Engineering analysis and design software

1

Bridge

Software information for

Post-tensioning and time-stage analysis

Account Manager NameJob Title, LUSAS

Software Information

LUSAS key benefits

• Can model all types of post-tensioning to various codes of practice including AASHTO, EuroCode, BS5400

• Will model full staged construction with beams, shells and solids including creep

• Model true cable behaviour• Change loading/stress/strain over time

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External Post-tensioning - LUSAS

• Equivalent load method or true tendon modelling available

• For true tendon modelling:– Tendons incorporated in the model as bar/

beam elements with applied forces– Tendons connected to deflector plates and

anchors– True behaviour of tendons due to

compression of concrete obtained

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Internal Post-tensioning - LUSAS

• Typical analysis types– beam models– plane stress models– 3D grillages and shells– Volumes

• Equivalent loads used; prestress effects combined with other load effects

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Internal Post-tensioning - LUSAS

• Wizard calculates forces and losses to AASHTO, Eurocode, China… and applies to model using equivalent load method

• Alternatively import forces and losses from user calculations (spreadsheet)

• Wizard used for tendon geometry or import from spreadsheet/CAD or use geometry in LUSAS

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Internal Post-tensioning - LUSAS

Example of Tendon defined by geometry in Model8LUSAS Post-tensioning and time stage analysis

Tendon Definition

• Straight, Arc, Parabolic, Spline Line Definitions

• Controls for radii of curvature and “pinch points”

• Tendon Layer

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Internal Post-tensioning - LUSAS Wizard

• Tendons defined using wizard

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Internal Post-tensioning - LUSAS

• Example of Tendons from Multiple Post tensioning

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Internal Post-tensioning - LUSAS

• Example of one Tendon effect from Multiple Post tensioning (Solid sections omitted for clarity)

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Time-stage analysis

• Considers the construction sequence• Near infinite number of stages with differing time-steps• Incorporates time-based material properties such as creep and

shrinkage• Effects can be “locked-in” between stages

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Time-stage analysis - Facilities

• CEB-FIP Creep Model available

• Allows creep recovery• Definition of age of concrete

and striking time• General creep models for

other materials

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Time-stage analysis - Facilities

• Tree Definition of Time-Stages• Stages easily modified• View stages individually or

create animations• Stages can be activated and de-

activated

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Time-stage analysis - Bridges

• Typical bridge needs for staged construction and time-dependent effects:

– Beam and slab bridges– Span-by-span construction– Segmental construction– Incremental launching– Cable-stayed bridges

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Beam and slab bridges

• Staged construction with locked-in stresses

• Same analysis model for construction and in-service conditions

• Model can be used for eigenvalue buckling (e.g. to find MCR in EN1993) or for second order analysis if required

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Beam and slab (integral) bridge

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Span-by-span construction

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Span-by-span construction

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Span-by-span construction

• Post-tensioning can be incorporated between stages• Creep/ shrinkage can be modelled• Activation and deactivation allows for temporary supports• Same analysis model for construction & in-service conditions

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Segmental construction

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Segmental construction

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Segmental construction

• Creep/ shrinkage analysis can incorporate age attribute (for precast elements)

• Checks on robustness e.g. – Segment dropped by

crane– Dynamic effects (impulse)– 2nd order (P-Δ) effects

could be included

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Segmental construction

• Example of dynamic effect of segment being dropped

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Incremental launching

• Incremented using ‘slidelines’ or• Supports moved backwards on “stationary” deck

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Incremental launching - Slideline

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Incremental launching - Supports

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Incremental launching - enveloped

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Incremental launching

• Can include – activation of each section– creep/ shrinkage of concrete– post-tensioning (first stage during launch & second stage at

completion)– temporary supports (and their removal) – allowances for differential settlement

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Cable Stayed construction

• Segmental Post-Tensioned Construction

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Case Study-Mississippi River Bridge

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Staged Construction AnalysisThis animation shows the staged construction analysis of the original design for the I95 Mississippi River Bridge incorporating creep and post tensioning.

Designed by Modjeski & Masters, for clients Missouri and Illinois DOT, the time-steps model an 800 day construction period and continue to 10000 days to allow for creep over that period. Closure pours are modelled with joints as either fixed or sliding when post tensioning is taking place.

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Tower Analysis

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Deck Analysis

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LUSAS key benefits

• Can model all types of post-tensioning• Staged construction readily modelled• Contact can be used, supports moved• Creep and shrinkage of concrete can be included• Tension stiffening (GNL) or indeed any GNL, MNL or dynamic facility

can be utilised• Same system and analysis model for construction and in-service

conditions• Beams, shells and solids all available

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Find out more at www.lusas.com