Yes, steel beams can be bolted together, and they can be welded together. Both are standard ways to connect beams to columns, beams to other beams, and two lengths of beam end to end. Most structural steel is welded in the shop and bolted on site: plates and angles are welded to the members under controlled conditions, then the pieces are bolted together during erection. Whichever method is used, the connection has to be designed by an engineer for the forces it carries, and welding on structural steel in Canada is done by CWB-certified companies.
This post explains the main connection and splice types, how bolting and welding compare, and what that means if you need to join, extend or support a beam.
Connections and splices: not the same thing
Two words get mixed up:
- A connection joins different members: a beam to a column, a beam to a girder, a beam onto a post or wall.
- A splice joins two lengths of the same member to make a longer one, usually because the full length cannot be rolled, shipped or installed in one piece.
Connections are part of every steel job. Splices are needed less often, and where they are used the location matters: the engineer places them where the forces can be carried and designs the splice for those forces. Our guide to standard steel beam lengths and delivery limits covers why long beams sometimes have to be spliced.
Common beam connection types
| Connection | How it is made | Typical use |
|---|---|---|
| Shear tab (single plate) | Plate welded to the column or girder, beam web bolted to it | Simple beam-to-column and beam-to-beam framing |
| Double angle (clip angles) | Two angles on the beam web, bolted or welded to the support | Simple framing, common in older and repetitive buildings |
| Shear end plate | Plate welded across the beam end, bolted to the support | Simple framing where a clean end detail is wanted |
| Seated connection | Beam sits on a seat angle or bracket, with a top angle for stability | Beams bearing on columns or walls |
| Bolted moment connection | Flange plates or an extended end plate, bolted | Frames that resist bending at the joint |
| Welded moment connection | Beam flanges welded to the column, often in the field | Moment frames where the design calls for it |
| Beam on post with cap plate | Post or column with a welded cap plate; beam bolted or welded to it | Basement beams and residential framing |
Shear connections (also called simple connections) carry the beam's reaction but allow the beam end to rotate a little. Moment connections also transfer bending, which makes them heavier and more demanding to detail and install. The type is set by the structural design, not chosen on site.
In houses, the most common joint is a beam sitting on a steel post with a cap plate, or two beam lengths meeting over a post.
Splicing beams end to end
When a beam has to be joined along its length, there are three common approaches:
- Bolted flange and web splice. Plates bolted across the flanges and the web on both sides of the joint. Easy to install in the field and easy to inspect.
- Bolted end plate splice. Each beam end gets a welded end plate in the shop, and the two plates are bolted together on site. Compact, but fit-up must be accurate.
- Welded splice. The two beam ends are prepared and joined with complete joint penetration groove welds. Usually done in the shop; field-welded splices need certified welders, access, weather protection and inspection.
A splice designed for the full strength of the beam can go almost anywhere; a lighter splice is only valid where the forces are low. That is an engineering judgment for the specific beam and load. A splice that just "looks strong" is not a design.
Bolted vs welded compared
| Factor | Bolted | Welded |
|---|---|---|
| Where the work happens | Mostly on site, with shop-welded plates | Mostly in the shop; field welding where needed |
| Speed of erection | Fast; pieces can be connected as soon as they are set | Slower in the field; preheat, weld and cool time |
| Weather | Little effect | Field welding needs protection from wind, rain and cold |
| Skills and certification | Trained ironworkers; correct bolt installation method | CWB-certified company, qualified welders, approved procedures |
| Fire risk on site | Low | Hot work, a real concern next to wood framing in houses |
| Inspection | Bolt type, count, tightening method | Visual inspection, plus testing where specified |
| Adjustment for tolerance | Slotted or oversized holes and shims allow some adjustment | Can be fitted to suit, but changes are harder to undo |
| Appearance | Bolts and plates visible | Cleaner lines, especially when ground |
| Connecting to existing steel | Drilling on site; no heat | Existing steel and coatings must be suitable for welding |
Neither method is stronger by nature. A welded joint and a bolted joint can both be designed for the same forces. The choice usually depends on the site, the schedule and what the erector can do safely.
Bolting: what goes into a bolted connection
Structural connections use high-strength structural bolts, typically ASTM F3125 Grade A325 or A490, with matching nuts and hardened washers. Hardware-store bolts are not a substitute. The engineer specifies:
- Bolt grade, diameter and number
- Hole type: standard, oversized or slotted
- How the bolts are installed: snug-tight, or pretensioned where the joint needs it
- Whether the joint is slip-critical, which also controls the condition of the faying surfaces and any paint on them
On Canadian projects, bolted connections are designed to CSA S16. The shop drills or punches the holes to the shop drawings, so a bolted connection depends on accurate detailing.
Welding: what goes into a welded connection
For structural steel designed to CSA S16, the fabricators and erectors who weld must be certified by the Canadian Welding Bureau to CSA W47.1 (Division 1 or 2), and the welds follow CSA W59. In practice that means approved welding procedures, qualified welders, a qualified welding supervisor and inspection. See why hire a CWB-certified fabricator and our overview of CSA W59.
Shop welding is preferred where possible because the piece can be positioned for easy access, conditions are controlled and the work is easier to inspect. Field welding is used where it has to be: certain moment connections, column splices, connections to existing steel, or details the designer chose to weld. Our article on structural welding services compares shop and field welding in more detail.
Joining or extending a beam in an existing building
Searches like "steel beam extension" and "how to join I-beams" often come from renovation projects: extending a basement beam after a wall comes out, adding a beam beside an old one, or tying a new beam into existing steel. A few points to know before you start:
- It needs a design. Extending a beam is a splice, and supporting a new beam off an old one adds load to it. A structural designer or engineer has to check the existing steel, the new connection and the supports below.
- It usually needs a permit. Structural changes in Ontario homes generally need a building permit, with drawings showing the beam, the connections and the posts.
- Existing steel is an unknown. Its grade, condition and coatings affect whether it can be welded and how. Old paint and galvanizing have to be dealt with before any welding.
- Hot work in a house is a fire risk. In finished or wood-framed spaces, a bolted connection fabricated in the shop is often easier and safer to install. The designer will weigh that.
- A new support may be simpler. Sometimes a new post and footing under the joint is a better answer than a long splice.
Do not weld or bolt a piece onto a beam to make it longer without an engineered detail. A poorly placed or undersized joint becomes the weakest point in the beam.
Getting connections fabricated
We fabricate beams, columns and posts with their connections: shear tabs, end plates, cap and base plates, and splice plates, cut, drilled and welded to the shop drawings we prepare in-house. Our shop welding is certified by the Canadian Welding Bureau, engineering services are available for projects that need them, and we supply and install structural steel, from basement beams and posts to commercial framing.
Send your structural drawings for a free take-off and quote, or see our steel products for beams, plates and posts fabricated to order.
Frequently asked questions
Can steel beams be bolted together?
Yes. Bolted connections and splices are standard in structural steel, using connection plates or angles and high-strength structural bolts. The plates, bolt size, grade, number and installation method all have to come from an engineered design.
Can steel beams be welded together?
Yes, by a certified fabricator or erector working to an engineered detail. On structures designed to CSA S16, welding must be done by companies certified by the Canadian Welding Bureau, and welds follow CSA W59. Most structural welding is done in the shop.
How do you join two I-beams end to end?
With a splice: bolted splice plates on the flanges and web, a bolted end plate splice, or a full penetration welded splice. Where possible, beams are joined over a column or post instead. Either way the splice is designed by an engineer for the forces at that location.
Is a bolted or welded connection stronger?
Neither is stronger by nature. Each is designed to carry the required forces. The choice usually comes down to site conditions, speed of erection, inspection, access, fire risk and cost.
Can a steel beam be extended?
Only with an engineered splice or a new support, under a permit where one is required. Welding or bolting a piece onto the end of a beam without a design can leave a weak point exactly where the beam needs strength.
