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HOT NEWSRated maximum capacity is the number most buyers quote first, yet it is the least informative figure on a tower crane specification sheet. A crane is a geometry, and that geometry decides what the machine can actually place where the building needs it. Two cranes with identical capacity ratings can differ by a factor of three in useful performance once the load is picked up at working radius. Before comparing prices, decide which platform family suits the building shape, the crane position and the material flow on site.
Most tower cranes fall into three recognised geometries. The traditional hammerhead carries a horizontal jib above a short horizontal counter-jib, tied by pendant bars. The saddle jib design bridges the tower top with two jibs, one on each side, which shortens the overall length for a given outreach. The flat top design removes the pendant bars from the upper works entirely, leaving a compact head that is easier to erect between surrounding buildings. Each solves a different site problem, and each carries a different penalty in headroom, transport length or erection time.
The practical implication is that a crane should be chosen from the duty it has to perform, not from the headline tonnage. Establish the heaviest pick and the radius at which it occurs, the maximum radius for lighter materials, and the height at which the hook must reach. Only then does a capacity chart become meaningful.
The table below sets out the practical differences that project engineers usually care about during tender and site planning. The values are typical of the class rather than guarantees for any single unit, and the final configuration must always be checked against the manufacturer load chart for the exact boom length, hook height and number of trolley positions.
| Criterion | Hammerhead | Saddle Jib | Flat Top |
|---|---|---|---|
| Upper works layout | Single jib with counter-jib and pendant bars | Two opposed jibs meeting at the tower top | Single jib without pendant bars over the cab |
| Height above tallest structure | Considerable, pendants sit above the working level | Moderate, less pendant hardware | Lowest, compact head over the operator cab |
| Suitability for dense city sites | Often restricted by overhead line and aviation rules | Good, balanced head suits narrow plots | Best, shortest obstruction above working level |
| Transport length on site | Longest, often split into several sections | Moderate, jib sections are shorter | Long, jib usually one or two sections |
| Typical duty range | Medium to heavy single-lift cycles | Balanced medium lifting with wide radius use | Urban lifting with frequent jib slewing |
Treat this table as a filter rather than a verdict. Many manufacturers offer hybrid designs that borrow features from more than one family, and a supplier that cannot supply a load chart for your working envelope should be excluded early, however competitive the price looks on paper.
A load moment chart plots the permissible load against radius, and it is the single most useful document in the tender pack. The shape of the curve tells you whether the crane suits the duty. A curve that falls away quickly is a crane for short radii, while a flatter curve indicates a design that keeps useful capacity at long outreach.
Three questions should be answered for every pick on the programme. What is the heaviest unit weight including the lifting accessory? At what radius is it lifted? And is that radius measured to the centre of the load, the hook, or the trolley, since a difference of one or two metres in the measurement convention can change the permitted load noticeably.
Account for dynamic effects as well. Wind loading during erection, the effect of the jib being slewed while the load is suspended, and the inertia of starting and stopping all reduce the safe working load compared with the static chart. Experienced planners apply an additional margin to the charted figure rather than relying on the theoretical maximum.
Cycle time determines how many picks a crane completes in a shift, and on repetitive high-rise structures that figure dominates the labour and programme comparison. Hoist speed matters most for the heavy picks: a tower crane that can raise a full load quickly returns the hook to the waiting truck in a fraction of the time of a slower unit. Trolley speed matters for horizontal repositioning along the jib, while slew speed matters when the layout requires repeated repositioning around the structure.
Modern towers commonly use stepped or variable speed drives rather than a single fixed hoist speed, which allows a fast light load and a controlled heavy load on the same machine. Compare the number of speed steps, the acceleration behaviour, and whether the drive can be set and locked for a specific lift. Also look at the trolley's usable jib travel: a trolley that cannot reach the counter-jib side of the working range will limit where materials can be landed.
The mast is the tower crane's vertical structure, assembled from repeating sections, and its final height is governed as much by site rules as by the building. A free-standing mast has a height limited by the structural stiffness of the tower and by overturning under wind. Above that limit the mast must be tied to the structure at defined intervals, and each tie transfers horizontal forces into the building frame.
Tying frames the calculation because the permitted height is then controlled by the stiffness of the structure, which is often still being built. If the crane will eventually outgrow the building, the erection sequence has to allow for the tower to be jumped up between phases, and that operation needs planned space, a clear exclusion zone and a specialist crew.
Wind limits also depend on the jib configuration in use. A crane with a short jib can usually be left operating in stronger wind than the same crane with its full length extended, because the wind moment grows with outreach. Site procedures should state which jib length may be used at which wind speed, and when the crane must be parked.
Every tower crane needs a foundation designed for its worst load case, and the design begins with the ground, not the machine. Common foundations include a cast-in-place reinforced concrete base block, a prefabricated ballast base sitting on a prepared mat, and ballasted base frames on a compacted hardcore platform. Piled or anchored bases are used where the ground is weak or the site is short of space.
The key number for the site team is the peak bearing pressure under the base, which the geotechnical report and the crane manual both need to agree on. The tower applies a large vertical load together with an overturning moment, and the combination can produce a much higher pressure at one edge of the base than the average suggests. Excavation, backfilling and temporary mats must be planned with that in mind, and the base area must be levelled and free of soft spots before the mast is erected.
Tower cranes draw substantial power for hoisting and travel, and the supply arrangement is often a hidden programme constraint. Sites are usually fed by a temporary distribution board with limited capacity, so the electrical contractor should confirm the crane's rated demand, the starting current of the drives, and the phase arrangement available. Where the supply is marginal, a soft starter, a frequency converter or a dedicated cable run may be needed, and any of these add cost and lead time that belong in the comparison.
The control system is worth reviewing as well. Modern cabs typically offer proportional lever control for the three motions, a display showing load percentage and radius, and an anemometer that warns the operator when the wind limit is exceeded. Anemometer wind cut-out and the safe working load limiter should both be active and calibrated, and the operator should be trained on what the display is telling them.
For cranes working in residential or mixed-use areas, the external impact can matter as much as the lift chart. Tyres, tracks and slew mechanisms all generate sound, and a crane that is quiet in still air can be intrusive at the start of a shift when the site boundary is close to housing. Planning a softer slew arrangement, avoiding the most sensitive hours for the noisiest tasks, and specifying a maintained hoist gearbox all reduce the impact without changing performance.
Lighting needs the same attention. Site lighting must illuminate the load hook, the trolley path and the jib tip, since poor visibility at the hook is a common cause of dropped loads. Aviation lighting on the jib tip is required in most urban areas, and it must be positioned so that it does not dazzle the operator working at night.
When several suppliers quote for the same duty, the differences between the machines are often smaller than the differences between the commercial terms. Build a comparison sheet that records, for each offer, the jib lengths available, the load at the critical radius, the hoist speeds, the mast section dimension and the foundation design, then add erection and dismantling method, delivery time and the support arrangement offered during the lease.
Read the exclusions carefully. Some quotations exclude the ballast, the foundation, the erection crew, the permits, the electricity supply or the dismantling cost, so a lower headline rate can hide a higher total. Request the load chart and the erection method statement as condition of the quotation, and confirm that the chart shown in the tender matches the machine that will be delivered and erected.
The cheapest hourly rate is not necessarily the cheapest way to build. A slower crane may need more operational hours to complete the programme, and the second cost of that is often an extension of the site overhead. A larger crane that shortens the programme may cost more in rent and foundations yet save on supervision, site facilities and subcontractor overheads. The comparison should therefore be made over the whole programme, using the pick rate and cycle time derived from the load chart and the site layout.
Include the knock-on effects. A crane with a fast cycle time can release the tower crane lift zone earlier, allowing follow-on trades to start sooner. A crane that can be assembled in fewer sections with a smaller crane reduces the need for a heavy erection crane on site, which may be a substantial saving in an urban location where such equipment is scarce and expensive.
Choosing a tower crane is a comparison of geometry, duty and programme rather than a search for the largest capacity figure. Start with the heaviest pick and its radius, read the load moment chart for the exact configuration you intend to use, and check the cycle time against the number of picks the programme requires. Then filter by platform family, headroom above the structure, foundation and ground conditions, power supply and the commercial terms behind the quote. The crane that survives that process is usually not the one with the highest number on the specification sheet, but the one whose load chart and cycle time match the real work on your site.
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