emprical and rational design

8/6/2019 Emprical and Rational Design

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Foundations

Empirical rulesWalls forming the structural system must be placed centrally on foundation, and soils

should be not heaving, clay or collapsing.

Concrete use must have a compressive of not less than 10MPa at 28 days, which is mixed1 part cement, 4 parts sand and 5 parts aggregate

With continuous Strip foundation the diameter must not be less than 200 mm, and the

width is to be not less than 600 mm with masonry walls, and 400 mm with timber framedstructures

When strip foundations are at more than one level, the upper portion and must extend

over the lower portion to at least the thickness of the foundation, using the same strength

of concreteWhere the floor slab is thickened to form the foundation, the thickness must be not be les

than the thickness required for a strip foundation, width of the thickened portion must not

be less than required thickness of a strip foundation

PiersWhere piers are used built into the wall, the thickness of the foundation must be the same

for the wall. The foundation must project at least 200 mm beyond the pier

Rational rules

When foundations are required for heaving, heaving clay or collapsing soils aprofessional engineer

To determine the compressive strength, test must be carried out

Floors

The floor must be supported by well compacted ground or on suitable filling and to be

constructed from an imperious layer not more than 40 mm thick composed of slate, rock

or brick or concrete slab with a compressive strength of not less 10mPA at 28 days,composed of 1 part concrete, 5 parts arrogate and 4 parts sand

concrete must be used in the construction of water resistant floors

in the construction of Timber Suspended floor, the boards must be places at least no less

than 550 mm from the ground, providing an area for ventilation.

under floor membrane

should not be less than 0.25 mm thick and paved on a surface free from sharp objectsIt must be turned up on the at least the thickness of the slab on the perimeter

Joints must be sealed by overlapping sheets by at least 150 mm

Walls


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empirical

Empirical rules for walls

Complies to walls that are internal, external , structural, non structural, parapet, free

standing or retaining

Masonry walls, that are load bearing must transfer resist loads and transfer these to the

ground, via the foundations

A non structural wall is where the masonry is used a sinfill or classing and does notexceed 25 m in height. In the case of a parapert wall, its thickness should not be less than

one fifth its height. . Non structural walls may be exposed to forces other than their own

weight, such as wind impact on a parapet wall. , its its strength is still of importance.

Materials

Minimum

average

compressivestrength (MPa)

Wall type position Solid units Hollow units Class of mortar

required

Structural

(other than

foundation or

retaining)

Single storey

(internal or

external)

7 3.5 II

Double storey

(Internal or

exctrenal0

10.5 or 14 ** 7 II

Non structural

(other than

parapet,

balustrade andfree-standing

wall)

External 7 3.5 II

Internal 7 3.5 II

Free-standing External or

internal

10.5 7 II

Foundation Supporting a

single storey

7 3.5 II

Foundation Supporting a


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Concrete roofs must not exceed 175mm in thickness when soild, or equivalent mass when

voided

wall dimensions

In regards intersecting walls form the lateral support,

must be constructed from masonry units and mortar of the same quality and

strength. Its height must not be less than 80% of the height of the wall it supports,

its width must not be less than 45% (or 90 mm, whichever is greater) of the wall it

supports

Its length must at least one fifth the length of the wall it supports, or one eighththe distance between intersecting walls

Walls must intersect supporting walls between 60 and 120 degrees

RationalWhere a masonry pier is used for lateral support

its perpendicular length must be 3 times the thickness of the wall its width along the length of the wall must at least twice the thickness of the wall

must be at least 80% the length of the wall it is supporting

Cavity walls

An external masonry cavity will be between 50 and 110 mm wide

Wall ties must be evenly spaces at a 2.5 ties per meter sqaured, if the cavity is not morethan 75 mm, if the cavity is more than 75 mm, 3 ties are required per meter square

foundation wallsfunctions as a retaining wall, must not exceed 1.5m

The level between the ground and the backfill should not be more than 1m

The thickness of the walls cant be less than the they carry

ballustarde walls

Solid masonry ballustrade wall, must be

tied to reinforced concrete, brick columns or bonded into return walls or reinforced

brick piers expansion joints are to be used when neccesary, no further than 8 m apartwhere a wall

is supportred by comulum and pier (both reinforced)

Where the structural beams are bonded to the return walls. The return walls must not bespaced more than 6m part when 230 thickness wall, 5m for 190 mm walls and 4m for 110

Brick ballustrade walls

Reinforced, consisting od galvanised steel wire not less than 3.5 mm in diameter, in thehighest 4 bed joints. these must overlap at least 150 mm with the supporting column


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Except for buildings containing more than 2 dwelligs (H3 classified), but no empirical

rules govern ballustrades except for materials

Ballustrade walls must be designed by an engineer or comptetnt person

Free standing walls

wall thickness(mm)

Max height of wall above groudlevel

Pier

Without piers with piers Min dimensions max spacing

(centre tocentre) m

90 0.8 1.2 290 x 290 1.9

110 1.0 1.5 350 x 350 2.1

140 1.3 1.8 340 x 340 2.5

190 1.5 2.2 390 x 390 2.7

230 1.8 2.4 470 x 470 3.7230 1.8 2.6 470 x 470

290 2.2 2.6 490 x 490

340 2.4

Roofs

Empirical rules

Where the roof is supported by a wall the following apply:

Miniun height requirements

In regards to a double pitched roof (Howe, single or douyble pitch span not exceeding10m, and bays no more than 1.5m apart)

roof

covering

truss

member

nominal

timber size(mm)

max span (m)

metal and

fiber-cementsheets

rafter 38 x 114 3.1 4.6 5.8

38 x 152 4.0 5.8 7.238 x 228 6.1 8.5 10.0

tie beam 38 x 114 3.1 4.5 6.2

38 x 152 4.5 6.4 8.3

38 x 228 7.1 10.0 10.0

Concrete

tiles, clay

tiles and

rafter 38 x 114 6.0 9.0 10.0

38 x 152 8.2 10.0 10.0

38 x 228 10.0 10.0 10.0


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thatch tie beam 38 x 114 4.7 6.7 9.4

38 x 152 5.9 8.5 10.0

38 x 228 7.2 10.0 10.0

metal roof

tiles

rafter 38 x 114 6.2 9.0 10.0

38 x 152 8.0 10.0 10.0

38 x 228 10.0 10.0 10.0tie beam 38 x 114 4.5 6.7 9.0

38 x 152 5.9 8.7 10.0

38 x 228 8.7 10.0 10.0

all web members need to be at leat 38 x 114

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