Strongest LEGO structure - (2) Floor What is the strongest LEGO box structure?

I am going to build a LEGO computer case. Different from Mike Schropp and greenyouse, I am planing to build an upright case.

(This is a general "strongest LEGO structure" question. Using the structures in building the computer case is just an example of applications.)

To make it more challenging (and more perfect), the case will have handles (like this type) for carrying the whole thing around, and it will have "legs" (like this bar type) to lift the whole case up for ventilation.

For better reference, here is the coordinate notation:



There are 4 parts (for now I can think of) in the case which has to encounter different types of strength challenges:


The pillars (Red)
The floor (dark grey)
The joints (purple)
The handles (yellow)


  

For the white bricks, they do not require special strengths, do they?

FYI, here are the LEGO dimensions: 

Horizontal pitch, or distance between knobs:  8mm.

Vertical pitch / Brick thickness:  9.6mm.

The horizontal tolerance:  0.1mm.

Plate thickness: 3.2mm.



Above is the common information across the 4 questions.

Below is the question for this specific part.



(2) The floor (dark grey)

Someone has done some experiences against the effect of weight on LEGO bricks (results at slide 11). From his experiments, the Flemish structure is a clear winner.

Like the pillar problem, I wonder why not stack plates/bricks up along the X/Y axis, instead of the Z axis?

My suggestion is basically the structure of the pillar rotated clockwise along the Y axis, and extending it along the Y axis.



For those who have not read the pillar section yet, this is simply stacking up plates along the Y axis.

Same as the pillar, there is a risk of the plates separating due to the weight. So I make a "doughnut" to secure the plates.



Here is how they look like together.



I assume using longer plates will be better than short plates, because fewer connecting points, lower risk to separate, isn't it? However, in the presentation mentioned above, the result suggests that a mix of long and short plates has the most strength. Does this theory apply to my "Y axis structure"? And how long and how short combinations will be the best?

In addition, in my "Y axis structure", will using bricks instead of plates be stronger?

However, thing is more difficult here than the pillar. It is because the tension is not only pulled along the X axis. Instead, the weight is applied down the Z axis, and tension is all along the X and Y axis. So I assume this structure, when used as floor, will be a lot weaker than used in the pillar.

Please suggest any of your structure ideas which will be the strongest.
Just like in the other question, I would recommend a Technic frame with more depth than your original idea and some plating on top of it. This project nicely illustrates how to build stable Technic structures using beams in triangle configurations.