Miquel Casafont

The influence of cross-sectional deformation modes, such as distortional or local buckling, and the characteristics of member connections are two key factors to determine the structural behavior of a pallet rack structure. This paper therefore aims to analyze the influence of both effects on a pallet rack structure using dynamic (modal and time history) Generalized Beam Theory (GBT) analyses. First of all, the influence of the deformation modes involved in a single cantilever member is assessed by means of a GBT and a Shell transient finite element analysis. The results show good agreement between both models when several cross-sectional deformation modes are involved in the GBT calculation. Next, modal and time history analyses of complete pallet rack structures are carried out using several GBT models. The results indicate that the use of bracings in the down-aisle direction as well as the connection modelling (beam-to-upright and upright-to-brace connections) has a relevant influence on the modal participation of distortional deformation modes, the displacement field, and the longitudinal membrane stress distribution in the columns of the pallet rack structure. Consequently, the paper provides an overview of scenarios in which GBT analysis, which takes cross-sectional deformation into account at low computational cost, is useful for dynamic analysis of pallet rack structures.

Mask Image Projection based on Stereolithography (MIP-SL) uses photocurable materials to built-up a 3D part by means of an Additive Manufacturing process. The accuracy, resolution and mechanical properties of printed parts depend on the material conversion ratio value at each location of the manufacturing domain. Therefore, the use of numerical models to determine the material conversion ratio according to the characteristics of the printing process is a key factor to optimize and improve the quality of printed parts. In this paper, a new numerical model to simulate the manufacturing process is presented. This model takes the pixel-blending effect as well as the multi-layered characteristics of the process into account. Several experimental measurements are performed to calibrate the numerical model. Finally, the estimated printed geometries provided by the numerical model are successfully compared with experimental results. Keywords: Mask Image Projection, Frontal Photopolymerization Process, Numerical Model, Additive Manufacturing, Pixel Blending

A global analysis of a rack frame conducted using the Generalised Beam Theory (GBT) is presented. This study specifically focuses on a down-aisle frame, showing the particular characteristics of this type of structure, such as its perforated columns, semi-rigid joints, and significant second-order effects. The single-column simplified approach is applied, meaning that the entire rack is modelled with one single column and its adjacent half-beams. This approach substantially reduces modelling time and allows for very quick parametric studies while adequately reproducing the general 2D down-aisle behaviour. The GBT single-column model is first verified against a similar single-column shell finite element model used by the authors in previous research. Afterwards, the model is applied to study the effects of various factors influencing the results of a rack global analysis, including perforations, imperfection magnitudes and combinations, and sectional deformations. The nature of GBT allows for deriving clear conclusions on the influence of these aspects on structural behaviour. Furthermore, this article also aims to demonstrate the potential advantages of the theory for performing global analyses of these structures in both research and design.

Ordinary (customary) light gauge steel framing is a convenient construction technology; however, given the studs low axial capacity, it has been considered mainly for low-rise buildings in low seismicity regions. This paper investigates the boundaries of application of this type of steel framing (in moderate and high seismicity areas) by designing the structures of three representative 5, 7 and 10-storey buildings in order to examine their feasibility. The necessity of using built-up columns consisting of two or more sections is investigated. The axial capacity of studs is estimated by code-type analyses. The critical buckling stress is determined with well-known closed-form expressions; as they do not contemplate the flexibility of the screwed connections (in built-up sections), the obtained results are complemented with those of the finite strip method and generalized beam theory formulations.

Mask image projection based on stereolithography is an additive manufactured technology based on a Frontal Photopolymerization Process. Therefore, photocurable resins are used to build-up parts layer by layer. In this paper, alumina particles have been used as a reinforcement filler in order to improve the material stress-strain behaviour. In addition, the increment of the photoconversion ratio is a key factor to enhance the mechanical properties. Consequently, a numerical model has been used to determine the optimal printing parameters to enhance the elastic mechanical properties of printed parts according to the characteristics of photocurable materials. Stable and homogeneous reinforced materials have been obtained with an alumina content ranging from 5 to 15 wt%. Furthermore, the compression behaviour of reinforced materials has been analysed by means of experimental tests. The results show an enhancement of mechanical properties after the addition of reinforcement fillers, obtaining a maximum improvement in 10 wt% of solid load content. Finally, the influence of the sample’s orientation on the construction platform has been discussed.

This paper presents a simplified stability-based method for practical structural predesign of down-aisle unbraced frames of selective racks. Given the uniformity of actual racks, only a single upright and its adjoining half beams were modeled, discretized with two-dimensional (2D) beam elements; the flexibility of the upright–beam and upright–floor connections was represented with linear springs. Such a model is used for linear buckling and second-order analyses. The proposed method consists of iteratively resizing the structural members according to cost and stability criteria (linear buckling analysis) until the serviceability limit state (SLS) and ultimate limit state (ULS) are satisfied (second order analysis). Specific procedures were developed to accelerate the computations. Two practical examples were analyzed to assess the performance of the proposed method. Compared with conventional design approaches for racks, the method was faster, and resulted in less-expensive structures. The simplification involved in the single-column consideration is sufficiently accurate. Some ideas about efficient methods of improving the stability of racks were presented.