buildings and bridges - nafems home engineering … · 2010-08-16 · • 40,000 masonry arch...
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Industry Sector RTD Thematic Area DateCivil Construction Durability and Life Extension 13 11 01
Application of Discrete/Finite Element Algorithms to the Analysis of Masonry Buildings and Bridges
Carl BrookesGifford Consulting Engineers, Southampton, UK
SummaryThe presentation describes the application of discrete/finite element (DE) algorithms to the analysis of masonry buildings and bridges. Several illustrations will be given where these highly non-linear simulations are being used for structural assessment and in the design of strengthening schemes.
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Introduction
Intoduction
• Discrete Element Technique Applied to Masonry• Ancient and modern
• Application to Masonry Arch Bridges• Static coded vehicle loads• Unstrengthened and strengthened conditions
• Application to Buildings - Seismic• In-plane behaviour of stone shear walls
– Earthquake loading– Existing and retrofitted structures
• Application to Buildings - Blast• Out-of-plane behaviour of brick/block walls
– Blast Loading– Existing and retrofitted structures
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Discrete Element analysis
A development of the distinct element technique, 1971Implemented by Rockfield Software Limited in ELFEN, current version 2001
Discrete modelled parts
Boundary interface models• To deal with contact, gaps, friction along perimeter edges
Adaptivity for evolving discrete parts• Required if fracturing takes place
Overall behavior is highly non-linear
Modelled parts are simple
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Discrete Element Simulation - Blocky2D seismic analysis to investigate in-plane behaviour of stone façade
Artificial horizontal ground motion 0.3g
Contours show principal compressive stresses with varying scale.
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Discrete Element Simulation - Brittle2D simple cyclic base shearing
Mesh adaptivity used to model fracturing process there after DE contact and interface laws apply.
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Application to Masonry Arch Bridges
Application to Masonry Arch Bridges• Static coded vehicle loads• Unstrengthened and strengthened conditions
Prediction and Verification• Study looking at past full scale tests of redundant bridges• Simulation of more recent laboratory models tested at TRL• Aim to concentrate on 2D behaviour (keep things as simple as possible)
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Torksey BridgeLincolnshire, 1986
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Spandrel Splitting from Barrel
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Arch starting to collapse
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Collapsefailure is not involving spandrel walls
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Torksey Bridge SimulationFirst discrete element simulation of arch in 1997
2D plain strain model. Ignores spandrel walls
Contours show principal stresses. Blue shows compression
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TRL Unstrengthened ArchCarried out in 1997
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Barrel construction
Hand made bricks, radial mortar joints weak mortar, circumferential sand joints to represent ring
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TRL Unstrengthened Test SimulationModel 18.elf, ELFEN v3.0.0b
2D plain strain model. Ignores spandrel walls.
Contours show principal compressive stresses. Blue shows highest compression.
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TRL Unstrengthened Test Strength Prediction
Unstrengthened Arch Test with Simulation in Load Control(contact damping set to 0.5, Fc to 3.5 N/mm2)
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-90000
-80000
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-60000
-50000
-40000
-30000
-20000
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0
-0.04 -0.03 -0.02 -0.01 0.00 0.01 0.02Vertical Intrados Displacement [m]
Load
[N] 1/4 Point
2/4 Point3/4 Point1/4 TRL Test
Test Data
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Strengthening Masonry Bridges
Background in UK
• 40,000 Masonry arch bridges in UK (highways, railways, canals)• most are over 100 years old• many have inadequate strength
• Environmental deterioration• Increased live loading
• EC directive requires trunk roads to have 40 tonne rating Type of strengthening
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Formulation of Strengthening and Requirements
Requirements• minimal change to the bridges appearance• minimal impact on bridge users and existing services• provide an adequate increase in load carrying capacity• exhibit long term durability• exhibit a ductile failure mechanism• be cost effective
Internal strengtheningRetrofitted reinforcement (Cintec)
• stainless steel reinforcement bars• bond to masonry by patented grout and sock• precision drilling and setting out
Rigorously engineered design
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Mass or Reinforced Concrete Saddle
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Mass or Reinforced Concrete SaddleExcavation of fill prior to installation of concrete saddle
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Tangential ReinforcementRetrofitted using Cintec Anchors
tangential reinforcement installedfrom carriageway and, in certain circumstances, from below
The System
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Tangential ReinforcementMode of Behaviour
To prevent classic 4 hinge failure
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TRL ARCHTEC TestFirst Test Carried out in 1998
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Modelled Cintec Anchors
Separate finite element meshShear coupling model for bondAxial formulation for elastic and non-linear
material behaviour
tension
compression
Axial stress
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Failure of Inner RingExposing Cintec Anchors
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Test After Inner Ring Collapse
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TRL First ARCHTEC Strengthened SimulationModel 24.elf, ELFEN v3.2.52
2D plain strain model. Ignores spandrel walls.
Contours show principal compressive stresses. Blue shows highest compression.
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First ARCHTEC Test Strength Predictions
TRL Test Strengthened in Load Control
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0
-0.04 -0.03 -0.02 -0.01 0.00 0.01 0.02Vertical Intrados Displacement [m]
Load
[N]
1/4 Point2/4 Point3/4 PointTRL Test 1/4TRL Test 2/4TRL Test 3/4
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Comparison of TRL Laboratory Test Results
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-0.03 -0.025 -0.02 -0.015 -0.01 -0.005 0
Intrados Displacement [m]
Load
Rea
ctio
n [N
/m]
UnstrengthenedFirst ArchtecSecond Archtec
44.8 Tonnes
41.5 Tonnes
20 Tonnes
Both Archtecarches more than double the capacity of the unstrengthenedarch
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ConclusionsApplication to Masonry Arch Bridges
CONCLUSIONS
The performance of unstrengthened and strengthened arches can be simulated using the discrete element technique
• Compared with conventional methods DE assessments give best possible estimate of strength
Best possible live load assessments can be carried out.• Over 60 bridges have now been strengthened using DE based designs
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Application to Buildings – SeismicShear wall investigation
Application to Buildings - Seismic• In-plane behaviour of stone shear walls
• Earthquake loading – dynamic loads• Existing and retrofitted structures
Macro-block - weak mortar• Ancient masonry with very weak or no mortar
Brittle material - strong mortar• Ideally suited to model masonry where mortar and block strengths are similar
Sensitivity analysis• various retrofitted reinforcement arrangements
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Masonry shear wall details(all dimensions in mm)
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General arrangement of idealised building
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Unstrengthened simulation – 0.3g loading
Principal compressive stresses in N/m2
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Strengthening arrangements (13,19,20,21)
Horizontal, Vertical and diagonal Cintecanchors installed from the roof and at the corners
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Strengthened simulation – 0.3g loading
Principal compressive stresses in N/m2
Combined arrangement No. 21
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ConclusionsApplication to Buildings – Seismic
CONCLUSIONS
Indications are that the overall performance of masonry acting compositely with retrofitted reinforcement can be predicted
• Predicted damage looks similar to that occurring in actual buildings• Verified for other masonry applications, static and high speed dynamic
Numerical modelling is valuable as a virtual test bench for strengthening• Currently strengthening of non-engineered buildings is often based on how
designs faired after Earthquakes• Full-scale testing is very expensive
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Application to Buildings – BlastOut-of-plane behaviour of brick/block walls
Application to buildings - Blast• Out-of-plane behaviour of brick/block walls
• Blast Loading• Existing and retrofitted structures
Very fast dynamic load• Load applied typically in 5ms• Strain rate in materials very important
Sensitivity analysis• Experimental test programme• various retrofitted reinforcement arrangements
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Strengthening to Resist Blast
Strengthened hollow concrete block wall subjected to severe blast load
Before – front view After – front view
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Strengthening to Resist Blast
Strengthened hollow concrete block wall subjected to severe blast load
Before – rear view After – rear view
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Strengthened Simulationdecoupled analysis, Elfen & Air3D
The wall was subjected to a blast load from 200kg TNT NEQ @ 12.5m; 534kPa, 1274kPa-ms (440lbs TNT NEQ @ 41ft; 77psi, 185psi-ms).