Determination method of mesh size for numerical simulation of blast load in near-ground detonation

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.

Simulation of ductile fracture initiation in steels using a stress triaxiality-shear stress coupled model

Micromechanics-based models provide powerful tools to predict initiation of ductile fracture in steels. A new criterion is presented herein to study the process of ductile fracture when the effects of both stress triaxiality and shear stress on void growth and coalescence are considered. Finite-element analyses of two different kinds of steel, viz. ASTM A992 and AISI 1045, were carried out to monitor the history of stress and strain states and study the methodology for determining fracture initiation. Both the new model and void growth model (VGM) were calibrated for both kinds of steel and their accuracy for predicting fracture initiation evaluated. The results indicated that both models offer good accuracy for predicting fracture of A992 steel. However, use of the VGM leads to a significant deviation for 1045 steel, while the new model presents good performance for predicting fracture over a wide range of stress triaxiality while capturing the effect of shear stress on fracture initiation.

Seismic performance of HWBBF considering different design methods and structural heights

Previous research has shown that using buckling-restrained braces(BRBs)at hinged wall(HW)base(HWBB)can effectively mitigate lateral deformation of steel moment-resisting frames(MRFs)in earthquakes.Forcebased and displacement-based design methods have been proposed to design HWBB to strengthen steel MRF and this paper comprehensively compares these two design methods,in terms of design steps,advantages/disadvantages,and structure responses.In addition,this paper investigates the building height below which the HW seismic moment demand can be properly controlled.First,3-story,9-story,and 20-story steel MRFs in the SAC project are used as benchmark steel MRFs.Secondly,HWs and HWBBs are designed to strengthen the benchmark steel MRFs using force-based and displacement-based methods,called HWFs and HWBBFs,respectively.Thirdly,nonlinear time history analyses are conducted to compare the structural responses of the MRFs,HWBBFs and HWFs in earthquakes.The results show the following.1)HW seismic force demands increase as structural height increases,which may lead to uneconomical HW design.The HW seismic moment demand can be properly controlled when the building is lower than nine stories.2)The displacement-based design method is recommended due to the benefit of identifying unfeasible component dimensions during the design process,as well as better achieving the design target displacement.

Experimental study on flexural behavior of ECC/RC composite beams with U-shaped ECO permanent formwork

To enhance the durability of a reinforced concrete structure, engineered cementitious composite (ECC), which exhibits high tensile ductility and good crack control ability, is considered a promising alternative to conventional concrete. However, broad application of ECC is hindered by its high cost. This paper presents a new means to address this issue by introducing a composite beam with a U-shaped ECC permanent formwork and infill concrete. The flexural performance of the ECC/RC composite beam has been investigated experimentally with eight specimens. According to the test results, the failure of a composite beam with a U-shaped ECC formwork is initiated by the crushing of compressive concrete rather than debonding, even if the surface between the ECC and the concrete is smooth as-finished. Under the same reinforcement configurations, ECC/RC composite beams exhibit increases in flexural performance in terms of ductility, load-carrying capacity, and damage tolerance compared with the counterpart ordinary RC beam. Furthermore, a theoretical model based on the strip method is proposed to predict the moment-curvature responses of ECC/RC composite beams, and a simplified method based on the equivalent rectangular stress distribution approach has also evolved. The theoretical results are found to be in good agreement with the test data.