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James Street Underbridge
Load Rating and Assessment
Marcia Prelog
2
▪Bridge description and background
▪Site investigation
▪Condition assessment
▪ Load rating
▪ FEA and dynamic response modelling
▪Proposed repair
▪Conclusion
Introduction
3
James St Underbridge - Lithgow
Location James St underbridge 1883
Railcorp photo source:
https://www.environment.nsw.gov.au/heritageapp/H
eritageItemImage.aspx?ID=4801535#ad-image-1
4
James St Underbridge - Lithgow
John Whitton Knapsack Gully viaduct
Central Station memorial
5
Site investigation findings
Cracked keystone
Mortar loss
Water seepage
Lateral movement of top
of wall
Longitudinal cracks on
arch intrados
6
▪ Mortar missing and
general weathering of
masonry
▪ Tie rods not in contact
with wall
Investigation findings
7
Key defects
Investigation findings
▪ Longitudinal cracks behind
the spandrel wall
▪ Longitudinal cracks at the
centre of the intrados (inner
face of arch)
▪ Water seepage along joints
and cracks
8
Site data
Site investigation
▪ Arch dimensions
‒ 6m diameter arch
‒ 8.2 overall width
▪ Concrete slab under
ballast
▪ Stone and mortar
dimensions for load rating
‒ 5 to 10mm mortar
9
▪ AS5100 Bridge Design
▪ T HR CI 12008 ST Load rating of underbridges
▪ Vol 3 Section 4 Part 3 BD 21/01-The Assessment of Highway Bridges and Structures
▪ Vol 3 Section 4 Part 3 BA 16/97-The Assessment of Highway Bridges and Structures
▪ Standard MEXE Method inappropriate
▪ Analysis using Archie-M
▪ Design assumptions:
‒ 10MPa sandstone - Class III to IV
‒ 10mm thickness mortar
‒ Internal slab treated as fill with even
load distribution
‒ DLA = 1.8 (BD21/01)
‒ Mixed passenger freight (MF)
232t loading specified
Load rating
10
▪ Archie M graphical output
▪ LA taken as the adjusted live load factor
𝐷𝐿𝐴 =𝐿𝑖𝑣𝑒 𝑙𝑜𝑎𝑑 𝑓𝑎𝑐𝑡𝑜𝑟 𝑎𝑡 𝑓𝑎𝑖𝑙𝑢𝑟𝑒
𝐶𝑜𝑑𝑒 𝑔𝑜𝑣𝑒𝑟𝑛𝑒𝑑 𝑙𝑖𝑣𝑒 𝑙𝑜𝑎𝑑 𝑓𝑎𝑐𝑡𝑜𝑟
▪ As New rating:‒ 1.19 for failure at pier
‒ 1.4 for failure in arch
▪ No evidence of pier weakness or failure
▪ Spandrel wall not modelled and did not influence analysis
Load rating
Arch failure
Pier failure
11
Load rating - condition rating
• Longitudinal cracks with no progressive
deterioration
• No settlement or arch movements
evident
• Condition factor = 0.7
• As Is LRF = 0.83 (MF load, pier critical)
• Arch LRF > 1Longitudinal crack example –
DMRB Vol 3 part 4 BA16/97
12
2006 2016 2006 2016
▪ Central longitudinal
crack with seepage
▪ Crack seepage
evident, crack form
remains the same
▪ Spandrel crack
through voussoirs
with seepage noted
▪ Crack form remains
the same, negligible
outer movement over
time
13
▪ 3D model used to correlate site monitoring results
▪ Calibrated model suitable for future assessments and load rating with defined loads
FEA Analysis and Dynamic Response monitoring
mainmark
STRAAM
14
Detailed design
▪ New tie bars
▪ New support slab
▪ Masonry stitching
▪ Mortar repair
▪ Safety rails
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