3. design of pad foundations according to ec2

3. Design of RC Pad Foundations to EurocodesCTR11101/CTR11501 Foundation to Design to Eurocode 7

3. DESIGN OF REINFORCED CONCRETE

PAD FOUNDATIONS TO ENROCODES

Dr. Ben Zhang

SEBE, Edinburgh Napier University

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CTR11101/CTR11501

Dr. Ben Zhang FOUNDATION DESIGN TO EUROCODE 7

3. Design of RC Pad Foundations to Eurocodes

2

Foundations

Those structural elements, primarily designed to distribute

the pressure more evenly onto the soil ground.

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3

Influencing Factors on Foundation Type

The magnitude and type of applied loading (dead loads,

imposed loads, wind loads, etc.)

The pressure the ground can safely support (permissible

bearing pressure)

The acceptable levels of settlement

The location and proximity of adjacent structures (structural

interactions)

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4

Requirements for Foundation Design (EC2)

Where ground-structure interaction has significant influence

on the effects of actions in the structure, the properties of the

soil and the effects of the interaction should be considered to

EN 1997-1.

When significant differential settlements are likely, their

influence on the effects of actions in the structure should be

checked.

Concrete foundation size should be determined to EN 1997-1.

Where relevant, the design should include the effects of

phenomena such as subsidence, heave, freezing, thawing,

erosion, etc.

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5

Special Requirements for Foundation Design

Where ground-structure interaction has significant influence, the properties of the soil and the effects of the interaction should be considered to EN 1997-1.

For the design of spread foundations, simplified models for soil-structure interaction may be used. For simple pad footings and pile caps, however, such effects may be ignored.

For the strength design of individual piles, the actions should be determined including the interaction between the piles, the pile cap and the supporting soil.

Where the piles are located in several rows, the action on each pile should be evaluated by considering the interaction between the piles.

This interaction may be ignored when the clear distance between the piles is greater than two times the pile diameter.

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6

Eurocode 7 Geotechnical Design

Two parts:

BS EN 1997-1 : 2004 General rules

BS EN 1997-2 : 2007 Ground investigation and testing

BS EN 1997-1 gives design guidance and actions for

geotechnical design of buildings and civil engineering works.

BS EN 1997-1 is intended for clients, designers, contractors

and public authorities and is intended to be used with

EN 1990 and EN 1991 to EN 1999.

BS EN 1997-1 contains a total of 12 sections and 1 normative

and 8 informative annexes.

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7

Assumptions and Conditions (1.3 of EC7-1)

Data required are well collected, recorded and interpreted;

Structures are designed by qualified and experienced personnel;

Adequate continuity and communication exist between the personnel in data collection, design and construction;

Adequate supervision and quality control are provided;

Execution is carried out according to the relevant standards and specifications by skilful personnel;

Construction materials and products are used as specified in this standard or in the relevant material or product specifications;

The structure will be adequately maintained to ensure its safety and serviceability for the designed service life;

The structure will be used for the purpose defined.

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8

Relevant BS Codes for Geotechnical Design

BS 1377 Part 1 - Part 8 : 1990 Methods of test for soils for

civil engineering purposes

BS 5930 : 1999 Code of practice for site investigations

BS 6031 : 1981 Code of practice for earthworks

BS 8002 : 1994 Code of practice for earth retaining structures

BS 8004 : 1986 Code of practice for foundations

BS 8008 : 1996 + A1 : 2008 Safety precautions and

procedures for the construction and descent of machine-

bored shafts for piling and other purposes

BS 8081 : 1989 Code of practice for ground anchorages

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9

Ultimate Limit States for Geotechnical Design

EQU: loss of equilibrium of the structure or the ground, considered as a rigid body, in which the strengths of structural materials and the ground are insignificant in providing resistance;

STR: internal failure or excessive deformation of the structure or structural elements, including footings, piles or basement walls, in which the strength of structural materials is significant in providing resistance;

GEO: failure or excessive deformation of the ground, in which the strength of soil or rock is significant in providing resistance;

UPL: loss of equilibrium of the structure or the ground due to uplift by water pressure (buoyancy) or other vertical actions;

HYD: hydraulic heave, internal erosion and piping in the ground caused by hydraulic gradients.

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10

Serviceability Limit States for Geo-Design

Serviceability limit states (SLS) needs to be verified for design

of individual foundations.

Limit state GEO often governs the dimensions of structural

elements, e.g. foundations and retaining structures, and

sometimes the resistance of structural elements.

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Geotechnical Categories of Structures

Category Description Risk of failure Examples in EC7-1 Responsibility

1 Small and relatively

simple structures

Negligible N/A Structural

engineers

2 Conventional types of

structure and foundation

with no difficult soil or

loading conditions

Non-exceptional Spread foundations

Raft foundations

Pile foundations

Retaining walls

Excavations

… …

Structural

engineers or

geotechnical

engineers

3 All other structures or

parts of structures

Exceptional Very large or unusual structures

Structures with unusual or

exceptionally difficult ground or

loading conditions

Structures in highly seismic areas

Structures in areas of probable

site instability or persistent

ground movements

Geotechnical

engineers

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12

Characteristic Values Actions

Characteristic and representative values of actions should be

derived in accordance with EN 1990 and various parts of

EN 1991.

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13

Characteristic Values Geo-Parameters

Effective stress c' and tan'

- Geological and other background information

- Variability of measured properties and other info

- Extent of the field and laboratory investigation

- Type and number of samples

- Extent of the zone of ground

- Ability of the geotechnical structure to transfer loads from

weak to strong zones in the ground

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Characteristic Values Geo-Data

Ground levels

Ground water levels

Free water levels

Dimensions of geotechnical structures or elements

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15

Design Values Actions

Fd = F Frep (Eq.(2.1a) of EN 1997-1

& Eq.(6.1a) of EN 1990)

with Frep = Fk

where

Fk is the characteristic value of the action

Frep is the relevant representative value of the action

F is a partial factor

is either 1,00 or 0, 1 or 2

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Design Values Geo-Parameters

Xd = Xk / M (Eq.(6.3) of EN 1990)

where

Xk is the characteristic value of the geotechnical parameter

M is a partial factor for the geotechnical parameter

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Design Values Geometrical Data

ad = anom + Da (Eq.(2.3) of EN 1997-1

& Eq.(6.5) of EN 1990)

where

anom is the nominal value of geometrical data

Da is the deviation in geotechnical data

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18

Design Values Material or Product

Concrete

fcd = acc fck / C (Eq.(3.15) of EN 1992-1)

fctd = act fctk,0,05 / C (Eq.(3.16) of EN 1992-1)

Reinforcement

fyd = fyk / S (Figure 3.8 of EN 1992-1)

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19

Verification of Static Equilibrium (EQU)

Edst;d ≤ Estb;d + Td (Eq.(2.4) of EN 1997-1)

where

Edst;d = E{F Frep; Xk / M; ad}dst (Eq.(2.4a) of EC7-1)

Estb;d = E{F Frep; Xk /M; ad}stb (Eq.(2.4b) of EC7-1)

Td is the design total shearing resistance around a block of

ground where a group of tension piles is placed

Use Tables A.NA.1 and A.NA.2 of UK NA to EN 1997-1!

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Effect of actions for EQU

(Eq.(6.10) of EN 1990)

d G,j k,j P Q,1 k,1 Q,i 0,i k,i

j 1 i 1

" " " " " "E G P Q Q

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21


Table A.NA.1 of UK NA to EN 1997-1

Partial factors on actions (F)Partial factors on actions (F)

Permanent Variable Action

Unfavourablea Favourable

b Unfavourable

a Favourable

b

Symbol G;dst G;stb Q;dst Q;stb

Recommended 1,1 0,9

Alternative 1,35 1,1 1,5 0

a Destabilising;

b Stabilising.

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Partial factors for geotechnical parameters (M)

Note: The values of partial factors for soil parameters in the brackets are quotes from Table A.2 of EN 1997-1.


Geotechnical

parameter

Angle of shearing

resistance

(applied to tan')

Effective

cohesion

Undrained

shear strength

Unconfined

strength

Weight

density

Symbol ' c' cu qu

Value 1,1 (1,25) 1,1 (1,25) 1,2 (1,4) 1,2 (1,4) (1,0)

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23

Verification of resistance for structural and

ground limit states (STR and GEO)

Ed ≤ Rd (Eq.(2.5) of EN 1997-1)

where

Ed = E{F Frep; Xk/M; ad} (Eq.(2.4a) of EC7-1)

Ed = E E{Frep; Xk/M; ad} (Eq.(2.4b) of EC7-1)

E is the partial factor for the effect of actions


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24

Verification of resistance for structural and ground limit states (STR and GEO)

Effect of actions for STR and GEO

(Eqs.(6.10a) and (6.10b) of EN 1990)

0,1

j

G,j k,j P Q,1 k,1 Q,i 0,i k,i

j 1 i 1

dG,j k,j P Q,1 k,1 Q,i 0,i k,i

j 1 i 1

" " " " " "

" " " " " "

G P Q Q

EG P Q Q

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25



(Tables NA.A1.2(B) and NA.A1.2(C) of UK NA to EN 1990)

Partial factors on actions (F) or on the effects of action (E)

Permanent Variable Action

Unfavourable Favourable Unfavourable Favourable

Symbol G Q

Set A1 1,35 1,0 1,5 0

Set A2 1,0 1,0 1,3 0

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26




Note: The values of partial factors for soil parameters in the brackets are quotes from Table A.4 of EN 1997-1.

Geotechnical

parameter

Angle of shearing

resistance

(applied to tan')

Effective

cohesion

Undrained

shear strength

Unconfined

strength

Weight

density

Symbol ' c' cu qu

Set M1 1,0 (1,0) 1,0 (1,0) 1,0 (1,0) 1,0 (1,0) (1,0)

Set M2 1,25 (1,25) 1,25 (1,25) 1,4 (1,4) 1,4 (1,4) (1,0)

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27


Design resistance Rd (ground properties Xd)

Rd = R{F Frep; Xk/M; ad} (Eq.(2.7a) of EC7-1)

Rd = R{F Frep; Xk; ad}/R (Eq.(2.7b) of EC7-1)

Rd = R{F Frep; Xk/M; ad}/R (Eq.(2.7c) of EC7-1)

where R is the partial factor for a resistance

Use Tables A.NA.5 to A.NA.8 and A.NA.12 to A.NA.14 ofUK NA to EN 1997-1!

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28

Verification of resistance for STR and GEO

Tables A.NA.5, A.NA.13 & A.NA.14 of UK NA to EN 1997-1

Partial resistance factors (R)

Resistance Bearing Sliding Earth

Symbol R;v R;h R;e

For spread foundations

Set R1 1,0 (1,0) 1,0 (1,0) /

Set R2 (1,4) (1,1) /

Set R3 (1,0) (1,0) /

For retaining structures

Set R1 1,0 (1,0) 1,0 (1,0) 1,0 (1,0)

Set R2 (1,4) (1,1) (1,4)

Set R3 (1,0) (1,0) (1,0)

For slopes and overall stability

Set R1 / / 1,0 (1,0)

Set R2 / / (1,1)

Set R3 / / (1,0)

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29

Verification of Uplift (UPL)

Vdst,d ≤ Gstb;d + Rd (Eq.(2.8) of EN 1997-1)

with Vdst,d = Gdst;d + Qdst;d

where

Gdst;d is the design destabilising permanent actions;

Qdst;d is the design destabilising variable actions.


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30

Verification of Seepage of Ground Water (HYD)

udst;d ≤ sstb;d (Eq.(2.9a) of EN 1997-1)

Sdst;d ≤ G'stb;d (Eq.(2.9b) of EN 1997-1)

where

udst;d is the design value of the destabilising total pore water

pressure at the bottom of the column

sstb;d is the design stabilising total vertical stress

Sdst;d is the design value of the seepage force in the column

Qdst;d is the design value of the submerged weight of the

column

Use Table A.NA.17 of UK NA to EN 1997-1!

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31

Verification of Serviceability Limit States

Ed ≤ Cd (Eq.(2.10) of EN 1997-1 or

Eq.(6.13) of EN 1990)

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32

Verification of Serviceability Limit States

Characteristic combination (Prescriptive method for spread)

(Eq.(6.14b) of EN 1990)

Normally used for irreversible SLS.

Frequent combination (Direct method for foundation size)

(Eq.(6.15b) of EN 1990)

Normally used for reversible SLS.

Quasi-permanent combination (Direct method for settlement)

(Eq.(6.16b) of EN 1990)

Normally used for long-term effects and appearance of the structure.

k,j k,1 0,i k,i

j 1 i 1

" " " " " "G P Q Q

k, j d 1,1 k,1 2,i k,i

j 1 i 1

" " " " " " " "G P A Q Q

k, j 2,i k,i

j 1 i 1

" " " "G P Q

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33

Approaches for Geotechnical Design

Design Approach 1 (Adopted in the UK!)

(not applicable for axially loaded piles and anchors)

Combination 1: A1 “+” M1 “+” R1


where

“+” denotes “to be combined with”;

A denotes actions;

M denotes ground strength;

R denotes ground resistance.

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34


Design Approach 1 (Adopted in the UK!)

(applicable for axially loaded piles and anchors)


Combination 2: A2 “+” (M1 or M2) “+” R4

where

“+” denotes “to be combined with”;

A denotes actions;

M denotes ground strength;

R denotes ground resistance.

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Design Approach 2 (Adopted in France!)

Combination: A1 “+” M1 “+” R2

where

“+” denotes “to be combined with”

A denotes actions

M denotes ground strength

R denotes ground resistance

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36


Design Approach 3 (Adopted in Germany!)

Combination: (A1a or A2b) “+” M2 “+” R3

where a F on structural actionsb F on geotechnical actions

“+” denotes “to be combined with”

A denotes actions

M denotes ground strength

R denotes ground resistance

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37

Geotechnical Design Report (from Ground Investigation Report)

a description of the site and surroundings

a description of the ground conditions

a description of the proposed construction, including actions

characteristic and design values of soil and rock properties

statements on the codes and standards applied

statements on the suitability of the site for the proposed construction and the level of acceptable risks

geotechnical design calculations and drawings, e.g. limit states, combinations, etc.

foundation design recommendations

a note of items to be checked during construction or requiring maintenance or monitoring

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Geotechnical Design Report

the purpose of observations or measurements

the parts of the structure to be monitored and observed

the frequency of readings

the methods of evaluation

the range of expected results

the period of post-construction monitoring time

the parties responsible for making measurements and

observations, for interpreting the results obtained and for

maintaining the instruments

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39

Spread Foundations

Pad foundations

Square pad

foundation

Rectangular pad

foundation

Square pad

foundation

Rectangular pad

foundation

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40

Spread Foundations

Combined foundations

Rectangular combined

foundation

Trapezoidal combined

foundation

Reversed T-section

foundation

Combined rectangular

foundation

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41

Spread Foundations

Strip foundations

Strip

foundation

Strip

foundation

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42

Limit States for Spread Foundations

Ultimate Limit States (ULS)

loss of overall stability

bearing resistance failure, punching failure, squeezing

failure by sliding

combined failure in the ground and in the structure

structural failure due to foundation movement

Serviceability Limit States (SLS)

excessive settlements

excessive heave due to swelling, frost and other causes

unacceptable vibrations

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43

Methods for Spread Foundation Design

Direct method: Separate analyses are carried out for each limit state. For ULS, the model should be close to the failure mechanism. For SLS, a settlement calculation should be used.

Indirect method: Experience and field or laboratory are used to determine SLS loads.

Prescriptive method: A presumed bearing resistance is used where calculation models are not available or not necessary. These involve conventional and generally conservative rules in the design, and attention is paid to specification and control of materials, workmanship, protection and maintenance procedures. (UK!)

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44

Presumed Allowable Bearing Values

For Category 1 and Category 2 structures (BS 8004)

Category Types of soil Presumed allowable

bearing values (kN/m2)

Remarks

Dense gravel, or dense sand and gravel > 600

Medium dense gravel, or medium dense sand and gravel < 200 to 600

Loose gravel, or loose sand and gravel < 200

Compact sand > 300

Medium dense sand 100 to 300

Non-

cohesive

soils

Loose sand < 100

Foundation width

not less than 1 m.

Groundwater level

assumed to be

below the base of

the foundation.

Very stiff boulder clays and hard clays 300 to 600

Stiff clays 150 to 300

Firm clays 75 to 150

Soft clays and silts < 75

Cohesive

soils

Very soft clays and silts Not applicable

Susceptible to

long-term

consolidation

settlement.

Note: These values are for preliminary design purposes only.

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45

Effects of Actions for Foundations

Horizontal forces due to lateral loading or friction between

the underside of the base and the soil

Vertical forces from columns and/or walls and bearing

pressure from the ground underneath

Moments due to loading from columns and/or walls, etc.

V

M

H

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46

Base Pressure Distribution at the ULS

V

M

V/B(L – 2e)

V

e e = M/V

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47

Middle Third Rule at the SLS

If the eccentricity e of the load lies within the middle third of

the base length, i.e. e ≤ L/6, then no tension will occur under

the base.

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48

Base Pressure Distribution at the SLS

Case 1 (uniform full compression): e = 0

Uniform compression and no tension

L

B

V / BL

V

V

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49


Case 2 (full compression): e ≤ L/6

Linearly distributed compression and no tension

e = M/V L

B

V

M

61

V e

BL L

Pmax

61

V e+

BL L

Pmax V

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50


Case 3 (partial compression): e > L/6

Linearly distributed partial compression and no tension

V

L

B

V

M

4

3 2

V

B(L - e)

e = M/V

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51

Design Procedure for Shallow Foundations

1. Start the design process.

2. Obtain soil parameters from Ground Investigation Report.

3. Decide if Direct Method is used. If not, go to Step 5.

4. Determine the foundation size (geotechnical design) using the worst of Combinations 1 or 2 (ULS) for actions and geotechnical material properties. Combination 2 will usually govern. Go to Step 6.

5. Use Prescriptive Method to determine the foundation size (geotechnical design) using SLS for actions and presumed bearing resistance.

6. Check if there is an overturning moment. If not, go to Step 8.

7. Check overturning using EQU limit state for actions and GEO Combination 2 for material properties.

8. Design foundation (structural design) using the worst of Combinations 1 and 2 (ULS) for actions and geotechnical material properties.

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52

Design of Reinforced Concrete Pad Footings

sufficient reinforcement to resist bending moments

punching shear strength

direct shear strength

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53

Critical Shear Surfaces for Pad Foundations

Punching shear perimeters,

(load within deducted from VEd)

h d

d

2d

Bends may be

required

Direct shear faces

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54

Punching Shear for Pad Footings at ULS

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55

Critical Punching Shear Checks for Pad

Foundations

At the column perimeter, or the perimeter of the loaded area

vEd < vRd,max

Punching shear reinforcement not required

vEd ≤ vRd

Punching shear reinforcement required

vEd > vRd

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Net Punching Shear Force VEd,red

VEd,red = VEd - ΔVEd Eq.(6.48) of EN 1992-1-1

where

VEd is the design value of the applied shear force;

ΔVEd is the design value of the net upward force within the

control perimeter considered, i.e. upward pressure from

soil minus self-weight of the base.

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Design Punching Shear Stress vEd

vEd = b VEd,red / (u1 d) Eq.(6.51) of EN 1992-1-1

where

d is the mean effective depth of the pad footing, which may

be taken as (dy + dz)/2

dy, dz are the effective depths in the y- and z-directions of the

control section

u1 is the length of the control perimeter being considered

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58

Typical basic control perimeters around

loaded areas, u1

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59

Basic control perimeters for loaded areas

close to or at edge or corner, u1

2d 2d

2d

2d 2d

2d

u1

u1 u1

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60

For concentric loading to the control perimeter

b = 1,0 (Eq.(6.49) of EC2-1-1)

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61

For eccentric loading to the control perimeter

(Eq.(6.51) of EC2-1-1)

where

k is a coefficient dependent on the ratio between the column

dimensions c1 and c2, its value depending on the proportions of

the unbalanced moment transmitted by uneven shear and by

bending and torsion, see Slide 62

W1 corresponds to a distribution of shear as shown in the figure in

Slide 62 and is a function of the basic control perimeter u1 as

dl is a length increment of the perimeter

e is the distance of dl from the axis the moment MEd acts about

Ed 1

Ed,red 1

1M u

β +kV W

1

10

u

W e dl

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62

Parameters k and W1

For rectangular column

(Eq.(6.41) of EC2-1-1)2

211 1 2 2 14 16 2

2

cW +c c + c d d π d c

c1/c2 0,5 1,0 2,0 3,0

k 0,45 0,60 0,70 0,80

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Parameter b

For internal circular columns

(Eq.(6.42) of EC2-1-1)

where D is the diameter of the circular column

1 0,64

eβ π

D d

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64

Parameter b

For edge columns

(Eq.(6.44) of EC2-1-1)

where

u1 is the basic control perimeter, see the figure in Slide 59

u1* is the reduced basic control perimeter, see the figures in Slides 65 and 66

epar is the eccentricity parallel to the pad edge caused by a moment about an

axis perpendicular to the pad edge

k may be determined from the table in Slide 62 with c1/c2 replaced by c1/2c2

W1 is calculated for the basic control perimeter u1, see the figure in Slide 62

1 1par

1* 1

u uβ k e

u W

2d 2d

2d

2d 2d

2d

u1

u1 u1

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65

Parameters W1 and u1*

For a rectangular column

(Eq.(6.45) of EC2-1-1)

222

1 1 2 1 24 82

cW +c c + c d d π d c

c1

c2

2d

2d

u1*

≤ 1,5d

≤ 0,5c1

2d

c2

c1 u1*

≤ 1,5d

≤ 0,5c2

≤ 1,5d

≤ 0,5c1

2d

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66

Parameter b

For corner columns

(Eq.(6.46) of EC2-1-1)

1 1*/β u u

c1

c2

2d

2d

u1*

≤ 1,5d

≤ 0,5c1

2d

c2

c1 u1*

≤ 1,5d

≤ 0,5c2

≤ 1,5d

≤ 0,5c1

2d

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67

Punching Shear Resistance Without Shear Reinforcement

(Eq.(6.47) of EC2-1-1)

where

k is a parameter considering size effect and k = min [ 1+ ; 2,0]

1 is a tension reinforcement ratio and

1y, 1z are the tension reinforcement ratios relating to the bonded tension

steel in y- and z-directions respectively

Ac is the area of concrete according to the definition of NEd

CRd,c is a parameter and CRd,c = 0,18 / C = 0,18 / 1,5 = 0,12

a is the distance from the column periphery to the control perimeter

1/3

Rd Rd,c l ck min (100 ) (2 / ) (2 / )v C k f d a v d a

200 / d

1 1y 1z= min ; 0,02

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68

Punching Shear Resistance with Shear Reinforcement

vRd,cs = 0,75vRd,c + 1,5(d/sr) Asw fywd,ef [1/(u1d)] sina

(Eq.(6.52) of EC2-1-1)

where

Asw is the area of one perimeter of shear reinforcement around the column

sr is the radial spacing of perimeters of shear reinforcement

fywd,ef is the effective design strength of the punching shear reinforcement,

according to fywd,ef = 250 + 0,25 d ≤ fywd, see the table in Slide 70

d is the mean of the effective depths in the orthogonal directions in mm

a is the angle between shear reinforcement and the plane of pad footing

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69

Punching Shear at Periphery of the Column

(Eq.(6.47) of EC2-1-1)

where

u0 is the periphery for calculations

u0 = length of column periphery in mm for an interior column

u0 = c2 + 3d ≤ c2 + 2 c1 in mm for an edge column

u0 = 3d ≤ c1 + c2 in mm for a corner column

c1, c2 are the column dimensions as shown in the figure of Slide 62

b see Clauses 6.4.3 (3), (4) and (5)

Ed,red

Ed Rd,max

0

=V

v vu d

b

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Maximum Design Punching Shear Strength

(UK NA to EC2-1-1)

where

n is the strength reduction factor for concrete cracked in shear

(Eq.(6.6) of EC2-1-1)

ck ck ckRd,max cd cc cc ck

C

0,5 0,5 0,6 1 0,2 1250 250

f f fv f fn a a

ck0,6 1250

fn

fck (MPa) 20 25 28 30 32 35 40 45 50

vRd,max (MPa) 3,13 3,83 4,23 4,49 4,74 5,12 5,71 6,27 6,80

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Design Procedure for Checking Punching Shear

Capacity of Pad Foundations

1. Start the design process.

2. Determine the value of b.

3. Determine the punching design shear stress at column face, vEd,max, from

Eq.(6.53)

vEd,max = b (VEd DVEd) / (u0 d)

4. Determine the value of vRd,max from the table in Slide 70.

5. Check if vEd < vRd,max . If yes, go to Step 6. Otherwise redesign the pad

footing.

6. Determine the punching design shear stress, vEd, from Eq.(6.51)

vEd = b (VEd DVEd) / (u1 d)

The control perimeter is normally located at 2d from the column surface.

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Design Procedure for Checking Punching Shear

Capacity of Pad Foundations (cont.)

7. Determine concrete punching shear capacity without shear

reinforcement, vRd, for a = 2d

where l = (ly lz)0,5.

8. Check if vEd ≤ vRd .

If yes, punching shear reinforcement is not required. Go to Step 9.

Otherwise either increase main steel area, or provide punching

shear reinforcement required. However, there are no

recommendations for foundations.

9. Finish.

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Design of Raft Foundation

Lightly loaded structures on soft ground

Heavy structures on normal ground

Structures on ground with uneven

settlement

Mining subsidence

Raft foundation

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Piled Foundations

Often used for transferring loads through strata with a low bearing

capacity to strata with a higher capacity or to rock.

Also used for resisting high uplift forces or to transfer horizontal

loads through poor soil.

Essentially long, slender members, mostly under compression.

Pile cap: resisting vertical and

horizontal loads and moments

Piles

Column

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Design of Piled Foundations

Both direct shear and punching shear should be checked

/5

/5

Direct shear: ≤ d from column

face

Punching shear: ≤ 2d from column

face

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Design of Piled Foundations

When assessing the shear capacity in a pile cap, only the

tension reinforcement placed within the compressed zone

should be considered as contributing to the shear capacity.

A A Compressed zone

≥ 50

mm

45

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Design of Plain Concrete Foundations

acc,pl = 0,6 and act,pl = 0,6 should be taken.

The following needs to be verified

Eq.(12.13) of EC2-1-1

where

hF is the foundation depth

a is the projection from the column face

sgd is the design ground pressure

gdF

ctd

90,85h

a f

s

a a

bF

hF

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Crack Control: Crack width wk

wk = 0,3 mm for all exposure classes under the quasi-

permanent combination, in the absence of specific

durability requirements (e.g. water tightness)

wk = 0,4 mm for exposure classes X0 and XC1, in the

absence of requirements for appearance

wk = 0,2 mm for prestressed members with bonded

tendons under the frequent load combination.

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Crack Control

Maximum bar size s,max or spacing sr,max to wk

Crack width wk = 0,4 mm Crack width wk = 0,3 mm Crack width wk = 0,2 mm Steel stress

ss

(MPa) s,max

(mm)

sr,max

(mm) *

s,max

(mm)

sr,max

(mm) *

s,max

(mm)

sr,max

(mm)

160 40 300 32 300 26 200

200 32 300 25 250 16 150

240 20 250 16 200 12 100

280 16 200 12 150 8 50

320 12 150 10 100 6 /

360 10 100 8 50 5 /

400 8 / 6 / 4 /

450 6

or

/ 5

or

/ /

or

/ Notes:

s,max is the maximum bar diameter, and sr,max is the maximum bar spacing. The values in the table are based on the following assumptions c = 25mm; fct,eff = 2,9MPa; hcr = 0,5; (h-d) = 0,1h; k1 = 0,8; k2 = 0,5; kc = 0,4; k = 1,0; kt = 0,4 and k' = 1,0.

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Minimum area of principal steel

As,min = max [0,26 fctm bt d / fyk; 0,0013 bt d ]

(Eq.(9.1(N)) of EC2-1-1)

where

bt is the mean width of the tension zone

fctm is the mean tensile concrete strength which should be

determined with respect to the relevant strength class

according to Table 3.1 of EN 1992-1-1

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Maximum area of reinforcement

As,max = 0,04 Ac

where Ac is the cross-sectional area of the concrete

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Minimum Spacing of Reinforcement

smin,slabs = smin,clear + s

= max [(k1 s); (dg + k2); 20 mm] + s

where

s is the bar diameter in mm

dg is the maximum aggregate size in mm

k1 is a parameter which is recommended as k1 = 1,0

k2 is a parameter which is recommended as k2 = 5 mm

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Deep elements (Section 9.7 of EN 1992-1-1)

A reinforcement ratio of 0,2% provided in each face

The distance between adjacent bars of the mesh not

exceeding the lesser of twice the beam depth or 300 mm

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Thank you!

3. design of pad foundations according to ec2

Documents

rc pad foundations

ground limit states

presumed bearing resistance

ground investigation report

axially loaded piles

denotes ground strength

geotechnical material properties

punching shear reinforcement