Rocking isolation of low-rise frame structures founded on isolated footings

F. Gelagoti, R. Kourkoulis, I. Anastasopoulos, G. Gazetas

    Research output: Contribution to journalArticle

    63 Citations (Scopus)

    Abstract

    This paper explores the effectiveness of a new approach to foundation seismic design. Instead of the present practice of over-design, the foundations are intentionally under-dimensioned so as to uplift and mobilize the strength of the supporting (stiff) soil, in the hope that they will thus act as a rocking-isolation mechanism, limiting the inertia transmitted to the superstructure, and guiding plastic 'hinging' into soil and the foundation-soil interface. An idealized simple but realistic one-bay two-story reinforced concrete moment resisting frame serves as an example to compare the two alternatives. The problem is analyzed employing the finite element method, taking account of material (soil and superstructure) and geometric (uplifting and P-? effects) nonlinearities. The response is first investigated through static pushover analysis. It is shown that the axial forces N acting on the footings and the moment to shear (M/Q) ratio fluctuate substantially during shaking, leading to significant changes in footing moment-rotation response. The seismic performance is explored through dynamic time history analyses, using a wide range of unscaled seismic records as excitation. It is shown that although the performance of both alternatives is acceptable for moderate seismic shaking, for very strong seismic shaking exceeding the design, the performance of the rocking-isolated system is advantageous: it survives with no damage to the columns, sustaining non-negligible but repairable damage to its beams and non-structural elements (infill walls, etc.).
    Original languageEnglish
    Pages (from-to)1177-1197
    Number of pages21
    JournalEarthquake Engineering and Structural Dynamics
    Volume41
    Issue number7
    DOIs
    Publication statusPublished - Jun 2012

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    footing
    Soils
    soil
    damage
    Seismic design
    seismic design
    Static analysis
    infill
    reinforced concrete
    inertia
    nonlinearity
    finite element method
    Reinforced concrete
    uplift
    plastic
    Plastics
    Finite element method
    history

    Cite this

    Gelagoti, F. ; Kourkoulis, R. ; Anastasopoulos, I. ; Gazetas, G. / Rocking isolation of low-rise frame structures founded on isolated footings. In: Earthquake Engineering and Structural Dynamics. 2012 ; Vol. 41, No. 7. pp. 1177-1197.
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    abstract = "This paper explores the effectiveness of a new approach to foundation seismic design. Instead of the present practice of over-design, the foundations are intentionally under-dimensioned so as to uplift and mobilize the strength of the supporting (stiff) soil, in the hope that they will thus act as a rocking-isolation mechanism, limiting the inertia transmitted to the superstructure, and guiding plastic 'hinging' into soil and the foundation-soil interface. An idealized simple but realistic one-bay two-story reinforced concrete moment resisting frame serves as an example to compare the two alternatives. The problem is analyzed employing the finite element method, taking account of material (soil and superstructure) and geometric (uplifting and P-? effects) nonlinearities. The response is first investigated through static pushover analysis. It is shown that the axial forces N acting on the footings and the moment to shear (M/Q) ratio fluctuate substantially during shaking, leading to significant changes in footing moment-rotation response. The seismic performance is explored through dynamic time history analyses, using a wide range of unscaled seismic records as excitation. It is shown that although the performance of both alternatives is acceptable for moderate seismic shaking, for very strong seismic shaking exceeding the design, the performance of the rocking-isolated system is advantageous: it survives with no damage to the columns, sustaining non-negligible but repairable damage to its beams and non-structural elements (infill walls, etc.).",
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    Gelagoti, F, Kourkoulis, R, Anastasopoulos, I & Gazetas, G 2012, 'Rocking isolation of low-rise frame structures founded on isolated footings', Earthquake Engineering and Structural Dynamics, vol. 41, no. 7, pp. 1177-1197. https://doi.org/10.1002/eqe.1182

    Rocking isolation of low-rise frame structures founded on isolated footings. / Gelagoti, F.; Kourkoulis, R.; Anastasopoulos, I.; Gazetas, G.

    In: Earthquake Engineering and Structural Dynamics, Vol. 41, No. 7, 06.2012, p. 1177-1197.

    Research output: Contribution to journalArticle

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    AU - Kourkoulis, R.

    AU - Anastasopoulos, I.

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    N2 - This paper explores the effectiveness of a new approach to foundation seismic design. Instead of the present practice of over-design, the foundations are intentionally under-dimensioned so as to uplift and mobilize the strength of the supporting (stiff) soil, in the hope that they will thus act as a rocking-isolation mechanism, limiting the inertia transmitted to the superstructure, and guiding plastic 'hinging' into soil and the foundation-soil interface. An idealized simple but realistic one-bay two-story reinforced concrete moment resisting frame serves as an example to compare the two alternatives. The problem is analyzed employing the finite element method, taking account of material (soil and superstructure) and geometric (uplifting and P-? effects) nonlinearities. The response is first investigated through static pushover analysis. It is shown that the axial forces N acting on the footings and the moment to shear (M/Q) ratio fluctuate substantially during shaking, leading to significant changes in footing moment-rotation response. The seismic performance is explored through dynamic time history analyses, using a wide range of unscaled seismic records as excitation. It is shown that although the performance of both alternatives is acceptable for moderate seismic shaking, for very strong seismic shaking exceeding the design, the performance of the rocking-isolated system is advantageous: it survives with no damage to the columns, sustaining non-negligible but repairable damage to its beams and non-structural elements (infill walls, etc.).

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