressive strength of concrete respec tively; characteristic valucs of axil comressive strength,axial tensile strength of conret during period of construction respectively; fkJu一 characteristic values of strength of ordinary steel reinforements,prestressed stee design values of tensile strength,compressive strength of ordinary steel reinforce