ALGOR AROUND THE WORLD - Ferrara, Italy

For many companies, the time-consuming and costly construction of prototypes is an accepted and unquestioned necessity for product development. Spreading awareness of the finite element method, however, is prompting many of these firms to ask how FEA can improve their designs and reduce costs.

One such firm is ECO Edilizia Coordinata, Abano, Italy, a developer of steel structures. This company enlisted the services of ABN CAD/CAE Development and Applications s.r.l., Ferrara, Italy, an engineering software company operating in the structural analysis field. ECO had ABN do a stress analysis on an architectural space frame system used to cover large areas with steel grids. ABN found that Algor's finite element software produced stress analysis results that consistently agreed with prototype tests.

Stress analysis of a global joint revealed a high consistency with the outcome of tests on prototypes like the one pictured.

The space system was designed by ECO, a recognized leader in the field of steel structures. Their patented steel grid construction system is used in a variety of applications such as framework for office buildings, skylight ceilings, and interior decorating. The modular nature of the parts makes the system easy to construct, take apart, and transport.

ECO's space system consists of a series of joints connecting trusses. The trusses are steel tubes with circular hollow sections, the ends of which are shaped to make the trusses easy to assemble. Each joint can be visualized as a cup with a triangular bottom, six sided edge, and cross plate. When assembled, the joints, horizontal trusses, and diagonal trusses generate pyramid-like structures, with bases both up and down.

"Modeling the system with Algor software was fast and easy," explains Paolo Nagliati, founder and partner of ABN and project engineer. "Using the ViziCad Plus submodule, SuperDraw II, we drew a pyramid. With the Modify:Copy option (with Join active) we completely generated the structure. The Modify and Update options enabled us to change the colors of lines corresponding to trusses in different sections.

"Next, boundary conditions, loads, and truss properties were applied with BEdit. The model was then analyzed with SSAP0, Algor's static stress analysis processor. Finally, by viewing color stress contours generated with the Superview post-processor, we were able to identify over-stressed bars."

	The ECO modular steel grid space system is comprised of joints, horizontal trusses, and diagonal trusses that assemble to make a series of pyramidal modules.
	A cup and its encasing joint.

The joints were analyzed in a similar manner. Basically, stress analysis was performed in three steps. ABN first analyzed the global joint (consisting of four cups, a cross plate, and bolts). Next, they analyzed a single cup subjected to forces that were generated by loads acting on the global model. Finally, the cross plate, also subjected to those forces, was analyzed.

After analysis ABN was able to predict:

• relative displacements between bolts,
• distribution of forces coming from horizontal trusses between cups and cross plates,
• distribution of forces coming from diagonal trusses between adjacent cups,
• distribution of stresses in cups, and
• distribution of stresses in cross plates.

Whenever the space system is analyzed, a simple auxiliary program which uses a database verifies the SSAP0 or SSAP3 (for seismic analysis) results. If bars are incorrectly designed, the auxiliary program suggests an optimum diameter for the bar. If the structure is verified, the program generates the necessary official reports.