Identification of Cracks
1 AIM : Modes of failure or damage in the beam Casued
- Earthquakes are the most destructive natural hazards throughout human history.
- Hundreds of thousand people lost their lives and loss of billions of dollars’ properties occurred in these disasters.
- Earthquakes can cause devastating effects in terms of life and property.
- The destructive potential of earthquakes depends on many factors such as focal depth, epicenter distance, and local site conditions. But the causes of fatalities and the extent of damages depend on lack of engineering service, design faults, material quality, and workmanship
PIC A :
- Caused Due to brittle failure
- In some R/C buildings, especially at the ground floor, walls may not be continuous along to height of building for architectural, functional, and commercial reasons.
- While ground floor generally encloses with glass window instead of brick infill walls, partition
- walls are constructed above from this storey for separating rooms for the residential usage.
- This situation causes brittle failures at the end of the columns
PIC B :
- Shear forces increase during an earthquake especially at columns and beam–column joints.
- Consequently, special attention should be paid to construction and design of beam–column joints and columns.
- Seismic design requires increasing of ductility of structures for performance-based design approach.
- In particular, columns of buildings can be having insufficient transverse reinforcement in the plastic hinge region
PIC C :
Shear failure
- when the shear stress on an object exceeds the max permissable shear stress and object undergo failure know as shear failure
- Failure caused due to insufficient of shear resistance available between gthe material
- A shear failure is a force that trend to produce a sliding failure on a material along with plane parallel to the direction of force
- shear force is max at 45 degree so the diagonal failure will occur at the beam where beam connect the column
- To avoid this type of failure stirrup are provided
Occurance of shear failure
- It may occur due to insufficient resistance between steel rod and column
- Insufficient strength of concrete used
2 AIM : Modes of failure or damage in the beam Casued
PIC B : Weak storey
- Weak storey mechanism during the Bingöl earthquake.
- Damaged structure due to inadequate spacing between shear reinforcement
PIC B : Short column
- This type of mechanism can be developed due to structural adjustments or to continuous openings at the top of infill walls between columns.
- Lateral forces that occurred by an earthquake are carried by columns and shear walls.
- Length of column is an important factor for dissipation of these loads. When the length of column decreases, the column becomes stiffer and brittle than the other columns and this column attracts more shear forces.
- Thus, shear failure which is a critical type of concrete column damage occurs at these columns.
- Buildings are sometimes constructed adjacent because of the lack of building lots.
- Consequently, the buildings that have not adequate gaps pound to each other during the earthquake.
- If the floors of the buildings are not at the same level, pounding effect of the buildings becomes more dangerous.
Strong beam–weak column
- Deep and rigid beams are used with flexible columns in type of buildings.
- Therefore, these beams resist more moments, occurred by dynamic loads, than weak columns.
- In such a design during an earthquake while deep and rigid beams show elastic behavior, shear failure or compression crushing causes plastic hinges at flexible columns.
Poor concrete quality and corrosion
- The other main reasons of damages are low concrete strength and workmanship.
- Concrete quality is an important factor for building performance against to earthquakes.
- Handmade concrete is used to without using vibrator in construction of old buildings. Thus, homogeny mixing was not obtained and expected compressive strength was not provided in these buildings.
- In addition to this, using of aggregates which have improper granulometry, corrosion which decreases reinforcement bar area, and using of smooth steel reinforcement effected strength of concrete.
In this book chapter, reasons of damages for reinforced concrete and masonry structures arose from earthquakes are presented.
For reinforced concrete structures,
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The reason of soft storey collapse is occurred due to low rigidity of reinforced concrete structural members at ground floor. In case of the absence of the infill wall, the rigidity of the ground floor is lower than the upper storeys. Thus, this failure mechanism is triggered by earthquake. This type of failure is prevented during design phase by designing with more detail.
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Inadequate transverse reinforcement and no bending of hooks of ties in structural elements cause damages. This problem can be solved by using close-spaced stirrups and 1350 bended hooks to increase shear resistance of structural elements.
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Failures reason of short column is especially occurred due to partially filled infill walls in R/C frame system. These failures can be prevented by increasing of shear strength of this part of the column.
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During the earthquake, after first shake, different natural vibration periods cause hammer effect and then result in total collapse. To prevent this problem, adequate gaps according to current codes should be left between the adjacent buildings.
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When deep and rigid beams are used with flexible columns, weak column–strong beam failure mechanism is developed. To refrain this type of problem, sum of moments at column connected to any of joint should be bigger than sum of moments at beam connected to the same joint.
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Low concrete strength, workmanship, and corrosion of steel bars decrease the lateral stiffness of the structural system. This important reason can be eliminated by inspecting concrete and workmanship.
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The reason of in-plane, out-of-plane, and gabble wall failures is lower strength of infill materials than reinforced concrete frame. To prevent this type of failure, adequate connection and high-strength mortar between wall and reinforced concrete frame should be used.