Page 10 - August-Month
P. 10

TECHNICAL PAPER


























                                                  Figure 12: Comparison of mode shapes
           the ground storey column is in the range of 10,000 microstrain.   The natural frequency of the building at different modes
           During the shake table tests, strain values are higher at ground   was determined analytically by finite element method. SAP
           storey columns. Inter storey drift is high at the first storey level   2000 software is used to analyze the building. The building is
           for the RC frame, which is due to the lack of stiffness in the   modeled with the same dimensions of the test specimen. Beams
           ground storey. The maximum strain magnitude in the ground   and columns are modeled as 3D frame elements. The brick
           storey column is nearly 7500 micro strain, whereas it is only 300   infill is modeled as diagonal compression strut elements. Rigid
           microstrain in the second-storey column. The variation in strain   joints connect the beams and columns, but pin joints at the
           (Figure 11) magnitude in the ground storey column of reinforced   beam-column junctions connect to the equivalent struts. Modal
           concrete building is higher than the second story column during   analysis is performed on two models in the excitation direction.
           different Earthquake (SFTM 10% to SFTM 100%).          The three dimensional reinforced concrete frame model in SAP
                                                                  2000 software is shown in Figure 13. Transient dynamic analysis
           It is observed that the natural frequencies are 2.93 Hz and
           4.0 Hz for the frame model 2 and RC frame model1 respectively
           as shown in Figure 12. Table 1 shows the comparison between
           theoretical and experimental natural frequencies. The
           Fundamental mode shape for model-2 frame is linear but for
           model-1 frame the mode shape is parabolic as shown in Figure 12.

           The shear force acting at the ground storey is higher than other
           floors. Damages are predominant spread in the ground storey
           of the RC frame which is due to the lateral shear force at the
           ground storey. Sliding cracks formed in the brick infill. During the
           shake table test, predominant failure hinges are formed in the
           ground storey columns of RC building (Jothi saravanan et al. ).
                                                           [7]
           In model-1 frame, column side sway mechanism is observed
           (failure hinges are formed at bottom ground storey columns).
           The Modal analysis is carried out for the two test specimens.
                                                                              Figure 13: 3D view of original building

           Table 1: Comparison of natural frequencies
             NATURAL FREQUENCY         MODEL-1              MODEL-1               MODEL-2              MODEL-2
                                   (WITHOUT DUCTILE       (WITHOUT DUCTILE      (WITH DUCTILE         (WITH DUCTILE
                                     DETAILING) EXP       DETAILING) FEM       DETAILING) EXP       DETAILING) FEM
                  First mode            4.1 Hz                4 Hz                 2.93 Hz              4.86 Hz
                Second mode             18.8Hz                18 Hz                8.59 Hz             15.66 Hz
                 Third mode             6.44Hz                  -                 12.65 Hz             26.45 Hz


                                                                             THE INDIAN CONCRETE JOURNAL | AUGUST 2021  15
   5   6   7   8   9   10   11   12   13