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Akegata
Joined: 30 Oct 2005
Posts: 3
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 Posted: Sat Feb 18, 2006 5:05 pm Post subject: Space frames, loading and span tables? |
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Has anyone ever come across a simple guide for space frame structures,
I am contemplating there use in a scheme I am curently working up at 1:200 but am unable to find span/loading tables or even some rough guidelines for them and its not really viable to employ an engineer at this stage.
Many Thanks
Akegata |
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TLWalkerAIA
Joined: 16 Apr 2004
Posts: 130
Location: Seattle Washington, USA
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| Posted: Wed Feb 22, 2006 12:05 am Post subject: |
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WOW that is a great question.
A space frame is a structural system which distributes loads to supports through linear arrangement of members placed in more than one plane. It is designed to transmit loads through its members by direct tension or compression without bending. It is a three dimensional truss.
Space frames are not easily observed in nature. However a section through a bone reveals something much like a space frame, optimal strength for a minimal amount of material.
Now to come up with any thing like a span table you would have to define the load distribution. Applied loads develop forces which are distributed within the plane of a conventional truss. Space frames ditribute forces in two or more planes simultaneously. Typically these planes form a series of diagonal trusses and may be a triagulated geometry or a rectangular geometry in the plan view. Aection through a space frame will typically reveal the three dimensional structure of the system and show that no major or minor trusses exist in the system. The size of each truss and each individual member indicates that the loads are distributed equally in several directions.
The geometry is typically composed of equilateral pyramid or tetrahedron, combined resulting in a hex grid in plan view (tetrahedron) or a rectilinear grid (equilateral pyramid).
Because the depth and member sizes of a space frame are less than that required for a conventional truss system. The depth required for a conventional truss system is aproximately 1/10 the span while the depth required of a space frame is aprox. 1/20 to 1/30 of the span.
I think there may be manufacturers of space frames that have charted the span capacities of their products. Custom applications and geometry will efect efficiencies significantly. Check with sweets etc. for manufacturers. Failing that info search the preliminary sizing can be done acording to conventional truss systems.  Your error will be on the plus side of the weight of structure.
Suppoting the space frame can be tricky. various methods alter the load distributions within each frame. Point support is different from lattice support and it affects the sizing of the members.
Good luck! I would like to see your peoject.
_________________
Terry L. Walker, AIA
Terry L. Walker, Architects
terry.walker20@verizon.net |
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