Bridge Design to AS 5100 Sydney May 25th 2005 Using High Strength Concrete with AS 5100 opportunities and restrictions

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

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

Information on H.P.C.  “Bridge Views” –  “High-Performance Concretes, a State-of-Art Report ( )” -  “A State-of-the-Art Review of High Performance Concrete Structures Built in Canada: ” -  “Building a New Generation of Bridges: A Strategic Perspective for the Nation” - /

Use of H.P.C. in Australia Maximum concrete strength limited to 50 MPa until the introduction of AS 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

Economics of High Strength Concrete

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

Economics of High Strength Concrete

AS 5100 Provisions for HSC Maximum compressive strength; 65 MPa Cl Alternative materials permitted Cl MPa fatigue limit on compressive stress - conservative for HSC Cl Part 2 - Deflection limits may become critical Cl Tensile strength - may be derived from tests Cl 6.1.7, Creep and shrinkage provisions conservative for HSC, but may be derived from test.

AS 5100 and DR 05252

AS 5100 and DR 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.

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)

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  In-situ concrete 40 MPa, 160 mm thick in all cases.  Assumed girder spacing = 2.7 m.

Case Studies

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.

Future Developments Strength-weight ratio becomes comparable to steel:

Future Developments

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 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.