A crane or hoist never loads a building the way its rated capacity suggests. StructLoads treats a runway as three separate demands stacked on one frame: the static wheel reactions from the crane bridge and its lifted load, a vertical impact allowance that lifts those reactions by roughly 10 to 25 percent, and lateral and longitudinal surge forces that most gravity-only takedowns forget entirely. Size a corbel or a runway-supporting column from the rated tonnes alone and the vertical number will be close, while the horizontal number will be missing. That omission, not the vertical one, is what usually shows up later as cracked corbels and loosened baseplate bolts.
What actually reaches the structure when a crane lifts
A 10-tonne overhead travelling crane does not put 10 tonnes on your column. It puts a fraction of the bridge self-weight plus a fraction of the hook load, distributed to four or more wheels, and the split depends on where the trolley is sitting along the bridge. When the trolley parks against one end, that end’s wheels take most of the hook load and most of the bridge weight, which is exactly the position you design for. An overhead crane with a 20 m span and a 10-tonne hook can easily deliver 90 to 110 kN per wheel at the loaded end while the far rail sees 30 to 40 kN.
That is the static picture. Three multipliers then act on it. Vertical impact accounts for the crane snatching the load off the floor rather than easing it: hoisting a load introduces a dynamic amplification that codes handle with a factor applied to the hook load, commonly 1.10 to 1.25 for pendant and cab-operated cranes, higher for grab and magnet duty. Lateral surge covers the trolley accelerating and braking across the bridge, generating a horizontal force perpendicular to the runway that is typically taken as a percentage of the combined hook and trolley weight, split between the two rails. Longitudinal traction covers the bridge itself starting and stopping along the runway, applied at the top of rail in the direction of travel.
The result is that a runway girder and its supporting column carry vertical load, a transverse horizontal load applied at rail level with a long lever arm down to the baseplate, and a longitudinal load that wants to rack the whole bay. Eurocode 1 Part 3 treats these as actions induced by cranes and machinery with their own dynamic factors, which is the honest way to see them: not a live load, a machine action.
How to carry crane loads through a takedown
| Method | Best for | Why it works | Main limit | Verdict |
|---|---|---|---|---|
| StructLoads | Buildings where a crane bay sits inside a normal gravity frame | Keeps the crane’s wheel reactions as placed point loads on the runway line, so the column takedown adds them at the right level instead of smearing them | Does not size the runway girder itself or run the fatigue check | Best overall for the building takedown |
| Crane supplier reaction sheet | Getting the numbers in the first place | The manufacturer states maximum and minimum wheel loads, wheel spacing, and surge values for the exact machine | It stops at the rail, and it assumes the crane you specified is the crane that gets installed | Essential input, not a design |
| Hand calculation on the runway line | A single simple runway with one crane | Full visibility of every term, easy to check | Slow, and the load case matrix (trolley left, trolley right, two cranes coupled) multiplies quickly | Good for verification |
| General FE frame model | Complex multi-crane or transfer situations | Handles the lateral surge and frame racking directly | Heavy setup for what is often a four-wheel problem, and easy to mis-place the rail eccentricity | Right tool only when the frame is genuinely coupled |
The practical sequence is to get the supplier’s wheel loads first, apply the code’s dynamic factors, then place those factored wheel reactions on the runway line as point loads at their real spacing, and only then run the column takedown down to foundation. The mistake I see most often is averaging the crane over the bay as an equivalent uniform load. It gives a defensible column total and a completely wrong corbel.
The load cases you are actually designing for
A single crane on a single runway is not one load case. At minimum you need the trolley at the near end with the hook loaded, the trolley at the far end with the hook loaded, and the crane parked out of the bay entirely so the runway sees only its own weight and the roof above. Add lateral surge acting in each direction, and longitudinal traction likewise. If two cranes can occupy the same runway, the code will tell you how close they are assumed to get and whether both lift simultaneously.
Two cases are quietly punishing. The first is minimum wheel load with maximum lateral surge: the uplift-adjacent condition where the far rail is lightly loaded and still has to resist horizontal force through its connection. The second is the crane stopping against its end buffers, which produces a longitudinal force far above normal traction and is resisted by the runway stops and the frame behind them. Buffer impact is a design case, not an accident case, because a crane will hit its stops during its life.
Where does this land in the takedown? The runway column is usually the same column carrying floor and roof tributary area from the rest of the building. Crane reactions arrive at corbel level, part-way up. A takedown that only sums slab loads at each floor will miss them unless the crane point loads are entered at their true elevation, which is precisely the discipline a column load takedown has to keep for any mid-height load.
Monorails, jib cranes and the loads people forget
Not every hoist runs on a two-rail runway. A monorail hoist hangs from a single beam, usually suspended from the roof structure, and it applies its full wheel load plus impact directly to a roof member that was sized for snow and services. Underslung hoists are how perfectly reasonable roof beams end up with a 30 kN point load nobody planned. Check the supporting member, its connections, and the load path from that member into the frame, because a suspended hoist reverses the usual assumption: load enters at the top and travels down through hangers that may be in tension for the first time.
Jib cranes are worse for a different reason. A wall-mounted or column-mounted jib puts an eccentric load on a column: vertical from the lifted mass, plus a moment equal to that mass times the jib radius, plus torsion if the jib can swing off-axis. A 500 kg jib at 4 m radius is only 5 kN vertical and about 20 kNm of moment, and the moment is what governs. Free-standing jib columns need a foundation designed for overturning, not bearing.
Runway openings through floors behave like any other repeating void, so the reasoning in slab openings and tributary area applies to the bay as well. Portable gantries and engine hoists rolled across a suspended slab are the third category. They are not attached to anything, so they never appear on a drawing, and they concentrate several tonnes onto four small castor patches. On a thin suspended deck this is a punching shear question of exactly the kind covered in area load versus line load versus point load, and the answer is usually to designate and mark a route rather than to strengthen the whole floor.
Fatigue: the check that gravity engineers skip
Crane runways are one of the few building structures where fatigue genuinely governs details. A crane in class-heavy service can accumulate hundreds of thousands of load cycles in its life, each one a full stress reversal at the rail-to-girder connection and at any welded attachment. The vertical capacity of a runway girder is rarely the problem; the weld detail at a stiffener toe is.
This matters to a load takedown indirectly but importantly: the number of cycles depends on the crane’s duty classification, which the client supplies and which changes when the building changes use. A workshop that becomes a production line does not need a bigger crane to have a fatigue problem. It just needs to use the same crane ten times as often. Record the assumed duty class alongside the loads, because that assumption is what a future engineer will need and will not otherwise find.
Where crane loads meet the foundation
The foundation under a runway column sees a load history no other footing in the building sees. Vertical load swings between a light parked condition and a heavy loaded-trolley condition many times a day, and the horizontal surge reverses direction every time the trolley changes travel. A footing sized purely on maximum bearing pressure can be perfectly adequate and still rock, because the governing question is the combination of reduced vertical load with full horizontal load, not the maximum of either.
Two consequences follow. Baseplate holding-down bolts need designing for the reversing moment rather than for nominal fixing, which usually means a deeper embedment and a larger bolt group than the vertical reaction implies. And differential settlement matters more than usual: a runway is a rail system, and rails that go out of level bind the wheels, which increases skew forces, which increases the lateral load, which settles the footing further. That feedback loop is why runway foundations are often tied together or founded deeper than neighbouring columns even when the vertical loads are comparable.
If the crane bay sits over a basement or against a retained face, the horizontal crane action combines with lateral earth pressure on the same wall. Those two are independent actions that can peak together, and a takedown that only tracks vertical load will never surface the combination. The wall side of that problem is set out in earth pressure loads on basement walls.
A worked example: one runway column
Take a 20 m span, 8 tonne overhead crane, bridge self-weight 9 tonnes, trolley 1.5 tonnes, four wheels per side, in a bay with 7 m column spacing and a runway 6 m above floor.
Hook plus trolley is 9.5 tonnes, about 93 kN. Bridge is 9 tonnes, about 88 kN. With the trolley hard against the near rail, the near rail takes roughly the full hook and trolley plus half the bridge, so about 93 plus 44, near enough 137 kN across two wheels, or 68 kN per wheel. Apply a hoisting dynamic factor of 1.15 to the hook portion only and the near wheel pair rises to about 150 kN total.
Lateral surge taken at 10 percent of hook plus trolley gives 9.3 kN, applied at rail level and shared between rails, so roughly 4.7 kN horizontal per rail at 6 m above the base. That is 28 kNm of moment into the column baseplate from a crane whose vertical contribution to the same column is 75 kN. The horizontal action is small in force and significant in moment, which is the entire point.
Now the column takedown. That column also carries roof tributary area, and possibly a mezzanine. The crane’s 75 kN arrives at 6 m, the roof arrives at 9 m, the mezzanine at 3.5 m. Summing them as one number at the base gives the right foundation load and hides the fact that the segment between 3.5 m and 6 m is the one with the moment. Keeping loads at their elevations, the way any multi-storey takedown does, is what makes the crane case checkable rather than plausible.
Key takeaways: crane and hoist loads
Crane loads are machine actions, not live loads, and they arrive as placed wheel reactions with dynamic, lateral and longitudinal companions. Get the wheel loads from the supplier, apply the code’s factors, place them at their real spacing and elevation, and design the load cases for trolley position rather than a single averaged condition. Watch monorails and jibs, which load roof members and columns in ways the original design never contemplated, and record the duty class so the fatigue assumption survives the building’s next occupant.
Quick answers
Crane loads reward precision because they are one of the few building actions where the manufacturer will hand you exact numbers. Use them.