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PAD FOOTING DESIGN AND

CONSTRUCTION PART 2

PREPARED BY AHMAD HAKIMI BIN MAT NOR

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CONSTRUCTION OF PAD

FOOTING

Construction Plan

Using the authorized construction plan, contractor will locate

the location of the footing and begin the construction works.

Excavation Work, Concreting and Curing

• It is usual for the excavated surface of soil to be blinded with a

thin layer of lean concrete before the overlying structure work

takes place.

• If the ground is soft and the reinforcement is heavy, blinding

layer may need to be 150 mm thick, reinforced with mesh

reinforcement.

•  Normal conditions blinding is 50-75mm thick grade 15 or 20

concrete, not reinforced, figure 2.1 illustrate this procedure.

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Figure 2.1: Construction of blinding layer.

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• In case of foundation constructed in the area where the ground

water level close to the surface, water pumped out so that the

construction work can be done, figure 2.1.

Figure 2.2: Blinding layer poured into the excavation after

water pumped out

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• In case of several pad footing to be connected by an earth

 beam there shall be room for the installation of earth adjacent

to the footing later on. Figure 2.3.

Figure 2.3: Location of earth beam between pad footing

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• Concrete should only be poured directly against the ground is

unlikely to collapse into the excavation. Generally shuttering or

temporary formwork is erected on the blinding surface. Figure 2.4.

Figure 2.4: Construction of formwork for pad footing base

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• At times, the steel column base with bolt is required to be

installed so as to make an easier installation of steel column

later on. Figure 2.5 show the bolt on the formwork before

concrete poured into the excavation.

Figure 2.5: Formwork with bolt as a base steel column installation

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• Figure 2.6 show the schematic location of spacing block and

the whole pad footing construction.

Figure 2.6: Location of spacing block and the whole pad footing

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Placing of Concrete• Some keys to successful placing concrete for foundation are as

follow:a) Timing- anticipating the time from completion of excavation until the

time for concreting for foundation shall proceed smoothly and rapidly

within the time period.

 b) Labor-arranging for the necessary labor to be available for the period

of time required, including overtime needs.

c) Concrete supply-for smaller pours, concrete is to be mixed on site but

the necessary materials will halt concreting; for larger pours off site

mixing is preferable. Concrete mixed off site (ready-mixed or pre-

mixed) is convenient to use for pours up to 100 m3

d) Concrete distribution on site- the methods of distributing are; site

truck, concrete skip, conveyor and concrete pump.

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Curing of the concrete footing•  Normal practice of curing concrete is by spraying of water and

the use of polyethylene sheets.• In Malaysia, as practiced by many is the use of gunny sacks by

constructors for their availability and cheaper cost.

• Some constructors have introduced the method of spraying for

concrete curing.

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Figure 2.8: Curing of concrete using poly-ethylene sheets

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Figure 2.9: Curing of concrete by spraying

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Preparation for steel reinforcement• Concrete reinforcement may take in the form of cage forming

at the bottom of the pad footing.

•

All reinforcement are to be arranged and hold up by spacer barat the correct distance. The bending of bar reinforcement is

specified by many codes such as BS 4466.

• All forms of reinforcement should be supported on spacer

 bocks, figure 2.6.

PREPARATION OF

REINFORCEMENT BAR 

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• Some of the dimensions that normally used for reinforcement bar and wire mesh are as show in figure 2.30. typical of bending and bending radius of reinforcement is shown inifigure 2.31,

Figure 2.30: Sizes of reinforcement bar and wire mesh

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Figure 2.31: Bending and bending radius

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• The most useful quick reference is the Osha’s guide to the

construction engineerrs or the manual of safety by the CIDB

(Construction industry Development Board) Malaysia.

• The guide by RoSPA (1982) has subsections relating to

 particular aspacts of site work, of which the following are

 particularly relevent to foundation construction,

 – General requirement ; safe working conditions; lighting; danger from

insecure structure; prevention from drowning; and explosives and

flammable materials. – Ladders

 – Gangways, run and stairs

ON SITE SAFETY PROCEDURES

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 – Excavations, shafts, earthworks and tunnels

 Note: especially on excavations, where a person may be liable to be

struck by a fall of earth from a greater height than 1-2m, are to be

inspected every day that persons are employed there, and that trenches

deeper than 2 m are to be inspected at the beginning of every shift.

Inspections must be made by a competent person.

 – Scaffolding: very detailed regulation, followed by a section an special

types

 –

Openings – Hoists.

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• Concrete normally achieve its adequate strength after some period and depends on the type of cement used namely,ordinary Portland cement or the quick hardened.

• Removal of formwork is accomplished as soon as the concrete

reach the strength that enough to sustain its own weight withother loadings attached on them.

• However, concrete shall be given a minimum hardening periodto prevent it from broken during the removal of formwork.

• Table 2.1 shows minimum period of formwork removal from a particular part of a structure.

• Backfilling of the excavations is done as the concrete attainsstrength.

BACKFILLING

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Location of formwork on

structure part

Normal Portland cement

(days)

Quick hardened Portland

cement (days)On the side of beam and

column without loading

3 2

With support under floor

slab

4 3

Without support underfloor slab

10 5

With support under beam 8 5

Without support under

beam

21 8

Table 2.1: Minimum period of removal

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