I wondered how much stronger a printed I-beam would be if it were reinforced with steel bar. So, I printed three beams and broke them.
The steel reinforced beam was 50% stronger and 100% heavier. However, I believe using smaller reinforcement bars and adding more web area to the beam would drive the strength results way up and the weight way down.
Details including the full test write-up here
This sparked my imagination a little and I really believe that using 3D concrete printers to make structural members with rebar installed layer by layer would be a very viable business. It would be much cheaper than making expensive molds while allowing for nearly limitless design possibilities.
I am a bit curious on why so many center holes compared to a traditional beam with no holes?
Those diamond shaped holes are forming a shear plane down the dead center causing a split. Changing these to true circles/ellipses would help prevent this. Also, printing them face-flat should also increase the strength. Very interesting testing, thanks for posting.
I forgot I had already posted this. I just put the diamonds in the center to make it print with less warping and without supports. I didn't play with it after this test. The most obvious change is probably to use a smaller steel bar (which I meant to do to start with) as well as adding more shear area in the web. If I were to do this again I'd probably try to run some simulations in CAD to get the stresses evened out all over the beam.
I was hoping it would spur some interest and others would post some tests of improved versions and novel applications.
I would like to see you try that using carbon rods instead of steel. It would not be quite as stiff, but I think you could get better bonding between the carbon and plastic than between steel and plastic. Also the thermal coefficients would be closer.