Niu Yichang 1, Hu Yanhai 2

(1. Henan Communications Science and Technology Research Institute Co., Ltd., Zhengzhou 450006; 2. Sixth Geological Brigade of Henan Nonferrous Metals Bureau of Geology and Mineral Resources, Zhengzhou 4500 16)

With the continuous development of China's social economy, the scale of concrete engineering is gradually expanding. As far as the cement concrete pavement structure is concerned, there are still many problems. For example, cement concrete pavement structure has short service life, serious early damage and low operation efficiency, so it is imperative to improve its reliability. In this paper, the reliability of cement concrete pavement structure is designed and evaluated, hoping to have reference significance.

Cement concrete; Pavement structure; Reliability; Design evaluation

doi 10. 136 16/j . CNKI . gcjsysj . 20 17 . 03 . 046

1 Introduction

At present, China's highway mileage is increasing, but there are still many problems in highway construction, such as short service life and serious damage. The main reasons for this problem are lax construction control, long-term overload use and imperfect design methods. Studying and controlling these reasons can comprehensively improve the quality of highway construction in China. At present, the design parameters used in the design of cement concrete highway pavement are unified and definite design schemes. In order to ensure that the pavement design meets the demand, it is necessary to consider the influence of different environments and road material loads on the design factors. But in fact, the pavement structure system is uncertain, and its measurable parameters (such as pavement design, construction and maintenance) are variable, so it is difficult to choose its deterministic design. If the average value is used, the reliability can only be 50%, which cannot meet the actual demand [1]. Some designers use conservative values for safety reasons, which leads to the final design result being too conservative. If the values of design parameters are selected at will, different design results will change greatly. Probability theory can effectively deal with uncertain factors, and applying probability method to pavement structure design can effectively solve the above problems.

2 Reliability design of cement concrete pavement structure

2. 1 deterministic design method

At present, in the design code of highway concrete pavement in China, the control of fatigue cracking and damage of pavement slab is taken as the standard for designing the thickness of cement concrete pavement. The sum of temperature fatigue stress and load fatigue stress of concrete slab should not be greater than the design bending and tensile strength of concrete pavement. The design standard this time is the comprehensive fatigue damage caused by temperature stress and load stress, so the pavement slab position with the largest comprehensive fatigue damage is taken as the critical load position. The first is the calculation of load stress. The load fatigue caused by the standard load at the critical load position is the product of the following four values, namely, the stress reduction coefficient based on the load transfer capacity of joints, the comprehensive influence coefficient of dynamic load and overload factors on pavement fatigue damage, the fatigue stress coefficient of cumulative fatigue of load stress within the design service life, and the load stress caused by the standard load at the critical load position without considering the load transfer capacity of joints [2]. Secondly, the calculation of temperature stress, because the temperature fatigue stress formed by the temperature gradient at the midpoint of the plate edge is the fatigue stress coefficient of concrete plate under the maximum temperature gradient and the cumulative fatigue effect of temperature stress.

2.2 Probability basis

2.2. 1 Definition of reliability

Structural reliability is measured by the probability of structural reliability. The standard engineering definition of the so-called reliability is the probability that the structure completes the predetermined function under the specified time and conditions. According to the characteristics of pavement structure, the definition of reliability can be considered as: the probability that the pavement performance meets the requirements of a predetermined level within the specified design service time and under the specified environmental traffic conditions [3].

Probability method

Factors such as load, geometric parameters, material properties, accuracy of calculation formula and so on will have certain influence on structural reliability. These factors are random and can be regarded as basic variables, and their structural functions can be expressed by functions, that is, Z=g(X 1, X2, …, Xn), where x is the basic variable, and if z is greater than zero, it indicates that the structural position is in a reliable state; If z is equal to zero, it indicates the limit state of the structure position; If z is less than zero, it indicates that the structural position is in a state of failure. That is, the limit state equation expression bit z = g (x 1, x2, …, xn)= 0；; The probability of structural reliability, failure and limit state can be expressed by P 1, P2 and P3. Because Xn is a continuous variable, we can assume that the distribution function of function z=g(X 1, X2, …, Xn) is a continuous function. Under this condition, we can know from the knowledge of probability theory that P3=0, P2+P3= 1.

2.3 Reliability design method

2.3. 1 Design parameters and their coefficient of variation

Because it is influenced by the heterogeneity of structure and material composition, quality control level and construction technology. The design parameters of pavement structure will fluctuate within a certain range. According to the actual distribution of coefficient of variation, the variation level of each design parameter is divided into three grades: high, medium and low, which are applied to different highway grades, quality control grades and construction technology grades respectively. Due to the characteristics of pavement structure itself, all parameters related to pavement design have been transformed to some extent. Among these conversion parameters, the most significant or decisive ones are: flexural-tensile elastic modulus of concrete, flexural-tensile strength of concrete, slab length, slab thickness, equivalent elastic modulus of top surface of base course, maximum temperature gradient of bottom surface and top surface, and standard axle load times of lanes designed in the initial stage of use (Ec, ZIN, L, H, E 1, J, N0 respectively). In the process of studying their variability, it is assumed that they are independent of each other [4]. Through large-scale investigation, the information of relevant design parameters of different cement concrete pavements is obtained. After many indoor and outdoor experiments, a statistical database is established by using stochastic theory, and the change level of these parameters is obtained. As shown in table 1.

Table 1 coefficient of variation of design parameters

Design parameters low, medium and high variation level variation level design parameters low, medium and high σ in0.10 ~ 0.120.15 ~ 0.180.21~ 0.25ec0./. 3 0 0 .3 5~0 .4 5 E 10。 1 0~0 .2 0 0 .2 5~0 .3 5 0 .4 5~0 .5 0 J 0。 0 4~0 .0 8 0 .0 8~0 . 1 2 0 . 1 5~0 .2 0 h 0。 0 1~0 .0 3 0 .0 5~0 .0 8 0 . 1 0~0 . 1 2 N00。 5 0~0 .8 0 0 .8 0~ 1 .2 0 1 .5 0~2 .00 10。 0 1~0 .0 3 0 .0 5~0 .0 8 0 . 1 0~0 . 1 2

2.3.2 Theoretical reliability and its coefficient of pavement structure

The theoretical reliability of pavement structure is based on the chart and calculation formula given in the specification, and only the reliability of pavement structure affected by the variability of design parameters is considered. The reliability of structural theory can be calculated by reduced integral method and interference theory. As far as the distribution law is concerned, the variability of all design parameters has a unified influence on the theoretical reliability. When the coefficient of variation of any parameter increases, the theoretical reliability will decrease, and the theoretical reliability coefficient can be introduced to consider this influence.

2.3.3 Actual reliability and its coefficient

According to the survey statistics, it can be seen that the actual reliability of pavement deviates from the theory, and the theoretical reliability is greater than the actual reliability, so the theoretical reliability needs to be revised. The concept of reliability coefficient is introduced, and the reliability deviation between them is expressed by the deviation of reliability coefficient, and then the correction of inconsistent deviation is considered. According to this idea, a benign linear relationship between theoretical and practical reliability coefficients F 1 and F2 can be obtained. That is F2=0.506+0.494F 1. Then the reliability design method is established. Therefore, the reliability theory can be used to express the structural design method of cement concrete pavement. The relationship is: the actual reliability coefficient F2= temperature fatigue stress of concrete slab+load fatigue stress, which is not greater than the design bending and tensile strength of concrete pavement slab.

3 Reliability evaluation of cement concrete pavement structure

Compared with the reliability design of pavement structure, its reliability evaluation mainly has the following characteristics: different specified conditions and time, different predetermined functions, changes in vehicle load and pavement bearing capacity [5]. The reliability evaluation of cement concrete pavement structure includes two aspects: new projects and existing projects. As far as new construction is concerned, under normal use and maintenance conditions, the ability to meet the predetermined performance requirements within the predetermined design reference period mainly considers the influence of environmental factors is the reliability of the new pavement structure. The formula is: P(TS)=P{Z(t)≥0, t∈[0, TX]}, where TX is the design reference period. According to the existing highway, its reliability expression is PS (t 1, ts ") = p (z (t 1, t 1) ≥ 0, t ∈ [t 1, t1+ts ". Among them, t 1 and TS "respectively represent the year that the pavement structure has been used and the year that it wants to continue to be used, that is, the service operation reference period. Its reliability is related to the generalized stochastic process of resistance and the stochastic process influenced by the technical conditions of pavement structure performance in use. Its performance evaluation needs to consider pavement damage, construction and maintenance time, bearing capacity of pavement structure, anti-sliding capacity, traffic conditions, smoothness and drainage of pavement subgrade.

4 conclusion

The quality of highway traffic is related to the national economy and people's livelihood. To measure the modernization level of a country, road traffic is an important content. In the past, the structural design of highway cement concrete pavement often used empirical methods and mechanical empirical methods for analysis and evaluation, which was difficult to achieve practical results. The application of reliability theory can effectively promote the improvement of pavement structure design in China and improve the quality of highways in China.

refer to

Fei Zhu, Jiang Tao 1 Zi Jianmin. Reliability design method of cement concrete pavement structure [J]. Highway Transportation Abstracts, 2002 (12):12-14.

2 Tan Zhiming, Yao Zukang and Liu Boying. Reliability design method of cement concrete pavement structure [J]. Highway, 2002(8):7- 10.

Three Jinning cards. Structural reliability analysis of cement concrete overlay old asphalt pavement [J]. Journal of Hebei University of Technology, 2010 (4):105-108.

4, Liu Kai, Wang Xuancang, et al. Structural reliability analysis of asphalt overlay on old cement concrete pavement [J]. Highway Traffic Science and Technology, 2015 (3):1-6+19.

5 feng. Reliability analysis of new cement concrete pavement structure design [J]. Shanghai Highway, 2013 (4): 7-10+19+1kloc-0/.

Reliability design and evaluation of cement concrete pavement structure

Niu Yi-Chang 1, Hu Yan-Hai 2.

(1. Communications Henan Institute of Science and Technology Co., Ltd., Zhengzhou, China 450006; 2. Team 6 of Nonferrous Metals Geological Brigade of Henan Bureau of Geology and Mineral Resources, Zhengzhou, China 4500 16)

With the continuous development of China's social economy, the scale of concrete engineering is gradually expanding. Forced concrete pavement structure, but there are still many problems. For example, it is imperative to improve the reliability of cement concrete pavement structure due to early damage and short service life with low operation efficiency. In this paper, the reliability of cement concrete pavement structure is designed and evaluated, and the importance of references is pointed out.

Keywords cement concrete; Pavement structure; Reliability; Design evaluation

China Library ClassificationNo. U 416.02; U4 16.2 16

Document identification code b

The article number is1007-9467 (2017) 03-0143-03.

Date of receipt: 2016-11-21

Author's brief introduction Niu Yichang (1984 ~), male, from Linzhou, Henan, is an engineer, engaged in the design and research of subgrade, pavement and geotechnical engineering.