Analysis Of Settlement Deformation And Cracking Damage Mechanism Of Viaduct Substructure In Soft Soil Foundation

The construction of roads and bridges in China has experienced great-leap-forward development and achieved historic transformation and breakthroughs.With the passage of bridge service time,bridge structure will inevitably be affected by various factors,resulting in different damage,resulting in the reduction of bearing capacity of bridge structure and other potential safety hazards.With the development of urban construction,a large number of viaduct structures have been constructed and put into use.Visual settlement of soft soil foundation is an important cause of structural settlement,deformation and crack damage,but the behavior mechanism of crack damage caused by soft soil foundation has not been deeply studied.Based on the above situation,this paper relies on an elevated bridge structure detection project,through the actual project settlement deformation and crack damage detection data in-depth analysis,and carries out vehicle load test on the bridge and loading test on adjacent auxiliary lanes.Midas FEA is used to carry out physical modeling and analysis,and to explore the mechanism of settlement,deformation and cracking damage of the structure.The main contents and conclusions of this paper are as follows:(1)Firstly,the basic properties of soft soil and the influence of soft soil foundation on structure are summarized.The basic characteristics of viaduct structure and the simple mechanism of crack propagation of concrete are introduced.The research status of concrete cracking damage is summarized.Based on the fracture damage mechanics of concrete,the damage constitutive model of concrete and the basic theory of concrete cracking are expounded.(2)Relying on the crack damage detection project of an elevated bridge,the existing domestic codes related to settlement deformation and crack damage detection are analyzed and summarized,and the judgment basis of settlement deformation and crack detection of elevated bridge is determined.Based on the crack damage detection data of the viaduct,the crack damage of pier,cap beam and cap of the lower structure is analyzed and judged,and the vertical horizontal deformation data of the bridge deck,cap and beam are analyzed.It is found that the most serious cracking damage components are right pier column 34,cap and cap beam,and the cracking damage severity is consistent with the distribution of settlement deformation,showing that the right-amplitude settlement is greater than the left-amplitude settlement,and the right-amplitude left-side disease is more serious than the right-side disease.It is inferred from the data rules that the causes of cracking damage are the uneven settlement of soft soil foundation and the long-term effect of vehicle loads on bridges and adjacent auxiliary roads.The necessity of field test and finite element simulation is also determined.(3)Based on the analysis of structural settlement,deformation and cracking damage,the position of pier 34 on the right side is selected to carry out the vehicle load test on the bridge and the vehicle load test on the adjacent auxiliary road.Through the analysis and comparison of pier column strain and crack with the change of automobile load on bridge,it is found that the right side pier column of No.34 has compressive strain,and the crack width decreases with the increase of load.This shows that the automobile load on bridge has little effect on the generation of pier column crack,and the residual strain is relatively small,indicating that the bearing capacity of pier column is adequate.Through the comparative analysis of pier and cap No.34 with the change of vehicle load near the auxiliary road,the strain and crack width of pier and column increase with the increase of load,and the change of left pier and column is greater than that of right pier,which is consistent with the field test results.It shows that the soft soil foundation is subjected to the long-term effect of the vehicle load near the auxiliary road,which has an impact on the settlement,deformation and crack damage of the structure.(4)According to the analysis of field test and analysis of field test results,the lower structure of right pier 34 with the most serious cracking damage is selected,and the finite element solid modeling analysis is carried out by Midas FEA.The influence of uneven settlement deformation on the structure is simulated by displacement loading.Through the analysis of concrete stress change,main reinforcement stress change,crack location and development change of cap,pier column and cap beam,it is found that cracks first appear in the left corner of cap,which is consistent with the crack damage of field cap.The variation rule of crack width of pile cap with settlement basically coincides with the measured data of settlement crack of field pile cap.The location and trend of pier cracking coincide with the actual detection.The main reinforcement stress of cap,pier column and cap beam does not reach yield stress,which is consistent with the field test results,indicating that the structural bearing capacity reserve is sufficient.The crack development of the whole structure first appears in the left corner of the cap,and then begins to appear in the right side of the pier column and expand upward with the increase of settlement.The whole process shows that the non-uniform settlement of the soft soil foundation leads to the settlement deformation of the structure and the cracking damage of the structure.The non-uniform settlement of the soft soil foundation is aggravated by the vehicle load near the auxiliary road.