Does there exist software to test the strength of a designed LEGO model? I would like to build furniture (chair, table,...) out of LEGO blocks.
For this purpose it would be good to be able to test the amount of force a certain LEGO design is able to withstand. I would like to actually use this furniture. 


Does anybody know of models or software I could use? 
Are there people who tried this before and could give me some pointers? 


So far I found some articles about different LEGO bonds and a few on combining LEGO techniques to increase the strength of the structure.
First step, have you read my paper? This should give you a good guide on what is the maximum force needed to break Lego.

With these limits in mind, the next thing to note is that breaking doesn't equal bending. Lego will bend quite a lot before breaking so designing structures that a rigid will basically meet most requirements.

The best book to read is Sariel's Technic Builders Guide. This outlines a number of design patterns that maximize strength.

In general, you should think of Lego as weak steel. Triangles everywhere and vertical plates.