soil-structure interaction 0

8/12/2019 Soil-structure Interaction 0

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Abdul Razzaq Touqan

Soil-Structure Interaction


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:

Input processing output


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Introduction

INPUT: Representation of mathematical model

INPUT: Representation of earthquake loadings

PROCESSING: Representation of mass and stiffnessproperties: analogical models

PROCESSING: Representation of mass and stiffnessproperties: anatomical models

OUTPUT: Models comparisons

OUTPUT: Conclusions

Further usage of concept

Reminder


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Fundamental lesson learned from earthquakes:

Necessity of correct matching between mathematical modeland reality (input)

Necessity of correct matching between earthquake loadingsand method of analysis (processing)

Introduction


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Representation of Mathematical Model

-Soil theory is based on assumption of rigid structures builton flexible foundations.

-Structural theory is based on assumption of flexiblestructures built on rigid foundations.


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Methods of analysis:

1. Time history: true dynamic analysis, all necessarymodes of soil-structure model

2. Response spectrum: one point dynamic analysis,all necessary modes of soil-structure model

3. Equivalent lateral load: static analysis, one modeof structure model

Representation of Earthquake loadings:


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basic assumptions of equivalent lateral load

General assumptions: uniform distribution of

mass and stiffness.Special assumptions: models used based onlevel of technology

maxV Ma

Representation of Earthquake loadings:Equivalent lateral load


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a one-story flat plate reinforced concrete building subjected toearthquake loading in the x-direction..


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ASCE/SEI 2010 0.90.0466 0.13 secn

T h


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the relative displacement output u* of a 1D model subjectedto an earthquake

M, K and are mass, stiffness and acceleration responsespectrum (dynamic magnification factor) respectively

*max

M u

K

Representation of mass and stiffness properties:analogical models


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For simplicity assume 1D model composed of two springs inseries. The combined stiffness K

If K soil is much larger than K str then the combined stiffness K isequal to K str and separation between soil and structure is

justified

1 / soil str str

soil str str soil

K K K K

K K K K



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Substructuring concept: static reduction

Representation of mass and stiffness properties:analogical models:


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Substructuring concept: static reduction



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Substructuring concept: dynamic reduction



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Representation of mass and stiffness properties:anatomical models


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Models comparisons


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-Neglecting soil structure interaction is reasonable ifassumptions prevails like:

- light structures in relatively stiff soil such as low risebuildings, structural assumptions prevails.

- simple rigid retaining walls: foundation assumptions prevails.

- -The effect of soil structure interaction becomes important for

heavy structures resting on relatively soft soils for exampletowers in a wadi (like wadi altufah)

Conclusions


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Further usage of concept


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Models comparisons


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1. Best structural shape to resist lateral loadings (wind,earthquake, is the pyramid shape. Such shapeprovides largest stiffness and smallest mass

2. Worst structural shape to resist lateral loadings is the

inverted pyramid shape. Such shape provides largestmass and smallest stiffness

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By the same philosophy, weakness in the soil increasesmass and decreases stiffness, thus structure becomesvulnerable to earthquake loads.

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Conclusions for further usage


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Reminder

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Thank you for listening


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What is your opinion of a structure withbasement wall on one side as a usualpractice in Palestine?

Question

soil-structure interaction 0

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