Comparative nonlinear seismic analysis of an existing RC bridge designed with obsolete codes

The evolution of seismic design and calculation criteria for highway bridges has a direct influence on their structural behavior. This paper presents a nonlinear dynamic analysis using a detailed 3D finite element model of an existing bridge, with different design criteria for the column transverse reinforcement, according to code requirements of different times. The numerical model is able to simulate both the collapse of the structure and the generation of damage in its elements when subjected to extreme seismic actions. Through the numerical model, it is possible to represent the cyclic behavior of the concrete, and to evaluate the influence of the transverse reinforcement assigned to the column on the overall response of the bridge. The formation of plastic hinges is verified, as well as the identification of different collapse mechanisms.

Mechanical strength of highly preloaded bolts affected by the ovalization of an aircraft wheel

This work presented in this paper concerns the modeling of the tensile and bending behavior of bolts in an airplane wheel. The design of a very rigid airplane tire means that the airplane wheel must be separated into two parts. In order not to have a separation between the two parts, several bolts with high preload are used. The main objective of this work is to predict the mechanical behavior of this assembly in a preliminary design phase with geometrical and global mechanical data. To achieve this objective, a simplified semi-numerical 1D model is developed. The complex geometry of the wheels is modeled by axisymmetric elements, while beam elements define the geometries and mechanical behavior of the bolts. The model is improved in non-axisymmetric cases to include the ring effect due to the wheel ovalization. Different cases are simulated (inflation and rolling). For each load case, the most stressed fastener is examined. Then, a comparison between its static and fatigue stress results and those of the 3D finite element reference model considered is analyzed for the validation of the developed tool. The semi-numerical model is used in the preliminary design phase and permits the geometric and mechanical properties of the aircraft wheel and fasteners to be defined so as to find the best assembly configuration that prevents separation.

Numerical Simulation and Experimental Study On Non-Axisymmetric Spinning With a Groove At The Middle of The Tube

Spinning is widely used in aerospace and automobile industries, and non-axisymmetric spinning is developing with the increasing demand of irregular shape forming. Based on this, an avoidance groove at the middle of the tube (AGMT) which has potential application value in aircraft structure weight reduction is proposed and formed by using non-axisymmetric die-less spinning. The roller path is analyzed. The relationship between radial displacement of roller and the rotation angle of the tube is deduced. Based on the roller path, 3D finite element model is established. Then, the AGMT spinning experiment is carried out to verify the simulation results. The maximum deviation between the simulation and experimental results is less than 15%. It is indicated that the 3D finite element model established in this study is reliable and the method for the AGMT forming is feasible. The wall thickness and strain-stress distributions are analyzed. The severe wall thicken and thinning occur in the transition zones, so more attention should be paid to these positions. The depth of the groove has great impact on the forming quality. Deeper groove results in distortion and larger wall thickness difference. The research laid a foundation for the further development and optimization of the AGMT spinning.

Effect of the bracketless orthodontics technique and resin composite material on the biomechanical response of the upper central incisor: 3D finite element analysis

Objectives: The bracketless orthodontic treatment (BOT) is an alternative technique which indicates using an orthodontic appliance composed of wires and composite resin assisted by 3D technology. However, the biomechanical response of central incisor orthodontic movement has yet to be investigated. Thus, the aim of the present investigation was to calculate the stress magnitude in central incisor movement through 3D finite element analysis using different wire diameters (0.012”, 0.014”, and 0.016”) of nickel–titanium wire and two different resin composites (Opallis and Filtek). Materials and Methods: A 3D volume composed of enamel, dentin, cortical bone, cancellous bone, periodontal ligament, composite resin, and different orthodontic wire diameters was designed. After the modeling process, the models were exported to computer-aided engineering software divided into a finite number of elements, and a mechanical structural static analysis was conducted. Results: The stress results were plotted on colorimetric maps and in tables for comparison between the different models. The results showed that the central incisor orthodontic movement with BOT does not induce damage to the periodontal ligament, dental root, or bone tissue, regardless of the simulated orthodontic wire diameter and resin composite materials. The palatal composite resin and orthodontic wire also presented acceptable stress magnitude during orthodontic movement. Conclusion: Thus, the BOT technique promoted a suitable biomechanical response during central incisor movement regardless the resin composite.