Identification of Cracks

Aim

Identification of Cracks by analysing the below images.

Ans 1.

A.

This images shown is of Flexure failure and 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.

In this type of failure, the crushing of concrete occurs prior to yielding of reinforcement steel at tension side of beam.

This is also called as brittle failure of structural member as there is no warning in form of deflection, before the structural failure of beam.

This failure predominantly occurs in over-reinforced sections, i.e. reinforcement provided is greater than required in balanced section.

There are several ways one can repair an RC beam in shear. All of these methods have their own merits and demerits. Therefore, based on professional expertise, resources, and materials available, one may select or use either of them. Here are the three most popular methods:

1. FRP Jacketing

This is the most popular method nowadays because of high strength, lightweight, easy to install, and so on. However, there might be some problem with adhesives or bonding between concrete and fiber polymer, as so many researchers have pointed out the premature failure of structures due to debonding.

2. Bolted Steel Plate System

In this system, the steel plates or strips of the steel plate are bolted on faces of RC beam. The two materials, concrete and bolted steel plate, are expected to act in a composite manner. Adhesives are, therefore, used often in addition to the anchors or bolts. The enhancement in shear performance is guaranteed with this method, however, certain compromises have to be made in this method too: debonding between concrete and steel plate, degradation of stiffness due to cracks formed during bolting, degradation of the effective strength of concrete due to bolting, and so on.

B.

This image shows Honeycombing and caused either by the compaction not having been adequate to cause the mortar to fill the voids between the coarse aggregate, or by holes and gaps in the formwork allowing some of the mortar to drain out of the concrete.

Honeycomb in Concrete may be present on the surface or it can be extended deep into concrete members. It is one of the major reasons for the strength reduction of concrete members. Generally, it creates a bad outer appearance, and depending on the depth and extent may reduce both the durability performance and the structural strength of the member.

Honeycombing can be avoided by

1. Mark this affected area of honeycombing and remove all loose aggregate and mortar from the concrete surface by using a wire brush and a chipping hammer.

2. Clean the concrete surface with a brush to remove finer particles and then wash the surface with water.

3. Wait for 2 – 3 hours for drying out the surface and apply Chemi-fix glue on the area.

C.

This is beam column joint failure

In framed structures, both steel and reinforced concrete, beam-column joints play 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 strength concrete, plain reinforcing bars, problematic anchorage details and inadequate transverse reinforcement in beam-column joints are the factors increasing the failure risk of the structures during severe earthquakes. In this paper, an experimental study on the cyclic behaviour of reinforced concrete exterior beam-column joints is presented.

Beam-column joints strengthened with steel caging, and subjected to cyclic and gravity loads, was carried out. As access to joint panels is very complex in existing structures, joint strengthening consists of external solutions: vertical or diagonal bars and capitals connecting columns.

Ans 2

A

This images shown is of Flexure failure and occurs when the imposed loads exceeds the flexural capacity of the structural member.

This failure predominantly occurs in over-reinforced sections, i.e. reinforcement provided is greater than required in balanced section.

This is the most popular method nowadays because of high strength, lightweight, easy to install, and so on. However, there might be some problem with adhesives or bonding between concrete and fiber polymer, as so many researchers have pointed out the premature failure of structures due to debonding.

B

This image shows Shear failure and occurs when the beam has shear resistance lower than flexural strength and the shear force exceeds the shear capacity of different materials of the beam. A shear load is a force that tends to produce a sliding failure on a material along a plane that is parallel to the direction of the force.

Shear failure in RC structures has not been an easy nut to crack for researchers. Although beams have been designed against shear failure for over a century or even two, we hadn’t really understood it well enough until a decade ago.

This is why resistant factor for bending is at 0.9 while that for shear is at 0.75 or something close depending on the code you use. The more closer they are to 1.0, the better we understand the mechanism.

C

This is Short column effect and posses high stiffness that attracts most of the force acting on the multi-story building. Inadequate design of short column to sustain these forces will result in damage and shear failure. This behaviour of the short column under excessive force is called as short column effect.

Special attention is required for short columns and hence recommended to avoid in building design especially for earthquake-prone areas. The effect of a short column is disastrous as they undergo brittle shear failure.

1. The first possible solution is to avoid the use of a short column in the architectural design stage itself.

2. If short columns cannot be ignored, special design requirements are followed.As per ACI code, for those columns that have chances to undergo short column effect will require special confining reinforcement called the ductile reinforcement.

Result

This images helpful for identifying the failure of different types in the practical way and by identifying those we can take the remedies that has to taken.