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There are number of common design faults that lead to the damage of concrete and hence the capacity of the structural member would be reduced. In adequate structural design, inadequate cover, improper joint detailing, incorrect placement of embedments in concrete, and improper connection details are most common design faults that concrete buildings have experienced. It is important for the designers that be aware of these design faults in order to prevent concrete damage in the future.
1. Inadequate Structural Design
Insufficient structural design makes structural members to support loads that are well above the design loads. cracking of concrete because of torsion and shear stress and spalling of concrete due to high compression stress are indicators of inadequate structural design. In order to specify inadequate design as a cause of damage, it is required 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
2. Inadequate Concrete Cover
If the cover to reinforcement is not sufficiently provided in the construction drawing as per the environmental exposure as suggested by the standard codes, steel reinforcement would corrode due to permeability of moisture into the concrete. This also becomes cause for freeze-thaw deterioration of concrete.
Due to the corrosion in steel reinforcement, the volume of corroded steel increases inside the concrete which may cause cracks in the concrete and spalling of concrete may take place. ACI 318-14 section 188.8.131.52 provides minimum concrete cover requirement for cast in place, prestressed, and precast concrete of various structural members.
3. Incorrect Placement of Embedments in Concrete
This is also the most 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 which may lead to damage of concrete due to corrosion and freeze thaw effect.
4. 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 that may occur.
Details of reinforcement, types of materials to be used, right placement of joining materials shall be clearly specified to prevent any error that may occur at 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.
5. 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; may cause the structure unfit for use.
6. 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. If the contractor is not aware of these things, then the proper placement of reinforcement in concrete is not done which may cause damage to the structure during its service.
Poor detailing of reinforcement may lead to localized concentration of high stress in structural member. Structural failure, concrete cracking, and seepage through structural element are signs of improper reinforcement detailing.
7. General and Special Notes
General and special notes on drawing shall be provided for whatever is assumed during design. If any assumption has been made in case of any details not available, then that should be mentioned in the drawing, so that contractor or supervisor at site while construction can verify the assumptions made and in case of any changes required, structure can be redesigned and detailed.