Shallow Foundation Azizi Yusoffi 2005 - · PDF fileSoils Report: 1. Site Investigation 2. Lab...
Transcript of Shallow Foundation Azizi Yusoffi 2005 - · PDF fileSoils Report: 1. Site Investigation 2. Lab...
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FOUNDATION ENGINEERINGFOUNDATION ENGINEERINGBFC 4043BFC 4043
Nor Nor AziziAzizi YusoffYusoffFKAAS, KUiTTHOFKAAS, KUiTTHO
1.0 SHALLOW FOUNDATION
FOUNDATION SYSTEMS
FOUNDATION SYSTEMS
“The foundation is the building element which distributes and transmits
the building load to the earth.”
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Building Load
Soil Bearing CapacitySoil Bearing Capacity
SettlementSettlementSettlementSettlement
ApplicationsApplicationsApplications
LowLowWeightWeight
Soft toSoft toFirm ClayFirm Clay
Large DistributedLarge DistributedWeightWeight
Very Large ConcentratedVery Large ConcentratedWeightWeight
Dense Sand
Strong RockStrong Rock
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“All foundations will settle to some extent”
Settlement Magnitude: Usually less that 1”Uniform Settlement: Acceptable if within the 1”Differential Settlement: Unacceptable if differences
exceed the 1”
Settlement Magnitude: Usually less that 1”Uniform Settlement: Acceptable if within the 1”Differential Settlement: Unacceptable if differences
exceed the 1”
What are the different loads which constitute the building load?
What are the different loads which constitute the building load?
Dead LoadLive Load
Wind Loads Thrusts Seismic
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Seismic
UBC’94 DESIGN BASE SHEAR (V)
= ( Z I C / RW) WZ = Seismic zone factor
I = Importance factor of the building
RW = Reduction factor
S = Site coefficient for soil characteristics
W = Total seismic dead load
T = Fundamental period of vibration
Developing seismic zone
map of Malaysia
Seismic
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Our own seismic zone map
SOIL
GOODGOOD
BADBAD
SOIL TYPES:
Gravel
Sand
Silt
Clay
SOIL TYPES:
Gravel
Sand
Silt
Clay
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How is the bearing capacity of a soil determined ?
1. Building Code provides minimum values that can be used for some structures.
2. Subsurface Exploration • Test Pits (digging a hole) • Test Borings (drilling a hole
with a hollow auger) In either case soil samples are obtained
and tested in a laboratory.
The soil samples are : 1. Classified 2. Properties determined:
• density • moisture content • shear strength • void ratio • bearing capacity • liquid and plastic
limits • plasticity index
The soil samples are : 1. Classified 2. Properties determined:
• density • moisture content • shear strength • void ratio • bearing capacity • liquid and plastic
limits • plasticity index
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GEOTECHNICAL EXPLORATION REPORT VALLEY HOSPITAL
EMERGENCY AND OPERATING ROOM ADDITIONS 629 SHADOW LANE
LAS VEGAS, NEVADA
STEPHENS GEOTECHNICAL INC.
SOILS REPORT:
Geotechnical Investigation or Exploration
SOILS REPORT:
Geotechnical Investigation or Exploration
Soils Report: 1. Site Investigation 2. Lab Investigation 3. Site Conditions 4. Engineering Analysis
and Recommendations • Site Grading &
Earthwork • Foundations & Slabs
on Grade • Lateral Earth
Pressures • Moisture Protection &
Subsurface Drainage • Paving
Soils Report: 1. Site Investigation 2. Lab Investigation 3. Site Conditions 4. Engineering Analysis
and Recommendations • Site Grading &
Earthwork • Foundations & Slabs
on Grade • Lateral Earth
Pressures • Moisture Protection &
Subsurface Drainage • Paving
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CLIMATIC FEATURES
1. Frost line
2. Expansive soil
3. Groundwater
4. Hydrostatic pressure
CLIMATIC FEATURES
1. Frost line
2. Expansive soil
3. Groundwater
4. Hydrostatic pressure
SOME JKR RECOMMENDATIONS
• If the soft layers exist more than 3 meters depth, shallow foundation is not a practical approach, too much digging
• size and types of foundation will depends on the weight (building etc.) and soil bearing capacity
• suitable for soil with SPT more than 5
• Pad footing cannot be build on embankment
• Pad footing is not recommended for cut and fill areas (to handle the differential settlement problem)
• Pad footing is also not suitable at slope areas
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FOUNDATIONS…..FOUNDATIONS…..
ShallowShallow
DeepDeep
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SHALLOW FOUNDATIONS
“Transfer building load at or near soil surface”
SHALLOW FOUNDATIONS
“Transfer building load at or near soil surface”
1. Footings • Column • Strip, Spread • Wall • Combined
2. Slabs • On-grade • Crawlspace • Basement
3. Mat or Raft
1. Footings • Column • Strip, Spread • Wall • Combined
2. Slabs • On-grade • Crawlspace • Basement
3. Mat or Raft
Types of Shallow FoundationTypes of Shallow Foundation
PAD IS CENTERED
UNDER COLUMN
PAD IS CENTERED
UNDER COLUMN
COLUMN FOOTINGCOLUMN FOOTING
FOOTING IS CENTERED
UNDER WALL
FOOTING IS CENTERED
UNDER WALL
WALL FOOTINGWALL FOOTING
COMBINED FOOTINGCOMBINED FOOTING
PROP. LINEPROP. LINE
EXTERIOR COLUMN
EXTERIOR COLUMN
1ST INTERIOR COLUMN1ST INTERIOR COLUMN
CANTILEVER FOOTINGCANTILEVER FOOTING
PROP. LINEPROP. LINE
EXTERIOR COLUMN
EXTERIOR COLUMN
1ST INTERIOR COLUMN
1ST INTERIOR COLUMN
COLUMN FOOTINGSCOLUMN FOOTINGS
CONCRETE BEAM (STRAP)CONCRETE BEAM (STRAP)
SHALLOW FOUNDATIONSSHALLOW FOUNDATIONS
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PLANPLAN SECTIONSECTION
REINFORCING STEEL IN BOTH DIRECTIONS IN BOTTOM FACE OF FOOTING RESISTS TENSIONS CAUSED BY BENDING
REINFORCING STEEL IN BOTH DIRECTIONS IN BOTTOM FACE OF FOOTING RESISTS TENSIONS CAUSED BY BENDING
BENDING OF FOOTING CAUSES COMPRESSION IN TOP FACE AND TENSION IN BOTTOM FACE
BENDING OF FOOTING CAUSES COMPRESSION IN TOP FACE AND TENSION IN BOTTOM FACE
UPWARD SOIL PRESSUREUPWARD SOIL PRESSURE
FOOTINGFOOTING
DOWNWARD COLUMN LOADDOWNWARD COLUMN LOAD
SINGLE COLUMN FOOTINGSINGLE COLUMN FOOTING
SHALLOW FOUNDATIONSSHALLOW FOUNDATIONS
SHALLOW FOUNDATIONSSHALLOW FOUNDATIONSFootingsFootings
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Types of Substructures: Slab on-grade
Types of Substructures: Slab on-grade
SHALLOW FOUNDATIONSSHALLOW FOUNDATIONS
Types of Substructures: Crawlspace
Types of Substructures: Crawlspace
SHALLOW FOUNDATIONSSHALLOW FOUNDATIONS
CRAWLSPACECRAWLSPACE
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KL Tower…..
KL Tower…..
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KL Tower…..
KL Tower…..
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KL Tower…..
KL Tower…..
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BasementBasement
Types of Substructures: Basement
Types of Substructures: Basement
SHALLOW FOUNDATIONSSHALLOW FOUNDATIONS
Types of Substructures: Basement
Types of Substructures: Basement
SHALLOW FOUNDATIONSSHALLOW FOUNDATIONS
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Types of Substructures: Basement
Types of Substructures: Basement
SHALLOW FOUNDATIONSSHALLOW FOUNDATIONS
HYDROSTATIC PRESSURE ON WALLS AND SLABS BELOW
GROUND WATER LINE
HYDROSTATIC PRESSURE ON WALLS AND SLABS BELOW
GROUND WATER LINE
GROUND WATER LINEGROUND WATER LINE
GROUND LINEGROUND LINE
Types of Substructures: Basement
Types of Substructures: Basement
SHALLOW FOUNDATIONSSHALLOW FOUNDATIONS
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Types of Substructures: Basement
Types of Substructures: Basement
SHALLOW FOUNDATIONSSHALLOW FOUNDATIONS
MAT or RAFTMAT or RAFT
Types of Substructures: Mat or Raft
Types of Substructures: Mat or Raft
SHALLOW FOUNDATIONSSHALLOW FOUNDATIONS
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SAFETY FACTOR, What is It???SAFETY FACTOR, What is It???
Soil 1
Soil 2 Stress=Wt./Area
40030010020
FoS=3FoS=3 FoS=1FoS>>3
400
FoS<1
σ
δ
Ultimate
Require more deformation which may not be OK for structures
Allowable
Allow some deformation which may not be problem in long term
Failure
Soil is unable to support load
Safety Factor=Soil capacity/applied load
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SAFETY FACTOR SAFETY FACTOR IN FOUNDATION DESIGNIN FOUNDATION DESIGNTHERE ARE UNCERTAINTIES IN DETERMINING THERE ARE UNCERTAINTIES IN DETERMINING ALLOWABLE STRENGTH DUE TOALLOWABLE STRENGTH DUE TO ::
COMPLEXITY OF SOIL BEHAVIOR COMPLEXITY OF SOIL BEHAVIOR INCOMPLETE KNOWLEDGE OF SUBSURFACE INCOMPLETE KNOWLEDGE OF SUBSURFACE CONDITIONCONDITIONINABILITY TO DEVELOP A GOOD MATH. INABILITY TO DEVELOP A GOOD MATH. MODEL FOR FOUNDATIONS.MODEL FOR FOUNDATIONS.LACK OF CONTROL OF ENVIRONMENTAL LACK OF CONTROL OF ENVIRONMENTAL CHANGE AFTER CONSTRUCTIONCHANGE AFTER CONSTRUCTIONINABILITY TO DETERMINE THE SOIL INABILITY TO DETERMINE THE SOIL PARAMETER ACCURATELYPARAMETER ACCURATELY
VALUE OF SFVALUE OF SF
FAILURE MODE FOUNDATION TYPE FAILURE MODE FOUNDATION TYPE SAFETY FACTORSAFETY FACTOR
SHEAR EARTH WORKS,DAM, FILL 1.2SHEAR EARTH WORKS,DAM, FILL 1.2 -- 1.61.6
SHEAR RET.STRUCTURE SHEAR RET.STRUCTURE 1.5 1.5 -- 2.02.0
SHEAR SHEET PILING COFFERDAM 1.2 SHEAR SHEET PILING COFFERDAM 1.2 -- 1.61.6TEMPORARY BRACED TEMPORARY BRACED EXC.EXC.
SHEAR FOOTINGS: MAT,SPREAD 2 SHEAR FOOTINGS: MAT,SPREAD 2 -- 33
SEEPAGE UPLIFT,HEAVING, SEEPAGE UPLIFT,HEAVING, 1.5 1.5 -- 2.52.5
PIPING PIPING 3 3 -- 55
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Assumption of soil reaction in Assumption of soil reaction in Analyzing shallow foundationAnalyzing shallow foundation
Soil reaction is uniformSoil reaction is uniform
Assumption σ = P/A
Actual
Steps of Shallow Foundation Steps of Shallow Foundation Design ( Footings )Design ( Footings )
1.1. Analyzing load from upper structureAnalyzing load from upper structure2.2. Analyzing soil Conditions, surrounding area, Analyzing soil Conditions, surrounding area,
environment.environment.Obtaining SI Data to Calculate BCObtaining SI Data to Calculate BC
3.3. To Calculate Bearing CapacityTo Calculate Bearing Capacity4.4. To assume a size of foundationTo assume a size of foundation5.5. To Control Stability of SoilTo Control Stability of Soil6.6. To control Settlement and differential To control Settlement and differential
settlementsettlement7.7. Reinforcement Reinforcement
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1.3 Bearing Capacity1.3 Bearing Capacity1.3 Bearing Capacity
Ultimate or serviceability limit state?Ultimate or serviceability limit state?““What is the maximum pressure which the soils can withstand for aWhat is the maximum pressure which the soils can withstand for agiven foundation before the soil will fail?given foundation before the soil will fail?””Design for less but how much less?Design for less but how much less?Uncertainty with respect to:Uncertainty with respect to:
LoadsLoadsCapacityCapacity
Obtaining Ultimate Bearing Obtaining Ultimate Bearing Capacity (Capacity (qquu))
Can be obtained from Soil Investigation; In Can be obtained from Soil Investigation; In situ tests or Laboratory tests.situ tests or Laboratory tests.Lab. TestLab. Test1. 1. TriaxialTriaxial CD, CU, UU, UCTCD, CU, UU, UCT2. Direct Shear Test2. Direct Shear Test3. 3. Lab.VSTLab.VST
..In Situ Test In Situ Test –– SPT,CPT,PMT,VST SPT,CPT,PMT,VST field,Loadingfield,Loading testtest
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Allowable bearing capacity ( Allowable bearing capacity ( qqallall))
qqallall = = qquu / SF/ SF
QQuu = ultimate bearing capacity= ultimate bearing capacity
SF = Safety FactorSF = Safety Factor( 2 ( 2 –– 3 ) for Shallow Foundation3 ) for Shallow Foundation
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Modes of Bearing FailuresModes of Bearing Failures
1.General Shear1.General Shear
2. Local Shear2. Local Shear3. Punch Failure3. Punch Failure
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Terzaghi Bearing Equationfor : - D/B< 1
- Strip Footing
TerzaghiTerzaghi Bearing EquationBearing Equationfor : for : -- D/B< 1D/B< 1
-- Strip FootingStrip Footing
Solution for c and φ only soil
qquu nettnett = = c.Nc.Ncc + q+ q NNqq + 0.5+ 0.5BBγγ'N'Nγγ
Solution for D and φ only soil
Solution for γ and φ only soil
Terzaghi Bearing EquationTerzaghiTerzaghi Bearing EquationBearing Equation
B
qquu nettnett = = c.Nc.Ncc + q+ q NNqq + 0.5+ 0.5BBγγ'N'Nγγ
qq = = γγ''oo DD
Generalized soil strength : c, Generalized soil strength : c, φφ(drainage as applicable)(drainage as applicable)
Soil unit weight : Soil unit weight : γγ'' (total or(total oreffective as applicable)effective as applicable)
Overburden
Failure Zone (depth ≈ 2B)
Adopt weighted average values !Adopt weighted average values !
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Terzaghi Bearing EquationTerzaghiTerzaghi Bearing EquationBearing Equation
applies to strip footingapplies to strip footingNNcc, , NNqq and and NNγγ are functions of are functions of φφ, and are , and are usually given in graphical form usually given in graphical form c, c, φφ and and γγ' ' refer to soil properties in the refer to soil properties in the failure zone below the footingfailure zone below the footingq q is the effective overburden pressure at is the effective overburden pressure at the founding levelthe founding levelshear strength contribution above footing shear strength contribution above footing level is ignored : conservative for deeper level is ignored : conservative for deeper footings footings
qquu nettnett = = c.Nc.Ncc + q+ q NNqq + 0.5+ 0.5BBγγ'N'Nγγ
MODIFICATION OF BEARING CAPACITY EQUATIONS FOR WATER TABLE
qquu nettnett = = c.Nc.Ncc + + qq NNqq + 0.5+ 0.5BBγγ''NNγγ
qquu nettnett = = c.Nc.Ncc + q+ q NNqq + 0.5+ 0.5BBγγ''NNγγ
qquu nettnett = = c.Nc.Ncc + q+ q NNqq + 0.5+ 0.5BBγγ'N'Nγγ
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GENERAL SHEAR FAILURE CASES
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GENERAL SHEAR FAILURE CASES
LOCAL SHEAR FAILURE CASES
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600 N
φ=0 ; C = 35 kN/m2
BEBAN
TANAH
Did u still remember….
QUIZ 1…. 15/7/05
Rajah S1(b) menunjukkan sebuah asas segiempat sama dengan dimensi 1.5m X 1.5m Dengan mempertimbangkan formula Terzaghi dan faktor keselamatan adalah 3, tentukan keupayaan galas yang dibenarkan (allowable bearing capacity capasity) berdasarkan keadaan paras air bumi berikut :(a) Pada permukaan tanah(b) 1.2 m di bawah permukaan
Diberi: qu =1.3 c.Nc + q Nq + 0.4Bγ'Nγ 1200 kN
1.5m x 1.5m
γdry = 11 kN/m3 γsat = 19 kN/m3 φ = 0° c = 22 kN/m2
γdry = 14 kN/m3 γsat = 21 kN/m3 φ = 0° c = 27 kN/m2
1.2 m
qu =1.3 c.Nc + q Nq + 0.4Bγ'Nγ
Chubaaa…
..
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Inclined LoadsInclined LoadsInclined Loads
Correction Factors, Correction Factors, FFcc , , FFqq and and FFγγempirically determined from empirically determined from experimentsexperiments
Fc = Fq = (1 - δ / 90)2
Fγ = (1 - δ / φ)2
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Meyerhof Approx AnalysisMeyerhofMeyerhof Approx AnalysisApprox Analysis
• differs from Terzaghi analysis particularly for buried footings– soil above footing base provides not only
surcharge but also strength– more realistic i.e. less conservative
qquu = = cNcNccssccddcciicc + + qNqNqqssqqddqqiiqq + + 0.50.5γγ'BN'BNγγssγγddγγiiγγ
• s, d, and i are shape, depth and load inclination factors
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qmin
qmax
e
P
e < B/6 :
qmin = P (1-6e/B)/BLqmax = P (1+6e/B)/BL
rigid
Footings with eccentric loadsFootings with eccentric loadsFootings with eccentric loads
qmin = 0qmax = 4P .
3L(B-2e)
qmin
qmax
e
P
e > B/6 : rigid
Footings with eccentric loadsFootings with eccentric loadsFootings with eccentric loads
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Meyerhof Method for eccentric loads
MeyerhofMeyerhof Method for eccentric Method for eccentric loadsloads
PP
ee
L
2e LL' = LL-- 22ee
B
2-way eccentricity22--way eccentricityway eccentricity
PP
ee11
LL
22ee11 LL' = LL-- 22ee11
BB ee2 2
22ee22
BB' =
BB-- 22
ee 22
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Steps of Design: Eccentrically Loaded Foundations
Steps of Design: Eccentrically Steps of Design: Eccentrically Loaded FoundationsLoaded Foundations
1.Define the ‘e’2.Define Qmin and Qmax3.Calculate qult’ using Meyerhof formula
* use B’ and L’ for ‘s’ and ‘i’* use actual B and L for ‘d’
4. Qult = qult’ (B’)(L’)5. FS = Qult / Q
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Analyses by Hansen, VesicAnalyses by Hansen, Analyses by Hansen, VesicVesic
qquu = = cNcNccssccddcciiccggccbbcc + + qNqNqqssqqddqqiiqqggqqbbqq + + 0.50.5γγ'BN'BNγγssγγddγγiiγγggγγbbγγ
Nc ,Nq ,Nγ : Meyerhof bearing capacity factorssc ,sq ,sγ : shape factorsdc ,dq ,dγ : depth factorsic ,iq ,iγ : load inclination factorsgc ,gq ,gγ : ground inclination factorsbc ,bq ,bγ : base inclination factors
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1.4 Assume a size of Foundation1.4 Assume a size of Foundation
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Requirements: Requirements: σσ > 0 , < > 0 , < qqallalle < B/6 , Ae < B/6 , A’’ = a= a-- 2e2eSFSFhorhor < (< (ΣΣV tanV tanδδ + P+ Ppp + C.A)/H+ C.A)/H
It can beIt can be……..Vertical Load onlyVertical Load onlyV + MV + MV + M + HV + M + HV + M + H , Base unsymmetricalV + M + H , Base unsymmetricalCombine footingCombine footing
1.5 Control Stability
SFSFverticalvertical = = qquu / / qqallall
SFSFhorizontalhorizontal = (= (ΣΣV tanV tanδδ + P+ Ppp + C.A) / + C.A) / ΣΣ HH
SFSFSlidingSliding = = ((ΣΣV x Coefficient between base and soil) / V x Coefficient between base and soil) / ΣΣ HH
SFSFOverturningOverturning = = ΣΣ Moment to resist turning / Moment to resist turning / ΣΣ Turning momentTurning moment
☺
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qmin
qmax
e
P
e < B/6 :
qmin = P (1-6e/B)/BLqmax = P (1+6e/B)/BL
rigid
Footings with eccentric loadsFootings with eccentric loadsFootings with eccentric loads
qmin = 0qmax = 4P .
3L(B-2e)
qmin
qmax
e
P
e > B/6 : rigid
Footings with eccentric loadsFootings with eccentric loadsFootings with eccentric loads
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Meyerhof Method for eccentric loads
MeyerhofMeyerhof Method for eccentric Method for eccentric loadsloads
PP
ee
L
2e LL' = LL-- 22ee
B
2-way eccentricity22--way eccentricityway eccentricity
PP
ee11
LL
22ee11 LL' = LL-- 22ee11
BB ee2 2
22ee22
BB' =
BB-- 22
ee 22
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1.6 Control Settlement & diff. 1.6 Control Settlement & diff. settlementsettlement
Allowable Total SettlementAllowable Total Settlement-- Buildings 15 Buildings 15 -- 50 mm50 mm-- Heavy Industrial bldg. 25 Heavy Industrial bldg. 25 -- 75 mm75 mm-- Bridges 50 mmBridges 50 mmAllowable angular distortionAllowable angular distortion-- Bridges L/125 Bridges L/125 –– L/250L/250-- Buildings L/250 Buildings L/250 –– L/500L/500
Probable additional Moment to upper structureProbable additional Moment to upper structureMM’’ = 6 E I = 6 E I ∆∆ / L/ L22
1.7 ReinforcementOther Subject ( Reinforced concrete design )
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Type of Shallow FoundationType of Shallow Foundation1.1. Rectangular, strip, circular footingRectangular, strip, circular footing2.2. Combined footing; rectangular, trapezoidalCombined footing; rectangular, trapezoidal
cantilevercantilever3.3. Mat / Raft FoundationMat / Raft FoundationThe previous analysis only valid for rigid condition , The previous analysis only valid for rigid condition , λλl < l < ππ/4 /4 For flexible beam condition in which For flexible beam condition in which λλl > l > ππ/4, solution to the analysis should consider/4, solution to the analysis should considerthe flexibility of foundation the flexibility of foundation
3
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References…•B.M., Das : Principles of Foundation Engineering
• Liu Evett : Soils and Foundations
• Coduto: Foundation Design
• Dunn, Anderson, Kiefer: Fundamentals of Geotechnical Analysis
•Monash University, Australia
• Ir Mohamed bin Daud, JKR, Kelantan
• Mr Azizul, JKR, Batu Pahat
Thank you for sharing….
Thank youThank you……Nor Nor AziziAzizi YusoffYusoff
[email protected]@kuittho.edu.my013013--76182237618223