Tower Crane Selection: 7 Spec Gates From Tip Load to Wind Class

A tower crane's job is to lift a 1.3 t load to 121 m of working height over a 50 m radius under wind, every shift, for the life of the project — so picking one is a geometry problem with a fatigue problem bolted on [S5].

For engineers who only ever specified mobile units, a tower crane reads like a different machine: the jib stays at one height, the hook travels on horizontal and vertical axes, and the slewing ring takes the duty a mobile crane would never see in a month. The 7 gates below are the spec checks that actually decide which model survives procurement review.

Gate 1 — Hook Height and Free-Standing Capacity

Free-standing height is the single number that wipes out half the shortlist. A typical Chinese-built flat-top such as the CMAX TC5013A (QTZ63) is rated 40 m free-standing and 121 m maximum lifting height, with 1.3 t tip load and 6 t maximum [S5]. If the building tops out below 40 m and the crane is anchored to a slab, that machine is in scope; if it tops out at 80 m, the same crane needs tie-ins every ~20 m and the foundation story changes.

Tie-ins are not optional on a real high-rise. A 60 m+ structure typically requires a climbing cage, anchorage collar and base frame sized to the mast section family in service — mast families such as H20, HA20-18.10B, HD23-22.3 and their derivatives are still the spare-parts lingua franca across the global Potain-compatible fleet [S6]. Spec the mast family first, then choose the crane, not the other way round.

Gate 2 — Jib Length, Tip Load and the Load Curve

Jib length sets the working radius, but tip load at that radius is the number that actually lifts bricks. The TC5013A posts a 50 m maximum working range and a 1.3 t tip load dropping off as the radius closes in, with 6 t at the inner radii [S5]. Larger models such as the CNBM TC7034 hold a heavier payload across a longer jib by using standard-section hydraulic climbing to grow the mast as the structure climbs [S4].

Always demand the load chart in tabulated form, not just the headline tip-load figure. The 1.3 t tip number assumes a particular reeving, counter-jib ballast and out-of-service wind limit; change any one of those and the chart shifts. If the project regularly lifts 2 t panels at 40 m radius, a "1.3 t tip / 50 m jib" machine is the wrong tool.

Gate 3 — Duty Cycle, Hoist Speed and Climbing Speed

Climbing speed of 0.5 m/min on the TC5013A tells you the crane is designed for slow, deliberate hydraulic self-climb, not rapid mast extension [S5]. On a high-rise that climbs one floor every three days, that is fine; on a fast-paced residential tower pouring a floor every two days, it becomes the schedule bottleneck. The hoist, slew and trolley motions, with their accelerations and decelerations, drive the slewing-ring duty far harder than static capacity ever does.

This is also where slewing ring bearing selection meets the crane spec sheet: the slewing ring's rolling-element family, gear geometry and dimensional envelope are dictated by the combined moment from out-of-service wind, in-service wind, payload eccentricity and the slewing torque budget. Specify a crawler crane duty pattern into a tower-crane slewing ring and it will eat the bearing inside two cycles.

Gate 4 — Wind Class and Out-of-Service Lock-Up

A tower crane is essentially a vertical sail. Manufacturers publish an in-service wind limit (often 20 m/s operational, 42 m/s out-of-service for the mid-size Potain and Chinese OEM classes) and a slewing-brake policy that either weathervanes the jib free or pins it to a defined storm heading. Site conditions on a coastal or ridge-top job will downgrade the permissible in-service wind speed, which then erodes productive hours. Build that loss into the programme, do not bury it in a crane supplier's marketing line. [S1]

Counterweight is the other half of the wind story. The TC5013A ships with 11 t of counterweight, and the load chart is balanced for exactly that mass [S5]. Reduce counterweight to ease a foundation and the whole chart has to be re-issued; do not accept a supplier "derate" without seeing the revised stamped chart.

Gate 5 — Foundation, Base Reaction and Tie-In Geometry

Base reactions on a 50 m jib machine in service can run 80–150 kN vertical with overturning moments that the foundation designer needs in writing, not as a verbal "it's about 100 kN·m." The four base options — cross-base on spread footings, ballast base on a gravity slab, tie-in to the structure, and travelling base on rails — have very different site implications. A travelling base is brilliant for a long linear project but punishes the site logistics team with track maintenance and gauge alignment. [S2]

For tall or repeating floors, climbing is the answer, and the climbing cage, anchorage collar and tie-in frame have to come from a supplier that already stocks the mast family in service [S6]. Mixing mast sections from two nominally "compatible" suppliers is the single most common cause of slewing-ring premature wear and tie-in collar cracking on Chinese-built fleets.

Gate 6 — Operator Cab, Controls and Safety Architecture

Remote-controlled self-erectors are pitched as "fast assembly, small footprint, cost-effective" for low-rise residential and light-commercial work [S2]. That is true for jobs under ~10 floors with a single crane that can be folded and trailered between sites. Once the project crosses into a long jib, multiple cranes, or a tight urban site with night-time wind alarms, a cab-mounted operator with anti-collision and zone limiting becomes the safer spec.

Anti-collision, load moment indicator (LMI), anemometer with audible alarm, slewing-zone limits and a real out-of-service park-brake sequence are not optional. The remote-control convenience on a self-erector is real, but it does not substitute for an LMI that has been calibrated to the actual load chart on that machine in that configuration.

Gate 7 — Vendor Footprint, Spares and the [Crane Scale] Question

Selection is also a logistics problem. Bronson Crane's positioning as the #1 Potain GMA dealer in the Americas since 2011 is a hint that dealer network and spares depth are part of the price you pay for the machine [S2]. On the rental side, fleets such as RMS Cranes offer all-terrain units from 120 to 900 t but explicitly do not list tower cranes as a core line — a reminder that the tower-crane supply chain is a separate ecosystem from mobile-crane rental, with its own rigging crews and climbing specialists [S1].

Finally, lift planning: any tower-crane contract should specify a crane scale verification regime, periodic load-test intervals and a documented procedure for gantry crane-style ground assembly if the site is constrained. The cheapest crane on paper is rarely the cheapest crane when climbing, tie-ins and standby time are added up. If the project also needs an aerial work platform fleet for façade work, spec both in the same procurement so rigging crews and outrigger pads can be shared, not double-ordered.

Next node: demand the manufacturer's stamped load chart for the exact mast + jib + counterweight + tie-in configuration that will sit on site, and a wind-class letter naming the in-service and out-of-service limits in m/s. If either is missing or hedged with "typical values," walk away from the quotation.