The Usage of CFRP on RC Silos

The Usage of CFRP on RC Silos

Causes of Damage and Failure of RC Silo Structures

Silos are structures in which their validity, as well as durability during design, construction and utilization, are of high importance.

1. Applied loads on silo walls:

Dead & live loads, the pressure of stored material, overpressure generated during filling or discharge, stress concentration on discharge openings, thermal loads, wind and earthquakes.

2. Reasons of formation of horizontal and vertical cracks on silo walls:

Static and dynamic applied loads on walls, periodic loading and unloading of silos, the influence of construction joints, thermal insulation, active environment chemistry, etc.

Negative effects of cracks on silo function

  • Concrete deterioration
  • Corrosion and rusting of steel bars
  • Reduced stiffness
  • Water penetration into the walls
  • Reduction in load bearing capacity of silo walls
  • Decreasing reliability of silo performance
  • Deformations and deflections (buckling of walls)
  • Reduction in service life of the whole structure
  • Concrete cracks expose the material inside the silo to the air, thus will affect the chemical properties of the material as well as their expiration date
The Usage of CFRP on RC Silos

Figure 1: Rhino Carbon Fiber™ CFRP Installation Surface Prep

Signals of distress in silos

Concrete cover deterioration, concrete cracks and falling dust from silo walls are the most common signals of silo failure. After realizing these problems, silo owners must start repairing and strengthening RC silos.

The Usage of CFRP on RC Silos
The Usage of CFRP on RC Silos

Figures 2 & 3: Cracking and concrete deterioration of a silo wall

Different methods of RC silo strengthening

One of the main reasons of silo failure is the short overlaps of horizontal reinforcement. The destructive effect of this problem is doubled if the overlaps are in the same line over the height of the silo. How can you fix this failure?

1. Adding steel hoops along the whole height of the silo. Disadvantages of this method:

Steel hoops are connected by screws; by reducing the cross-section of the steel hoops at the area of connection, the strength of bars in the connection area will reduce as well. If all connecting screws are in one vertical line, there will be one line in the silo with weakness. Also, the risk of corrosion of rebar is significant in this method.

2. Externally pre-stressed tendons. Disadvantages of this method:

For the main deficiencies of this method, we can name “breaking off” as well as “corrosion” of strings. Breaking off of strings in any location will destroy their pre-stressing properties.

Strengthening RC silos using CFRP

The other globally accepted method of RC silo strengthening is the usage of externally bonded CFRP. The most important positive benefit of CFRP is corrosion resistance.

Some strength points of CFRP that will increase silo durability significantly are:

  1. High strength of CFRP
  2. High elastic modulus
  3. High resistance to harsh environments (for example ports and marine areas)
  4. Increasing flexural as well as confinement capacity of the cracked silo
  5. Easy and fast installation
  6. Reducing interruption in serviceability of the silo
  7. Reducing costs of repairing and strengthening of silos
  8. Corrosion resistance
The Usage of CFRP on RC Silos

Figure 4: Strengthening RC Silo using RHINO CARBON FIBER™ CFRP

The benefits of cracked silo strengthening with Near-Surface Mounted (NSM) over externally-bonded CFRP

1. Improved anchorage capacity of NSM CFRP reinforcement with concrete. Also satisfies the required embedded length of CFRP reinforcement in concrete due to larger bond surface

2. Higher load-bearing capacity and higher deflection up to failure compared to EBR

3. Requires minimum surface preparation

4. Requires much less installation time compared to externally-bonded CFRP

5. High speed of grooving concrete and inserting CFRP strips

6. The low weight of the CFRP strips

7. Cost-effective

The Usage of CFRP on RC Silos

Figure 5: Silo concrete wall cross-section illustrating steel reinforcement and NSM CFRP strips

Authors

Parastoo Azad and Dr. Mehrtash Soltani (January 15, 2021)

References

  1. ACI313. (2016). Design Specification for Concrete Silos and Stacking Tubes for Storing Granular Materials (ACI 313-16) and Commentary. American Concrete Institute.

  2. Maj, M. (2017). Some Causes of Reinforced Concrete Silos Failure. Procedia Engineering, 685-691.

  3. Maraveas, C. (2020). Concrete Silos: Failures, Design Issues and Repair/Strengthening Methods. Applied Sciences.

  4. Prota, A. (n.d.). Upgrade of RC Silos Using Near Surface Mounted FRP Composites. Retrieved from https://pdfslide.net/documents/upgrade-of-rc-silos-using-near-surface-mounted-frp-composites-upgrade-of-rc.html

  5. Sezen, A. D. (2009). Cause of Damage and Failures in Silo Structures. Journal of Performance of Constructed Facilities, 65-71.