Title: Optimising Precast Bridge Girders for Sustainability With the use of High Performance Concrete
1Optimising Precast Bridge Girders for
SustainabilityWith the use of High Performance
Concrete
Doug Jenkins - Interactive Design Services Joanne
Portella DMC Advisory, Melbourne. Daksh Baweja
DMC Advisory, Melbourne, The University of
Technology, Sydney.
2Introduction
- Focus of emissions reduction strategies in
Australia has been on cement reduction. - Can significant emissions reductions be made with
the use of high strength concrete? - Outline of study
- Effect of high strength concrete and high
supplementary cementitious material (SCM) content
on total CO2 emissions. - Typical 2 Span freeway overbridge
- 5 grades of concrete
- 3 deck types
3Alternative Concrete Mixes
4Component Emissions
5Embodied Energy Calculation
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7Typical Super T Girder Section
8Design Constraints
- High strength concrete allows increased prestress
force and/or reduced bottom flange depth. - Pretension force limited by concrete strength at
transfer and number of available strand
locations. - Provision of post-tensioned cables allows higher
total prestress force. - Reduced girder depth will often provide
additional savings to emissions and cost (not
considered in this study). - Live load deflection may control minimum girder
depth. - Moment connection over pier reduces deflections.
9Alternative Girder Dimensions
10Design Options
- Type 1 - Fully Pre-tensioned Design Typical
current practice Standard Super-T girders with
in-situ top slab and link slab. - Type 2 - Post-tensioned Design As Type 1 but
post-tensioned after casting top slab. - Type 3 - Post-tensioned Continuous Design As
Type 2, but with full structural continuity over
the central support.
11Typical Grillage Layout
12Beam / Slab Detail
13Live Load (Max Moment)
14Girder Bending Moments
15Live Load Deflections
16Live Load Deflections
- Maximum allowable deflection (AS 5100) 47.5 mm.
- Decks Type 2-E and 2-D exceeded this limit by 3
and 11 respectively. - Deflections may be reduced by
- Using the next deeper girder
- Using a higher strength concrete
- Providing momemt continuity over the pier
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18Emissions Analysis Results
19Emissions Analysis Results
20Research and Development
- Optimise SCM content for in-situ slab
- Optimise design procedures for high strength
concrete - Shear strength
- Creep and shrinkage losses
- Deflection limits
- ULS design factors
21RD Optimise ULS Design
Rectangular Section 90 MPa
22Research and Development
- Post-tensioning at the precast yard
- Use of ultra high strength concrete
- Geopolymer concrete
- For precast work
- In-situ top slab
23Conclusions
- SCMs allowed significant reductions in CO2
emissions in all cases, compared with the
standard reference case concrete. - High SCM concrete showed greatest reduction, but
reduced compressive strength at transfer, and
increased curing period. - Emissions from the 80 MPa and 100 MPa concretes
were about equal to the 65 MPa concrete. - Higher strengths allowed the use of a reduced
depth of girder, with associated savings in other
works.
24Conclusions
- Precast post-tensioned girders allowed
significantly higher levels of prestress, and
reduction in concrete volumes and emissions. - Structural continuity over the central support
allowed an additional small saving in emissions. - The overall reduction of CO2 emissions was not a
simple function of the reduction of Portland
cement in the concrete, but was also based on how
the material properties of the concretes used
influenced the structural efficiency of the
design.
25Conclusions
- Engineering is the art of directing the great
sources of power in nature for the use and
convenience of man. -
- - Thomas Tredgold, 1828 .