Diagonal Compression Failure in RC Beams RC

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Diagonal Compression Failure in RC
BeamsRC?????????

• M2 KOBAYASHI Chikaharu

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What is Diagonal Compression Failure?
Diagonal compression failure is a kind of failure
types which lead to the end by diagonal
compression.
Concrete
Reinforcement
Computation of shear capacity

• Vu Vs Vc
• Vs shear carried by truss model
• Vc shear carried by mechanism except truss model

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What is Diagonal Compression Failure?
Diagonal compression failure is a kind of failure
types which lead to the end by diagonal
compression.
Concrete
Reinforcement
The case diagonal compression failure can occur in
Beams with thin web cross-section and dense
reinforcement
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Background
Recently, high-strength and high-performance
concrete and steel have been developed.

• Ultrahigh-strength concrete
• (fc?100MPa)
• Ultrahigh-strength steel
• (fy?1000MPa)

• Bridges with more slender and longer span can be
  constructed.

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Background
Bridges with slender and long span

• Very thin web
• Dense shear reinforcement

Ultimate capacity for diagonal compression
failure relatively decrease.
Calculation of load carrying capacity for
diagonal compression failure is needed
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Calculation Method of Diagonal Compression
Failure
Proposed equation by Placas et al.
Vwc(1.0420.8rw)(10.75/tana)fc1/2bwd

• Formula decided by experiment

Not yet fully understood because of the lack of
sufficient research in this failure
Standard Specification for Concrete Structures of
JSCE
Vwc1.25fc1/2bwd

• Quite conservative for safety reasons

• This equation is covered only for concretes not
  exceeding fc 50 N/mm2

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Objective

• To investigate the diagonal compression failure
  mechanisms of RC beams
• To clarify effect factor on diagonal compression
  failure in RC beams

To propose calculation formula of diagonal
compression failure in order to estimate the
ultimate capacity of RC beams
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Research of Last Year and Future Plan
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Specimen
Parameter compressive strength of concrete fc,
ratio of stirrup rw
Compression bar
B
A
240
240
a660
a660
d220
A
B
Stirrup (ultrahigh-strength steel)
Tensile bar
A-A
B-B
250
250
50
h260
40
70
146
146
unit mm
High-fluidity concrete
? pw8.8, a/d3.0
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Comparison with JSCE Provision
JSCE Provision
Safe design
Vwc1.25fc1/2bwd

• Quite conservative for safety reasons

• This equation is covered only for concretes not
  exceeding fc 50 N/mm2

JSCE provision calculate safely, including beams
using high-strength concrete
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Plan in this year
To clarify the effect by using ultrahigh-strength
concrete
There is a possibility to reach a peak.
?
Recently, concrete with a compressive strength of
150MPa or more was also developed.
It is necessary to investigate the effect!
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Future Plan
To clarify other effect factors on diagonal
compression failure of RC beams
Placas formula Vwc(1.0420.8rw)(10.75/tana)fc1/
2bwd JSCE formula Vwc1.25fc1/2bwd
In order to propose calculation formula of
diagonal compression failure, it is considered
that other factors also affect the ultimate
capacity on diagonal compression failure
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Thank you for kind attention!
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Destruction Property
Normal-strength concrete
Crack pattern
Crush section
High-strength concrete
Crack pattern
Crush section
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Load-Displacement Curve
Sharp drop
High-strength concrete
load
Normal-strength concrete
displacement
In case of high-strength concrete, web
compression failure would be brittle.