Concrete Strengthening and Stabilization Methods
MODULE 5
1. Explain the difference between strengthening and stabilisation.
2. Explain the necessity of strengthening and stabilisation.
Concrete structures need to be strengthened for any of the following reasons: Load increases due to higher live loads, increased wheel loads, installations of heavy machinery, or vibrations. The need for structural strengthening is commonly driven by building codes, deterioration, change in use, or deficiencies caused by design and/or construction errors.
3. Explain the types of upgradations.
Upgrade Construction Activities means and is limited to action taken by any person or entity in connection with designing, planning, coordinating, constructing, providing material or services for, or otherwise participating in implementing the Upgrade Plan. The rehabilitation and upgrading of a road presupposes an existing road constructed to certain standards and requiring repair works (rehabilitation) following traffic- and climate-induced deterioration, as well as some improvement of design standards (upgrading) to cope with increasing traffic demands.
4. Elaborate factors affecting strengthening and stabilisation ?
- Quality of Raw Materials.
- Water / Cement Ratio.
- Coarse / fine aggregate ratio.
- Aggregate / Cement Ratio.
- Age of concrete.
- Compaction of concrete.
- Temperature.
- Relative humidity.
5. Explain passive and active strengthening ?
Bars, mats, or cages of steel are used as reinforcement. These can be classified as active or passive. The active ones are those used for prestressing and the passive ones are those subjected to stress upon the application of loads. Fibre-reinforced polymers can be used in the strengthening of existing buildings with variable techniques: FRP wrapping, FRP Laminates, near surface mounted (NSM) FRP reinforcement, FRP strings and lately sprayed-FRP. Concrete jacketing, bonding steel plates and FRP wrappings on structural members are examples of passive strengthening system. This system is relatively easy in application but does not utilize the materials full properties.
6. Explain flexural strengthening methods ?
In concrete flexural strengthening, the chosen system involves the use of FRP either as an externally bonded system in the form of FRP laminate (sheets, plates, or strips) applied to the tension side of reinforced concrete (RC) members or as a near-surface mounted system. The flexural strength of a material is defined as the maximum bending stress that can be applied to that material before it yields. The most common way of obtaining the flexural strength of a material is by employing a transverse bending test using a three-point flexural test technique. METHODS OF BEAM STRENGTHENING Flexural strengthening. Shear strengthening. Flexural strengthening. Beams are strengthened in flexure through the use of FRP composites bonded to their tension zone using epoxy. The direction of fibers is parallel to that of high tensile stresses. Both prefabricated FRP strips, as well as sheets are applied.
7. Explain section enlargement ?
Section-enlarging Reinforcing Method: for Concrete Enlarged Cross Section Method Is a Method Used to Increase the Components of the Structure or Increase the Components of the Reinforcement Area, Not Only Enhance the Bearing Capacity, but Also Can Increase Its Cross Section Stiffness and Change the Natural Frequency of Vibration, the Normal Use of Stage Performance Is Improved, the Reinforcement Method Is Widely Used in Reinforced Concrete Structure of the Beam, Slab, Column, Etc. Enlarged Cross Section Method Is a Method Used to Increase the Components of the Structure or Increase the Components of the Reinforcement Area, Not Only Enhance the Bearing Capacity, but Also Can Increase Its Cross Section Stiffness and Change the Natural Frequency of Vibration, the Normal Use of Stage Performance Is Improved, the Reinforcement Method Is Widely Used in Reinforced Concrete Structure of the Beam, Slab, Column, Etc.
1. Unloading before reinforcement
2. Connection surface treatment
3. The construction of new layer
8. Explain use of FRP composites in strengthening ?
Fiber-reinforced polymer (FRP) systems are simply defined as high-strength and lightweight reinforcements created by combining carbon (CFRP) or E-glass fibers with a polymer material. Traditionally, FRP has been used in the civil, aerospace, and automotive industries for applications requiring high strength-to-weight ratios and rigidity. More recently, the performance characteristics of FRP strengthening have become increasingly popular in construction and retrofit applications, specifically in aging, damaged or overloaded concrete structures. FRP strengthening solutions are engineered, specified and installed to solve a host of structural deficiencies or demands in existing structures:
- Durability problems due to poor or inappropriate construction materials
- Inadequate design or construction
- Increased loading requirements due to code or use changes
- Increased life-span requirements made on aging infrastructure
- Exceptional or accidental loading
- Seismic retrofit
- Blast mitigation
9. Explain use of bonded steel plates in strengthening.
Bonded steel plate reinforcement method is a kind of reinforcement method, which uses high-strength building structural adhesive to bond the steel plate to the surface of the component, so as to improve the bearing capacity of the component. This method was started in 1967. Fleming and King, South African scholars, carried out an experiment to reinforce concrete beams with external bonded steel plates instead of steel bars. In the experiment, steel plates were bonded to the tensile side of the bottom of concrete beams, which proved the feasibility of this reinforcement method. Over the next decade, scholars at home and abroad have done a lot of experimental research, theoretical analysis and engineering practice. The bonded steel plate reinforcement method has gradually matured, and has been widely used in concrete flexural, eccentric compression, tension member reinforcement projects. OR
Bonded steel plate reinforcement is use high-performance epoxy adhesive bonded to the surface of concrete components, steel and concrete to form a unified whole, to achieve good tensile strength to enhance the bearing capacity and rigidity. Bonded steel plate reinforcement is use high-performance epoxy adhesive bonded to the surface of concrete components, steel and concrete to form a unified whole, to achieve good tensile strength to enhance the bearing capacity and rigidity.
10. Explain external post tensioning ?
Tendons are used on the outside of a steel, concrete, or wood structure to bolster its strength. Cores are drilled through the concrete walls and columns in order to attach the tendons. External post-tensioning is an effective solution to improve the structural performance of beam bridges. The tension force from the external cables is applied eccentrically to the neutral axis through deviators, which produces a bending moment opposite to that caused by the external load.
External post-tensioning is an effective retrofitting technique, in which external tendons are placed outside the concrete members, and the Pres -Tressing forces are transferred to the concrete members with end plates and deviators. Deviators are used for deviating the tendons so that the tendon profile will be made.
12. What are the various methods of strengthening columns?
1) Reinforced Concrete Jacketing: It is one of the techniques used to improve or restore capacity of reinforced concrete column. The size of the jacket and the number and diameter of the steel bars used in the jacketing process depend on the structural analysis that was made to the column.
2) Steel Jacketing: This technique is chosen when the loads applied to the column will be increased, and at the same time, increasing the cross sectional area of the column is not permitted.
3) FRP Confining or Jacketing: For detailed description and design of strengthening reinforced concrete columns using FRP confining
15. Explain methods to strengthen concrete walls ?
1. Concrete Jacketing: This is a traditional retrofitting method, where the retrofitting technique is performed to increase the dimension of the wall. This increase in dimension is achieved by adding new concrete to the existing concrete wall. For this, additional steel reinforcement is placed to increase the strength and ductility of the R.C wall. The new steel reinforcement is made into a mesh of horizontal and vertical bars, which is then anchored to the wall foundation. The reinforcement mesh can also be inserted into a hole drilled into the foundation after which it is grouted by epoxy and seale.
2. Concrete Replacement: This is one of the simplest and cheapest way to restore the strength and the ductility of the R.C walls. The method initially involves the removal of the damaged concrete. The final surface is cleaned and brushed properly to remove all loose materials. If the reinforcement present in the compression zone is buckled in small amounts, then it should be straightened.
3. Retrofitting by Steel Materials: The use of steel for retrofitting R.C walls only adds a small weight to the old structure. It is a retrofitting technique that causes minimum disruption to the building occupants.
16. Explain various joints in concrete.
- Construction Joints
- Expansion Joints
- Contraction Joints
- Isolation Joints
17. Explain the significance of Injection grouts for concrete repairs ?
It is used for repairing the cracks and strengthening the damaged or deteriorated structures. Its application includes; Reduce or fill the cracks or voids in the structural members. Repairing the cracks in walls columns and other structural members