Over time, many existing buildings experience a decline in their seismic resistance, making them vulnerable to structural instability during earthquakes. As a result, an increasing number of construction companies are focusing on reinforcing and renovating these buildings, leading to intense competition in the industry. The key challenge lies in developing reinforcement plans that satisfy building owners.
Thorough Building Inspection: The Foundation of Effective Reinforcement
Conducting a comprehensive inspection of a building’s structural condition is essential. Reliable data gathered through these inspections serves as the foundation for designing reinforcement schemes, improving their feasibility and cost-effectiveness.
The main objectives of assessing existing buildings include:
- Providing a technical basis for routine management, as well as major, medium, minor, or emergency repairs.
- Supporting changes in building usage, renovations, or expansions.
- Determining the extent of damage caused by accidents or disasters to guide repair or reinforcement plans.
- Offering technical insights for resolving issues stemming from design or construction errors.
Some property owners hire third-party agencies to inspect buildings. Construction companies must critically evaluate the credibility of such reports to avoid basing reinforcement plans on inaccurate data. If testing methods are unsuitable or data appears questionable, companies should conduct on-site inspections and verifications to ensure precision.
Reinforcement Methods
1. Masonry Structures
Masonry structures rely on blocks and mortar to form walls and columns that bear loads. These structures typically exhibit low tensile and shear strength and poor overall integrity. Assessing their safety requires two main steps:
- On-site investigation of structural conditions, especially since many older masonry buildings lack detailed design drawings. Special attention should be paid to the locations of structural columns and ring beams.
- Distinguishing load-bearing walls, gable walls, and partition walls, and verifying any changes in their functional use.
Because masonry is composed of two different materials with inherently poor overall integrity, current testing methods struggle to accurately reflect true masonry strength. Common testing techniques include rebound methods, flat hydraulic jack loading, cutting tests, and in-situ axial compression tests.
2. Frame Structures
Frame structures consist of beams and columns connected by steel reinforcements, designed to resist both horizontal and vertical loads during use. Unlike masonry, frame structures typically have complete design drawings. Inspections should verify the building’s layout against these plans and pay close attention to cracks in beams, columns, nodes, and floor slabs.
Cracks accelerate steel reinforcement corrosion in reinforced concrete, creating a harmful cycle that reduces durability and shortens the structure’s lifespan.
Testing methods for frame structures include:
- Concrete strength testing using rebound methods or core drilling.
- Measurements of component dimensions, main reinforcement quantity, and stirrup spacing.
- Re-examination of reinforcement protective layers and overall structural bearing capacity.
Principles of Reinforcement
The process of structural reinforcement and renovation involves three key stages: structural reliability assessment, scheme design, and construction. The core technical tasks include assessing the existing structure, selecting the appropriate reinforcement methods, and managing the construction process. Reliable detection data is crucial for determining the most effective reinforcement strategy.
When developing reinforcement plans, two important points must be considered:
- Avoid blindly adopting new reinforcement technologies; instead, choose methods that suit the project’s specific needs.
- Ensure strict adherence to reinforcement technology disclosures, guaranteeing that workers follow every detail of the plan.
Many reinforcement schemes incorporate innovative techniques such as carbon fiber reinforcement, adhesive steel plate methods, and prestressed reinforcement. While these methods can be effective, they tend to be costly and are not always necessary. Selecting an appropriate method requires balancing effectiveness, construction complexity, and cost to meet reinforcement goals efficiently.
During technical disclosure, it is critical to emphasize the reinforcement procedures and processes, including detailed handling methods. Construction acceptance should strictly follow these disclosures, and all materials must meet specified standards to ensure the desired reinforcement outcomes.
Additional reinforcement principles include:
- If authoritative assessments recommend reinforcement, it should be conducted promptly, whether for the entire building or specific areas.
- Designs should consider both the feasibility of construction methods and ease of implementation. For concrete structures, increasing concrete strength and strengthening connections or construction measures is advisable.
- For damage caused by vibration, freeze-thaw cycles, corrosion, or high temperatures, the best approach involves eliminating or mitigating these factors.
- Reinforcement should be as economical as possible, aiming to maximize effectiveness without halting building operations or damaging original components.
- Safety during reinforcement construction is paramount. If serious defects are found, work must stop immediately until hazards are fully resolved.
Important Precautions
When planning structural reinforcement, the safety of construction personnel, reliability of results, simplicity of methods, optimal construction timelines, and cost-effectiveness must all be balanced. Studies from China show that some projects overly focus on reinforcement outcomes while neglecting safety, economy, and technical rationality.
It is advisable to incorporate new processes, materials, and technologies whenever possible to meet reinforcement needs effectively. Experience demonstrates that applying these advanced solutions leads to significant construction benefits.
Seismic Verification After Reinforcement
Seismic performance must be reassessed based on seismic forces, gravity, seismic influence coefficients, and combined effects to verify the design intensity. Additionally, it must be confirmed that the building continues to meet its original functional requirements.
For buildings undergoing only seismic reinforcement or partial renovation, seismic deformation checks are not required. However, if additional floors are added during renovation, seismic deformation verification is mandatory.
Buildings reinforced with prefabricated residential structures and having a design service life of 25 years or less can apply a seismic capacity reduction factor of 0.85, as specified in regulations.
If changes in the stiffness and gravity representative values of the reinforced structure are less than 10% and 5% respectively, seismic impact may be disregarded. However, if the original structural system is altered, a comprehensive seismic review must be conducted based on the updated structure.
Article source: Architectural Technology Magazine
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