Marijke Mollaert

Design and Analysis of a Foldable Mobile Shelter System

A concept for a mobile shelter is proposed, based on the geometry and kinematic behaviour of foldable plate structures. The folding pattern and the associated design parameters are discussed, along with their influence on the geometry and the kinematic behaviour. It is shown that the transition can be made from a foldable plate structure to a foldable bar structure, while retaining an identical kinematic behaviour. This is done by introducing custom-built joints for connecting the bars which allow the system to deploy in the desired way, maintaining the same D.O.F (degree of freedom) as the plate system. For the structure to be employable as a fully-fledged temporary space enclosure, a lightweight textile membrane is incorporated beforehand and deployed along with the bar structure.

Shell Elements of Textile Reinforced Concrete Using Fabric Formwork: A Case Study

Innovations in formwork solutions create new possibilities for architectural concrete constructions. Flexible fabric replaces the stiff traditional formwork elements, and takes away a limiting factor for creative designs. Combined with textile reinforcement, the production of a new range of curved and organic shapes becomes possible without the intensive labour for formwork installation. Besides a general introduction about the concepts of fabric formwork and textile reinforcement, this paper focuses on the production and structural evaluation of doubly curved shells. Creating a very interesting type of element from a structural point of view, the shape flexibility of both the fabric formwork and textile reinforcement make a perfect match to overcome practical production issues for thin shell elements. The application of shotcrete and the integration of non-metallic reinforcement allowed first of all the production of very thin concrete shell elements based on the design approach of the textile architecture. Comparing a shell structure with traditional reinforcement and one with textile reinforcement, a case study evaluates furthermore both the design and the structural performance of such a shell structure.

Shaping Tension Structures with Actively Bent Linear Elements

To achieve sufficient anticlastic (negative) curvature, membrane structures are tensioned between high and low anchor points, attached to the ground, buildings or poles. By integrating flexible bending elements in the membrane surface, an internal support and shape-defining system is created that provides more freedom in design and allows reducing the amount of external supports compared to traditional membrane structures. This paper presents a computational framework for form finding of tension structures with integrated, elastically bent, linear elements, based on three-dimensional bending moment vectors and a mixed force density formulation. With an implementation of this framework in CAD modelling software, users can control form and forces by prescribing any combination of force densities, forces, stiffness or lengths to the spline and cable-net elements. Sparse matrix operations are used to compute the resulting equilibrium shapes. The shape-defining possibilities of integrating ‘bending-active’ elements in tension structures are demonstrated through a series of design studies with various boundary conditions and spline configurations. The presented framework and implementation provide a straightforward method for the design of this hybrid structural system, and, therefore, facilitate its further exploration.

Scissor-hinged retractable membrane structures

This paper introduces scissor-hinged retractable membrane structures, a system for retractable membrane roofs that require a fully retractable supporting structure and multiple stable roof-configurations. A vaulted, foldable, supporting structure is developed consisting of two scissor-hinged frames that can retract towards opposite sides of the space below. Structural membranes are spanned in these frames in a ridge-and-valley configuration to form the roofs outer surface. Actuators are integrated to control the tension in the membrane surface in different roof-configurations. Transformation from one configuration to another is controlled by cables running through the supporting structure over series of pulleys. The characteristics of these components are discussed, and their implementation illustrated with a design for a retractable roof over a tennis arena. The structural behaviour of this roof is analysed under representative load conditions. A procedure for such analyses using conventional software tools for the design and analysis of tensile surface structures is presented.

Numerical evaluation of structural stay-in-place formwork in textile reinforced cement composite for concrete shells

This article presents the structural evaluation of textile reinforced cement composite elements as formwork and reinforcement for concrete shells. Different shell geometries of 10 m span and a height between 2.5 and 5 m are examined. On one hand, the minimum thickness of the composite element functioning as formwork for these shells is determined when supported with a different number of supports and for different concrete sections. On the other hand, the minimum thickness of the composite functioning as reinforcement is calculated to withstand the occurring maximum bending moment. For shells with a 10 to 15 mm concrete section, a minimum composite formwork of 5–6 mm is needed to carry the load of the cast concrete, while the minimum composite reinforcement needed to withstand the maximum occurring bending moment equals 2–3 mm. Conclusively, this preliminary numerical study demonstrates the structural potential of textile reinforced cement composite stay-in-place formwork for concrete shells and indicates the dominance of the casting stage over the final stage. More specifically, local buckling of the formwork is the determining factor and should drive future work towards this issue.

Numerical and experimental research on annular crossed cable-truss structure under cable rupture

The Annular Crossed Cable-Truss Structure (ACCTS) is a new type of Tensile Spatial Structure with a configuration suitable to cover large-span stadiums. Its configuration has potential to perform well in resisting disproportionate collapse. However, its disproportionate collapse resistance hasn’t yet been analyzed in depth. In this study, numerical and experimental research was carried out to investigate the performance of ACCTS under cable rupture. The numerical analysis was done for ten cable-rupture plans using LS-DYNA (explicit method) and the experimental test on an ACCTS with a diameter of 17.15 m was performed for three cable-rupture plans. It is concluded that, while deflections increase with the number of removed cables, an ACCTS does not undergo a disproportionate collapse and it provides a promising structural concept for tensile spatial structures.

Textile shelters for archaeological or heritage areas: design references

The paper gives a short summary of the properties of tensile surface structures made out of technical textiles. Tensile surface coverings can protect archaeological or heritage areas against deterioration and revalue these sites for visitors. Covering systems have to combine several preservation requirements like protection from environmental and pollution load, low maintenance, compatibility of new materials, reversibility, ease of disassembly, reusability, adaptability and flexibility. Textile lightweight structures present a great number of advantages like easy mounting, natural aeration, elegant design and filtered natural day lighting. Building on archaeological or heritage areas is a delicate task. Architects have to compare alternative approaches and find solutions appropriate for the situation under consideration. The discussion on built shelters, presented together with the underlying concepts, the performance, the used primary structure and the chosen coated fabric can support design decisions in future. A recent research activity has been started in Sardinia (Italy). The aim is to analyse technical aspects and to clarify which solutions really serve to protect while others contribute to further damage. Prototypes have been built in order to evaluate the behaviour of some innovative textile materials in comparison with traditional ones.

Preventing disproportionate displacements in an annular crossed cable-truss structure

Disproportionate displacements in prestressed mechanisms raise concerns widely. Component rupture can result in disproportionate displacements of a major part of prestressed mechanisms. In general, increasing the cross-sectional area of structural members will be of little effect to prevent this kind of failure. A new type of prestressed mechanism named annular crossed cable-truss structure has been proposed. The new configuration shows advantages in preventing disproportionate displacements. An annular crossed cable-truss structure ( R = 68 m ) is analyzed to evaluate the effect of the sudden rupture of a connection through the instantaneous component removal of the elements linked to it, using ANSYS/LS-DYNA. It is illustrated by the simulations that disproportionate displacements do not occur. Increasing the cross-sectional area of structural members with an appropriate amount can be an effective way to postpone failure of the structural members in which the axial force increases due to internal force redistribution and dynamic amplification effect. Hence, it can be concluded that the annular crossed cable-truss structure has an excellent performance with respect to hazards causing individual connections to fail.

Structural Reliability in Design and Analysis of Tensile Structures

In order to achieve a semi-probabilistic verification format such as used for the analysis of conventional structures in the Eurocodes, research into structural reliability calculations for tensile surface structures is needed. Appropriate partial factors have to be proposed and evaluated. To gain insight, a scholastic example with three cable segments is analysed. In order to take into account the uncertainties associated to the pre-tensioned system, Latin Hypercube Sampling is applied to sample six main influencing variables. The cable system is designed according to the ultimate limit state under loading, considering a partial factor of 1.35 for the pretension. The structural reliability of both designs is evaluated. An increase of the partial factor for pretension from 1 to 1.35 results in an increase of the reliability index from 2.27 to 5.42.

Variations In Form And Stress Behaviour Of AV-shaped Membrane In A Foldable Structure

Adaptable tensile structures are often considered to be either completely opened or completely closed. The current study is part of a research project studying adaptable tensile structures which demonstrate stable behaviour within a wide range of opened positions. In this paper a simple V-shaped membrane is studied during the unfolding process. Starting from an initially flat folded membrane, which is not pre-tensioned, a slight curvature is obtained when it is unfolded due to the fact that along the folding line a curved section is cut out of the fabric. The tension introduced in the transverse direction implies a tension in the longitudinal direction too. Two cases are analysed: one with a high curvature in the diagonal cable (~5% sag) and one with a low curvature (~1.3% sag). Based on computer simulations the form and the tensions are verified for different opening angles. The deformation under loading is checked for the shape with a low curvature of the diagonal cable at an opening angle of 70o. The results indicate that the membrane could be used as a fabric roof. Further refined analysis is needed to be able to implement the presented concept for real applications.