INTRODUCTION AND LITERATURE REVIEW
3.3 DESCRIPTION OF THE SPECIMEN
In the present study, six types of specimens, namely, (a) Beam-column joint with beam weak in flexure : control, (b) Beam-column joint with beam weak in shear : control, (c) Beam-column joint with column weak in shear : control, (d) Beam-column joint with beam weak in flexure : retrofitted, (e) Beam-column joint with beam weak in shear : retrofitted and (f) Beam-column joint with column weak in shear : retrofitted, were considered. In each type, three geometrically similar specimens : full scaled, two third scaled and one third scaled sizes were considered. The naming of the specimens was done TH-951_06610408
with five alphabets, the first three alphabets cover the deficiency type, the fourth for size and the fifth for type of specimens, which can be either control or retrofitted. For example, BWFLC stands for beam weak in flexure large control specimen, similarly BWSMR stands for beam weak in shear medium retrofitted and CWSSC stands for column weak in shear small control specimens.
3.3.1 Beam Weak in Flexure : Control Specimen
The detailing of all the bam weak in flexure : control specimens has been shown in Fig.
3.2. The cross section of the column was chosen as 300 mm × 300 mm and that of the beam as 300 mm × 360 mm for the full scaled model. Four numbers of high strength deformed bars (Yield strength 500 : MPa) of 20 mm diameter was used as reinforcement in column and beam. Lateral ties of 12 mm diameter high strength deformed bar at 75 mm c/c spacing was used in the special confinement zone of the column as per guidelines proposed by IITK-GSDMA document [2006]. In the remaining part of the column, lateral ties of 6 mm diameter mild steel bars were used with a spacing of 150 mm c/c. In the beam, shear reinforcement of 8 mm diameter high strength deformed bar with a spacing of 75 mm c/c was used near the beam column joint for a length of 675 mm and 6 mm diameter with a spacing of 120 mm c/c was provided for the remaining part of the beam.
The beam was designed as under reinforced beam following the provisions of IS: 456 [2000], IS: 1893 [1993] and IITK-GSDMA guidelines for design and detailing of buildings [2006]. The strong column-weak beam principle was adopted for the design of the beam-column joint. Moreover, the beam was idealised as a cantilever beam for arriving at the tip failure load of beam. The details design is furnished in Appendix-B.
Adequate shear reinforcement was provided to avoid shear failure. Two third and one third scaled specimens were proportionately scaled down in all the three dimensions. The diameter of the reinforcing bars, development length, length of special confinement zone, cover of reinforcement etc. were also scaled down appropriately. These specimens were TH-951_06610408
cast with concrete of target cube strength of 30 N/mm2. The detailed descriptions of all the specimens are given in Table 3.1. In the same table, the detailed about column weak in shear specimens are also given, which will be described in subsequent section.
3.3.2 Beam Weak in Shear : Control Specimen
The specimens under this category are exactly similar in all respect to that of beam weak in flexure : control specimens, except the shear reinforcement in beams. Amount of shear reinforcements were reduced to make the beam weak in shear. In BWSLC, 2-legged 6 mm diameter mild steel bars with a spacing of 600 mm c/c were provided as shear reinforcement. However, only the first two stirrups near the joint was placed with spacing of 600 mm c/c in order to maintain a pre-defined failure location and for the remaining part of the beam the spacing was reduced to 240 mm c/c. Shear reinforcement was proportionately reduced for scaled down models maintaining geometric similarity. The dimensions and reinforcement details of all the three specimens are shown in Fig. 3.3.
3.3.3 Column Weak in Shear : Control Specimen
The specimens under this category were cast by comparatively weaker grade of concrete than those used in earlier cases in order to make the column weak in shear. Concrete of target strength of 25 N/mm2 was used for casting. The detailed description of all the specimens are given in Table 3.1. The detailed drawings for these specimens are shown in Fig.3.4. The cross section of the column was reduced than earlier cases while the cross section of beam was increased to make the beam-column joint as a strong beam-weak column joint. The supporting calculation have been furnished in Appendix-B. The main reinforcements in column were maintained similar to those of earlier cases, while same was increased in beam. Spacing for the lateral ties in the columns were increased to ensure the shear weakness of these specimens in column. In CWSLC, 2-legged 6 mm diameter mild steel bars with a spacing of 900 mm c/c were provided as lateral ties.
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Table 3.1 Description of beam weak in flexure control specimen Component
of Beam- column joint
Beam Column
Designed Parameters
Effective Span (mm)
Section (mm×mm)
Longitudinal Reinforcement
% Tensile Reinforcement
Length (mm)
Section (mm×mm)
Longitudinal Reinforcement
% Reinforcement BWFLC 1500 300×360 2-20φ-top
2-20φ-bottom
0.58% 3300 300×300 4-20φ-total 1.396%
BWFMC 1000 200×240
2-12φ+1-8φ- top 2-12φ+1-8φ-
bottom
0.578% 2200 200×200 4-12φ+2-8φ- total
1.382%
BWFSC 500 100×120
1-8φ+2-6φ- top 1-8φ+2-6φ-
bottom
0.65%
(equivalent) 1100 100×100
2-8φ+4-6φ- total
1.57%
(equivalent)
CWSLC 1500 240×450 3-20φ-top 3-20φ-bottom
0.873% 3300 240×300 4-20φ-total 1.745%
CWSMC
1000 160×300
3-12φ+1-8φ- top 3-12φ+1-8φ-
bottom
0.812% 2200 160×200 4-12φ+2-8φ- total
1.723%
CWSSC 500 80×150 2-8φ-top
2-8φ-bottom
0.837%
(equivalent)
1100 80×100 2-8φ+4-6φ- total
1.963%
(equivalent)
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