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Design Faults Causing Damage to Concrete Structures

It is not uncommon to see concrete structure developing unwanted deformations, cracking, spalling, severe honeycombing, displacement of supports and eventual collapse. Some of the major factors responsible for these failures are use of inferior iron rods (rebars), corrosion, insufficient reinforcement, exposure to extreme temperature, structural damage, fire hazard, seismic damage, weather exposure, and chemical damage. But another factor that is rarely given attention is detailing and design errors.

Detailing and design errors of concrete structures can create several types of damage to concrete structures. These design faults, which often lead to reduction in structural members, include but not limited to, insufficient cover to steel reinforcement, inadequate structural design, improper joint detailing, improper connection details, and incorrect placement of embodiments in concrete.

For reinforced concrete construction, mainly inadequate column designs and over-weight structures are the causes of fatal building failure, collapse and related human victims. Heavy and stiff floor constructions are not useful for the overall strength and ductility of the reinforced concrete buildings. Inadequate execution skills and non-expected thermal expansion are other problems.

Insufficient Cover to Concrete Reinforcement

If the cover to reinforcement is not sufficiently provided in the construction drawing as per the environmental exposure by the suggested standard codes, this will cause the corrosion of steel reinforcement. This is also the cause of freeze-thaw, and deterioration of concrete. The volume of corroded steel increases inside the concrete as a result of corrosion in steel reinforcement, and this may cause cracks and spalling in the concrete.

Incorrect Placement of Embedment in Concrete

This is another common type of error which may occur in the detailing of concrete. Placement of embedment in right location and position is important to prevent damage to concrete.

Embedded metals, electrical conduits or outlet boxes should not be near the exterior surfaces of the concrete structure. Cracks may develop over and around the embedment, leading to damage of concrete due to corrosion and freeze thaw effect.

Inadequate Structural Design

Cracking of concrete because of torsion and shear stress and spalling of concrete due to high compression stress are indicators of inadequate structural design. To discover whether inadequate design is the cause of damage in concrete structure, it is important to compare the location of the damage with the types of stresses that should be present in the concrete.

For instance, if spalls are present on the underside of a simply supported beam, high compressive stresses are not present and inadequate design may be eliminated as a cause. However, if the type and location of the damage and the probable stress are in agreement, a detailed stress analysis would be required to determine whether inadequate design is the cause or not. Inadequate design is best prevented by thorough and careful review of all design calculations.

Improper Connection Details

Improper connection details between concrete members such as beams, columns, and slabs can lead to damage of concrete structure. If the detailing of connecting members at the junction is not proper, the load transfer from one member to the other may not be as expected from the design. As a result, concrete member may deflect or suffer durability issues during the occupancy of the structure, rendering the structure unfit for use.

Detailing of Joints

Detailing of joints in drawings for concrete structure is substantially crucial. Joints allow the concrete to expand and contract as temperature changes. It also allows the concrete to transfer loads through joints. Detailing of contraction joints, expansion joints, and construction joints for concrete structure is needed to prevent any kind of damage.

Details of reinforcement, types of materials to be used, right placement of joining materials should be clearly specified to prevent any error on site during construction. Concrete slabs constructed with insufficient or too narrow expansion joints can cause serious damage to bridge deck surfaces, dam roadways, and the floors of long, steeply sloping, south facing spillways where the large temperature changes occur on daily and seasonal basis.

Reinforcement Detailing

Reinforcement detailing errors like development length of bars, and lapping methods of reinforcement for the given size may also cause trouble to the concrete structure. Poor detailing of reinforcement may lead to localised concentration of high stress in structural member. Structural failure, concrete cracking, and seepage through structural element are signs of improper reinforcement detailing.

Final Words

These design faults are not to be taken with levity. Designers must be aware of them as the ultimate goal of construction is to ensure the safety of the users.

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