Craneage & Site Logistics

The single fact that governs craneage is this: a crane's lifting capacity drops as its radius increases. Reach is leverage working against you. Close to the mast, a crane can lift a great deal; extend the jib out to the far corner of a building and the same crane can safely lift only a fraction of that. The relationship is captured in a load chart — a table or curve, specific to each crane and configuration, that states the maximum safe load at each radius. A lift is only feasible if the module's weight sits *under* the curve at the radius you actually need.

This turns three things into a linked design problem: the weight of the heaviest module, the reach from where the crane can stand to where that module must land, and the crane itself. Increase any demand and you may jump to a much larger, more expensive crane — or find that no available crane can do it, forcing a redesign. The reach is driven by the building's geometry and by where the crane can physically sit: a crane parked tight against the building has a short reach to the near side but must still reach across to the far side and over the top. Tall buildings add a height-under-hook demand on top of radius. The heaviest module at the greatest reach is the critical lift that sizes the whole operation.

There are broadly two families of machine. Mobile cranes drive or are transported to site, set up on outriggers, perform the lifts and leave — ideal for fast, low-to-medium-rise modular work where the whole building can be reached from one or a few standing positions. Tower cranes are erected on or beside the building and stay for the duration — suited to tall or deep-plan buildings where reach and height-under-hook exceed what a mobile crane can give, at the cost of erection, standing time and dismantling. Choosing between them, and sizing them, depends on the critical lift and the site.

The design consequences run straight back to the module. A lighter module lifts at a greater reach or lets a smaller crane do the job. Keeping the heaviest modules near where the crane stands, and the lightest at the far reach, can keep an affordable crane in play. Concentrating weight — a module packed with heavy finishes, a bathroom pod full of tile and fittings — can quietly push you up a crane class. None of the actual capacities, de-rating factors or lift feasibility is yours to assert: the load chart, the ground-bearing checks, the rigging and the lift plan belong to the crane and lifting specialists. What is yours is to design modules and a layout that make the lift possible and cheap.

Getting a module into the air safely is a planned engineering operation, not an improvisation, and several of its requirements reach back into the design of the module itself. The first is how the module is picked up. A module must have designed lifting points — engineered connections (corner castings, lifting lugs, a spreader-frame attachment) through which the whole weight, plus dynamic forces as it swings and accelerates, passes safely into the structure. These are not afterthoughts welded on at the yard; they are part of the module's structural design, positioned so the module lifts level and does not rack or distort. A module that is strong sitting on its foundations may still need temporary strengthening to survive being dangled from four points — the 'transient' load cases of lifting and transport are often what governs a module's frame, not its life in the finished building.

The second is the rigging between hook and module: slings, shackles and very often a spreader beam or lifting frame that keeps the sling angles safe and the pull vertical, so the module is not crushed inward or lifted off-level. The third is the lift plan itself — a formal, pre-agreed document that states the crane and its configuration, the load and its centre of gravity, the radius, the rigging, the ground preparation under the outriggers, the exclusion zone, wind limits and the step-by-step method. Wind matters enormously: a large module is a sail, and lifts are routinely stopped when wind exceeds a limit, which is one reason modular programmes can be weather-sensitive at the assembly stage even though the modules themselves were built indoors.

For the designer, the practical takeaways are concrete. Know that lifting points and the forces of lifting are real constraints on module design and must be coordinated with the manufacturer and the structural engineer. Understand that a module's centre of gravity must be known and reasonably placed — an unevenly loaded module lifts crooked and dangerously. Appreciate that the lift plan, like the transport permit, is a piece of specialist work with legal weight behind it. You are not writing the lift plan or sizing the shackles; you are designing so that the module *can* be lifted cleanly — sensible proportions, known weight and centre of gravity, room for lifting points, and no surprises — and leaving the binding lift engineering to the appointed lifting specialists.

Many modular projects are chosen precisely for sites where conventional construction is slow and disruptive — dense urban infill, live hospital campuses, sites over railways. These are exactly the sites with no room to store anything. A module is enormous; even a handful of them parked on site would fill it. This simple fact reshapes the whole logistics of assembly and, through it, the design.

The first casualty is the lay-down area — the space to set modules down and stage them before lifting. On a generous site you might stage a day's modules and lift at leisure. On a tight urban site there may be room for *one* module at a time, or none: the module must be lifted straight off the trailer into its final position, a method sometimes called direct or 'load-from-the-wheels' placement. That demands far tighter coordination, because now every delivery is on the critical path of the lift.

The answer to having nowhere to store modules is just-in-time (JIT) delivery, borrowed from lean manufacturing: modules arrive from the factory (or a nearby holding yard) in the exact sequence they will be lifted, at the times the crane is ready for them, so the site holds almost no inventory. JIT is powerful and fragile in equal measure. It compresses the site footprint and keeps the crane fed, but it depends on a reliable factory output, a dependable transport link, and a holding yard somewhere off site where trucks can queue without clogging the neighbourhood, released one by one as the crane calls them forward. A single late truck in a JIT sequence can stall the crane and cascade delay through the day.

Around all this sits access: can the articulated trailer physically reach the gate, turn, and present the module to the crane? Tight corners, weak bridges on the final approach, low cables, parked cars, delivery windows imposed by the council, and neighbours who will not tolerate night moves are all real constraints that shape where the crane stands and when work can happen. The designer's role is to anticipate this early — to understand that a constrained site may dictate module size (small enough to deliver and lift from the one available position), sequence and even the structural grid, and to plan the site so the choreography is possible. The detailed traffic management, crane positioning, exclusion zones and lift sequencing are, again, for the logistics and lifting specialists; designing a building and a site that *can* be served this way is the architecture.

Put the lift and the constrained site together and modular assembly reveals its true character: a choreography, timed to the hour, in which the crane is the dancer everyone else serves. The crane is the most expensive resource on the site by the hour, so the entire operation is organised to keep it working and never waiting. Every other actor — the factory, the trucks, the holding yard, the banksman, the team connecting modules — is arranged around the rhythm of the lift.

A typical day runs like a score. The crane is set and checked. The first truck, called forward from the holding yard only when needed, arrives with the module that is next in the lift sequence. It is rigged, lifted, swung and landed onto its prepared bearings; the connection team secures it enough for the crane to release. The empty truck leaves as the next is called forward, and the cycle repeats. Good operations measure themselves in modules placed per day, and that number — not the factory's output alone — often sets the overall programme. The whole point of just-in-time is to keep this cycle unbroken: a module always ready for the hook, never a pile of modules waiting and never a crane waiting for a module.

This is where logistics, which can sound like a back-office concern, becomes visibly a design and planning discipline. The lift sequence must be worked out in advance and must be physically possible — you cannot land a module where the crane cannot reach, or where the module it depends on is not yet placed (the subject of the next lesson). The module numbering, the delivery order, the holding-yard schedule and the crane cycle are designed together, long before the first truck rolls. When it works, a building can rise astonishingly fast — storeys in days — precisely because the slow, sequential, weather-exposed making has already happened in the factory, and what is left on site is a rehearsed assembly.

The honest caution is that this balletic speed is also brittle. The choreography has little slack: a damaged module, a late truck, a windy morning, a crane breakdown or a neighbour complaint can stall the whole line, and because the trades are working in tight sequence there is nowhere for the delay to hide. This is why assembly logistics is planned so obsessively and handed to specialists, and why the designer's early choices — module weight, size, landing positions, a sequence that is actually buildable — matter so much: they set how forgiving or how fragile the choreography will be. Design for a lift that is easy and a sequence that is robust, and the dance goes well.