Recent Developments in Stay Cable Systems Convention/Shawwaf...Glider and strand are inside cable pipe. Pull-through winch at top of ... 2006 PTI TECHNICAL CONFERENCE –SESSION 4

Recent Developments in Stay Cable Systems

PTI Technical Conference, Reno- 2006 Khaled Shawwaf, Technical Director

2006 PTI TECHNICAL CONFERENCE –SESSION 4 RECENT DEVELOPMENTS IN STAY CABLE SYSTEMS KHALED SHAWWAF

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* Cable Stayed Bridges areefficient and attractive

* Over 350 have been builtin the last 25 years

* Spans are getting longer andcables larger

* Also used for medium spansand non-highway bridges

* Evolution: lock-coil to wiresto PT bars and strands

* Continuous enhancementsand innovations

* Recent developments



Wedge-Only Anchorages (Dyna Grip) Standard Cable System:

• All loads (static and dynamic) are resisted by the wedges• No structural socket- All strand types• Anchorage cavity is filled with grease/wax compound and sealed with compressed rubber disks• Individual strands may be removed for inspection and replaced• Special Feature of DSI DYNA-GRIP anchors: Strand sheathing continues to the wedge

Dyna-Grip



Rosario-Victoria Bridge, Argentina. 61-0.62 strand DYNA GRIP cable



Bond Socket Anchorages (Dyna Bond) Standard Cable System:

• Structural grout filler injected into steel socket at the end of construction• All loads applied before grouting resisted by the strand wedges• Loads applied after grouting transmitted by bond to the socket and directly to the structure• Fraction of dynamic loads (live load, vibrations and seismic) reach the wedges• Corrosion Protection: All anchorage voids are filled with a solid and robust filler• Enhanced fire resistance and protection against vandalism, impact and blast effects• All strand types. Greased strands must be cleaned in bond zone

Dyna-Bond



Alamillo Bridge- Spain. 61-0.62 strand DYNA-BOND cable



Provencher Bridge, Canada- 19-0.6 Dyna Grip and Clevis Anchors



Clevis Cable Anchorage:

• Attach to outer surfaces of Tower or Deck• Real ‘pin’ connection- No bending moment• High friction damping• Hand-hole for inspection & exchange

Corrosion Compound



* The clevis anchorage isfixed to the tower plateswith 120 mm pins

* Easy to install

* Accommodates large sagduring installation

* Self Aligning

* Non-stressing anchorage



Clevis type cable anchorage:fatigue and static strength test

Heavy wall pipe and weldedpin plates

Wedge plate threaded intoclevis pipe

2 million cycles 160 Mpa stress range



CONTEN- single strand stressing:

• Cable stayed bridges are getting longer• Cable sizes larger: 156-0.6 strands is the current world record• Stressing equipment- bulky and heavy- need for lightweight equipment!• Strand by Strand stressing• Reduction of crane & manpower needs• Accurate & Reliable

TENSA 8600 Multi-Strand Jack • Nearly 5 feet long• Close to 2 tons



156 STRAND ANCHOR WEIGHT ABOUT1.1 METRIC TONS

ELECTRO-GALVANIZED FORTEMPORARY CORROSION PROTECTION

ALLOWS UP TO 270 MM THREAD FORCABLE ADJUSTMENT



Cables are becoming longer and larger- up to 156-0.6 strands

Stressing equipment- Kap Shui Mun Bridge, Hong Kong (91-0.6 strands)

There got to be an easier way to stress!



CONTEN single strand stressing:

To obtain the required strandforce in the last strand, theforce in the first strand hasto be stressed higher

Using the required cable forceand the corresponding endpoint movements, DSI willcompute the forces in the individual strands

Strands are installed and stressedone by one. Two interconnectedjacks are used: Pilot and Stressingjacks. When Stressing jack reachessame pressure as Pilot jack it willstop. Forces in strands are equal.





Standard Cable Strand Installation- IWindow at deck and tower not shown. Winch line is inside cable pipe.

StrandGlider

Winch Line



Standard Cable Strand Installation- IIGlider and strand are inside cable pipe. Pull-through winch at top of tower not shown.

Strand

Glider

Winch Line



• ConTen Stressing: Two inter-connected jacks- One acts as pilot• Initial cable stressing and positive force adjustment• New force equal to current force- not sensitive to construction activity



Provencher Pedestrian Cable Stayed BridgeCable Designation: CW18

0

10

20

30

40

50

60

70

80

90

100

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Number of Strands

Stre

ssin

g Fo

rce

(kN

)

1st stage2nd stage



Cable Adjustment Jacksare required to turn the Ring Nut: small stroke

Modular Design: more jacks for larger cables

Lightweight

Easy assembly

Low Profile



Strand Force Sensors- Dyna-Force system:

• Uniformity of strand forces within the cable- verification is required• Lift-offs during construction stages are routinely performed• Cable force verification during service- very important to bridge owners• Lift-offs time consuming and impractical during service • Load cells bulky and need calibration• Dyna-Force is Plug and Read!

• Dyna-Force: Non-contact compact sensor placed ‘on’ the strand and measuresthe stress in the steel by measuring its permeability to electro-magnetic field



Measurement Principles

• Magnetization forces are introduced into the primary coil by a current, which in turn produces an output voltage across the second coil due to mutual inductance.

• As the permeability of the core changes, the output voltage changes. The output voltage can then be calibrated to measure the applied stress in the core.

DYNA FORCE



0

5

10

15

20

25

30

35

40

45

50

0 5 10 15 20 25Steps

Load

(kip

s)

Load Cell

EM-M (kips)

EM-E (kips)

Test results on EM Sensors made by DSI on 0.6 Bare strand



Penobscot River- Waldo Bridge, Maine:

Both Conten and Dyna-Force systems are used in this bridge



Con-Ten Stressing System- Individual Strand Stressing

Pilot JackWorking Jack

Bare, galvanized & epoxy coatedstrands may be stressed with Conten



Dyna-Force system Capacitor and data storage unit



DYWIDAG-SYSTEMS INTERNATIONAL

WALDO CABLE STAY BRIDGE-STAY 11B

0369

12151821242730

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70STRESSING SEQUENCE

ST

RA

ND

FO

RC

E (

KIP

S)

COMPUTED-80%FIELD-80%DYNAFORCE-80%COMPUTED-100%FIELD-100%DYNAFORCE-100%

NO OF STRANDS =67

LENGTH OF STAY = 373 FT

NOTE: 1ST & 2ND STRANDS STRESSED TO 2ND CONTEN FORCE AT 80% OPERATION



Nitrogen Gas Corrosion Protection System:

• Waldo bridge: First application of inert gas to cable stays

• Multi-level corrosion protection & monitoring system

• Sealed positive pressure gas system- about 2 psi

• Pressure maintained with special valve system

• Breach to the seal will be immediately identified- early remediation

• HDPE cable sheathing system must be leak proof- difficult!

• PE pipe and joints to withstand thermal stresses

• No need for grease in the anchor zone or sealing cap

• See-through sealing cap- clear polycarbonate

• Tests to validate the gas tight system



Corrosion Protection Levels: PE external pipe, Epoxy coating & Nitrogen









Maumee Bridge:

Sealing cap: very thin stainless steelshell (0.10 and 0.13 inch) with closely spaced bolts

Filled with corrosion preventivegrease

Anchorage components not readilyinspect able

Standard solution for current cablesystems



See-through cap surrounds all anchor components, is bolted against the bearingplate to seal against leaks of Nitrogen gas and maintain pressure



Linear Elastic Behavior:

Below the yield stress, metals behave in a linear elastic manner

Stress S2 = strain x elastic modulus

Visco-Elastic behavior:

HDPE behaves in an entirely different way, where relaxation wouldreduce the resulting stress depending on the strain rate!

Stress S3 depends on strain rate andtime under load- Boltzmann Equation



s3

0

ts

uξ η⋅

η ξ ts⋅+ ξ u⋅−SR⋅

⌠⎮⎮⌡

d:=

Boltzmann Equation for Constant Strain Rate:

s3= stress at end of time period ts

ts= time period

ξ= elastic constant

η= viscous constant

u= time integration variable

SR= strain rate

Material properties obtained from tests



1.9 meters

160 mm

OD

, SD

R 17

Visco-elastic Behaviorof HDPE pipe:

• To determine the material properties ofthe HDPE pipe for use in the Boltzmannequations tests were conducted to determine the force resulting from imposing a deformation at two differentstrain rates

• These tests were performed at twodifferent temperatures

• Results from these tests were used toto solve two independent equationsfor the required visco-elastic materialconstants. With these constants the behavior of the PE under any strainrate and temperature may be obtained.



0.00

0.50

1.00

1.50

2.00

0.00 1.00 2.00 3.00 4.00 5.00 6.00

Time, hrs

Load

, kip

s

Specimen 10.0497 in./hr for 6 hoursTemperature = ambient

PE pipe axial load test- Specimen 1:• Strain rate= 0.0497 in/hr for 6 hours (Equivalent to 40F in 6 hrs.)• Ambient temperature 68 F

• Specimen 2 was tested for 3 hours at double the strain rate of specimen 1

Load vs. Time



s1 K1

0

t1

uξ η⋅

η t1 ξ⋅+ ξ u⋅−

⌠⎮⎮⌡

d⋅

s2 K2

0

t2

uξ η⋅

η t2 ξ⋅+ ξ u⋅−

⌠⎮⎮⌡

d⋅

Solving two simultaneous integral equations to obtain the valuesof ξ and η for each temperature. ‘K’ and ‘t’ are test parametersand ‘s’ is measured at time t.



fp3fp2

0.357=Ratio of relaxed stress to linear elastic stress:

psifp3 449.404=fp3 s3 145⋅:=

MPas3 3.099=s3

0

ts

uξ η⋅

η ξ ts⋅+ ξ u⋅−SR⋅

⌠⎮⎮⌡

d:=

Resulting stress at the end of the time period:

SR 2.5 10 7−×=SRα ΔT⋅

ts:=

Strain rate per second:

ts 2.88 104×=ts th 602⋅:=Time period in seconds:

η 15020000:=Material viscous constant:

ξ 669:=Material elastic constant:th 8:=Time period for temperature change, hours:ΔT 80=Maximum daily temperature change, deg. F:

From tests

About 36%



41 strand fatigue and leak test



* 41-0.6 strand full scalefatigue and leak test

* After PE pipe system was fixedand connected, Nitrogen wasintroduced

* Specimen subjected to73,000 load cycles

* Nitrogen pressure maintainedat 4.33 psi for 96 hours andmonitored for leaks

* Tests were successful



Test specimen instrumentation



Cables are critical structural elements andvulnerable to corrosion, fatigue, vibration and accidental damage…

Their safety, performance and durabilityshould receive continuing focus and efforts to improve them…





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Recent Developments in Stay Cable Systems Convention/Shawwaf...Glider and strand are inside cable pipe. Pull-through winch at top of ... 2006 PTI TECHNICAL CONFERENCE –SESSION 4