Reinforced concrete (RC) frame structures are the most widely adopted structural form in civil infrastructure, government facilities, commercial buildings and critical public premises, undertaking irreplaceable roles in normal political and economic operations. However, with the growing frequency of terrorist explosion attacks, accidental industrial and gas explosion incidents, alongside the complex and volatile global security environment, RC frame structures have become both high-priority attack targets and the critical line of defense for personnel protection. To investigate the damage effects of multiple explosion scenarios on RC frame structures, a full-scale two-story RC frame structure with infill masonry walls, designed in line with current building design codes, was constructed. A series of field explosion tests, including external and internal explosion scenarios with TNT equivalents of 11.573 kg and 20 kg, were conducted on this structure. The load characteristics of shock waves, dynamic response and failure modes of structural components were examined. The results show that under close-range external explosion, the floor slabs and masonry walls can attenuate the shock wave loads propagated into the adjacent room, with a peak overpressure reduction of 84.75%. The floor slabs and masonry walls exhibit local shear failure, while the damage to the internal components and the global structure remains limited. In contrast, under internal explosion, the floor slabs and masonry walls show global shear failure, with more severe damage compared to the RC columns and beams. In addition to the shock wave loading, the explosive ejection of wall and slab fragments from the detonation room is the primary cause of damage to the masonry walls and slabs along the shock wave propagation path. Finally, based on damage assessment criteria, the damage levels of components, rooms, and the RC structure for each test were determined. The damage severity and affected range of the RC structure under internal explosion are significantly greater than those under external explosion with the same equivalent.

Reinforced concrete (RC) shed tunnel serves as an effective in-situ solution for rockfall protection along mountainous highways and railways. Using the commercial software LS-DYNA, refined numerical simulations were conducted to investigate the damage and failure assessment of a prototype framed T-beam type RC shed tunnel under rockfall impact. The simulations considered scenarios both with and without cushions, including 600 mm and 1200 mm sand cushions, as well as 1200 mm sand-expandable polyethylene (EPE) composite cushion. Firstly, a refined finite element model of a prototype framed T-beam type RC shed tunnel located on the Shanghai-Kunming railway under rockfall impact was developed, of which the rockfall masses ranging from 1 t to 30 t and impact velocities ranging from 10 m/s to 57 m/s. Secondly, by comparing with the results of existing impact tests on bare RC slab, as well as RC slabs with sand and EPE cushions, the accuracy and reliability of the adopted material constitutive model, mesh size, contact algorithm, and corresponding parameters of the finite element model were validated. Furthermore, the damage patterns and dynamic responses of the prototype shed tunnel without cushion, with sand cushion, and with sand-EPE composite cushion were compared and analyzed. Finally, taking the maximum penetration depth of the rockfall reaching the total thickness of the roof slab and cushion as the failure threshold of the shed tunnel, the corresponding relationship between the rockfall mass and the critical impact velocity was established, which enabled rapid assessment of protective performance of shed tunnel. It indicates that: (1) Under the impact of a 15 t rockfall at velocities of 10 m/s and 25 m/s, the damage to the shed tunnel without cushion is primarily concentrated in the impact area of the roof slab. On average, the use of sand cushion and sand-EPE composite cushion reduces the peak impact force by 92.8% and 91.6%, respectively; (2) At impact velocity of 10 m/s, the sand-EPE composite cushion exhibits superior buffering and energy dissipation performance compared to the sand cushion. However, with impact velocity increasing to 25 m/s, the EPE in the composite cushion is rapidly compacted, leading to a diminished protective effect. In this scenario, the impact force and energy transferred to the roof slab with the composite cushion are 89.3% and 37.8% higher than those with the sand cushion, respectively; (3) The critical impact velocity of rockfall corresponding to the failure damage of the shed tunnel follows an exponential decay trend as the rockfall mass increases. The application of cushions can increase the critical impact velocity by 52% to 155%, significantly improving the protective performance of the shed tunnel.

With the rapid development of hypervelocity weapons, analyzing the penetration effectiveness of hypervelocity weapon warheads on concrete shields is significant for the design of newly-built protective structures and the safety evaluation of as-built protective structures. Focusing on the penetration performance of AGM-183A hypervelocity weapon warhead against three typical shields: normal strength concrete (NSC), ultra-high performance concrete (UHPC), and corundum rubble concrete (CRC), firstly, the reliability of the numerical algorithms, mesh size, and material model parameters used in the finite element analysis method was fully validated by comparing the experimental and simulation results of three types of target subjected to penetration of steel/tungsten alloy projectiles. Subsequently, a numerical analysis method for the prototype scenario was established based on a mesh transition strategy equivalent to penetration depth and recovered projectile length. Finally, a series of simulations were conducted for the AGM-183A hypervelocity weapon warhead penetrating the aforementioned three shields at Ma ranging from 3 to 8. The results indicate that: (1) the AGM-183A hypervelocity weapon warhead reaches maximum penetration depth when NSC, UHPC, and CRC shields subjected to penetration at Ma=4, Ma=4, and Ma=3, respectively, with depths of 4.26, 3.74, and 1.00 m. Due to instability phenomena of projectiles, such as fractures at the junction between the head and body caused by local stress concentration, further increases in penetration velocity lead to a decrease in penetration effectiveness; (2) compared with the combined penetration and explosion damage depths of conventional sound speed penetrating warheads SDB, WDU-43/B, and BLU-109/B, the penetration depths induced by AGM-183A into NSC, UHPC, and CRC shields are 3.2, 1.6, and 1.8 times, 4.7, 2.1, and 2.2 times, and 3.4, 1.3, and 1.5 times higher, respectively; (3) the recommended design thicknesses of the three shields against the AGM-183A hypervelocity weapon warhead are 8.01, 7.03, and 1.88 m, respectively. The UHPC shield shows no significant improvement subjected to hypervelocity penetration compared with the NSC shield. Comparatively, the CRC shield is recommended for shield design, which can be effectively subjected to both conventional subsonic and hypervelocity impacts.

Aiming to investigate the performance and design approach of the carbon fiber reinforced polymer (CFRP) sheet strengthened masonry infilled walls subjected to blast loads, the commercial finite element program LS-DYNA is firstly used to develop the simplified micro-finite element model of masonry infilled walls and the corresponding blast-resistant analysis model of the CFRP sheet strengthened walls. By comparing the numerical simulation results with the nine groups field explosion test results of the unstrengthening and CFRP sheet strengthened masonry infilled walls, the applicability of the present simplified micro-modeling approach, as well as the material models and parameters of masonry and CFRP sheet and the corresponding contact algorithm, is thoroughly verified. Furthermore, referring to the CFRP sheet seismic strengthening methods recommended by China standard GB 50608—2020, the dynamic behaviors of the prototype masonry infilled walls strengthened with CFRP sheets under blast loads are analyzed and compared. It is recommended that the diagonal two-way strengthening method be advocated, followed by the vertical two-way and horizontal full-cover strengthening methods. In contrast, the vertical full-cover and mixed three-way strengthening methods are not recommended. Finally, to simultaneously satisfy the conditions of intact CFRP, no scattering debris and the peak central deflection than wall thickness to meet the blast-resistant design goal, the ranges of the scaled distance of the prototype masonry infilled walls with different arrangements of tie bar (non-/cut-off/full-length tie bar) that need to be strengthened under typical sedan (227 kg equivalent TNT) and briefcase bombs (23 kg equivalent TNT) specified by Federal Emergency Management Agency explode at different scaled distances are determined to be 0.8–2.0 m/kg^1/3 and 0.2–1.2 m/kg^1/3, respectively. The suggestions for the optimal number of CFRP sheet layers for effective blast-resistant design are further provided. The arrangement of the tie bar has little effect on the optimal number of strengthening layers, only affecting the critical scaled distance at which the wall needs to be strengthened.