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ENCV600101 - PerancanganStruktur Beton 1

FondasiSjahril A. Rahim

Departemen Teknik Sipil FTUI November 2006

Sjahril A Rahim Perancangan Struktur Beton

Pokok Bahasan:

Slab Dua Arah Portal Beton Bertulang Pertemuan Balok Kolom Cobel dan Perletakan Dinding Geser dan Balok Tinggi Pondasi Beton Bertulang Strut and Tie Modelling Pengantar Struktur Beton Pratekan

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Sjahril A Rahim Perancangan Struktur Beton

Fondasi (Footing)

Fungsi: Mentransfer beban dari strukturatas ke tanah atau rock

pendukung struktur

Sjahril A Rahim Perancangan Struktur Beton

Kriteria:

Bearing capacity tanah tidak dilampaui; Settlement yang berlebihan, differential

settlement, atau rotasi harus dicegah; Keamanan yang cukup terhadap overturning

atau sliding dipertahankan

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Sjahril A Rahim Perancangan Struktur Beton

Types of Footings:

Sjahril A Rahim Perancangan Struktur Beton

Types of Footings:

Wall footing Single footing (Isolated footing) Pile caps Combined footing

Cantilever (Strap footing) Continuous footing Raft (mat foundation)

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Sjahril A Rahim Perancangan Struktur Beton

Pressure distribution under footings

Sjahril A Rahim Perancangan Struktur Beton

Assumsi distribusi untuk analisa/design:terdistribusi linear

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Sjahril A Rahim Perancangan Struktur Beton

Limit state governed by the soil: Modes of

failure fondasi setempat Bearing failure of

footing Serviceability failure Excessive total

settlement

Sjahril A Rahim Perancangan Struktur Beton

FS q

q ult a -geotechnical Engineering-Shape of footing-Kedalaman-Overburden + surcharge-Water table-Type of soils

Settlement: - immediate settlement- consolidations

Service load pressure Note: struktur fondasi/beton di design dengan factored load strength design

FS=2-3

Secondmayor limit

state

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Sjahril A Rahim Perancangan Struktur Beton

Elastic di stribution of soil under a footing:

Soil pressure under a footing: loadswithin kern:

I My

AP

q

Sjahril A Rahim Perancangan Struktur Beton

Pressure under eccentrically loaded footing:

6 L

ek

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Sjahril A Rahim Perancangan Struktur Beton

Gross and net soil pressure:

Sjahril A Rahim Perancangan Struktur Beton

Berat sendiri dan beban surcharge tidakada efek pada footing, momen dan geser =0

Berat sendiri dan beban surcharge + Pc Net soil pressure q n=P c/A, menimbulkan

internal forces pada footing

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Sjahril A Rahim Perancangan Struktur Beton

Structural action of strip and spread footing:Flexure:

2 f

bf q M nuu

Soil pressure acting under thecross-hatched portion of thefooting, Figure (b) cause themoments about axis A-A at theface of column:

This moment must be resist

reinforcement placed asshown in Figure (c).In similar manner, momentabout B-B.

Sjahril A Rahim Perancangan Struktur Beton

Flexure:

In case the thickness of footing control by shear,

)2

( a

d f

M A

y

us

The minimum area of flexural tensile reinforcement shall be thesame as that required for shrinkage and temperaturereinforcement in the code:

(a) Slab where Grade 280 or 350 deformed bar 0.0020(b) Slab where Grade 420 deformed bar or welded wire 0.0018(c) Slab where reinforcement with yields stress exceeding 420

MPa measured at a yield strain of 0.35 percent is used

y f 4200018.0

Maximum spacing: 5 h450 mm

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Sjahril A Rahim Perancangan Struktur Beton

Equivalent Area

d b

b

Critical Sections for flexure:

2

4

22

d b

d b