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For the first time, the isogeometric analysis (IGA) approach is used to model and analyze free and forced vibrations of doubly-curved magneto-electro-elastic (MEE) composite shallow shell resting on the visco-Pasternak foundation in a hygro-temperature environment. The doubly-curved MEE shallow shell types include spherical shallow shell, cylindrical shallow shell, saddle shallow shell, and elliptical shallow shell subjected to blast load are investigated. The Maxwell equation and electromagnetic boundary conditions are used to determine the vary of the electric and magnetic potentials. The MEE shallow shell's equations of motion are derived from Hamilton's principle and refined higher-order shear theory. Then, the IGA method is used to derive the laws of natural frequencies and dynamic responses of the shell under various boundary conditions. The accuracy of the model and method is verified through reliable numerical comparisons. Aside from this, the impact of the input parameters on the free and forced vibration of the doubly-curved MEE shallow shell is examined in detail. These results may be useful in the design and manufacture of military structures such as warships, fighter aircraft, drones and missiles. [ABSTRACT FROM AUTHOR]

For the first time, the isogeometric analysis (IGA) approach is used to model and analyze free and forced vibrations of doubly-curved magneto-electro-elastic (MEE) composite shallow shell resting on the visco-Pasternak foundation in a hygro-temperature environment. The doubly-curved MEE shallow shell types include spherical shallow shell, cylindrical shallow shell, saddle shallow shell, and elliptical shallow shell subjected to blast load are investigated. The Maxwell equation and electromagnetic boundary conditions are used to determine the vary of the electric and magnetic potentials. The MEE shallow shell's equations of motion are derived from Hamilton's principle and refined higher-order shear theory. Then, the IGA method is used to derive the laws of natural frequencies and dynamic responses of the shell under various boundary conditions. The accuracy of the model and method is verified through reliable numerical comparisons. Aside from this, the impact of the input parameters on the free and forced vibration of the doubly-curved MEE shallow shell is examined in detail. These results may be useful in the design and manufacture of military structures such as warships, fighter aircraft, drones and missiles.

In order to improve the overall resilience of the urban infrastructures, it is required to conduct blast resistant design for important building structures in the city. For complex terrain in the city, it is recommended to determine the blast load on the structures via numerical simulation. Since the mesh size of the numerical model highly depends on the explosion scenario, there is no generally applicable approach for the mesh size selection. An efficient method to determine the mesh size of the numerical model of near-ground detonation based on explosion scenarios is proposed in this study. The effect of mesh size on the propagation of blast wave under different explosive weights was studied, and the correlations between the mesh size effect and the charge weight or the scaled distance was described. Based on the principle of the finite element method and Hopkinson-Cranz scaling law, a mesh size measurement unit related to the explosive weight was proposed as the criterion for determining the mesh size in the numerical simulation. Finally, the applicability of the method proposed in this paper was verified by comparing the results from numerical simulation and the explosion tests and was verified in AUTODYN.

Investigating natural-inspired applications is a perennially appealing subject for scientists. The current increase in the speed of natural-origin structure growth may be linked to their superior mechanical properties and environmental resilience. Biological composite structures with helicoidal schemes and designs have remarkable capacities to absorb impact energy and withstand damage. However, there is a dearth of extensive study on the influence of fiber redirection and reorientation inside the matrix of a helicoid structure on its mechanical performance and reactivity. The present study aimed to explore the static and transient responses of a bio-inspired helicoid laminated composite (B-iHLC) shell under the influence of an explosive load using an isomorphic method. The structural integrity of the shell is maintained by a viscoelastic basis known as the Pasternak foundation, which encompasses two coefficients of stiffness and one coefficient of damping. The equilibrium equations governing shell dynamics are obtained by using Hamilton's principle and including the modified first-order shear theory, therefore obviating the need to employ a shear correction factor. The paper's model and approach are validated by doing numerical comparisons with respected publications. The findings of this study may be used in the construction of military and civilian infrastructure in situations when the structure is subjected to severe stresses that might potentially result in catastrophic collapse. The findings of this paper serve as the foundation for several other issues, including geometric optimization and the dynamic response of similar mechanical structures.

This work uses refined first-order shear theory to analyze the free vibration and transient responses of double-curved sandwich two-layer shells made of auxetic honeycomb core and laminated three-phase polymer/GNP/fiber surface subjected to the blast load. Each of the two layers that make up the double-curved shell structure is made up of an auxetic honeycomb core and two laminated sheets of three-phase polymer/GNP/fiber. The exterior is supported by a Kerr elastic foundation with three characteristics. The key innovation of the proposed theory is that the transverse shear stresses are zero at two free surfaces of each layer. In contrast to previous first-order shear deformation theories, no shear correction factor is required. Navier’s exact solution was used to treat the double-curved shell problem with a single title boundary, while the finite element technique and an eight-node quadrilateral were used to address the other boundary requirements. To ensure the accuracy of these results, a thorough comparison technique is employed in conjunction with credible statements. The problem model’s edge cases allow for this kind of analysis. The study’s findings may be used in the post-construction evaluation of military and civil works structures for their ability to sustain explosive loads. In addition, this is also an important basis for the calculation and design of shell structures made of smart materials when subjected to shock waves or explosive loads.

In this paper, UR50 ultra-early-strength cement-based self-compacting high-strength concrete slabs (URCS) have been subjected to contact explosion tests with different TNT charge quality, aiming to evaluate the anti-explosive performance of URCS. In the experiment, three kinds of ultra-early-strength cement-based reinforced concrete slabs with different reinforcement ratios and a normal concrete slab (NRCS) were used as the control specimen, the curing time of URCS is 28 days and 24 h respectively. The research results show that URCS has a stronger anti-explosion ability than NRCS. The failure mode of URCS under contact explosion is that the front of the reinforced concrete slab explodes into a crater, and the back is spall. With the increase of the charge, the failure mode of the reinforced concrete slab gradually changed to explosive penetration and explosive punching. The experiment results also show that the reinforcement ratio of URCS has little effect on the anti-blast performance, and URCS can reach its anti-blast performance at 28 days after curing for 24 h. On this basis, the damage parameters of URCS for different curing durations were quantified, and an empirical formula for predicting the diameter of the crater and spalling was established.

The structural performance of perforated steel columns (PSCs) is significantly more complex than the one of solid web I-shaped elements under the diversity of blast loading scenarios. The damage criterion of PSCs is not only related to initial deformation response during the blast but also the residual axial load capacity and it can be considered as a reliable index after the blast effects. Therefore, the PSCs damages will be studied in two stages; direct and post blast effects. In the present study, the dynamic response of PSCs was numerically evaluated under different levels of blast threats using LS-DYNA software. Extensive explicit finite element (FE) analyses are carried out to investigate the effect of various parameters, such as web opening shapes, boundary conditions and strengthening details on the damage index and toughness of the PSCs compared to the parent steel sections. The results of the comparative study show that the damage and toughness decrease when the support condition changes from pinned to fixed ends through the two stages of loadings. PSCs give high toughness compared to its parent sections during blast shock stage while, a remarkable decrease in toughness is observed during the application of axial gravity after blast shock. Furthermore, the web opening shapes have slight effects on the global dynamic behavior of PSCs, particularly in terms of residual capacity. On the contrary, the retrofitting strategy using both closed holes at end and vertical stiffeners have an effective enhancement to get higher toughness in case of the extreme blasts.

The structural performance of perforated steel columns (PSCs) is significantly more complex than the one of solid web I-shaped elements under the diversity of blast loading scenarios. The damage criterion of PSCs is not only related to initial deformation response during the blast but also the residual axial load capacity and it can be considered as a reliable index after the blast effects. Therefore, the PSCs damages will be studied in two stages; direct and post blast effects. In the present study, the dynamic response of PSCs was numerically evaluated under different levels of blast threats using LS-DYNA software. Extensive explicit finite element (FE) analyses are carried out to investigate the effect of various parameters, such as web opening shapes, boundary conditions and strengthening details on the damage index and toughness of the PSCs compared to the parent steel sections. The results of the comparative study show that the damage and toughness decrease when the support condition changes from pinned to fixed ends through the two stages of loadings. PSCs give high toughness compared to its parent sections during blast shock stage while, a remarkable decrease in toughness is observed during the application of axial gravity after blast shock. Furthermore, the web opening shapes have slight effects on the global dynamic behavior of PSCs, particularly in terms of residual capacity. On the contrary, the retrofitting strategy using both closed holes at end and vertical stiffeners have an effective enhancement to get higher toughness in case of the extreme blasts. [ABSTRACT FROM AUTHOR]

The load-carrying capacities and failure patterns of reinforced concrete components can be significantly changed by membrane effects. However, limited work has been carried out to investigate the blast resistance of Hybrid Fiber Reinforced Lightweight Aggregate Concrete (HFR-LWC) members accompanying membrane action. This paper presents a theoretical approach to quantitatively depicting the membrane behavior and its contribution on the behavior of HFR-LWC beams under close-range blast loadings, and the suitability of the proposed model is validated by a series of field tests. An improved Single-Degree-of-Freedom (SDOF) model was employed to describe the dynamic responses of beam-like members under blast loadings accompanying membrane action, where the mass-load coefficient is determined according to the nonuniformly distributed load induced by close-range explosion, and the membrane action is characterized by an in-plane (longitudinal) force and a resisting moment. The elasto-plastic and recovery responses of HFR-LWC beams under the combined action of blast load and membrane force were analyzed by the promoted model. A specially built end-constrain clamp was developed to provide membrane action for the beam member when they are subjected to blast load simultaneously. It is demonstrated that the analytical displacement-time histories are in good agreement with experimental results before peak deflections and that the improved SDOF model is an acceptable tool for predicting the behavior of HFR-LWC beams under blast loadings accompanying membrane action.