Highways Agency BD on New Masonry Arch Bridges Paul Jackson

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Highways Agency BD onNew Masonry Arch
BridgesPaul Jackson
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Arch Experience

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KimboltonButtsBridge
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Background

• Masonry arches have been in use for 2000 years
• Have given very good service lowest maintenance
  costs of all bridges
• A few built recently
• Whole life cost competitive
• No existing design standard
• No bridge part to EN 1996

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Suggests new standard desirableBut

• Less well understood than other types of bridge
• Very few built since we expected to understand
  everything we build

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Based on

• Babtie Draft (1995)
• Experience from deign (limited) and
  assessment/strengthening of existing
• Recent research (mainly for assessment)
• Codes for other types of bridge
• Gives
• Limit State Approach
• A problem BS/BD or EN?

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Scope

• Unreinforced masonry arches
• Single or multiple span
• Right or skewed
• Span/rise ratio of between 2 and 10
• Spans not exceeding 40m
•  

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Mass Concrete?

• Need crack control steel?
• Unlikely to be economic not to use this steel
  structurally
• Might use fibre reinforced
• But No accepted standard

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(No Transcript)
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Limit States

• ULS (as assessment)
• SLS (?)

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Loading
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Babtie Draft Used

• HA HB
• (Assumes HB governs for local)
• But
• Not all bridges designed for HB
• HA does not cover AW vehicles on arches
• Concept of Loaded Length not strictly valid
• HB being replaced by more realistic SV

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So Use

• Real Vehicles for AW
• SV for abnormal

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Normal (AW) Traffic

• BD 37 HA and EN 1991-2 LM 12 not intended for
  arch bridges
• Uses real vehicles
• Vehicles as BD 21 Annex D 10
• Also single axle (assessed separately)
• 3m Lanes
• As EN 1991-2
• More severe than BD 21 HA Lanes
• Less severe than BD 21 Annex D lanes

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Abnormal Vehicles

• Based on BD 86/Draft EN 1991-2 NA
• Closer to (simpler) NA
• Uses SV Vehicles
• More Realistic than HB
• No Separate overload/impact factor
• Load Factor as HB

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SV 80(as BD 86 and EN 1991-2 NA)
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SV100 (as BD 86 and EN 1991-2 NA)
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SV 196(as EN 1991-2 NA)
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SV TT (as BD 86)
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Combination of SV and AW(case where SV is in
lane)
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Combination of SV and AW(straddling case)
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Other Actions

• Imposed Deformations
• Temperature range and difference
• Creep and shrinkage
• Foundation movement
• Can usually ignore, consider for flat arches
• Wind
• Can usually ignore
• Longitudinal
• Consider for multi-span

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ULS

• Relatively well established
• Uses partial safety factors (unlike BD 21)

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Babtie Draft Used

• Stress lt 0.66 fk/?m
• gives P lt 0.44bfk (h-2e)
• V lt 0.4 fkP
• Also had a limit on depth in compression (100mm)
  

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Analysis(ULS)
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MEXE

• Widely used and long established
• Defined in BA 16
• No sound theoretical basis!
• Tends to be less conservative than other methods
  for short span bridgeswhy?

• PAL 740(dh)2/L1.3
• Fp (rc rq)/rc0.6
• Fm (Fb.d) (Ff.h)/(d h)

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Mechanism

• e.g. ARCHIE/ARCHIE-M
• Mechanism Analysis
• Widely used
• Consistent with criteria
• Most likely approach

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Mechanism

• RING
• Advanced mechanism analysis
• Include multi-ring behaviour
• Not yet widely used

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Advanced

• e.g Elfen
• Discrete Element Analysis
• Realistic and Fundamental modelling of behaviour
• Verified against tests
• Can consider serviceability
• Widely used by Gifford in Archtec

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Summary of Elfen predictions against tests
 
 
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Result comparison
Intrados vertical displacements measured at the
load position (1/4 span)
Softening of wide and soft mortar joints modelled
Single span test
Multi-span arch test
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Serviceability

• Serviceability criteria are not established
• Current assessment criterion is service loads
  should remain below ½ ULS levels
• Limits could be set in terms of the following but
  more research is required
• Live load deflections
• Crack widths or macro strains
• Crack depth
• Maximum absolute SLS stresses
• Maximum SLS stress range/load cycles in masonry

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Babtie Draft Used

• Eccentricity lt 0.25h
• (i.e. crack depth lt 0.25 h)
• Stress lt 0.4 fk
• No permanent tension/cracking

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But

• No standard programs to give service stresses
• No experience or research to justify full load
  criteria
• More justification for 0.5 ultimate criterion
• Many existing arches do have tension/cracking
  under permanent load

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So

• Requirement for no tension/crack under permanent
  load removed
• Option of allowing higher ULS factors with no
  explicit SLS checks introduced
• But
• Not when you have to consider imposed
  deformations (flat arches)

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Other Issues

• Parapets
• Expansion joints in parapets/spandrel walls
• Foundation flexibility

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Parapet Options

• Separate Conventional parapets
• (as Babtie draft design to BD 70)
• Reinforced masonry
• (as Kimbolton)
• Unreinforced masonry
• (as most exiting)

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Separate Parapets(Required for Trunk
Roads/Motorways)
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Reinforced Masonry Parapets
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KimboltonButts Parapet(over spandrel)
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Kimbolton Butts Parapet(over crown)
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Kimbolton Butts Bridge
(HalfLongitudinal Section)
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Conclusions

• Document allows masonry arches to be designed
• Gives most of what is needed for simple cases
• Does not answer all the questions

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KimboltonButtsBridge