Lift loads arrive in a building at three specific places and nowhere else, and that concentration is what makes them easy to miss in a takedown that thinks in floors. StructLoads carries a lift as what it physically is: a large point load at the pit, a set of guide rail reactions up the shaft walls, and a machine reaction at the head, with a dynamic factor on top because a lift is a machine that accelerates a mass. A shaft drawn as a hole in every slab is a hole in the load path too.
Where a lift actually loads the structure
A traction lift suspends a car and a counterweight from ropes over a machine at the top of the shaft. The machine therefore carries the sum of the car, its rated load, and the counterweight, plus rope weight, and that whole sum lands on the machine beams or the machine room slab. For a 1000 kg rated, eight person passenger lift, car mass around 1200 kg and counterweight around 1700 kg, the static sum at the head is roughly 3900 kg, about 38 kN, before any dynamic allowance.
Dynamic allowance is not small. Lift standards apply an impact factor to account for acceleration, emergency braking and safety gear operation, commonly a factor of 2 on the static load for the machine support, and higher for the buffer condition at the pit. A 38 kN static head load therefore becomes something like 76 kN for design, applied to a beam or slab at the very top of the building where the structural load inventory is usually thinnest.
At the bottom, the pit carries the buffers. If the car overruns and strikes the buffer, the deceleration force is far above the static weight, and the pit slab is designed for it. Buffer impact loads on the order of several times the car plus rated load are normal design values, applied as a point load onto a slab that is often the lowest structural element in the building and bearing directly on ground or piles.
How to carry lift loads through a takedown
| Method | Best for | Why it works | Main limit | Verdict |
|---|---|---|---|---|
| StructLoads | Lifts inside a building takedown | Keeps the head, rail and pit reactions as placed point and line loads at their real elevations, so the shaft walls and the pit pick them up instead of the load vanishing into a hole | Does not design the guide rails, the machine beams, or the buffer | Best overall for the building side |
| Lift supplier reaction schedule | Getting the actual numbers | States head, rail, pit and buffer reactions for the exact lift, with the dynamic factors already applied | Arrives late in the programme, and lift suppliers get substituted after the shaft is built | Essential input, always ask early |
| Rule of thumb allowance at concept | Early massing and shaft sizing | Lets a shaft be reserved before the lift is selected | Wrong by a factor of two either way, and it does not size a machine beam | Placeholder only |
| Full shaft wall analysis | High rise, high speed, or multiple lifts in one shaft | Captures the rail reactions and the wall spanning properly | Heavy for a low rise lift, and only worth it when the numbers are large | Right tool above a certain height |
The working order is to reserve the shaft, get the supplier’s reaction schedule as early as the procurement allows, place the head load on the machine support, place the rail reactions on the shaft walls at bracket levels, place the buffer reaction at the pit, and check that the shaft walls have a load path down.
Guide rails put horizontal load into the shaft walls
The reactions most often missed are the guide rail brackets. Rails run the full height of the shaft, fixed back to the walls at brackets typically 1.5 to 3.0 m apart, and they carry horizontal forces in normal running from car imbalance and from passengers moving inside the car. They also carry the safety gear case, where the car’s safety wedges clamp onto the rails to arrest a fall, which puts a large vertical force into the rail and a corresponding horizontal reaction into every bracket resisting the buckling of that rail.
Those bracket forces land on the shaft wall as point loads out of plane. A masonry or blockwork shaft wall spanning vertically between floors and picking up a horizontal bracket load at mid-height is a bending problem, and it is the reason lift shaft walls are so often required to be reinforced concrete rather than blockwork above a certain height or speed. The Approved Documents framework and the lift standards between them set out that the shaft is a structural enclosure rather than a partition, and treating it as a partition is the standard error.
Where the shaft forms part of the building’s stability core, the rail loads are a minor addition to a wall already sized for wind and seismic actions. Where the shaft is a standalone blockwork box in the middle of a steel frame, they are the governing action on that box, and the box needs a designer.
Machine room, machine room less, and where the load moves
Traditional installations put the machine in a room above the shaft, and the load is a set of beam reactions onto the machine room floor, which is a small heavily loaded slab at roof level. Machine room less systems put the motor inside the shaft at the head, usually bearing on the shaft walls or on a beam spanning between them, which moves the same load from a dedicated slab onto the walls themselves.
That relocation matters to a takedown. The head load stops being a floor load and becomes a wall load applied at the top, which then runs down the shaft walls to foundation. If the shaft walls are not continuous, or if the shaft sits on transfer structure at podium level, the whole lift load arrives on the transfer element as a concentrated point rather than being spread across a floor plate. A lift shaft landing on a transfer beam is a specific case worth naming, and the reasoning is the same as any transfer beam carrying a discontinuous element.
Hydraulic lifts move the load again. A direct acting hydraulic lift puts the entire car, load and ram reaction into the pit floor rather than the head, so there is no significant machine load at the top and a very large one at the bottom. The pit slab and its foundation carry the lot.
The shaft is a hole in every floor
From the perspective of a slab, a lift shaft is a large opening repeated at every level, and openings redistribute load. A 2.5 m by 2.5 m shaft in a flat slab removes support around a column zone and forces load to travel around it, exactly the behaviour covered when reasoning about tributary area on an irregular floor plate.
Two practical consequences follow. The slab edge around the shaft is a loaded edge that needs its own trimming, often a beam or a thickened band, and that beam collects the load from the strip it interrupts. And the tributary area of the columns adjacent to the shaft is not the grid rectangle: it is the grid rectangle minus the shaft, plus whatever the trimming beam delivers to them. Taking the grid area at face value over-estimates the load on some columns and under-estimates it on others, and the error is exactly the kind that a careful tributary area calculation exists to prevent.
Pit depths, overruns and the loads below the lowest floor
A lift pit extends below the lowest served level, typically 1.2 to 1.6 m for a low rise passenger lift and considerably more for high speed installations. That means the pit slab is below the general basement slab, forming a local sump. Structurally it is a small deep box: it carries the buffer reaction downward, it resists groundwater uplift over its own footprint at a greater head than the surrounding slab, and its walls retain soil or the surrounding slab construction.
The uplift case is the one that surprises. A pit 1.5 m below a basement slab that already has 2 m of head sees 3.5 m of head over its base, about 34 kPa upward, on a small area with limited dead weight above it. Pits float. The resistance comes from the pit walls’ friction and the slab it is tied into, and it needs checking rather than assuming.
Goods lifts, platform lifts and firefighting lifts
A passenger lift is the light case. Goods lifts carry rated loads of 2000 to 5000 kg and sometimes far more, and because the rated load dominates the car and counterweight rather than the other way round, the head and pit reactions scale roughly with it. A 3000 kg goods lift can put three to four times the head load of a passenger lift into the same shaft head detail, and it is frequently specified after the shaft has been sized.
Loading also changes character. A goods lift is loaded by a pallet truck driven into the car, so the car floor sees a concentrated wheel load during loading, and the shaft sill and the landing threshold outside it take the same wheel load as the truck crosses. That threshold is a slab edge at every level, and it is a detail rather than a member, which is precisely why it gets missed.
Firefighting lifts add a further requirement. They serve a protected shaft that must remain usable during a fire, which usually makes the shaft a fire resisting structural core with its own performance requirements, and they carry a specified rated load with the machine and its supports designed to remain functional. Structurally the effect is to push the shaft further towards being a designed concrete core, and away from a lined blockwork box, for reasons that have nothing to do with the rail loads and everything to do with fire.
Platform lifts and small home lifts sit at the other end. They are light, but they are frequently installed into existing buildings, cutting an opening through timber or concrete floors that were never trimmed for it. There the governing issue is not the lift load at all, it is the load path from slab to foundation being interrupted by an opening cut after the fact, and the trimming needed to restore it.
Multiple lifts in one shaft, and the bank problem
Lift banks put two, three, or four cars in a shared shaft enclosure with a common set of walls. The individual reactions are unchanged, but they multiply and they arrive at the same head structure at the same time. A bank of four lifts can deliver 300 kN or more of factored head load into one roof level structure, concentrated over a plan area of a few tens of square metres.
Rail brackets multiply too. Four lifts mean eight rails, so eight columns of out of plane bracket loads on the shared walls, and the walls between adjacent cars carry brackets from both sides. Those dividing walls are often the thinnest elements in the core because they are not part of the stability system, which makes them the ones to check. A dividing wall picking up bracket loads from two lifts, spanning between floors, with no in plane role, is a member designed by the lift installation rather than by the building. Naming it as a structural element on the drawings is what stops it being built as a partition, and it is the same discipline as making sure any bearing wall load takedown reaches the elements that actually carry load.
The counterweight side deserves one specific check. In a shared shaft the counterweights run in their own rail sets close to a wall, and a counterweight is a dense mass of steel or cast iron plates. Its rails carry the same safety gear case as the car rails where counterweight safety gear is fitted, and the Eurocode 1 actions framework treats accidental actions of this kind as their own design situation rather than as a factored version of the normal one.
A worked example: one passenger lift in a six storey building
Take a 1000 kg, eight person traction lift, machine room less, in a 6 m by 3 m concrete core, six storeys at 3.5 m, rail brackets at 2.0 m centres.
Head: car 1200 kg plus rated 1000 kg plus counterweight 1700 kg is 3900 kg, about 38 kN static. With an impact factor of 2 for the machine support, design head load is about 76 kN applied to the beam spanning between the core walls at the top.
Rails: each bracket resists a horizontal force in the region of 1 to 3 kN in normal running, rising sharply under safety gear operation. With 21 m of shaft and brackets at 2 m centres, that is about 11 bracket levels per rail, two rails, so 22 out of plane point loads distributed up the core walls. Individually small, collectively the reason the core is concrete.
Pit: buffer impact for this car might be taken at several times car plus rated load, so on the order of 100 to 150 kN as a design point load onto the pit slab, plus 34 kPa of uplift over the pit footprint if the water table is high.
Takedown: the 76 kN head load runs down the core walls, which also carry the floor loads framing into them at each level, to a foundation that additionally resists the pit’s uplift. None of that appears if the shaft is modelled as an opening and the lift as an architectural item.
Key takeaways: lift and shaft loads
A lift loads three places: the head, the rail brackets, and the pit, each with its own dynamic factor. Ask the lift supplier for a reaction schedule early, because rule of thumb allowances are wrong by a factor of two. Guide rail brackets apply out of plane point loads that make a shaft a structural enclosure rather than a partition. Machine room less systems move the head load onto the shaft walls, which matters most when the shaft lands on transfer structure. And the pit is a small deep box with its own uplift case.
Quick answers
The useful question for any lift is simple: where does this machine touch my structure, and how hard.