Design of artwork & sub-structure

[valleyboy]

I have been asked to design some 'artwork' which is to be erected in a local town.

The artwork takes the form of three polished stainless steel conical tubes which are 600mm diameter at the base, 100mm diameter at the top. The top of these 'spikes' are to be 15m above ground level. The base of the 'spikes' are arranged virtually on a common centre line, spaced approximately 3m apart. The 'spikes' are not vertical, but are inclined. One of them is to be inclined at approximately 55 degrees to the horizontal.

I have yet to put any figures to the problem, but initially thought to approach the design of the members as a chimney structure. Clearly, chimneys are normally erected vertically so I will have to account for the additional moment caused by the self weight of the member. Do you think this is a fair approach to the design?

I also wondered about the foundation arrangement. I am in the process of arranging a site investigation, but considered the use of a common mass base to achieve stability. If I employ this method, can I consider the passive resistance generated over the depth of the foundation, or do I just rely on the self weight of the base? I am unsure whether sufficient rotation of a shallow base will be achieved to mobilise passive pressure at the sides.

Either that or tension piles I guess??

Any thoughts?

Valleyboy

 

[pba]

I had one of these years ago when I was a graduate engineer. Mine was three curved spikes of different heights made of wood.

I remember designing a concrete foundation to support them and it turned out to be massive. It was intended only to be a temporary insallation so we changed the design to a steel sub-frame and held it down using ground anchors. I can't remember the name of the anchors but they were a flat hinged plate which was pushed deep into the ground by (I think) the excavator. The anchor was then loaded and the plate rotated in the ground and provided the key. The cable was then connected to our frame. We galvanised the whole assembly as we didn't know how short term the installation was going to be.

For a concrete foundation, I wouldn't rely on any passive pressures - Design the foundation to resist the overturning by its own weight only. Now steel cones could behave dynamically under strong winds ( I assume you are not designing the actual cones?) so you should allow a healthy factor of safety.

 

[jheidt2543]

valleyboy:

I just finished a somewhat similar structure in stainless steel. Two spires one 60' the other 55'. The cross-sections were triangular, but the spires were basically vertical with multiple waves in them, like flames. I designed the internal framing of the spires with an FEA program which also gave the gravity and wind loadings to the foundation.

The foundation was a combination of a concrete pad 5' thick for gravity and mass and Chance Anchors for wind overturning and uplift. The scupture sat along a river bank and could be subject to periodic flooding. The anchors were on the order of 20' deep, to avoid possible scour. It is supprising how much force those drill-in Chance Anchors can produce in the right soil.

The fun part was working with the sculptor. I've always had an interest in art, but my ability is pretty limited - as an engineer I think in a coordinate system. The artist was more of a free-form thinker. It worked, once we got used to each other. We also had a very good fabricator for the final piece.

 

[AlohaBob]

I built a piece with a local artist again. It's sure a change from buildings. Temperature effects are more significant for statues than buildings. Frost depth can extend deeper. Pole design for foundations can apply.