Expt # 1. Behavior of reinforced concrete beams under flexure

Aim: To study the flexural behavior of reinforced concrete beams Details of test specimen: Provide a neat sketch of the test specimen along with its dimensions and geometric properties

Reinforcement Details for Flexure Test Apparatus used: List the apparatus used in the experiment and describe them briefly Background: Brief description of the response of the reinforced concrete in flexure

o Behavior of singly reinforced beams Under reinforced, Over reinforced, Balanced sections

o Behavior of doubly reinforced beams Assumptions in the flexure theory for reinforced concrete beams and its implications Brief derivation of the cracking and ultimate moment for singly reinforced sections

o Cracking moment, Mcr ckfbD2*12.0 = kNm, fck

o Ultimate moment for under reinforced beam, M

in MPa, b, D in mm is the width and depth of the beam respectively

ur = 0.54fckbxu(d 0.42xu), xu = fyAst /(0.54fck

o Ultimate moment for the over reinforced beam, Mb)

ur = 0.54fckbxu(d 0.42xu), xu

cksstsst dbfEAEA362 10*56.710*12)( +

= ( -0.0035AstEs)/ (1.08bfck

Obtain the ultimate moment capacity for doubly reinforced section )

Obtain an equation for the deflected shape of a simply supported beam subjected to two-point loading assuming linear elastic behavior

Sketch of experimental setup: Neat sketch of the setup showing the location of the steel pellets, dial gauge, point of application of the loads, support condition

EXPERIMENTAL SETUP

Test specimen

Dial gauges

Demec points

Moment Curvature relation for under-reinforced section

Moment Curvature relation for over-reinforced section

Mu

Moment (M)

Curvature ()

First crack(at cracking moment)

Yield of tension steel(at yielding moment)

Secondary compression failure

Compression Failure

First crack at cracking moment )

Mu

Moment (M)

Curvature ()

Procedure: List the procedure followed to collect the required data Observation: 1. Table 1: Readings from the DEMEC gauge at various locations Under reinforced

beam Load,

kg DEMEC gauge reading, mm 1 2 3 4 5

2. Table 2: Readings from the dial gauge and crack width Under reinforced beam

Load, kg

Crack width, (mm)

Raw Dial Gauge Reading, (mm) 1 2 3

Main Vern Main Vern Main Vern

3. Table 3: Readings from the DEMEC gauge at various locations Over reinforced beam

Load, kg

DEMEC gauge reading, mm 1 2 3 4 5

4. Table 4: Readings from the dial gauge and crack width Over reinforced beam

Load, kg

Crack width, (mm)

Raw Dial Gauge Reading, (mm) 1 2 3

Main Vern Main Vern Main Vern

5. Figure 1: Sketch of Crack pattern Under reinforced beam:

6. Figure 2: Sketch of Crack pattern Over reinforced beam:

Detailed Calculations: 1. Table 5: The value of the strains at various locations Under reinforced beam

Load, kg

Strain, (10-6) 1 2 3 4 5

2. Table 6: Deflections at various locations Under reinforced beam

Load, kg

Observed Deflection, (mm) Theoretical Deflection, (mm) 1 2 3 1 2 3

3. Table 7: The value of the strains at various locations Over reinforced beam

Load, kg

Strain, (10-6) 1 2 3 4 5

4. Table 8: Deflections at various locations Over reinforced beam

Load, kg

Observed Deflection, (mm) Theoretical Deflection, (mm) 1 2 3 1 2 3

5. Table 9: Various quantities computed from strains tabulated in Table 5 and 7.

Under reinforced beam Over reinforced beam Load,

kg Moment,

Nm Curvature,

Depth of NA,

mm

Load, kg

Moment, Nm

Curvature,

Depth of NA,

mm

6. Figure 3: Plot of depth vs. strain for various loads 7. Figure 4: Plot of load vs. deflection (3 curves, compare theoretical predictions with

experimentally obtained values) 8. Figure 5: Plot of moment vs. curvature 9. Figure 6: Plot of moment vs. depth of neutral axis 10. Figure 7: Plot of load vs. crack width 11. Compare the response of under reinforced vs. over reinforced beams in the above

plots and describe the qualitative difference in their response 12. Compare the predicted and observed ultimate capacity and cracking moment. Discussion: Comment on the results obtained and the observed vs. expected behavior

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