Setra Cable Stays

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Laboratoire Central des Ponts et Chaussees

Driving research accross networks

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Recommendations of French interministerial

commission on Prestressing

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2002

Issued by the Service d'Etudes Techniques des Routes et Autoroutes Centre des Techniques des Ouvrages d'Art

46, avenue Aristide Briand -BP 100 -92225 BAGNEUX CEDEX -France Tel. 33 (0)1 46 11 31 53 -Fax 33 (0)1 46 11 3355 -www.setra.eQuipement.gouv.fr

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CIP recommendations on cable stavs

CHAPTER 5. STATIC BEHAVIOUR OE CABLE STA~

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39 39 42 47 51 53 Article 5.1 Introduction

Article 5.2 Linear model of a cable stay

Article 5.3 Approximate effect of cable-stay selfweight.

Article 5.4 Catenary model

Article 5.5 Model of inextensible sagging cable

Article 5.6 Modelling a real cable stay

57 58 63 63

Article 6.1 Cable stay deviated at a saddle

Article 6.2 Taking account of the flexural stiffness of a cable at its anchorage.

Article 6.3 Vibrations in the free length of a cable stay

Article 6.4 Cable bending and durability ..""""'..."'.""'."""""""""""""".'

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7. CABLE-STAY MECHANICS DURING CONSTRUCTION

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Article 7.1 Preloading of cable stays ₆₇

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CIP recommendations on cable stavs ,.

Article 7.2 Intrinsic characterization of cable-stay preloading 71

Article 7.3 Calculating the instantaneous tension of cable stays 77

Article 7.4 Strand-by-strand tensioning 78

CHAPTER 8. DYNAMIC BEHAVIOUR OF CABLE STAYS -- 81

Article 8.1 Taut-string model.. '..." ' '...'.' ' ' ' 81

Article 8.2 Vibration modes of a sagging cable stay 83

Article 8.3 Excitation by lateral displacement of an anchorage 91

Article 8.4 Parametric excitation by longitudinal displacement 93

Article 9.1 Common general requirements ."..."'.."'...' ' 99

Article 9.2 PSC category: parallel strand cable stays 103

Article 9.3 PWC category: parallel- wire cable stays 108

Article 9.4 MLS category: multi-layer-strand cable stays , 111

Article 9.5 Collective external barrier " ' ' 115

Article 9.6 Other kinds of main tensile element 119

CHAPTER 10. CABLE-STAY ANCHORAGE -- 121

Article 10.1 Functions of a cable-stay anchorage 121

Article 10.2 General provisions common to all anchorage types 122

Article 10.3 Classification of anchorages 125

Article 10.4 Type C anchorages for parallel-strand cable .stays 126

Article 10.5 Type S anchorages for parallel-strand cable stays 130

Article 10.6 Type B or B+R anchorages for parallel-wire cable stays 131

Article 10.7 Type F+R anchorages for MLS cable stays 133

CHAPTER 11. QUALIFICATION TESTING OF A CABLE-STAY SYSTEM 139

Article 11.1 General 139

Article 11.2 Mechanical qualification of cable stays 140

Article 11.3 Qualification of cable-stay watertightness ' ' 147

CHAPTER 12. CABLE-STAY INSTAllATION 151

Article 12.1 Organizational aspects 151

Article 12.2 Supply 152

Article 12.3 Manufacture of cable stays 153

Article 12.4 Erection of cable stays 156

Article 12.5 Tensioning and adjustment 158

Article 12.6 Permanent corrosion protection 162

CHAPTER 13. MONITORING AND MAINTENANCE OF CABLE STAYS 165

Article 13.1 Principles and objectives of cable-stay maintenance 165

Article 13.2 Monitoring and maintenance 165

Article 13.3 Cable-stay adjustment 167

Article 13.4 Cable-stay replacement 168

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CHAPTER 14. CABLE-STAY DESIGN AND VERIFICATION RULES 173

Article 14.1 General 173

Article 14.2 Actions and combinations of actions 173

Article 14.3 Cable-stay strength. ' 176

Article 14.4 Ultimate limit states 179

Article 14.5 Serviceability limit states.. 180

Article 14.6 Verifications of fatigue 182

Article 14.7 Saddles 184

Article 14.8 Extradosed prestressing tendons 184

CHAPTER 15. REFERENCES 189

Article 15.1 Standards 189

Article 15.2 Bibliograpical references ' ' ".' ". 191

CHAPTER 16. DEFINITIONS AND NOTATIONS 193

Article 16.1 Glossary , 193

Article 16.2 Notation , 197

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CIP recommendations on cable stays

1. FOREWORD

Early in 1997, the French Interministerial Commission on Prestressing (Commission

Interministerielle de la Precontrainte -CIP) set up a working group to study the technological

problems involved in cable stays and to establish an approval procedure similar to that

implemented for prestressing systems.

The working group drafted these Recommendations, a state-of-the-art review advising on the

design, qualification, and implementation of cable-stay systems. It calls on the experience acquired with cable-stayed bridges in France and elsewhere in the last thirty years or so. This experience

includes large cable-stayed bridges such as the Brotonne Bridge and the Pont de Normandie

Bridge in France, the Second Severn Crossing in the UK, and the Vasco de Gama Bridge in Portugal, but also involves a wide range of smaller bridges.

The cable technology described in these Recommendations principally concerns cable-stayed bridges, the cables of which are characterized by large variations in tension, fatigue effects, and

direct exposure to the elements. More generally, it is hoped the recommendations will be of use for all cables exposed to climatic aggression, particularly to the ties of bowstring bridges, extradosed or intradosed prestressing tendons, and cables used in any stayed civil engineering structures, such as stadium roofs, masts, etc.

On the other hand, the applications of interconnected cable networks are beyond the scope of these Recommendations which do not, therefore, deal with cabled spaceframe structures or suspension-bridge technology. In addition, cable-stay saddles are addressed only in the form of a few recommendations on design, but using them is advised against, because of their effect on the durability of cable stays and because of maintenance and replacement difficulties.

These Recommendations are broken down into four parts:

.Part 1 (Chapters 2 to 8) is a review of current scientific knowledge in the matter. It takes the

form of a manual which can be referred to by designers and which substantiates the choices recommended in the subsequent parts.

.Part 2 (Chapters 9 and 10) describes the cable-stay systems commonly used at the moment,

and gives recommendations on the technology that can achieve the greatest durability.

.Part 3 (Chapters 11 to 13) is the benchmark for approval and implementation of cable-stay

systems that the CIP required.

.Part 4 (Chapter 14) presents limit-state cable-stay design rules.

Texts in standard type are recommendations. Texts in italics are comments.

Texts in small type are descriptions or examples.

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MEMBERS OF THE CIP CABLE-STAYS WORKING GROUP

Chairman:

Robert Chaussin (Roads Department, Ministry of Public Works)

Yves Bournand (VSL) Alain Chabert (LCPC) Louis Demilecamps (GTM)

Andre Demonte (ISPAT -Trefileurope) Pierre Jartoux (Freyssinet International) Patrick Laboure (ISPAT -Trefileurope) Dominique Le Gall (Baudin Chateauneuf) Benoit Lecinq (SETRA 1)

Daniel Lefaucheur (SETRA) Claude Neant (ETIC -BBR)

The following also helped in the drafting of the Recommendations: Michel Marchetti (Formule Informatique)

Michel Virlogeux (Consulting Engineer)

These Recommendations were co-ordinated by Jocelyne Jacob (SETRA) and Benoit Lecinq Drawings by Philippe Jullien and Louis Risterucci (SETRA).

Translation by Alex Greenland.

Photo credits:

Cover photos:

1, 5, 9 (Freyssinet) -2 (Etic) -3, 4, 10 (SETRA) -6 (VSL) -7 (Fontainunion) -8 (GTM)

Photos 43, 51, 55 to 57: Etic Photos 6, 11, 35: Fontainunion Photos 8,16,17,18,20,22 to 24,26,31,33,34,41,44,45,48,54,58,59,61 to 63: Freyssinet Photos 30, 39, 40, 46, 49, 50: GTM Photos 13 to 15, 27 to 29: LCPC Photos 1 to 5,7,9,10,12,19,21,25,36 to 38, 42, 47, 52, 53, 60: SETRA Photo 32: VSL

1 Benoit Lecinq has joined the Freyssinet International group since these Recommendations were published.

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Analysis of the fatigue strength of cable stays must consider two complementary factors:

.pure tensile stresses due to imposed loads, whose amplitude is much greater than in the case

of prestressing tendons;

.flexural stresses at anchorages, due principally to cable-stay vibration, but also to relative

deformation of the cable stables and the bridge structure. These stresses are negligible in the case of prestressing tendons.

2.2.3 Environmental

aaaression

Contrary to prestressing tendons, cable stays are directly exposed to environmental aggression: rain, wind, ultraviolet radiation, freeze-thaw cycles, etc. (see Chapter 3).

2.2.4 Corollary on the desian of cable stays

Cable stays, which are the key factor in the stability of cable-stayed bridges, must provide the best possible operational guarantees. Their durability must be analyzed very rigorously at the initial design stage or at the stage of qualification of a cable-stay system.

However, the cable stays will remain the most vulnerable elements of the structure, and there will

remain some imponderables in the appreciation of their durability. Moreover, the possibility of

damage due to a road accident cannot be excluded.

For these reasons the design of cable stays must allow for their rapid replacement, without harmful consequences to the structure or serious disruption to traffic. All the protective arrangements must guarantee that inspection, adjustment, and maintenance can be carried out to attain the required lifetime or to determine the need for replacement.

2.2.5 Cateaories of utilization

High-performance cable-stay systems are appreciably more expensive than prestressing systems.

In order to restrict these extra costs for structures where the cables are less heavily loaded, a second category of utilization has been defined (see Chapters 11 and 14).

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Photo 28: Wear at point of contact (contact between crossed wires in a cable stay)

Photo 29: Crack at point of contact (wire in an inner layer of a cross-layed multi-layer-strand

cable)

6.4.3.2 Consequences for cable design

The external parameters that limit initiation and propagation of fatigue cracks are:

.

limitation of the maximum axial stress in service;

increase in inter-wire contact areas, by increasing the lay length, by prestressing cables to a higher tension or by plastification of contact areas, or by preferring linear contact to point contact;

limitation of variations of curvature and of the maximum curvature, by increasing the radius of saddles or by reducing the angles of deviation in anchorages;

limitation of flexural stress variations, by damping vibration due to wind or traffic;

reduction in coefficients of inter-wire friction, by using a lubricant whose effect can be

maintained, or, on the contrary, by preventing any relative movement between wires and thus eliminating fretting fatigue and fretting corrosion phenomena.

The experiments performed by Waterhouse, Patzak, and Siegert show that the 100 million cycle fatigue limit of multi-layer strands with bright or galvanized wires loaded to 50% of their breaking stress is about 100 MPa.

For shorter lifetimes involving contact fatigue phenomena, the fatigue strength at 2 million cycles can attain 120 to 150 MPa. These values do not take account of the presence of an effective lubricant which might durably maintain the coefficient of inter-wire friction below 0.2 (value below which the fatigue strength increases).

6.4.4 Conclusion:

detailina

In practice the following detailing is recommended

.

Abandon saddles and replace them by anchorages. If saddles are used all the same, ensure they provide a sufficiently large radius of curvature (see Article 14.7).

Eliminate any unnecessary metal-on-metal contact between cables and parts of anchorages or saddles or deviators.

Use flexible materials in zones of deviation: nylon, polychloroprene, zinc, aluminium alloy. Use a flexible guide to attenuate or even eliminate free bending of the cable where it leaves the

anchorage, on both the bridge deck and the pylon. .

Inject flexible lubricants to reduce the coefficient of inter-wire friction, and use cables made

from galvanized wire. Galvanization is primarily associated with corrosion-protection of steel,

but it also reduces coefficients of friction and the contact pressure between wires: the zinc is flattened and partially extruded around the edges of the contact areas.

.

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Photo 30: Roof of Stade de France stadium on temporary supports

Conversely, if the deck of a concrete cable-stayed bridge were built on falsework, and if the deck were encastered into the pylon, when the falsework was removed there would be substantial sag of the main span, resulting in an unacceptable negative moment near the pylon (Figure 20). The solution for preventing this situation of course involves pretensioning the cable stays with a jack before removing the falsework. This means we are dealing with active structural elements.

This is why, in most cases, cable-stayed structures require pre-tensioning. They are highly

statically indeterminate, and pre-loading the cable stays by pre-tensioning is nothing other than

introduction into the structure of a set of self-balanced forces. These forces-two equal and

opposite forces at the two anchorages-induce no boundary forces overall, but are balanced by

the distribution of forces in the structure (bending moments in the deck and pylon in the case of a cable-stayed bridge). This distribution of preloading forces enables the structure to take the effects of permanent loads with only very little bending.

It is therefore natural to regard a cable stay as a preloaded2 structural element. Adjusting a cable stay then involves applying preloading of a given intensity.

7.1.2 Cable-stay adiustment from the desian point of view

During the design of a cable-stayed bridge, finding the right adjustment involves optimizing

adjustments of cable-stay tension in order to achieve the following objectives:

.allowable stresses in the cable stays and in the structure, both during construction and after

commissioning, under variable loads;

.if at all possible, zero or very low bending moment in the structure under permanent loads

(selfweight and any prestressing of concrete) in order to limit redistribution due to creep and to facilitate mid-span jointing.

~

2 Or 'prestressed', but in civil engineering this term is often considered to using tendons, as within a bridge deck, for instance.

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CIP recommendations on cable stays

Photo 32: Uddevafla Bridge under construction

7.2.4 Deck saa

Another restriction on using the initial tension for cable-stay adjustment comes to light in the case of flexible structures: the tension is determined by the pendulum rule (see § 7.1.2) and the vertical component is practically the same irrespective of cable length. This method results in irregular tension from stay to stay, an overtensioned cable stay being following by an undertensioned one, and soon.

A means of overcoming this problem has been envisaged in the case of very flexible decks; it involves tensioning the cable stay until the correct deck sag is obtained at the end of the cable stay. This method cannot be used when the structure is rigid, especially not for adjusting the first cable stays of a cantilever end-fixed to a pylon. Nor is it very satisfactory to use both methods together, depending on whether a rigid or flexible part of the structure is being dealt with.

Finally, deck sag does not directly characterize cable-stay preloading; on the contrary, it introduces unfortunate confusion between geometrical adjustment and adjustment of cable-stay preloading.

7.2.5 Cable lenath under no tension (neutrallenath)

Cable-stay preloading is entirely determined by the following three things:

.definition of a reference state (most commonly this involves the bridge geometry, which is

defined by drawings and which is used to define the design model),

.the distance I between anchorages fixed to the structure, when the structure is in its reference

state,

.the neutral length 10 of the untensioned cable stay, which is shorter than distance I.

It is theoretically possible to adjust cable stays on the basis of their neutral length, by accurately measuring cable-stay length 10 when they are made, and then tensioning them by appropriate means to tie the anchorages into the structure. This method is not affected by actual construction

74

The neutral length of cable 10 is the length of cable measured between two anchorages when the cable is not tensioned and rests on a support which cancels out the effects of selfweight. Like cable mass, 10 is an intrinsic quantity that is independent of the conditions to which the cable stay is

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.protective metal coating of zinc or standard zinc/aluminium alloy applied at coverage of between

190 al:ld 350 g/m2 (mean thickness of 26 to 40 11m approximately); .

.strength class fclass 1770 MPa or 1860 MPa;

.strain under maximum load Agt at least 3.5%;

.modulus of elasticity of the bundle of parallel strands of about 195 GPa :t 5%;

.very low relaxation: no more than 2.5% at 1000 hours at 0.7 Fm ( at 20°);

.category B of French standard NF A 35-035 (revised 2000), i.e. MTEs with special capacities

meeting the following test conditions:

~ fatigue strength: 2 million cycles with maximum stress of 0.45 FOUTS and stress variation of

300 MPa;

~ deflected tensile strength coefficient of no more than 20%.

The nominal values and tolerances apply to coated products, i.e. they include for the metal

coating. The strand lengths commonly produced can have welds made on individual wires before drawing, but may not be welded during or after drawing.

Photo 35: Detail of strand

The project specifications may lay down more stringent requirements, particularly with respect to

the protective metal coating, within the scope given in § 9.1.2.1.

9.2.2 Individually

sheathed multi-strand

cable stavs

A sheathed, waxed/greased galvanized strand is a product made especially for cable-stay

applications. The individual sheath is made by extruding high-density polyethylene (HOPE) directly onto the strand previously coated with an infilling material.

The use of strands sheathed by threading a preformed sheath over an MTE is prohibited for permanent cable stays.

Experimental French standard NF XPA 35-037 (currently being drafted) contains most of the

following requirements. 9.2.2.1 Individual sheath

The individual sheath is an very important factor in cable-stay durability. Its functional

characteristics are specific to each cable-stay system. It must meet at least the following

conditions: "

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9.2.2.3 Outer sheath (stay pipe)

The individually sheathed strands can be enclosed in an outer sheath, or stay pipe-which mayor

may not be watertight-whose purpose is fulfil supplementary functions, in addition to corrosion

protection. It is therefore not necessarily a barrier, but the recommendations of Article 9.5 apply

nonetheless.

The outer sheath may consist of a one-piece stay pipe through which the strands are threaded, or it may consist of two split shells clipped to each other around the cable stay

once it has been tensioned. It

improves the aerodynamic

behaviour of the cable stay, and possibly also its watertightness and its CBsthetics. The surface of the outer casing may be textured or carry other relief; such as spiral ridges for example, to counter the effects of rain & wind instability.

Photo 36: Individually sheathed strands inside a stay pipe 1

9.2.2.4 Diagram illustrating the principle of PSC stays made with individually sheathed,

waxed/greased strands

Individual sheath

-Optional outer sheath

'"

_"-A!L

Figure 31.. Diagram of PSG stay with individual sheaths

9.2.3 Ducted multi-strand

cable stays

9.2.3.1 Stay pipe

For the free length of a cable stay, the external barrier of ducted multi-strand stays is generally one of the following continuous stay pipes:

.plastics stay pipe made of rigid or semi-rigid tubes (high-density polyethylene (HOPE) or

similar);

.steel stay pipe made from pipe sections welded together; they are either protected against

corrosion or are made of stainless steel.

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The thickness of the sheath should be taken into account to determine the total volume of the MLS cable. Refer to the technical data sheets on the cable-stay system for more details.

Photos 37 and 38: MLS cables

Cables with round wires Locked-coil cables with round and Z-shaped wires Oext of bare cable (mm) Resisting section (mm1 Resisting section (mm1 Lineic mass (kg/m) F GUTS (kN) F GUTS (kN) 20 30 40 50 60 70 80 90 100 110 120 130 140 150 219 530 942 1501 2125 2936 3779 4869 5897 7364 8532 12285 11578 13536 316 766 1362 2034 3000 4100 5327 6625 8179 9854 11844 13819 16405 18850 Lineic mass (kg/m) 1.8 4.3

7.6

12.9 18.5 25.3 31.9 40.8 50.9 60.3 72.8 86.3 97.6 115.8 594 1090 1801 2502 3406 4552 5690 7060 8466 9999 11731 13423 15645 858 1580 2594 3716 4946 6604 8454 10316 12441 14497 17004 20170 23314 5.3

9.8

15.0 21.6 30.5 40.2 49.0 61.2 72.8 85.8 101.5 115.1 133.9

Table 3: Common MLS cables

9.5.1 Watertiaht outer orotection

For the free length of ducted PSG or PWG stays, the collective external barrier consists of a strong, watertight tube of regular shape throughout its entire length.

The characteristics of this tube, especially its thickness and chemical composition, must meet the following requirements:

.the materials of which it is made must not be aggressive to the injection materials and MTEs;

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If tube sections are to be welded together, the tube must be no less than 3 mm thick. Welds must comply with the terms of appropriate standards (e.g. NF P22-471, quality 1). The fatigue strength of welded joints must be substantiated.

Steel stay pipes must have an external corrosion-protection system guaranteeing at least 6 years

before rust index Ri 1 defined by the applicable standard is reached.

At the time of publication of these Recommendations, the applicable standard is French standard

NF T30-071, "Degradation des surfaces peintes". This level of guarantee of corrosion protection can be achieved by cleaning the surface to level OS 2.5 and painting the bare steel. Regular maintenance is required thereafter (every ten to fifteen years approximately). Alternatively, painted galvanized or stainless-steel tubes can be used.

9.5.2 Blockina comDound

The filling material injected into the intermediate areas must not be a cause of wear (fretting corrosion or fretting fatigue) of the MTEs it is supposed to protect. It is for this reason that cement grout is prohibited.

A flexible protective material is generally used to fill the inside of the duct. Alternatively, a dry air flow can be kept up around the MTEs by means of a dehumidification system.

Flexible protective products are generally pumpable petroleum products:

.a microcrystalline wax, i.e. a malleable crystallized solid consisting of saturated hydrocarbons

which are injected in a liquid state (temperature between 80 and 120°C) [6]; or

.a mineral-oil-based grease, i.e. a plastic lubricant obtained by dispersion of an insoluble

thickener (such as complex metallic soap) in a lubricating fluid (mineral oil) to form a stabilized

three-dimensional network; or

.a resin or flexible polymer injected at an appropriate temperature.

The filling material must not be aggressive to the MTEs or the material of which the stay pipe is made. The absence of aggressivity is determined by physical testing or by reference to previous projects.

The filling material must retain its protective properties without interruption, and continue to protect the steel despite the extreme thermal loading to which it might be subject throughout the lifetime of the project.

Photo 39: Pump for injecting cable stays Photo 40: Check of injection

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10.1.4 Corrosion

protection

and watertiahtness

The design of anchorages must extend the two barriers defined in Chapter.9 without a break, to protect against corrosion and keep water out of the free length of the cable stay.

10.1.5 Removability

Anchorage design must allow for renewal of cables.

ARTICLE 10.2 GENERAL PROVISIONS COMMON TO ALL ANCHORAGE TYPES

10.2.1 Filterina out anaular deviations

As stated in Chapter 6, angular deviation of cable stays engenders stresses which can be of the

same order of magnitude as those due to the axial loads and can have harmful effects in terms of

fatigue.

Appropriate systems should therefore be provided to limit or eliminate the effect of cable-stay deviations at the anchorage head, i.e. to "filter out" changes in angle between the cable and

anchorage.

There are two main techniques for this, the effects of which are quite similar:

.stiffening the anchorage zone: this involves increasing the flexural stiffness of the cable stay.

One means of achieving this is to attach a steel tube around the cable, near the anchorage, and mechanically fix the end of the tube to the anchorage head or to the structure.

.guiding the cable: this involves partially or totally preventing transverse cable-stay movement,

i.e. the movement of each of its component parts, using a guide system placed a certain distance from the anchorage. The effectiveness of such a guide system depends on its distance from the anchorage, as seen in § 6.2.4.1

The angular-deviation filtering system can also playa role in damping (absorption of vibrational

energy by viscosity or friction).

The design of a cable stay's guide system must take account of transverse and flexural forces resulting from cable deformations.

10.2.2 Directional

adiustment

Initial directional adjustment is made

possible by allowing the stay or its

anchorage head to rotate. This is achieved

by inserting suitable connecting parts

between the anchorage and the structure.

Such connecting parts may be an

adjustment screw with a spherical seating

surface, bicylindrical shims, a fork attached

to a plastic hinge or to a single or double

shaft, etc.

In most cases, however, the systems for initial directional adjustment of stays cease to be very effective once the stay has been tensioned. They are useful above all during I

construction, and cannot be considered to Photo 42: Bottom anchorage of a stay on the Pont de eliminate the effects of bending due to Normandie Bridge, with hinged fork

cable-stay vibration.

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Abbreviation _Gripping Category of cable concerned

Conical wedges (split-cone) gripped in the anchorage head *

c

PSC (sheathed or ducted)

Swaged sleeves bearing on the anchorage head *

5 PSC (sheathed or ducted)

Buttonheads bearing against a plate + possible conical socketing action by

filling with Resin, etc.

--B

or B+R PWC

Fanning out + conical socketing action byI filling the socket casing with Resin, etc.

F+R MLS

* May be complemented with a suitable rigid filling material to improve fatigue strength

Further distinctions can be made between the different kinds of anchorage:

.live (or stressing) anchorage, where the cable is tensioned, and dead-end (or fixed) anchorage where no tensioning is performed;

.bottom anchorage, on the deck, and top anchorage in the pylon. The bottom anchorage of a cable stay is particularly exposed to water running down the stay, and therefore requires special preventative measures,.

.static anchorage, the head of which is static with respect to the structure, and adjustable anchorage, the head of which can be moved axially.

There is an important difference between cable stays using type C anchorages and all the others: the unloaded length of a cable made up of parallel strands anchored by split-cone wedges can be changed during adjustment phases, unlike the other kinds of cable stays for which the unloaded length of the tensioned wire, strand, or cable is irreversibly fixed before jacking takes place.

ARTICLE 10.4 TYPE C ANCHORAGES FOR PARALLEL-STRAND CABLE STAYS

Type C anchorages are used for sheathed or ducted multi-strand cable stays.

10.4.1 Principle of the system

Type C anchorages rely on wedging of each strand in a separate tapered hole in the anchorage head by means of jaws made up of two to four split-cone wedges.

In some cable-stay systems the grip of the

wedges is complemented by injecting the

anchorage head with an appropriate rigid

filling material such as resin with satisfactory

fatigue performance. It would therefore be

more appropriate to code these anchorages as type C + R.

Photo 45: Split-cone wedges

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Photo

46: Anchorage of a cable stay for the Stade de France stadium

~14 ",:";'"

FREE LENGTH TRANSITION ZONE ZONE D'ANCRAGE

7 -Strand deviation zones

8 -Sealing system

9 -Transition piece

10 -Deviator

11 -Stay pipe I transition piece joint

12 -Stay pipe (where applicable)

1 -Protection cover

2 -Sheathed 7 -wire strand

3 -Wedge

4 -Anchorage block

5 -Fork

6 -Spacer tube

Figure

38: Principle of type-C anchorages for sheathed strands -Static anchorage on fork

The transition zone, which extends from the end of the free-length part of the cable stay to the anchorage proper is where the strands fan out from the free length to the anchorage head.

The length of the transition zone depends on the number of strands and the technologies used to deviate them. The transition zone contains one or more deviators which convert(s) a bundle of parallel strands into a cone of divergent strands.

Steps must be taken to prevent fretting corrosion and fatigue at critical points: at each deviation of the bundle of strands, where the strands enter the anchorage head, etc. These measures must take account of axial overtension of the cable stay and permanent or transient angular deviations of the cables.

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of as

The commonly used means

connecting socket casings are

follows (see Figures 41 and 42):

INTERNALLY THREADED SOCKET CASING WITH THREADED EXTENSION

:g>

~

.socket casing with threaded bore

behind the socket: this threading

takes a threaded transfer rod

anchored to the structure by means of an adjustment and locking nut,.

.socket casing with external threading

taking an adjustment and locking nut;

.socket casing with fork and pin

transferring the cable-stay force to a knuckle plate welded to the structure;

.socket casing with lugs taking

several high-strength threaded rods

with adjustment and locking nut.

Adjustement~

1 -Socket

2 -Internally threaded socket casing

3- MLS cable stay

4 -Externally threaded transfer rod

EXTERNALLY THREADED SOCKET CASING WITH ADJUSTEMENT NUT

Adjustement

~

1- Socket 3 -MLS cable stay

2 -Externally threaded socket casing 4 -Adjustement and locking nut

Figure 41.. Different kinds of adjustable type F+R socket casings for MLS cable stays

FORK-TYPE SOCKET CASING @)

4 -Knuckle pin 5 -Knuckle plate 1 -Socket

2 -Fork-type socket casing 3 -MLS cable stay

SOCKET CASING WITH FIXING LUGS

..Photo 47: Top anchorage of a cable stay on Seyssel Bridge

Figure 42: Different kinds of adjustable type F+R socket casings for MLS cable stays (contd)

3 -MLS cable stay 4 -High-strength threaded rods

1 -Socket

2 -Lug-type socket casing

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Each specimen tested should reflect actual conditions of use, and have all the actual anchorage systems used with the cable stays, corrosion-protection accessories, and any products injected into the cable stays. Appropriate measures should be taken to reproduce the actual conditions in which the anchorages work in the actual structures. If the cable-stay system uses different live and dead-end anchorages (dead-end anchorage with swaged sleeves and live anchorage with jaws, for instance), both anchorages should be tested simultaneously.

PWC and PSC cable-stay systems generally use a deviator a certain distance from the anchorage which allows the MTEs to fan out from the free length to the anchorage (see Chapter 10). MLS cable stays too are sometimes configured this way. On test specimens the deviator should be placed no further from the anchorage than the distance specified for the cable-stay system.

In actual structures the deviator may be connected to the structure, either rigidly or with some freedom of movement, as when it is connected to the structure by an elastic tube or viscous damper. Since it is not reasonable to attempt to reproduce exactly the particular conditions of each structure for the qualification test, the most unfavourable transverse guide system should be used, i.e. that with a totally free deviator without any damping.

11.2.2.2 Fatigue test procedure

Once the specimen has been set up on the test bed, 5 to 10 cycles (possibly more, depending on the requirements of the party requesting the test) are carried out between O'max/2 and O'max to stabilize the components of the system. These cycles are not counted in the two million test cycles.

Photo 48: LCPC fatigue test bed

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