FRP as a retrofitting solution
Generally structures are subjected to natural and man-made loads during their service life. When the magnitude of these loads exceed the capacity or strength of the structures, they are likely to be damaged. Sometimes the strength of a structure is reduced because of the use of substandard materials in its construction or due to the application of additional load because of change in functioning or due to seismic forces for which the structure had not been designed originally. These situations warrant strengthening or up-gradation of the structure to carry the enhanced loading. Considering the economy of putting up another new structure in place of the damaged structures with the associated loss of revenue due to interruption in the functioning of the structure as well as economic and environmental factors, a decision to repair the structure becomes essential.
A variety of structural up-gradation and retrofitting techniques has been evolved over the years for different structures and also has been used. Some methods of seismic upgrading such as addition of new structural frames or shear walls have been proven to be impractical because they have been either too costly or restricted in use to certain types of structures. Other strengthening methods are grout injection, insertion of reinforcing steel, pre-stressing, jacketing, different surface treatments, etc. Each of these methods involves the use of skilled labor and disrupts normal functions of the building. These well-known techniques may sometimes be inadequate for applications that should preserve architectural heritage with historical value. FRP composites are now increasingly used in the construction industry and offer considerable potential for greater use in buildings, including large primary structures. In recent years more complex applications have been developed to satisfy the desire for more dramatic features in building design. FRP composites have numerous potential advantages in building construction including the following:
- offsite fabrication
- modular construction
- reduced mass
- superior durability
- ability to mould complex forms
- special surface finishes and effects
- improved thermal insulation
- lack of cold bridging
As a repair material also confinement with polymeric matrix or Fiber Reinforced Plastic (FRP) composites presents significant advantages over a traditional confinement techniques: the cross sectional dimensions of the column do not increase, which permits compliance with architectural restraints; the mass of the column does not increase; which means that the seismic behavior of the building remains unchanged; the low weight of FRP materials implies that the installation procedure is faster, easier and less dangerous for the operator than implementation of traditional confining techniques, Modern techniques of confinement consist of wrapping with FRP sheets or laminates. They were introduced in engineering practice as an innovative confinement technique during the last decade as an alternative to wood or steel ties adopted in the past. Therefore the use of FRP laminates for retrofitting and strengthening is a valid alternative because of their small thickness, high strength-to-weight ratio and ease of applications.
The following are some applications of FRP products:
FRP systems can be used to increase the structural performance of both reinforced concrete, steel and wood beams. Given the basic project parameters (specifically the detailed performance goal and the existing capacity of the structural element), Afzir Company engineers will provide a preliminary composite design and cost estimate at no obligation.
Carbon or Glass FRP are very effective in repair and strengthening of slabs and decks. FRP can be designed to increase the live load capacity of the slab or restore the original capacity that has been reduced by corrosion of reinforcing steel. Depending on the project conditions, strengthening can be achieved by applying the FRP to the top or bottom surface of the slab. We have also developed solutions for increasing the punching shear capacity of slabs around columns. Another common application of FRP is to reinforce the areas around an opening that may have to be cut in a slab (e.g. for stairways, etc.).
Columns in buildings and bridges often corrode with aging and require repair and strengthening. Construction errors can also lead to weaker columns that require strengthening. Virtually all concrete columns constructed prior to the mid-1970s when modern earthquake codes were developed are unsafe when subjected to seismic loads. In all these cases, FRP offers a fast and cost-effective repair alternative.
- Bridge piling
Recent earthquakes have demonstrated the failure of bridge pilings worldwide and the economic and human losses that such failures can cause. In many cases, these structures are submerged in water, making the repairs more challenging. Larger bridge piers are particularly difficult to retrofit. Many of these structures are submerged in water and their large size makes the repairs challenging. A recent technique developed by Afzir engineers is ideal for repair of these structures and makes use of FRP wet layup in combination with pre-manufactured lightweight FRP panels.
Glass and carbon FRP offer ideal repair and strengthening solutions for a variety of wall types, including concrete, brick, Unreinforced Masonry (URM), and Parapet Walls. FRP systems can be used for shear and flexural strengthening of walls, seismic and blast protection, repair of damage, replacing deteriorated steel, waterproofing, etc. Another common application of FRP is to strengthen the areas around openings in walls that may have to be created for doors and windows.
The chemicals and gases leaving chimneys cause rapid deterioration and corrosion of the reinforcement in concrete chimneys. FRP products offer unique advantages for such repair. Thin sheets of FRP with a thickness of approximately 0.05 inch (1.3 mm) can be applied similar to wallpapers to strengthen the chimney. Afzir engineers will determine the number and orientation of fibers in each layer of the FRP fabric and will provide sealed engineering drawings for such repairs.
Grain silos are widely used in the agricultural industry. Environmental conditions that may include dry/wet loading cycles lead to corrosion of reinforcing steel and cracking of the concrete walls. Although the cracks can be injected and filled with epoxy, this solution does not address the loss of strength caused by corrosion of steel reinforcement. Attaching steel plates to the outside of the silos results in an unsightly solution that will require maintenance of the steel plates to prevent them from corroding. The connection of the plates at a few discrete points to the silo introduce their own design challenges for proper load transfer.
FRP offers a great solution for the above conditions. Thin (0.05 inch or 1.3 mm) layers of carbon FRP can be bonded to the surface of the silo. These layers will transfer the load over a large area, eliminating stress concentration points. The FRP will also provide an impervious layer that will protect the concrete steel from future corrosion. Afzir engineers can provide the design for these applications and sealed engineering drawings will be provided to the owner.
- Submerged Piles
Submerged piles are often used in river crossings and offshore platforms. The combination of dry-wet cycle results in rapid corrosion of concrete or steel submerged piles. In addition, marine wood borers and shipworms attack timber piles and weaken these structures. Afzir engineers will provide designs for retrofit of submerged piles that enhance axial, flexural and shear capacity of the pile. In all cases, the piles can be strengthened to levels far beyond the original undamaged pile. The sealed engineering drawings and calculations will be provided to the client.
- Foundations & Pedestals
The adverse environmental conditions in coastal, marine, refineries, and mines, etc. often result in corrosion of steel reinforcement and cracking of concrete in foundations. In some cases, improper design that did not call for adequate reinforcing steel may have to be addressed. In all these cases, FRP products offer unique and cost-effective solutions.
- Repairing Pipes
Deteriorated and leaking pipes are a major concern for pipeline owners and operators. FRP products offer unique solutions particularly when strengthening existing pipelines are required. Most of these techniques are performed as trenchless, requiring zero or minimal excavation.
Corrugated Metal Pipe (CMP) and concrete culverts are frequently used in highway and road construction. These pipes deteriorate and corrode with time, leading to a reduction in the load-carrying capacity of the culvert. Similar to deteriorated bridges that limit the load rating on highways, corroded culverts can lead to unsafe conditions. In extreme cases, the culvert may partially or fully collapse. In all cases, Afzir engineers will recommend the most suitable product for the repair. They will design the retrofit including the number and orientation of fibers in each layer of the FRP fabric and will provide sealed engineering drawings for such repairs to the client.
Concrete, steel or fiberglass tanks are extensively used in various industries to contain water, sewage, oil, and chemicals. The adverse service environment result in fast corrosion and deterioration of tanks. In concrete tanks, cracks in concrete allow passage of moisture and chemicals which expedites corrosion of the reinforcing steel. In steel tanks, the coating on the tank lasts only a few years and the bare metal begins to corrode rapidly. All these cases can be addressed using FRP products. Fabrics of carbon or glass FRP saturated with epoxy resin can be applied to the interior or exterior surface of the tank to strengthen the tank. Afzir engineers will calculate the required number of layers and orientation of the fabric for each project and will submit sealed engineering design drawings to the owner.
- Seawalls & Sheetpiles
Steel sheet piles and seawalls are commonly used in waterfront projects. The daily tidal changes introduce dry/wet cycles that lead to rapid corrosion of these structures. Most of the damage in sheet piles and seawalls occurs over the splash zone, which is defined by the low and high tide water elevation. The large size of sheet piles and seawalls and the fact that they are partially submerged in water makes their repairs very challenging. Afzir FRP system is an economical solution to such repairs.
- Utility Poles
Utility poles made with concrete, steel or wood are used in a various industries such as electrical, telephone and wireless communication industries. These structures face a variety of challenging issues. FRP technology offers a unique cost-effective method to repair or strengthen utility poles. Our technologies can address virtually all conditions for strengthening timber, concrete or steel poles and towers.
- Manhole/Access Points
Access points, commonly referred to as manholes provide access for the workers to buried infrastructure such as pipes, tunnels, utility vaults, etc. These structures are often made with concrete or brick. The moist environment combined by presence of H2S gases, lead to rapid deterioration of manholes. Our FRP technology offers an innovative cost-effective solution for repair of access points and manholes.
- Cooling Towers
The dry/wet loading cycle in cooling towers provides an ideal environment for corrosion of the structure. Many of these cooling towers are constructed with concrete, and the reinforcing steel corrodes after a short service life. In addition, larger cooling towers such as those used in the nuclear power industry include concrete beams and columns in the interior of the tower that corrode rapidly. Repairs must consider both a reinforcement scheme to replenish the area of steel lost to corrosion, and a protection mechanism to slow down the future corrosion rate of these elements. FRP fabrics and can be used to achieve both of the above objectives.
- Force Protection
With increased threat of terrorism, force protection and blast proofing buildings against explosions has become interesting to the public and government agencies in recent years. A great majority of the existing built infrastructure does not meet the strength and ductility requirements under blast loading. Afzir FRP products offers a solution for many such buildings.
- Historical Preservation
Preserving and restoring historic buildings is vital to understanding any nation’s heritage. None of these older buildings meet the current seismic (earthquake) or wind codes and must be upgraded for such load effects. In addition, general deterioration and aging or change of use often leads to repair and retrofit. In most cases, conventional repairs using steel and concrete may significantly alter the historic character of the building and thus become unacceptable. Afzir carbon or glass FRP products offer sustainable solutions for restoration and preservation of historic buildings with minimal change in the appearance of the structure.
- New Pipeline Construction
Pipeline construction is a multi-billion dollar industry worldwide. To date, all pipes have been built in short pieces (20 feet or 6 m long) in plants and are shipped to the site and connected together in the field to form a long pipeline. This system is very inefficient resulting in leaking joints and costly transportation of pipe segments from the factory to the site. Recently, Afzir Company introduced InSitePipeTM, a revolutionary technique for onsite manufacturing of pipes. The technique allows a pipeline of virtually any length and diameter to be made continuously on site – eliminating all joints
- Utility Vault
Access to utility vaults is normally provided through a manhole at the street level. Moisture is often entrapped in these vaults, resulting in corrosion of the side walls and the ceiling slab. This results in an unsafe condition for the traveling public that drive over these utility vaults. The limited access through manholes makes the use of repair with conventional materials such as steel and concrete challenging. Afzir engineers can provide solutions utilizing carbon or glass FRP fabric.
- Utility tunnel
Utility tunnels are frequently used in major government, university, medical, etc. campuses. These network of concrete tunnels can be very long and have cross sections of typically 7 ft. x 7 ft. (2m x 2m). Utility tunnels house various water, hot water, pressurized air, gas, etc. pipelines and communication and fiber optics cables. These tunnels are subject to water penetration from ground and the lack of ventilation leads to a hot and humid environment that is a fertile ground for corrosion of the reinforcing steel. Carbon or glass FRP fabric offers a great solution to repair and strengthen these utility tunnels.