CAD DESIGN

How we use CAD design to create architectural fabric structures which are beautifully formed, efficient in achieving their design objectives, long lasting, and, most important of all, safe

CAD DESIGN - what is it exactly?

“Computer-aided design (CAD) is the use of computer technology by architects, engineers, and others for design and drawing”

We use specialist design software to:

allow our designers the freedom to explore any and all possible design solutions for a specific task
to optimize such designs in terms of component materials, dimensions and shape, and
to ensure structural integrity of designs under all expected site conditions

STEP 1 : FORM-FINDING

Unlike most other building materials, fabric can take on many shapes according to a whole range of factors which designers make use of to produce those shapes they require:

The location and nature of attachment points, supporting structures such as beams, and other elements which constrain the ultimate shape of the fabric such as edge rigging and attachment links
Applied tension
Degree of elasticity of the fabric
Form-finding software allows designers to explore and experiment with some or all of those factors to create the optimal 3-dimensional fabric shape which fits existing or proposed supporting infrastructure, ensures efficient shade patterns & water run-off, and achieves the design objectives.

Form-finding software allows designers to explore and experiment with some or all of those factors to create the optimal 3-dimensional fabric shape which fits existing or proposed supporting infrastructure, ensures efficient shade patterns & water run-off, and achieves the design objectives.

STEP 2: SHADE & WATER RUN-OFF OPTIMIZATION

For many fabric structures, the product is often the degree of sun or rain protection it affords, rather than the structure itself. In such cases our designs are guided by those requirements and by simulations provided by specialist software.

STEP 3 : LOAD ANALYSIS

When designing a building, a structural engineer needs to know the weight of its roof, and the added forces on the roof when the wind blows. With that information (“loadings”) the supporting structure below can be designed to resist those loads.

It's no different with fabric structures, with one exception: unlike roofing made from rigid materials like steel, fabric structures deform under load (that is, they change their shape in response to wind forces). When this happens, loads on the supporting structure change as well.

We need to be able to provide our structural engineer with realistic loadings transferred by the fabric membrane onto its support/attachment structures: the columns & their footings and supports, beams, and rigging, in all expected wind conditions (strength & direction.

That’s where we employ a second suite of software: FINITE ELEMENT ANALYSIS (FEA)

FINITE ELEMENT ANAYSIS (“FEA”)

FEA is a mathematical solution to the problem of determining (as applied to building structures) the overall effect of applying known loads to parts of the structure. It allows a simulation of what stresses will form within components of the structure.

The structure is broken down into a large number of small elements which together form a “mesh”, representing the entire structure. This is a way of transcribing a 3D object into a series of mathematical points that can then be analyzed.

Calculations are run for every single element or point of the mesh and then combined to make up the overall final result for the structure.

Such simulations allow optimization of elements of the structure to select appropriate structural elements, their location and their materials and dimensional specifications.

STEP 3 (a)

After determining the desired membrane design (Steps 1 & 2), the loads produced by it are calculated by FEA:

“static loads”: (ie. those produced by the self-weight of the membrane and additional loads induced by bringing it to full design tension)
Wind loads (at maximum expected wind velocities from nominated directions)
Including acceptable or stipulated safety margins

Plot showing stresses within a membrane (left) at a given wind load case, and (right) the “reserve factor” (ie. safety margin) of the final model, indicating any areas where stresses may exceed those regarded as outside limits of the materials (after including the selected safety margin).

The same simulations can be done on the links and edge (catenary) cables of the membrane.

STEP 3 (b)

Optimization of supporting structure design by structural engineer.

Using loads determined in Step 3 (a)

optimize the design of all supporting infrastructure (footings, columns, attachment points, frame connections)
Including provision for appropriate or stipulated safety margins

Frame design optimized by FEA and including simulated loadings from membrane FEA analysis