Diagonal crack

Figure 2.2 Schematic shear bands (rosette) and diagonal cracks at an indentation in MgO (after Armstrong and Wu, 1978).

Helical or diagonal cracks are caused by instability or settlement of the embankment. 

Figure IS. 10 Helical or diagonal cracks, (a) Helical crack, after treatment (b) Helical crack formation and (c) diagonal crack.

YES - Diagonal cracks in mid-sections of walls, vertical cracks in upper regions of walls, damage and/or cracks in wall-to-wall or wall-to-floor connections, significant cracks in bed and head joints, significant horizontal cracks especially due to differential settlement, significant out-of-plane deformation in the wall. 

A qualitatively different type of failure mechanism has also been observed. The strengthened model does not suffer separation of bearing walls and vertical crack, but the failure is transferred to the lower zone and results in occurrence of diagonal cracks (Fig. 8.4). 

Expansion of diagonal cracks in MRM infill walls of 1st and 2nd floors was the main damage observed during D2-1 ground motion (Fig. 10.9). The IDR demands reached 0.32, 0.41, and 0.32 % at first, second and third stories, respectively, at the maximum top displacement of 14.5 mm. As the time span of D2 ground motion applications were all different (Fig. 10.7), the first 2.9 s of all D2 motions common in all tests were considered, in order to compare the maximum IDR demands of the test subjected to successive earthquakes. Fig. 10.9. 

During the D2-2 ground motion, new diagonal cracks opened up in infill walls in addition to existing cracks. Moreover, new shear cracks were observed at the joints of the middle bay of the first floor. Shear and flexural-shear cracks formed in the bormdary columns of the first story s infill wall. Flexural-shear cracks were also observed at the ends of some beams (Fig. 10.9). The IDR demands were measured as equal to 0.51,0.58 and 0.57 % for first, second and third stories, respectively. The measured maximum top displacement was 23.4 mm. 

The D2-3 ground motion caused additional diagonal cracks in the infill walls of the first and second stories. Furthermore, flexural cracks at the boundary colunuis of the second story s infill wall were extended (Fig. 10.9). The maximum top displacement measured during the test was 28.8 nun and the corresponding IDRs were 0.61, 0.76 and 0.75 % for the first, second and third stories respectively. 

Fig. 13.25. Stress Ox at collapse load of the specimen in DIANA analysis at the bottom of the beam ranges between 15 and 20 MPa whereas in the actual experiment the stress in concrete at the bottom of the beam was found to be 15.3 MPa, as shown earlier. The diagonal crack pattern at the joint closely resembles the crack pattern observed in the experiment as shown in Fig. 13.26.

Two cracking loads have been identified. One is associated with flexural cracking of the beam and the other with a diagonal crack in the joint which occurs when the maximum principal stress exceeds the tensile strength of concrete in the joint itself. 

The subassemblage failure mode was characterized by large and deep diagonal cracks and concrete wedge spalling off, as typically found in post-earthquake in situ inspectiOTis, see Fig. 14.9, as well as in available experimental test reports (Priestley 1997 Pantelides et al. 2002). 

The other approach for the shear resistance of masonry shear walls is based on the Tumsek and Sheppard (1980) criterion, which is based on the assumption that diagonal cracking occurs when the maximum principal stress at the center of the wall reaches the tensile strength of the masonry. 

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