The tower crane: design and special conditions

While the jib crane dominates inside the hall and the mobile crane drives up to the task, the tower crane is the one that stays on the site, often for months or years, while a building grows up around it. The vertical silhouette with the horizontal outrigger arm is one of the most recognizable images from a larger construction site.

§Building: tower, slewing crane and boom

The tower crane consists of a vertical tower built up of sections, a rotating crane at the top that lets the entire top section rotate, and a horizontal arm (jib) which is often divided into a lifting arm with a trolley and a shorter counterweight arm. The counterweight at one end balances the load at the other so the crane stays in balance whether it is lifting or not. The operator cabin is typically located high up at the slewing mechanism where the operator has a view down over the site.

§Fixed, mobile, and semi-mobile tower crane.

The classic tower crane is founded or anchored to the building and stands until the task is complete. But there are also mobile and semi-mobile tower cranes that can be moved between tasks on their own wheels or transported in pieces and reassembled. The certification rules for these specific hybrid forms have been a point of attention in the industry because they share features with both the stationary tower crane and the mobile crane — and it has therefore been clarified which certificate is required for them.

§Assembly and disassembly — the most critical phases

The tower crane is erected and dismantled with a mobile crane or another auxiliary crane and these two phases are among the most accident-prone in the entire life of the crane. The sections must be lifted and bolted together in sequence, the tower must be erected vertically and the counterweight must be installed in the order the manufacturer specifies so the crane never stands unstable during the process. The work is led by an expert and follows a fixed assembly plan — the sequence is not improvised.

§Catch the error before it becomes many.

When the tower crane is not in use—at night or in strong wind—the slewing brake is often released so the upper structure can rotate freely with the wind like a flag. This is called flag positioning or free-slewing. The purpose is that wind pressure on the boom shouldn't press the crane in one position where the forces can become too great for the tower and anchoring. A crane that can't rotate freely in a storm can in the worst case tip or break. So it's a fixed part of operation to ensure the free-slewing function works and that there's space around the crane so it can rotate unimpeded.

§Radio control and remote control

Some tower cranes are operated from a cabin at the top, others are driven by radio remote control from the ground. Remote control gives the operator the opportunity to follow the load more closely to the ground, but instead requires that the signal is stable and that there is a clear procedure for what happens if the connection drops in the middle of a lift – typically the crane stops automatically.

§Safety for the surrounding community and neighbouring spaces

Because the tower crane stands fixed for long periods and often swings the arm over neighbouring areas, roads or other construction sites, planning its swing radius and what the arm is allowed to pass over is part of the project from the start. On sites with multiple tower cranes close together, you must also ensure that the cranes cannot collide when they swing — something that is handled both by planning installation heights and with technical anti-collision equipment.