Identification of Cracks

Questions - 1

a)   b)    c)

What is the mode of failure or damage of the beams in the figure above?Are the damages repairable?Elaborate

Answers

Introduction:

• The Crack identification in structures by detecting changes in their dynamic behavior has been studied in the past, and various methods have been developed, enabling the calculation of crack location and depth along a beam. 
• Most of these methods utilize the frequency changes caused by the crack.The clamp rigidity of a beam tends to soften as time goes on and this unexpectedly brings large errors in crack identification.
• The present research examines the problem of crack identification in a beam when clamp rigidity is unknown.
• The identification method is based on the genetic algorithm (GA). The proposed method is verified by numerical simulation.

Aim:To check the beams to damage repairable

Procedure:

a)Beam and cloumn joint failure

• In framed structures, both steel reinforced concrete, beam-column joints plays a very crucial role in terms of seismic resistance. 
• Under the effects of high lateral seismic loads, beam-column joints are subjected to high forces and moments and their behaviour have a significant influence on the response of the structure. 
• Poor seismic performance of inadequately detailed joints can lead to the total or partial collapse of reinforced concrete frame structures. 
• The use of low sttrength concrete, plain reinforcing bars, problematic anchorge details and adequate transverse reinforcement in beam-column joints are the factors increasing the failure risk of the structures during severe earthquakes. 

Observation:

• It seems to be an beam failure and structural too an corrosion and damaged
• The slab as good condition and no cracks 
• The column and beam joint as to be damaged

Repair:

• Before starting the repair of a concrete column, the axial dead load, axial live load, horizontal load and its associated moments must be known.
• Repairs to concrete columns can be divided into two categories. 
• Surface or cosmetic repair only covers local deterioration and structural repair restores or strengthens the affected columns.
• If the deterioration does not significantly reduce the cross section, the conventional concrete repair can successfully be employed.
• Encasement or enlargement of the column cross section (jacketing).
• Cathodic protection to stop reinforcing steel corrosion.
• Re-alkalization of the reinforcing steel to stop corrosion.
• Chloride extraction to retard the reinforcing steel corrosion.
• Confinement using steel plate, carbon, or glass fiber materials.
• Addition of shear collars to increase the shear capacity of intermediate floors.
• Addition of a steel plate assembly to increase moment capacity.
• Supplemental columns.
• The application of a protection system to prevent future corrosion.

b)Honey combs in column

• Honeycombs are hollow spaces and cavities left in concrete mass on the surfaces or inside the mass where concrete could not reach. 
• These look like honeycombs or honey bess nests.
• Improper vibration and workability of concrete are main causes of honeycombs in concrete. 
• Honeycombs which are on sides are visible to naked eyes and can be detected easily as soon shuttering is removed. 
• Honeycombs which are inside mass of concrete can only be detected by advanced techinques like ultrasonic testing etc.
• Places like junction of beam to beam to column and to one or more beams are the typical spots where honeycombs are observed. 
• This is due to jumbling of reinforcement of beam and column rods at one place during concreting and vibrating.
• Presence of more percentage of bigger size of aggregate in concrete also prevents concrete to fill narrow spaces betweeen the reinforcement rods.

Observation:

• The picture will shows the crack at the column the proper mixing is not honeycomb is attained
• The Strctural as to be an correded

Repair of Honeycombs:

• The affected area should be broken and the portion should be re-concreted after applying grouting chemical to the old surface.  Honeycombs as a defects not only reduces the rods and rusting and corrosion strats.
• At places of junction of column and beam concrete with strictly 20mm and down aggregate should be used with slightly more water and cement to avoid honeycombs. 
• Taping with wooden hammer the sides of shuttering from outside during concreting and vibrating will help minimizing honeycombs to a great extent in case of column and beams. 
• Use of thinner needle say 25mm or kess with vibrator at intricate places or concreting will also help in reducing honeycombs.

c)Stronger column weak beamFailure:

• Flexure failure occurs when the imposed loads exceeds the flexural capacity of the structural member. Flexural strength is defined as stress in material just before the yielding starts in flexure test; it represents the highest stress value experienced at moment of rupture.
• Depending on yielding of steel and crushing of concrete, flexure failure is further

Observation:

• To see that the picture will shows cracking at the bottom of the beam joints
• It will attained at the unproper mixing of the concrete 

Repair:

• All structural elements should be designed to be capable of withstanding the stress developed due to all combination of loads irrespective of whether column or beam.
• Failure of any beam element may occur due to non compliance in construction or subjected to exceeding design loads.ign loads.
• Columns are connected with 2,3 or 4 beams and designed for maximum load transfer from these beams .we need to understand that at a time it is remote chance that all beams are subjected to maximum load and implies that columns are subjected to load less than design load and never reach to design load
• Also due to grouping of columns inherant reduntance exists in most of columns.
• Early failure warning in beams essential and can be achieved by avoiding brittle failure of concrete. Beam design to be steel failure first and ductility of steel and stirrups play important role in early warning.
• To conclude there is no such thing of weak beam and strong column.
• The fact is Max imum load transfer does not occur for columns and they are strong , where as there is every possibility that excess over design load could occur in beams hence redundancy is less in beams and are weak in these terms.
• Beams to be designed as first steel failure criteria .the word under reinforced should be dropped and changed as first steel failure criteria.

Result:

Finally we identify the crack and repir it.

Questions - 2

a)   b)   c)

Answers

Introduction:

• Structural members made of concrete are usually reinforced by steel bars. Steel reinforcement is used to resist tension, to distribute cracks and to limit cracks’ width. But the first aim of reinforcement is to protect against a brittle failure.When reinforcing steel bars are not designed properly, the structure will crack excessively and may fail.
• The failure behavior of concrete and reinforced concrete beams under flexure was analyzed by numerous researchers.The analyses were mostly dedicated to typical reinforced concrete beams with longitudinal and transverse reinforcement. Much smaller database of experimental results can be found for longitudinally reinforced concrete beams without transverse reinforcement .
• The performed experimental investigations have shown that the efficiency of longitudinal reinforcement depends on its ratio. Furthermore, the failure process in flexural beams without transverse reinforcement can vary according to the longitudinal reinforcement ratio.
• The question arises as to what the influence of reinforcement ratio on crack initiation and development is and as to when steel reinforcement effectively protects against brittle, dangerous failure. 

Aim:To identify the crack and gives the solution how do repair

Procedure:

a)Compression Failure

Observation:

• The column is an element that transfers the weight of a structure as axial stress to the foundation or supporting element.
• Concrete is capable of carrying the compressive load is dominant in carrying loads whereas in other elements such as beams compressive stress is taken only by part of the section.
• Reinforcement is also provided to columns where it is not possible concrete to carry the whole load or as nominal reinforcements.
• The column can fail in compress due to the increase of the axial stress than its capacity. These types of failure could be due to the following reasons.

Repair:

• Reinforcement and concrete have certain capacity based on there amount and area of the section. If axial stress is greater than that capacity column will fail in compression.
• Further, the reinforcement and concrete have their own stain that they can bear.
• As per the British standards, concrete is capable of carrying a strain up to 0.0035 and steel starts yielding at a strain of 0.002 and it can increase greater than the concrete.
• When the axial stress exceeds a certain amount resulting in concrete strain grater than 0.0035 concrete will fail suddenly. It will be a sudden crushing of concrete.
• If the section is sufficiently reinforced, it will provide warnings before these types of column failure.
• The article published as strctural cracks in concrete could also be referred more information on cracking.

b)Shear Failure

Observation:

• 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 structures, etc.
• Shear links are provided to columns based on the shear forces excreted on them.
• Further, the size of the columns is increased in the direction of shear to increase the shear capacity.

Repair:

• Shear cracks in concrete beams can be avoided by providing additional shear reinforcement near to the supports, where the shear is maximum.
• The shear capacity of the beam element is inadequate.
• Load coming over the structure is more than design load.
• Inadequate amount of shear reinforcement.

c)Buckling Failure

Observation:

• It is formed due to the column of buckling is sudden change of shape of the columns due to the lateral load applying.
• Mainly, the buckling failure can be identified as a failure of the design as we consider the buckling effect in the design.
• If the designer aware of these types of column failures, he could attend this.

Repair:

• The additional bending moment of the column slenderness of the column is considered in the design.
• Further, the effective height of the column is considered based on its pattern of bucking.
• Buckling failure, the name itself provide the idea about the mode of failure.Therefore, we consider it in the design.
• Buckling failure is the other basic mode of failure of columns in addition to crushing failure of columns.

Result:

Finally we identify the crack and gives the solution