Installing anchor bolts correctly is one of the most important parts of setting out a steel frame. A small alignment error can cause serious issues during column erection — leading to on-site delays, rework, or even structural risk.
This guide from BoltBox explains how to fit anchor bolts for steel columns step by step, covering setup, alignment, and key safety checks.
What Are Anchor Bolts for Steel Columns?
Anchor bolts (or holding down bolts) are threaded steel bars cast into concrete foundations.
They secure the baseplates of steel columns and transfer the loads safely into the foundation.
When installed correctly, they:
Hold the column in position during erection,
Prevent lateral movement, and
Provide a permanent, load-bearing connection.
Most anchor bolts for steel frames are cast-in bolts supplied in M16, M20, or M24 diameters, made from grade 8.8 high-tensile steel.
Tools and Materials Required
Before starting, ensure you have the correct tools and components:
Tools
- Steel tape or laser level
- Spanner set / torque wrench
- Vibrator (for concrete compaction)
- Spirit level or column plumb line
- Marker stakes / chalk line
Materials
- Anchor bolt sets (M16–M24)
- Bolt boxes or templates
- Square plate washers and nuts
- Waxed cardboard cones
- Reinforcement bars and shuttering
- Concrete (as per structural specification)
Step-by-Step Installation Procedure
Step 1 — Review Drawings and Bolt Layout
- Check the foundation and steelwork drawings for bolt positions, projection height, and spacing.
- Mark centre lines on the foundation using chalk or string to establish accurate grid lines.
- Verify the bolt pattern matches the baseplate hole configuration.
💡 Tip: A small error in bolt spacing can prevent the baseplate from fitting later — double-check all measurements before fixing.
Step 2 — Prepare and Assemble the Bolts
- Fit square plate washers and nuts at the base of each bolt.
- Insert bolts into bolt boxes or steel templates to maintain alignment.
- Ensure the projection height allows for the baseplate, washers, and nuts above the finished concrete level.
🔧 If required, fix temporary supports to hold the assembly in place before pouring.
Step 3 — Position the Bolts
- Place the bolt boxes or templates in the foundation according to the set-out marks.
- Check both horizontal and vertical alignment using a spirit level or laser.
- Ensure adequate concrete cover and clearance from rebar.
Correct positioning now saves significant time later during column erection.
Step 4 — Protect the Threads
- Slide waxed cardboard cones or protective sleeves over the bolt threads before pouring.
- These cones prevent concrete from blocking threads and make nut fitting easier after curing.
⚠️ Never pour concrete directly onto exposed threads — this leads to contamination and reduced strength.
Step 5 — Pour and Compact the Concrete
- Pour concrete carefully around the bolt assemblies, avoiding displacement.
- Use a vibrator to remove air pockets and ensure proper compaction.
- During the pour, re-check alignment visually — bolts can shift slightly as concrete flows.
Allow the foundation to cure for at least 7–28 days (depending on design requirements).
Step 6 — Remove Cones and Clean Threads
- Once the concrete has cured, remove waxed cones to expose clean bolt threads.
- Brush away any loose debris or laitance.
- Apply a light oil or anti-corrosion coating to protect exposed steel until column installation.
Step 7 — Fit the Steel Column Baseplate
- Position the baseplate or column carefully over the bolts.
- Fit washers and nuts, then hand-tighten to hold in place.
- Check the column is plumb and level before tightening to final torque.
- Tighten nuts gradually in sequence using a calibrated torque wrench to prevent uneven stress.
🔩 Follow the engineer’s torque specification — overtightening can crack the surrounding concrete.
Post-Installation Checks
| Check | Purpose |
|---|---|
| Bolt alignment and projection | Ensures baseplate fits accurately |
| Thread condition | Confirms nuts can be tightened properly |
| Torque values | Verifies correct tension for load transfer |
| Concrete curing and finish | Confirms integrity of the foundation |
If any bolts are out of position, consult the project engineer before attempting correction.
Design and Standard References
- BS 7419: Specification for cast-in holding down bolts.
- BS EN ISO 898-1: Mechanical properties of fasteners (grade 8.8).
- BS 8539: Code of practice for the selection and installation of post-installed anchors.
Compliance with these standards ensures that every bolt performs safely under load.
Common Mistakes to Avoid
Skipping templates: Leads to misalignment.
Concrete vibration too close to bolts: Can shift assembly.
Wrong projection height: Insufficient thread for nuts.
Over-tightening: Can crack concrete or strip threads.
Unprotected threads: Concrete contamination and rework.
Why Use BoltBox Anchor Bolt Systems
At BoltBox, we supply complete holding down bolt sets, including:
- Galvanised M16, M20, M24 bolts,
- Square plate washers and nuts, and
- Waxed cardboard cones to protect threads during pouring.
Our systems are manufactured in the UK and designed to meet BS 7419 for consistent accuracy and safety on site.
🔗 Shop Now: Holding Down Bolt Sets (M16–M24)
🔗 Request a Quote: Get a Custom Quote
Product Availability and Ordering Options
All BoltBox anchor bolt sets are held in stock for fast UK delivery and can be ordered online through our secure checkout or trade desk.
We supply standard sizes (M16, M20, M24) and custom configurations on request.
Trade customers can access bulk pricing and dedicated support for repeat orders or site-specific designs.
Accessories such as square plate washers, nuts, and waxed cones are available to order individually or as part of complete kits.
📞 Need Expert Help with Anchor Bolts?
BoltBox provides engineer-approved anchor bolt sets and technical support for steel and concrete foundations across the UK.
Speak to our team for project advice or a custom quotation.