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Introduction. Increasing international use of HSC in bridges Mainly in response to durability problems; de-icing salts; freeze-thaw conditions Focus of this paper - direct economic benefit Saving in materials Reduced construction depth Reduced transport and erection cost. Overview.

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slide2

Introduction

  • Increasing international use of HSC in bridges
  • Mainly in response to durability problems; de-icing salts; freeze-thaw conditions
  • Focus of this paper - direct economic benefit
    • Saving in materials
    • Reduced construction depth
    • Reduced transport and erection cost
slide3

Overview

  • What is High Performance Concrete?
  • Use of HPC in Australia
  • Economics of High Strength Concrete in N America
  • HSC in AS 5100 and DR 05252
  • Case Studies
  • Future developments
  • Recommendations
slide4

What is High Performance Concrete?

  • "A high performance concrete is a concrete in which certain characteristics are developed for a particular application and environments:
  • Ease of placement
  • Compaction without segregation
  • Early-age strength
  • Long term mechanical properties
  • Permeability
  • Durability
  • Heat of hydration
  • Toughness
  • Volume stability
  • Long life in severe environments
slide5

Information on H.P.C.

· “Bridge Views” – http://www.cement.org/bridges/br_newsletter.asp

· “High-Performance Concretes, a State-of-Art Report (1989-1994)”

- http://www.tfhrc.gov/structur/hpc/hpc2/contnt.htm

· “A State-of-the-Art Review of High Performance Concrete Structures Built in Canada: 1990-2000” - http://www.cement.org/bridges/SOA_HPC.pdf

· “Building a New Generation of Bridges: A Strategic Perspective for the Nation” -http://www.cement.org/hp/

slide6

Use of H.P.C. in Australia

  • Maximum concrete strength limited to 50 MPa until the introduction of AS 5100.
  • Use of HPC in bridges mainly limited to structures in particularly aggressive environments.
  • AS 5100 raised maximum strength to 65 MPa
  • Recently released draft revision to AS 3600 covers concrete up to 100 MPa
slide8

Economics of High Strength Concrete

  • Compressive strength at transfer the most significant property, allowable tension at service minor impact.
  • Maximum spans increased up to 45 percent
  • Use of 15.2 mm strand for higher strengths.
  • Strength of the composite deck had little impact.
  • HSC allowed longer spans, fewer girder lines, or shallower sections.
  • Maximum useful strengths:
    • I girders with 12.7 mm strand - 69 MPa
    • I girders with 15.2 mm strand - 83 MPa
    • U girders with 15.2 mm strand - 97 MPa
slide10

AS 5100 Provisions for HSC

  • Maximum compressive strength; 65 MPa
  • Cl. 1.5.1 - Alternative materials permitted
  • Cl 2.5.2 - 18 MPa fatigue limit on compressive stress - conservative for HSC
  • Cl 6.11 - Part 2 - Deflection limits may become critical
  • Cl 6.1.1 - Tensile strength - may be derived from tests
  • Cl 6.1.7, 6.1.8 - Creep and shrinkage provisions conservative for HSC, but may be derived from test.
slide12

AS 5100 and DR 05252

  • Main Changes:
  • Changes to the concrete stress block parameters for ultimate moment capacity to allow for higher strength grades.
  • · More detailed calculation of shrinkage and creep deformations, allowing advantage to be taken of the better performance of higher strength concrete
  • · Shear strength of concrete capped at Grade 65.
  • · Minimum reinforcement requirements revised for higher strength grades.
  • · Over-conservative requirement for minimum steel area in tensile zones removed.
slide13

Case Studies

  • Concrete strength: 50 MPa to 100 MPa
  • Maximum spans for typical 3 lane Super-T girder bridge with M1600 loading
  • Standard Type 1 to Type 5 girders
  • Type 4 girder modified to allow higher pre-stress force:
    • · Increase bottom flange width by 200 mm (Type 4A)
    • · Increase bottom flange depth by 50 mm (Type 4B)
    • · Increase bottom flange depth by 100 mm (Type 4C)
slide14

Case Studies

  • · Compressive strength at transfer = 0.7f’c.
  • · Steam curing applied (hence strand relaxation applied at time of transfer)
  • · Strand stressed to 80% specified tensile strength.
  • · Creep, shrinkage, and temperature stresses in accordance with AS 5100.
  • · In-situ concrete 40 MPa, 160 mm thick in all cases.
  • · Assumed girder spacing = 2.7 m.
slide18

Case Studies - Summary

  • · Significant savings in concrete quantities and/or construction depth.
  • Grade 65 concrete with standard girders.
  • Grade 80 concrete with modified girders and Type 1 and 2 standard girders.
  • More substantial changes to beam cross section and method of construction required for effective use of Grade 100 concrete.
slide19

Future Developments

  • Strength-weight ratio becomes comparable to steel:
slide21

Recommendations

  • · 65 MPa to be considered the standard concrete grade for use in precast pre-tensioned bridge girders and post tensioned bridge decks.
  • · The use of 80-100 MPa concrete to be considered where significant benefit can be shown.
  • · AS 5100 to be revised to allow strength grades up to 100 MPa as soon as possible.
  • · Optimisation of standard Super-T bridge girders for higher strength grades to be investigated.
  • · Investigation of higher strength grades for bridge deck slabs, using membrane action to achieve greater spans and/or reduced slab depth.