EG-222 Section 1 Revised(1)

8/13/2019 EG-222 Section 1 Revised(1)

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Module EG-222

ec on :

Actions onStructures

Dr C. Wood

College of Engineering


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EG-222 REINFORCED CONCRETE DESIGN - Section 1

Characteristic loading

Loads are direct actions (forces) that are applied to a structure. Loads are

Permanent loads Imposed Loads Variable LoadsWalls

Occupants

Furniture

Floor slabs

Beams

Stored

materials

Roofs

Finishes

partitions

Moveable a ng

Permanent

machiner

machineryWind loads

Loads are s ecified b their characteristic values, as defined in BS EN 1990 and the

now oa s

National Annex.


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Characteristic weights o bui lding materials for calculation o permanent loads

WallsColumns

Floor slabs

Beams

Roofs

Finishes

Cladding

Loads due to the weight of the oads due to the weight of thestructure

continuedoverleaf

Note: The values provided here are unit masses in kg/m2 or kg/m3. To convert this to a unitweight in N/m2 or N/m3, take the constant of gravitational acceleration, a=9.81m/s2.


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Characteristic weights o building materials continued

Note: The values provided here are unit masses in kg/m2 or kg/m3. To convert this to aunit weight in N/m2 or N/m3, take the constant of gravitational acceleration, a=9.81m/s2.


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Imposed loads due to building use Table NA.2Occupants

Furniture

Stored

materials

Moveable partitions

Variable actions due to imposed loads are

Moveable machinery

ca egor se rom o accor ng o e

specific use and subcategorised according to

intensity of loading arising from that use.

a e or es:

Residential, social, commercial and

administration areas (A,B,C,D)

Garages and vehicle traffic areas (F,G) Roofs (H, I, K)

Be aware that the National Annex applies

here:

Refer to National Annex Table NA.2 to

Refer to Table NA.3 to find the value of

the imposed loadqk


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mpose oa s ue o u ng use a e . con nue


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Imposed loads due to building use Table NA.3

determination of general effects i.e.calculation of structural self weight.

Point load value is intended for

determination of local effects, such as shear

punching.

Further details relatin to the correct use ofthese tables must be read in your copies of

the Eurocodes


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Variable load due to snow loading

A significant source of imposed loading.

ground loading due to snow is set out in

EN1991-1-3:2003 Eurocode 1: Actions

on structures Part1-3: General actions

Windloads

Snow loads (from p1-24 of Eurocodeextracts).

Snowloads

The third class of loading set out in the

Extracts is wind loading. The standard is

named in full as: EN1991-1-3:2003

Eurocode 1: Actions on structures

Part1-4: General actions Wind actions,

from p1-48 of extracts.

Calculation of wind actions is taught it

-


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Design loads are obtained by multiplying characteristic loads by their appropriatepartial safety factors e.g. 1.35G + 1.5Q for simple beam cases.

ar a sa e y ac ors or avoura e an un avoura e oa s

Partial safety factors for actions allow for:

Design assumptions and inaccuracy of calculation

Possible unusual increases in the magnitude of the actions Unforeseen stress redistributions

Construction inaccuracies

In order to make a structure as safe as possible we must consider whether the load

that is acting is having a favourable or unfavourable effect on the structure this will.

Loads that are considered unfavourable will have a higher partial safety factor

applied.

Loads that are favourable will have a lower partial safety factor applied.

Load combination k k,

Unfavourable Favourable Unfavourable Favourable

Permanent + Imposed 1.35 1.0 1.50 0.0


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Example: Partial safety factors for favourable and unfavourable loads


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So far you have dealt with problems onlycontainin ermanent load t icall due

Action Combinationfactor 0

Imposed load in buildings, categorysee EN 1991-1-1

Load combinations

to the self-weight of the building) and

imposed load (due to building occupancy).Category A: domestic, residentialareas

0.7

Cate or B: office areas 0.7,

variable loading is introduced e.g. wind?

In this case you must consider one of the

Category C: congregational areas 0.7

Category D: shopping areas 0.7

variable loads to be leading and the

other accompanying.

.

Category F: traffic area,

vehicle weight < 30kN

0.7

to be acting with full magnitude, whilst the

accompanying variable action is reduced

b a combination factor

a egory : ra c area,

30kN


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Example: Using the load combination factor0


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Favourable and unfavourable loading with load combination factor

Factors for design of structural members

members of a building structure at the ultimate limit state

Type Load combinationPermanent Load Gk Imposed Load Qk,1

Wind

n avoura e avoura e n avoura e avoura e1 Permanent + Imposed 1.35 1.0 1.50 0.0 -

2 Permanent + Wind 1.35 1.0 - - 1.50

3 Permanent + Imposed(leading) + Wind (secondary)

1.35 1.0 1.50 0.01.5 x0=1.5x0.5=

0.75

4 Permanent + Imposed(secondary) + Wind (leading)

1.35 1.0 1.5 x0 0.0 1.50

1 The unfavourable artial safet factor is a lied to an loads which tend to roduce a more criticaldesign condition at the section considered

2) The favourable partial safety factor is applied to any loads which tend to produce a less criticaldesi n condition at the section considered

3) For Type 3 wind is considered to be the secondary variable load with 0= 0.5 and partial safetyfactor calculated as 1.50 x 0.5 = 0.75

calculated as 1.50 x 0 (typically 0 = 0.7)


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Favourable and unfavourable loading with load combination factor

Factors for checking static equilibr ium

of a building structure at the ultimate limit state

Permanent Load Gk Imposed Load Qk,1

Unfavourable Favourable Unfavourable Favourable1 Permanent + Imposed 1.10 0.9 1.50 0.0 -

2 Permanent + Wind 1.10 0.9 - - 1.50

3 Permanent + Imposed(leading) + Wind (secondary)

1.10 0.9 1.50 0.01.5 x0=1.5x0.5=

0.75

4 Permanent + Imposed(secondary) + Wind (leading)

1.10 0.9 1.5 x0 0.0 1.50

1) The unfavourable partial safety factor is applied to any loads which tend to produce a more critical

design condition at the section considered

2) The favourable partial safety factor is applied to any loads which tend to produce a less criticaldesign condition at the section considered

3) For Type 3 wind is considered to be the secondary variable load with 0= 0.5 and partial safety

factor calculated as 1.50 x 0.5 = 0.754) For Type 4 imposed load is considered to be the secondary variable load with partial safety factorcalculated as 1.50 x 0 (typically 0 = 0.7)


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Example: Partial safety factors for load combinations

Considering the stability of the office block for overturning about point B, calculate theminimum allowable characteristic load due to the foundation block at A recallin thatthere will be two possible load combinations of permanent, imposed and wind loading.


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Loading arrangements on continuous beams

Loading arrangements can be defined as patterns of load which are chosen to produce.

In reinforced concrete beam or slab design we look for the loading arrangement that

will generate:

The worst (i.e. largest magnitude) in-span moment

The worst (i.e. largest magnitude) support moment

arrangements.

Loading for maximum span moments

To produce a maximum in-span moment, the span must carry the maximum load, the

adjacent spans the minimum load, and the spans next to those the maximum load.

This produces two load cases:

Unfavourable FavourableLoad Case 1 Unfavourable Favourable Unfavourable

L d C 2

ax mummoment

ax mummoment

ax mummoment

Load Case 2Maximummoment

Maximummoment


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For maximum moment at a support, adjacent spans carry maximum load and thenspans alternate with maximum and minimum load. This producesn-1load cases.


Unfavourable Unfavourable Favourable Unfavourable Favourable

Maximum

Load Case 4 Unfavourable Unfavourable Favourable UnfavourableFavourable


Unfavourable Unfavourable FavourableUnfavourable Favourable

Maximummoment

Obviousl this set of load cases could take a ver lon time to anal se for a lar e

Load Case 6 Unfavourable UnfavourableUnfavourableFavourable Favourable

structure, so the UK National Annex permits a simplification for the load case for

maximum support moments shown on the next slide..


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Loading for maximum support moments UK National Annex simplif ication

For simplicity, the UK National Annex permits the single load case of all spans loaded. , , ,

previous slide.

This means that all continuous beam analyses will only need to consider three load

cases, regar ess o ow many spans ere are.

However, the resulting support moments (except those at the supports of cantilevers)

must be redistributed by 20% into the beam/slab span.

This requires a procedure known as moment redistribution detailed in Section 2.

Load Case 3 UK NAoad Case 3 UK NAUK National Annex

load case for

moment

moment

moment

moment

moment

moment

Unfavourable Unfavourable Unfavourable UnfavourableUnfavourable

moments

met:

In a one-way spanning slab, the area of each bay must exceed 30m2.

The ratio of the characteristic variable load Q to the characteristic ermanent load G mustnot exceed 1.25

The characteristic variable load Qkmust not exceed 5kN/m2.

S ti 1


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Load cases for continuous beams summarised using UK National Annex

simplification with partial safety factors for design of structural members

Unfavourable FavourableLoad Case 1For maximum in-span Unfavourable Favourable Unfavourable

1.35Gk+ 1.5Qk 1.35Gk 1.35Gk+ 1.5Qk 1.35Gk 1.35Gk+ 1.5Qk

moment

moment

moment

Load Case 2For maximum in-span Favourable Unfavourable Favourable Unfavourable Favourable

1.35Gk 1.35Gk+ 1.5Qk 1.35Gk 1.35Gk+ 1.5Qk 1.35Gk

momen Maximummoment

Maximummoment

Load Case 3 UK NAUK National Annex load 1.35Gk+ 1.5Qk 1.35Gk+ 1.5Qk1.35Gk+ 1.5Qk 1.35Gk+ 1.5Qk1.35Gk+ 1.5Qkcase or max mum support

moments 20% support

moment redistribution must

Maximum Maximum Maximum MaximumMaximum Maximum

Unfavourable Unfavourable Unfavourable UnfavourableUnfavourable

e app e . moment moment moment momentmoment moment

Documents

EG-222 Section 1 Revised(1)