Study Effect the Shear Spacing and Width of Beam on Behavour of Reinforced Concrete Wide Beams

ABSTRACT


Introduction
The use of wide concrete beams in the structural sector Framing technologies have improved in recent years.This is an adjustment that responds to the need for low-cost keys that reduce structural and building complexities.For instance, New high-rise building engineers are Frequently tasked with carrying column loads Free spaces in the pedestal or parking areas below are required from the tower portion above.Wide beams may provide suitable crosssection areas to provide the necessary capacity at a shallower depth than the slender beam system at parallel spacing in the plan.
Reinforced concrete wide beams are commonly used in commercial buildings, parking buildings, and large warehouse with large spans.The main use of reinforced concrete wide beams is to reduce story height (Kim, M. S., [1]. Ibrahim, A. M. et.al., [2].Eight specimens with dimensions of 215x560x1800 mm were examined.The variables studied struggle with the substitution of 10 mm diameter stirrups spaced at 125 mm by shearing steel plates providing an equal cross-section area for stirrups in the middle legs Height with circular openings of various thicknesses (3, 4 and 5 mm).Four specimens had no bubbles, and the others had no bubbles.This study has shown that shear steel plates are a good alternative for the replacement of stirrups and provide improved yield, eventually.Load and deflection (at duty load) with an average of 5 percent, 15 percent and 9 percent when using bubbles.
Said, M., & Elrakib, T. M. [3].The experimental program consisted of nine 29 MPa concrete beams tested with a shear span depth Ratio is equivalent to 3.0.One of the beams examined did not have a web reinforcement as a control specimen the flexicurity mode of failure was protected for all specimens to allow the shear mode of failure.The main parameters covered by this investigation are the effect of the life, spacing, quantity and yield stress of the vertical stirrups on the shear ability and ductility of the large beams tested.The study shows that the contribution of web reinforcement to shear capability is important and is directly proportional to the volume and spacing of the shear reinforcement.
Lubell, A.S., et.al., [4], stated that the concrete large, wide beams, and thick slabs are used as transfer elements when the structural depth must be kept to a minimum value, these members have large cross sectional are which is used to resist shear demands; however, shear reinforcement might be still required.Wide beams are the most desired construction members that can be used for low depth structural members, it can provide small depth in the cross-sectional area, moreover, it can be used when semi unequal loads in the plan should be supported, where a heavy transfer slab can prove to be an expensive solution.
Kim, M. S., [1] made experimental program to study the shear behavior of concrete wide beams taking into account the reinforcement spacing, and support conditions.From this experimental program shear strength was estimated by a developed equation.The results showed that when the transverse reinforcement spacing increased the shear strength decreased.
Abass, A. L. et.[5] al The current study presents the results of four full-scale wide RC beams in order to study their shear behavior and investigate the effectiveness of carbon fiber reinforced polymer (CFRP) when using as shear reinforcement to improve the shear capacity of wide RC beams, The results showed an increasing in ultimate load of strengthened beams with inclined, vertical CFRP and beam with shear reinforcement by (19.9%), (7.14%) and (39.8%) respectively as compared with the control beam, and this results means possibility of replacing the internal shear reinforcement with externally bonded CFRP.
Sherwood, E. G. et.al, [6] this paper discusses nine recent issues Tests designed to resolve these issues.The width of the Member was Finding to have no major impact on shear stress at failure for one-way slabs and wide beams.In addition, the presence of Reduction and temperature reinforcement did not have an effect on the One-way shear capacity.Based on the findings of the experiment and Related narrow slab strip tests in the literature, the paper concludes That the provisions of the ACI 318-05 Shear can result in insufficient levels of Safety for both thick slabs and wide beams 2.

2.The significance of the research
The focus of the study is behavior of shear reinforced concrete wide beam whin increase the spacing between stirrups and increasing the width of beam, this study handled the Crowding between shear reinforcement and reduced time and cost, also this study Explained The effect of increase beam width on shear capacity, and study the effect that to: load, deflection and crack patterns.

Details of the experimental tests
The experimental program consists of eight beams in two groups each group four beams.with nominal compressive strength of (f c) =30MPa, Concrete tensile strength (ft) =2.59MPa, Concrete flexural strength (fcr) =3.77MPa, Ordinary Portland Cement (OPC)(Type-I) (TASLUJA-BAZIAN) was used for all test beams the chemical and physical tests were in accordance with the Iraqi specification (Iraqi standards/No.5,1984).Al-Siddur natural sand with a maximum size (4.75mm) has been used for this purpose, crashed gravel with a maximum size (19mm) of the AL-Suddor fields has been used in the work.each was tested in a four-point loading arrangement.All beams were constructed in the laboratory of the Engineering College of the University of Diyala.All beams in group one was 500 mm wide, 200 mm deep, 1600 mm long, and shear reinforcement spacing (d/2) (control beam), and other three beams with variable shear reinforcement spacing (S, 3/4d, d), where S=0.65d in this group, these group all beams are identical in width to depth ratio (2.5), tension steel reinforcement area (As=1280mm2), This beam with flexural reinforcement; (7 Ø 16) and (2Ø 12) in the tension and compression zone of RC beams respectively.
Group two consists of four beams one beam has shear reinforcement spacing (d/2) (control beam), and other three beams with variable spacing shear reinforcement (S, 3/4d, d), where S=0.55d in this group, these group all beams are identical in width to depth ratio (3), tension steel reinforcement area (As=1536mm2), This beam with flexural reinforcement; (8 Ø 16) and (2Ø 12) in the tension and compression zone of RC beams respectively.
LVDT gauges were used for deflection reading, the data logger was used to read the steel and concrete strains and measurements of micro cracks were used to measure crack widths at loading stages due to failure of beams.Development of deflection, strain and crack width at each stage was measured on the beams to track the growth, sequence and pattern of cracking.as shown in Table (1) and plates (1A, B) and (2A, B).

Results and discussion
Strength characteristics of all specimens (crack, ultimate load and deflection at crack, Failure mode) shown in Table (2).This can be seen in Table (3) that the measured flexural crack load increased by 11.7 % for all beam (WB2-G1, WB3-G1 and WB4-G1) respectively compared with WB1-G1 Because the lower the Ultimate load, the later the cracks will appear.and the diagonal crack load give same result in WB2-G1 exactly and increased by14.3% in WB3-G1, but WB4-G1 decreased by 8.3% compared with control beam.All results were close and the differences did not exceed 12% whether they were increased or decreased.

Ultimate load
As shown in the table (3), all beam They gave close results that did not exceed 10%, they beam decreased by (4.25%, 6% and 9.5%) for WB2-G1, WB3-G1 and WB4-G1 respectively compared with WB1-G1, this descent into the final load is normal due to the increased the shear reinforcement spacing, that means the effect of increasing the distance between stirrups from (d/2 to d) very small for reinforcement concrete wide beam.

Load -Deflection behavior
From Table (3) the deflection in WB1-G1 control beam 13.1mm, the other beams decreased compared with control beam by 6.9%, 20.6% and 22% for WB2-G1, WB3-G1 and WB4-G1 respectively, that means the lower the load, the less deflection Figure (3) show the Relationship between load and deflection for all beams in this group, from this figure it can be noted All beams have the same behavior, especially up to 300 kN loads.

Crack pattern
The beams tested at different stages of loading are shown in detail in Figure (4) and plate (1).The numbers in red color inside the diagram represent the development of the cracks at each loud, while the black numbers under the cracks represent the sequence of the appearance of the cracks during the test.

First crack width and number of cracks
The crack width of the first crack at cracking and ultimate load can be seen from Table (4).In the crack load WB3-G1 gave the lowest width among the beams, as it decreased by 33% compared with control beam, While the WB2-G1 gave the highest width as it increased by 25% compared with control beam, but the WB4-G1 give same width with control beam, in ultimate load all beams width increased relation to WB1-G1, the WB2-G1 and WB3-G1 increased with the same increase By 50%, but WB4-G1 increased by 41.7% compared with control beam, the number of bending cracks is equal across all beams as a result of the same properties of concrete and longitudinal reinforcing , the number of shear cracks increased in WB2-G1 by 8.3% , and decreased by 10% in WB3-G2 and WB4-G2 compared with control beam, The first crack occurred randomly in the middle third of the span it wasn't exactly the widest.

Spacing of shear cracks
It can be seen from Table (4) the shear spacing distance in minimum and average decreased in WB2-G1 and WB4-G1 by (13.6% and 41%) in minimum and (5.7% and 8.6%) in average compared with WB1-G1, but in maximum spacing distance all beams increased compared with the control beam by (5.5% ,16.8% and 9%) for WB2-G1, WB3-G1 and WB4-G1 respectively.

Ultimate load
The main objective of this study is to determine the effect of the ultimate load of concrete reinforced wide beams whin increase spacing of shear from (d/2) to (3/4d, S and d), and to compare it with the references RC beam specimens.The ultimate load of the tested beams in this group was shown table (5).The results show that the (WB2, WB3 and WB4) give Very close values Not exceed 16%compared with (WB1) (control beam).

Load -Deflection Behavior
From Table (5) the deflection in WB1-G2 control beam 16.6mm, the WB3-G2 and WB4-G2 decreased compared with control beam by 22.9% and 31.3%, but WB2-G2 give close increasing with WB1-G2 by 2.4, Figure (5) Show the relationship between load and deflection for all beams in this group.

Crack pattern
The beams tested at different stages of loading are shown in detail in Fig. (6) and plate (2), The numbers in red color inside the diagram represent the development of the cracks at each loud, while the black numbers under the cracks represent the sequence of the appearance of the cracks during the test, New in this group is the increase in the width to depth ratio from 2.5 to 3.

First crack width and number of cracks
Table (6) displays the crack width of the first crack at cracking and the ultimate load which was considered to be the maximum crack width compared to other cracks.The crack width at first crack increase in WB2-G2, WB3-G2 and WB4-G2 by 27% at Average.And the crack width at ultimate load increase by 14.6% at Average in WB2-G2 and WB3-G2 compared with control beam, but WB4-G2 decreased by 8.5%.The number of flexural cracks Equal in all beams except WB2-2 increase by 14%.While number of shear cracks increased in wide beam WB2-G2 and WB3-G2 by 10% and the WB4-G2 are given the same number of cracks cumbered with WB1-G2.

Spacing of shear cracks
From Table (6) it can be seen the effect the increase maximum spacing of shear reinforcement, minimum, maximum and average crack spacing increased in WB2-G2 and decreased in WB3-G2 and WB4-G2, minimum spacing increased by (21% and maximum spacing increased by 17.8%, and average spacing increased by 5.5% for WB2-G2 compared with control beam, for WB3-G3 and WB4-G2 at minimum, maximum and average spacing decreased by (50%), (20.6%) and (18.8%) respectively compared with the control beam.

Comparison the results of the groups one and two
In fact, the main difference between Group One and Two was related to the increase in beam width from 500mm in group One (the width to depth ratio 2.5) to 600mm in group Two (the width to depth ratio 3), Tables (7) Explain the comparison between the strength characteristics of Groups One and Two.From table (7) noted the first flexural and diagonal crack decreased in all beams of group two by (11.8,15.8,22.2,8)% in flexural and by (28.6,35.7,51,51.4)% in diagonal for (WB1-G2, WB2-G2, WB3-G2and WB4-G2) respectively compared with group one, the ultimate load and ultimate deflection increased in all beams in group two by (16.7, 20, 9.4, and 10.6 ) % in ultimate loud and by (21, 28.2, 18.7, 16.7)% in ultimate deflection for (WB1-G2, WB2-G2, WB3-G2and WB4-G2) respectively compared with group one, as shown in figure (7,8,9and 10).

Conclusions
Increasing the spacing of shear reinforcement from (d/2 in WB1-G1) control beam to (0.65d ,3/4d and 1.0d) in WB2-G1, WB3-G1and WB4-G1 gives close results in RC wide beam when use width to depth ratio 2.5 (width of beam 500mm) (group one) in all the following tests: 1.The ultimate shear load gives very close value with control beam (spacing d/2), all beams decreased by 4.25%, 6% and 9.5% respectively 2. the first flexural crack increased by 10.5%, 5.6% and 15% respectively, the first diagonal crack too increased in all beams by 8.5%, 10.7% and 12.7% for respectively.3. The ultimate deflection decreased in all beams by average 16.5%.4. The width of first flexural crack increased in WB2-G1 by 25% and decreased in WB3-G1 by 33%, and the WB4-G1 give same width with WB1-G1. 5.The number of flexural cracks was equal in all beams, the number of shear cracks increased in WB2-G1 by one crack and decreased by one crack in WB3-G1 and WB4-G1.
When increase the width to depth ratio from 2.5 to 3 (the width from 500mm to 600mm) (group two) notice the following : 1.The increase width in group two give increase ultimate loud by average 14.25% for all beams compared with group one, when increasing the spacing between stirrups in this group WB2-G2 give same ultimate load with WB1-G2 and the WB3-G2, WB4-G2 decreased by 13.5% and 16.6% respectively compared with WB1-G2 control beam.2. The increase width in group two It led to the emergence of the first flexural cracks early by average 14.25% for all beams compared with group one, increasing the shear spacing in this group give increased in WB2-G2 and WB4-G2 by 5.9% and 13% respectively and decreased in WB3-G2 by 12.5% compared with WB1-G2,The first diagonal crack in beams of width 600 mm (group two) decreased in all beams by average 41.7% compared with beams of width 500 mm (group one), but whin increasing the shear spacing in this group give decreased in all beams by 1.5%, 23% and 22% for WB2-G2, WB3-G2 and WB4-G2 respectively compared with WB1-G2 control beam.3. The increase width in group two give increase ultimate deflection in all beam by average 22.6% except WB4-G2 (spacing 1.0d) decreased by 16.7% compared with beams in group one (width 500mm), increasing the shear spacing in this group give decreasing in ultimate deflection by 27% compared with WB1-G2 control beam.4. The increase width in group two give increase in width of first flexural crack by average 32% compared with beams in group one (width 500mm), increasing the shear spacing in this group gives increased for all beams by average 27.3 % compared with WB1-G2 control beam. 5.The increase width in group two give increase in number of flexural cracks by average 2 cracks, the diagonal cracks increased too by average 2 cracks, increasing the shear spacing in this group gives decreased by 1 crack in WB3-G2 and increased by 1 crack in WB4-G2 and WB2-G2 give same number of crack compared with WB1-G2 control beam and the number of diagonal cracks decreased in WB2-G2 and WB3-G2 by 2 cracks and the WB4-G2 gives same number of diagonal cracks compared with WB1-G2 control beam.6.The increase width in group two give increase in average spacing between shear cracks by 14% in WB1-G2 and WB4-G2 and decreased by 13.5% in WB2-G2 and WB3-G2 compared with beams in group one (width 500mm), increasing the shear spacing in this group gives increased by 5% in WB2-G2 and decreased by 25%and13% for WB3-G2 and W4-G2 respectively compared with WB1-G2 control beam.

Figure 4 .
Figure 4. Plate (1) cracking patterns of specimens of Group One

Figure 2 .
Figure 2. Plate (1) cracking patterns of specimens of Group One

Figure 5 .
Figure 5. Load-Deflection Curve of wide beams in Group Two

Figure 6 .
Figure 6.Plate (2) cracking patterns of specimens of group Two

Table 1 .
Details of beams in groups one and two Plate (4-1A): Beam section for group one

Table 2 .
Strength characteristics of specimens tested

Table 3 .
Comparison of the strength characteristics of Group One Load-Deflection Curve of wide beams in Group One

Table 4 .
First crack width, number and spacing of cracks for Group One

Table 5 .
Comparison of the strength characteristics of Group Two

Table 6 .
First crack width, number and spacing of cracks for group two

Table 7 .
Comparison between the strength characteristics of groups one and two

Table 8 .
First crack width, number and spacing of cracks for Groups One and Two