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prestress concrete
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ADVANTAGES OF CONTINOUS MEMBERS
TOPIC 1
EVEN DISTRIBUTION OF MOMENTS
• Between center of span and supports
• Lesser span moments
• Longer spans
REDUCTION OF SIZE
• Vertical load carrying capacity is more
• Lighter structures
• Economical
HIGHER LOAD CARRYING CAPACITY
• Redistribution of moments
• Reduced cross sectional dimensions
INCREASED STABILITY
• Redundancy in load path
• Formation of hinges in extreme events
PRECAST UNITS CONNECTED BY PRESTRESSED CABLES
• Segmental construction
• Precast units
• Connected by pre-stressed cable
SUITABLE POSITIONING OF CURVED CABLES
• In post tensioned girders
• Resist span and support moments
REDUCTION IN NO: OF ANCHORAGES
• One pair of post tensioned anchorages
• A single stressing operation
• Less maintenance
SMALLER DEFLECTIONS
• Higher load carrying capacity
• Even distribution of moments
• Safer
DISADVANTAGES
• Secondary stresses
• Losses
• Skill of workmanship
• Analysis and design
• Concordant cables
METHODS OF ACHIEVING CONTINUITY
TOPIC 2
USING STRAIGHT CABLES
• Wide web necessary
• Large anchorage blocks
• Form work
• Skilled workmen
• High strength threaded
rods
USING CURVED CABLES
• Higher resistance to
stress
• Longer spans
• Cracking over piers
eliminated in multistage
post-tensioning
USING CAP CABLESNegative moment taken care of
USING STRAIGHT TENDONSLimited length
COMPOSITE CONSTRUCTION
• Beam ends embedded in
cast-in-situ diaphragms
• Reinforcement for
negative moment within
deck thickness
• SS under major loads
COUPLING
• Pre-tensioned precast members
• Optimized strands• Top strands at adjacent
interior members coupled
• Performance of full length post tensioning
• Lesser cost
TWO TYPES
FULLY CONTINOUS
• Using straight cables
• Using curved cables
• Larger size tendons
• Secondary reinforcements
• Expensive
PARTIALLY CONTINOUS
• Using cap cables
• Using straight tendons
• Tendons not used to
achieve continuity
• Negative moment at
supports
• Cheaper
EFFECT OF PRESTRESSTOPIC 3