To investigate the damage characteristics of the shield segment of the subway tunnel under impact loading, the combined research method of the light gas gun experiment and the numerical simulation were adopted. The damage conditions of the tunnel shield segments subjected to impact loading were analyzed. By analyzing the stress states of shield segment elements, the failure mechanism of shield segment under impact loading was studied. Results show that with the impact position as the center, the surface of the shield segment specimen is mainly subjected to compression in the radial direction and tension in the circumferential direction, and the compressive strain is greater than the tensile strain at the same monitoring position. Under the impact of bullets with different velocities, the horizontal and vertical dimensions of the impact crater on the front of the segment are not much different. With the increase of bullet velocity, the size of the impact crater on the front of the shield tunnel segment increases and so does the depth of the impact crater. The equivalent diameter of the impact crater increases in a "three-stage pattern" with the increase of the impact velocity of the bullet. Along the bullet impact direction, the element stress state of the shield segment specimen changes from triaxial compression to triaxial tension. When impacted by the bullet, the concrete in the impact side of the tunnel shield segment will be crushed by compression and the concrete in the back of the tunnel shield segment will be damaged by tension. The research results can provide a certain theoretical basis for the impact resistance design of shield segment.

Revealing the failure mechanisms of reinforced concrete beams and columns under drilling and blasting conditions is essential for achieving precise blasting demolition design and accurate assessment of blasting effects. Based on an actual deep foundation pit support beam blasting demolition project, this research investigated the dynamic strain characteristics of the hole wall, near-field zone, and the mid-to-far zones under single-hole blasting conditions through field blasting tests and strain measurements. Through explosion dynamics theory, the study calculated borehole wall pressure, damage factors, and damage zoning characteristics. Results demonstrate that under combined blast stress waves and quasi-static gas effects, reinforced concrete support beams exhibit first compression and then pull′ strain characteristics in borehole walls and near-field concrete, with measured strain curves closely aligning with numerical simulation results at both tensile and compressive peaks. The damage distribution in reinforced concrete beams subjected to blasting exhibited a nonlinear attenuation pattern, characterized by rapid decay in the near-field region and gradual reduction to zero in the far-field region. Both numerical simulations and theoretical calculations demonstrated good agreement in the extent of the crushing and fracture zones, with approximately 10% absolute deviation between the two methods. The theoretical and numerical models developed in this study effectively analyze blast-induced damage zoning, with findings offering valuable references for assessing damage characteristics and affected areas in reinforced concrete components during demolition blasting.

To reveal the propagation characteristics of blasting vibrations induced by blasting demolition of a reinforced concrete support beam in a deep foundation support system, the vibration velocities and frequencies in the horizontal and vertical directions of the support system and the response spectrum characteristic of the enclosure structure of the foundation pit are analyzed based on the monitored vibration data. The vibration test lines were laid in the same and the upper layer to the support beam. The results show that the vibration velocity decays rapidly with the increase of distance. The peak vibration velocity at the blasting layer is 5~7 times than that of the upper layer within 50 m of the blasting area. However, the peak vibration velocity of the blasting layer gradually attenuates to 1~2 times than that of the upper layer outside 50 m of blasting area. Besides, there are obvious differences among the components of vibration velocities in three directions in the blasting layer. The radial component has the largest peak value, which is 2~5 times of the vertical component. On the contrary, the three components of vibration velocities in the non-blasting layer are close to each other. Meanwhile, it is high frequency vibration in the support beam, and the vibration frequency of the blasting layer is slightly smaller than that of the non-blasting layer, and both of them have a steep increase phenomenon in the supporting structure of the foundation pit. When the support beam is demolished by blasting, the short-period response spectrum of the enclosure structure of the foundation pit is obviously beyond the designed spectrum, and the blasting vibrations will have a certain influence on the enclosure structure. The related results can provide references for the design of blasting demolition of support beams, vibration control, and the dynamic response analysis of enclosure structure of a deep foundation pit.

The dynamic response characteristics such as deformation capacity, acceleration, and load transfer of high-rise frame structure buildings under the condition of single column failure in different parts were studied. Firstly, according to the Code for Design of Concrete Structure (GB50010), a 4×6 span 8-story reinforced concrete frame structure model was established by using PKPM design software. Secondly, based on the component removal method, the finite element software SAP2000 was used to calculate the dynamic response characteristics of the frame structure with the failure of different single columns at the first floor, including the center column, long side middle column, short side middle column and corner column. The results show that the plastic angle is less than 6 for all the four column failure conditions, and the structure will not collapse. When the central column fails, the structural stability is the worst, and the probability of continuous collapse is the highest, followed by that of the short side and long side middle columns, and the corner column has the least probability. Under the condition of center column failure, the dynamic impact of the load on the residual structure is the most significant, with a maximum negative acceleration of about 3 g, which is twice as high as that of the short side middle column and the long side middle column. After the failure of the columns, the loads will be redistributed. The axial force will be borne by the adjacent columns, while the stress form of the upper beam will also change from bending to tension, resulting in a catenary effect. In the scenario of the central column failure, the axial force of the adjacent columns will increase by nearly 20%.

To study the continuous collapse resistance and dynamic response characteristics of the structure after the blasting failure of the local columns of the RC frame building, the deformation and stress adjustment process of the beam-column substructures adjacent to the columns were observed in real-time through an on-site blasting test of the central column of a blasting and demolition project of an 8-storey frame building. The PKPM was used to establish the corresponding building model. Meanwhile, the dynamic response characteristics of the remaining structure under the failure of the central column and the resistance to continuous collapse was calculated by the demolition component method and the demolition component method in SAP 2000. The results show that the theoretical value of strain after the blast failure of the center column is about 260 με using the strain-moment theoretical formula. The dynamic strain measured in the field is about 377 με, and the value calculated by the numerical simulation is about 238 με. The results of the dynamic strain by the three methods are relatively close. The computed value of the vertical displacement at the failure point is 3.2 mm, close to the field displacement of 2.67 mm, and the calculated value of the plastic angle is 0.051°, close to the field angle of 0.05°. The remaining structure experienced a significant dynamic impact at the instant of the central column failure, and the acceleration values along the positive and negative directions are roughly the same, with a maximum value of 3.5 m/s. After the failure of the central column, the load redistribution occurs in the remaining structure, and the vertical load originally borne by the central column is shared by the surrounding columns, resulting in a significant catenary effect on the upper beam body.

The impact vibration caused by blasting demolition of tall buildings (structures) may affect the service status of adjacent subway tunnels. In order to demolish a 24 story frame structure building only 6.5 meters away from the subway tunnel, on-site tests and analysis of blasting vibrations and dynamic strains were first conducted. And then, a three-dimensional finite element calculation model was established for analyzing the dynamic response of the subway tunnel structure by ANSYS/LS-DYNA, which can reasonably describe the impact of the collapsed part on the ground during the blasting demolition of the building. Finally, the vibration response characteristics and dynamic stress changes of the tunnel structure under the impact of building collapse were simulated and compared with the field measured data. The research results show that the peak particle vibration velocity (8.61 mm/s) in the subway tunnel caused by the drilling and blasting of the load-bearing columns is greater than the peak particle vibration velocity (4.95 mm/s) caused by the impact of the building on the ground. The main frequency of the blasting vibration and the collapse impact vibration are about 100 Hz and 2 Hz, respectively. The vibration velocity of the subway tunnel under the action of the collapse impact load is equivalent to the structural vibration caused by an earthquake with an intensity of Level Ⅲ (3.82~8.19 mm/s). The low-frequency collapse impact vibration can cause relatively obvious additional dynamic stress to the subway tunnel. The dynamic compressive stress generated in the circumferential direction of the tunnel is about 4 MPa, and the dynamic tensile stress generated in the axial and tangential directions is about 0.4 MPa. The existing cracks may expand, or delamination may occur when the internal damages or construction defects are generated in the tunnel structure under the impact of dynamic tension and compression cycles. The safety allowable particle vibration velocity value of 10~12 cm/s when f<10 Hz required in the current blasting safety regulation (GB6722—2014) is dangerously high, and it should be adjusted in combination with the frequency and dynamic strain characteristics.