2 Terms and Symbols 2.1 Terms 2.1.1 Permanent load In the service period of stcture,the value of load is not varied with the time,or the variation of load,which is compared with the mean value,can be neglected,or the variation of load is in one sense and can attainsome limiting value 2.1.2 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,can not be neglected. 2.1.3 Accidental load In the service period of structure,the load is notoccured definitely,once it is occured,that the load is with a significant value and its continuous time is very short. 2.1.4 Representative values 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 quas-pemanent value. 2.1.5 Design reference period The time parameter is selected for determing the represenative values of the variable load. 2.1.6 Characteristic value The fundamental representative value of a load,which denotes the characteristic value for the sta tistical distribution of the maximum load in the design reference period (such as,mean-value,mode, mid-value or certain fractile) 2.1.7 Combination value For the values of variable loads after combination,that their transcendental probability for the load effects in the design reference period can be tended toward indentical with the eponding prob- ability for the load effect of the appearance of single load alone;or the values of variable loads after combination,that the should has the unified stipulated reliability index 2.1.8 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. 2.1.9 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. 2.1.10 Design value of a load The design value of a load is the product of representative value of load and partial safety coeffi-