UR Beam Test

Behaviour of an under reinforced conrete beam.

Objective: To study the behavior of an under reinforced concrete beam in flexure.

Requirements before starting the experiment:

1. RC beam of the shown cross-section, cast at least 28 days before the experiment.
2. Four point loading setup
3. LVDT
4. Hydraulic Jack
5. Concrete of grade, (f_ck) = M25
6. Reinforcement of grade, (f_y) = Fe 500

Dimensions of specimen
1. L = 2000 mm
2. L^l = 1800 mm
3. b = 150 mm
4. D = 200 mm
5. A_SV = 2L - 8 mm Φ @ 100 c/c
6. A_st = 2-12 Φ = 226.19 mm²

Observed strength
1. Obs. mean cube strength of concrete (f_cm) = 29.5 MPa
2. Obs. mean tensile strength of reinforcement (f_ym) = 565 MPa

STEP 1

PLACEMENT OF BEAM:

Choose the simply supported beam setup to be used in the experiment.

CLICK ON THE CORRECT IMAGE TO MOVE FORWARD

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STEP 2

EXPERIMENTAL SETUP:

Choose the four point loading setup to be used in the experiment.

CLICK ON THE CORRECT IMAGE TO MOVE FORWARD

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Specimen Preparation Make RC beam with given geometric and material properties. Concrete cubes for compressive strength test – 3 nos.
Steel reinforcement, same as used in beam specimen for tensile strength test.

L'	2000
L	1800 mm
L_AA	600 mm
b	150 mm
D	200 mm
Cover	25 mm (to shear reinforcement)
Ast	2-12φ
Steel Grade	Fe500
Concrete Grade	M25

STEP 1
Test three cube specimens in compression testing machine and determine the average value
of compressive strength.

Specimen	Compressive strength(MPa)
1	35.11
2	34.44
3	30.88
Average Cube Strength (f_cm)	33.50

STEP 2
Perform tensile strength test on the reinforcement and determine the average value of the yield strength.

Specimen	Yield strength (MPa)
1	532
2	518
3	522
Average Yield Strength (f_ym)	524

STEP 3
Attach the loading arrangment, LVDT and load cell to the specimen.

STEP 4
MEASURING DIMENSIONS OF THE BEAM Click on the measuring tape to measure the length of the beam.

Total Length(L)

2012 mm

STEP 4
MEASURING DIMENSIONS OF BEAM Click on the measuring tape to measure width of the beam.

2012 mm

Total Breadth(b)

150 mm

STEP 4
MEASURING DIMENSIONS OF BEAM Click on the measuring tape to measure the depth of the beam.

2012 mm 150 mm

Total Depth(D)

205 mm

STEP 5
Click on the measuring tape to measure the distance between the supports and the points of application of load. Measure the distance between support 1 and 2 when the measuring tape is placed as shown. Measure the distance between support 2 and 3 when the measuring tape is placed as shown. Measure the distance between support 3 and 4 when the measuring tape is placed as shown. Measure the distance between support 1 and 2 when the measuring tape is placed as shown. 2012 mm 150 mm 205 mm 1800 mm 603 mm 598 mm 599 mm

A B C D Length between the supports

1800 mm

Length between Support and point of application of load
AB

603 mm

Length between Support and point of application of load
BC

598 mm

Length between Support and point of application of load
CD

599 mm

STEP 6
Apply the load using the hydraulic system uptill failure.

STEP 6
The following types of cracks are observed.

Load v/s Displacement Graph

Shear Crack

Flexure Shear Crack

Flexure Crack

STEP 7
Load at failure
Record the load (from load cell) and mark the shear and flexure cracks.

STEP 8
1. Start increasing the load after marking the cracks.
2. After marking once keep increasing the load till failure or the time when beam fails and shear crack appears as shown in next slide.
3. Note down the failure load as P

Graph

Input1	Input2
Input3	Input4
Input5	Input6
Input7	Input8
Input9	Input10
Input11	Input12
Input13	Input14
Input15	Input16
Input17	Input18

Observation

Select the observed failure crack.

Click any one image:

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Left Cracks Right Cracks

Observation 1. Mark the shear crack as shown below (at approximately 45 degrees)
2. Measure the distance La and Lb as shown below to determine the location of the shear crack.

L_a

L_b

L_a =

460 mm

L_b =

640 mm

Observations

Measured length of beam (L^l)	= 2012 mm
Measured width of beam (b)	= 150 mm
Measured depth of beam (D)	= 205 mm
Measured span of beam (L)	= 1800 mm
Cover	= 20 mm
Efective depth	= (205-20-8-16/2) = 169 mm
Load at failure	= 7.34 ton = 72.00 kN

Calculations

$$ x_{u,max} = \frac{0.0035 }{0.0055 \ + \frac{f_{Y}} {E_{S}} \ } \ d \ = 77\, mm\, (x_{u} < x_{u,max }) \,(Under Reinforced)\\\ $$

M_UR = 0.87 f_y A_st (d - 0.416 x_u) = 13.66 kNm

(2) Predicted moment carying capacity based on observations

$$ x_{u\,predicted} = \frac{f_{ym} \, A_{st}}{0.543 \, f_{ym} \ b} \ = 53\,mm\\ \ $$

$$ x_{u\,max\,predicted} = \frac{0.0035 }{0.0055 \ + \frac{f_{ym}} {E_{S}} \ } \,d \ = 71\, mm\\ \,(x_{u,predicted} < x_{u,max,predicted})\, (Under Reinforced)\\\ $$

M_{UR predicted} = f_ym A_st (d - 0.416 x_u,predicted) = 18.76 kNm

Moment at failure = PL/6 = 21.60 kNm
(1) Design moment of resistance: $$ x_{u} = \frac{0.87 \, f_y \, A_{st}}{0.36 \, f_{ck} \, b} = 72 \, mm $$

Results Moment of the beam
Behaviour of the beam (Observed) = Under Reinforced, Ductile
Observed moment at failure = 21.60 kNm
Designed behaviour of the beam = Under Reinforced
Design Moment of reistance = 13.66 kNm
Predicted behaviour of the beam = Under Reinforced
Predicted Moment of resistance based on observed data = 18.76 kNm

7.34 T

Report

Grade of concrete = M25

Mean cube strength of concrete = 33.5 MPa

Grade of reinforcement = Fe500

Mean yield strength of steel (MPa) = 524 MPa

Estimated ultimate moment of resistance as per IS:456 (2000) = 18.32 kN-m

Observed ultimate moment of resistance = 19.35 kN-m