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Mechanical response of shallow foundations - Some experimental/theoretical and numerical issues: monotonic and cyclic loading Introduction Prof. ing.

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Presentation on theme: "Mechanical response of shallow foundations - Some experimental/theoretical and numerical issues: monotonic and cyclic loading Introduction Prof. ing."— Presentation transcript:

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2 Mechanical response of shallow foundations - Some experimental/theoretical and numerical issues: monotonic and cyclic loading Introduction Prof. ing. Claudio di Prisco

3 2 Indice Outlook of the presentation a)Introduction b)Failure mechanisms and punching c)The macro-element concept d)Cyclic soil-structure interaction: constitutive modeling observations e)A simplified approach

4 Prof. ing. Claudio di Prisco 3 Definitions: shallow foundations GEOMETRIES Shallow (B/H>4) and deep foundations (B/H<4) Strip footings Mat foundations Grid foundations Lancellotta e Calavera, 1999

5 Prof. ing. Claudio di Prisco 4 The soil-structure interaction Statically determinate interaction Redundantly constrained interaction

6 Prof. ing. Claudio di Prisco 5 What are the consequences? Irreversible differential settlements, damage to the structure energy dissipation The soil structure interaction site amplification Depending on topography and stratigraphy Soil- foundation interaction Dynamic structural response

7 Prof. ing. Claudio di Prisco 6 1. The pseudo-static approach: the rigid-plastic approach Static equivalent horizontal load: step 2 is disregarded whereas step 4 is abruptly simplified. A design pseudo-static distribution of forces is applied to the structure, additional loads H and M are applied on the foundation and new limit conditions have to be accounted for In this perspective the design of the shallow foundation under inclined and eccentric loads become essential

8 Prof. ing. Claudio di Prisco 7 Failure mechanisms: the interaction domain in quasi static conditions Failure mechanisms: small scale 2D experimental test results (drained and undrained conditions, cohesive and granular soils) Nova e Montrasio, 1988

9 Prof. ing. Claudio di Prisco 8 Punching mechanisms Punching mechanisms and 2nd order effects Lancellotta e Calavera, 1999 Lancellotta, 1993

10 Prof. ing. Claudio di Prisco 9 The limit analysis The limit analysis and the Prandtl mechanism Rigid-plastic mechanical behavior of the material Associated flow-rule Mohr-Coulomb failure criterion The kinematic limit analysis approach Lancellotta, 1993 Nova, 2008

11 Prof. ing. Claudio di Prisco 10 The Terzaghi Theory The Terzaghi bearing capacity equation for vertical and centered loads Lancellotta, 1993

12 Prof. ing. Claudio di Prisco 11 Inclined and eccentric loads: Brinch-Hansen coefficients Lancellotta, 1993 H/M V

13 Prof. ing. Claudio di Prisco 12 The interaction domain for rigid shallow footings m = M/ψBV MAX, h = H/μV MAX ξ = V/V MAX 1.To each point belonging to the failure locus a distinct failure mechanism corresponds 2.Difficulty in defining the failure locus when loose sand strata are concerned 3.Extension to rectangular footings 4.Extension for D/B>0 5. MONOTONOUSLY INCREASING LOADING

14 Prof. ing. Claudio di Prisco 13 Centered vertical load Centered inclined load Elasto-plastic finite element numerical analyses Tochnog perfect elasto-plastic numerical analyses

15 Prof. ing. Claudio di Prisco 14 The uplift Shirato et al. 2007

16 Prof. ing. Claudio di Prisco 15 The uplift of rigid shallow foundations

17 Prof. ing. Claudio di Prisco 16 Inclined LOADS Rigid strip footing Dense sand B 0.5B INTERACTION DIAGRAMS GENERALISED STRESS PATHS LOAD CONTROLLED TESTS THE EXPERIMENTAL TEST SERIES

18 Prof. ing. Claudio di Prisco 17 Failure mechanism in unreinforced dense sand layer Failure mechanism in unfastened reinforced dense sand layer DENSE SAND, vertical loading

19 Prof. ing. Claudio di Prisco v [mm] V [kPa] Unreinforced Unfastened reinforced fastened reinforced u [mm] H [kPa] H/V = 0.1

20 Sabbia sciolta non rinforzata V [kPa] H [kPa] Sabbia sciolta rinforzata con geosintetici non allacciati V [kPa] H [kPa] Sabbia sciolta rinforzata con geosintetici allacciati V [kPa] H [kPa] EXPERIMETNAL DATA and NUMERICAL INTERPOLATION INTERACTION DIAGRAMS Unreinforced loose sandUnfastened reinforced loose sand Fastened reinforced loose sand

21 Prof. ing. Claudio di Prisco 20 Numerical simulations Tochnnog finite element code elasto-perfectly plastic constitutive model Non associated flow rule ( = 0) Truss elements

22 Prof. ing. Claudio di Prisco K =k( )? = ( ) ? The visco-elastic approach

23 Prof. ing. Claudio di Prisco 22 M - curves PWRI experimental test results,2005 Dense sand stratum Loose sand stratum FOOTING UPLIFT

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25 Prof. ing. Claudio di Prisco 24 Cross section Plan view Ispra Laboratory Elsa di Elsa di (Pedretti, 1998)

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30 Prof. ing. Claudio di Prisco 29 A simplified approach A symmetric generalised stress-paths

31 Prof. ing. Claudio di Prisco 30


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