ORIGINAL: billdor
Excuse me for butting in but it seems to me that what we are talking about here is a truss. The whole purpose of the webbing is to keep the top and bottom spars apart. In order for the wing to bend the spars must collapse together, if they can not do this because of the shear webbing then the tensile strength of the spars comes into effect. In other words the spars would have to break. The ribs alone are not strong enough to keep the spars apart because the grain is horizontal, so adding more horizontal grained webs is not going to help much.
It is easy to prove this point. Take two sticks of equal length and put them together side by side then bend them both together and observe what happens to the length. The one on the outside of the curve having a longer circumference to cover will end up shorter. Now hold them apart a little and attempt to bend them keeping the ends at equal length. At some point they will have to come together because the inside one will have to form itself to a smaller radious.
Most of what you say in the quote is correct, you are just slightly in error in the way you interpret the results. What happens is that the upper spar is put in tension while the lower spar is put in compression, the resulting forces between the upper and lower spars is a shear force at a 45 degree angle to the spars where the upper spar is trying to elongate while the lower spar goes into compression (assuming a positive G load). Now what happens if no shear web exists and you exceed the breaking stress of the lower spar is that it will snap and move upward toward the upper spar at the break. Reverse the load (negative G load) and the forces shift 90 degrees with the upper spar in compression and the lower on in tension and the shear forces shift that 90 degrees.