Research On Lectotype And Mechanical Performance Of Monorail Transit Emergency Track Beam

As the vehicle guiding and load bearing structure in monorail transit system, PC track beams (prestressed concrete track beam) may get damaged in the case of emergency situations during operation, resulting to interrupted operation of the monorail transit system. Therefore, it is very necessary to develop an emergency track beam system to facilitate rapid replacement of the damaged PC track beam, thereby reducing the economic losses and social impacts due to the interrupted operation of the monorail transit system.Track beams on the monorail transit serve as both load bearing structure and the guiding track for the vehicle, with the latter realized by the alignment of the track beams. However, in existing monorail transit systems, track beam alignments are very complex, so it is impossible to design emergency track beams individually for all PC track beams. Therefore, in addition to meeting the basic load bearing capacity and stiffness requirements, how to achieve rapid replacement of PC track beams with different alignment characteristics has become a key factor that affects the lectotype of emergency track beams. In this paper, based on the analysis of alignment and load bearing characteristics for PC track beams on the monorail transit, and also considering the characteristics of emergency repair work for PC track beams, the lectotype of emergency track beam for monorail transit is properly selected. The main research contents and contributions are in the following aspects:1) Proposed the alignments and mechanical indicators for emergency track beam for monorail transitThere are two key factors in emergency track beam design, namely how to replace PC track beams with different alignment characteristics and at the same time making sure they have enough load bearing capacity and stiffness. In this paper, firstly, based on analysis of the various factors that influence the design of PC track beams; and statistical analysis of alignments for PC track beams on the existing monorail transit, the types and ranges for the alignment characteristics are summarized for those PC track beams to be replaced by emergency track beams. Secondly, according to domestic and international design standards for monorail transit and considering the special circumstances for emergency track beams, the types of design loads for emergency track beam were analyzed and the limit for the stiffness of emergency track beam was proposed, providing important basis for the lectotype of emergency track beam for monorail transit.2) Study on the alignment replacement methods for emergency track beamOut of all consisting elements of track beam alignment, the most critical ones are the replacements of the plane alignment and beam length of PC track beams by emergency track beams. The alignment replacement concept using segmentally assembled emergency track beam was proposed in this paper, on the basis of which the replacement methods for plane alignment and beam length of emergency track beams are studied. Work has been completed mainly in the following three aspects:â‘ Referencing to the technical parameters of turnout track beam for monorail transit as well as the erection accuracy requirements for track beams, the target replacement precisions for plane curve alignment and beam length are determined;â‘¡According to the plane alignment characteristics of track beams, three different replacement plans are proposed, the parameter equations for track beams under various plane curve alignments are established, and computer programs are created to calculate the plane alignment replacement error. By comparing the errors of the three plans, ultimately a replacement plan using emergency track beams with four different circular curve radii is proposed to realize replacement for all PC track beam plane alignments;â‘¢Based on analysis of the distribution range and distribution characteristics of the length of PC track beams on monorail line, and according to the target adjustment precision for track beam length, a beam length realization scheme for emergency track beam is proposed, that is, select prefabricated emergency beam segments with different lengths and assemble them to achieve an emergency track beam with the proper span. Also, considering the rapidity and economical aspects of the emergency repair work, the types of segment length for emergency track beams are reasonably classified.3) Conducted a research on structural form lectotype for emergency track beams on monorail transitBased on alignment adjustment for wheel-rail contact surfaces of emergency track beams, and also considering the load bearing capacity and stiffness of emergency track beams, the structure of the emergency track beam is designed. By comparing the advantages and disadvantages of various structure forms, ultimately the emergency track beam with assembled segments of prestressed steel box-concrete composite beam is proposed. According to the characteristics of the emergency repair work for track beam, its structural details are studied, mainly including the following aspects:â‘  Based on the basic theory of the elastic buckling of thin plates, along with the mechanical characteristics for the web of composite beams and related experimental studies, the optimal placement of stiffening rib for the web of the steel box for the composite emergency track beam is investigated.â‘¡Based on the torsional resistance theory and combined with related torsional experiments for composite beams, the calculation method for regular tendon reinforcement configuration is analyzed for the composite emergency track beam.â‘¢The configuration, tensioning sequence as well as the tension control values of the prestressed tendons in the composite emergency track beams are analyzed and discussed.4) Built numerical models for composite emergency track beamsUsing the large scale finite element software Abaqus, numerical analysis models are built for the segmentally assembled prestressed steel box-concrete composite emergency track beam. Based on this,5sets of finite element models are built with a total of17composite emergency track beams with different structural design parameters. The influences of structural design parameters, such as reinforcement ratio, axial compressive strength of the concrete, the strength of steel and the plate thickness of the steel box beam, on the bending performance of the composite emergency track beams are investigated. Based on the analysis results with respect to these parameters influencing the bending performance, the structural design parameters for emergency composite track beams are optimized.5) Analysis and evaluation of the load bearing capacity of emergency track beams and their performance under normal useBased on associated computational theory for steel box-concrete composite beams, and along with their specific characteristics, the bending and shear capacities of composite emergency track beams are analyzed and investigated through both theoretical analysis and finite element analysis. Using the established finite element numerical model, the deformation of composite emergency track beams under vehicle load is analyzed. The results show that the load bearing capacity and stiffness of the composite emergency track beam fully meet the operation requirements.