FORCES - ALTERNATIVE ONE

93 kN Overturning moment from concrete pressure force about base is:-

OTM = (72 x 1.25 ) + ( 21 x 0.275) = 90.00 + 5.78 = 95.78 kNm/m OTM base Platform Loading

Construction operation load on platform is 1.50 x 0.8 = 1.2 kNm/m.

Lever arm of loading about face of wall is

Alternative One 170 + 225 + 8002 = 795mm Alternative Two 350 + 2

800 = 750mm

Weight of Formwork

Weight of formwork is 0.45 x 2.85 (say) x 1.0 = 1.28 kN/m run.

Assume it acts approximately 80mm from face of wall.

FORCES - ALTERNATIVE ONE

Take moments about E to find uplift force Tuplift at position C. The effect of the imposed load on the working platform cannot be considered in this case as it is acts as a restoring moment for

considering uplift. The c.o.l. may actually not happen if there are only few people on the platform!

Overturning moment about base is 95.78 kNm The restoring moment about position E is

= ( Tuplift x 1.225 ) + {1.28 x (1.225 + 0.285 – 0.080)}

= ( Tuplift x 1.225 ) + 1.83

Restoring moment must be ≥ overturning moment hence Tuplift = 1225 =7819

83 1 -78

95. . . . _{kN/m run}

Refer to Section 3.5.7 for relevant factors of safety on anchors.

{Note: the minimum factor of safety of 1.2 (Section 5.1.5) refers to overturning of freestanding double faced formwork, and is not applicable when calculating the required uplift fixing force.}

Tuplift

78.19 kN/m

Forces – Alternative One continued Output To establish maximum load in prop DE consider worst case of

overturning about position C to find horizontal force Hd required at position D to stabilise the formwork. The c.o.l. is now relevant and is included in the calculation. Hence:

95.78 + {1.2 x (0.795 – 0.285) ≤ Hd x 1.925 Hence Hd = 1925

61 0 + 78 95

. .

. = 50.07 kN

At position C, the lateral force to be resisted is:- FT – Hd = 93 – 50.07 = 42.93 kN

This example uses a separate fixing in the slab at position C to resist the lateral shear force, hence the anchor for uplift is only designed to take tension.

By Pythagoras Theorem the length DE is 1.225² +1.925² = 2.282m Hence by similar triangles the maximum load in prop DE is:-

PropDE = 50.07 225

. 1

282 .

2  = 93.26 kN per metre run

The vertical load downwards at position E is thus:- Vertical LoadE = 1225×5007

925

1.. . = 78.68 kN per metre run

Prop DE 93.26 kN/m run

Design of Wall Formwork

The formwork would be designed in a similar way to Worked Example One using the appropriate concrete pressure and material properties.

Output from Design

The output from Alternative One gives following information for TWD to design the fixings and propping necessary per metre of wall as:- Uplift at position C 78.19 kN

Lateral Shear Force at C 42.93 kN Axial Load in prop DE 93.26 kN Vertical load at position E 78.68 kN Horizontal force at position E 50.07 kN

Fixings Output per metre

FORCES - ALTERNATIVE TWO Output Design philosophy

The method of calculating the forces in Alternative Two is different from that in the previous calculations in Alternative One.

The A frame in use is a proprietary welded structure with internal bracing. This means that it acts as a rigid body under load so that lateral forces, such as concrete pressure forces, are transmitted through the structure to the base, and allows the angled tie and anchor to resist the lateral forces with no residual overturning moment.

{NOTE: The calculation in this example is intended to illustrate the magnitude of the forces in principle on a typical example. Always refer to the proprietary equipment supplier for the geometry and technical data for the A frame used. }

Forces acting

The maximum lateral force from the concrete pressure is 93 kN.

The tie and anchor assembly at F acts at 45° to the base, so the axial load in the tie assembly will be 93  2 = 131.50 kN per metre of wall.

This load in the tie assembly will in turn generate a downward vertical load of a similar amount, i.e. 93 kN.

Refer to Section 3.5.7 for relevant factors of safety on anchors and the tie rods used to connect to such anchors.

{Note: the minimum factor of safety of 1.2 (Section 5.1.5) refers to overturning of freestanding double faced formwork, and is not applicable when calculating the required tie force.}

Load in anchor 132 kN/m

Diagram of Forces acting on system

c.o.l. c.o.l.

Concrete Concrete Force Force Anchor

Force F G H G H F

(a) Actual Force location (b) Resolved Forces for calculation

self weight self weight

Forces Alternative Two continued Output To establish the maximum vertical load VH at position H take

moments about G, allowing for the self weight of the formwork and including the c.o.l. as it is to the right of support G and increases the moment. (The self weight of the A frame is ignored) See (b) page 28.

Moment about position G is

95.78 - {1.28 x (2.140 + 0.180 – 0.080 – 1.885)}

+ {1.2 x (2.140 + 0.180 – 1.885 – 350 -

800 )} 2 - (93 x 0.255)

= 95.78 - 0.45 + 0.38 - 23.72 = 71.99 kNm Hence the vertical reaction at H is VH =

885 . 1

99 .

71 = 38.19 kN.

Maximum VH 38 kN

To establish the maximum vertical load VG at position G take moments about H, allowing for the self weight, but excluding the c.o.l. as it is to the right of support G and would decrease the moment. See (b) page 28.

Moment about position H is:-

95.78 - {1.28 x (2.140 + 0.180 – 0.080)} - (93 x 2.140) = 95.78 - 2.87 – 199.02 = -106.11 kNm

Hence the vertical reaction at G is:- VG = 885 . 1

11 .

106 = 56.29 kN.

Maximum VG 56 kN

There is no requirement to check the design of the proprietary suppliers A frame as it is a suppliers item, but the TWD MUST check that the loads applied in the Alternative Two design are acceptable for the type of A frame envisaged.

Output from Design

The output from Alternative Two gives the following forces per metre run of wall as information for the TWD to design the fixings and supports:-

Force in 45° angled tie/anchor assembly at position F 132 kN Vertical load at position G 56 kN Vertical load at position H 38 kN NOTE: To reduce tip deflection at B caused by elongation of the tie rod in tension under load, the anchor/tie asembly may be

pre-tensioned. A kicker must be used. Refer to the suppliers data.

WARNING: The use of proprietary panel systems and A Frames will usually have predetermined positions for the A Frames.

Output per metre