Chapter 2: General Discussion
2.1 Research Design
2.1.2 Details of Deep Beams
gravity of the RCAs compared to that of the NAs, in addition to the inclusion of steel fibers in some mixes, the corresponding volumes of the mixes containing RCAs/steel fibers slightly changed. This difference in volume was trivial and negligible, as shown in the last column of Table 2.2. Mixes were labeled as RX-SFY, where ‘X’ denoted the percentage of RCAs, relative to total amount of coarse aggregate, and ‘Y’ represented the steel fiber volume fraction (vf). For instance, the control mix without RCAs and steel fibers is designated by R0-SF0. The RCA replacement percentage (RCA, %) was taken as 0%, 30%, 70%, 100%, while steel fiber volume fraction percentage (vf, %) was altered between 0, 1, 2 and 3%.
Table 2.2: Mix proportions of different concrete mixes
Mix Designation
Mass (kg)
Volume (m3)
Cement RCA NA
Dune
Sand Water Steel Fibers Total
R0-SF0 470 0 1130 570 230 0 2400 1.00
R30-SF0 470 339 791 570 230 0 2400 1.01
R70-SF0 470 791 339 570 230 0 2400 1.02
R100-SF0 470 1130 0 570 230 0 2400 1.03
R30-SF1 470 339 791 570 230 78 2478 1.02
R70-SF1 470 791 339 570 230 78 2478 1.03
R100-SF1 470 1130 0 570 230 78 2478 1.04
R30SF2 470 339 791 570 230 156 2556 1.03
R70SF2 470 791 339 570 230 156 2556 1.04
R100SF2 470 1130 0 570 230 156 2556 1.05
R30-SF3 470 339 791 570 230 234 2634 1.04
R70-SF3 470 791 339 570 230 234 2634 1.05
R100-SF3 470 1130 0 570 230 234 2634 1.06
2.1.2 Details of Deep Beams
under four-point loading. The large-scale deep beam specimens were divided into two groups S and N. Group S included seven solid RC deep beam specimens having a/h of 1.6. The beams in this group are designated using the notation SRX-SFY. The group N included seven RC deep beam specimens with a/h of 0.8 and web openings in their shear spans. The beams in this group are designated using the notation NRX-SFY. In the deep beam specimen notations, ‘SRX’ stands for solid deep beams with ‘X’ RCA replacement percentage, ‘NRX’ stands for deep beams with openings and with ‘X’ RCA replacement percentage and ‘Y’ is the steel fiber volume fraction (vf). The notation SRX-SFY-S and NRX-SFY-S designate beams with internal shear reinforcement. In each group, two beams were made of NAs without steel fibers. One of them included minimum conventional steel stirrups while the other one was kept with neither steel stirrups nor steel fibers. The remaining five beams in each group were made of 100% RCAs.
Out of these five beams, one beam had neither steel stirrups nor steel fibers, one beam had minimum conventional steel stirrups, and three beams contained steel fibers at vf of 1, 2, and 3%.
Table 2.3: Test matrix of the deep beam specimens
Group Specimen Designation
a/h RCA (%)
vf (%)
Presence of Traditional Shear Reinforcement
Presence of Openings
S
SR0-SF0 1.6 - - - -
SR0-SF0-S 1.6 - - -
SR100-SF0 1.6 100 - - -
SR100-SF0-S 1.6 100 - -
SR100-SF1 1.6 100 1 - -
SR100-SF2 1.6 100 2 - -
SR100-SF3 1.6 100 3 - -
N
NR0-SF0 0.8 - - -
NR0-SF0-S 0.8 - -
NR100-SF0 0.8 100 - -
NR100-SF0-S 0.8 100 -
NR100-SF1 0.8 100 1 -
NR100-SF2 0.8 100 2 -
NR100-SF3 0.8 100 3 -
2.1.2.2 Test Specimens
Figure 2.5(a) and Figure 2.5(b) show the concrete dimensions and details of reinforcement of deep beam specimens in group S, with and without traditional shear reinforcement, respectively. Figure 2.6(a) and Figure 2.6(b) show the concrete dimensions and details of reinforcement of deep beam specimens in group N, with and without traditional shear reinforcement, respectively. In the deep beam specimens of group N, two circular openings, one in each shear span, were placed symmetrically about the midpoint of the beam to fully interrupt the natural load path as shown in Figure 2.6. The center of each opening was located at the mid-height of the beam (250 mm below the top surface) and at the middle of the shear span (200 mm away from the center of the support). This was done to induce an extreme discontinuity in the shear span. The openings had a diameter of 150 mm which corresponded to an opening height-to-depth ratio (h0/h) of 0.3. All deep beam specimens in groups S and N had a width of 150 mm and a depth of 500 mm. The beams in group S had a length of 3300 mm and an effective span of 2900 mm. A distance of 200 mm from each side of the beam was left free to provide a sufficient development length for the longitudinal steel reinforcement. The a/h was 1.6, resulting in a shear span of 800 mm and a constant moment region of 1300 mm. The beams in group N had a length of 2500 mm and an effective span of 2100 mm. Accordingly, the value of a/h was 0.8, resulting in a shear span of 400 mm and a constant moment region of 1300 mm.
The beams were reinforced with four No. 25 (25 mm in diameter) longitudinal steel reinforcing bars at the tension side and two No. 25 (25 mm in diameter) at the compression side. Based on testing of three replicate steel samples, the average measured yield strength of the No. 25 was 539 MPa, whereas the ultimate tensile strength was 649 MPa. The elastic modulus of
the reinforcing steel bars was 200 GPa. The concrete cover to the center of the steel reinforcement was 50 mm, rendering an effective depth (d) of 450 mm. This arrangement of steel reinforcement was decided to ensure that a shear mode of failure would dominate. The traditional shear reinforcement, when employed, was detailed in accordance with the minimum shear reinforcement provisions of ACI 318-14 (2014) for deep beams, resulting in two curtains of No.5 (5 mm in diameter) plain steel bars spaced at 80 mm in both vertical and horizontal directions. Based on testing of three replicate steel samples, the average measured yield strength of the No. 5 was 505 MPa, whereas the ultimate tensile strength was 543 MPa. Steel plates (150 mm x 150 mm x 20 mm) were placed at the load and support points.
Figure 2.5: Details of deep beam specimens of group S (dimensions are in mm): (a) A beam without traditional shear reinforcement; (b) A beam with traditional shear reinforcement
(a) (b)
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Figure 26: Details of deep beam specimens of group N (dimensions are in mm): (a) A beamwithout traditional shear reinforcement; (b) A beam with traditional shear reinforcement (a)(b)
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