How Does Steel Jacketing Increase Structural Strength?
This system works by confining the concrete core. Steel angles and plates resist part of the compressive and bending forces, while transverse straps increase member shear strength. The main results include:
- Increased column axial strength
- Increased structural member flexural capacity
- Prevention of brittle shear failure
- Increased structural ductility
- Prevention of longitudinal reinforcement buckling
- Increased earthquake energy absorption
- Improved building performance under seismic loads
Components of a Metal Jacketing Strengthening System
This method comprises several main components, each playing an important role in increasing load-bearing capacity and improving seismic performance.
Angles are placed at the four corners of the column to transfer axial and bending forces. Their dimensions and thickness are determined by structural calculations.
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Confinement Straps and Plates
Steel straps are connected to the angles at specified intervals to confine the concrete core. In addition to increasing shear strength, they prevent local buckling of longitudinal members.
Voids between existing concrete and steel components are filled with cementitious mortars or specialist resins to ensure uniform stress transfer between steel and concrete.
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Bolts and Mechanical Anchor Bolts
Some installation details use post-installed rebar and bolts to provide suitable connections and force transfer between existing concrete and new components.
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Corrosion Protection Coating
Because steel is susceptible to environmental exposure and moisture, epoxy paints and protective coatings improve durability and prevent rusting.
Fire-resistant coatings are essential in many projects to improve fire resistance and maintain the load-bearing capacity of steel members.
Steel Jacketing Design Rules and Code Requirements
Design and installation must comply with recognized national and international codes to ensure suitable structural performance during service and earthquakes.
- FEMA 356 Guidelines: A key reference for building seismic rehabilitation, providing criteria for increasing structural member strength and ductility.
- Publication 360 of the Plan and Budget Organization: Publication 360 is the main reference for seismic rehabilitation of existing buildings in Iran, explaining design and installation requirements for various strengthening methods.
- ACI 318: This standard provides requirements for reinforced concrete member design and behavior, strength checks and construction details.
- National Building Regulations: Chapter 9 and other National Building Regulations must also be considered in strengthening project design and execution.
The main design checks include:
- Local buckling of longitudinal angles
- Appropriate spacing of confinement straps and plates
- Shear transfer at the column base
- Suitable foundation connection design
- Beam-column connection details
- Foundation load-bearing capacity
- Structural seismic performance after strengthening
- Welding and connection quality
