Stress Analysis And Damage Assessment Of Concrete Under Wind-sand Load

Strong sand-dust storm is a kind of disastrous weather with high harmfulness.Many areas in northwest and north China are the areas with high incidence of sand-dust storm.Severe natural conditions make the concrete structures such as roads,bridges and houses in this region suffer from sand-dust storm for a long time.According to statistics,more than 90 % of the bridges built in Inner Mongolia are damaged by different degrees of sand erosion.Although the wind erosion(the erosion effect of wind sand on concrete,hereinafter referred to as wind erosion)does not cause structural damage,the long-term cyclic effect of wind sand load will cause micro cracks in the cement mortar on the surface of concrete,and material spalling occurs.These a coupling effect with the complex and changeable external environment such as dry-wet cycle,freeze-thaw cycle and carbonization,which accelerates the durability damage of concrete and reduces the service life of the structure.Therefore,it is necessary to deeply study the stress state of concrete model under wind-sand load,and evaluate the material damage caused by wind erosion during the whole life,so as to provide reference for the design and calculation of concrete structure in dust storm areas.The main research contents of this paper are as follows :(1)The numerical model of concrete wind erosion is established to verify the correctness of parameter setting and reduce the dependence of calculation results on mesh size.The average wind-sand pressure obtained by numerical simulation is in good agreement with the existing wind erosion test data,which verifies the rationality of the two-Euler fluid model to calculate the wind-sand two-phase flow.By comparing the numerical calculation wind-sand pressure values calculated of different mesh sizes,it is found that the mesh size in the fluid domain has little influence on the numerical calculation results,and the mesh size of the interface between the fluid domain and the solid domain has great influence on the calculation results.(2)The fluid-structure interaction method was used to study the wind-sand flow field under different wind-sand velocity,sand ratio and sand particle size,and the variation law of wind-sand pressure with wind-sand flow parameters was obtained.The variation law of principal stress of concrete model under different wind-sand load is analyzed,and the calculation formula of maximum tensile stress of concrete model under different windsand velocities is given,which has certain practical significance for determining the principal stress of concrete unit under wind-sand load.The analysis shows that under the change of wind-sand flow parameters,the distribution law of wind-sand pressure on the windward surface of the concrete model is the same,which decreases from the middle area to the surrounding edge.The distribution of the first principal stress on the windward surface of the concrete model under different wind-sand load is also the same,increasing from the middle area to the surrounding edge.(3)The critical wind-sand pressure and the stress state of concrete under the action of critical wind-sand pressure are calculated from the contact mechanics theory and numerical simulation.Based on the theory of contact mechanics,the calculation formula of wind-sand pressure in literature 47 is given,and the calculation results are quite different from those of numerical calculation.Therefore,it is necessary to consider the maximum wind-sand pressure when analyzing the structural stress in wind-sand environment.Under the critical wind-sand pressure,along the windward side to the leeward side of the concrete model,the concrete element is in the three-dimensional stress state of tension-tension-compression,tension-compression-compression and compression-compression-compression.(4)The damage of the windward surface of the concrete model under wind-sand load with different wind-sand flow parameters,such as wind-sand flow velocity,sand content and sand particle size,was studied,and the performance degradation degree of concrete materials within the design service life was evaluated.The variation law of wind erosion on the windward surface of the concrete model under different wind-sand loads is the same,which is corresponding to the distribution law of wind-sand pressure.During the service life of the building structure,the elastic modulus,tensile strength and compressive strength of C40 concrete material have a certain degree of attenuation,and the fatigue damage caused by wind-sand load should be considered in the structural design and calculation.