bản chất về cáp dự ứng lực ví dự thiết kế cáp ảnh hưởng của cáp dự ứng lực

 The “H” loading consists of two-axial truck  The number following the H designation is the gross weight in tons of the standard truck W = Total weight of truck and load Live Loads fo

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Live Loads for Bridges

 In our previous discussions we mentioned that the

primary live loads on bridge spans are due to

traffic

 The heaviest loads are those produced by large

transport trucks

 The American Association of State and Highway

Transportation Officials (AASHTO) has a series of

specifications for truck loadings

 For two-axial trucks AASHTO designates these vehicles as H series trucks

 For example, a H15-44 is a 15-ton truck as reported in the 1944 specifications

 Trucks that pull trailers are designated as HS, for example HS 20-44 (a 20-ton semi-trailer truck)

 In general, a truck loading depends on the type of bridge, its location, and the type of traffic

anticipated.

The size of the “standard truck” and the distribution of its

weight is reported in the AASHTO code

 The “H” loading consists of two-axial truck

 The number following the H designation is the gross weight

in tons of the standard truck

W = Total weight of truck and load

 The “HS” loading consists of tractor truck with semi-trailer

 The number following the HS designation is the gross weight in tons of the standard truck

HS20-44 8 kips 32 kips 32 kips HS15-44 6 kips 24 kips 32 kips

The AASHTO standard H20 and HS20 trucks

The AASHTO specifications also allow you to represent the truck as a single concentrated load and an uniform load

For H20-44 and HS20-44:

 Concentrated load 18 kips for moment

26 kips for shear

 Uniform loading 640 lb/ft of load lane

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The AASHTO specifications also allow you to

represent the truck as a single concentrated load

and an uniform load

For H15-44 and HS15-44:

 Concentrated load 13.5 kips for moment

19.5 kips for shear

 Uniform loading 480 lb/ft of load lane

 You can probably see that once the loading has been selected, you have to determine the critical position of the truck on the structure (bridge)

This is an excellent application for influence

lines

 In many cases, vehicles may bounce or sway as

they move over a bridge

This motion produces an impact load on the

bridge

AASHTO has develop an impact factor to

increase the live load to account for the bounce

and sway of vehicles

50 0.3 125

I L

 where L is the length of the span in feet

Impact loading is intended to transfer loads from the superstructure to the substructure

 Superstructures including legs of rigid frames

 Piers excluding footings and those portions below ground line

 Portions above ground line of concrete and steel piles that support the super structure

Impact shall not be included in loads transferred to

footings or to those parts of piles or columns that

are below ground

 Abutments, retaining walls, piles excepts as specified

Example: Consider our standard AASHTO HS20-44 truck

traveling over the span of some structure.

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Shear - To examine how a series of concentrated

loads effect the shear lets consider our “standard

truck” and its effect on the shear at point C on the

beam shown above

 First we need the influence line for the shear at

Let’s try to find the maximum positive shear at point C

 There are three cases to examine, one for each of the

three wheel forces as they pass over the point C

 V C Case1  8 (0.5) 32 (0.36) 32 (0.06)k  k  k 17.44k

14 ft 30 ft.

32 k 32 k

8 k

 The maximum positive shear at point C is 19.52k

 Let’s rework the previous problem to find the

maximum negative shear at point C

 There are three cases to examine, one for each of the three wheel forces as they pass over

the point C

In this case, use the largest negative value from

the influence line

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14 ft 30 ft.

32 k 32 k

8 k

Let’s try to find the maximum negative shear at point C

 V C Case3  8 ( 0.06) 32 ( 0.2) 32 ( 0.5)k  k  k  22.88k

The maximum negative shear at C is -22.88k

 In this case, the largest shear at C is the largest

negative value, or V max= -22.88k

14 ft 30 ft.

32 k 32 k

8 k

Example: Determine the maximum moment created at point

B in the beam below due to the wheel loads of a moving

truck The truck travels from right to left

Example: Determine the maximum shear created at point C

in the beam below due to the wheel loads of a moving truck

The truck travels from right to left

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End of Influence Lines - Part 3

Any questions?

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OCT 2019

VSL Australia

Post-Tensioning

Systems

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INTRODUCTION 5

VSL CAPABILITIES 6

MULTISTRAND POST-TENSIONING 9

STRAND PROPERTIES – TO AS 4672 10

TENDON PROPERTIES 10

SELECTED DESIGN CONSIDERATIONS 11

VSL STRESSING ANCHORAGE TYPE SC LIVE END 12

VSL COUPLING ANCHORAGE TYPE KAS - FOR USE WITH SC ANCHORAGE 13

INTERMEDIATE ANCHORAGE TYPE Z 14

VSL DEAD END ANCHORAGE 15

SHEATHING & CORROSION PROTECTION 16

DIMENSIONS OF PT-PLUS® DUCTS 16

ECCENTRICITY OF TENDONS 16

STRESSING SEQUENCE 17

STRESSING 17

GROUTING 17

JACK CLEARANCE REQUIREMENTS 18

STRESSING JACK DETAILS 18

SLAB POST-TENSIONING 21

STRAND PROPERTIES – TO AS 4672 22

TENDON PROPERTIES 22

SELECTED DESIGN CONSIDERATIONS 23

VSL STRESSING ANCHORAGE TYPE S5 – S6 LIVE END 24

VSL DEAD END ANCHORAGES TYPE H – TYPE P 25

VSL SLAB COUPLING ANCHORAGE TYPE S 26

JACK CLEARANCE REQUIREMENTS 27

INTERNAL STRESSING POCKET 27

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ANCHORAGE REINFORCEMENT – S5-3, S5-4, S5-5, S6-3, S6-4 ANCHORS 28

ANCHORAGE REINFORCEMENT – S6-5 ANCHORS 28

ANCHORAGE REINFORCEMENT - TIES 29

GROUND ANCHORS 32

VSL PERMANENT ANCHOR FULLY ENCAPSULATED 33

VSL TEMPORARY ANCHOR 33

VSL PERMANENT GROUND ANCHORS - 15.2mm STRAND 34

VSL CT STRESSBAR GROUND ANCHORS 34

VSL TEMPORARY GROUND ANCHORS 34

VSL PERMANENT GROUND ANCHORS BEARING PLATE AND ANCHORHEAD 35

STRESSING 36

FLAT JACKS 39

CONTACT US 40

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Post-tensioning is, even so being a mature technology, still a fantastic tool for the design engineer to actively define the internal load path in concrete structures by superposing a favorable internal stress state This permits to minimize deformations, helps to increase slenderness of members, reduces reinforcement congestion, enables segmental construction without need for wet joints and allows the use of high strength steel

This brochure gives an overview of the available post-tensioning systems and their fields of application It provides guidance to

practising engineers in the design of post-tensioned structures using VSL post-tensioning systems

VSL is a recognised leader in the field of special construction systems Well proven technical systems and sound in-house engineering are the basis of the group’s acknowledged reputation for innovative conceptual structural solutions VSL has developed, manufactured and installed durable, state-of-the-art post-tensioning systems for over 60 years The VSL post-tensioning systems comply with

international standards and approval guidelines for use on both new and existing structures

VSL does not only select and offer the best suited post-tensioning hardware and layout for a given project but proposes also innovative detailing of the permanent work and construction techniques with the aim to improve durability, increase site safety and reduce construction time and costs

VSL likes to work in partnership with owners and clients right from the conceptual stage VSL’s engineers can work closely with the design engineer during the design development stage and with the contractor's estimating team during the tender stage What

differentiates VSL from other players in the market, is its holistic approach, which is fundamental in arriving at well balanced technical solutions respecting equally permanent work and construction aspects VSL’s biggest asset however is the quality of its highly

experienced, multicultural staff

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VSL’s capabilities can be categorised into four different services:

We ensure the development and constant improvement of our

portfolio of in-house technologies

Our Services:

Bridge Construction Containment Structures Heavy lifting

Engineered Precast Structures Offshore Structures

We offer tailored services to ensure the stability of your structure’s

life cycle, from inspections and assessment through to repair works

and upgrading

Our Services

Structural Diagnostics & Monitoring

Repairs & Strengthening

Infrastructure Protection

High Strength Concrete Solutions & Products

We are specialists in ground engineering and special foundations thanks to our long history of proven design and build capabilities gained on the most complex and varied projects

Our Services

Diaphragm walls Micro Compaction Subsurface grouting Micro Piling & Ground Anchors High Directional drilling & Coring Ground Freezing

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VSL Multistrand

Post-Tensioning

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8 ///

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The VSL Multistrand system comprises from three to fifty-five strands (either 12.7 or 15.2mm diameter), round duct and anchorages Prestressing force is applied to the tendons after the casting and curing of surrounding concrete All strands are stressed simultaneously using a hydraulic jack and are fastened at the live end by wedge grips The free space inside the duct is then pressure-filled with cement grout

A number of features are incorporated as a result of many years of experience in the field:

 Stressing carried out in any number of stages;

 Accurate control of prestress force;

 No need to determine tendon length in advance;

 Simultaneous stressing of all strands in a tendon, with individual locking of each strand at the anchorage point; VSL stressing equipment is easily operated to ensure a safe and rapid stressing procedures Special emphasis has been placed on rationalised manufacturing of equipment and anchorage parts as well as efficient work site practice

Ballina Bypass, Australia

PT Strands, Australia

Westlink M7, Sydney, Australia

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Nominal Mass (kg/m)

Minimum Breaking Load (kN)

Minimum Proof Load (0.2% Offset) (kN)

Min Elong To Fracture in 500mm (%)

Relaxation After 1,000 Hrs at 0.8 Breaking Load (%)

Modulus of Elasticity (GPa)

Tendon Unit No of Strands Minimum Breaking Load

(kN)

Steel Duct Internal Diameter (mm)

4 Corrugated PT-Plus duct is also available, refer to page 16

5 For special applications, other strand and tendon capacities are available

load strand available as special order from overseas

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 Tendon in conventional steel duct: µ = 0.20

 Tendon in PT-PLUS® duct: µ = 0.12

Irrespective jack or tendon jack, a loss due to wedge draw-in of nominally 6mm occurs at lock-off If necessary

compensation can be provided by appropriate procedures

Spiral and/or rectangular stirrup reinforcement is required for all anchorages to control local zone stresses The design of this reinforcement is the responsibility of the Consulting Engineer For assistance, please contact your local VSL office

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12 ///

Note: Antiburst reinforcement to Engineers details not shown

Strand Type 12.7mm Tendon Unit

1 Dimension R does not allow for Lift off force check Small recesses can be provided for special cases Please check with your local office for details

2 *Plate type anchorages (Type P) Also available for other tendon units

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Tendon Unit A Dimensions (mm) B C Tendon Unit A Dimensions (mm) B C

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14 ///

Centre-stressing anchorages are used for ring tendons in circular structures, or for those tendons where the ends cannot be fitted with normal stressing anchorages

Tendon Unit

Dimensions (mm)

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Tendon Unit A Type H B C D Type P E F Tendon Unit A Type H B C D Type P E F

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16 ///

For conventional applications, corrugated galvanised steel ducts are used.For diameters of steel ducts refer to page 10 For applications requiring enhanced corrosion protection and improved fatigue resistance of the tendons, the use of the VSL PT- PLUS® System with corrugated plastic duct can provide a number of important advantages This fully encapsulated, watertight system offers outstanding corrosion protection, and the plastic duct eliminates fretting fatigue between the strand and duct It also provides reduced duct friction The PT-PLUS™ System may be configured with special details and

installation techniques to provide Electrically Isolated Tendons (refer to GC system in VSL International Technical Catalogue) These tendons may be electrically monitored at any time throughout the life of the structure

All ducts are manufactured in a variety of standard lengths and are coupled on site

Strand Type

12.7mm Strand Type 15.2mm Duct Dimensions (mm)

Tendon Unit Tendon Unit d D thickness

e (mm)

Tendon Unit Steel Duct e

(mm)

Plastic Duct

e (mm)

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on-18 ///

Dimensions

(mm)

VSL Jack Type VSL50 VSLB7 VSL190 VSL290 VSL460 VSL670 VSL750 VSL1000 VSL1250 VSL1650 VSL1700

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VSL Slab

Post-Tensioning

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20 ///

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VSL post-tensioning offers economies over other systems, especially when construction cycles are considered There is less material handling on site, reducing site labour force which reduces site activity congestion

Most importantly, there is the quality and service of VSL specialised high-performance site teams and unequalled back-up The VSL post-tensioning slab system has been used in many thousands of buildings and other structures throughout

Australia The system uses up to five strands in flat-shaped ducting and anchorages

Strands are stressed individually and then gripped by wedge action The entire duct is subsequently fully filled with cement grout injected under pressure so that the strands are fully bonded to the surrounding concrete

Coles National Distribution Centre, Melbourne, Australia

Austrak Industrial Park, Melbourne, Australia

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Nominal Mass (kg/m)

Minimum Breaking Load (kN)

Minimum Proof Load (0.2% Offset) (kN)

Min Elong To Fracture in 500mm (%)

Relaxation After 1,000 Hrs at 0.8 Breaking Load (%)

Modulus of Elasticity (GPa)

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 Minimum tangent length behind the anchorage: 0.5m

The friction losses in the anchorage due to curvature of the strand and friction of the strand in the wedges usually amount to:

 Edge stressing: 3% average

 Internal pocket stressing: 5% average

Frictional losses along the tendon can vary fairly widely and depend upon several factors, including the nature and surface condition of the prestressing steel; the type, diameter and surface conditions of the duct and the installation method The following values may be assumed for design:

 Tendon in conventional steel ducts: µ = 0.20

 Tendon in PT-PLUS® duct: µ = 0.12

A loss due to wedge draw-in of nominally 6mm occurs at lock-off

Duct Type Bi Ba Dimensions (mm) Hi Ha

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26 ///

Strand Type Tendon Unit

Dimensions (mm)

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Plan and sections of stressing pocket Details shown are typical and may vary for particular applications

Plan and Stressing pocket

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28 ///

Helix anchorage for slab tendon and typical detail at slab edge

Note:

located centrally about and hard up against cast in anchor as shown

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Anchorage at slab edge and anchorage at slab beam

Detailing at the slab edge and beam

Strand Type Tendon Unit No of Ties each side

Dimensions (mm)

located centrally about and hard up against cast in anchor as shown

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30 ///

Ground Anchors

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Corrosion protection is provided by the cement grout in temporary anchors and by full encapsulation of the entire anchor in a thick walled polyethylene sheath for permanent anchors

VSL Rock Anchors range in ultimate capacities up to 23,750kN Tendons are constructed from either a number of 12.7mm or 15.2mm diameter, high tensile steel strands or single VSL stressbars

VSL Soil Anchors are used in alluvial soils, stiff clays or highly weathered rock The ultimate capacity of these anchors is determined by the capability of the ground in the bond zone to transfer the load from the anchor Anchor details are similar

to rock anchors

VSL Soil Nails are used to reinforce soil in an excavation or embankment They are formed by inserting VSL Bar into a drilled hole which is filled with cement grout Corrosion protection similar to ground anchors can be provided depending on the application Soil nails have no or only nominal initial applied force

VSL Rock Bolts are used to strengthen and stabilise jointed rock, and to stabilise defined blocks of rock They are formed by inserting VSL Bar into a drilled hole and anchoring it in place with either a mechanical anchorage, a chemical anchorage or cement grout The bar is stressed to apply an initial force

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Sheath Diameters (mm)

1 Where block outs, voids or drill hole casing are required, drill hole diameters and bearing plate dimensions should

be confirmed with your local VSL office

2 Drill hole sizes are based on 10mm external cover

(mm)

Temporary Drill Hole Dia

(mm) Jack Type Required

Drill Hole Dia

(mm)

Corrugated Sheath (mm)

15.2mm

Super (kN)

Minimum Drill Hole Dia (mm) Jack Type Required

Ultimate Capacity 15.2mm Super (kN)

Minimum Drill Hole Dia (mm) Jack Type Required

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No of Strand Tendon Unit

Dimensions (mm)

10 Bearing plate dimensions are suitable for 15.2mm super and 15.2mm EHT strands

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