Concrete anchor bolts are installed in concrete to facilitate the installation of embedded items like lamp posts, bollards, steel items, equipment, machines, landscape features, and structures. Most prominently, anchor bolts facilitate the installation of structural steel items like columns, posts, braces, and more.
A concrete anchor bolt is typically cast in place, with the item to be installed or drilled after the fact. When concrete anchor bolts are installed in situ, the anchor bolt placement must be within fine tolerance to ensure an architecturally sound installation.
Anchor Bolt Installation
That said, there is a bit of lee-way, but not much.
In addition to the placement of the anchor bolts, a contractor has to ensure that the embed depth is met. This ensures that the concrete adequately secures and counters any lateral or uplifting forces, anchoring the bolt in place. The tolerance of the anchor bolt placement depends on the installation requirements.
Concrete embed depth is typically noted on structural drawings or installation instructions for specific components.
If you have large structural requirements and loads bearing on your concrete slab, expect tighter tolerances; with that, a surveyor’s professional services might be useful. Tolerance in anchor bolt layout is needed for layout with baseplates, location in concrete elements, embed depth, and clearance from other elements if dictated by the engineer. For example, minimum cover might be necessary.
Coordination of Anchor Bolts
When installing anchor bolts, for instance, with concrete pilasters, footings, or foundation walls, the anchor bolts will coincide with the reinforcement installed within the concrete item. This has to be coordinated on-site with the formwork contractor and the rebar installer to ensure that minimum concrete cover is maintained on all sides, proper spacing between the concrete anchors is kept, and that the concrete embed anchor bolts clear rebar too as necessary.
Typically, on larger construction projects you will find that part of the general contractor’s job is to ensure compliance in the positioning of these anchor bolts. Furthermore, anchor bolt patterns of layout are specific to the baseplates or mounting components for the item. This could be, for instance, a steel column baseplate with a specific setting point for the anchors.
Light Post Baseplate Installation
Light posts are a commonly installed utilization of anchor bolts. Light posts come from the factory with baseplates and manufactured bases with holes already established for the correct placement of the anchor bolts and subsequent threading of bolts.
One of the ways we ensure proper placement of anchor bolts, as close as humanly possible to the desired set point for the structural integrity of the item to be installed, is through the use of rebar ties and formwork. The formwork and rebar ties can be used to correctly set anchor bolts and hold them in place during the concrete placement and pouring. Even through the necessary vibration of concrete, properly securing anchor bolts, such as with similar methods to tying rebar, can ensure they do not shift or move from the desired installation pattern.
Securement is key to ensuring tolerances are not exceeded with anchor bolt installations.
Anchor Bolt Embed Depth
Furthermore, anchor-bolt embed depth is subject to the requirements dictated by a structural engineer for a structural steel column or other structural element. What is known as baseplate designs and layouts are provided as part of the structural design blueprints for a construction project. Baseplate blueprints are to coincide with the structural concrete blueprints for the job, laying out the necessary anchor bolt pattern for each structural steel item and setting the correct baseplate elevation.
Commonly, if baseplate elevations are incorrect in some scenarios and subject to the approval of a structural engineer, steel columns can be modified. However, the sizing of the steel anchor bolts and layout is a connection between the steel and concrete, where neither the specialty steel contractor nor the concrete contractor takes full responsibility. The structural engineer typically needs to determine how to connect separate trade disciplines to achieve the correct structural integrity of the building using anchor bolts.
Baseplate Layouts – Anchor Bolts
As such, determining baseplate layouts, anchor bolt size, and embed depth would be a discipline borne by the over-arching structural engineer in practice. For manufactured products, layout and embed may be specified from factory, such as with bollards or light posts.
As a professional concrete company, we must ensure that the structural concrete design plans are followed. However, it is not our responsibility to ensure that the structural steel subcontractor’s shop drawings, as in the fabrication drawings, align with the structural design intent of the engineer of record for the concrete drawings. Rather we pour to the structural concrete foundation drawing requirements.
Where contracted to do so, a contractor could ensure anchor bolts at the correct depth of embedment (e.g. 180mm), the correct baseplate layout is utilized (e.g. BP #1 through #30), and that the overall centredness and placement of the anchor bolt pattern aligns correctly with project means & methods for the formwork of the grade beam, pilaster, foundation wall, or concrete slab.
Photo Above: Anchor bolts for light posts typically are provided pattern, size, and embed depth based on the manufacturer’s instructions.
Post-Pour Concrete Anchor Bolt Installation
Alternatively, post-pour methods can be used to install concrete anchor bolts for less structurally intense concrete items, like handrails, guardrails, ladders, hangers, or other miscellaneous steel items. Concrete anchors like these should still be specified by the structural engineer or an architect on the job based on the requirements of the specific item. A concrete contractor would simply pour the concrete and not get involved in any items to be installed after the fact.
Photo Above: Certain elements, like handrails, can be installed with concrete anchor bolts after the fact, or provided embeds for welding/bolted connections. Both conditions would typically require installation on-site.
Concrete Scanning
Proper reinforcement alignment is essential when installing anchor bolts after the fact, as this could, in some cases, avoid the need to scan concrete for longer embeds. However, for most serious post-pour concrete anchor bolt installations, concrete scanning is typically suggested to ensure that the rebar installed is not damaged as anchor bolts or other concrete drilling procedures are installed/performed.
So, how do concrete anchor bolts work?
How do concrete anchor bolts work?
Well, structurally, the curing of the concrete in line with the utilization of appropriately sized, adequately secured, and professionally installed anchor bolts allows for baseplates, steel items, products, and miscellaneous metal items to be installed properly. Anchor bolts typically act as securement methods for these baseplates or other steel items, creating the perfect intersection between steel and concrete, from a structural perspective but also from a scope/discipline standpoint. A nut is threaded onto the bolt to finalize the installation process.
Where anchor bolts are utilized en-masse, typically, you will find the involvement of a general contractor to ensure no scopes are adversely affected through the installation, such as concrete, formwork, reinforcement, and steel scope.
The concrete secures the anchor bolts based on embed depth and some of the anchor bolt’s design characteristics, such as L-shape or U-shape bottoms.
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If you did, please consider sharing it. Concrete anchor bolts play an integral role in many multi-residential and commercial concrete projects, facilitating the installation of structural and architectural elements key to a project’s success. Your concrete contractor, steel contractor, or general contractor may be responsible for installing these items.
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