Reinforced concrete slabs, as the main load-bearing components in the structure of construction projects, are very likely to suffer serious damage in explosive accidents, while polyurea elastomers, with their better anti-blast and anti-impact properties, have been widely used in the field of protective engineering. It is well known that the mechanical properties and deformation mechanisms of thin slabs in the range from 100 mm to 250 mm and thick concrete slabs above 250 mm are not the same, and the thickness of reinforced concrete substrates studied so far is generally concentrated in the range from 100 mm to 250 mm, and there are relatively few studies on thick slabs of polyurea-coated reinforced concrete with a slab thickness of 250 mm or more. In order to study the anti-blast performance of the polyurea/reinforced concrete thick slab composite structure, firstly, the contact explosion experiments were carried out on the polyurea/reinforced concrete thick slab composite structure with different charges, while the overall and local damage characteristics were analyzed. Secondly, numerical simulations were carried out using LS-DYNA finite element simulation software to verify the correctness of the numerical model by comparing with the experimental results. Based on LS-DYNA finite element simulations, the damage process of polyurea/reinforced concrete thick plate composite structure and the evolution of shock wave inside the polyurea/reinforced concrete thick plate were investigated, which revealed the anti-blast mechanism of the polyurea coating, and further analyzed the damage mode and damage characteristics of the polyurea/reinforced concrete thick plate composite structure. The experimental and finite element results showed that the polyurea/steel-reinforced concrete composite structure exhibited six damage modes under the contact explosion load (i.e., crate; spall; spall and bulge; threshold spall, bulging deformation of the polyurea coating; severe spall, serious bulging deformation of the polyurea coating; perforation). The investigation also demonstrated that the backside polyurea-coated reinforced concrete thick slabs effectively improved the anti-blast performance of the composite structure. The results of the study can provide a basis and reference for the design of blast resistance of polyurea/reinforced concrete thick slab composite structures.

In order to study the anti-explosion performance of a single-room reinforced concrete building under internal explosion loads, a full-scale reinforced concrete single-room building, whose dimensions were 4m×4m×3m, was designed and constructed. For the internal explosion test, 3 kg TNT was placed in the geometric center of the room. Sensors were installed at the center of the shear wall and roof to record data and analyze the damage characteristics of the single-room structure. In addition, an anti-explosion numerical model of the reinforced concrete single-room structure was established and verified using the LS-DYNA software. The weight of the explosives in the numerical model was changed to study the damage process and shock wave propagation law of the single-room building. Based on the experimental and simulation results, the damage modes of the single room structure were categorized by the dimensionless weighted parameter D_r, and relevant empirical formulas were obtained through data fitting. The results show that when 3 kg TNT explodes in the geometric center of the room structure, the single-room structure exhibits roof bulging, with long cracks appearing along the roof edges. However, the whole structure does not collapse; Under the internal explosion condition, the local damage characteristics of reinforced concrete buildings are not only closely related to the explosive yield, but also significantly affected by the design of structural connection nodes and structural details; Due to the delayed dynamic response of reinforced concrete, the next shock wave has acted on the building before the last shock wave has reacted obviously, which subjects it to multiple impacts within a very short time; By varying the charge weight, five damage-aggravating modes (Model Ⅰ to Model Ⅴ) were identified. The five damage modes were quantitatively defined using the weighted parameter D_r, and a function curve relating it to the explosive equivalent was fitted.

Because of the difficulty in obtaining granite materials and the high cost of conducting penetration tests on granite targets, an equivalence study between reinforced concrete and granite targets was carried out. To establish the equivalence relationship between the two target types, dimensional analysis and a modified compensation method were adopted, with the projectile residual velocity taken as the equivalence criterion, and a computational method for determining equivalent thickness was derived. Based on existing experimental data, numerical models for medium-velocity projectile penetration into reinforced concrete and granite targets were developed and validated using the LS-DYNA software. By varying the projectile impact velocity and target thickness in the numerical simulations, the similarities in damage characteristics between reinforced concrete and granite targets were systematically investigated, and the corresponding failure regions were classified. On the basis of the simulation results, specific equivalent design formulas for granite and reinforced concrete targets were obtained through data fitting. The results show that the established numerical models can accurately predict the projectile residual velocity and reproduce the failure characteristics of both target types during penetration. Compared with reinforced concrete, granite exhibits a smaller compaction zone and tunnel diameter, finer and longer cracks with higher propagation velocities, larger surface crack areas, and a greater tendency to form large spallation craters. Under identical penetration conditions, granite targets and reinforced concrete targets of equivalent thickness display similar failure characteristics, and both can be divided into five distinct failure regions. Through dimensional analysis and compensation correction, a dimensionless residual-velocity function for projectile penetration into reinforced concrete and granite targets was derived, together with an equivalent thickness formula relating the two materials. The fitted equivalent thickness coefficient between granite and reinforced concrete was determined to be 1.699 66. Validation of the proposed equivalence formula indicates that the residual-velocity error between the prototype and equivalent model targets is less than 5%. These results provide a useful reference for the equivalent design of rock targets subjected to medium-velocity projectile penetration and offer a systematic methodology for substituting reinforced concrete for granite in related experimental and engineering applications.

Rock materials are extensively employed in protective engineering and various civil-works structures such as tunnels; investigating their dynamic mechanical behaviour is therefore of great significance. Red sandstone from a stone quarry in Jinan, was selected as the test material. A triaxial testing machine and a split Hopkinson pressure bar (SHPB) apparatus were used to study the mechanical properties of the sandstone under different confining pressures and strain rates, respectively. On the basis of the static and dynamic test data, the parameters of the Holmquist-Johnson-Cook (HJC) constitutive model for red sandstone were calibrated. Using these calibrated parameters, a finite-element model of the dynamic compression test on a large-diameter SHPB was established; verification was performed by comparing the numerical results with the experimental results in terms of both the failure pattern of the red sandstone and the corresponding stress-strain curves. The results show that: (1) under confining pressure, the propagation direction and extent of internal cracks are constrained, preventing rapid crack penetration, so that the peak stress increases with increasing hydrostatic pressure; (2) under different loading air pressures, red sandstone exhibits a pronounced strain-rate effect, with both dynamic compressive and splitting tensile strengths positively correlated with the average strain rate; (3) analysis of the dynamic increase factors for compressive strength (DIFc) and tensile strength (DIFl) indicates that the strain-rate effect on the dynamic tensile peak stress is more pronounced. The calibrated HJC constitutive parameters accurately reproduce the damage and fracture process of red sandstone under dynamic impact in LS-DYNA; prior to the maximum peak stress, the stress-strain curves obtained numerically are essentially consistent with the experimental curves. The calibrated parameters for this dense, high-strength red sandstone can serve as a reference for future studies on the dynamic mechanical properties of red sandstone and for its engineering applications.

In order to obtain the anti-blast performance of polyisocyanate-oxazodone (POZD) coated reinforced concrete beams under contact explosion, numerical simulation studies were carried out on reinforced concrete beams of the same size. Hypemesh and LS-DYNA were used to establish the model of POZD-coated reinforced concrete beams, and the failure modes and damage effects of POZD-coated reinforced concrete beams under contact explosion were analyzed. The failure mode of ordinary reinforced concrete beams under contact explosion was simulated and verified, the failure modes and damage conditions of reinforced concrete beams under different POZD coating positions and different charge amounts were studied, and the protective effects of different POZD coating positions were evaluated.

In order to investigate the dynamic response process, damage characteristics and damage mode of polyurea coated masonry infill walls with built-in tie reinforcement under close-range explosion load, a series of close-range explosion tests were performed on masonry wall with different polyurea coating methods and thicknesses. Additionally, numerical studies were carried out using the LS-DYNA software. Based on the resistance function of the brick wall, steel bar and polyurea coating, an improved equivalent single degree of freedom (ESDOF) theoretical calculation model was established. This model can accurately describe the displacement response of the polyurea coated masonry infill walls with built-in tie reinforcement under close-range explosion load. Three damage modes: surface mortar layer damage, open pit dislocation with back bulge, and penetration damage were identified according to the wall’s out-of-face response characteristics during close-range explosion load. With the increase of the number of tension reinforcement, the anti-explosion performance of the wall improves and the critical penetration damage charge increases.