Numerical Simulation of Dynamic Response and Evaluation of Flexural Damage of RC Columns under Horizontal Impact Load

By using the ABAQUS finite element (FE) model, which has been verified by experiments, the deformation and internal force changes of RC columns during the impact process are investigated, and a parametric analysis is conducted under different impact kinetic energies Ek. According to the development path of the bottom bending moment-column top displacement curve under impact, the member is in a slight damage state when the curve rebounds before reaching the peak and in a moderate or severe damage state when the curve exceeds the peak, in which case the specific damage state of the member needs to be determined by examining whether there is a secondary descending stage in the curve. Accordingly, a qualitative method for evaluating the bending failure of RC column members under impact is obtained. In addition, the damage state of RC columns under impact can also be quantitatively evaluated by the ratio of the equivalent static load Feq and the ultimate static load-bearing capacity Fsu.

The difference-based equivalent static load method: an improvement of the ESL method’s nonlinear approximation quality

Nonlinear dynamic structural optimization is a real challenge, in particular for problems that require the use of explicit solvers, e.g., crash. Here, the number of design variables is typically very limited. A way to overcome this drawback is to use linear auxiliary load cases which are derived from nonlinear dynamic analysis results in order to enable the application of linear static response optimization. The equivalent static load method (ESLM) provides a well-defined procedure to create such linear auxiliary load cases. The main idea here is that after the selection of a number of representative time steps, a set of equivalent static loads (ESLs) is computed for each time step such that the resulting displacement field in the linear static analysis is identical to the respective field in the nonlinear dynamic analysis. Each set of ESLs defines an auxiliary load case, which is used in the linear static response optimization. The crucial point is that the finite element (FE)-model for each auxiliary load case describes the undeformed initial geometry. This can lead to insufficient approximation quality in the linear static system for highly nonlinear problems. To overcome this drawback, a difference-based extension of the ESL method called DiESL has been developed for nonlinear dynamic response optimization problems. Here, the FE-model for each auxiliary load case describes the deformed nonlinear geometry at the respective time, and the corresponding ESLs create only the displacement field leading to the deformed state of the subsequent ESL time step. Consequently, responses in each linear auxiliary load case (corresponding to a time step) are computed as the accumulated sum of the previous linear auxiliary load cases. Furthermore, the linear static response optimization problem consists not only of one but of nT FE-models where nT is the number of selected time steps. Such a multi-model optimization (MMO) can be solved with commercial FE solvers. It turns out that the DiESL approach leads to a significant improvement of the nonlinear approximation quality and faster convergence to the optimum when compared to standard ESLM. This will be demonstrated and discussed based on selected test examples.

Design and Static-Performance Evaluation of Concrete-Filled-Tube Rock Shed Structure

Rockfall protection facilities are necessary to reduce damages from rockfall or debris flow on roads near steep cut slopes. In Korea, rockfall protection fences and rock sheds are widely utilized for rockfall protection facilities. The rock shed is made of reinforced concrete or steel in the shape of a tunnel, and it is used for protecting the road from massive rockfall (up to 3,000 kJ of rockfall energy). In this study, a new type of rock shed comprising a Concrete-Filled-Tube (CFT) was designed. First, the proposed CFT rock shed could resist up to 3,000 kJ rockfall energy. Next, the performance of the CFT was verified through static analysis in which the 3,000 kJ rockfall energy was considered as the equivalent static load.

Experimental Study and Theoretical Verification of Explosion-Proof Performance of Insulated Glass

Building glass fragment in a blast-related environment is the main cause of casualties. In order to analyze the explosion-proof performance of insulated glass quantitatively in conventional buildings, the explosion experiment under different shock wave loads was carried out on the insulated glass, the pressure sensor was used to collect the overpressure value of the explosion shock wave, and the high-speed camera was used to record the breaking process of glass. The broken state of the insulated glass and the critical overpressure value of the broken state under different working conditions were obtained. And the theoretical calculation method based on the equivalent static load was used to verify the critical overpressure value of the insulated glass. The research showed that the fragments scattered toward the center of the explosion source when the layer of the insulated glass face to the explosion wave front was broken, and the fragments mainly scattered in the direction of the shock wave propagation when it was completely broken. The theoretical calculation method based on the equivalent static load could be used to evaluate the explosion-proof performance of the insulated glass.

Evaluation of textured journal bearings under dynamic operating conditions in rotating machinery

In order to obtain rotating machinery with improved energy efficiency, the approach of surface texturing journal bearings has been adopted to reduce the viscous dissipation in the lubricant. A possible reduction in shear viscous forces in the bearings of rotating machines could reduce the amount of heat released along its operation, resulting in a lower operating temperature that tends to improve journal bearings performance and the machine’s energetic efficiency. Thus, this work aims to investigate the texturing of journal bearings under dynamic loading conditions, considering the application in rotating systems. For this, computational simulations are performed through a rotating system model constructed by means of the finite element method in which the hydrodynamic journal bearings that support the rotor are modeled by Reynolds’ equation using the finite volume method and the full multigrid technique. The numerical results show that textured journal bearings can be applied to rotating machines, providing reductions in shear viscous forces. However, the magnitude of this reduction should be carefully evaluated, as the Reynolds cavitation model was applied to ensure a lower computational spent time and thus enable the simulations involved in this study. The novelty of this study is related to determining the appropriate distributions and geometric parameters of the textures for the journal bearing under dynamic load condition considering its equivalent static load condition what tends to drastically reduce computational time to perform this procedure, representing an important alternative for industrial application.

Numerical simulation of stress-strain state of oblique sections of reinforced concrete structures subjected to compression and bending on yielding supports under short-term dynamic load

This research is aimed at studying the method for improving blast resistance of buildings and structures by using yielding supports. The paper reports the data on dynamic analysis of reinforced concrete elements subjected to compression and bending on yielding supports under the condition of elasto-plastic stress-strain state performed in ANSYS software package. Algorithms and techniques for dynamic amplification factor calculation for reinforced concrete elements subjected to compression and bending are presented. The paper provides load diagrams of dynamic amplification factors with the account of yielding capacity of supports for subsequent dynamic analysis of structures for equivalent static load.