Research On Collapse Rupture Factors During The Demolition Blasting Of The Towering Building

During the directional blasting demolition of a brick towering building, security of the directional blasting was influenced seriously by the premature rupture near the middle part of the towering building. Whether the premature rupture appears or not depends on the status of blasting cut shaped instantly. However, for the lack of research on problems such as the premature rupture, most blasting projects still rely on experiential theories. By means of commercial FEA software ANSYS, FEA three-dimensional chimney models are established. And various factors that affect the forming of blasting cut and damage in the middle part of the chimney, including parameters of blasting cut, load of blasting vibration and wind, are deeply analyzed by theoretical methodology and numerical simulation. According to the result of this paper, the design principle of demolition blasting in towering buildings can be proposed and applied to practical blasting projects. And main conclusions can be shown as follows:First, the optimum parameters of blasting cut are presented. In choosing the height of blasting cut, 2 .0 to 3.0 times of the wall widths of a towering building are used instead of from 1.5 to 3.0. And the lengths of blasting cut that range from 62% to 64% of the bottom perimeter of a towering building should be more reasonable than from 60% to 64%. No doubt adopting the upper limit is not suggested, but the conservative percent should not be adopted neither. In addition, echelon is the best shape of blasting cut among echelon, inverse echelon and rectangle.Transient dynamical FEA of ANSYS 5.7 is applied in calculation of demolition blasting. In quantitatively analysis including process of loading and stress distribution along the body of a chimney, load of blasting vibration induced by the forming of blasting cut was analyzed and the premature rupture of upper chimney was certainly affected by it. And it is also the main reason that induces the premature rupture and the reverse collapse of a chimney. Under blasting vibration load, the dangerous zonesrange from 58% to 75% of the chimney body. Considering the situation that the chimney was weathered seriously and the strength was so lower that single charge and blasting delay interval should be well-chosen especially. On the same condition, it is another reason that the premature rupture induced by the low strength of a chimney.Characteristics and calculational methods of wind load are discussed in this paper. The extent of impact of wind load is analyzed quantitatively by means of numerical simulation, especially when the towering building rotates after blasting.The process of stress change near the blasting cut was displayed objectively by the numerical simulation in different solid FEA models. Moreover, results of numerical analysis in blasting vibration load agree with the practical results, which show that ANSYS can be helpful to design and optimize the parameters of demolition blasting.