1st International Conference on Transportation Infrastructure and Materials (ICTIM 2016) ISBN: 978-1-60595-367-0
Analysis of Cross Tensioned Concrete Pavement Damage
Guo Chao1, Zhang Minjiang2, Wang Zijing3, Wang Xiaolin4
1Associate professor, Research Institute of Environmental Pavements Material, Shenyang Jianzhu Univ., No.9, Hunnan Road, Hunnan District, Shenyang City, Liaoning, P.R. China; [email protected] 2Professor, Research Institute of Environmental Pavements Material, Shenyang Jianzhu Univ., No.9, Hunnan Road, Hunnan District, Shenyang City, Liaoning, P.R. China; zhangminjiang1 @163.com 3Graduate student, Research Institute of Environmental Pavements Material, Shenyang Jianzhu Univ., No.9, Hunnan Road, Hunnan District, Shenyang City, Liaoning, P.R. China; 459540671 @qq.com 4Graduate student, Research Institute of Environmental Pavements Material, Shenyang Jianzhu Univ., No.9, Hunnan Road, Hunnan District, Shenyang City, Liaoning, P.R. China; 451212071 @qq.com
ABSTRACT: Cross tensioned concrete pavements are constituted with cement concrete slab and prestressed tendons. The prestressed tendons could provide lateral restraint of pavement, make road unit from unconfined to active confined stress state, so as to eliminate transverse joints and constricting the cracking capability of the pavement. Based on concrete fatigue damage development theory, plain concrete and cross tensioned concrete through numerical simulation are constructed, and the mechanism of improve anti fatigue strength of cross tensioned concrete pavements are researched. The result shows prestressed tendons can applying an external force to concrete slab and achieve the target which control from pavement fatigue damage development to improve pavement fatigue resistance.
INTRODUCTION
Cross tensioned concrete pavement can solve problems which caused by transverse joints in plain concrete pavement, prolong the service life of pavement. Scholars have conducted extensive studies. According to fatigue problem of concrete under confined, Song Yupu(2004) established the damage model; Luh-Maan Chang(2012) carried out research on practical application of longitudinal tensioned pavement; Mustaque Hossain(2003) put forward the concept of cross tensioned concrete pavement and analysised by numerical; Qian Zhendong(2000) established prestressed concrete pavement design guidelines; Li Na(2014) carried out studies of indoor and outdoor tests. Plain concrete and cross tensioned concrete are analyzed by numerical simulation, and the influence of stress distribution about prestressed tendons spacing on pavement, proved that cross tensioned concrete pavement can effectively control the early cracks in concrete road surface and improve the anti-fatigue strength of concrete.
THEORETICAL ANALYSIS
The difference and connection between plain concrete pavements and cross tensioned concrete pavements are compared, the reason why cross tensioned concrete anti-fatigue strength improved are obtained. The analysis process is in Figure 1.
893 σ1,pc σ3,pc 31 1 2 σ1 σ2,pc σ2,pc
σ3,pc p pc 2 pc c O 3 σ1 σ3,pc σ1,pc
Figure 1. Mohr Stress Principle.
Fatigue failure of concrete crack is the process of generated - expansion - fracture. Plain concrete pavement resists tensile stresses by its own capacity, as σ3=0 in Mohr, and fatigue cracks developed from initial tension; cross tensioned concrete pavement makes joints appearing later than plain concrete due to active confined stress from cross tendons. Besides, tensile strength of prestressed tendons are much higher than plain steel, which can resist tensile stress from vehicle loading efficiently, ensure the pavement in triaxial compression state is under normal circumstance, so, the rate of fatigue development is lower than plain concrete. This process can be explained by N-S relationship. N-Sequation of concrete fatigue life is shown in formula 1.
Smax 1 RN lg f (1)
Sfmax max /' (2)
R min/ max (3)
f’ ：static strength of concrete; α，β：material constants, obtained from experiments.
Figure 1 shows, plain concrete: σmin=0 ， σmax=σ1,c ， cross tensioned concrete: σmin=σ3,pc，σmax=σ1,pc，when maximum stress level at the same time, the fatigue life of cross tensioned concrete is longer than plain concrete, so as to cracks appearance.
NUMERICAL MODEL Model size Taking concrete pavement for study, regarding it as homogeneous elastic-plastic material, through the probability analysis means to return the fatigue damage constitutive model, confining pressure was used to simulate prestressed. Builds axisymmetric model and determines the stresses in two directions, σ1, σ3. The mesh used CAX4R model. Retard - bonded prestressed tendons of 12.7mm, layout spacing of s= 0.25m, angle of α=30°, A=section area of tendons, σloss=300MPa; the same goes for plain concrete. Model of entity and mesh generation are shown in FIG. 2.
894 con loss A 3 (4) hssin
σ1 =1.58MPa 1.57 5 σ3 =3.5MPa
Cross tensioned 0.2 concrete m
0.25m Figure 2. Model of entity and mesh generation.
Calculation parameters
Table 1. Survey of Traffic Volume.
Models 112 115 117 122 125 1127 Traffic volume/% 0.36 69.89 0.04 0.04 0.22 1.01 Models 1157 12 12Car 15 127 157 Traffic volume/% 0.07 13.85 2.33 1.69 0.29 10.23
Table 2. Traffic Analysis.
Symbol AADT/cars Ps/kN Pmax/kN p/MPa B/cm Parameter 1364 100 350 0.7 21.3
Table 3. Material Properties.
2 Symbol Ec/MPa Es/MPa Fy/MPa μc μs σb/MPa σcon/MPa S/mm Parameter 3.15×104 1.9×105 210 0.2 0.3 1860 1395 98.7
Surveys of traffic volume and material properties are shown in Table 1~Table 3. Axle load spectra were drawn according to survey results which show in FIG. 3.
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Figure 3. Axle Load Spectra.
NUMERICAL SIMULATION ANALYSIS Boundary conditions for unit model: fixed on bottom of pavement structure, vehicle loads applied on the top, prestressed on the side. The nephogram of damage factor, hysteresis loop and stress-strain curve of model are shown in FIG. 4~FIG. 7.
a. Plain Concrete b. Cross Tensioned Concrete
Figure 4. Numerical Simulation Results of compressive damage.
a. Plain Concrete b. Cross Tensioned Concrete Figure 5. Numerical Simulation Results of compressive damage.
damage. 896 Loading number of cross tensioned concrete module is approximately 1.5 times of plain concrete when degree of damage under the same circumstances.
a. Plain Concrete b. Cross Tensioned Concrete Figure 6. Numerical Simulation Results of Hysteresis Loop.
a. Plain Concrete b. Cross Tensioned Concrete Figure 7. Numerical Simulation Results of Stress-Strain Curve.
Comparing the hysteresis loop which from plain concrete with the other, when loads applied, concrete cracks come from pressure, steel tensile yield made stiffness of component reduced, after yielding a second load at the same displacement level, bearing capacity and stiffness of the component were lower than the first time. With the increase of loading number, the hysteresis loop of cross tensioned structure almost entirely coincidence, while the hysteresis loop of unconfined structure pretty full. With the increase of loading number, energy consumption of cross tensioned concrete structure is much fewer, stiffness and strength degradation are slower, and could afford more fatigue loading than the other; when strength and stiffness degradation to a certain extent, hysteresis loops of them come back to full gradually, the loss of stiffness and strength keep increasing, until structural damaged. Besides, each cycle of stress-strain curve can form an obvious hysteresis loop, and generates the corresponding fatigue deformation increment, with the growth of cyclic number, incremental became lower, the same goes for slope. Prestressed still take 1395 MPa, setting angle of 30°, analysis damage factor of different layout spacing of prestressed concrete pavement by simulation, results shown in FIG. 8. As can be seen from the diagram, increasing the distance of prestressed tendons in pavement slab, ratio of prestressed concrete scope and lateral restraint area decreased,
897 making distribution of internal stress uneven, damage factor increased after reloading the same number, and the service life of pavement structure decreased; layout spacing keep increasing, reaching the status of plain concrete which do not need to layout tendon, damage factor reaches the highest level, and then pavement damaged. This paper suggested proper spacing value of prestressed tendons for 0.25 ~ 0.6 m.
Figure 8. Prestressed tendon layout spacing influence on structure damage.
CONCLUSIONS
From embarks of Mohr stresses principle, combined with concrete fatigue crack propagation theory of three stages, based on theoretical research, the following conclusions come out by numerical simulation: Through numerical simulation, prestressed tendons could provide lateral restraint to pavement unit, offset part of the tensile stresses caused by vehicle load on the road, slow down the degradation of pavement structure stiffness and strength, so as to achieve the target of improving pavement fatigue strength by controlling the pavement fatigue damage development. When the pavement thickness unchanged, change the layout of prestressed tendons spacing, can lead to pavement stresses redistribution which affects the ability of the structure under load. Through the numerical simulation, determine the reasonable layout spacing of the prestressed tendon, so as to provide theoretical basis for pavement designing.
ACKNOWLEDGMENTS
This research project was supported by the National Natural Science Foundation of China (No. 51308255, No. E080601), the Colleges and Universities of Liaoning Province Outstanding Young Scholars Growth Plan (No. LJQ2014059), Liaoning Province Research Institute of Environmental Pavements Material.
REFERENCES
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