M Tech. Thesis Presentation

Shear Failure Analysis of Over-reinforced SCC Beams

By

Sukhwinder Singh Roll. No. 1168269

(Structural Engineering)

Under the guidance of:Assoc. Prof. K.S. Bedi G.N.D.E.C. Ludhiana

1

TABLE OF CONTENTS

INTRODUCTION REVIEW OF LITERATURE EXPERIMENTAL PROGRAMME RESULTS AND DISCUSSION CONCLUSIONS FUTURE SCOPE OF WORK

2

The shear transfer mechanisms include:

The shear in the un-cracked compression zone.

The dowel action of the longitudinal reinforcement.

The interface shears transfer due to the aggregate interlocks or the surface roughness of the cracks.

The residual tensile stresses across the cracks.

SHEAR TRANSFER MECHANISMS

3

PARAMETERS INFLUENCING THE SHEAR STRENGTH OF THE BEAMS

Previous investigatory researches concluded that shear and diagonal tension strength of concrete beams without web reinforcement depends upon: Percentage of tension reinforcement Shear span-to-effective depth ratio Characteristic strength of the concrete Cross-sectional Area of the beam

Other variables which influences the shear strength of concrete members are: Maximum aggregate size Diameter of tensile reinforcing bars 4

But even today, the various codes of practice world-over have not incorporated all these variables in estimating and predicting theoretically the shear strength of reinforced concrete beams.

The shear strengths of reinforced concrete as given by Tables 19 and 20 of the Indian Code of Practice for Plain and Reinforced Concrete, IS 456: 2000, till date depend only on the characteristic strength of concrete and the percentage of main reinforcing steel used.

This results in underestimation of shear strength of the beams.

5

Cont….

Architectural requirements or space constraints sometimes compels to use a high percentage of steel reinforcement in a concrete flexural member in order to minimize structural depth and still provide adequate stiffness.

Self-compacting concrete has been used in the study to ensure effective concreting of the over-reinforced beams.

So this is potentially very useful to clients, consultants and contractors who wish to use shallower concrete members.

6

WHY OVER-REINFORCED SCC BEAMS

SELF COMPACTING CONCRETESelf compacting concrete (SCC), is a new kind of high performance concrete with: Excellent deformability and segregation resistance Capable of filling spaces in dense reinforcement or

inaccessible voids without hindrance or blockage.

In particular, there are some concerns among designers/engineers that SCC may not be strong enough in resisting shear because of the presence of comparatively smaller amount of coarse aggregates compared to normal concrete (NC) which can lead to the formation of smooth fractured surfaces and subsequent development of weak aggregate interlock mechanism.

7

INFLUENCE OF COARSE AGGREGATES ON THE NORMAL

CONCRETE

INFLUENCE OF COARSE AGGREGATES ON THE SELF-

COMPACTING CONCRETE

8

COMPARISON OF AGGREGATE INTERLOCK MECHANISM

MODES OF FAILURES OF BEAMS

Beams with low span-to-depth ratio or inadequate shear reinforcement, the failure can be due to shear. The following five modes of failure due to shear are identified Diagonal tension failure Shear compression failure Shear tension failure Web crushing failure Arch rib failure

9

Diagonal tension failure :- In this mode, an inclined crack propagates rapidly due to inadequate shear reinforcement.

10

Shear tension failure:- Due to inadequate anchorage of the longitudinal bars, the diagonal cracks propagate horizontally along the bars.

Shear compression failure: There is crushing of the concrete near the compression flange above the tip of the inclined crack .

11

Web crushing failure: The concrete in the web crushes due to inadequate web thickness.

Arch rib failure :-For deep beams, the web may buckle and subsequently crush. There can be anchorage failure or failure of the bearing.

12

Name Study

Clark

(1951)

Investigated resistance of RCC beams without and with varying ratios of web reinforcement to diagonal tension. Beams of two cross sections, four span lengths and concrete strengths ranging from 2000 to 6000 psi were tested for five different positions of concentrated loads. The results were reasonably consistent and exhibited good evidence that the shear capacity of a beam increases with the strength of concrete when other factors are kept same and the shear span-to-depth ratio influences considerably its shear carrying capacity.

Moody et al 15 (1954)

Tested 40 beams without and 2 beams with web reinforcement. There were series of parameters as • Percentage of longitudinal and web reinforcement• Size and % of long. reinforcement and strength of concreteIt was found that the ratio of ultimate load to the load at first cracking decreased as the ratio of shear span to the effective depth increased. Test results also indicated that the strength of beams with large a-d ratios may be governed by the first cracking load whereas strength of shorter beams is governed by the load causing destruction of the compression zone of concrete.

13

LITERATURE REVIEW

NAME STUDY

Kani (1966)

Tested 133 rectangular beams to study the influence of Concrete strength, percentage of reinforcement, span to depth ratio affecting shear strength of reinforced concrete beams. The results indicated that shear strength of rectangular reinforced concrete beams does not depend on concrete strength within the entire range of fc’ = 2500 to 5000 psi and p = 0.50 to 2.80.There is considerable influence of the amount of main reinforcement on the relative beam strength.

Mphonde and

Frantz (1984)

Tested three series of reinforced concrete beams without shear reinforcement. Within each series the shear span-depth ratio was held constant at 3.6, 2.5, or 1.5, while normal compressive strength was varied from 3000 to 15000 psi. The authors had also compared ACI equations and Zsutty’s ultimate shear strength equation with the regression equations developed by them.Test results indicated that for slender beams, the ACI 318-77 beam shear strength equations are conservative but their accuracy varies greatly with concrete strength. The effect of concrete strength on shear capacity becomes more significant as the beams become shorter.

14

LITERATURE REVIEW

15

Name Study

Rebeiz et al 26 (2001)

Tested the RCC beams without the web reinforcement with different variables as concrete compressive strength, fc’, the shear span to depth ratio (a/d), and the tensile reinforcement ratio (ρ). The intent of their study was to clear the distinction between the cracking shear strength, vc, and the ultimate shear strength, vu, when referring to shear strength of concrete. The author depicted that:• In case of short beams (a/d < 2.5), a very significant amount of

additional loading can be resisted by reinforced concrete beyond the formation of first diagonal crack before total as cracking shear strength and ultimate shear strength are almost equal in magnitude.

• The failure mode in long beams (a/d > 2.5) is diagonal tension with the formation and propagation of first fully developed inclined crack.

• This failure mode is very sudden as total shear failure occurs almost immediately after the formation of first major diagonal cracking.

LITERATURE REVIEW

Name Study

ACI-318-98

Code

The basic equation for the shear strength of RC concrete beams proposed by ACI-318-08, makes the shear span to depth ratio as one of the basic parameters for calculating the shear capacity of RC section.

IS Code 456-2000

It states that shear strength of a concrete member is nominal shear resistance and which is summation of shear strength provided by concrete itself and the strength provided by the vertical shear reinforcement in the form of steel shear strength. Table 19 of IS:456-2000, presents value of shear stress which is dependent only upon longitudinal reinforcement.

16

LITERATURE REVIEW

NAME STUDY

Hassan(2008)

Experimented with SCC and CVC beams. Main variables were a/d, concrete compressive strength and type and amount of the longitudinal steel. SCC showed similar shear resistance characteristics in pre-cracking stage as compared with CVC. No significant difference noted between SCC and CVC beams in terms of crack widths, crack lengths, crack angles or overall failure mode.

17

LITERATURE REVIEW

CONCLUSIONS DRAWN FROM PREVIOUS RESEARCHES

Studies have shown that shear strength of concrete beams without web reinforcement is provided by the combined action of many factors namely The compressive strength of concrete The aggregate interlocking Shear span to depth ratio The percentage of longitudinal reinforcement Cross-sectional Area of the beam

18

OBJECTIVE OF THE STUDY

To experimentally analyze the shear failure of the over-reinforced SCC beams without stirrups having different shear spans to effective depth, different characteristic strengths of concrete with constant longitudinal reinforcement ratio.

To compare the provisions and procedures in IS 456:2000 and with the various models.

19

SCOPE OF RESEARCH Simply supported longitudinally reinforced concrete

beams without any stirrups are used for the experimental investigations.

The test beams were cast with Self Consolidated Concrete with 28-days nominal compressive strength of 40, 60 and 80 MPa

Beam size with overall depth of 300 mm with varying shear span to depth ratio (a/d) of 1.5, 2.5 and 3.5.

A constant, 3.1% of longitudinal reinforcement ratio were used in all the beams.

Distance between the two points loads was fixed at 600mm for all the beams.

20

SCOPE OF RESEARCH

Effective cover in all the beams was kept at 25mm For comparison of the observed shear strength of SCC

beams, the provisions of building codes and models have been selected i.e. ACI, Canadian Code, CEP-FIP Model, Zsutty Model, Bazant Model and IS:456-2000.

21

Cont….

METHODOLOGY

To study the shear behaviour of beams, 27 beams of overall cross-section 150mm x 300mm were selected without shear reinforcement.

Characteristic strength of concrete, fck as 40, 60 and 80 MPa was selected.

Percentage of longitudinal steel ratio was kept constant at 3.1%.

Shear span to depth ratio (a/d) of three values were selected as 1.5, 2.5 and 3.5 mainly to check the behaviour of SCC beams in shear.

22

METHODOLOGY

The beams were tested under Four Point Loading system and the observations were recorded in terms of Ultimate Failure Capacity.

The shear strength of the beams was determined at the failure point and the observed values were compared with the provisions of selected Building Codes and Design Models .

The effect of various parameters on the shear strength of SCC beams was studied on the basis of observations from the testing.

23

Cont….

TEST SET-UP CONFIGURATION

24

PROPOSED BEAM SIZES AND LOADING ARRANGEMENTS

a/d ratio 1.5, Overall Length 1600mm, Shaer Span = 398 mm Overall Depth = 300mm

a/d ratio 2.5, Overall Length 2200mm,Shear Span = 663 mm Overall Depth = 300mm

CONT….

26

a/d ratio 3.5, Overall Length 2600mm, Shear Span = 928 mm Overall Depth = 300mm

REINFORCEMENT DETAILS IN BEAM SPECIMENS

Percentage of longitudinal reinforcement was constant at 3.1%

27

CONT….

28

Percentage of longitudinal reinforcement was constant at 3.1%

DIFFERENT MODELS TO PREDICT SHEAR CAPACITY

ACI code Equations Canadian Code Equations IS 456-2000 Code CEP-FIP Model Zsutty Equation Bazant Equation

29

ACI CODE EQUATION

According to ACI Building Code 318-08 , the shear strength of concrete members without transverse reinforcement subjected to shear and flexure is given by following equations.

f′c= Compressive strength of concrete at 28 days in MPa.bw= Width of cross section in mm.d= Effective depth in mm.Mu = Factored moment at Cross sectionVu= Factored shear force at Cross section.ρ = Longitudinal Reinforcement Ratio.

Eqn. 1

30

CANADIAN CODE EQUATION

According to Canadian Standard, the shear strength of concrete members is given by following equation.

f′c= Compressive strength of concrete at 28 days in MPa.

bw= Width of cross section in mm.

The Canadian standard in this Eqn. has not considered the effect of shear span to depth ratio and longitudinal tension reinforcement effect on shear strength of concrete.

31

IS 456-2000 CODE EQUATION

The design shear strength τc depends on grade of concrete (fck) and the percentage of tension steel pt = 100Ast/bd. The ultimate shear load can be computed by following equation.

or unity, whichever is greater

32

CEP – FIP MODEL

According to CEP–FIP Model, the shear strength of concrete members is given by following equation.

The CEP–FIP model considered size effect and longitudinal steel effect.

33

ZSUTTY EQUATION

Zsutty (1968) has formulated the following equations for shear strength of concrete members;

Zsutty equation also takes into account size effect.

34

BAZANT &YU EQUATION

Bazant (2005) has formulated the following equation for shear strength of concrete members;

where,

k = 693.7623

35

EFNARC GUIDELINES FOR MIX DESIGN OF SCC (2002)

A concrete mix can only be classified as Self-compacting Concrete if it consists the three properties as Filling Ability Passing Ability Segregation Resistance

To ensure the above properties in concrete following are the recommended tests by the EFNARC.

36

CONT….

37

Sr No. Method Property

1 Slump-flow by Abrams cone Filling ability

2 T50 cm slump flow Filling ability

3 J-ring Passing ability

4 V-funnel Filling ability

6 L-box Passing ability

7 U-box Passing ability

8 Fill-box Passing ability

9 GTM screen stability test Segregation resistance

10 Orimet Filling ability

ACCEPTANCE CRITERIA FOR SCC AS PER (EFNARC, 2002)

Method Units Minimum Maximum

Slump flow by Abrams cone mm 650 800

J- ring mm 0 10

V-ring sec 6 12

L-box(h2/h1) - 0.8 1

U-Box(h2-h1) mm 0 30

GTM Screen stability test % 0 15

Orimet Test sec 0 5

38

MATERIAL AND MIX PROPORTION

Cement: Ordinary Portland Cement 43 grade was used corresponding to IS-8112(1989). The typical content of cement is 350-450 Kg/m3 as per the guidelines of EFNARC (2002).

Coarse Aggregate: Coarse aggregates used for the study was natural coarse aggregates (angular type of 20 and 10mm of size).They were used in ratio of 60:40 of 20mm to 10mm.

Fine Aggregate: Natural river sand is used as fine aggregate.

Fly ash: F-Class Fly Ash was used in the study made available by Ultra Tech RMC Plant, Ludhiana.

39

CONT….

Silica Fume: Silica fume is a by product of producing silicon metal or ferrosilicon alloys. One of the most beneficial uses for silica fume is in concrete as it is a very reactive pozzolan. The silica fume used in this study is provided by Elkem India Pvt. Ltd. (Microsilica Grade 940-D).

Chemical Admixture (SP): GLENIUM B233 was used as an Super Plasicizer in the concrete. It is an admixture of a new generation based on modified poly-carboxylic ether and compatible with all types of cements.

40

CONT….

Steel reinforcing bars: The reinforcing bars used were 12 mm, and 16 mm diameter high yield strength deformed bars of brand TATA Tiscon of grade Fe415.

Water: In the present investigation, portable tap water available for both curing and concrete mix in the laboratory was used.

41

PHYSICAL PROPERTIES OF CEMENT

42

Characteristics Specified values as per IS:12269-1987Results

observed

Standard Consistency (%) - 33

Specific gravity 3.15 3.15

Initial Setting Time (min.) >30mins 65

Final Setting Time (min.) <600mins 215

Compressive strength of Cement (OPC 43 grade)

Specified values as

per IS:12269-1987Results obtained

3 Days (N/mm2) 24.5 27

7 Days (N/mm2) 36.0 41

28 Days (N/mm2) 46.3 43

CUBE STRENGTH OF CEMENT

PHYSICAL PROPERTIES OF COARSE AGGREGATES

43

Characteristics Results obtained

Type Crushed

Shape Angular

Specific gravity 2.66

Colour Grey

Water absorption 1.0%

Fineness modulus 7.87

IS: Sieve designation

Wt retained on sieve (gm)

% wt retained

Cumulative % wt retained

% passing

40mm 0 0 0 100

20mm 200 4.0 4.00 96

10mm 4200 84 0.88 0.12

4.75mm 355 7.1 95.1 4.9

Pan 245 4.9 100 -

SIEVE ANALYSIS OF COARSE AGGREGATES FOR (AS PER IS: 383-1970)

PHYSICAL PROPERTIES OF FINE AGGREGATES

44

Characteristics Results obtained

Specific gravity 2.66

Water absorption (%) 1.0%

Fineness modulus 2.2

Grading zone Zone-II (IS:383-1970)

SIEVE ANALYSIS OF FINE AGGREGATES (AS PER IS: 383-1970)

45

IS sieve

designation

IS 383-1970

requirements for

zone II

wt retained

on sieve (gm)

%wt

retained

cumulative

%wt retained

%

passing

4.75mm 90-100 6 0.6 0.6 99.4

2.36mm 75-100 94 9.4 10 90.0

1.18mm 55-90 274 27.4 37.4 62.6

600 micron 35-40 234 23.4 60.8 39.2

300 micron 8-30 286 28.6 89.4 10.6

150 micron 0-10 79 7.9 97.3 2.7

0.75 micron 0-5 18 1.8 99.1 0.9

Pan 9 0.9 100 0.0

CHEMICAL PROPERTIES OF FLY ASH (CLASS-F)

46

CharacteristicsASTM Specified

values (%)Results

ObtainedSilicon dioxide (SiO2) + aluminium oxide (Al2O3) + iron

oxide (Fe2O3) (% by mass)70.00(Min) 91.69

Silicon dioxide (SiO2) (% by mass) 35.00(Min) 59.08Magnesium oxide (MgO) (% by mass) 5.00(Max) 0.36

Total sulphur as sulphur trioxide (SO3) (% by mass) 2.75(Max) 0.11

Available alkalis as sodium oxide (Na2O) (% by mass) 1.5(Max) 0.62Loss on Ignition (% by mass) 12(Max) 2.08Moisture content (% by mass) 3.0(Max) 2.0

Characteristics ASTM C 618 (Specified values)Results

ObtainedFineness Specific Surface (cm2/gm) 3200(min) 3800

Residue on 45 micron seive 34(max) 30.17

PHYSICAL PROPERTIES OF FLY ASH (CLASS-F)

PHYSICAL PROPERTIES OF SILICA FUME (ELKEM MICROSILICA)

Characteristics Specified valuesSpecific Gravity 2.5

Colour Pale grey to dark greyH2O (Moisture content when packed in %) 0 to 1

Specific Surface AreaAbout 2000m2/kg (approximately

10 times more than PC)

Particle sizeMostly fine spheres with a mean

diameter of 0.1 micronLoss on Ignition (%) 0 to 3

Retained on 45 micron sieve (%) 1 to 5Bulk Density- Densified (when packed in kg/m3) 500-700

47

CHEMICAL PROPERTIES OF SILICA FUME (ELKEM MICROSILICA)

Characteristics Specified Values

SiO2 (%) 90-96

Al2O3 (%) 0.5-0.8

MgO (%) 0.5-1.5

Fe2O3 (%) 0.2-0.8

CaO (%) 0.1-0.5

Na2O (%) 0.2-0.7

K2O (%) 0.4-1.0

C (%) 0.5-1.4

S (%) 0.1-0.4

48

TYPICAL PROPERTIES OF GLENIUM 233 (SP)

49

Characteristics Results Obtained

Aspect Light brown liquid

Relative Density 1.09 ± 0.01 at 25°C

pH >6

Chloride ion content < 0.2%

PROPERTIES OF STEEL REINFORCING BARS

CharacteristicsPermissible values as per

IS-800-1984

Results

obtained

Ultimate Stress (N/mm2) >485 625

Proof Stress (N/mm2) >415 482

Elongation (%) >14 20.5

50

MIX PROPORTIONS

51

Mix Type

Binder (Kg/ m3)

Cement (Kg/ m3)

Fly Ash (Kg/ m3)

Silica Fume (Kg/ m3)

Water (Kg/ m3)

20 mm (Kg/ m3)

10mm (Kg/ m3)

Sand (Kg/ m3)

SP (litre/ m3)

SCC_40 480 384 96 28.8 136.42 443.81 295.87 844.65 4.32

SCC_60 533 383.76 106.6 42.64 196.67 463.10 308.74 836.04 4.79

SCC_80 580 406 116 58 141.61 492.05 328.03 809.29 7.54

SCHEDULE OF BEAMS CASTED CASTING

52

Sr.

No.

Specimen

Desig.

Shear

span-

to-

depth

Ratio

ρt =

100Ast/

bd

Width

of

Beams

(mm)

Overall

Depth of

Beam,

mm

Effective

Depth (d)

(mm)

Nos. of

Long.

bars

provided

Effec.

span,

mm

Overall

length

provided

L (mm)

1 B1SCC40 1.5 3.1% 150 300 265 6 - Ø16 1395 1600

2 B2SCC60 1.5 3.1% 150 300 265 6 - Ø16 1395 1600

3 B3SCC80 1.5 3.1% 150 300 265 6 - Ø16 1395 1600

4 B4SCC40 2.5 3.1% 150 300 265 6 - Ø16 1925 2200

5 B5SCC60 2.5 3.1% 150 300 265 6 - Ø16 1925 2200

6 B6SCC80 2.5 3.1% 150 300 265 6 - Ø16 1925 2200

7 B7SCC40 3.5 3.1% 150 300 265 6 - Ø16 2455 2600

8 B8SCC60 3.5 3.1% 150 300 265 6 - Ø16 2455 2600

9 B9SCC80 3.5 3.1% 150 300 265 6 - Ø16 2455 2600

RESULTS AND DISCUSSION

FRESH STATE PROPERTIES OF THE SCC MIX

54J-Ring Test

Slump Flow Test

SCC MixSlump Flow

( mm) V funnel Flow

(sec) L box h2/h1

J Ring Test (mm)

U-Box (h2-h1) (mm)

Limits 650-800 mm 0-5 sec. 0.8-1.0 0-10 mm 0-30 mm

M40 690 4 0.81 5 25

M60 665 4.2 0.81 6 26

M80 690 4.1 0.98 3 22

55

U-BoxTest

V-Funnel Test L-BoxTest

56

Mix NameAvg. Compressive Strength (MPa)

7 Days 28 Days

M40 26.75 44.5

M60 40.1 64.1

M80 54.85 83.74

COMPRESSIVE STRENGTH OF SCC MIX

SPLIT TENSILE STRENGTH OF THE SCC MIX

57

FLEXURAL STRENGTH OF SCC MIX

SCC MixAvg. Split Tensile Strength (MPa)

7 Days 28 Days

M40 3.2 5.19

M60 3.9 6.68

M80 5.26 7.93

SCC MixAvg. Flexural Strength (MPa)

7 Days 28 Days

M40 3.5 5.25

M60 3.65 6.8

M80 5.26 7.74

EXPERIMENTAL SHEAR LOAD AND SHEAR STRESS OF SCC BEAMS

58

Sr. No

Specimen Desig.

% of long. Reinf,

ρt

Shear span-

to-depth Ratio (a/d)

Effective depth of beam, d

(mm)

Cube Strength,

MPa

Ultimate Shear Load,

Vu (kN)

Normalized Shear

Failure Load, Vun = Vu/√fcu

(KN)

Ultimate Shear Stress, Vus = Vu/bd (MPa)

Normalized Shear Stress,

(Vu/bd)/√fcu (MPa)

1 B1SCC40 3.1 1.5 265 44.5 112 16.79 2.82 0.4222 B2SCC60 3.1 1.5 265 64.1 155.25 18.11 3.65 0.4563 B3SCC80 3.1 1.5 265 83.74 167.8 18.34 4.22 0.4614 B4SCC40 3.1 2.5 265 44.5 51 7.65 1.28 0.1925 B5SCC60 3.1 2.5 265 64.1 63 7.87 1.58 0.1986 B6SCC80 3.1 2.5 265 83.74 78.3 8.56 1.97 0.2157 B7SCC40 3.1 3.5 265 44.5 35.3 5.29 0.89 0.1338 B8SCC60 3.1 3.5 265 64.1 46.2 5.77 1.16 0.1459 B9SCC80 3.1 3.5 265 83.74 56.2 6.14 1.41 0.155

COMPARISON OF EXPERIMENTAL AND PREDICTED SHEAR STRENGTH OF BEAMS

59

Specimen Desig.

long. Reinf.

(%)

Shear span-

to-depth Ratio (a/d)

Normalized Exp. Shear

Failure Load f, Vun

(kN)

Normalized Predicted Shear Failure Load (kN)

ACI Code

CAN Code

CEP FIP Zsutty

Equation Bazant

Equation

IS 456-2000 Code

B1SCC40 3.1 1.5 16.79 8.15 7.54 10.49 18.06 5.01 6.10B2SCC60 3.1 1.5 18.11 7.93 7.69 10.01 22.57 5.11 5.41B3SCC80 3.1 1.5 18.34 12.11 7.77 9.63 26.33 5.16 4.93B4SCC40 3.1 2.5 7.65 7.30 7.54 8.85 7.89 3.97 6.10B5SCC60 3.1 2.5 7.87 7.21 7.69 8.44 8.13 4.29 5.41B6SCC80 3.1 2.5 8.56 9.53 7.77 8.12 9.48 4.33 4.93B7SCC40 3.1 3.5 5.29 6.94 7.54 7.72 4.89 3.84 6.09B8SCC60 3.1 3.5 5.77 6.91 7.69 7.54 5.80 3.92 5.41B9SCC80 3.1 3.5 6.14 6.88 7.77 7.26 6.77 3.96 4.92

HYDRAULIC ACTUATOR & LOAD CELL

60

TYPICAL SHEAR FAILURE OF BEAM

61

B1SCC40_1.5

B3SCC80_2.5

CONT…

62

B7SCC40_1.5

63

GRAPH 1

64

GRAPH 2

65

GRAPH 3

GRAPH 4

66

RESULTS

Grade of Concrete a/d Ratio

Decrease in Normalized Shear

Strength (%)

M40 1.5 to 3.5 217.28

M60 1.5 to 3.5 213.85

M80 1.5 to 3.5 198.58

a/d Ratio

Grade of Concrete

Increase in Normalized

Shear Strength (%)

1.5 M40 to M80 9.22

2.5 M40 to M80 11.92

3.5 M40 to M80 16.06

67

The shear resistance of the SCC Beams was found to be strongly influenced by a/d ratio, showing decreasing shear capacities with increasing a/d ratio of the beams

It is also noticed that there is modest gain in shear strength with increase grade of the concrete.

CONCLUSIONS

1. Irrespective of the strength (40/60/80 MPa) the shear resistance of the SCC Beams was found to be strongly influenced by a/d ratio, showing decreasing shear capacities with increasing a/d ratio of the beams, as there is 217.28% increase in shear strength of M40 grade concrete beams for the change in a/d ratio from 1.5 to 3.5. Similarly there is 213.85% and 198.58% rise in the shear strength of M60 and M80 grade beams for change in a/d ratio from 1.5 to 3.5.

68

CONT….

2. Irrespective of the a/d ratio, with increase in the grade of the concrete, a modest gain in shear strength of just about 9-16% was observed as the compressive strength of concrete increased from 40 N/mm2 to 80 N/mm2. The lower shear strength of SCC is attributed to the development of lesser aggregate interlock as a consequence of the lower coarse aggregate quantity present in SCC beams.

3. The shear strength predictions of IS 456:2000 was conservative with respect to the a/d ratio of 3.5; the degree of conservatism is significantly lower when compared to the exp. shear strength of beams with a/d ratio of 2.5

69

70

IS 456-2000 does not take into account the influence of a/d ratio on shear strength and gives a constant value above M40 grade concrete and 3.0% percentage of longitudinal reinforcement.

4. As compared to experimental values ACI-318 code, it is relevant only for a/d ratio of 2.5. Whereas it underestimates the Normalized shear strength of SCC beams by 51 to 106% for shear span to depth ratio of 1.5 and over-estimates by 20% to 29% for a/d ratio of 3.5.

5. The Normalized shear strength prediction as per Canadian Code is also relevant for a/d ratio of 2.5 as compared to the experimental values, but not relevant for a/d ratio of 1.5 and 3.5. Canadian code has not considered the effect of a/d ratio of the beams.

6. The CEP-FIP model of shear strength prediction has considered the effect of beam size, % of longitudinal ratio and the a/d ratio of the beam, but still under-estimates the shear strength of the beams for lower a/d ratio beams.

71

CONT….

SCOPE OF FUTURE STUDY

The dimensional parameters such as depth and width of beam could be varied in order to check the influence of beam sectional area/depth on shear strength.

In this experimental investigation M40, M60 and M80 grade of concrete was used. Further investigation can be done for other high grades of concrete.

72

73

Thank you .............