Transcript D&C PT Contractor`s Role & Responsibilities

D&C PT Contractor’s Role &
Responsibilities
Chris M. Harris
Contracts Manager, Structural Systems
& PTIA Technical Committee
Introduction
• Why do PT contractors get involved in the design of
the project to start with?
• What are the common efficiencies introduced to the
structure by a PT contractor?
• Integration of the PT contractor into the design team.
• What aspects of the existing design will the PT
contractor review/change
• Examples
• Conclusion
Why do PT contractors get involved
in the design of the project to start
with ?
• Commercial desire
• Specialist engineers, design draftspersons, &
design software
• Risk & reward allocation
• Time
• Constructability
What are the common efficiencies
introduced to the structure by a PT
contractor ?
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Element thicknesses
Support optimisation
Slab structure type optimisation & formwork
Reinforcement rationalisation
Integration of the PT contractor into
the design team.
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Definition of structure performance
Documentation status
Coordination
Design Program
Certification
What aspects of the existing design
will the PT contractor
review/change?
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Depends on the type of project
Ieff / Igross (for buildings)
Concrete grade / volume / thickness
Structure type (flat plate / flat slab / banded)
Restraint design
Rebar content
Eureka Tower
• Conforming design
• Reinforced slabs
Eureka Tower
• Non conforming design
• PT bands and slabs
• Driving force TIME
Conclusions
• Project Engineers to coordinate with contractors
• Involve a PT contractor early
PT in buildings
PT is likely to be considered for most projects.
If the consultant doesn’t consider it, then the
contractors will
Why PT?
• Savings in materials
• Savings in construction
time
• Improved durability and
robustness
• Cost savings
Some perceived down side
issues
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Time consuming to design by the
occasional designer ?
PT applies real force into a structure
hence analysis (incl. secondary
effects) needs to be realistic and
specific.
Some perceived down side
issues
• System and process
needs to be understood
and details coordinated
sufficiently
• Finding most economical
proportions of concrete,
PT & reinforcement can
be a lengthy iterative
process, but usually
yields substantial
benefits. Software &
experience is key.
Other effects to consider
• Secondary effects in all
indeterminate PT
structures, but can be
beneficial
• Structural movements
(creep, shrinkage, thermal)
• Structural restraints
(walls, stability elements)
• Dynamic behaviour (may be
a lighter, livelier structure)
If doubt exists, talk to a
specialist PT designer (or
the PTIA)
PT design is not different
however...
• Effective & efficient design does
require experience
• With sound engineering knowledge
and practice this can be done
successfully.
• Assistance and guidelines can
normally be obtained from the
specialist contractors
Design philosophy
• Consider the general
concept of partially
prestressed concrete
• Appropriate
proportions of
reinforcement and
prestressing steel
depends on the
application (restrained
v. unrestrained
concrete)
The D&C route for PT delivery
The usual variants here
are:
• D&C by tender
invitation
• D&C by alternative
design
If D&C is expected and
planned for, time
efficiencies and
innovations can
occur
D&C Design Brief
A Post Tensioning Design Brief is
critical for a successful D&C
arrangement.
It should focus on the performance
requirements on the design
 The extent of D&C area required
 The loads and load paths
 Member sizes with acceptance tolerances
 Serviceability and durability requirements
 Movements and Jointing strategy
 Define the Design, certification & approval
process
Performance requirements
As far as possible indicate:
Architectural requirements (tolerances, finishes etc)
Site constraints and constructability issues
Pour sequence & any limitations on edge stressing access
Limitations of the supporting structure.
Any frame actions that need to be considered in floor design.
Expected areas of restraint and strategy for its management incl.
location & types of pour strips &/or temporary movement joints
&/or permanent building joints.
Roles and responsibilities in the design process
Inspections and installation signoffs
Quality and safety requirements.
Types of PT Contract
•Supply and Install (S&I)
–Structural design, documentation, inspection &
certification by engineer
–Shop drawings, install, QA by specialist contractor
•Design and Construct (D&C)
–structural floor design, documentation by specialist
contractor
–Install, inspection & certification by specialist contractor
–Engineer remains responsible for vertical elements,
stairs, wind & earthquake design, etc.
D & C Tender Information
•Post Tensioning Price
•Conventional Reinforcement Quantities
•Concrete Properties and Profiles
•Structural Design Criteria
•Detailed Scope of Work
•Client Responsibilities
•Contract Conditions
Design Considerations for PT Price
•Pour Size
•Strand Diameter
•Number of Strands per Tendon
•Couplers
•Efficient Approval Process
Concrete Properties and Profiles
• Concrete outlines and grade needs to be
provided with PT price for client to
determine total cost of solution.
• Be aware of concrete testing & strength
requirements for initial & final stressing,
these are essential for performance of
concrete & safety at PT anchorages.
Structural Design Certificate
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Loads
Durability Requirements
Deflection Criteria
Analysis Assumptions
Detailed Scope of Work
• Design Deliverables for D&C, usually:
– Concrete outlines
– PT drawing (design & shop in one)
– bottom reinforcement drawing
– top reinforcement drawing
– sections & details
• Construction Services
Client / Builder Responsibilities
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Site Amenities
Supply of Power and Water
Lifting of our Materials on to the Decks
Supply and Install of Conventional Reinforcement
including Studrails where applicable
• Concrete Infill of Top Surface Stressing Pans
• Anything else (job specific)
Contract Conditions
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Reference to Standard Conditions of Contract
Reference to EBA
Variation Rates
Payment Terms
Retentions
Liquidated Damages
Insurances
Project Relationships
Developer
Architect
Structural Engineer
Head Contractor
Post Tensioning
D&C
Subcontractor
Formwork Sub-Contractor
Reinforcement Supplier
Steel Fixer
Concreter
Timely Co-ordination
Co-ordination between:
•services consultants
•architect
•structural engineer
•builder’s services (alimaks etc)
all by others.
Co-ordination between:
•structural engineer
•pt design
shared by engineer & specialist pt designer.
Timeliness & information sharing is critical.
Late information will lead to re-work & additional costs.
Failure to co-ordinate will lead to re-work & additional costs.
Acknowledgements
John Fairweather
Frank Filippone
Jamie Mackenzie
who are the authors of most of these slides.
However any errors are mine.