Topic 14 - Foundation Design

[Pages:38]FOUNDATION DESIGN

Proportioning elements for: Transfer of seismic forces Strength and stiffness Shallow and deep foundations Elastic and plastic analysis

Instructional Materials Complementing FEMA 451, Design Examples

Foundation Design 14-1

Load Path and Transfer to Soil

Soil Pressure

Pile supporting structure

Force on a pile

EQ on unloaded pile

Inertial force

deflected soil

shape

pressure

Unmoving soil

deflected soil

deflected

shape pressure

shape

EQ Motion

soil pressure

Instructional Materials Complementing FEMA 451, Design Examples

Foundation Design 14-2

Load Path and Transfer to Soil Soil-to-foundation Force Transfer

Passive earth pressure

Shallow

Friction

EQ motion

Instructional Materials Complementing FEMA 451, Design Examples

Foundation Design 14-3

Load Path and Transfer to Soil Soil-to-foundation Force Transfer

Deep

Motion

Soil pressure

EQ Motion

Instructional Materials Complementing FEMA 451, Design Examples

Bending moment

Foundation Design 14-4

Load Path and Transfer to Soil

Vertical Pressures - Shallow

Overturning moment

EQ motion

Instructional Materials Complementing FEMA 451, Design Examples

Foundation Design 14-5

Load Path and Transfer to Soil

Vertical Pressures - Deep

Overturning moment

EQ Motion

Instructional Materials Complementing FEMA 451, Design Examples

Foundation Design 14-6

Reinforced Concrete Footings: Basic Design Criteria (concentrically loaded)

Outside face of concrete column or line midway between face of steel column and edge of steel base plate (typical)

(a) Critical section for flexure

extent of footing (typical)

(b)

Critical section

d

for one-way shear

Instructional Materials Complementing FEMA 451, Design Examples

(c) Critical section for two-way shear

d/2 (all sides)

Foundation Design 14-7

Footing Subject to Compression and Moment: Uplift Nonlinear

P M

(a) Loading

(b) Elastic, no uplift

(c) Elastic, at uplift

(d) Elastic, after uplift

(e) Some plastification

(f) Plastic limit

Instructional Materials Complementing FEMA 451, Design Examples

Foundation Design 14-8

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