Identification of Cracks

IDENTIFICATION OF CRACKS:

1) What is the mode of failure or damage of the beam in the figure above? Would you characterize the case as damage or as a failure? Are the damages repairable? Elaborate.

a)

This crack will be formed due to the flexural failure of a beam. The flexural strength, known as modulus of rupture, bend strength, or fracture strength, is a material property, defined as the stress in a material just before it yields in a flexure test. The flexural strength represents the highest stress experienced within the material at its moment of rupture. It is measured in terms of stress. To overcome this type of failure, main steel is provided at the bottom or top of the beam. The damages aer repairable, to repair damaged beams, locate a local welder or metal shop and request angle iron, cut and drilled to the length of the beam being repaired. Remove any pipes, wiers, etc, currently going through beam. Be sure turn off water, power, etc, before doing so. Pry the joint hanger away from the beam. Screw the angle iron into the beam and remove the temporary post. Slide any pipes or wiers previously removed back through the beam and turn the water and power back on.

b)

This crack are formed due to the mistakes done in the construction and honeycombing in concrete.To avoid cracks in concrete, avoid using high slump concrete. Concrete of moderate slump (less than 5 inches) results in less cracking. High slump concrete can only be used if it is controlled by concrete admixtures or designed such that segregation and bleeding of concrete is controlled. Concrete admixtures such as water reducers or super plasticizers can be used to increase slump while reducing addition of water content. Air entertained concrete can also be produced to increase slump especially when concrete is to be subjected to freeze and thaw cycles. The honeycombing occurs when the fine mortar fails to thoroughly fall and fill the gaps created by the coarse aggregate. As mentioned previously, poor concrete consolidation is usually the top cause of honeycombing, along with poor vibration, improper ratio of fine to coarse aggregate, dry concrete and construction conditions that are not up to standard.

c)

This cracks are formed due to the beam-column joint failure. In the strong column-weak beam desgin, beams are expected to form plastic hinges at thier ends and develop flexural overstrength beyond the design strength. The high internal forces developed at plastic hinges cause critical bond conditions in the longitudinal reinforcing bars passing through the joint and also impose high shear demand in the joint affects the shear resisting mechanism to a significant extent.

QUESTION 2:

a)

This crack will be formed due to the flexural failure of a column. Columns have the most important role in all structural members of a building. According to the base civil engineering concept, columns faliure wants to be occurring after beam and the other components damages. Performance of existing buildings in earthquakes indicates that the beams are less vulnerable to damage during earthquakes and their damage appears to be less critical to performance as compared with that of columns and column-beam joints.

b)

This crack will be formed due to the shear failure of a column. Lateral loads in a structure are carrying by vertical elements such as columns and shear walls. When there are no shear walls, columns carry these lateral loads. Lateral loads are generated by winds, earthquake loads, from retaining structure, etc. Shear links are provided to columns based on the shear forces excreated on them. Further, the size of the size of the columns is increased in the direction of shear to increase the shear capacity.

c)

This cracks are formed due to the short column faliure.

In short columns, failure takes place due to yeilding and we define this phenomenon as CRUSHING. Short columns are classified based upon "slenderness ratio" which is the ratio of the effective length (Length between point of zero moments) and least lateral dimension of the column. Failure of a column usually occurs due to anyone of the following stresses developed in the column. Short column will fail only because of direct compressive stress developed in the column or we can also say that short column will usually fail due to direct compression or crushing.