What Is a Tower Crane?

Tower cranes lift on building sites from low-rise housing to city towers. Four main kinds are set side by side below, with the permissions and checks a crane needs before it lifts.

Overview

What is a tower crane?

A tower crane is a fixed crane that lifts from a tall lattice mast, with a jib at the top balanced by a counterweight on a shorter arm behind it. It stands in one place on a building site while the work goes on, placing loads at height anywhere within the reach of its jib.

In short

A level jib carries the hook out on a trolley. A luffing jib is raised and lowered instead, with the load hanging from its tip.
Self-erecting models are the small end of the range and put themselves up on site.
The Civil Aviation Authority recommends notifying it at least eight weeks before a crane it has to be told about goes up.
Before the crane arrives, settle what the jib will swing over, in use and when it is left out of service.

Tower cranes are among the cranes our crane hire and contract lifting service supplies: luffing, flat top and self-erecting models, from makes such as Liebherr, Potain, Terex/Comansa and Wolff.

How it works

How a tower crane works

On a top-slewing tower crane, the slewing unit at the top of the mast turns the jib and counterjib together, so the hook can reach any point inside the circle the jib sweeps. Our guide Parts of a Tower Crane Explained names each part and what it does.

Base, height and erection

A full-size tower crane stands on a base designed for it, such as anchors set in a concrete foundation or a cross base. Above the free-standing height the maker allows, the crane is tied in to the building, and a tall crane climbs as the building rises. Liebherr describes these bases, tie-ins and climbing for its own cranes. Apart from self-erecting models, the crane arrives in sections on lorries and is built up with another crane lifting them into place. How Are Tower Cranes Erected and Dismantled? follows it from the base to the dismantle.

Red tower crane standing behind a single-storey building on a construction site — A tower crane on a construction site, lifting from a fixed position for the length of the build.

The types at a glance

Liebherr and Potain both build top-slewing cranes with level jibs and with luffing jibs, and sell self-erecting cranes as a separate range. The table compares the four main kinds.

Type	How the hook reaches out	How it gets to site	Where it fits
Hammerhead	Trolley along a level jib, held by tie bars from a tower head	Built on site in sections	Sites with room to swing the full jib; Potain adapts its large models for special applications
Flat top	Trolley along a level jib with nothing above it	Built on site in sections	Open sites, including those with several cranes whose jibs overlap
Luffing jib	Jib raised and lowered, with the load hanging from the tip	Built on site in sections	High-rise work, and sites where a small working circle helps
Self-erecting	Trolley along a shorter jib	Travels folded and unfolds itself	Small sites and low-rise building

Type

Hammerhead and flat top tower cranes

Hammerhead and flat top cranes both keep the jib level and carry the hook on a trolley that runs in and out along it. The CPA’s guide to top-slewing tower cranes (TCIG 0701) uses the terms trolley jib and saddle jib for this kind. The difference is at the top: a hammerhead has a tower head above the jib, with tie bars holding the jib up, and a flat top has nothing above the jib at all.

Changing the radius

The operator changes the radius by moving the trolley, and covers the site by slewing. Because the jib stays level, its slewing circle is always the full length of the jib. The crane can lift less the further out the trolley goes, so every lift is checked against the load chart at the furthest radius the load reaches. What size crane do I need? explains radius and capacity for any crane.

Where a level jib works well

On an open site, a level jib can swing freely and the trolley can place a load anywhere beneath it. Potain markets its topless cranes for sites with several cranes, where the jibs overlap and each crane has to stay clear of the others.

Level jibs on tight sites

On a cramped site, a level jib may have to pass over neighbouring property or a public road. That needs permission, which may be refused or come with conditions the job cannot meet.

Type

Luffing jib tower cranes

A luffing jib tower crane raises and lowers its jib to move the load in and out, with the load hanging from the jib tip.

A smaller circle when raised

With the jib raised, the crane works at a short radius and its slewing circle shrinks with it. In use it can keep clear of neighbouring buildings and other cranes, lowering the jib only when a load has to go further out. Left out of service in free slew, a luffer can still swing over its neighbours, so the agreements to oversail neighbouring land cover that too.

City and high-rise work

A small working circle helps on congested city sites, and beside roads and railways a level jib would swing over. Potain says its luffing jib cranes build supertall skyscrapers, and Liebherr develops its HC-L luffers for sites needing efficiency and flexibility.

Leaving it in high winds

HSE issued a safety bulletin on luffing jib tower cranes in high winds in 2014, after three collapsed. It asks for a luffer left unattended to be in free slew, with the jib at a safe out-of-service radius confirmed with the crane’s supplier or maker, so the wind can turn it.

Yellow luffing-jib tower crane with its jib raised against a blue sky — A luffing jib tower crane with its jib raised, keeping its slewing footprint small.

Type

Self-erecting tower cranes

A self-erecting tower crane is a smaller tower crane that travels folded and unfolds its own mast and jib on site. Nobody has to build it section by section, and no assist crane is needed.

Fast-erecting cranes

Liebherr sells these as fast-erecting cranes. Potain’s small Evy models give a sense of scale: the Evy 30-23 lifts up to 4 t, with a 30 m maximum radius and a hook height of about 23 m.

What they are used for

Potain describes its self-erecting cranes as especially suited to small construction sites, and designs its Igo M 24-19 for house building and renovation.

Self-erecting or mobile tower crane

Self-erectors are generally lower and lighter-lifting than cranes built from sections, so a tall building or heavy loads call for a sectional tower crane. For a job of days, a mobile tower crane is another option, with the crane mounted on its own truck chassis.

Planning

What to plan for with a tower crane

A tower crane built from sections stays for much of the build, so the planning starts well before it arrives.

The base and the dismantle

An engineer designs the base for the crane and the ground under it, and the base has to be ready before erection begins. Plan the dismantle at the same time, because a building put up around the crane can leave no room for the crane that takes it down.

Swinging over neighbours and roads

Where the jib will swing over property the principal contractor does not control, CPA guidance on top-slewing tower cranes says the contractor must get oversailing rights in advance, allowing for the jib in free slew out of service. In England and Wales, a jib over a public road needs the highway authority’s consent under section 178 of the Highways Act 1980; Bristol, for example, issues it as a section 178 licence. Beside a railway, the CPA’s guidance on cranes next to Network Rail lines says a tower crane oversailing Network Rail infrastructure is not normally approved and, where it cannot be avoided, needs a formal oversailing agreement. Network Rail should be told in advance of the date and time of any erection, alteration, climbing or dismantling.

Aviation

In the UK, the Air Navigation Order makes it mandatory to notify the Civil Aviation Authority of any crane 100 m or more above ground level. The Civil Aviation Authority’s crane notification guidance also covers a crane more than 10 m above ground used within 6 km of an aerodrome, which is notified to that aerodrome. It makes the hirer of the crane (the principal or other contractor) responsible for notifying the aerodromes concerned.

Power lines and wind

Overhead power lines near the jib’s path are planned around using the HSE’s guidance on avoiding danger from overhead power lines. Wind limits for working, and the position the crane is left in out of service, follow the maker’s instructions for that crane. Our guide Crane Wind Speed Limit: Lifting in Wind covers wind more widely.

Thorough examination

In Great Britain, regulation 9 of LOLER says that where the safety of lifting equipment depends on how it is installed, the employer must have it thoroughly examined by a competent person after installation and before first use, and after assembly at each new site before it is put into service. HSE’s LOLER guidance (L113) says a tower crane should be thoroughly examined in this way after installation. How Are Tower Cranes Erected and Dismantled? covers that step, and our guide to the Lifting Operations and Lifting Equipment Regulations 1998 (LOLER) explains the regulations.

Contract lift

Tower cranes on a contract lift

We supply tower cranes on contract lifts, with erection and dismantling arranged as part of the job. The crane comes with CPCS or NPORS carded operators, and the lifts are planned to BS 7121.

Who plans the lifts

In Great Britain, regulation 8 of LOLER requires employers to make sure every lifting operation is properly planned by a competent person, appropriately supervised and carried out in a safe manner. The appointed person, the planning role set out in BS 7121-1, does that planning, and BS 7121-5 applies it to tower cranes.

On crane hire, the hirer’s own appointed person does the planning. On a contract lift, each lift plan is written in house by our appointed person. Our guide to crane hire or a contract lift sets out who is responsible for what under each.

What we need to know

The heaviest loads, and the furthest radius each has to reach
A site plan showing where the crane could stand and what lies around the site
The height of the building and how long the crane is needed
Any known ground conditions, and whether a site investigation has been done

Questions

Common questions

What are the main types of tower crane?

The main types of tower crane are hammerhead, flat top, luffing jib and self-erecting. The first two keep a level jib and run the hook out on a trolley, while a luffer raises and lowers its jib instead. Self-erecting cranes are smaller models that fold up for transport and unfold themselves on site.

What is the difference between a luffing and a flat top tower crane?

A flat top tower crane keeps its jib level and moves the load on a trolley, so the jib swings its whole length whenever it slews. A luffing jib crane raises its jib to shorten its reach, which shrinks the circle it turns through. Left out of service in free slew, a luffer can still swing over its neighbours.

What is a self-erecting tower crane?

A self-erecting tower crane is a small tower crane that puts up its own mast and jib on site without help from another crane, and folds away again when the job is done. Makers aim them at small sites: Potain describes its Evy 30-23 as ideal for buildings of up to three floors.

Which crane is used for high-rise buildings?

High-rise buildings are put up with tower cranes. Potain builds luffing jib cranes for supertall skyscrapers, and a raised luffing jib keeps the working circle small on a crowded city site. As the building rises, the crane climbs with it and is tied to the structure, so the hook keeps working above the top floor.

How high can a tower crane go?

It depends on the model and how it is supported. Potain lists maximum hook heights on a base of about 39 m to 136 m across its top-slewing models. Above the free-standing height its base allows, the mast may need to be tied to the building it serves, and from there it can keep pace with a tall tower.

How much can a tower crane lift?

Tower crane capacity depends on the model and the radius. Potain’s top-slewing range lifts from 5 t to 80 t close to the mast, and from 1.15 t to 26 t at the jib end. Capacity falls as the radius grows, so each load is checked at the furthest radius it reaches.

Do I need to tell anyone about a tower crane?

In the UK, any crane 100 m or more above ground must be notified to the Civil Aviation Authority, and one over 10 m within 6 km of an aerodrome is notified to the aerodrome. In England and Wales, a jib over a public road needs the highway authority’s consent. HSE closed its tower crane register in 2013.

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