Welding techniques explained in the last chapter are doubly important when constructing a ferrocement girder. The photo below is me holding the upper left end of the girder while friend Peter Burgess positions it in the armature of a ferro pillar which was also a small closet. The upright reinforcing steel bars were bent in a right angle and welded into a straight piece of angle iron. This is the type of weld that can only be done on one side of the round bar where it meets the flat and straight angle iron.
Again. HereÕs how it works. The welding rod tensile strength is equal or better than the steel being welded. True, for large machinery, welds are filled first with lower strength steel, but that is a different discussion, more like what good cooks are all about. This work is not space science, the girder is simply made by welding L shaped reinforcing bar into the L shape of lengthwise angle iron at the bottom.
Notice the angle iron protruding from the stone wall, which the girder is being placed on. That angle iron is attached to an over-window reinforcement further into the stone wall, as described in the last chapter.
Everyone who has read this should definitely know for certain sure that when the weld shrinks as it cools, it is strong enough to bend very strong angle iron; if, and only if, one welds both sides of roundness to flatness. Interestingly, for those who visualize these things in their own way, the bent shape is like a corkscrew because the shrinkage happens.... Hmm-mm. I had it in words but my fingers couldnÕt keep up. Maybe somewhere later on, here-in. Big machinery workers know about controlling bends like this to straighten, with Òpurdy goodÓ precision. I helped one do it, as mentioned previously. First cut away steel, then weld the cut to use the shrinking weld to pull the bent member to eyesight straight.
Straighten and secure the angle iron the vertical re-bars are welded to before welding horizontal bars, which morph to fit the roof intersection curve, measured as previously described, with a ruler, scaled from the plan. An additional feature of girder awareness to notice is that the girder may be any portion of the supported roof plane. Specifically, the girder in the photo ceases where the stone wall takes over.
The complete girder shape shown above is about 6.5 meters long when scaled to span from the pillar at PeterÕs back to the just finished girder work he is viewing. One small 5 by 10 centimeter post is all that is required mid-span to maintain a straight girder. A tight string line is utilized for precision girder armature positioning.
Ferrocement girders are an intriguing form of insurance. Walls are better described as partitions which are not required to maintain structural integrity. Earthquake or fire may damage inner walls but the structure will remain. If there is no wood other than partition walls there is not enough fuel to destroy concrete. A wooden floor and supporting wood girders would change the game significantly. Large upper skylights and windows which will burst from fire will release extra heat energy that might otherwise prove damaging to the basic structure.
Economics is a subject which cropped up and was then purged from discussion, so far, in the ferrocement.com bio-fiber book. I shant do that again here. As the sensitive and keen of mind may already have noticed, Economics is one of my raisins de okra. As a graduate economics student, I alone did not need further undergraduate studies. Statistics, mathematics, physics, philosophy, and surfing requirements had all been fulfilled. Yes, even surfing. Then, toward the end of the Vietnam war, I, the surfer, was declared a communist.
Some present day proponents of nuclear power label people not fond of nukes as dissident or even terrorist. I actually went to graduate school to find out what a communist is. Should I live an extra long life, I may return to graduate school and try to find out what a terrorist is. Seems to me that anyone with radioactive exhaust pipes and huge sirens requiring howling tests that pierce neighborhoods are among the worst of terrorists. I find it increasingly weird that there are homeless people and wars.
This drawing, though slightly different than the structure in the photo, presents the design philosophy behind the girder Peter installed. The photo showed the horizontal armature re-bar gradually assuming the curve of the roof over the living room area, leftward in the above drawing. Notice that the hinged overhead window viewed from the bed has a flat bottom and arched top. Thus the girder appears as an arc from the living room and as a straight rectangle from the bedroom.
The following picture gives an idea how these structural components mesh together and become a complete structure. Solar power is visible directly below.
This detail from FrankÕs drawing uses the ferrocement girder to span the opening from living room to kitchen.
Girders are not at all limited to the examples provided so far. A book many times larger this one could be filled with photos and descriptions of girders used in different construction instances The first of the following two girders is one way to replace a rotten or insufficient wooden girder with ferrocement. The second illustrates a flat top supporting girder arched underneath rather than above.
