| The utility tunnel,also known as a comprehensive pipe trench or common trench,refers to the structure and its ancillary facilities built underground to accommodate two or more types of municipal pipelines and its ancillary facilities.It is a modern and intensive urban infrastructure.The precast utility tunnel is a modern and industrialized utility tunnel construction method.Its main structural components are hoisted and assembled by mechanized methods after being produced in a precast concrete factory and transported to the site.Currently,the precast utility tunnel can be mainly divided into four types: integrated precast utility tunnel(IPUT),precast utility tunnel composed of composite slabs(PUTCCS),precast utility tunnel composed of solid slabs(PUTCSS),and precast utility tunnel composed of groove-shaped elements(PUTCGE).Existing studies have shown that the IPUT,PUTCCS,and PUTCSS all have the same mechanical performance as cast-in-place.Nevertheless,the PUTCGE needs to consider the influence of the semi-rigidity of the joints.In the current national standard,only the design regulations for single-cabin PUTCGE are given.The critical calculation parameters in the relevant calculation model need to be determined through experiments,and there is no theoretical calculation model for multiple cabins that considers the semi-rigid effect of joints.The PUTCCS is China’s most widely used structural form of a precast utility tunnel.However,the connection structure of a PUTCCS is complex,and its structural measures need to be optimized and improved.Currently,some research on the mechanical performance of the PUTCCS has been carried out at home and abroad.However,research on the seismic performance of the PUTCCS is limited mainly to static performance.Based on this,this paper conducts experimental research on PUTCGE and PUTCCS and theoretical research on the structural calculation model of PUTCGE.The main research work and achievements are as follows:(1)Full-scale test research on the mechanical performance of PUTCGE jointsThe static load test of three joint bending specimens and the static load test of three joint shear specimens were carried out,focusing on the influence of the thickness of the sidewall and the number of prestresses on the mechanical performance of the specimens.The joint bending test study shows that: The three specimens have experienced three evident stress stages of decompression,working with tension angle and yield failure.The joint surface maintains a flat section state in the range of section height,and bending failure occurs.Increasing the sidewall thickness or increasing the amount of prestressed reinforcement can significantly improve the specimens’ flexural bearing capacity and rotational stiffness.The displacement ductility of the three specimens is above 8.80,and the rotation ductility is above 9.16,all showing good ductility characteristics.The results of the joint shear test show that: All three specimens experienced three stress stages of static friction,belt slip work,and shear failure,and finally,the joint surface was a shear failure.Increasing the sidewall thickness or increasing the amount of prestressed reinforcement can improve the shear bearing capacity of the specimen.However,increasing the amount of prestressed reinforcement is more significant.(2)Full-scale test research on the double-cabin PUTCGE under reversed cyclic loading.The low-cycle repeated load test of 2 full-scale double-cabin PUTCGE specimens(one precast specimen and one cast-in-place comparative specimen)was carried out.The results show that: The final failure modes of the two specimens are all flexural failures,mainly manifested in the collapse and spalling of the concrete cover of the wall slab near the haunch and the steel bar yielding under tension.The plastic hinges of the cast-in-place specimen were first generated on the internal sidewall and then appeared on the external sidewalls;the plastic hinges of the precast specimen were first developed on the interior sidewall and then appeared on the top and bottom slabs.The precast specimens’ positive and negative bearing capacities are 21.8% and 26.6% higher than those of the cast-in-place specimens,respectively.The ductility of the precast specimens and the cast-in-place specimens are 3.35 and 3.46,respectively,with similar displacement deformation capacity.The stiffness degradation trend is the same,and the positive and negative stiffness of the precast specimen is higher than that of the cast-inplace specimen.The energy consumption capacity is slightly higher than that of the cast-in-place specimen.(3)Finite element analysis on joints and structure of PUTCGEBased on the software ABAQUS,the nonlinear characteristics of reinforced concrete materials,the interface characteristics between precast concrete members,and other factors were comprehensively considered.The finite element model of the joints and the precast groove-shaped utility tunnel was established,and the experimental results were carried out.The comparison verifies the rationality of the model.The influence of factors such as pre-compression stress,sidewall thickness,axial compression ratio,effective prestress,friction coefficient,burial depth,and haunch on the mechanical performance of PUTCGE was mainly investigated.The flexural finite element analysis results of the joint show that the flexural bearing capacity and rotational stiffness of the joint increase with the increase of the prestressing stress of the joint surface,the thickness of the sidewall,and the axial compression ratio;the rotational stiffness of the joint increases with the increase of the effective prestressing force.The effective prestress has no significant effect on the flexural bearing capacity of the joint.The shear finite element analysis results of the joint show that the shear bearing capacity and shear stiffness of the joint increase with the increase of the precompression stress of the joint surface,the thickness of the side wall,and the axial compression ratio,the effective prestress and the friction coefficient.The finite element analysis results of the utility tunnel under the lateral load show that the bearing capacity of the specimen decreases with the decrease of the pre-compression stress and effective prestress of the joint surface and increases with the increase of the buried depth.The bearing capacity was reduced by 33.7% if the haunch was canceled.The finite element analysis results of the utility tunnel under the action of the circumferential load show that the bearing capacity of the specimen decreases with the reduction of the precompression stress and the effective prestress of the joint surface.However,compared with the lateral load case,the reduction range is less than Not obvious.The bearing capacity was reduced by 27.7% if the haunch was canceled.(4)Research on the calculation model of the PUTCGEBased on the joint bending test results,according to the structural characteristics of the joint,and considering the influence of factors such as the nonlinear mechanical properties of concrete,the load transfer characteristics of the contact surface,and the prestressing effect of the prestressed tendons,a model that can characterize the joint pressure relief and joint surface tension is established.The joint bending calculation model of the semi-rigid force characteristics of open,prestressed tendon yielding and joint failure is further proposed.A simplified joint rotational stiffness calculation method can calculate the serviceability limit and ultimate limit states.Based on the structural characteristics of the PUTCGE,the stiffness reduction coefficient of the sidewall and the bending moment adjustment coefficient are introduced,and a stiffness reduction calculation method suitable for the double-cabin PUTCGE is proposed.Based on the characteristic that the sidewall joints of the PUTCGE are located in the mid-span of the sidewall,a beam-line model suitable for the analysis of the internal force of the PUTCGE is established.(5)Full-scale test research on PUTCCS joints under reversed cyclic loadingLow-cycle repeated load tests were carried out on four joints of the PUTCCS and four contrasting nodes with cast-in-place,focusing on investigating the influence of prefabrication or cast-in-place,with or without a haunch on the seismic performance of the utility tunnel.The research shows that: All specimens suffered a flexural failure,the exterior joint was concretely crushed and spalled at the ends of the side walls and the roof,and the longitudinal bars at the ends yielded.The concrete manifestation of the interior joint is that the concrete at the lower end of the sidewall is crushed and spalled,and the longitudinal reinforcement is yielded.However,the roof failure is not apparent.For exterior joint specimens,the bearing capacity of precast specimens differs from that of cast-in-place specimens by-16.0% to 2.1%;for interior specimens,the bearing capacity of precast specimens differs from cast-in-place specimens by-7.2% to 5.7%.For the exterior joint specimens,the forward bearing capacity of canceling the haunch angle is reduced by 1.6% to 12.8%,and the reverse bearing capacity is reduced by 17.7%to 29.0%;for interior specimens,the canceling of the haunch angle is reduced by 28.4%to 37.1%.For exterior joint specimens,the ductility of precast specimens differs from that of cast-in-place specimens by-5.7% to-14.5%.For interior joint specimens,the ductility of precast specimens differs from that of cast-in-place specimens by 1.6% to9.7%.For the exterior and interior specimens,the energy dissipation capacity of the precast and cast-in-place specimens is the same.In the latter loading stage,the energy dissipation capacity of the specimen with haunch is slightly larger than that of the specimen without haunch.(6)Full-scale test research on the PUTCCS under reversed cyclic loadingThe low-cycle repeated load test of 3 single-cabin PUTCCS specimens(one precast specimen with haunches,one precast specimen without haunches,and one contrast specimen with cast-in-place haunches)was carried out.They focused on investigating the influence of prefabrication or cast-in-place,with or without haunch,on the seismic performance of the utility tunnel.The research shows that: The final failure modes of the three utility tunnel specimens were all bending failures,and plastic hinges were formed at the upper and lower ends of the sidewalls,which were manifested in the crushing and spalling of the concrete cover of the upper and lower ends of the sidewalls,and the tensile yielding of longitudinal bars;The bearing capacity of the specimen with haunches was close to that of the cast-in-place specimen with haunches,with a difference of 7.8%;the precast specimen without haunches was 24.6%lower than that of the precast specimen with haunches,and the cancelation of the haunch resulted in a significant decrease in the bearing capacity;The ductility of the precast specimen with haunches is close to that of cast-in-place specimens with haunches,with a difference of 2.1%,and the ductility of the cast-in-place specimens without haunches will be reduced by 22.8%;The energy dissipation capacity of castin-place and precast specimens with haunches is the same,while the energy dissipation capacity of precast specimens without haunches is poor.The research results of this paper will provide a basis for the revision of the Shanghai standard "Technical Specifications for Precast Utility Tunnel," as well as the preparation of the CECS standard "Specifications for the Design of Precast Utility Tunnel " and the CECS Standard "Seismic Design Standards for Urban Municipal Precast Utility Tunnel."... |
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