Numerical Simulation Study And Optimization Of Bridge Structure In Blasting Demolition

In recent years, bridges which are in danger and needed to be demolished have received much more concern in China. Although blasting demolition technology has been widely used in practice, there is not enough related theoretical guidance for the technology implementation. In order to summarize and optimize a design project of blasting demolition for common piers and bridges, several technologies were applied to the design of bridge blasting demolition, including the analysis on the internal force and geometric construction, strength theory, numerical calculation, computer graphics technology and computer simulation. The main research contents and results are as follows:1. Under the condition that the cut angle meets the criteria of collapsing stress and bending moment, and at the same time, the cut height meets the minimum blasting cut height, the calculation formulas of the cut angle and height were established for the bridge piers with circular and rectangular cross section through mathematical models of piers’ directional collapse. On this basis, the directional collapse effect of solid piers, high hollow thin-wall piers and column piers were optimized by numerical simulation. Finally, the blasting cut parameters of solid pier with rectangular cross section, hollow thin-walled high pier with rectangular cross section and single-column pier with circular cross section were all verified by the calculation formulas, the directional collapsing of these above mentioned piers were successfully realized by simulation results.2. Based on the analysis of shear force, bending moment and axial force of main arch under the gravity action and the caving bending moment of a single-span arch bridge, different blasting design schemes were made according to blasting cuts’ forming sequence in different locations. And then, the blasting demolition processes of reinforced concrete arch bridge and stone arch bridge in different schemes were numerically simulated and optimized, respectively. In this article, some stage forms in collapsing process and cracking effect were extracted and compared with each other, the results show that the single-span arch bridge will successfully be collapsed by placing the blasting cuts in vault and arch springing, and three locations of the blasting cuts can be taken as alternative options, which is the 1/4 across of the main arch, the vault of spandrel arch and spandrel column.3. Based on the analysis of a four-span continuous beam bridge in respects of the bending moment and shear force of main girder under the gravity action, and the design location and forming sequence of blasting cuts, the blasting demolition of the bridge was systematically divided into ten kinds of schemes. Firstly, the caving bending moment of main girders in different cuts of every scheme was briefly analyzed. Secondly, different blasting schemes of the bridge were numerically simulated and optimized. At last, the results of blasting collapsing and falling breaking effect were contrastively analyzed respectively, which show that the falling form of the blasting cuts developing from one side of the bridge to the other at different times present as the domino effect. However, the falling form of the blasting cuts developing from the middle of the bridge to the sides at different times present like symmetrically “W”. The total time during which the cuts formed from the middle of the bridge to the sides takes less than that from one side to the other. The breaking effect can be improved by placing the blasting cuts in the middle span of the main girder. Comparing results of the numerical simulation and the actual blasting demolition effects, it can be found that the results are quite close to each other, which verifies that numerical simulation can guide and optimize engineering practice.4. Based on the analysis of shear force, bending moment and axial force under the gravity action of a three-span rigid frame bridge, the blasting demolition of the bridge was divided into twelve kinds of schemes in accordance with the location and forming sequence of the cuts. The caving bending moment of the main girders and piers in each scheme was analyzed at times when different cuts formed. Afterwards, all blasting schemes of the bridge were numerically simulated and optimized, and the falling process and breaking effect of each scheme was compared and analyzed. The results indicate that the symmetrically “W” and inverted trapezium appear sequentially in the formation of blasting cuts from the middle span of the bridge to the sides at different times. The folding ladder or the continuous oblique appear as blasting cuts forming from one side of the bridge to the other at different times. The total falling time during which the blasting cuts formed from the middle span of the bridge to the sides take less than that from one side to the other. The total falling time can be saved if the blasting cuts formed simultaneously in the consolidation part of the pier and beam and in the bottom of the pier.