Composite Concrete Construction

shootperchUrban and Civil

Nov 26, 2013 (3 years and 11 months ago)

89 views

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.

V =

V * S

I

* b

THE SHEAR STREES AT ANY POINT ALONG THE
COMPOSITE INTERFACE CAN BE COMPUTED AS:

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

b)
Under ultimate load:

Horizontal shear stress distribution along

composite interface, under ultimate load

V
h

=

C
1

b * L
s

The horizontal shear stress:

WHERE :


C
1
: 0.85
F
c
’ * b * t
1


L
s
:
D
istance between maximum and zero moment points.


T
1
: Depth of equivalent rectangular stress distribution over the


composite interface

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

=

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:


A
h


(in mm
2
/m)

A
h

=

1000 * b * V
h

0.87* fy

B)
DIN 1045 (1978):


a) In case of floors, with live loads up to 500 kg/m
2

it is not


necessary to check direct shear strength at interface


provided that the contact surface is rough.


b) For