Strip Footing Design Example

Design Example 3: Reinforced Strip Foundation. | Builder's Engineer

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The load-bearing wall of a single-storey building is to be supported on a wide reinforced strip foundation. A site investigation has revealed loose-tomedium granular soils from ground level

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to some considerable depth. The soil is variable with

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a safe bearing capacity

ranging from 75–125 kN/m2. Also some soft spots were identified,

where the

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bearing capacity could not be relied upon.

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The building could be supported on ground beams and piles taken down to a firm base, but in this case the solution chosen is to design a wide reinforced strip foundation capable of spanning across a soft area of nominal width. To minimize differential settlements and allow for the soft areas, the allowable bearing pressure will be limited to na = 50 kN/m2 throughout. Soft spots encountered during construction will be removed and replaced with lean mix concrete; additionally, the footing will be designed to span 2.5 m across anticipated depressions. This value has been derived from the guidance for local depressions given later on raft foundations. The ground floor slab is designed to be suspended, although it will be cast using the ground as permanent formwork. Loadings

If the foundations and superstructure are being designed to limit state principles, loads should be kept as separate unfactored characteristic dead and imposed values (as above), both for foundation bearing pressure design and for serviceability checks. The loads should then be factored up for the design of individual members at the ultimate limit state as usual. For foundations under dead and imposed loads only, factoring up loads for reinforcement design is best done by selecting an average partial load factor, γP, to cover both dead and imposed superstructure loads from Fig. 11.22 (this is a copy of Fig. 11.20 Reinforced

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Fig. 11.22 Combined partial safety factor for dead + imposed loads.

Labels FOUNDATIONS

(134) PILES (61) WATERPROOFING (58) STRUCTURES (57) SOILS (47) FOOTINGS (30) SITE EXPLORATION (30) BUILDING (29) PAD FOUNDATIONS (18) STRIP From Fig. 11.22, the combined partial safety factor for superstructure loads is γP = 1.46.

FOUNDATIONS

(18)

CONCRETE

(15)

RAFT

FOUNDATIONS (14) DRILLED PIER FOUNDATIONS (13) Weight of base and backfill, f = average density × depth

RETAINING WALLS (10) EXCAVATIONS (9) SURFACE

= 20 × 0.9 = 18.0 kN/m2 This is all dead load, thus the combined partial load factor for foundation loads, γF = 1.4. Sizing of foundation width New ground levels are similar to existing ones, thus the (weight of the) new foundation imposes no additional surcharge, and may be ignored. The minimum foundation width is given by

Popular Posts COMPONENTS OF A BUILDING: Sub-structure and Superstructure. A building has two basic parts: (i) Substructure or foundations, and (ii) Supers1ructure. Sub-structure or Foundation is the lower p... Design Example 3: Reinforced Strip Foundation. The load-bearing wall of a single-storey building is to be supported on a wide reinforced strip foundation. A site investigation has revea... Example: Pile cap design.

Adopt a 1.2 m wide × 350 mm deep reinforced strip foundation, using grade 35 concrete

A pile cap is required to transfer the load

(see Fig. 11.23).

from a 400 mm × 400 mm column to four 600 mm diameter piles, as shown in Fig. 14.30 . Pile caps... BORING METHODS - SITE EXPLORATION. The following are the various boring methods commonly used: (i) Auger boring. (ii) Auger and shell boring. (iii) Wash boring. (iv) Percus... FOUNDATIONS FOR BLACK COTTON SOILS. Black cotton soils and oher expansive soils have typical characteristics of shrinkage and swelling due to moisture movement through them. Du... TIMBERING OF TRENCHES - SOILS. When the depth of trench is large, or when the sub-soil is loose, the sides of the trench may cave in. The problem can be solved by adopting... Design Example 5: Pad base – axial load plus bending moment (small eccentricity). A column pad base is subject to an axial load of 200 kN (dead) plus 300 kN


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(imposed), and a bending moment of 40 kNm. To suit site constrai... ECCENTRICALLY LOADED FOOTINGS. The footings are so designed and proportioned that the C.G. of the superimposed load coincides with the C.G. of the base area, so that the f... LIVE LOADS IN A BUILDING: on floors, on roofs. Live loads, also called as super-imposed loads, consisi of moving or variable loads, due to people or occupants, their furniture, temporary ... Grillage Foundations - Description. Grillage foundations consist of a number of layers of beams usually laid at right angles to each other and used to disperse heavy point load... Powered by Blogger.

Blog Archive ► 2015 (6) ► 2014 (29) Fig. 11.23 Reinforced strip foundation design example – loads and bearing pressures.

▼ 2013 (158) ► December (4)

Reactive upwards design pressure for lateral reinforcement design ► November (4) ► October (4) ► September (5) ► August (4) ► July (5) ► June (5) ► May (8) ► April (9) ► March (17) ► February (31) ▼ January (62) Design Example: Rectangular Balanced Foundation. Balanced foundations (rectangular, cantilever, tr... Lateral bending and shearb = 1000 mm.

Design Example: Tied Portal Frame Base. Tied foundations - Design. Tied and Balanced Foundations. Tied and Balanced Foundations. Design - Jacking Raft Design - Buoyancy Raft. Design - Beam Strip Raft. Design - Lidded Cellular Raft. Design - Cellular Raft. Design Example: Slip Sandwich Raft. Design - Slip Sandwich Raft. PIPING FAILURES IN SAND CUTS. BRACED CUTS.


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ANCHORAGE OF BULKHEADS. Crust Raft - Design. Design Example: Nominal Crust Raft. Design - Nominal Crust Raft – Semi-Flexible Semi-Fexible Rafts: Design Span for Local Depressi... Bearing Pressure Design - Semi-Fexible Rafts. Design of Semi-Fexible Raft Layouts Design Principles - Semi-Flexible Rafts. Design Example: Floating Slab. Sizing of the Slab. Design Decisions - Floating Slabs. Floating Slabs (Ground Slabs). Sizing of the Design: Continuous Beam Strips. Design Decisions: Continuous Beam Strips. Rectangular and tee-beam Continuous Strips. Design Example 5: Pad base – axial load plus bendi... Pad Foundations with axial Loads and Bending Momen... Design Example: Reinforced Pad Base. Design Example 3: Reinforced Strip Foundation. Design Decisions - Sizing up of the Design - Reinf... Reinforced Concrete Pads and Strips. Unreinforced Concrete Strips. Thus vu < vc , therefore no shear reinforcement is required.

Design Example: Deep Mass Concrete Pad Base.

Loading for spanning over depressions

Design Example: Trench Fill Strip Footing.

Where a local depression occurs, the foundation is acting like a suspended slab. The ultimate load causing bending and shear in the foundation is the total load i.e. superstructure load + foundation load, which is given by

Trench Fill Foundation Design Decisions. Trench Fill Strips. Unreinforced Concrete Pads and Strips. Foundations: General Design Method. Structural Design of Foundation Members. Foundation Design: Calculation of Applied Bearing ... Foundation Design: Definition of Bearing

Longitudinal bending and shear due to depressions

Pressures....

Ultimate moment due to foundation spanning – assumed simply supported – over a 2.5 m local depression is

FOUNDATION DESIGN CALCULATION PROCEDURE. Exploitation of Foundation Stiffness and Resulting... Select Foundation: Questioning the information and... General Approach to Choice of Foundations. Information collection/assessment - Structural Co...

Width for reinforcement design is b = B = 1200 mm.

Selection of the Appropriate Foundation. Grillage Foundations - Description. Retaining Walls. Pier and Beam Foundations. Floating Ground Foor Slabs.


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Suspended Ground Floor Slabs. Pile Caps and Ground Beams. Anchor Blocks - Description. Anchor Piles - Description. Steel Piles - Description. Timber Piles - Description.

► 2012 (304)

Thus vu < vc = 0.49 N/mm2, therefore no shear reinforcement is needed. Depression at corner of building The previous calculations have assumed that the depression is located under a continuous strip footing. The depression could also occur at the corner of a building where two footings would meet at right angles. A similar calculation should then be carried out, to provide top reinforcement for both footings to cantilever at these corners.

Fig. 11.24 Reinforced strip footing design example – reinforcement. Categories: STRIP FOUNDATIONS

Related Post: STRIP FOUNDATIONS Sizing of the Design: Continuous Beam Strips. Design Decisions: Continuous Beam Strips. Rectangular and tee-beam Continuous Strips. Design Decisions - Sizing up of the Design - Reinforced Concrete Pads and Strips.. Reinforced Concrete Pads and Strips. Unreinforced Concrete Strips. Design Example: Trench Fill Strip Footing.


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Trench Fill Foundation Design Decisions. Trench Fill Strips.

1 comentarios: sathya said... really helpful...sharp and to the point April 2, 2015 at 10:39 PM

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Strip Footing Design Example

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