Identification of Cracks
1a)The beam and column joints are very critical regions in which the lateral forces, generated by boundary elements are active on the concrete core and reinforcing bars with a very high magnitude. They are linking elements between horizontal and vertical structural elements, and therefore, they have significant involvement in the transfer of seismic forces. Thus, they are crucial to studying the seismic behavior of reinforced concrete (RC) structures. To fully understand the seismic performances and failure modes of beam-column joints in RC buildings, a simplified analytical model of joint response is proposed and theoretical simulations are performed.
1b) This kind of problem will occur due to construction errors. Columns could fail due to construction defects. For example, an improperly treated honeycomb in a column could lead to a failure when the loads are applied. These types of column failure can be avoided if attended to with much care. Cavities inside the column that were not filled properly with construction ground reduce the compressive area of the column. As a result, axial capacity will be reduced.
1c) The cracks are preoccupied in the region where the column is continuing upwards, mainly because there is a lateral load effect or flexure caused by the forces traveling along the length of the beam towards the column. The forces being huge, could not be mitigated thus causing, cracks in the column element. This type of crack can be avoided by providing confining zone reinforcement to the column and beam interface to take excessive shear forces caused due to earthquake shaking locally at the interface of the beam and column joint. This type of crack can be repaired using grouting and by placing a higher amount of steel at the beam and column interface in the form of development length.
2a) The column has evidently failed in the compression and bending due to the yielding of the steel with the angle of zero degrees with the crossectional area of the column. The load on the column has caused the steel near the interface(which is the most critical in tall buildings) to reach the inelastic range. This failure, however, cannot be dedicated to compression only as it can be linked to lesser moment and compression capacity (combined flexure and compression) because the moment at the top end of the column should have been higher or the top part of the column could have been weaker than the bottom part due to possible construction defects.
2b)During the seismic loading on the structure there are various forces acting on the structure. If the governing force on the column is the shear then there are cracks forming on the structure at an angle of 45 degrees to the vertical as shown by the picture. If there are confining reinforcements provided at the interfaces of beams and columns then there would be mitigation of the additional shear forces due to seismic forces. This failure could be due to torsion or shear. The reinforcement for torsion is again calculated as equivalent shear and provided near joints.
To a certain extent, these cracks can be repaired by providing jacketing technique and additional reinforcement welds in the columns to support the structure uniformly. But, this is not possible if the shear failure has caused the beam and column to separate and joint connectivity is lost. In general, any crack in the member can be filled using the grouting method and providing steel and welds
2c)The column seems to be completely crushed due to the vertical loads and the beam is completely disjointed from the column. There are temporary supporting members placed at the interface of the beam and column joint. The supports ensure temporarily that the beam does not fall off causing progressive collapse, if possible. There are various factors that can cause such a failure like the bending moments and shear forces both are dominantly causing failure and the beam is incapable to take both. The provided supporting structures are not capable of taking the loads for a long period of time because they may not be of equal stiffness as that of a column altogether. The vertical and lateral loads on the column are distributed between these temporary members.
Such kinds of damages are more often not repairable because there is a high extent of disconnectivity and disjunction of the members, which even when repaired could have stiffness uniformity issues in the structural elements.