When discussing building reinforcement, most people immediately think of structural reinforcement. However, the construction process involves many different aspects. Let’s explore these together.
Frame Structure
01. Reinforcement of Frame Columns
(1) If the axial compression ratio of a frame column exceeds the specified limits, reinforcement can be done by wrapping the column with carbon fiber cloth based on test results. This increases lateral restraint of the concrete and enhances the component’s deformation performance under seismic loads.
(2) Depending on site conditions and construction feasibility, reinforced concrete can be added around existing columns to boost their load-bearing capacity.
(3) The original structural columns can be retained by wrapping steel frames around them and pouring structural adhesive between the layers. Then, high-strength mortar is applied to the reinforced columns wrapped with steel wire mesh.
02. Frame Beam Reinforcement
(1) Structural adhesive steel plate shear hoops are used to strengthen frame beams, with cement slurry applied on the surface of the steel plates.
(2) For beams whose end stirrups do not meet specifications, U-shaped carbon fiber cloth can be applied at the beam ends to improve shear resistance.
(3) Non-structural vertical cracks are treated with structural adhesive injection and pressure sealing.
(4) Steel bars are treated for rust prevention, reinforced full-length bars are inserted, U-shaped stirrups implanted, shear steel brackets installed, and everything fixed with tension bolts.
03. Isolated Foundation
Some existing independent foundations can be retained, with their length, width, and height increased. A concrete cushion layer is poured in the widened area to avoid damaging the bottom plate reinforcement. The original foundation is then treated with steel reinforcement to prevent rust and coated with new concrete interface adhesive.
04. Column Root Position
Main reinforcement of the column pier is implanted around the column and tied together. Newly poured concrete in this area is coated with interface adhesive to refresh old concrete. After pouring, formwork is supported, then removed after curing, completing the demolding and maintenance.
05. Floor Area
Carbon fiber cloth reinforcement is applied to existing floor and roof panels. The underside of the original floor slab undergoes steel reinforcement rust prevention, and the surface of the carbon fiber cloth receives fire protection treatment.
06. Structural Connection
When connecting original structural beams with newly added beam sections, main steel bars at the lower part of the secondary beam are anchored into the original beam, followed by concrete pouring to ensure the secondary beam’s shear strength. Demolding and curing processes follow.
Steel Structure
01. Pivot Reinforcement Method
Adding support points at mid-span of beams and slabs reduces the span, significantly increasing bearing capacity and limiting flexural deformation. This method suits horizontal structures such as beams, slabs, and trusses in large-span buildings where headroom is not restricted. Its advantages include simplicity and reliability, though it may reduce usable space.
02. Bonded Outer Steel Reinforcement Method
This wet wrapping technique reinforces reinforced concrete beams by externally wrapping steel using epoxy resin grouting to bond the steel to the concrete. Post-reinforcement, the cross-sectional steel area under tension and compression greatly increases, enhancing bearing capacity and stiffness.
03. Adhesive Fiber-Reinforced Plastic (FRP) Reinforcement Method
This method shares the benefits of bonded outer steel reinforcement but also offers corrosion and moisture resistance, minimal weight increase, durability, and low maintenance costs. It requires specialized fire protection and suits various concrete structural components and general structures.
After reinforcement, the steel plates should be lightly tapped with a small hammer to evaluate bonding based on sound, or ultrasonic testing can be used to assess bonding density.
If the adhesive area in the anchorage zone is below 90%, or below 70% in the non-anchorage zone, the adhesive is considered invalid and must be removed and reapplied.
For major projects, load tests are required to verify reinforcement effectiveness. Typically, standard load tests involve reapplying previously removed loads. Structural deformation and cracking during assembly should meet design criteria.
04. Prestressing Reinforcement Technology for Steel Structures
Bolt connections require drilling holes near damaged areas, which weakens the cross-section and creates new stress concentration zones. Ordinary bolts can loosen under dynamic loads, and high-strength bolts may suffer stress relaxation, reducing repair effectiveness.
Adhesive steel reinforcement uses specially designed structural adhesives to bond steel plates onto the steel structure surface, creating a unified load-bearing system and improving capacity. However, this method adds significant weight, complicates shaping, transportation, and installation, and is prone to corrosion, which affects bonding strength and increases maintenance costs.
Foundation Reinforcement
01. Shallow Reinforcement Methods
1. Soil Replacement Cushion Layer Method
This involves excavating weak soil layers below the foundation and backfilling with high-strength, low-compressibility, non-erosive materials like medium coarse sand, crushed stones, gravel, gray soil, plain soil, stone chips, or slag. The method is simple, cost-effective, and materials are readily available.
Soil replacement cushion layers are typically used for foundation reinforcement less than 2 meters deep, classified by backfill materials such as lime soil, sand, or crushed stone cushions. Lime soil cushions are mixed in a 1:3 ratio of quicklime to cohesive soil and are suitable where groundwater is low and foundation trenches are dry.
2. Lime Pile Method
This technique uses quicklime to absorb moisture from soil around piles, triggering hydration, reducing moisture content, compacting soil, and hardening piles. It’s generally applied for foundation reinforcement deeper than 4 meters.
During construction, steel casings are drilled and filled with quicklime blocks, supplemented with hydraulic admixtures like fly ash or volcanic ash in ratios of 8:2 or 7:3.
02. Deep Reinforcement Methods
1. Deep Mixing Method
This method blends cement, lime, or other solidifying agents with soft soil using specialized deep mixing machinery, hardening the soil and boosting foundation strength. It is commonly used for silt, silty soils, and cohesive soils with moisture content and bearing capacity below 120kPa.
Depending on the reinforcement material state, it is classified as slurry mixing (wet) or powder mixing (dry).
2. High-Pressure Jet Grouting Method
Using a drilling rig, a grouting pipe with a nozzle is inserted into soil layers to a set depth. High-pressure cement slurry or water is sprayed, mixing with soil to form cement soil solids, reinforcing the foundation. This method treats silt, silty soil, cohesive soil, sandy soil, artificial fill, and gravel foundations up to 30 meters deep.
Reinforcement of Existing Pipelines
01. Protection and Reinforcement Method
When pipelines intersect and the trench width is within 1.5 meters, this method applies. After excavation exposes the pipeline, hard materials like square timber or steel pipes matching trench width are placed alongside the pipeline and tightly tied with ropes, then wrapped with reflective tape. These protective materials are firmly secured to the trench walls at both ends, and warning signs are installed on both sides.
If the vertical clearance between pipelines is more than 1.5 meters, the soil around the pipeline is retained for protection. After excavating 1 meter on either side, an arched culvert section is manually created beneath the pipeline, sized to required space and integrated for finishing.
02. Suspension Reinforcement Method
When trench width exceeds 1.5 meters and the protection method causes excessive pipeline deflection, suspension reinforcement is necessary. This builds upon the protection method by placing steel beams along the trench top, spanning the trench and suspending the pipeline support from the hard protective materials with ropes spaced about 0.5 meters apart. Warning signs are posted on both sides.
If pipelines run parallel within the trench excavation area, hard materials are combined with the pipeline and suspended with ropes tied to wooden stakes or fixed objects outside the trench at 0.5-meter intervals. Warning signs are also installed.
Article source: Architectural Technology Magazine
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