A force-balance test measures overall shears and moments at the base of a stiff and lightweight model. The base moments are used to estimate the generalized forces for further dynamic analysis. The force-balance test has several advantages:

1. The required model has to be stiff and lightweight but no other requirement is necessary except for the scaled geometry of the building.

2. A force-balance model can be constructed quickly (typically within two to three weeks).

3. The measurements of base moments inherently include the correlation of the wind forces on various part of the building. 

4. Structurally-connected towers can be tested by collecting simultaneous measurements on each component using a multiple-balance setup.

On the other hand, the force-balance analysis relies on the assumption of nearly linear mode shapes. It is not suitable for flexible structures where the mode shapes may be significantly non-linear. It is also not suitable for flexible structures where the natural frequencies for higher modes lie in the range where significant wind energy is available.

Additional Information:

• Wind Tunnel Testing: A General Outline