How to design a pad foundation - Revision history

Designing Buildings at 09:31, 14 September 2020

2020-09-14T09:31:32Z

← Older revision		Revision as of 09:31, 14 September 2020
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	* Institution of Structural Engineers - [https://www.istructe.org/getattachment/98c7f9ac-499b-4857-9dae-15096ba485c5/TGN7-2.pdf Designing a concrete pad foundation]		* Institution of Structural Engineers - [https://www.istructe.org/getattachment/98c7f9ac-499b-4857-9dae-15096ba485c5/TGN7-2.pdf Designing a concrete pad foundation]

−	[[Category:Construction_techniques]] [[Category:Design]]	+	[[Category:DCN_Guidance]] [[Category:DCN_Product_Knowledge]] [[Category:Construction_techniques]] [[Category:Design]]

Designing Buildings at 14:26, 15 January 2018

2018-01-15T14:26:49Z

← Older revision		Revision as of 14:26, 15 January 2018
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	* Groundworks.		* Groundworks.
	* How deep should foundations be?		* How deep should foundations be?
−	* How to lay foundations.
	* Pad foundation.		* Pad foundation.
	* Piers.		* Piers.

Designing Buildings at 15:16, 11 January 2018

2018-01-11T15:16:07Z

← Older revision		Revision as of 15:16, 11 January 2018
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	(Ref. Manual for the design of concrete structures to Eurocode 2.)		(Ref. Manual for the design of concrete structures to Eurocode 2.)

−	For low-rise buildings, it is generally recommended to limit the overall depth of a pad foundation to 1 m from ground level~~, as placing it too deep can cause problems later in the construction~~. When designing the pad, care should be taken to ensure that it is large enough to prevent tension within the concrete, which could result in cracking and failure.	+	For low-rise buildings, it is generally recommended to limit the overall depth of a pad foundation to 1 m from ground level. When designing the pad, care should be taken to ensure that it is large enough to prevent tension within the concrete, which could result in cracking and failure.

−	Reinforced concrete pads should be designed so that the depth is sufficient to resist a shear force known as ‘punching shear’. This can develop around the perimeter of the column, wall or other vertical component that the pad is supporting. Bending can also occur as the pad footing spreads the load onto the stratum~~, so resistance is important~~.	+	Reinforced concrete pads should be designed so that the depth is sufficient to resist a shear force known as ‘punching shear’. This can develop around the perimeter of the column, wall or other vertical component that the pad is supporting. Bending can also occur as the pad footing spreads the load onto the stratum.

	To resist bending moments, the pad footing should be designed so that the force is applied within the middle third of the base. This is known as the ‘middle third rule’ – a design practice that means the size of the foundation is defined according to the resultant force’s centralisation. There is an equation that defines the distribution of compression stress across the pad foundation:		To resist bending moments, the pad footing should be designed so that the force is applied within the middle third of the base. This is known as the ‘middle third rule’ – a design practice that means the size of the foundation is defined according to the resultant force’s centralisation. There is an equation that defines the distribution of compression stress across the pad foundation:
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	* Zy = elastic modulus of the pad foundation in its minor axis in plan.		* Zy = elastic modulus of the pad foundation in its minor axis in plan.

−	Depending on the loads, either welded steel fabric or reinforcing bars will be necessary, and arranged in both directions. It is common to approach the design of the pad as though it were an inverted cantilever supported by the column and carrying the pressure of the soil.	+	Depending on the loads, either welded steel fabric or reinforcing bars will be necessary, and arranged in both directions.
		+
		+	It is common to approach the design of the pad as though it were an inverted cantilever supported by the column and carrying the pressure of the soil.

	The reinforcement must be designed to be capable of resisting the bending stress, and is similar to that of floor slabs.		The reinforcement must be designed to be capable of resisting the bending stress, and is similar to that of floor slabs.

Designing Buildings at 15:08, 11 January 2018

2018-01-11T15:08:52Z

← Older revision		Revision as of 15:08, 11 January 2018
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	Pad foundations are a form of spread foundation formed by rectangular, square, or sometimes circular concrete ‘pads’ that support localised single-point loads such as structural columns, groups of columns or framed structures. This load is then spread by the pad to the bearing layer of soil or rock below. Pad foundations can also be used to support ground beams.		Pad foundations are a form of spread foundation formed by rectangular, square, or sometimes circular concrete ‘pads’ that support localised single-point loads such as structural columns, groups of columns or framed structures. This load is then spread by the pad to the bearing layer of soil or rock below. Pad foundations can also be used to support ground beams.

−	A pad foundation should be designed to effectively spread a concentrated force into a bearing stratum. They are a popular design solution ~~due to being~~ cost-effective and relatively easy to design and construct, and are suitable for most subsoils except loose sands, loose gravels and filled areas.	+	A pad foundation should be designed to effectively spread a concentrated force into a bearing stratum. They are a popular design solution as they are generally cost-effective and are relatively easy to design and construct, and are suitable for most subsoils except loose sands, loose gravels and filled areas.

	In order for pad foundations to spread the load into the soil, the pad must be either sufficiently deep (allowing the force of the load to spread out at a pre-defined angle), or be constructed with adequate reinforcement. The soil’s bearing capacity, as well as the concrete’s strength, are the factors that define the angle of the load’s spread.		In order for pad foundations to spread the load into the soil, the pad must be either sufficiently deep (allowing the force of the load to spread out at a pre-defined angle), or be constructed with adequate reinforcement. The soil’s bearing capacity, as well as the concrete’s strength, are the factors that define the angle of the load’s spread.
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	Depth/projection ratios for unreinforced footings:		Depth/projection ratios for unreinforced footings:

		+	Unfactored ground pressure (kN/m²)

		+	a/hf

		+	a = the projection from the face of the column

		+	hf = the depth of the footing

		+	C20/25

		+	C25/30

		+	C30/37

−	{\|	+	C35/45
−	\|	+
−	~~Unfactored ground pressure (kN~~/~~m²)~~	+

−	~~\| colspan="4" rowspan="1" \|~~	+	≤200
−	~~a/hf~~	+

−	~~a = the projection from the face of the column~~	+	1.2

−	~~hf = the depth of the footing~~	+	1.1

−	\|-	+	1.1
−	\|	+
−	\|	+
−	~~C20/25~~	+

−	\|	+	1.0
−	~~C25/30~~	+

−	\|	+	300
−	~~C30/37~~	+

−	\|	+	1.5
−	~~C35/45~~	+

−	\|-	+	1.4
−	\|	+
−	~~≤200~~	+

−	\|	+	1.3
−	1.2	+

−	\|	+	1.2
−	1.1	+

−	\|	+	400
−	~~1.1~~	+

−	\|	+	1.7
−	1.0	+

−	\|-	+	1.6
−	\|	+
−	~~300~~	+

−	\|	+	1.5
−	1.5	+

−	\|	+	1.4
−	1.4	+

−	\|
−	~~1.3~~
−
−	\|
−	~~1.2~~
−
−	\|-
−	\|
−	~~400~~
−
−	\|
−	~~1.7~~
−
−	\|
−	~~1.6~~
−
−	\|
−	~~1.5~~
−
−	\|
−	~~1.4~~
−
−	\|}
	(Ref. Manual for the design of concrete structures to Eurocode 2.)		(Ref. Manual for the design of concrete structures to Eurocode 2.)

Editor at 15:03, 16 November 2017

2017-11-16T15:03:48Z

← Older revision		Revision as of 15:03, 16 November 2017
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	Depth/projection ratios for unreinforced footings:		Depth/projection ratios for unreinforced footings:
		+
		+


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	* Groundworks.		* Groundworks.
	* How deep should foundations be?		* How deep should foundations be?
		+	* How to lay foundations.
	* Pad foundation.		* Pad foundation.
	* Piers.		* Piers.

Editor at 13:51, 13 November 2017

2017-11-13T13:51:59Z

← Older revision		Revision as of 13:51, 13 November 2017
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	Depth/projection ratios for unreinforced footings:		Depth/projection ratios for unreinforced footings:
		+
		+


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	* Footings.		* Footings.
	* Groundworks.		* Groundworks.
		+	* How deep should foundations be?
	* Pad foundation.		* Pad foundation.
	* Piers.		* Piers.

Editor at 16:32, 2 November 2017

2017-11-02T16:32:24Z

← Older revision		Revision as of 16:32, 2 November 2017
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	For a general introduction, see Pad foundation.		For a general introduction, see Pad foundation.
		+
		+	For different types, see Types of pad foundation.

	[[File:Padfoundation.JPG\|link=File:Padfoundation.JPG]]		[[File:Padfoundation.JPG\|link=File:Padfoundation.JPG]]
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	Depth/projection ratios for unreinforced footings:		Depth/projection ratios for unreinforced footings:
		+
		+


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	* Strip foundation.		* Strip foundation.
	* Trench fill foundation.		* Trench fill foundation.
		+	* Types of pad foundation.

	=== External resources ===		=== External resources ===

Editor at 15:24, 2 November 2017

2017-11-02T15:24:22Z

← Older revision		Revision as of 15:24, 2 November 2017
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	Depth/projection ratios for unreinforced footings:		Depth/projection ratios for unreinforced footings:
−
−

Editor at 15:24, 2 November 2017

2017-11-02T15:24:10Z

← Older revision		Revision as of 15:24, 2 November 2017
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	In order for pad foundations to spread the load into the soil, the pad must be either sufficiently deep (allowing the force of the load to spread out at a pre-defined angle), or be constructed with adequate reinforcement. The soil’s bearing capacity, as well as the concrete’s strength, are the factors that define the angle of the load’s spread.		In order for pad foundations to spread the load into the soil, the pad must be either sufficiently deep (allowing the force of the load to spread out at a pre-defined angle), or be constructed with adequate reinforcement. The soil’s bearing capacity, as well as the concrete’s strength, are the factors that define the angle of the load’s spread.

−	For following table should be referred to when determining the spread of force within an unreinforced concrete pad.	+	The type of skeletal frame will determine the pad foundation design. For example, a cast insitu concrete column will require a kicker and continuity bars to be cast into the pad. Steel frame, timber frame or precast concrete framed structures will require holding-down bolts to be cast into the top of the pad or sockets to be formed.
		+
		+	The following table should be referred to when determining the spread of force within an unreinforced concrete pad.

	Depth/projection ratios for unreinforced footings:		Depth/projection ratios for unreinforced footings:
		+
		+

Editor at 15:13, 2 November 2017

2017-11-02T15:13:23Z

← Older revision		Revision as of 15:13, 2 November 2017
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	Depth/projection ratios for unreinforced footings:		Depth/projection ratios for unreinforced footings:
−
−