Influence of Structural Stiffness Representation in Settlement Calculations and Practical Advice

State-of-the-art geotechnical and structural analyses commonly rely on finite-element analysis, treating soil and structure models separately. Incorporating the overall stiffness of the structure into the geotechnical model enables more realistic settlement predictions and assessments of founding force distribution, ensuring optimized and cost-effective designs. Although stiffness increases with building height, the effective contribution to settlement control is limited to a finite number of floors, making the internal stiffness distribution more relevant than the construction method itself. Reliable predictions require modeling approaches that realistically represent structural stiffness. This study evaluates various equivalent-model techniques in PLAXIS 3D and SOFiSTiK for their practicability and accuracy and explains their application. While simplified methods can adequately capture total stiffness under uniform distribution, constructing a full 3D model may be faster or more practical than elaborate simplifications requiring extensive setup and post-processing. Moreover, the construction sequence and evolving stiffness during the build, as well as time-dependent effects like creep and limit-state-dependent stiffness changes within structural elements, significantly influence settlements. A 3D structural model allows these factors to be accounted for comprehensively. Therefore, whenever feasible, geotechnical settlement analyses should employ full 3D structural models.