Use of spatially variable subgrade modulus for improved accuracy in structural modeling of raft foundations

Date

2023-7

Author

Özyurt, Gökhan

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While designing the foundations of buildings, soil-foundation interaction must also be considered, alongside the load distributions, sectional forces, and deformations in the soil layers due to the structural loads. In routine structural engineering practice, the Winkler (1867) spring idealization is commonly used to address this requirement. In the literature, although the simple Winkler method is distinctly asserted as insufficient in representing the contact pressure distribution beneath the foundation, in current commercial structural engineering software programs, Winkler models are frequently used for simulating soil behavior. PLAXIS 2D/3D and SAP2000, commonly used commercial software in geotechnical and structural analysis applications, are used to carry out a series of analyses for several cases to examine the behavior of shallow raft foundations on dry sands under static loading and thus, obtain more accurate distributions of subgrade modulus. The variables considered in the analyses are foundation thickness, structure width, soil stiffness, number of stories, and column positions. Distributions of subgrade modulus that accurately correspond to the PLAXIS results of bending moment and settlement are obtained through iterative processes conducted on springs in SAP2000. After all, relations are proposed to comprehensively account for all parameters that significantly influence the distributions of subgrade modulus. Additionally, 3-D parametric studies are conducted to illustrate the extrapolation of findings from two-dimensional assessments to three-dimensional scenarios. The results indicate that the distribution of subgrade modulus significantly impacts the analysis of raft foundations. The findings provide insights into the usage of subgrade modulus and inform the design and optimization of foundation systems.

Subject Keywords

Subgrade modulus, Winkler springs, Dry sand, Soil-Structure interaction, SAP2000 spring constant

URI

https://hdl.handle.net/11511/105217

Collections

Graduate School of Natural and Applied Sciences, Thesis