Equivalent Structural Stiffness for Settlement Analyses: A Practical Workflow Accounting for Cracking and Creep

Reliable settlement predictions require a consistent representation of both soil behavior and evolving structural stiffness. While advanced soil models are available in geotechnical analyses, reinforced concrete structures are commonly represented by linear elastic elements, neglecting stiffness reductions caused by cracking and creep. This paper presents a practical workflow for incorporating load- and time-dependent structural stiffness into geotechnical settlement analyses. An equivalent linear elastic foundation slab stiffness is derived from nonlinear structural analyses considering cracking and creep and transferred construction-stage-wise into the geotechnical model. The methodology is validated against nonlinear reference analyses and investigated through parametric studies and a three-dimensional case study. The results show that isolated local cracks have little influence on the global equivalent stiffness. A pronounced reduction occurs only when cracked regions expand and progressively interconnect across the foundation slab, demonstrating that the spatial development of cracking is more relevant than its first occurrence. In the reference analysis, the cracked area increases from approximately 11% at the end of construction to 26% under the settlement load combination. Subsoil stiffness and reinforcement ratio show the strongest influence on stiffness evolution, while concrete strength and construction duration are less significant. The proposed methodology predicts the maximum differential settlement within approximately 3% of the nonlinear reference analysis, compared with approximately 6% using a constant 50% stiffness reduction. The presented results refer to building-load-induced settlements and the investigated structural and parameter ranges.