Composite Concrete Construction

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Composite Concrete Construction
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6- Calculation of shear stress at composite
interface

• A)Under service load

Strain and stress distributions across composite
beam cross- section, under service and ultimate
loads.
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THE SHEAR STREES AT ANY POINT ALONG THE
COMPOSITE INTERFACE CAN BE COMPUTED AS
V S
V
I b
WHERE V Shear force at any section under
consideration S Statical moment of area on one
side of the composite inter face about the
neutral axis I Moment of inertia of the
transformed composite section, neglecting
the tensile resistance of concrete b Breadth of
the composite interface at the section under
consideration
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• b) Under ultimate load

Horizontal shear stress distribution
along composite interface, under ultimate load
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The horizontal shear stress
C1
Vh
b Ls
WHERE C1 0.85 Fc b t1 Ls Distance
between maximum and zero moment points. T1
Depth of equivalent rectangular stress
distribution over the composite interface
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7- Code Requirements

• A) BS 8110 (1995)
• i) Average horizontal design shear stress
• the average design shear stress should then
  be distributed in proportion
• to the vertical design shear force diagram
  to give the horizontal shear
• stress at any point along the length of
  member .

Design shear force

Beam width length between max ve or -ve
moment and zero moment
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• ii) nominal links
• 1) should be at least 0.15 of the contact
  area.
• 2) the spacing in T- beam ribs with
  composite flange should not
• exceed the max of
• a) Thickness of in situ concrete
• b) 600 mm
• 3) Links should be adequately anchored on
  both sides of interface.
• iii) links in excess of minimum
• when the horizontal shear stress exceeds
  the value given in table
• all horizontal shear force should be carried
  reinforcement anchored
• on either side of interface
• Where
• Ah (in mm2/m)

1000 b Vh
Ah

0.87 fy
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• B) DIN 1045 (1978)
• a) In case of floors, with live loads up to
  500 kg/m2 it is not
• necessary to check direct shear
  strength at interface
• provided that the contact surface is
  rough.
• b) For