Additively manufactured lattice structures enable the design of tissue scaffolds with tailored mechanical properties, which can be implemented in porous biomaterials. The adaptation of bone to physiological loads results in anisotropic bone tissue properties which are optimized for site-specific loads; therefore, some bone sites are stiffer and stronger along the principal load direction compared to other orientations. In this work, a semi-analytical model was developed for the design of transversely isotropic lattice structures that can mimic the anisotropy characteristics of different types of bone tissue. Several design possibilities were explored, and a particular unit cell, which was best suited for additive manufacturing was further analyzed. The design of the unit cell was parameterized and in-silico analysis was performed via Finite Element Analysis. The structures were manufactured additively in metal and tested under compressive loads in different orientations. Finite element analysis showed good correlation with the semi-analytical model, especially for elastic constants with low relative densities. The anisotropy measured experimentally showed a variable accuracy, highlighting the deviations from designs to additively manufactured parts. Overall, the proposed model enables to exploit the anisotropy of lattice structures to design lighter scaffolds with higher porosity and increased permeability by aligning the scaffold with the principal direction of the load.

Steel cylindrical shell structures such as silos and tanks are very sensitive to geometric imperfections and prone to a plastic instability failure known as elephant's foot (EF) buckling. This type of buckling arises under axial compression. The aim of this paper is to explore the plastic collapse response in conical shells with low semi-vertex angle values under compression. In a first step, the initial geometric imperfection shapes that dictate which plastic mechanisms arise were identified using finite element (FE) models. In a second step, a parametric study reported two plastic collapse mechanisms and showed that the elephant's foot plastic collapse mechanism is the most likely to appear in compressed conical shells with low d/t values, followed by the Yoshimura collapse mechanism, more common with larger d/t values. Finally, a practical model in which the parameters have been adjusted from numerical models has been derived for the elephant's foot plastic mechanism. This model provides the load-deformation behaviour of compressed conical shells at the post-collapse region. The load vs. end-shortening curves provided by the model have been validated through comparison with curves given by the FE models. The good agreement between the results proves the efficiency of the practical model to predict the collapse response of conical shells.

As result of the advances made in additive manufacturing in recent years, the design of porous materials with controlled mechanical properties has gained importance due to their capability to offer case-specific solutions in multiple applications. In terms of biomaterials, the use of lattice structures provides a considerable variety of mechanical and geometric properties that can enhance osseointegration and reduce stress shielding. In this paper, the elastic response of a modified face-centered cubic (FCC) unit cell was studied, and analytical expressions for macroscopic effective Young's moduli, shear moduli and Poisson's ratios were obtained, thus providing the necessary parameters for the homogenization of the unit cell. The analytical expressions of the homogenization parameters open the possibility for implementation in other research fields, such as topology optimization. Timoshenko beam theory was used to model the struts of the modified FCC unit cell and a finite element analysis using shear flexible beam elements was performed to assess the accuracy of the analytical expressions. In addition to modelling the bending of the beams, axial and torsional displacements were also considered for a more detailed analysis. It can be concluded that the expressions obtained represent the elastic behavior of the modified FCC unit cell with high accuracy.

This paper deals with a new designed joint system for single-layer spatial structures. As the stability of these structures is greatly influenced by the joint behaviour, the aim of this paper is the characterization of the joint response in bending through Finite Element Method (FEM) analysis using ABAQUS. The behaviour of the joints studied here was influenced by many geometrical factors, such as bolts and plate sizes, distance between bolts and end-plate thickness. The study comprised five models of joints with different values of those parameters. The numerical results were compared to the results of previous experimental tests and the agreement was good enough. The differences between the numerical and experimental initial stiffness are attributed to the simplifications introduced when modelling the bolt threads as well as the presence of residual stresses in the test specimens.

This paper presents what we call the Multiple Approach Experimental Project (MAEP), a project based on the model-building approach to learning. The MAEP complements theoretical lectures by placing students in a real situation where they design and build a physical structure. A total of 65 students divided into 24 teams voluntarily took part in the competition. Assessments from students who participated in the MAEP along with assessments from the instructors who implemented it are presented. Results show that the MAEP was welcomed and that the objective of engaging students in the subject was met.

The necessity to offer differentiated solutions for architectural projects is fostering the development of single-layer spatial structures. As the stability of these structures largely depends on the stiffness of the joints, new joint designs have to be sought. The authors performed various experimental tests on a new kind of joint for tubular members of single-layer structures in order to evaluate the joint stiffness. The aim of the study is to find a finite element model to reproduce the experimental responses, so that the behaviour of the joint can be predicted without the need for further experimentation. The proposed models mainly differed in the way the bolt connection was simulated, as bolts were the most complex elements. The paper presents the comparison between experimental results and numerical results obtained from the different finite element models developed for the joints. One of the three models provided good results even though it was simple.

Although there is a great deal of papers on single-layer latticed structures, practically the totality of them is devoted to domes. Therefore, the authors have chosen to analyse squared plan-form single-layer structures studying the influence of joint-rigidity, mesh-density, rise-to-span ratio and load combination in their behaviour, through a Design of Experiments analysis. After identifying the most influential parameters, more FEM analyses were run resulting in interesting conclusions which included economic considerations. The influence of initial imperfections was also investigated. (C) 2011 Elsevier Ltd. All rights reserved.

The paper presents a comparative study of a well-established steelwork design standard, the American AISC LRFD, and the new European code for the design of steel structures, Eurocode 3. The study is focused on the resistance capacity of steel members subjected to one of the following load cases: axial compression, bending, and combined axial compression and bending. First, the paper compares the formulation of both codes in order to identify similarities and differences. Particular attention is given to the resistance of beam columns since many steel structural members in building structures fall into this category. In the case of pure bending and combined axial compression and bending, the paper considers two extreme cases of linear moment distribution: equal end moments and opposite end moments. The results are presented graphically in order to make possible their interpretation and to detect significant differences in resistance. The comparative study shows that the resistance capacities given by LRFD and EC3 can differ appreciably for some of the cases considered. Moreover, there are also significant differences between the two methods proposed by the Eurocode when slenderness is high and the beam is subjected to linear moment distribution with opposite end moments. Finally, the paper stresses those points where each standard offers a simpler approach.

Experienced structural engineers have an intuitive understanding of the buckling behavior of uniform members subjected to compressive loads. The Euler critical load and the concept of buckling length are extensively used in this context. Unfortunately, the extension of this intuitive approach to cases with non-uniform load or non-uniform members is not straightforward. Based on an extensive numerical parametric study, the paper first presents a closed-form expression for the buckling load of constant cross-section members with non-uniform axial loading. Consequently, an equivalent load approach for non-uniform members subjected to non-uniform axial load distribution is proposed and validated. The combination of both procedures has the power of transforming the general complex case of a non-uniform member under non-uniform load into an equivalent simple case of a uniform member subjected to uniform load. The new methodology is simple and direct, and produces more than acceptable approximate results. (C) 2011 Elsevier Ltd. All rights reserved.

In the design of single-layer structures, the hypothesis of pinned joints leads to structures with low capacity in terms of stability and resistance. Therefore, one of the main concerns of structural designers in recent years has been to find an appropriate joint design which would endow the joint with sufficient stiffness. In this paper, the results of experimental tests conducted with the aim of establishing geometrical parameters for a semi-rigid joint that may be used in single-layer structures are presented. They showed how the combination of different parameters can improve the stiffness of the joint and its rotational capacity. At the same time, the experimental tests provided the initial rotational stiffness of the tested joints which is to be introduced into the analysis of the structure. The paper presents an analytical method for the determination of the initial rotational stiffness of the joint. The method follows a technique similar to the component method of Eurocode 3 part 1.8, although it has been adapted to the geometry of this particular joint. (C) 2010 Elsevier Ltd. All rights reserved.