A Study On Foundation Settlement Difference And Low-rigidity Bearing Application Of The Widened T-beam Bridge

As the widening of the highway bridge is increasing,the uneven settlement of foundation results in additional stress in the superstructure after the connection of old and new part of widened bridge affecting the use and safety of bridges.The actual bridge widening projects are complex and diverse.At present,the foundation settlement pattern is not clearly defined and classified,which is very important for settlement stress and control standard,and the settlement control standard is mainly focused on the simply supported and continuous widening bridges not combined with comparative analysis to accommodate actual projects basically in the study of highway widening bridge.In addition,the current measures to deal with the uneven foundation settlement of widened bridge have the disadvantages of complex implementation,long time or high cost etc.and need to be improved.In order to reduce the adverse effects caused by uneven foundation settlement of the widened bridge,the foundation settlement pattern is simplified into two types,based on a widened bridge to establish model and analyze its basic mechanical properties,it is concluded the control standard.Finally,a new measure to deal with the uneven foundation settlement is proposed and analyzed in the rationality and superiority.In this paper,the main research is as follows:(1)Based on some typical settlement monitoring data and the existing research conclusions,the foundation settlement pattern of the widened part is simplified into two types after analysing reasons: one is the linear settlement,which means the foundation settlement of the widened part increases gradually from the inside to the outside,basically with a linear change,and the outermost settlement can be regarded as an accumulated value;the other the uniform settlement,that is to say,the foundation settlement value of the widened part is almost close,and the settlement can be regarded as the relative settlement value of the old and new T-beams at the junction.(2)Based on a widened T-beam bridge,Midas FEA and Midas Civil are used to establish model and analyze data.It is concluded that the most unfavorable position of the widened T-beam bridge is located at the upper edge of joints of the vertical section of the fulcrum;the best way to connect the old and new T-beams is to set the diaphragms across the joint,but not across the beam-end;and the most unfavorable settlement of the piers is that all the piers in the widened part are all involved in settlement.(3)According to the most unfavorable settlement and the best connection way,whether the maximum tensile stress of the upper structure exceeds the standard value of concrete tensile strength is taken as the control standard in this paper.It is concluded that the allowable settlement differences of the widened part of the simply supported and the continuous T-beam bridges are 8mm and 7mm respectively under the linear settlement,and 3mm under the uniform settlement,which means the relative settlement difference between any two adjacent T-beams,especially between the old and new T-beams should be controlled within 3mm.(4)In order to improve the capacity of widened T-beam bridge to withstand the settlement difference of foundation,it is proposed to set the bearing with low axial rigidity under the connection middle beam of the old bridge(formerly the old bridge' s side beam),it is called low-rigidity bearing.After the application of the low-rigidity bearing,the adverse effect can be neglected.But the maximum stress of widened T-beam bridge decreases by 12.5%-38.1%;and for the widened part of the simply supported and the continuous T-beam bridges,the allowable settlement difference increases by 2mm under the linear settlement,respectively to 10 mm and 9mm,and the allowable settlement difference increases by 1-4mm under the uniform settlement.All these data indicate that the application of the low-rigidity bearing can significantly improve the adverse effects exerted by the foundation settlement difference of the widened T-beam bridge on its upper structure.In addition,the low-rigidity bearing has the advantages of simple implementation,short time and low cost etc.and it is worth popularizing and applying.