The analysis of the quality of pre-buried anchor bolts is essential, not only due to the construction quality of the bolts themselves but also because of the overall process involved in their embedding within the foundation. This process typically includes: steel bar binding, template installation, pre-burial of anchor bolts, concrete pouring, curing, and formwork removal. When the pre-burial of anchor bolts is inaccurate—whether due to misalignment in spatial positioning, incorrect geometric dimensions, or insufficient fixation—it can lead to serious issues. The quality of both the anchor bolt installation and the formwork construction plays a critical role in ensuring accurate and stable placement of the bolts. These factors are among the primary causes of pre-burial quality failures in projects.
Formwork serves as a crucial element in the construction process, acting as a mold for cast-in-place concrete. It ensures that the structure takes the correct shape and size, and it provides a working platform and safety during concrete pouring. Therefore, anchor bolts must be securely fastened to the formwork to maintain their precise position. If the formwork system lacks sufficient strength, rigidity, or stability, it can result in deformation of the formwork under the weight of the poured concrete, which directly affects the accuracy of the embedded anchor bolts.
In this particular project, the construction site was originally a pond channel, and the building area was formed by backfilling. However, the original backfill contained a large amount of domestic waste, such as plastics and used tires, making the soil composition unstable. During the installation of the foundation and beam formwork, the side supports were fixed on the slope and pile areas, which were weakened by the garbage-filled backfill. This led to poor soil stability and reduced strength, causing some formwork supports to fail. As a result, the formwork deformed under the load of the concrete, leading to displacement of the embedded anchor bolts. The failure of the template workers to adapt the construction process to the site conditions was the main cause of the quality issue.
Concrete pouring also significantly impacts the quality of pre-buried anchor bolts. During the pouring process, vibration is usually done using a rod or a flat vibrator. If the construction team does not properly protect the pre-buried bolts, rough handling can cause them to bend or shift, affecting their final placement. Additionally, if the concrete is over-poured, it may reduce the exposed length of the anchor bolts, making it difficult to install structural components. In severe cases, uncontrolled pouring can lead to defects like honeycombing or leakage, resulting in non-compliant concrete elements and rendering the anchor bolts unusable. To prevent these issues, it's essential to have dedicated personnel monitoring the entire process and working closely with the concrete crew to address any potential problems promptly.
Regarding the quality accident in this project, the deflection of the anchor bolts was not severe, with the maximum deviation being less than 10 mm. In such cases, straightening is usually an effective solution. For bolts that caused issues with the column base plate installation, the base plate was reamed, and a 50x50 mm pad of the same thickness was added before welding and installing the foot nut. If the exposed part of the bolt was too short, it was handled based on a review of the required height. If the issue was due to over-pouring, excess concrete was cut away. If the problem stemmed from the anchor bolt sinking, the internal bolt could be machined to extend its length.
To address the root causes of the pre-burial issues, the formwork support system was reinforced, especially in weak soil areas, to ensure better strength, rigidity, and overall stability. Concrete pouring crews were also trained more thoroughly, with increased awareness of protecting the finished anchor bolts. By implementing these corrective actions, the project moved forward smoothly, effectively reducing the risk of future quality issues and ensuring the successful completion of the construction.
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