| Underground civil air defense building is an important part of national defense engineering and urban protection system,and response to the modern urban construction development goals of the 14th Five-Year Plan.However,in the process of vigorously building underground civil air defense engineering,there are some large-span buildings such as underground shopping malls,parking and etc.If the traditional reinforced concrete structure is still used,it is difficult to resist the impact load caused by explosions without increasing the geometric size.Largespan prestressed reinforced concrete channel slabs have significant advantages in the construction of underground civil air defense engineering due to the small cross-section,low flexure-to-span ratio and good crack resistance.However,there is a lack of blast resistance research data.In the course of service,civil air defense engineering is susceptible to cracking due to explosion and environmental factor,seriously reduce the bearing capacity of the structure,meanwhile,in order to meet the design requirements of leak-proof and gas-proof,the areas of cracked concrete should be repaired,and the mechanical properties of the repaired structure under impact load still need to be tested.The selection of polymer power to modify cement-based materials can fundamentally inhibit the generation and expansion of cracks.The high temperature mechanical properties of polymer-modified cement should also be tested and evaluated because of the threat of fire before and after explosion.This paper adopts a combination of experimental research and numerical simulation to investigate the dynamic response of prestressed concrete channel slabs for the top slabs of large-span underground civil air defence engineering under the impact of explosion and to propose post-maintenance and anti-cracking measures to provide relevant research basis for the construction of underground defense engineering.The main research contents and results of this paper are as follows.(1)Based on the damage and force analysis results of different sizes reinforced concrete slabs in explosion impact tests,the influence law of explosive weight,aggregate size and reinforcement ratio on the size effect of reinforced concrete slabs under dynamic impact is revealed,which provides the selection range of scale ratio for explosion tests.(2)The plane charge simulation low-altitude explosion test is carried out on the prestressed concrete channel slab under four loading levels.The failure mode and vibration response of the prestressed channel slab under the plane wave are analyzed,the stress distribution and damage mode are given,and the influence law of the positive pressure time of the shock wave is obtained.(3)Coupling agent and curing agent are used to modify the repaired mortar,making it suitable for the repair work of wet concrete surface in underground civil air defense engineering.The influence law of loading conditions,interface roughness and repaired mortar strength on the failure mode of specimens is explored,and the dynamic mechanical properties of repaired materials are tested.The fracture parameters,crack growth forms and energy variation laws of concrete before and after repair are analyzed,and the fitting relationship between dynamic fracture energy and loading rate is given.(4)The influence of ethylene vinyl acetate-ethylene copolymer(EVA)latex powder on the properties of cement stone is studied.The mineral composition,hydration products,distribution of elements of EVA material and the mechanism of action on the cracking resistance,high temperature resistance and microstructure of cement-based materials are revealed.The appropriate dosage of EVA material is proposed through comprehensive test analysis. |
PDF Full Text Request