Development of a Simplified PWR Fuel Assembly Nonlinear Model

This paper proposes a computation technique to develop a simplified nonlinear model for a typical nuclear fuel assembly. Because more than a hundred fuel assemblies are packed in the reactor, simplistic model generation is critical to evaluate the motion during an anticipated event such as earthquake. Two straight beams are introduced to simplify the fuel assembly, and the beam properties are moderately defined to represent the skeleton structure and a bundle of slender fuel rods. Because nonlinearity is caused by the interaction between the rods and the spacer grids in the skeleton structure, the two beams are connected with multilinear joints that characterize the mechanical interaction between them. An equation of motion for the model is provided, and the degree of the freedom of the model can be reduced by using a few major modes of the beams. Significant mechanical parameters must be defined reasonably, so a method is proposed to identify unknown parameters through a deterministic calculation and an optimization process. All the information, including the identified parameters, are utilized to develop a nonlinear finite element model with a commercial code. The performance of the model is compared with the test results.

The Influence of the Inclination of Lattice Columns on the Safety of Combined Tower Crane

The combined tower crane foundation is widely used in construction sites due to its advanced utilization rate. However, the immature construction method, unavoidable construction deviation during the installation process, and influence of the surrounding construction generally cause the lattice columns to tilt. As the main force transmission components of the tower crane foundation, once its stress and deformation exceed the limit, the entire tower crane will collapse, which requires engineers to accurately control its safety. Therefore, the objective of the work reported here was to study the safety of the lattice columns during operation. A geometrically nonlinear finite element model was utilized to simulate the strain and deformation capacity of tower cranes under various working conditions, including vertical and inclined working conditions, operation and shutdown conditions, and conditions with the tower boom in different orientations. In addition, this study combines the simulation with the on-site measurement. The results of on-site measurement were also recorded to verify the correctness of the proposed calculation model. It was concluded that the inclination of lattice columns has a significant effect on the deformation and stress of the lattice columns of the tower crane foundation, and the measured data and the calculated data trend are consistent. Engineers can accurately judge the safety of the lattice columns of the tower crane foundation through geometric nonlinear finite element model analysis and on-site monitoring to avoid the failure of the lattice columns and the occurrence of safety accidents.

Application of Viscoelastic Materials in Ship Collision

With the expansion of global trade routes, ship collision has become a major problem. This article proposes an approach by laying viscoelastic material on the inner side of the ship to increase the crashworthiness. By using the nonlinear finite element model software, this study simulates ship collisions as well as models and analyzes ships along with viscoelastic materials. The results from the simulation suggest that viscoelastic materials can effectively protect ships during collisions.

A comparative analysis of resistance models for austenitic stainless steel girders subjected to concentrated loads

The increasing use of stainless steel in construction has led to the need of developing resistance models for structural elements made of this material. Unlike carbon steels, stainless steel alloys exhibit stress-strain curves with a pronounced strain hardening capacity and reasonable ductility that should be considered in the design. This difference in behavior makes the formulations used for carbon steel conservative when designing with stainless steel. Therefore, this paper presents a comparative analysis of resistance models for slender austenitic stainless-steel beams subject to concentrated loads. First, the failure mechanisms of stainless-steel beams are presented using a nonlinear finite element model. From this validated numerical model, a database obtained from a parametric analysis that covers a wide range of geometries is presented. Subsequently, this database is used to perform a comparison between various resistance models available in the literature. These models correspond to both international design codes and models obtained through machine learning. Finally, the numerical results show considerable improvement in the predicted ultimate resistances for slender stainless steel plate girders subjected to patch loading.

Seismic Fragility Analysis of Base Isolated Structure Subjected to Near-fault Ground Motions

In order to better evaluate the performance of the base isolated structure under the near-fault earthquakes, this paper takes into consideration an existing engineering case study in China as the prototype, and uses OpenSEES platform to establish the nonlinear finite element model of the base isolated structure. The nonlinear response of the isolated structure under the near-fault earthquake is analyzed. The incremental dynamic analysis (IDA) method is used to calculate the damage probability of the structure under the near-fault earthquake, and the fragility curve of the base isolated structure is established. The fragility equation is obtained by nonlinear regression, and the error of fragility equation is analyzed. The results show that the maximum value of the inter-story drift of the upper structure under the action of near-fault earthquake is significantly greater than that under the action of far-fault earthquake. With the increase of seismic intensity, the damage probability of base isolated structure increases nonlinearly, and the maximum response value of horizontal displacement of bearing and inter-story drift of superstructure increases generally. In addition, the exceeding probability of the fragility curve based on PSDA is greater than that based on EDP criterion. When the sample points of the two methods are the same, the exceeding probability points calculated based on PSDA can be regarded as accurate values. The fragility curve based on PSDA may overestimate the exceeding probability to some extent, and the overestimation may be enlarged with the increase of failure stage.

Modelling Short-Term Monotonic Response of Timber-Concrete Composite Structures

Timber-concrete composite is an efficient hybrid construction material which exploits the advantageous properties of timber and concrete. The use of shear connectors enables the two dissimilar materials to act together, resulting in an increase in global stiffness as well as load-carrying capacity. As this composite material is becoming increasingly more popular in the construction industry, there is a need to develop analysis tools which have general applicability to timber-concrete composite systems with variations in loading schemes, specimen configurations, materials, and types of shear connectors. One such tool, a generic two-dimensional nonlinear finite element model, is proposed in this paper; it is verified through numerical simulations of six experiment series carried out by other researchers. Good agreement between experimentally observed behaviour and numerical simulations was generally obtained.