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Desirable characteristics of lightweight, corrosion resistance, high strength and stiffness, whilst offering design flexibility, means composite structures are of increasing interest beyond their usual industries. One of which is architecture, building and construction where several recent market surveys predict a healthy annual growth of around 6% in the coming years. Some of the reasons given are the awareness of cost of ownership, where – put simply – initial higher composite material costs are offset by reduced lifetime maintenance compared with conventional materials; erosion of the price difference between composites and construction materials; evolution of standards and building codes to include composites; importance of energy-efficient structures.
Composites offer designers the ability to create a material and engineer its properties to resist particular load cases and environments. Such infinite possibilities can be daunting and a big step away from the more conventional way of working with a material having a known set of characteristics. It is here that architects and structural engineers can be aided by Altair’s software, such as ESAComp, now available as a standalone product in Altair HyperWorks advanced simulation and optimization software suite, to produce efficient, stable and durable composite structures.
To illustrate Altair’s ESAComp solution for composites, let’s take a quick look at the design-development behind the proposal submitted by Digital Architects (Vienna, Austria) and Archicoplex Ltd (Tokyo, Japan) for the “Varna Regional Library” in Bulgaria.
With the proposed building’s façade foreseen as an ideal opportunity for an innovative, composite solution, ESAComp was put to work for the preliminary laminate analysis, to evaluate the structural component behaviour along with the development of the joint system. A parallel study of manufacturing processes ensured both materials and parts were economically feasible and met the as-simulated performances.
Although the material proposed, an innovative wood-carbon composite, is different from the typical materials used in ESAComp, e.g. fiber-reinforced plies, foam/honeycomb cores, the same approach applies: build the composite layer by layer, determination of the stacking sequence, correct thicknesses and proper orientations intelligently to meet the service requirements.
Wood Composite Material Development
The goal was a laminated structure comprising of thin sheets of birch wood, with layers of carbon fibre interspersed between them, all adhesively-bonded together: a classic plywood-type construction, but with a modern twist provided by an advanced composite reinforcement to enhance structural performance.
Before adding in the carbon plies, ESAComp was first used to compare the structural strength of a wood-only laminate having equal thickness plies with those having different thicknesses of wood, either on the external faces or in the middle. Properties for the wood ply can be added to the ESAComp database, and then used to create the lay-ups. Comparative studies of laminate constructions are easily set-up in ESAComp, with results reported in tabular or graphical form.
The behavior with different orientation of the carbon layers focused on comparing the effects of carbon fiber in +45/-45 and in 0/90 degree to the main structural load. Working with the preferred all-wood laminate, the lay-up can be easily modified within ESAComp to include different types of carbon fibre plies – unidirectional, fabrics having different styles – at any orientation and position within the stacking sequence and then determine the mechanical performances for each. Given the façade is made of relatively narrow beams and taking into account their orientation affects the load case (in some zones the structural load is in-plane and the wind load as an out-of-plane force, whereas in others the structural load is out-of-plane and the wind load is in-plane), ESAComp determined the optimized composite lay-up and the ratio between +45/-45 and 0/90 oriented carbon plies necessary to achieve the desired more isotropic behavior having well-distributed elastic responses in all directions.
Structural Component Behavior
For proof of concept or preliminary design stage, the façade’s organic, very complex geometrical form can be considered as three simplified main elements (vertically-oriented; horizontally-oriented; transition between those elements with different radius of curvature). Having the correct dimensions and using the optimised wood-composite laminate developed, ESAComp determined their performances under precise structural and wind load cases, without the need for the complete geometrical model.
Key points or details within a design cannot be ignored at this stage. Here, ESAComp analysis provided good input for those areas of the façade where the wooden lamellas separate and join at different points across the entire structure. This helped understand that the more horizontally-oriented elements need to be thicker compared with the more vertically-oriented elements owing to the structural load being bigger than the wind load and to the decrease in performance of the composite to out-of-plane shear.
Joint System Development
Any discontinuity in a composite structure needs to be considered early in the design, and joints are definitely a topic to be addressed because often they require a modification in the composite lay-up that then becomes an integral part of the manufacturing process. For this reason, ESAComp includes analysis tools for mechanical and bonded joints, both of which were used to investigate the means of attaching the wood-composite façade to the concrete structure.
Holes drilled for bolts effectively damage the wooden façade and require the structure to be supported by big, heavy steel members that spoil the elegant, fluid design of the façade. Whereas a bonded joint gives the possibility to use a thinner carbon fiber beam than the steel counterpart and, using a newly-developed epoxy concrete as a structural adhesive, enabled a bonded joint to both the wood façade and the concrete slab.
The joint analysis performed in ESAComp determined the thickness of the joining member required to make this process possible. Two different lay-ups for the carbon beam were evaluated to see the different responses and how to minimize the thickness of the beam so that the façade retained its elegance.
Interested to know more? Throughout JEC World 2018 visit the Altair stand N90 / Hall 5 and sign-up to our conference where Atanas Zhelev from Digital Architects will show more about the role of ESAComp within the design-development of innovative composite solutions for modern, organic architecture.