For structural engineers, specifying this standard adds minimal cost but eliminates massive liability. For contractors, using these chairs reduces rework and callbacks. For building owners, it means a foundation that will outlast the steel frame above it.
| Step | Better Practice | |------|------------------| | | Show exact slot length, washer type, weld symbol, and grout thickness | | Material | Use 50 ksi min. thickness ≥ 3/16″ (0.1875″) for base plate | | Welding | Double-fillet lap welds; no skip welding on tension faces | | Anchor bolt placement | Use a bolt template jig (not just string line) | | Grouting | Dry-pack grout with 1% expansion; cure 3 days before column erection | | Torque | Tighten nuts to 30–40 ft-lbs only (to avoid bending chair plate) | | Inspection | Verify chair is level within 1/16″ per ft, bolt centered in slot |
: For high-stress applications, using a continuous ring that connects the tops of all chairs can significantly improve stability. If used, the shell within 16 times its thickness (
Because anchor bolts sit on a bolt circle outside the actual shell diameter, an inevitable gap exists between the centerline of the bolt and the centerline of the shell. This gap represents the .
Many traditional methods for designing anchor bolt chairs rely heavily on rules of thumb or simplified empirical formulas. These approaches often result in "over-designing"—using excessive steel to compensate for a lack of precise calculation—or, conversely, under-designing in areas of high stress concentration. aisi e 1 volume ii part vii anchor bolt chairs better
Part VII harmonizes the design of anchor bolt chairs with modern steel design philosophies, including Load and Resistance Factor Design (LRFD) and Allowable Strength Design (ASD). This compatibility allows structural engineers to integrate chair design seamlessly into broader building information modeling (BIM) and finite element analysis (FEA) workflows. Enhanced Safety in Seismic Zones
To help tailor this design information to your specific project, tell me: What is the you are using? What is the thickness of the bottom tank shell course ?
This article delves into the world of anchor bolt chairs, exploring the "why," "how," and the crucial details that separate a robust design from a problematic one.
The "better" part of your query likely refers to why chairs are preferred over simple base plate bolting. Specifically, chairs are necessary to distribute the load to the shell and minimize secondary bending in the shell wall. Key Design Parameters | Step | Better Practice | |------|------------------| |
The AISI design methodology is explicitly referenced by premier design codes like for vertical storage tanks. It stands out as superior over generic or simplified handbook approximations for several critical reasons: Exact Quantification of Localized Shell Stresses
When a storage tank experiences overturning moments from wind or earthquakes, the anchor bolts are pulled taut in tension. Because the anchor bolt must physically clear the shell wall, it sits at a specific distance—called —away from the centerline of the shell plate.
An optional plate used for stability or to increase the bearing area on the foundation. Why the AISI E-1 Method is Superior
The welding of the chair itself is robust, ensuring the chair doesn't fall apart during the vibration of the concrete. This gap represents the
Anchor bolt chairs are specialized structural attachments used to distribute high uplift loads from anchor bolts into a shell or column. They are essential because anchor bolts are typically positioned at an (a distance away from the shell's centerline). Without a chair, this eccentricity would cause severe localized bending in the thin shell, potentially leading to buckling or failure. Key Advantages of the AISI E-1 Part VII Standard
The "better" chair isn't just a holder—it's a structural transfer device.
Why AISI E-1 Volume II Part VII Anchor Bolt Chairs Provide Superior Structural Integrity
The primary challenge in designing an anchor bolt chair is avoiding localized buckling or yielding of the tank shell. Because the shell is relatively thin compared to the forces it encounters, the chair must distribute the eccentric bracket load smoothly. AISI formulas calculate the exact bending and membrane stresses induced in the shell wall. 2. Prevention of Top Plate Yielding