CONCRETE–STEEL COMPOSITE BEAMS

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					 INTERNATIONAL Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
International Journal of Civil JOURNAL OF CIVIL ENGINEERING AND
ISSN 0976 – 6316(Online) Volume 3, Issue 1, January- June (2012), © IAEME
                                TECHNOLOGY (IJCIET)
ISSN 0976 – 6308 (Print)
ISSN 0976 – 6316(Online)
Volume 3, Issue 1, January- June (2012), pp. 99-110
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CONCRETE–STEEL COMPOSITE BEAMS OF A FRAMED STRUCTURE
     FOR ENHANCEMENT IN EARTHQUAKE RESISTANCE
                                1
                                    Vidula S. Sohoni, 2 Dr.M.R.Shiyekar
     1
         Ph.D. Research Scholar-Civil Engineering, Bharati Vidyapeeth University College of
               Engineering, Pune, Maharashtra -411043,India. vssohoni@gmail.com
          2
              Professor and Head-Civil Engineering, SCOE, Pune-411052, Maharashtra, India
                                      mukundshiyekar@gmail.com

ABSTRACT
Behavior of flexural members in a framed structure is a function of their stiffness properties.
These stiffness properties in turn depend upon the ductility of the member. Conventional
reinforcement of Torsteel bars if replaced by rolled steel sections may change these properties.
This also reduces the congestion of reinforcement at the beam column junction and facilitates for
more ductility. This is advantageous for high rise structures most susceptible to earthquakes.
This paper covers a comparative study of members with conventional reinforcement and
reinforcement using rolled steel sections. Beams were cast and tested for failure load and
deformation by keeping the percentage of reinforcement and cross section the same.
Experimental results were compared analytically using software ANSYS. Results show that the
use of rolled steel sections is more effective in terms of load carrying capacity in flexure,
deflection and stiffness properties.
Key Words: Composite Members, Rolled Steel Sections, Stiffness

1. INTRODUCTION
         To know the behavior of building frames comprising of R.C.C .members under the
combination of gravity and lateral loading is a topic of interest over the years. The total response
or behavior of the structure is influenced by many parametric variations such as cross sectional
sizes of the members, moment of inertia, amount of loading, material/grade of the members etc.
In all these cases for high rise buildings of framed structure, ductility requirements dominate the
behavior and deflected shape of the members. Especially at the beam–column junction, heavy
reinforcement creates difficulty in concreting which in turn adds to the difficulty in making the


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International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online) Volume 3, Issue 1, January- June (2012), © IAEME

portion of joint homogeneous. Beam column junction may reduce the response to earthquakes
making the structure less earthquake resistant.
       To make the R.C. structure earthquake resistant, it is desirable to increase its ductility. This can
                                                                                                      1
be achieved by increasing the ductility of the brittle matrix by adding steel fibres. The
combination of fibres and conventional reinforcement increases the flexural strength of the
beams and also higher postcracking rigidity may be obtained. The flexural behavior and analysis
of reinforced concrete sections may be studied by using refined modeling technique2.An
analytical study has been performed on the flexural response of an R.C. element to variations in
characteristics like longitudinal steel ratio, yield strength, concrete compressive strength etc.
Effect of compressive strength and tensile reinforcement ratio on flexural behavior of high-
strength concrete beams has been investigated.3This effect is with reference to the load-
deflection behavior and displacement ductility .The results show that flexural rigidity increases
as concrete compressive strength increases. Further experimental study has been carried out to
measure the Poisson’s Effect in reinforced concrete membrane elements4and thus entire shear
stress versus shear strain curves may be predicted. Through innumerable attempts, the elastic
properties of all the structural materials have been worked out and quantified by the I.S. codes5
and are known fairly accurately. However, it remains to be seen how concrete responds to
embedding of fabricated steel sections, in view of elastic properties. This forms the core of the
proposed study. In the proposed study, the strength and deformation characteristics of composite
section are investigated and studied. It may be another way to increase the ductility by using the
members of composite nature i.e. rolled steel sections encased in concrete instead of
conventional steel reinforcement. This type of composite member which is a combination of
concrete and structural steel section may enhance the load carrying capacity and stiffness of the
structure. A clear comparison between the beams of composite nature and the conventional
R.C.C. beams with respect to the load carrying capacity, stiffness , economy is proposed
experimentally and to validate the results analytically. The properties of the composite members
are compared with conventional members experimentally with reference to variety in the rolled
steel sections by keeping the cross sectional dimensions and grade of concrete the same.

2. DEFINITION OF THE STUDY

      •   Studying the feasibility of composite members.
      •   Assessing the structural properties of composite members-especially stiffness
          properties.
      •   Investigating experimentally the use of composite members.
      •   Validation of the experimental results analytically by using a software ANSYS.
      •   Arriving at a conclusion for the stiffness properties of the composite members.

3. FORMULATION OF THE PROBLEM

Step 1: Identify various combinations of rolled steel sections and concrete with
reference to variety in the rolled steel sections.

Step 2: Casting of the required number of beams of every combination.



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ISSN 0976 – 6316(Online) Volume 3, Issue 1, January- June (2012), © IAEME

Step 3: Testing these beams for flexure and arrive at failure loads and failure modes
experimentally.

Step 4: Establish the failure load analytically using software ANSYS.
Step 5: Compare the analytical and experimental results based on the stiffness of the members
and thus to verify the feasibility of use of rolled steel sections in place normal torsteel
reinforcement.

4. METHODOLOGY
4.1 Experimental Work:
Following three types of beams involve in experimental work.
   Type ‘N’ members: Beams with Normal i.e. conventional torsteel reinforcements.
   Type ‘A’ members: Beams with rolled steel Angle sections as reinforcements.
   Type ‘P’ members: Beams with Pipe sections as reinforcements.
   In preparing these beam models, cross sectional area , percentage steel and grade of concrete
   is kept same. The beams were cast and cured for 28days.

4.2 Testing Work:

   Following testing work was carried out.

I) CUBES:

   Cubes were tested under compression testing machine to know and verify the grade

   of concrete used. Average of the strength was taken as the crushing strength of cubes
   and hence the grade of concrete used.

II) BEAMS:
   a) The beams are tested for two point loads           on UTM under the standard loading
   arrangement.
   b) The load was applied gradually and crack pattern was observed.
   c) The deflection under the two point loads were recorded with the help of dial
      gauge.
   d) The crack pattern, deflection, cracking & ultimate load were noted down.
   e) Graphs of load v/s deflection were plotted.


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ISSN 0976 – 6316(Online) Volume 3, Issue 1, January- June (2012), © IAEME

4.3 Analytical Verification Using ANSYS:
Software ANSYS based on Finite Element Analysis was used to compare the results analytically.

   •   For the analytical purpose, SOLID 45 element (brick element) is used for three
       dimensional modeling of beam specimens. The element is constructed using eight nodes
       having three degrees of freedom at each node .i.e. translations in the nodal x, y ,and z
       directions respectively.

   •   A clear cover of 30 mm is provided to the reinforcement in the beam specimens on
       compression as well as on tension side. Material properties of steel and concrete entered
       in the software as obtained from experimental results.

   •   To mark support conditions, the nodes on the bottom surface of the beam specimen at a
       distance of 45 mm from each edge are assigned translational and rotational fixity in all
       directions.

   •   For the application of middle third loading, the nodes on the upper surface of the beam
       specimen at a distance of 265 mm from each edge are loaded.

   •   The deflection of the beam specimen is then calculated by the analysis procedure of the
       software.

4.4 Comparison between experimental and analytical results:
    In the present study, following aspects are critically examined.

   1) Maximum load carrying capacity of the beams under flexure.
   2) Maximum deflections obtained analytically and experimentally
   3) Values of Modulus of Elasticity of R.C.C. as obtained from experimental observations
      and that obtained from ANSYS .

4.5 Conclusions:
    Based on the results obtained from experimental and analytical work, conclusions are drawn
    for the use of rolled steel sections.

5. SUMMARY OF THE BEAM SECTIONS
   Size of the beam: 150mm x150mm x750mm
   Grade of Concrete: M 25
   Water/Cement Ratio: 0.426




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ISSN 0976 – 6316(Online) Volume 3, Issue 1, January- June (2012), © IAEME

                           Table 1: Summary of the Beam Sections

Details             I)    Type      ‘N’ II)                      III)TYPE ’P’sections
                    sections            Type’A’sections
Main                   2 #12            2 ISA 20x20x3            2 pipes 25mm outer diameter,
Reinforcement                                                    thickness 1.5mm
Percentage Steel       1.32%              1.31%                        1.28%
(pt)
Hanger Bars         2 # 8mm             2 #8 mm                     2#8mm
Stirrups            2legged #8mm @ 2legged                       2legged #8mm@200mmc/c
                    200mmc/c            #8mm@200c/c.
6. Cross-sectional Details of the Beams
 Type ‘N’ beams :




                           Fig 1. Beam with Normal Reinforcement

Type ‘A’ Beams :




                                 Fig 2.Beam with Angle Section


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ISSN 0976 – 6316(Online) Volume 3, Issue 1, January- June (2012), © IAEME

Type ‘P’ Beams:




                             Fig 3. Beam with Pipe Reinforcement

7. Loading Arrangement For Beams:
       The beams were tested on Universal Testing Machine(UTM) for middle third loading by
loading two point loads. The crack pattern, deflection, mode of failure and ultimate load were
recorded. Graph of load versus deflection were plotted.
The loading arrangement is as follows.




                           Fig 4. Loading Arrangements for Beams




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ISSN 0976 – 6316(Online) Volume 3, Issue 1, January- June (2012), © IAEME

8. Load-Deflection Plots for beam specimens:
Type ‘N’ beams:




                          Fig 5. Load-Deflection plot-Type N-beams

Type ‘A’ beams:




                          Fig 6. Load-Deflection plot-Type A-beams




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ISSN 0976 – 6316(Online) Volume 3, Issue 1, January- June (2012), © IAEME

Type ‘P’ beams:




                          Fig 7. Load-Deflection plot-Type P-beams

9. COMPARISON OF CRACK PATTERN BETWEEN VARIOUS BEAMS:-
                 Table 2: Comparison of crack patterns between various beams

S.NO. BEAM TYPE              CRACK PATTERN                     REMARKS

1       Type – N             Diagonal cracks at support        Shear failure

2       Type – A             Cracks        emerged        first Combined shear and
                             perpendicular      and      then flexure failure
                             diagonally near the quarter span
                             indicating combined failure

3.      Type-P               Vertical cracks at midspan        Flexure failure



10. Cube Test Results:
                     Table 3: Cube Test Results

Type     Age of Testing      Average Compressive Strength
Type ‘N’   28 days                28.19 N/mm2
Type ‘A’   28 days                28.63 N/mm2
Type ‘P’   28 days                28.73 N/mm2



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11. Analytical Verification using ANSYS

   •    The analysis is carried out using the software ANSYS, version 11.0, based on finite
        element modeling.
   •    The element used for FEM model is as follows.

                        Table 4: Elements used for FEM model
        Sr. No.   Component/Sub assembly Approach Element Type
        1.        Concrete                    Solid     Solid 45
        2         Reinforcement               Solid     Solid 45
        3         Stirrups                    Solid     Solid 45

   •    Material Properties of Beam Specimens:
                          Table 5: Material Properties of Beam Specimens

       Sr.    Beam Marked                   Steel                                Concrete
       No.                       Young’s Modulus Poisson’s          Young’s          Poisson’s
                                 In N/mm2         Ratio             Modulus          Ratio
                                                                    In N/mm2
         1.   Type ‘N’ beams     2.1 x 105                 0.3      26,547 .13           0.15
         2.   Type ‘A’ beams     2.1 x 105                 0.3      26,753.50            0.15
         3.   Type ‘P’ beams     2.1 x 105                 0.3      26,800.18            0.15

   •   Boundary Conditions and Loading for Beam Specimens:
       The nodes on the bottom support line of the beam at a distance of 45 mm from each edge
       are applied fixity in all directions.
       i.e. for these nodes, Ux = 0 , Uy = 0 , Uz =0 .
       Two point loads of same magnitude are applied in Z – direction
   • Displacements :
       As per the loading and boundary conditions entered in the software as prescribed above,
       the analysis of beam specimens is carried out for flexural middle third two point loading.
       The displacements as shown below are obtained.
Type ‘N’Beams:




                                  Fig 8. Displacements-Type-N beams


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ISSN 0976 – 6316(Online) Volume 3, Issue 1, January- June (2012), © IAEME

 Type ‘A’ Beams :




                             Fig 9. Displacements-Type-A beams
 Type ‘P’ Beams:




                            Fig 10. Displacements-Type-P beams

12. Experimental and Analytical Results

   •   Experimental values for the maximum load carrying capacity for the three types of
       beams are as under.
                            Table 6: Maximum Load Carrying Capacity

          Maximum Load Type         Type      Type
          in kN          ‘ N’ beams ‘A’ beams ‘P’ beams
          Experimentally    75        98.66    98.95




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   •    Values of deflections obtained experimentally and from ANSYS are equal in all the
       three cases.
                                Table 7:Deflection obtained

           Deflections in mm Type      Type      Type
           as obtained       ‘N’ beams ‘A’ beams ‘P’ beams
           Experimentally      1.45     1.756      1.0
           From ANSYS          1.557    1.552      1.167

   •    Values of Modulus of Elasticity of R.C.C. as obtained experimentally and from
       ‘ANSYS’ are nearly equal in all the three cases.
                          Table 8: Values of Modulus of Elasticity

           Modulus of Elasticity ( ERCC) Type      Type      Type
           in N /mm2 as obtained         ‘N’ beams ‘A’ beams ‘P’ beams

           Experimentally                 4.72 × 104 4.94 × 104 8.66 × 104
           From ANSYS                     4.39 × 104 5.58 × 104 7.43 × 104

13. CONCLUSIONS

   •   It is observed that maximum load carrying capacity of ‘A’ and ‘P’ type beams is 31.54%
       and 31.93% respectively higher than that of ‘N’ type beams. Though the deflection of
       ‘A’ type beams appears to be 21.10% on the higher side, it is at a31.54% higher value of
       load. Type ‘P’ beams prove to be preferable as the deflection value is 25.05% less even
       at a 31.93% higher value of load.

   •   Modulus of Elasticity of R.C.C. is 83.47% more for ‘P’ type sections and 4.66% more
       for Type ‘A’ sections as compared to the sections with normal reinforcements. The
       increased Modulus of Elasticity for Type ‘A’ and Type ‘P’ sections indicates the
       increase in flexural rigidity of the beam specimens and proves to be more suitable
       for earthquake resistant construction as the use of increased ductility may prove to be
       advantageous especially at the beam – column junction, thereby reducing the congestion
       of reinforcement at the beam- column junction.

   •   Error in experimental and analytical values is of the order of 5 % only.




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14. REFERENCES

1) A.Bentur and S. Mindess,(1983) “ Concrete beams reinforced with conventional steel
   bars and steel fibres :properties in static loading” , The international Journal of
   Cement Composites and Lightweight Concrete , Vol. 5, Number 3.
2) Parviz Soroushian , Jongsung Sim , and Jer-Wen Hsu,(1991) “Axial /flexural
   behavior of reinforced concrete sections: effects of design variable” , ACI Structural
   Journal, Title no. 88-S3.
3) Samir A.Ashour ,(1998) “Effect of compressive strength and tensile reinforcement
   ratio    on     flexural  behavior     of    high-strength    concrete     beams”    ,
   www.sciencedirect.com, 25th Nov.
4) Ronnie R.H.Zhu and Thomas T.C.Hsu,(2002) ”Poisson Effect in Reinforced
   Concrete Member Elements” ,ACI Structural Journal , Title no. 99-S65.
5) I.S. 456-2000, Code of Practice for plain and reinforced concrete structures.




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