Multi-pultrusion fibre composite truss systems for deployable shelters

Multi-pultrusion fibre composite truss systems for deployable shelters

Deployable shelters of various forms have been utilized since ancient civilization. The need for these systems has not diminished over time and development continues
for military forces, civilian humanitarian aid, and natural disaster scenarios. Recent developments have focused mainly on tent-type structures, air-beam technology and steel frames supporting soft fabric; yet none of these have fully satisfied the deployability requirements. The Military Modular Shelter System (M2S2) initiative is a research project with the University of Southern Queensland that aims to develop a fibre composite re-deployable arched shelter system with rigid PVC or fabric cladding. The main frames are formed from modular fibre composite truss panels that are connected and stressed into position by prestressing cables. Flexibility in defining the geometry of frames constructed by using this system is achieved by changing the number of panels per frame and the packer sizes between panels.

The current study is the first to investigate a suitable truss system for the M2S2 concept. Accordingly, it was necessary to validate the M2S2 concept by searching the
literature for previously developed deployable shelter concepts and locate the currently used fibre composite truss systems. Then try to establish a suitable truss
system that fulfils the deployability needs with sound structural performance.

An innovative all-composite truss concept, named Multi-Pultrusion Truss-System (MPTS), was developed as a result of this study. It overcame the classical difficulty
of joining composite members by loading each component of the truss in its strength direction. In addition, the system had inherent redundancy that provided alternate
load paths after reaching ultimate capacity. The basic idea of this system was to have chord and vertical members formed from a few pultrusions of the same size. The
traditional usage of gussets was eliminated by using laminates for the bracing system which directly connected between the pultrusions. This system allowed direct transfer of the bracing forces to the connected members (pultrusions). This layout led to reducing the concentration of stresses in the adhesive layers (due to its continuous nature), while providing symmetric joints with two double-lap joints. All these
factors contributed to having failure away from the joint area. The confinement of the bracing system, due to its finite dimensions, was one of the characteristics of this
construction technology.

Two MPTS alternatives were developed, tested and investigated. The first alternative used a Discrete-Diagonal (DD) bracing system made of sandwich
diagonal. Two panels DI-MPTS panels were tested using this configuration, one with the diagonals under tension and the other with the diagonals under compression.

The second alternative used a Diaphragm (DI) bracing system. Three different DI-MPTS panels were investigated. The first panel had an empty diaphragm (no core); the second panel had a partially-filled sandwich diaphragm while the third panel had a completely-filled sandwich diaphragm.

To achieve understanding of the basic behaviour of each of these panels, finite element (FE) analyses were conducted at micro level. The different components of
the panel were included in each model, with idealisations to achieve an efficient analysis process. The FE analysis results were used to investigate the distribution of
forces in each of the panel components.

Due to the associated costs of micro-model analyses, macro-analysis models are important tools for engineers interested in modelling this system, conduct pre-microanalysis parametric studies and in modelling the overall frame structure. This study ended with presenting simplified analysis procedures for the different panel types.

The work conducted in this study has revealed that this new fibre composite truss system suits the characteristics of fibre composites and accordingly provides an
efficient solution for general truss applications. It combines simplicity, easiness of manufacturing, high-load carrying capacity and structural redundancy. In addition, its behaviour and failure modes can be accurately predicted by using the currently available finite element software packages.