Increased load capacity of arch bridge using slab reinforced concrete T.G. Hughes & M. Miri Cardiff School of Engineering Arch 04, Barcelona, Nov , 2004

Outline Introduction Introduction Strengthening Techniques Strengthening Techniques Model details and description Model details and description Soil / Masonry interaction Soil / Masonry interaction Service load results Service load results Ultimate load results Ultimate load results Conclusions Conclusions

Introduction Considerable interest in the UK in repair techniques Considerable interest in the UK in repair techniques Closure of the road during construction is an issue Closure of the road during construction is an issue Much debate about “Strengthening” v “Repair” Much debate about “Strengthening” v “Repair” Objective of this study – to investigate a less intrusive form of reinforcement Objective of this study – to investigate a less intrusive form of reinforcement

Strengthening Techniques Grouting Grouting Saddling Saddling Lining Lining Reinforced masonry Reinforced masonry

Grouting Effectively stiffens soil and random rubble masonry Effectively stiffens soil and random rubble masonry Can be achieved with minimum disruption from surface or soffit Can be achieved with minimum disruption from surface or soffit Unquantifiable improvement Unquantifiable improvement May create difficulties with future flexibility May create difficulties with future flexibility

Saddling Forms new arch with existing barrel as shutter Forms new arch with existing barrel as shutter Disruptive to traffic during construction Disruptive to traffic during construction Composite action difficult to model Composite action difficult to model A “new” bridge A “new” bridge Some question marks on long term flexibility Some question marks on long term flexibility

Lining Less disruption during construction Less disruption during construction Normally “adds” to existing barrel Normally “adds” to existing barrel Loss of headroom Loss of headroom Loss of visual effect Loss of visual effect Some concern about durability Some concern about durability

Reinforced Masonry Undertaken by drilling or slot cutting in intrados Undertaken by drilling or slot cutting in intrados Can be achieved with minimum disruption Can be achieved with minimum disruption Slot cutting can cause loss of visual effect Slot cutting can cause loss of visual effect May create difficulties with future flexibility May create difficulties with future flexibility May be issues about long term durability of bond between reinforcement and masonry May be issues about long term durability of bond between reinforcement and masonry

Surface Slab Reinforcement

Can be achieved with minimum disruption Can be achieved with minimum disruption Maintains integrity of arch behaviour Maintains integrity of arch behaviour Issues about utility service access Issues about utility service access Relatively cheap solution Relatively cheap solution

Surface Slab Reinforcement Works by increasing load distribution without increasing load Works by increasing load distribution without increasing load Also provides additional support to soil in preventing sway movements Also provides additional support to soil in preventing sway movements Increases resistance of soil Increases resistance of soil

Effects 1

Effects 2

Effects 3

Centrifuge Models Undertaken some 50+ scale models of arch bridges at 6, 12g, 20g and 55g Undertaken some 50+ scale models of arch bridges at 6, 12g, 20g and 55g Stresses are as full scale, similar materials –therefore full scale strains Stresses are as full scale, similar materials –therefore full scale strains Full range of instrumentation pressure sensors, LVDTsm Load cells and moving loads Full range of instrumentation pressure sensors, LVDTsm Load cells and moving loads

Model description 1/12 scale, 6-m single span 1/12 scale, 6-m single span Shallow & Deep geometry Shallow & Deep geometry Three ring arch Three ring arch Bricks Bricks Micro concrete Micro concrete Reinforcement Reinforcement

Test Methodology Build “New” Arch Build “New” Arch Undertake service load – typically 14 passes Undertake service load – typically 14 passes Load at 1/4 or 1/3 point to peak and unload Load at 1/4 or 1/3 point to peak and unload Remove and strengthen Remove and strengthen Repeat service loading Repeat service loading Load at 1/4 or 1/3 point until collapse Load at 1/4 or 1/3 point until collapse

Model Details Model Details ParameterDimension Intrados span ( mm) Span to rise ratio Fill depth at crown before & after repair ( mm) Arch ring thickness ( mm) Model width ( mm) Mortar Mix ( cement: lime: sand) Backfill Angel of friction Micro concrete Mix (cement: fine: coarse : water) Micro concrete compressive strength ( N/mm2) & 2 13 & : 3 : : 1.8 :2.8 :0.6 56

Model Package Model Package

Model under construction

Concrete slab being cast

Typical model under test

Service load Steel roller (equal 12 tonnes) Steel roller (equal 12 tonnes) Whole Width Whole Width Soil / Masonry interaction Soil / Masonry interaction Arch deflection Arch deflection Load direction effect Load direction effect

Result Nomenclature Actual benchmark (“new”) result Actual benchmark (“new”) result Average over a series of “new” arches Average over a series of “new” arches Strengthened result Strengthened result

Soil / Masonry interaction

Service load results Shallow arch at ¾ span

Service load results Deep arch at 3/4 Span

Service load results Arch deflection (Load at 50% of Span)

Ultimate load results Load deflection curve for deep arch geometry

Ultimate load results Load deflection curve for Sallow arch geometry

Conclusions Better distribution of pressures within the soil at service loads Better distribution of pressures within the soil at service loads Decrease arch deflection after repair at service loads Decrease arch deflection after repair at service loads Significant improvement in ultimate load capacity Significant improvement in ultimate load capacity

Conclusions Construction with limited disruption Construction with limited disruption Reinforced concrete equally as effective as when acting compositely with the barrel Reinforced concrete equally as effective as when acting compositely with the barrel Should maintain flexibility of exiting arch to respond to future movements Should maintain flexibility of exiting arch to respond to future movements