modeling of post-tensioned segmental box girders
DESCRIPTION
Use of Midas in the analysis of Post Tensioned Box Girder BridgesTRANSCRIPT
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Modeling of Post-Tensioned Segmental
Box Girders
Cast Study Calgary West LRT
Neon Koon, P.Eng. July 12 2012
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Overview
Post Tensioned Segmental Concrete Bridges
Case Study Calgary West LRT
Modeling Techniques and Applications in Design Process
Conclusion
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What Are Segmental Concrete Bridges?
Built in short pieces of concrete sections, one piece at a time
The concrete segments can be cast-in-place or precast
Large size cranes, referred to as gantry, are typically used to erect the precast segments or slip forms are used to produce cast-in-place concrete
The segments are joined together by applying a high compressive force from high strength bundled wires, referred to as strands
Post Tensioned Segmental Concrete Bridges
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What Are Segmental Concrete Bridges?
Post Tensioned Segmental Concrete Bridges
Precast segment at batch plant Segments being erected using gantry
19-strand tendon Tendon stressing in operation
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Issues To Be Considered in Segmental Bridge Construction
Span length
Project size
Site restrictions
Local labor and material costs
Aesthetic/Appearance
Quality Assurance / Quality Control (QA/QC)
Construction Methods and Continuing Engineering Services During Construction
Post Tensioned Segmental Concrete Bridges
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Various Types of Segmental Bridge Construction
Span-by-Span
Balanced Cantilever
Incremental Launching
Cable Stayed
Post Tensioned Segmental Concrete Bridges
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Various Types of Segmental Bridge Construction
Span-By-Span
Courtesy: VSL Systems (CZ) Ltd.
Post Tensioned Segmental Concrete Bridges
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Various Types of Segmental Bridge Construction
Balanced Cantilever
Courtesy: VSL Systems (CZ) Ltd.
Post Tensioned Segmental Concrete Bridges
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Various Types of Segmental Bridge Construction
Incremental Launching
Courtesy: VSL Systems (CZ) Ltd.
Post Tensioned Segmental Concrete Bridges
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Various Types of Segmental Bridge Construction
Cable Stayed
Post Tensioned Segmental Concrete Bridges
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Typical Concrete Box Girder Section
Single cell box preferable due to its high torsional resistance, ease of construction and inspection access
For constant girder depth, span to depth ratio ranging from 15 to 30, with optimum value around 18 to 20
Top flange width is preferably limited to 6 times the box depth and can be pushed up to about 18 m
Web spacing normally between 4.6 m to 7.6 m
Post Tensioned Segmental Concrete Bridges
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Typical Concrete Box Girder Section
Minimum top flange thickness = 200mm
Minimum ribbed web thickness = 180mm
Very wide bridge deck can be accommodated by using several box girders with a joint between the two box sections
Post Tensioned Segmental Concrete Bridges
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Typical Concrete Box Girder Section
Post Tensioned Segmental Concrete Bridges
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Major Components of Segmental Box Girders
Tendons Longitudinal post-tensioning vs transverse post-tensioning
External tendons vs internal tendons
Courtesy: FHWA
Typical Tendon Profile for Longitudinal Post-Tensioning
Post Tensioned Segmental Concrete Bridges
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Major Components of Segmental Box Girders
Longitudinal External Tendons
Post Tensioned Segmental Concrete Bridges
Mid Span Deviator
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Major Components of Segmental Box Girders
Transverse Post-Tensioning
Courtesy: FHWA
Post Tensioned Segmental Concrete Bridges
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Major Components of Segmental Box Girders
Prestressing Strands in Tendons in bridge structures Each strand composed of 7 bundled wires, low relaxation
Tensile strength = 1860 MPa
Size typically 13 mm or 15 mm diameter
Nominal cross sectional area = 99 mm2 or 140 mm2
Duct at least 2.5 times > the net area of post-tensioning strands
Corrosion protection Water-proofing membrane/sealant at the exterior surface of concrete
Cover
HDPE duct
Grout
Sheathing/coating
Proper design detailing and construction procedures
Post Tensioned Segmental Concrete Bridges
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Major Components of Segmental Box Girders
Levels of Corrosion Protection to Internal Tendons
Courtesy: FHWA
Post Tensioned Segmental Concrete Bridges
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Major Components of Segmental Box Girders
Levels of Corrosion Protection to External Tendons
Courtesy: FHWA
Post Tensioned Segmental Concrete Bridges
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Major Components of Segmental Box Girders
External Deviators Function as a intermediate anchorage point to transfer the vertical
component of the post-tensioning force
Anchorage Blocks Provide an anchorage point at the ends of the span to develop the
required post-tensioning forces
Provide a jacking area for the post-tensioning equipment
Special attention and design details required to increase the levels of corrosion protection at anchorages
Post Tensioned Segmental Concrete Bridges
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Major Components of Segmental Box Girders
Stressing of Strands in Process at Anchorage Block
Post Tensioned Segmental Concrete Bridges
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Design Aspects of Post-Tensioned Box Girders
Design Codes AASHTO LRFD Bridge Design Specifications
AASHTO Guide Specifications for Design and Construction of Segmental Concrete Bridges
Ultimate Flexure, Shear, Torsion, Axial
Bursting at anchorages, jacking of superstructure during launching
Service Stress within concrete segments and at segment joints
Fatigue
Deflection
Seat width
Post Tensioned Segmental Concrete Bridges
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Factors Affecting the Expected Performances
Concrete mix
Temperature
Creep and shrinkage
Curing methods
End restraints (secondary effects)
Stress losses in tendons
Construction sequence
Construction practice/load
Post Tensioned Segmental Concrete Bridges
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Case Study Calgary West LRT
Case Study Calgary West Light Rail Transit
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Case Study Calgary West Light Rail Transit
Total length 8 km extending from west end of 7th Ave Downtown to 69th St S.W.
Track works on elevated guideway, trenches, tunnels, and grounds
Expected opening schedule in early Spring 2013
Case Study Calgary West LRT
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Case Study Calgary West Light Rail Transit
Total length of the elevated guideway is about 1.5 km
Comprised of standard 30m, 33m, and 36m single span segments and two-continuous spans constructed using the span-by-span method as well as a four-span continuous structure using the balanced cantilever method
Case Study Calgary West LRT
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Courtesy: City of Calgary
Mewata Bridge
11 th St SW
Bow Trail SW
Bow River
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Courtesy: City of Calgary
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Launching Trusses
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Launching Trusses Stored on Ground
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Steel Form for End Segment Casting
Cured End Segment at Batch Plant
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Preparation of Reinforcing Cage
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Standard segment for spans constructed using balanced cantilever method Standard segment for
spans constructed using span-by-span method
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Erected girder segments using the span-by-span method
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Erected girder segments using the balanced cantilever method
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Crews applying stressing to tendons at end segment
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Two Span Continuous with Integral Connection at Straddle Bent
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Two Span Continuous with Integral Connection at Straddle Bent
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Crews working in a heated tent in winter
Courtesy: City of Calgary
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Modeling Demonstration of a Two-Span Continuous Structure
Modeling Techniques and Applications in Design Process
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Modeling Demonstration of a Two-Span Continuous Structure
Plan View
Modeling Techniques and Applications in Design Process
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Modeling Demonstration of a Two-Span Continuous Structure
Elevation View (Longitudinal)
Modeling Techniques and Applications in Design Process
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Modeling Demonstration of a Two-Span Continuous Structure
Elevation View (Transverse)
Modeling Techniques and Applications in Design Process
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Defining the Geometry
Can be either imported from Midas Civil, CAD, or other structural software such as SAP or Lusas
Define nodes and elements manually using the geometry defining features under the Menu Tab
Modeling Techniques and Applications in Design Process
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Defining the Geometry
Modeling Techniques and Applications in Design Process
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Non-time dependent material
Time dependent material including creep and shrinkage as well concrete strength development used in construction staging analysis
Plastic material for non-linear analysis
AASHTO and Canadian Codes implemented in material database
Defining Material
Modeling Techniques and Applications in Design Process
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Various guidelines such as the CEB-FIP (1990), ACI, PCA, and AASHTO implemented to predict the creep and shrinkage effects
Defining Material
Modeling Techniques and Applications in Design Process
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Sections can be found from the database or manually enter dimensions
Sections like basic bare steel, generic sectional properties, hybrid sections, prestressed concrete section, taper section, and composite section can be defined
Additional stress points can be defined using the Section Manager feature
General sections using SPC
Defining Sections
Modeling Techniques and Applications in Design Process
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Box Section Developed by SPC
Modeling Techniques and Applications in Design Process
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Used AutoCAD to accurately define the tendon profile
Simply copy & paste the coordinates in 2D / 3D into Midas Civil
Defining Tendons
Modeling Techniques and Applications in Design Process
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Tendon property was defined based on the CEB-FIP
Tendon diameter, relaxation coefficient, tensile strength, and anchorage set, and first jacking force were all defined in the model
Defining Tendons
Modeling Techniques and Applications in Design Process
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Structure, Boundary, Load, and Tendon Groups were defined accordingly for construction stage analysis and subsequent data manipulation
Defining Groups
Modeling Techniques and Applications in Design Process
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Defining Construction Stage Analysis
Construction staging had to be accurately defined to capture accumulated stresses built up during construction
Tendon stresses at service after all the losses, secondary moment effects, and stresses at the segmental box girders and other structural components were all examined
Challenges
Integral connection between the straddle bent beam and each end of the spans, resulting consideration of secondary moment effect
Excessive amount of flexural reinforcing originally required in the bent beam, resulting issue of proper concrete placement
Defining Construction Stage Analysis & Challenges
Modeling Techniques and Applications in Design Process
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Accurately defined all the member section properties, their design locations, time dependent materials, tendon properties, stressing and construction sequences in the construction staging analysis
Used internal post-tensioning to replace the flexural reinforcing
Solution...
Modeling Techniques and Applications in Design Process
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Construction Staging Rendering
Modeling Techniques and Applications in Design Process
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Canadian and AASHTO LRFD available
Traffic lanes can be defined based on beam or plate elements
Program can consider a number of sub-load cases and perform independent analyses of each sub-load case and provide the maximum and minimum results at a particular location or run combined analyses of all sub-load cases and provide the maximum and minimum results
Dynamic load factor in Canadian code
Defining Moving Load
Modeling Techniques and Applications in Design Process
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Simulate the construction staging and review stresses and forces at each stage
Report forces and stresses in tendons over time
Post-processing Information
Modeling Techniques and Applications in Design Process
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Moving load tracer used to find out location of live load to produce the maximum/minimum forces/stresses at a certain point
Post-processing Information
Modeling Techniques and Applications in Design Process
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Advantages of Post-Tensioned Box Girder Constructed Using Segmental Construction Methods
Design Issues
Challenges Encountered During Construction of CWLRT
Useful Modelling Techniques
Conclusion
Modeling Techniques and Applications in Design Process
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Case Study Calgary West Light Rail Transit
http://www.westlrt.ca/contentdesign/constructiondashboard.cfm
Modeling Techniques and Applications in Design Process
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Segmental Concrete Bridge Design Resources
AASHTO LRFD Bridge Design Specifications
AASHTO Guide Specifications for Design and Construction of Segmental Concrete Bridges
American Segmental Bridge Institute (AASHTO-PCI-ASBI Segmental Box Girder Standard Drawings)
ASBI Recommended Practice for Design and construction of Concrete Segmental Bridges
FHWA
Post Tensioning Manual, PTI
Modeling Techniques and Applications in Design Process
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THANK YOU FOR YOUR TIME!
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