When constructing a Pre-Engineered Building (PEB), the foundation design and construction play a critical role in ensuring the structure’s integrity and longevity. The foundation serves as the primary support for the entire building, making it essential that its design meets specific criteria and adheres to local building codes. This article will guide you through the key factors in foundation design and construction for PEBs, offering insights into proper practices that can help prevent common issues and ensure successful assembly.
Key Considerations in Foundation Design
1. Foundation Design Criteria
For any building, especially Pre-Engineered Buildings, the foundation must be designed by an experienced foundation engineer. This professional is responsible for ensuring that the foundation meets the specific load conditions required for the building. The foundation must also be coordinated with all local city, county, and state codes, as these codes outline the necessary structural requirements for safety and performance.
2. Foundation Integrity
To guarantee that a PEB performs optimally, the foundation must be constructed with precise specifications. This means ensuring that the foundation is sharply formed with true corners, straight sides, and a level top. Such precision allows for the correct alignment of the building components, reducing potential assembly issues and ensuring that the structure is properly supported from the ground up.
3. Adherence to OSHA and Local Laws
Construction sites must comply with Occupational Safety and Health Administration (OSHA) regulations and local laws regarding excavation. One critical aspect is the “shoring” of excavations to prevent accidental cave-ins. This is not only a safety measure but also ensures that the foundation excavation process goes smoothly, avoiding delays and additional costs.
4. Anchor Bolt Drawings
Pre-Engineered Building manufacturers provide anchor bolt drawings that outline the basic guidelines and requirements for foundation design. These drawings are essential for accurately placing anchor bolts in the foundation. Ensuring the correct placement and alignment of anchor bolts is one of the most important factors in achieving trouble-free assembly and maintaining building integrity.
Essential Characteristics of a Proper Foundation
1. Square, Level, and Smooth Foundation
A foundation’s shape and smoothness are key to the overall performance of a PEB. The foundation must be both square and level to ensure that all components of the building align correctly. The sides of the foundation should be straight, and the top should be smooth, without significant irregularities that could affect the assembly process.
2. Accurate Anchor Bolt Placement
Anchor bolts play a crucial role in securing the structural components of a Pre-Engineered Building. These bolts must be set with incredible precision—within +/- 1/16” of the specified dimensions on the anchor bolt plan. Any errors in bolt placement can lead to misalignment during the assembly of the building, potentially causing delays and requiring costly corrections.
Foundation Layout and Anchor Bolt Setting
1. Foundation Layout
The process of laying out the foundation should begin with careful and accurate planning. Before any excavation occurs, the perimeter of the foundation should be carefully marked. Ideally, a transit or similar tool should be used to lay out the foundation outline, ensuring precise corner placement and an accurate, square shape. Measuring the diagonals of the foundation frame or string-line is an effective way to confirm that the layout is square—if the diagonal measurements are equal, the foundation is square.
2. Setting Anchor Bolts
Anchor bolts must be set accurately to ensure the correct fit of the building components. One important consideration is the curing time of the concrete. It is essential not to begin erecting building components on “green” concrete, which is concrete that has not properly cured. For standard Portland cement, allow at least seven days for curing before any components are erected. For high-early-strength concrete, at least three days of curing is required. The reason for this is that concrete that hasn’t fully cured may be weakened or damaged by the weight and force of construction equipment.
Accurate anchor bolt placement (+/- 1/16”) is essential. These bolts must be positioned exactly as specified in the anchor bolt plan to avoid misalignment during the building’s assembly. It is also important that the bolts are securely held in place during the concrete pour, often by using templates or other methods to maintain their plumb alignment.
Detailed Steps for Setting Anchor Bolts
1. Use of Templates
One of the most effective ways to ensure the correct placement of anchor bolts is through the use of templates. Templates are typically made from plywood or a similar material and are designed to hold the anchor bolts in place during the concrete pour. These templates should be prepared ahead of time to ensure they can be quickly and efficiently secured in place when needed.
2. Air Relief in Templates
To further improve the accuracy of the anchor bolt placement, templates should include air relief holes. These holes allow trapped air to escape during the concrete pour and ensure that the concrete fully surrounds and encapsulates the anchor bolts. Proper vibration of the wet concrete is also crucial to ensure it fills all gaps and voids around the bolts.
3. Final Inspection
Before pouring the concrete, a final inspection of the foundation layout and anchor bolt settings should be conducted. This step ensures that all aspects of the foundation are correct and that the anchor bolts are in the proper locations. Any mistakes at this stage could result in costly delays during the building’s assembly.
Conclusion
The foundation design and construction process for Pre-Engineered Buildings is fundamental to the overall success of the project. A carefully planned, well-executed foundation provides a strong, stable base for the building and ensures that all components fit together correctly. By adhering to the guidelines outlined in this article—especially with regard to anchor bolt accuracy, proper layout, and curing times—you can avoid common pitfalls and ensure that your Pre-Engineered Building is built to last. Remember, attention to detail during the foundation phase ultimately leads to smoother construction, greater structural integrity, and reduced long-term maintenance costs.