MBA Health and Safety Conference - PE 15 March 2018 MBA Temporary Works...Special structural steel and timber SANS 10162 and SABS 0163. Wind = SANS 10160-3. DV 4 ... per one meter

MBA Health and Safety Conference - PE15 March 2018

Considerations essential to safe temporary works design and execution on site.

Dévan Venter

Lead Engineer – PERI KZN Region

■ Introduction.

■ Engineering considerations.

■ Codes, good practices and safety.

■ Typical considerations for shoring.

■ Typical errors and what to look out for on site.

■ Typical considerations for walls / columns.

■ Typical considerations for scaffolding.

■ Bracing 101.

DV2

Engineering considerations

Unstable founding conditions

Mobile / movable

Removable after casting concrete

Dynamic / impact loading

Labour intensive construction opposed to mechanized (South Africa).

Instability condition before concrete is cast.

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Codes, good practices and safety

BS 5975.

DIN EN 12810 / 12811 / 12812.

SANS10085-1 (Scaffolding) and Unit Standard 243035.

Special structural steel and timber SANS 10162 and SABS 0163.

Wind = SANS 10160-3.

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Type verification


Is only valid for a predefined application area.

Has to be described through a valid assembly instruction.

Proof engineer needs to check, if the type test is valid for that system.

Proof in structual analysis

Applied stress ≤ Permissible stress

When using a structural analysis, type verifications

have to be proofed from scratch every time.

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Type test


Test report from an authority (e.g. state / federal testing office) is available.

Is a service offer.

Avoids a type varification from being

checked for every project individually.

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Vertical impacts - ∑V

Typical considerations for shoring

Q1 - Permanent actions - self weight of formwork / superstructure

Q2,1 - Variable imposed actions - self weight of fresh concrete

Q2,3 - Variable imposed actions - construction operations loading

Q4,1 - Variable imposed actions - additional load of pouring (heaping)

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Horizontal impacts - ∑H


Q3 - Variable actions - variable persistent horizontal imposed action (1% of SV)

Q4,2 - Variable actions - concrete pressure on side formwork (may not be

transferred into shoring)

Q5 - Wind (acc. DIN EN 1991-1-4)

Q6 - Flowing water actions

Q7 - Seismic effects

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Vertical impacts - ∑V

Self-weight of the formwork Q1

Q1 = 0.6 kN/m² (60 kg/m²) timber secondary girders and steel main girders

Q1 = 0.4 kN/m² (40 kg/m²) timber secondary girders and timber main girders

Self-weight of concrete Q2,1

Q2,1 = gB * d

Normal reinforced concrete

gB = 2500 kg/m³ x 9,81 m/s²

gB = 24,5 kN/m³ (DIN EN 12812)

Note DIN EN 12812: „For calculation of ultimate limit state (ULS) a concrete weight of 25,0 kN/m³ can be used

per one meter thickness.“


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Wind:

Maximum wind = 0.5kPa up to 8.4m, 0.8kPa over 8.4m or according to

SANS10160-3.

Working wind = 0.2kPa (DIN EN)

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Q5 - qp(z) - Beaufortgrade


Q5 ≈ 0.20 kN/m² -

18m/s = 65km/h

Q5 ≈ 0.50 kN/m² -

28m/s = 100km/h

Q5 ≈ 0.80 kN/m² -

36m/s = 129km/hDV

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Q3 - variable persistent horizontal imposed actions

A horizontal load of 1% of the vertical load shall be taken into account

applied externally at the point of application of the vertical load Q2

in addition to the effects caused by imperfections.

100

V*1Q3


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Additional horizontal forces

It should be avoided to transfer horizontal load from

fresh concrete pressure into the shoring system


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Example


These horizontal loads must be calculated in the support:

ƩV / 100 (site work activities)

0.01 rad geometrical imperfections

(unavoidable inclination)

Without slope

Wind

GG

Scheduled inclined towersRighted towers

ƩV / 100 (site work activities)

0.01 rad geometrical imperfections

(unavoidable inclination)

Slope angle [%]

Wind

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Load combinations according to DIN EN 12812

Load case 1:

Unloaded falsework,

e.g. before pouring

Load case 2:

Falsework during loading

e.g. during pouring

Load case 3:

Loaded falsework

e.g. during curing

Load case 4:

Loaded falsework subjected

to seismic effects


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Q5 - k – service time factor (DIN EN national appendix)


Duration of limited

situation

With securing

safeguards

With increased

securing safeguards

Without any

safeguards

Up to 3 days 0.1 x q 0.2 x q 0.5 x q

Up to 3 month

from May to August

0.2 x q 0.3 x q 0.5 x q

Up to 12 month 0.2 x q 0.3 x q 0.6 x q

Up to 24 month 0.2 x q 0.4 x q 0.7 x q

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Without Design

class factor

Design class factor

g = 1.15

Design class factor

g = 1.00

Design class A - Installation height up to 3.5 m

- Span up to 6.0 m

- Slab thickness up to 300 mm

Design class B2 - A proof is needed for load-carrying

members and connections which are

necessary for the stability (simplified

assumptions are allowed).

Design class B1- Precise methods used for calculating the

actual load carrying characteristics of the

static system (eccentricities) and the

supports (settlements)

Design class according DIN EN 12812

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Imperfections and eccentricities

The following influences shall be taken into account

Eccentricities of loads

Angular imperfections and eccentricities caused by looseness

Differences from the theoretical axes (bow and sway)


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The load eccentricity at load

points shall be taken as a

minimum of 5mm.

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Angular imperfections and eccentricities caused by looseness

Spigot angular

imperfection

Spigot eccentric imperfection


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Deviations from the theoretical axes

Sway imperfection Bow imperfection

Frames with an offset in one direction

(n-1) x e

Frames with a restraint at the top

(n-1)/2 x e


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Bow imperfections for compression members


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Sway imperfections for compression members


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How to consider the effects in a analyses tool

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System “restrained at the top“


Vertical actions

Q1 Selfweight of formwork

Q2,1 Selfweight of concrete

Q2,3 Construction operations loading

Q4,1 In-situ concrete

loading allowance

Horizontal support at the top

½ x Q5 Wind on shoring*

Q5 Wind on superstructure

Bow imperfection*

Variable persistent horizontal

imposed actions

* These factors of influence have

already been considered in PERI

design tables.

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System “frees-tanding“

Vertical actions

Q1 Selfweight of formwork

Q2,1 Selfweight of concrete

Q2,3 Construction operations loading

Q4,1 In-situ concrete

loading allowance

Horizontal loads to transfer

Q5 Wind on superstructure

Q5 Wind on shoring*

Sway imperfection*

Q3 Variable persistent horizontal

imposed action

Q4,2 Concrete pressure

* These factors of influence have

already been considered in PERI

design tables.


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Spring support / prop elastic shortening by compression

3,0 m

8,0 m

12,5 m


shoring height

[m]

Spring constant

[kN/cm]

h

A* EC

Support in

dependent of

the height

317,1 kN/cm

118,9 kN/cm

76,1kN/cm

C spring constant

E modulus of elasticity

A cross section area

h shoring height

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Elasticity modulus and cross section areas

PERI UP Rosett E = 21,000 kN/cm² A = 4.53 cm²

ST 100 E = 21,000 kN/cm² A = 4.53 cm²

Multiprop 120-480 E = 7,000 kN/cm² A = 13.94 cm²

Multiprop 625 E = 7,000 kN/cm² A = 16.91 cm²

HD 200 (Steel) E = 21,000 kN/cm² A = 27.70 cm²

HD 200 (Aluminium) E = 7,000 kN/cm² A = 27.70 cm²


Spring support / prop deformation by compression

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Project example: Lora Arena Split, Croatia

(Courtesy of PERI Weißenhorn shoring department)



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length of influence = 1.25m



Project example: Lora Arena Split, Croatia Structural system - rigid supports

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length of influence = 1.25m

E = 21000 kN/cm²

A = 4.53 cm²

h = 1000 cm

Ctz = 95.13 kN/cm

Structural system - elastic supports

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Proof of ULS

The maximum stress induced is a single component must be lower than permissible stress!

Stability has to be provided for the complete system as well as for

every single component.

Ed = design value of an effects of influence

Rd = corresponding design value of resistance

1R

E

d

d


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safety factors for proof with characteristic loads

M = 1.1 “Material steel“

F = 1.5 “Forces“ M x F = 1.65 „global safety factor“

E = Effects of influence (Stress)

R = Resistance

k = characteristic

d = design

safety factors for proof acc. DIN EN 12812

M = 1.1 “Material steel“

F = 1.35 “Permanent actions“ (e.g. selfweight Q1)

F = 1.5 “All other actions“


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■ Proof of SLS


Important for a satisfactory result is to proof the real deflections on the complete system

It is essential to check the following influences:

⎯ Settlement of foundation;

⎯ Compression / buckling of shoring system below

⎯ Deflection of girders and beams

To find out the real deflection of each sytsem it is necessary to calculate without

any safety factors. That means γF = 1.0

Superelevation / precamber

due to constant load (G)

due to variable load (G)DV

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Overturning

Unloaded falsework has to be prevented from overturning!

1.01.5xM

0.9xM

dst

stb


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Local sliding

id,m,ddf, R N x R g

1.0R

F

d,f

d

Fd Design value parallel to the plane of bearing

Nd Design force normal to plane of sliding

Rm,d,i Design value fo the resistance of

mechanical device

γµ Particial factor for friction (γµ = 1,3)

µ Minimum friction coefficient

Unloaded falsework has to be prevented from sliding!


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Friction coefficient – DIN EN


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Backpropping / Re-shoring


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• Concrete strength at time of backpropping / Re-shoring

• Sufficient prop capacity under slabs

• Can slab span between props?

• Involve permanent structure engineer for approval of backpropping before

commencing stripping.

• Backpropping percentages.

Backpropping / Re-shoring


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• Peter Pallett - ISTRUCTE – TWf - The structural

Engineer Dec, 2016.

Typical errors and what to look out for on site.

The main causes of formwork failure are:

1 - Improper stripping and shore removal

2 - Inadequate bracing

3 - Vibration

4 - Unstable soil under mudsills* (Sole Plates), shoring not plumb

5 - Inadequate control of concrete placement

6 - Lack of attention to formwork details

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• Failure to install intermediate props.

• Insufficient bracing.

• Correct Bracing installation

• Incorrect grid used.

• Patching around columns.

• Insufficient founding (soil, sole boards etc.)

• Striping and re-propping – Upstand beams


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Photos from PERI archives.


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Bracing 101

A brace must

Be installed at the correct position

Be strong enough

Be stiff enough


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Bracing 101 – Quickstage example


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Typical considerations for walls / columns

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Ciria Report for alteral comcrete pressure


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0.000

4.685

6.725

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

0 10 20 30 40 50 60

He

igh

t (m

)

Pressure (kN/m2)

Ciria: Height - Concrete Pressure

Horizontal concrete pressure - Ciria


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Typical considerations for Scaffolding

Access scaffolding

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Access scaffolding

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Access scaffolding

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Important Extracts from SANS10085-1:2005

For knots, refer to 6.3.3


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This is a good practise guideline – designers should still calculate stability.

For stability ratios refer to Table 3.


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Take care of maximum allowed number of platforms – usually 2x working platforms.

For classification refer to Table 5.


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For deviations refer to 10.1.4


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For scaffold boards refer to Table 6


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For ladders refer to 10.7


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For ledgers refer to Table 9

For Maintenance and housekeeping refer to 11.4


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For inspection refer to Clause 12


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16.2 Training of Scaffolding erector to Inspector.

SANS details the minimum required training program and experience.

For training refer to 16.2.5

Thank You.

Questions?

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Flanders Drive

bridge over R102.

References

Shoring presentation extracts, PERI Weißenhorn shoring department.

PERI RSA local project photos, PERI photo archives.

PERI international project photos, www.peri.com

Table extracts, DIN EN 12812, SANS10085-1:2005.

Graph extracts, DIN EN 12812.

Beaufort wind scale, Francis Beaufort.

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Documents

MBA Health and Safety Conference - PE 15 March 2018 MBA Temporary Works...Special structural steel and timber SANS 10162 and SABS 0163. Wind = SANS 10160-3. DV 4 ... per one meter