It will only act as a solid beam IF the solder is strong enough to resist the shear stresses (very similar to laminated wood beams) - and joined along (mostly at least) the entire length.

If the two strips were not joined in any fashion they would slide past each other and be weaker than the solid beam of 2xthickness.

also see previous similar thread:

http://cr4.globalspec.com/thread/37103

The answer to your question depends on the characteristics of your solder/braze joint. Most bi-metal strips are welded together, and there is no third metal involved. If the material between the two outer layers is thick and has a low elastic modulus (like solder), The two outside layers will tend to become independent of each other. There can also be an effect caused by relaxation or creep in the joining material.

I agree with the earlier responders but another method of laminating two plates or strips together without brazing, soldering, etc. is a metallurgical bond, achieved through a combination of friction and/or pressure. The most common method is friction welding in which an alloy of the two metals (in the case of joining dissimilar metals) is created at the bond. Friction welding is commonly used to join copper and aluminum for example and, in that case the result is a copper/aluminum alloy with no discrete boundry.

Friction welding is an option too. Thanks for pointing that out.

I also agree with the other answers provided. What has puzzled me at first was to think that the neutral line near the center has no loads. It must have, just no bending stress. Based on the answers shear stress must be present even in a solid peace of material. That is interesting.

Thanks to all.

Floram

Yes - see this discussion

http://www.bgstructuralengineering.com/BGSCM/BGSCM010/BGSCM01002.htm

If the two strips are joined together so that they act as a unit, the neutral axil will shift toward the metal having the higher modulus of elasticity. To determine where it is, you could transform one of the strips to an equivalent width of the other. Say the bottom strip has a modulus of E and the top strip has a modulus of 0.5 E. Both strips have thickness t and width b. The transformed section would behave the same as a solid bar of modulus E with cross section b/2 x t on top of b x t.