PSI - Issue 52

Rakesh Katam et al. / Procedia Structural Integrity 52 (2024) 72–88 Rakesh Katam/ Structural Integrity Procedia 00 (2019) 000 – 000

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based on assumptions and had no reduction of any material properties. The second and third models are created using material characteristics obtained from NDT (steel and concrete). The plan view, 3D views, and analysis performed in ETABS are shown in Fig. 8. The analysis is performed using ETABS, and the standard loads considered for the analysis are in accordance with IS:875, which includes both dead and live loads as shown in Table 7.

Table 7. Load specifications.

Loads

Specifications

Live load Dead load Floor load Wall load

3 kN/m 2

Gravity loads

1 kN/m 2 7 kN/m 3 kN/m

Parapet wall load

In Table 7, the axial loads coming on the columns are shown, but the demand is less than the capacity of the columns because the analysis is being performed using Indian Standards (IS: 875), which assumes dead and live loads. 4. Results and Discussion The causes of column failures in the building are examined in three cases. The first case considering the structure with design material properties at the time of construction i.e., M20 grade of concrete. With theoretical design calculations, each column capacity is observed to be 602.8 kN and its corresponding demand is shown in Table 8. But with the addition of a concealed beam being placed on the first story in the in-situ condition, the floor load is increased to 1.5 kN/m2 and its demands are recalculated using the increased dead load. It is observed that columns B1, B2, and C1 failed due to the structure's sudden increase in dead loads. The column failure in the first particular case is depicted in Fig. 9(a).

Table 8. Axial loads on the columns (kN). Column No. Capacity

Demand (Designed loads)

Demand (Increased dead loads)

A1 A2 A3 A4 B1 B2 B3 B4 C1 C2 C3 C4

602.8 602.8 602.8 602.8 602.8 602.8 602.8 602.8 602.8 602.8 602.8 602.8

117.9 105.4

433.8 410.1 277.4 273.4 773.1 790.2 526.3 554.2 678.4 677.2 418.3 438.5

70.6 72.3

211.9 209.1 133.7 148.5 179.6 177.6 108.2 116.3

From the NDT result in the second case, M15 grade of concrete is considered. As a result of the material grade being lowered and the dead loads being increased, six columns have failed. We estimated the increase in rebar when the concrete grade is lowered for the analysis. Table 9 displays the current reinforcement, in the building the impact