| In recent years,with the rapid development of economy and technology,more and more high-rise buildings inevitably have to be demolished in the process of modern urban renewal and industrial upgrading.At this stage,the main building demolition manual demolition,mechanical demolition,demolition by blasting and other three methods.Manual demolition has the disadvantages of high labor intensity and high construction risk,and is generally not used,mechanical demolition and demolition by blasting is still the preferred solution for high-rise buildings and towering structures,of which demolition and blasting is the preferred method of demolition at this stage because of its safety,efficiency and environmental protection.However,due to the complexity of the damage mechanics of reinforced concrete structures in the demolition process,the theoretical study of structural instability damage and its dynamic response is not deep enough,and the theoretical results at this stage cannot better meet the needs of engineering practice,so that the rationality of the demolition plan is difficult to guarantee,leading to demolition accidents from time to time.Based on a typical demolition project of a high-rise frame structure,the dynamic response characteristics of the structure and the mechanical adjustment mechanism of instability damage under different demolition conditions of reinforced concrete load-bearing columns with single failure and multi-heel failure are systematically investigated by means of field experiments and numerical simulation techniques.The main contents are as follows.(1)The mechanical model of single column failure was established,and the moment distribution method was proposed to be used for the theoretical calculation of the bending moment change at the beam end after the removal of the first floor column.Combined with SAP2000 structural design software,the dynamic response characteristics and internal force adjustment mechanism of the structure after the removal of the single column under four different working conditions were calculated respectively.It is found that the structural stability is the worst when the middle column is removed,and the dynamic impact effect of the building load on the remaining structure is the greatest.And after the column removal,the load will be redistributed and its axial force is borne by the immediately adjacent column,and the axial force of the adjacent column increases by nearly 20% under the middle column removal.(2)Through the numerical simulation of the on-site experiment in the friendly apartment,the finite element software LS-DYNA was used to simulate the mechanical demolition and blasting demolition of a single column under actual conditions,and the dynamic response characteristics of the adjacent structural beam were analyzed,and it was found that the numerical simulation results under the two working conditions showed that the bottom of the beam was also subject to tensile stress at the proximal end and compressive stress at the distal end,and the settlement displacement was 1.71 mm under the mechanical demolition condition and 2.16 mm under the blasting.(3)Relying on the blasting and demolition project of the Friendly Apartment,the dynamic response characteristics of the structure under the mechanical demolition of a single column and the blasting and demolition conditions were analyzed through the field experimental conditions,and the strain changes of the proximal and distal beam bottom of the adjacent beam under the proposed static and dynamic loads were studied.It was found that under both demolition conditions,the structure was subjected to gravity loading and the internal forces were to be redistributed,and the strain at the bottom of the beam at both the proximal and distal ends of the demolished column was a loaded process,with the bottom of the beam subjected to tensile strain at the proximal end and compressive strain at the distal end,and the settlement displacement was 1.73 mm for the mechanical cutting condition and2.67 mm for the demolition by blasting.It is basically consistent with the numerical simulation results,which verifies the reasonableness of the numerical simulation.(4)Taking the friendly apartment building as the object,numerical simulation techniques were used to simulate the mechanical demolition of the high-rise building,and the dynamic response characteristics of the structure under the gradual failure condition of the load-bearing columns of the high-rise building were analyzed.The stress adjustment process of each row of columns and the stress change law at the nodes of beams and columns during the gradual failure of load-bearing columns were analyzed.It is found that as the columns are gradually removed to the outside,the load above is also gradually distributed to the external supporting columns,and the compressive stresses in the external columns become larger and larger.(5)The dynamic response characteristics and internal force adjustment mechanism of the remaining structure during the blasting and demolition of load-bearing columns in high-rise buildings were studied by using field experiments and numerical simulations.The stress change laws of the columns and main beams above the incision zone and the support zone were analyzed.It was found that the columns located in the support zone were mainly subjected to gradually increasing compressive stresses,which were several times of the initial state of the blast initiation.The main beam located in the incision zone forms a cantilever after the column blast,and the rear row of beams undergoes sinking speed difference with the front row of beams due to consolidation,resulting in shearing between adjacent rows of beams and causing the beam-column nodes to twist. |
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