CS2 Session 6 Shallow Foundations

8/17/2019 CS2 Session 6 Shallow Foundations

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CONSTRUCTION SYSTEMS 2

FOUNDATIONS

PART1: SHOLLOWFOUNDATIONS


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I!a$e" http"))www*&'*o*n+)onlinereports)propert%dou!ents

Foundatio

here would %ou hoose toput down %our foundations-

Au.land 'olani !ap


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Foundatio/oundations are bearin$

diretl% on the soil, thus thes%ste! !ust"

• 0istribute 'ertial loadsso the settlin$ of abuildin$ is ne$li$ible or

• unifor! under all parts ofthe buildin$*

• #iftin$ /ores"

• Anhor the buildin$1s

superstruture to pre'entupliftin$ due to wind andearth&ua.e fores*

The foundation system fora building is the criticallink in the transmission ofbuilding loads down tothe ground


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LOADS

Building loads(Forces)

Gravity Loads Lateral Loads

Dead Loads Live loads

Building mass

Fixed content

Floor Live loads

Roof Live loads

Wind Earthquae!oil " ground#ater $ressure


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Foundation SettlementPatterns


a buildin$ bears downon the supportin$ soil,

so!e settle!ent is tobe e3peted*

The ause of settle!entis t%piall% due to a

redution in the 'olu!eof air 'oids in the soil*

A properl% desi$nedand onstruted

foundation s%ste!should !ini!i+esettle!ent


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Foundation SettlementPatterns


*

Une'en or

4di5erential4settle!ent anause a buildin$ toshift out of plu!bausin$ ra.s inthe foundation,struture, or 6nish*

E3tre!e di5erentialsettle!ent an lead

to failure of abuildin$7s struturalinte$rit%*


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To get the distrit !lanma!s"

ISoure" Stroud /oster p*89


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Foundations T#!es: TheRange

/oundations

Shallow 0eep


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Foundations T#!es

SHALLOW

Shallow foundations

transfer the load to

soil at the base of

the substructure

Column orwall

Column orwall

> 3m

DEEP

Deep foundations

transfer loads far

below the

substructure

These foundations penetrate incompetent soil

until a satisfactory bearing stratum is reached.


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Shallow : deep foundation


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Foundations T#!es:The Range Shallow

Strip

idestrip

Narrow

strip

(ads

Isolated

Continuo

us

Cantile'er

Raft

SolidSlab

;ea! :

Slab

Cellular


12/36Strip /ootin$


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Rafts

Rafts


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Stress Distri$ution in Soil

Strip footin$s are

plaed underontinuous walls, thusarr%in$ a unifor!l%distributed load*

The re&uired width isrelated to" thei!posed load and

the bearin$ apait%

of the soil*

The strip footin$ !a%be stepped on aslopin$ site to !ini!ise

trenhes and the


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Shallo% Foundation:

Foundation !ad si&e de!endent on"- The soil stren$th or bearin$ apait%

- The pad thi.ness is dependent on the olu!nloadin$*

- The upper surfae an be


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To get the distrit !lanma!s"

/or!in$ a pad footin$ for isolated olu!n

step >" (o.et e3a'ated to 6r! bearin$, ;lindin$

la%er ?optional@ and 0(M plaedStep 2" /or!wor. ereted and steel a$e dropped inplae

Note a$e in ba.$round


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Portal Frame Pad:


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Portal Frame Pad:


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Rafts

Rafts

Strip /ootin$ 0eep Strip/ootin$


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Portal 'rame Footing:


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Shallo% Foundations:

Strip /oundations : (ads"Co!bined /oundations" Spread t%pe foundations andare desi$ned to o'ero!e

partiular restritions, thusare less o!!on *

/or e3a!ple"

!a% be used to distributeloadsbetween une&uall% loadedolu!nsusin$ a tapered pad shape


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(om$ined Foundations:

/or i!pro'ed loaddistribution"

(ad /ootin$s !a% beo!bined b% lin.in$pads to$ether with$round bea!s , in orderto pro'ide support toslab ed$es and)orloadbearin$ walls


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Shallo% Foundations:

Strip /oundations : (ads Cantile'ered /oundations"

hen so!e obstrution at the left olu!n positionpre'ents an ade&uate foundation bein$ plaeddiretl% below the olu!n,


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Formwork for a pad footing for an isolated column with linking tie beams to adacent columns!ebar" #$D%&&'3( longitudinal


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)ad footings and ground beams *in foreground+ may be combined with reinforced slab on grade.

Differential mo,ement checks b 'n ineer" isolation oints-

0ual s%ste!" (ads : Slab on $rade


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Preast Wall !anel 'ooting:


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Ra't Foundations:

• Raft /oundations

– Solid Slab Raft"

• solid slab of reinforedonrete

• load bearin$ arethi.ened

– ;ea! : Slab

• thi.ness 8BB!!

• ea. soils, bea!s down

– Cellular Raft

• depth BB!!

• a hollow ellular raft*


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)http"))www*6rth*o*n+)!edia)88>D)RibraftF2BTehnialF2BManual*pdf

(ellular Ra't

• ;ase!ent wallsfor!s Ribs

• Twin slabs" belowand abo'e


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Ra't Foundations:

The raft foundation a'oids

!an% of these issues b%sittin$ on top of the$round and ha'in$ alattie of steel reinfored

onrete ribs and bea!sto pro'ide support andsti5ness* ;eause the% do notre&uire e3a'ation and arespei6all% desi$ned foreah buildin$ the% an be!ore robust, &ui.er to

build and often less


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Ra't Foundations: The RibRaft


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)http"))www*theubedubai*o!)inde3*php-onstrutionwor.supdate

(ellular Ra't


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Ra't Foundations:• It pro'ides an insulated


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(ellular Ra't


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)http"))www*6rth*o*n+)!edia)88>D)RibraftF2BTehnialF2BManual*pdf

Seismi Fores

• 0urin$ an Earth&ua.e the $round !o'es rapidl%

while buildin$s tr%• to resist displae!ent 'ia their inherent inertia• Ma=or da!a$e tend to be aused b% the hori+ontal

o!ponents

• of these i!posed loads


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)http"))www 6rth o n+)!edia)88>D)RibraftF2BTehnialF2BManual pdf

Seismi Fores

Primar# Fators A)eting Foundation (hoie:

Subsurfae soil ?Heotehnial (ro6le@ Hround water table onditions ;uildin$ strutural re&uire!ents

Seondar# Fators A)eting Foundation (hoie"

• Constrution aess, !ethods and site onditions• En'iron!ental fators ?i*e* seis!i +one@• ;uildin$ Codes and Re$ulations ?i*e* setba.s@• I!pat on surroundin$ strutures ?subsidene@

• Constrution shedule ?lead ti!es for piles@• Constrution ris.s ?see pilin$ 'ideo lips+

Documents

CS2 Session 6 Shallow Foundations