2 Terms
2.0.1 Load
This term generally refers to the concentrated force or distributed forceacting on structures（also called direct action）.
2.0.2 Permanent load
In the service period of structure，the value of load is not varied with the time，or the variation of toad，which is compared with the mean value，can be neglected，or the variation of load is in one sense and can attain some limiting value.
2.0.3 Variable load
In the service period of structure，the value of load is varied with time，or the variation of load，which is compared with the mean value，cannot be neglected.
2.0.4 Accidental load
In the service period of structure，the load does not occur definitely，once it occurs，that the load is with a significant value and its continuous time is very short.
2.0.5 Representative value of a load
Measuring values of a load are adopted for the checking calculations of the limit states in design，such as，the characteristic value，the combination value，the frequent value and the quasipermanent value.
2.0.6 Design reference period
The time parameter is selected for determining the representative values of the variable load.
2.0.7 Design working life
Service life of structures or structural members for intended use without major repair.
2.0.8 Characteristic value/nominal value
The fundamental representative value of a load，which denotes the characteristic value for the statistical distribution of the maximum load in the design reference period（such as，mean-value，mode，mid-value or certain fractile）.
2.0.9 Combination value
For variable loads，the exceedance probability of the combined load effect in the design reference period is consistent with the corresponding probability of separate load effect；or the combined load provides a unified reliability index for structures.
2.0.10 Frequent value
For the value of variable load in the design reference period，that the transcendental total time is in small ratio of stipulated time，or the transcendental frequency is the stipulated frequency.
2.0.11 Quasi-permanent value
For the value of variable load in the design reference period，that the transcendental total time is about one-half of the design reference period.
2.0.12 Design value of a load
The design value of a load is the product of representative value of load and partial safety coefficient of load.
2.0.13 Partial safety factor
A factor used in the design calculation for the specified reliability of structures or members and it is classified into partial safety factor for action（load）and partial safety factor for resistance.
2.0.14 Partial safety factor for load
A factor used in the design calculation for loads.It is classified into the partial safety factor for permanent loads and the partial safety factor for variable loads.
2.0.15 Fundamental combination
When in the calculation of ultimate limit states，the combination of permanent loads and variable loads belongs to the fundamental combination.
2.0.16 Accidental combination
When in the calculation of ultimate limit states，the combination of permanent loads，variable loads and an accidental load belongs to accidental combination.
2.0.17 Characteristic/nominal combination
When in the calculation of serviceability limit states，the characteristic values or the combination values are adopted as the representative values of loads for combination.
2.0.18 Frequent combination
When in the calculation of serviceability limit states，for the variable loads that their frequent values or quasi-permanent values are adopted as the representative values of loads for combination.
2.0.19 Quasi-permanent combination
When in the calculation of serviceability limit states，for the variable loads that their quasi-permanent values are adopted as the representative values for combination.
2.0.20 Reference wind pressure
The reference pressure of wind load，its maximum value of wind velocity with a 50-year mean recurrence interval，can be commonly determined according to the observational data of the 10min mean wind velocity at the 10m height from the open，plane terrain in locality through the probability statistics，while considering the relative air density.
2.0.21 Reference snow pressure
The reference pressure of snow load，its maximum value with a 50-year mean recurrence interval，can be commonly determined according to the observational data of the self-weight of snow cover on the open，plane terrain in locality through the probability statistic.
2.0.22 Tornado
A strong rotating column of air，pending in circle from a cumuliform cloud to the ground or a condensed funnel on the bottom of cloud or rotating dust cloud rising from the ground.
2.0.23 Tornado load
A collective term of three load effects of tornado including wind pressure，differential pressure and impact loads of missiles.
2.0.24 Design reference tornado
A hypothetical tornado used to assess the occurrence possibility in a certain area or on a site.It is featured with an acceptable low probability and is only used for design.
2.0.25 Main building of fossil-fired power plant
A building composed of turbine house，deaerator bay，bunker bay and central control building.
2.0.26 Central control building
A complex building that consists of central control room，electronics room，LV switch gear room，storage battery and uninterruptible power supply，diesel generator room，and rooms providing associated functions.
2.0.27 Main building of conventional island of nuclear power plant
Turbo-generator building，composed of turbine house，deaerator bay and associated auxiliary equipment rooms including condensate polishing room，lube oil storage room and HVAC room.