Strong Floor
6.7.1 Description of the Test
advantages of adobe bricks, most of the modern-day construction practices have not opted for adobe bricks due to the inherited shrinkage problems, labour intensive construction and the regular maintenance.
In the current study, in lieu of the above constraints, very weak and soft burnt clay bricks, which are referred as Class III according to the current Indian specifications, were chosen. Generally, three kinds of clay bricks are available in India depending upon their mode of manufacturing: country bricks, table-moulded bricks and wire-cut bricks.
Country bricks are mostly ground moulded and burned in clamps without proper temperature control. Table-moulded bricks are manufactured in semi-urban areas using intermittent or continuous kilns for burning. In the manufacturing process of table moulded bricks, moulds are lubricated with sand so that the plasticized clay will not stick to the sides of the mould. Wire-cut bricks are produced in factories by extrusion process and the quality of the bricks is superior when compared to both country and table- moulded bricks. In developing countries, including India, table-moulded bricks were very widely used due to the semi-mechanized skill requirement and cost effectiveness in the manufacturing of bricks. The other major beneficial influence of table-moulded bricks is low-compressive strength and low-elastic modulus when compared to the commonly used cement mortar in the construction of infill wall.
In the current study, to obtain weak and soft masonry, not only low-strength and soft bricks were chosen but also low strength mortar was selected, such that, a more deformable failure mechanism was observed in infill under lateral loading. Two frames were tested in the current study: frame infilled with class I burnt clay bricks (IF-CC1) and frame infilled with class III burnt clay bricks (IF-CC2). The following section describes in detail the construction of the frame using the adopted methodology.
675 175 2-8Y
1500 175 300
400 1500 175 300
675 A
A
C C
2-10Y Section BB
6Y@ 110
15 12Y@ 4 corners 115
175 115
175 6Y@120
Section DD 2-8Y
3200 300
3-8Y
2-10Y Section AA
115
175 6Y@90
B
B
D D
6Y@ 90
15 12Y@ 4 corners 115
175
Section CC 2-8Y 15 15
342.5115342.5
8-16Y
40 350
8Y@
120 Key: All dimensions are in mm
3-8Y = 3 bars of 8 mm dia.
6Y@90 = 6 mm dia. bars at 90 mm spacing
behind testing of RC frame with higher strength infill was to use the frame as a reference for validating the performance of frame with low-strength infill. In case of IF-CC2, class III burnt clay bricks were used in the construction of infill wall. The reason to choose class III burnt clay bricks was mainly the low-strength and soft nature (low-elastic modulus) of class III bricks compared to class I burnt clay bricks and fly ash bricks. The other major advantage of class III burnt clay bricks was their low shrinkage compared to adobe bricks. The infill wall was constructed with 1:8 (cement:sand) mortar grade so as to obtain low strength masonry. Detailed material characterisation of class I and class III brick masonry was discussed in chapter 3.
Fig. 6.10. Reinforcement detailing of infilled frames IF-CC1 and IF-CC2.
Summary of material properties of both class I and class III brick masonry are presented in the Table 6.7 along with frame material characteristics. From the material characterisation of class I and class III bricks, it was observed that class III bricks were low-strength and soft (low elastic modulus) when compared to class I burnt clay bricks.
At the same time, it was also observed that the average compressive strength and modulus of elasticity of considered class III brick masonry with 1:8 cement mortar was found to be very low compared to class I burnt clay and fly ash brick masonry. Both the infilled frame specimens (IF-CC1 and IF-CC2) were tested under slow-cyclic displacement loading applied at the slab level using servo-controlled hydraulic actuator of 250 kN load capacity and a stroke length of ± 125 mm (Fig. 6.11). Three cycles of each displacement level were applied and the response was recorded using a data acquisition system. Similar
instrumentation and data acquisition was employed as that of methodology I.
Experimental results were recorded continuously using load cell and displacement transducer located in the actuator arm, external LVDTs, and strain gauges as discussed in methodology I.
Table 6.7. Material properties of infilled frame with class I and class III clay bricks
Fig. 6.11. Details of experimental setup and instrumentation of IF-CC1 and IF-CC2.
R
ESULTS ANDD
ISCUSSION OFM
ETHODOLOGYII
Experimental results of IF-CC1 and IF-CC2 specimens are reported in terms of hysteretic curves (lateral load resistance vs applied drift at the actuator level), and the envelope curves. Influencing parameters (lateral strength, stiffness, energy dissipation, deformation Material Characteristics Units Class I Bricks Class III Bricks Concrete Compressive strength MPa fck = 37, Ec = 30414
Split tensile strength MPa fct = 2.8 Longitudinal steel (12Y) Tensile strength MPa fy = 530, Es = 2×105 Longitudinal steel (10Y) Tensile strength MPa fy = 546, Es = 2×105 Longitudinal steel (8Y) Tensile strength MPa fy = 562, Es = 2×105 Stirrups (6Y) Tensile strength MPa fy = 569, Es = 2×105
Brick Dimensions mm 230×110×75 230×110×75
Compressive strength MPa fb = 19.2, Eb = 2061 fb = 6.3, Eb = 516 Split tensile strength MPa fbt = 1.03 fbt = 0.44 Mortar Compressive strength MPa fj = 17.3, Ej = 7403 fj = 3.2, Ej = 3795
Split tensile strength MPa fjt = 1.2 fjt = 0.4 Masonry prism Compressive strength MPa
fm′= 4.4, Em = 1744 fm′= 1.5, Em = 608 Masonry wallette Shear strength MPa
fv′= 0.2 fv′= 0.1
All dimensions are in mm LVDT
Base Beam
St ro ng Wa ll
Strong Floor
1 2
3
4 750
1260
70 180
Hydraulic Actuator
SG - Strain Gauges
Left Column A
B
Side View Front View
Clay Brick Infill
Right Column SG 1-4
SG 5-8 SG 9-12
SG 13-16 SG 17-18 SG 19-20
Section A Section B
SG 21 SG 24
SG 23 SG 22
175 115
115 175
SG 1-16: on columns SG 17-20: on beams SG 21-26: on stirrups in columns and beams
SG 25 SG 26
characteristics, and failure mechanisms) and their variation with respect to previously tested infilled frame specimens with fly ash bricks are discussed in the following sections.