Friday, February 17, 2012

Tension cables in a masonry dome or sphere

The interlocking triangular block which I’ve developed and refer to as a dimp (dual inverse mirror plane) has a symmetry which allows a clear line-of-sight path along the center of each interlocking abutting edge of the block, as shown below.

This means that cable, or wire, or rope, or any appropriate tensile element can be incorporated into an assembled structure.  These cables can be placed on each of the three sides of a given masonry unit and woven together (I ask the reader to forgive my sloppy lines!).

A number of different types of regular polyhedra can be assembled from these triangular interlocking blocks.  These configurations can be used as templates for making spheres, or domes, or parts of domes.  The polyhedra which can be assembled from the hex and pent blocks include icosahedrons, dodecahedrons, icosidodecahedrons, truncated icosahedrons, and snub dodecahedron, among others.



Truncated Icosahedron

Snub Dodecahedron

 In addition to the different polyhedral arrangements to choose from, different frequencies of these structures can be used to make larger or smaller domes or spheres.  Many different sizes of structures can be made from just a couple of unit shape triangular blocks.

As a given polyhedral dome is built, the first triangular blocks are laid on the starter course.  The starter course is a circular ring.  In between block anchors are cast in the concrete foundation, to which cables are attached.  These cables are placed in the abutting edge of the interlocking face and woven into the structure as it is assembled.  Shown below is a complete sphere being made, with a few of the cable loops pictured (I didn’t draw them all, it would be too sloppy).

Upon completion a sphere or dome has an interconnecting tensile web of great circle arc cables which hold the structure together.  Springs may be incorporated into the cable system to allow movement while also providing a restoring force, which will respond to any deformation by returning the structure to its original round shape.  The drawing below shows just some of the great circle arcs described by weaving cable elements into the abutting edges of blocks.

This tensile configuration system is applicable in cases where extreme loading conditions are expected.  This includes seismic activity, hurricanes, tornadoes, blast resistant structures, hardened structures, etc.

The combination of a mortarless gasket system (as described in my previous entry)  together with a woven tensile cable system creates an efficient, inexpensive, easy to assemble, high performance masonry construction method.

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