PD CEN-TR 15728 2008 Inserts for Lifting and Handling Precast Elements

PUBLISHED DOCUMENT

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Design and Use of Inserts for Lifting and Handling of Precast Concrete — Elements

ICS 91.100.30

12&23 800 N / mm² or f yk / f uk > 0.8

Max(1,5; 1,2 fuk/fyk)

1,7

2,0

-

Steel wire ropes

-

1,8

Prestressing strands

-

1,8

Type of insert Solid steel lifting systems Solid steel (smooth bars) lifting loops

*)

*)

The material for smooth bar lifting loops should be at least equivalent to S235J2+N.

Table 2 — Partial factors γc for concrete failure

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Loading in

5 5.1

Certified FPC

Tension

1,5

Shear, combined tension and shear

1,5

Actions on inserts Actions

The forces acting on an insert should be calculated for all relevant loading situations taking into account the product properties, the position of the inserts, condition of the form, lifting equipment, number and length of the ropes, chains or straps and the static system. In some cases it might be necessary to take into account the deformations of the precast element during lifting and handling.

5.2

Effect of lifting procedures on load directions

Inserts for lifting and handling may be subjected to loads acting in different directions during operation. As examples information on slabs and wall elements are given. The lifting equipment should allow statically determinate load distribution to the inserts (see Figure 2). To ensure that all inserts carry their required part of the load, sliding or rolling couplings between the lifting wires or chains should be used when there are more than two lifting points. In a statically indeterminate system the load distribution on the inserts depends in most cases on the unknown stiffness of the ropes and the position of the insert (see Figure 3). Therefore only the statically determinate part of a system should be used in calculating the actions on the inserts.

9

CEN/TR 15728:2008

a)

b)

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Figure 2 — Examples of handling equipment for slabs

Figure 3 — Statically indeterminate system, only two inserts loaded

Figure 4 — Example of statically determinate lifting of a slab and resolution of forces

10

CEN/TR 15728:2008 Depending on the equipment used during lifting the inserts may be subjected to combined parallel and transverse shear load (Figure 5a), combined tension and parallel shear loads (Figure 5b), transverse shear loads (Figure 5c) or axial tensile loads (Figure 5d).

a)

b)

c)

d)

Key a) b)

Combined parallel and transverse shear load Combined tension and parallel shear load

c) Transverse shear load d) Axial load

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Figure 5 — Examples of loads on lifting inserts for walls

Shear loads acting on inserts may be assumed to act without a lever arm, if the design of the inserts and its key avoids significant concrete crushing in front of the insert during loading. If this condition is not satisfied the lever arm should be taken as the actual distance between the shear force and the concrete surface plus half the nominal diameter of the insert.

5.3

Actions from adhesion and form friction

Adhesion and form friction will occur when the precast element is removed from the formwork. The values should be taken from National provisions. In the absence of National provisions the values for the combined effect of adhesion and form friction qadh given in Table 3 may be considered. General values for form friction are difficult to assess and friction should be avoided as far as possible. For some types of uneven form surfaces (structured matrixes, reliefs, structured timber etc.) the forces may be much larger than given in the table, and should be considered separately. The forces may be zero if the concrete does not come in contact with the form at all, for example if the concrete is poured on a layer of bricks that has been laid out on the form bottom. Large vertical form surfaces may create extensive friction forces due to undulations in the form. Prestressed components will usually have a camber caused by the prestressing force, and will therefore have lower friction against the vertical sides of the form. Table 3 — Examples of values of qadh Formwork and condition

qadh *) 2

Oiled steel mould, oiled plastic coated plywood

1 kN/m

Varnished wooden mould with planed boards

2 kN/m

Oiled rough wooden mould

3 kN/m

2 2

*)

The area to be used in the calculations is the total contact area between the concrete and the form.

The actions, Ed, for demoulding situations should be determined from: Ed = γ G ⋅ G + γ Q ⋅ qadh ⋅ A f with G

=

weight of the precast concrete element ; 11

CEN/TR 15728:2008

5.4

Af

=

form area in contact with concrete ;

γG and γQ

are partial safety factors for permanent and variable actions respectively.

Dynamic actions

During lifting and handling the precast elements and the lifting devices are subjected to dynamic actions. The magnitude of the dynamic actions depends on the type of lifting machinery. Dynamic effects should be taken into account by the dynamic coefficient ψdyn given in National regulations. In the absence of National Regulations the values of Table 4 may be considered. Other dynamic influences than covered by Table 4 should be based on special provisions or engineering judgement. Table 4 — Influence of dynamic actions on site Dynamic influences

Dynamic coefficient (ψdyn)

Tower crane and portal crane

1,2 x)

Mobile crane

1,4 x)

Lifting and moving on flat terrain

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Lifting and moving on rough terrain

2 – 2,5 3–4

x)

In precasting factories and if special provisions are made at the building site lower values may be appropriate.

The actions, Ed, for lifting situations should be determined from Equation (5.3): Ed = γ G ⋅ G + (ψ dyn − 1)γ Q ⋅ G

6

Choice of inserts

Having determined the actions on the insert for all relevant load combinations the task remains to choose an appropriate insert and relevant reinforcement. The insert load capacity depends on the field of application. The designer has three options in choosing the appropriate lifting arrangement : 1)

The recommendations given by the insert suppliers may be used directly. This option is further described in clause 7;

2)

The design charts provided in clause 8 may be used;

3)

Tests may be carried out specific to the intended application as outlined in clause 9.

Figure 6 indicates which option could be appropriate in a given situation.

12

CEN/TR 15728:2008

7

Use of Supplier’s recommendations

The commercially available lifting systems are usually designed and optimised for defined fields of application, in some cases based on results from proprietary test programs. Catalogue material from the supplier often describes corresponding design methods. These methods may be used provided that one of the following conditions is satisfied : 1)

The method is certified by an accredited third party in accordance with a relevant ETAG;

2)

The method is certified by an accredited third party in accordance with a CEN product standard;

3)

The method is certified by an accredited third party based on tests according to Annex A;

4)

The method is given by national provisions.

The supplier’s declaration of the product should state the method chosen. If the supplier cannot satisfy either of these conditions, or if the intended application falls outside the range of validity for the design methods recommended by the supplier, the designer should choose one of the options in clause 8 or clause 9.

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Information given by the supplier should conform to Annex B. NOTE Suppliers’ catalogues may disclaim the responsibility for the use of the data. Consequently, such catalogues should not be used as a recommendation.

13

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CEN/TR 15728:2008

Key 1)

The application of the insert is fully within the limits stated in the catalogue of an insert supplier or manufacturer. These limits include weight, concrete strength, edge distance, dimensions of the concrete member, local reinforcement and mode of lifting. 2) To verify the design model of chapter 8 for a certain type of insert it might be necessary to perform tests according to Annex A. The reinforcement provided to transfer loads from the insert into the element should be designed according to National provisions. Reinforcement for other purposes such as flexural or shear capacity of the precast element in use would not normally be considered in this. 3) Specific testing is intended to justify the capacity in a particular situation. As an example, this might include inserts for tunnel segments or bridge beams. It does not provide information for a wide range of applications.

Figure 6 — Flow chart for the design of lifting inserts

8 8.1

Use of CEN/TC 229 recommendations for typical user situations General conditions

For most common applications, present practice and available general information concerning the load capacity of inserts can be combined into a design model. This model is described in further details in sections 8.3 – 8.4. The 14

CEN/TR 15728:2008 model is not universally applicable. Limitations on the range of validity are used to exclude situations where other types of failure than concrete breakout failure (cone failure), failure of supplementary reinforcement or steel failure in the insert can occur. Within the indicated limited range of validity the model yields results that are very close to present practice. The limitations on the range of applicability are the following: 1)

Field of application The most common fields of application are:

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2)

a)

walls and other linear elements (such as beams and columns), where the insert is typically long compared to the edge distance (the smallest distance from the insert to a concrete surface parallel to the insert) and where the concrete in the vicinity of the insert is uncracked.

b)

slabs and pipes, where the edge distance is large while the possible length of the insert is limited by the thickness of the element and where the concrete in the vicinity of the insert is uncracked. This section covers the use of some common types of inserts in these two situations, cp tables 7 and 10.

Reinforcement is provided in the region of the insert, either as complementary reinforcement or as supplementary reinforcement. Minimum reinforcement is typically provided according to EN 1992-1-1. Although provided for other reasons the reinforcement may also act as a safeguard against failure in case cracking should unexpectedly take place in the concrete around the insert. If minimum reinforcement is not provided complementary reinforcement should be provided. If the minimum reinforcement is left out the risk of accidental cracking and brittle failure might be unacceptable. The presence of complementary reinforcement also makes it possible to postpone the development of a breakout failure so that the capacity of the insert becomes somewhat larger than in unreinforced concrete, see e.g. ref. [2]. Supplementary reinforcement is designed specifically to transfer the full load on the insert to the concrete element as a whole. The suggested models for design of the supplementary reinforcement are in accordance with the rules given in EN 1992-1-1.

3)

Minimum characteristic strength of concrete. Where no other indication of minimum concrete compressive strength is given, it is assumed that the concrete strength (at the time of lifting) is at least 15 MPa measured on cubes, side length 150 mm (or 12 MPa measured on cylinders).

4)

Factory Production Control (FPC). It is assumed that the precaster applies a Factory Production Control system according to the requirements in EN 13369, clause 6. It is furthermore assumed that the inspection scheme for finished product inspection includes a check that no harmful cracking has occurred in the neighbourhood of the inserts at the time of delivery.

5)

No extrapolation of design graphs. The validity of the calculation model outside the range covered by the graphs is not sufficiently known and therefore the graphs should not be extrapolated.

15

CEN/TR 15728:2008 6)

Safety factors. To facilitate the use of nationally determined partial factors the capacity values given in this chapter could be used as characteristic values. Figure 7 — Type a) inserts. Headed bolts and spread anchors Headed bolts and spread anchors transfer axial load to the concrete through mechanical interlock at the built-in end while shear load is transferred more or less directly between the recessed lifting key and the concrete at the top end.

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Figure 8 — Type b) inserts. Anchors with additional rebar These inserts maintain the possibility of shear transfer directly from the lifting key to the concrete, while the axial load is transferred to the concrete through a separate reinforcement bar to be threaded into a hole in the insert.

Figure 9 — Type c) inserts. Anchor systems with threaded sockets These inserts may utilize a simpler, threaded key to transfer the load to the insert. The axial load is transferred to the concrete through a bonded rebar either in the form of a separate bar threaded into a hole or as a built in rebar (e.g. waved anchors) included in the system. The corresponding key may or may not be suitable for transfer of shear forces. Figure 10 — Type d) inserts These inserts are short versions of type a) inserts – possibly with an extended bearing area at the built-in end of the insert. They are intended for use in slabs and pipes to sustain axial load and shear load. Figure 11 — Type e) inserts. Similar to type a) Inserts intended for use in slabs and pipes with short embedment lengths and large bearing areas that are also suited for supporting the necessary minimum reinforcement. Axial load as well as shear load may be accommodated.

16

CEN/TR 15728:2008 Figure 12 — Type f) inserts. Plate sockets A threaded socket mounted on a plate providing a bearing area for axial load. The corresponding keys are usually not suited for transfer of shear, but special options exist.

8.2

Types of inserts covered

8.2.1

Commercially available inserts

Many types of inserts are commercially available as illustrated in Figure 7 – 12. All these standard lifting systems consist of an insert embedded in the concrete element and a matching unit (key) that connects to the insert (Figure 7). The crane hook or hook of a lifting sling attaches to the key. The combination of components from different systems is prohibited. Threaded lifting devices and corresponding keys should be marked with a colour corresponding to their diameter. The colours given in Table 5 are recommended.

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Table 5 — Recommended colour identification codes of lifting systems for threaded lifting systems Diameter

Colour

Rd 12

orange

Rd 16

red

Rd 20

light-green

Rd 24

dark-grey

Rd 30

dark-green

Rd 36

light-blue

Rd 42

silver-grey

Rd 52

yellow

For other than threaded systems, the following method of marking is possible. The marking consists of a System ID and an Insert ID (Table 6). It should be fixed directly to the cast-in part and the lifting key. Table 6 — Marking of insert and key System ID

Insert ID

Producer

System

Lifting key

P

S

Insert

P

S

Specification

X

The System-ID consists of the identification of the producer P (minimum two letters or logo) and the producer’s name for the system S. In many cases different types of cast-in-inserts belong to the same system. Therefore the insert has to be marked with an Insert-ID containing additional information such as the specification by the supplier X and the length of the anchor Y. It should be visible after pouring the concrete. It is recommended to mark the insert directly with its length or to use a length identification code (capital letter or colour).

17

CEN/TR 15728:2008 8.2.2

Inserts made by the precaster

In addition to the commercially available inserts the precasters may produce their own lifting loops from smooth bars, prestressing strands or steel wire ropes. Necessary information on the handling of the element, e.g. lifting hook dimensions, shall be given in erection specifications. Lifting loops should only be used if the lifting angle is approximately the same in all lifting and handling situations. Furthermore, the lifting angle should be kept within the limits indicated in Figure 14.

Figure 13 — Lifting loops made of smooth bar, strand or steel wire rope (Type g) inserts)

Examples of the inserts are shown in Figure 13 and they should conform to the following specifications:

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 Smooth bars The material for smooth bar lifting loops should be at least equivalent to EN 10025-2, S235J2+N. During operation the minimum bending diameter of the smooth bar should not be less than 5 bar diameters. The size of the lifting hook may require a larger bending diameter.  Strands The shape of the strands may be adapted to the various types of elements. Prestressing strands that have been deformed before shaping should not be used. Bending of the strands during stocking or turning of elements should be avoided. The bending diameter of the strand loop (illustrated by the curvature of the sleeve in Figure 13) should be equal to or less than twice the diameter of the lifting hook (the diameter is 2⋅s in the figure in Table 8). The bending diameter of the strand loop must be larger than the diameter of the lifting hook. The strand diameter should not exceed 13 mm and the bending radius should be at least 50 mm. Bundling of maximum four strands may be used only when provided with a steel sleeve bent together with the strands, see Figure 13. To take into account effects of lifting hook diameter and different load distribution to the strands within a bundle, capacity reduction factors are given in Tables 8 and 9.  Steel wire ropes Only steel wire ropes, which comply with EN 12385-4 and 13414-1 should be used. 2

2

Steel and fibre cores are allowed. The rope grade should be 1770 N/mm or 1960 N/mm . However, in 2 calculations only a value of 1770 N/mm should be considered. To ensure sufficient flexibility of a rope the steel wire ropes should consist at least of the following number of wires: d = 6 mm: 42 wires minimum d ≤ 14 mm: 114 wires d > 14 mm: 200 wires The bending diameter of the steel wire rope should not be less than 2 rope diameters. 18

CEN/TR 15728:2008 To ensure sufficient bond steel wire ropes must be cleaned. The ends of the lifting loop made of a steel wire rope should be ferrule-secured or split. Split ends should not be taken into account in the design, but a ferrule-secured end will provide some extra anchorage.

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The loading angle, β, (angle between the direction of the force and the axis of the insert) should not exceed 30°, (see Figure 14). The effect from β on the distribution of the force to the legs of the loop should be considered.

a)

b) Figure 14 — Loading angle for lifting loops

19

Licensed copy:Benaim Group, 17/01/2009, Uncontrolled Copy, © BSI CEN/TR 15728:2008 Table 7 — Design summary for inserts under inclined tensile loading in walls and linear elements Anchor type

b)

a)

c)

g)

Walls and linear elements

Basic steel capacity

Choose an insert with sufficient steel resistance based on supplier declaration

Choose an insert and associated rebar both Choose an insert with sufficient steel with sufficient steel resistance based on resistance based on supplier declaration supplier declaration, see Figure 21

Wall thickness

Prevent blow-out failure by using Figure 16

Ensure that wall thickness is sufficient to obtain normal anchorage conditions: wall thickness larger than 7 times bar diameter (straight bars) or 11 times bar diameter (other than straight bars). If smaller thickness: the embedment length shall be increased.

Amount of complementary reinforcement

Choose an insert with sufficient steel resistance based on supplier declaration

Prevent brittle failure due to concrete cracking, see Figure 17

Anchorage

Anchorage length, see Figure 1

Anchorage length for axial load

Determine required anchorage length corresponding to concrete cone capacity from Figure 18.

Determine required anchorage length for bent rebar, see Figure 22.

Supplementary hairpin reinforcement (replaces complementary reinforcement)

If concrete cone capacity is too small or if shear load component: determine required reinforcement to carry the whole anchor load, see Figure 19, 20 and 22

Supplementary diagonal pull reinforcement, see Figure 23

None for tension

Determine required anchorage length for hooked rebar, Figure 22. Check that necessary anchorage length determined from Figure 17 is smaller None for tension

None for tension

Choose reinforcement arrangement and amount

Choose reinforcement arrangement and amount

Choose reinforcement arrangement and amount

Not used. Insert to be tilted according to load direction

Capacity reduction due to shear in wall plane

20% for loading angle 300