Experimental Study And Theoretical Analysis On Vertical Load-bearing Performance Of Precast Concrete Roof Structure Of Shallow Silos

Food security is an important part of national security,and in the background of the new era,China has a large demand for food and material reserves,and the scale of the demand for construction of high-standard grain silos is considerable.Shallow silos have low construction cost,small footprint,large storage capacity,high degree of mechanization and automation,stable grain storage,which is easy to meet the requirements of safe grain storage for grain reserves.The traditional shallow silo needs to set up a lot of scaffolding and formwork,which has the problems of difficult construction,long construction period,prohibitive costs,and material waste.Because of the large angle of the conical shell of the silo roof structure,the concrete cannot be pounded conventionally leading to the difficulty of guaranteeing the compactness of pouring,which makes it difficult to guarantee the air-tightness and water-tightness of the silo roof structure and affects the quality of grain storage and even the safety of grain storage.Precast concrete structures have good force performance and can bring practical benefits in social,economic and environmental aspects.Warehouse buildings,such as storage and food factories,have larger spans and simpler shapes,which are suitable for construction and building by precast concrete.Based on the distributed connection fully assembled RC building roof system,the group proposes an assembled reinforced concrete roof structure of silos(referred to as precast concrete roof of shallow silos)with a high degree of component standardization and construction efficiency.The precast concrete roof structure of silos is a conical shell structure with special spatial force state,the force performance of the structure is still unclear,and its promotion and application will be hindered.Therefore,it is of great scientific significance to carry out research on the key technology of precast concrete roof structure of silos to maintain food security in China and to promote the industrialization of grain silo structure.Based on this,the static load test of the standard roof slab of the precast concrete roof structure of silos and the precast concrete roof structure of silos under vertical uniform load were designed and carried out to study the flexural performance of the standard roof slab and reveal the bearing mechanism of the standard roof slab under vertical uniform load;the damage pattern,flexural deformation and strain development of the precast concrete silo roof structure were studied in a systematic way.Based on the experimental research,the force mechanism and damage morphology of the standard fan-shaped roof slab of the precast concrete roof structure of silos and the precast concrete roof structure of silos are revealed,the vertical bearing capacity calculation method of the standard fan-shaped roof slab of the precast concrete roof structure of silos and the precast concrete roof structure of silos are proposed,details are as follows.(1)Through the static force test under vertical uniform load of the standard fanshaped roof slab of the precast concrete roof structure of silos,the vertical bearing mechanism of the standard fan-shaped roof slab of the precast concrete roof structure of silos is revealed,and the vertical bearing capacity design method of the standard fanshaped roof slab of the precast concrete roof structure of silos is established.The damage process,crack generation and development,flexural deformation and strain development law of the shallow silo precast concrete standard fan-shaped silo roof slab were studied to obtain the vertical bearing mechanism of the shallow silo precast concrete standard fan-shaped silo roof slab.The results show that the vertical bearing performance of the precast concrete standard fan-shaped roof slab of shallow silos is good and meets the design requirements.The damage form is typical bending member,with the maximum deflection appears near the span,the span of the slab needs to be considered as a control section for the design of the precast concrete standard fan-shaped roof slab of shallow silos.The vertical bearing capacity design method of precast concrete standard fan-shaped silo roof slab of shallow silos is established,by comparing the theoretical calculation value with the test value,the reasonableness and accuracy of this calculation method is verified.(2)The vertical load-bearing mechanism of the precast concrete roof structure of the shallow silos was revealed through static tests of the full-size model of the precast concrete roof structure of the shallow silos under vertical uniform load.The test results show that the precast concrete scheme and connection technology of the shallow silo roof structure are practical,feasible and have good vertical bearing performance.The mid-span deflection of the structure under the design load is l/465,and no obvious signs of damage appear,which can meet the requirements of bearing capacity limit state and normal use limit state,indicating that the precast concrete silo roof structure has good vertical bearing capacity and stiffness.Under the vertical load,the first crack is the circumferential crack of the roof plate at 2l/5 span from the upper ring beam;under the design load,the cracks of the roof plate are all circumferential cracks with the maximum width of 0.18mm;after loading,the circumferential cracks are basically penetrated and accompanied by a small amount of radial cracks,and the roof plate is in the state of compression-bending stress,which indicates that the plate joint can effectively transfer the transverse plate bending moment.The reinforcement and open plate did not yield under the design load,and no cracks appeared at the nodes of beam-slab connection and slab-slab connection,and all the members and connections were in good working condition.(3)The calculation method of vertical load bearing capacity of the precast concrete roof structure of the shallow silos is proposed.Based on conjugate method,the method of circumferential stiffness calculation of the precast concrete roof structure of the shallow silos is proposed,based on conical shell moment-free theory and moment theory,the vertical bearing capacity design method of precast concrete roof structure of shallow silos is proposed,through the comparison analysis of theoretical calculation data and test data,it is found that the moment theory can solve the displacement of the precast concrete roof structure of the shallow silos accurately in the elastic working stage,and the feasibility of the calculation method of vertical bearing capacity of shallow silo precast concrete roof structure is verified.