This paper discusses the effect of rotational degrees of freedom in System Analysis (SA) via the Building Block Approach (BBA). The paper describes a correlation example in which an experimental modal model is modified using system analysis to predict the effect of adding a finite element beam. The experimental data include only translational degrees of freedom for connection points. A parallel correlation example is considered in which a Finite Element model is modified using System Analysis to predict the effect of a finite element beam addition. Two eases were analyzed: a) including only translational degrees of freedom for each node; b) including the full six degrees of freedom. A comparison between the results using the experimental and finite element derived modal models as the initial model is made and the effect of the rotational degrees of freedom is discussed. Finally, recommendations are made for a method of accounting for the rotational effect from experimental translational data.
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