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.

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.