First time I saw these shelves was in Budapest, at a friends apartment. I was told they had been designed by a physicist. That's why I think they are safe. The ones in the photos have been up for more than a year now.
Step 1: The model 240 cm by 240 cm
This is just one model. You can personalize the design to fit your needs.
Step 2: The materials
For the model showed in Step1 the materials are:
4 sticks of pine of 240 cm by 5 cm by 6 cm (5 is front; 6 is deep) (photo1)
6 selves of DM of 240 cm by 22 cm by 3 cm (photo2)
4 wall metal peg screws to hold large weigths (one for each stick) (photo3)
12 regular wall plastic peg screws to hold medium weigths (three for each stick) (photo4)
Step 3: Cut off mortices on sticks and shelves
The whole set is assembled like pieces in a puzzle without glue or screws.
In the sticks make a mortice for every shelf.
In the shelves make a mortice for every stick.
In our case this means 6 mortices in each stick and 4 mortices in each shelf.
As a rule, in sticks make a mortice 2/3 deep of the side of the stick and in shelves make a mortice 1/3 deep of the side of the stick. (In the example this means 4 cm in sticks and 2 cm in shelves because the side of the stick is 6 cm).
Step 4: Hold vertical sticks on the wall
Use the strong screw in the middle of the stick.
Check verticality with a bubble level.
Fix the other 3 screws in every stick.
Step 5: Finishing
Once all the sticks are on the wall, assemble the shelves and VOILA! you have it done.
BUT THERE IS STILL ONE MORE THING...
PLEASE DO NOT MISS THIS DETAIL WHETHER YOU THINK IS IMPORTANT OR NOT!
The last thing to do is to insert wedges of wood under all the shelves and in every stick untill all the shelves are ortogonal (=perpendicular) (=90 degres) to the sticks.
Step 6: Another example
This is another one we made for a "used things" shop in our city.
It is 15 meters wide and 2,5 meters high with vertical sticks every 0,5 meters.
It was made with all kind of particles boards we had around.
As it can be seen in the photo it has no mortices in the selves --just in the vertical sticks-- and it works too.