Civil Engineering Reference
In-Depth Information
been tightened more than once. Ideal compression of the bales will occur over several
days, which would not suit this product.
Threaded rod
One option for compression is to fix a threaded steel rod into the concrete. As the layers
of bales are fed over the rod a female threaded connector nut is used to join another
section of threaded rod to the previous to extend the threaded rod for additional layers.
This process continues until all of the bales are in place. The top boxing is then fed over
the threaded rod and bolted into position. As the nuts are tightened the bales between the
top and bottom boxing are compressed.
Beware of the temptation to cut the excess threaded rod of with an angle grinder!
Sparks and straw are not good companions as was discovered in Victoria not that long ago.
Conventional construction in cyclone areas often require steel rods from the
foundation up to the roof, not dissimilar to that used in this compression system, so it
would be fair to assume that the same requirements would apply to straw bale
construction. The primary complaint about this method is that the bales have to be fed
onto the steel as they are laid which I am told is frustrating and slow compared to external
compression methods.
Fencing wire
Fencing wire combined with gripples, a mechanism for joining fencing wire, has been
used quite successfully. Extreme care needs to be taken with this method. There are many
farm-fencing contractors that have sustained a serious eye injury from fencing wire. With
this method it is important to install a connector on either side of the wall, as once the
wire is bent over the top boxing it will not slide to allow even tension on both sides of the
wall. I have used gripples in farm fencing and have found them to be simple to use,
however I have had more than a few fail.
Flat filament polyester
Flat filament polyester strapping is my preferred method of compression. The alternative
that we recommend is the application of flat filament polyester strapping with a breaking
strain of 1000 kg. This strapping is quite supple and tends to slide over the top boxing,
however I still recommend that a connector buckle be installed on either side of the wall.
While the strapping is more costly than fencing wire, the overall cost is the lowest of all
methods as the heavy duty joining buckles are in the vicinity of 25 cents each as opposed
to around $1.50 for wire connectors (2005).
Using flat filament polyester strapping
Prior to fitting the bottom boxing to the floor you will have positioned the strapping on
the floor at 450 centres. Lay the straw bales as detailed previously, paying particular
attention to alternating the direction of the cut side of the bales.
Position the top boxing on the top of the straw bale wall. To protect the top of the
wall from unexpected rain, lay a section of builder's plastic approximately 1.8 metres
wide over the top boxing. If you are particularly concerned about the possibility of bales
getting wet from rain, additional plastic can be laid from the floor on one side of the wall
to the other in a single piece, over the top of the compression strapping.
