SHEAR STRENGTH OF SELF COMPACTED CONCRETE WITH AND WITHOUT STIRRUPS AT DIFFERENT SHAPES 3

Eighteen self-compacted concrete (SCC) beams at different shaped were designed and tested to determine the effect of using SCC on the shear strength under two concentrated loads. The tested beams were divided into three groups according to the shape of the cross section, rectangular sections, T-sections and I-sections. Each group was divided into two series with and without stirrups. All the series beams have the same longitudinal steel ratio, gross section area and clear span to effective depth ratio but have different values of compressive strength (fc ). It was found that the ultimate shear strength predicated by ACI 318M-08 is conservative relative to the experimental values, the ultimate shear strength of SCC beams with and without stirrups increased when the compressive strength of the SCC increased. When the compressive strength increased from (29.36 to 49.2 MPa) at clear span to effective depth ratio (ln/d) equal to 5.84 the ultimate shear strength of SSC beams without stirrups increase about 31.22%,55.55%and 18.931% for rectangular, Tsection and I-section respectively ,while the ultimate shear strength of SCC beams with stirrups increased 17.17%,28.57%and 15.584% for rectangular, Tsection, I-section respectively .The ultimate shear strength of SCC rectangular beams with stirrups increased about 85.41%, 68.96% and 65.52% as compared with ultimate shear strength without stirrups at compressive strength 29.36,41.42 and 49.2 MPa respectively, the ultimate shear strength of SCC T-beams with stirrups increased about 133.3%, 97.916% and 92.857% as compared with ultimate shear strength without stirrups at compressive strength values of 29.36,41.42 and 49.2 MPa, respectively . Finally the ultimate shear strength of SCC I-beams with stirrups increased about 44.6%, 38.1% and 40.53% as compared with ultimate shear strength without stirrups at compressive strength values of 29.36,41.42 and 49.2 MPa respectively.

and developments were made to improve the performance of concrete, especially in term of strength and workability.Engineers found new technology of concrete called self-compacting concrete.The main objective of the work described in this study is to investigate and to get more information and more understanding about the shear strength of self-compacting concrete beams with and without stirrups at different shapes.

3-TEST PROGRAM: 3.1 Description of specimens:
The tested beams were divided into three groups according to the shape of the section rectangular sections, T-sections and I-sections.each beam of the first group has overall length 1140 mm, the cross sectional dimension of 100 mm (width of beams) by 170 mm (total depth).The longitudinal steel reinforcement consist of six bar (diameter of the bar 8 mm, with area of 50.265mm 2 ) laid in two layers at bottom and two bars (diameter 4 mm, area of 12.566 mm 2 ) laid in one layer at top.The internal steel stirrups are 4 mm in diameter (12.566 mm 2 ) spaced 73 mm center to center as shown in Fig. (1).Beams of the second group consist of T-cross sections have overall length 925 mm, the cross sectional dimensions of 220 mm (width of flange) by 200 mm (total depth).The thickness of web is (60) mm and the thickness of flange is (50) mm.The longitudinal deformed steel reinforcement consist of four bars of 8 mm diameter laid in two layers at bottom and four plane bars of 4 mm diameter laid in one layer at top.The internal steel stirrups are 4 mm in diameter centrally spaced 89 mm as shown in Fig. (2.The third group consists of I-sections beam each of 1443mm overall length, The cross section is of 250 mm total depth and 200mm flange width .The longitudinal steel reinforcement consists of four (8 mm diameter bar, of (50.265mm 2 area) laid in one layer at bottom, and four 4 mm diameter bars of (12.566 mm 2 area) laid in one layer at top.The internal steel stirrups are 4 mm in diameter (12.566 mm 2 area ) at spacing 115 mm on center as shown in Fig. (3).The total description of the beams used in this study is listed in Tables (1)and (2 5/1984 [2] , Tables (2) and (3) show the chemical and physical properties of the used cement. Fine Aggregate: Al-Ukhaider natural sand was used.Which complies with the Iraqi Standard Specification No.45/1984, [3] zone(2).The specific gravity, sulfate contents (SO3) and absorption of the used sand were 2.66,0.4% and 1.7% respectively. Coarse Aggregate: Crushed gravels of 10mm maximum size from Al-Nibaee area was used in this study.This complies with the Iraqi Standard Specification No.45/1984, [3] The specific gravity, sulfate contents(SO3) and absorption of the used gravel were 2.65,0.07%and 0.57% respectively. Water: Ordinary potable water was used throughout this work for both mixing and curing of concrete. Steel Reinforcement: Deformed longitudinal steel bars with 8mm and 4mm nominal diameters were used in this study.Reinforcing bars were tested to determine the yield stress of 8mm and 4mm which were found to be 400 and 350 MPa respectively. Limestone Powder: Fine limestone powder (locally named as Al-Gubra) of northern origin with fineness (3100 cm²/ gm) was used as a filler for concrete production for many years.It was found to increase workability and early strength, as well as to reduce the required compaction energy.The increased strength is found particularly when the powder is finer than the Portland cement (4) .The cement in SCC mixes is generally partially replaced by fillers like lime stone powder in order to improve certain properties such as;  avoiding excessive heat generation,  enhancing fluidity and cohesiveness,  enhancing segregation resistance,  Increasing the amount of powder (cement +filler), to become more economical than using cement alone. Superplasticizer (5) : To produce SCC, a superplasticizer known as (High Water Reducing Agent) based on polycarboxylic ether is used; it has the trade mark of Glenium 51, which is free from chlorides and complies with ASTM C494, types A and F. It is compatible with all Portland cements that meet recognized international standards.Table (4) shows the typical properties of Glenium 51.

Mix Design for Self-Compacted Concrete
Mix proportioning is more critical for SCC than for NSC (normal strength concrete) and HSC (high strength concrete).Many trials are carried out on mixes incorporating superplasticizer by increasing the dosage of the admixture gradually, adjusting the w/c ratio to ensure the self-compact ability (6) .Table (5) indicates the mix proportion of SCC mixes.For each concrete mix, three standard cube specimens (150×150×150) mm are taken, they were tested at 28 days of age, the test result of fresh concrete properties are shown in Table (6) these results are within the acceptable criteria for SCC given by ACI committee-363 (7) and indicate excellent deformability without blocking.

TEST PROCEDURE OF TESTED BEAMS:
All the beam specimens were white washed in order to aid the observation of the crack development during the testing.They were tested under gradually increasing load up to failure under two point symmetric top loading by the universal-Testing machine (MFL systems) in the structural laboratory of the college of the engineering , Al-Mustansiriya university as shown in Fig.( 5).The tested beam specimens were simply supported at ends over an effective span.A dial gauge of (0.01 mm) accuracy with (30 mm) capacity was fixed at the middle of the bottom of the beam to measure the mid span deflection, the test set-up is shown in Fig. (4).Loading procedure was started by the application of single point load from the testing machine to the upper midpoint of the loading bridge.The single load was then divided equally between the two point loads that were transferred to the concrete beam through two (Ф 30 mm) steel bars loaded at the end of the bridge.Beam specimens were placed at the testing machine and adjusted so that the centerline, supports, point loads and dial gauge were fixed at the correct and proper locations.Loading was applied in small increments of (4 kN).At each load stage the deflection readings at the mid span was recorded.The loading increments were applied until failure.

SHEAR STRENGTH OF BEAM IN CODE PROVISIONS:
ACI 318M-08 estimates the nominal shear capacity (Vn) of beam as follows (9) : Where:-Vc and Vs are shear transfer capacity of concrete and shear reinforcement respectively; Mu and Vud are factored moment and shear force; ℓw = As/bwd is the longitudinal bottom reinforcement ratio; As is the longitudinal bottom reinforcement area; bw is the width of the web; d is the effective depth; Av is the vertical shear reinforcement area, S is the spacing between the vertical stirrups reinforcement;   ′ is the compressive strength of concrete and y f the yield strength of shear reinforcement.The clear span to effective depth ratio (ln/d)is the main variable in this research , Eq.(3) will be used since the shear stress at cracking depends on the bending moment and shear force at critical section ratio (Vud/Mu)and the longitudinal steel ratio (ℓw) that lead to reduce the shear crack and improved the ultimate strength.

RESULTS:
6.1 Load-Carrying Capacity of the Tested Beams.
The relationship between the applied load and the deflection for the tested beams is shown in Fig. ( 6) to Fig. (11).At every stage of loading, the deflection at mid-span is obtained by using dial gage, it can be noticed that:  During the early stage of loading no interface slip was recorded and this continue until the applied loading was equal to first crack loading approximately, Beyond that loading each beam behaved in a certain manner. The ultimate shear strength obtained from testing of SCC beam specimens were compared with that obtained by using the ACI code provisions and given in Table (8).By the inspection of this table it can be noted that the ultimate shear strength predicated from ACI 318M-08 is conservative in comparison with experimental values because the SCC will improves durability, and increases bond strength (10) . The ultimate shear strength of SCC beams specimens without stirrups increased when the compressive strength of the SCC increased as shown Fig

Failure
As is expected, all the tested beams failed in shear as shown in Fig. ( 17) and Fig. (18),where the diagonal cracks formed independently.The beam specimens remained stable after such cracking.Further increase in shear force caused the diagonal crack to penetrate into the compression zone at the loading point, until eventually crushing failure of concrete occurred there (11) .
Based on the tested results of this experimental investigation for evaluation of shear strength of SCC beams, the following conclusions are drawn:  The ultimate shear strength predicated from ACI 318M-08 is conservative prediction than the experimental values for the SCC beams. The ultimate shear strength of SCC beams without stirrups increased when the compressive strength of the SCC increased.
) and the test set-up is shown in Fig. (4) 3.2 Materials: General description and specification of materials used in the tested beams are listed below; tests are made in the National Center for Construction Laboratories and Research  Cement: Ordinary Portland cement type I produced at northern cement factory (Tasluja-Bazian) is used throughout this investigation which conforms to the Iraqi specification No.

Fig
Fig. (1): Details of rectangular section (all dimensions in mm) Fig. (4): Schematic diagram of test set-up

Fig
Fig. (10): Load -deflection curve for SCC I-section beam specimens without stirrups

Fig
Fig. (13): Effect of compressive strength.(  ′ ) on the ultimate shear strength for SCC beam specimens with stirrups

Fig
Fig. (14): Effect of absence of stirrups on the the ultimate shear strength at compressive strength (  ′ ) =29.36 MPa.

Fig
Fig. (15): Effect of absence of stirrups on the ultimate shear strength at compressive strength (  ′ ) =41.42 MPa.

Fig ( 17 )
Fig (17): Crack pattern of the tested SCC beam specimens The ultimate shear strength of SCC beam specimens with stirrups increased when the compressive strength of the SCC increased as shown in Fig.(13).When the compressive strength increased from (29.36 to 49.2 MPa) at clear span to effective depth ratio (ln/d) of value 5.84 ,the ultimate shear strength increased about 17.17%,28.57%and15.584%forrectangular,T-section,I-sectionrespectivelyas given in table(10).Theultimateshearstrength of SCC beam specimens with stirrups is greater than these without stirrups as shown in Figs.(14),(15) and.(16).The ultimate shear strength of SCC rectangular beams with stirrups increased about 85.41%, 68.96% and 65.52% as compared with ultimate shear strength without stirrups at compressive strength 29.36,41.42and 49.2 MPa respectively.The ultimate shear strength of SCC T-beams with stirrups increased about 133.3%, 97.916% and 92.857% as compared with ultimate shear strength without stirrups at compressive strength values 29.36, 41.42 and 49.2 MPa respectively, while the ultimate shear strength of SCC I-beams with stirrups increased about 44.6%, 38.1% and 40.53% as compared with ultimate shear strength without stirrups at compressive strength values 29.36, 41.42 and 49.2 MPa, respectively as given in Table (11).

Table ( 1
): Total Description of the Tested Beams without Stirrups

Table ( 2
): Total Description of the Tested Beams with Stirrups

Table ( 3
): Chemical Composition of the Used Cement Table (4): Physical Properties of the Used Cement

Table ( 9
): Effect of Compressive Strength (  ′ )) on the Percentage Increase in the Ultimate Shear Strength of Tested Beams without Stirrups

Table ( 10 ) :
Effect of Compressive Strength (  ′ )) on the Percentage Increased in the Ultimate Shear Strength of Tested Beams with Stirrups.Effect of Absence of Stirrups on the Percentage Increased in the Ultimate Shear Strength.