1 / 21

Introduction

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.

galeno
Download Presentation

Introduction

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. 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

  2. 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

  3. 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

  4. 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/

  5. 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

  6. Economics of High Strength Concrete

  7. 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

  8. Economics of High Strength Concrete

  9. 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.

  10. AS 5100 and DR 05252

  11. 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.

  12. 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)

  13. 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.

  14. Case Studies

  15. 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.

  16. Future Developments • Strength-weight ratio becomes comparable to steel:

  17. Future Developments

  18. 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.

More Related