Basildon's new landmark is a glass campanile that lets passers-by watch the bell-ringers at work. How did Buro Happold stop the lightweight tower swaying with the motion of the bells?
Bell-ringing is not usually a spectator sport. But an innovative bell-tower, set at the western end of Basildon's 1960s shopping centre, is about to change this.

Clad entirely in glass, the 27 m high bell-tower of St Martin's Church puts the campanologists and their bells in full view of the public. The bells sit 13 m above the ground behind glass louvres, and the first-floor bell-ringers' platform effectively sets the ringers on their own stage.

The £660 000 tower, which has been more than 20 years in gestation, is the brainchild of Canon Lionel Webber, rector of Basildon. It was designed by local architect and parish council member Douglas Galloway to commemorate the Essex town's 50th anniversary. As the world's first steel and glass bell-tower, it is something of an architectural coup for the bland new town.

The layout is simple. Beneath the copper-clad spire, the bells are arranged in a circle on the bell platform. Immediately below is an acoustic sounding chamber, and below this is the ringers' platform. The ground floor is an exhibition space and entrance lobby.

The challenge for the tower's structural designer, Buro Happold, was to produce a structure that could withstand the horizontal forces created by the swinging bells without obscuring the view. Traditional stone towers have enough mass to cope with horizontal loads; the tower, however, was lightweight. Unless it was designed carefully, it would sway, affecting the bells' performance.

The circular layout of the tower's eight different-sized bells helped, as it meant that horizontal forces from the swinging bells were not all acting in the same direction. However, the forces were still massive, and the frame had to resist them.

To create a frame that was rigid and strong enough for the job, Buro Happold came up with an octagonal structure. Eight triple columns of 140 mm diameter steel tubes formed the corners of the tower. These were connected to each other by horizontal bracings, like the spokes in a bicycle wheel, positioned below the floor levels. Vertical support was provided by X-shaped bracings, visible in the picture opposite, that tied each column to its neighbour.

The foundations also had to help keep the structure rigid. The 5.75 m diameter campanile rests on 16 piles which are 15 m long and splayed out at 10° angles. These are connected to a 600 mm wide, 700 mm deep concrete ring beam.

Additional resistance to the bells' momentum was provided by the mass of the concrete forming the tower's upper floor.

This comprises two, 250 mm thick concrete doughnuts, one on top of the other, separated by a layer of cork to reduce vibration.

Acoustic adviser Fleming & Barron had to ensure that the bell-ringers could hear the bells without being deafened by them.

So, it placed eight slots around the perimeter of the bell platform and eight smaller ones around the central access hatch to allow a controlled amount of sound to pass down to the campanologists.

The tower is clad in glass panes measuring 3 × 1.2 m. Because the tower is the first of its kind, it is not yet known whether or not the glass facade will vibrate when the bells are rung. Buro Happold therefore isolated the structure from the glass; it also specified 15 mm toughened glass to cope with stresses generated by the sound of the bells.

Building the tower posed fewer problems. Brian Houghton, site manager for main contractor Mowlem, says the critical path of the construction programme "was fairly obvious" to the project team. "With a small diameter tower, there was only room for one subcontractor on site at any one time." The long lead time necessitated by funding problems also helped the contractor because, as Houghton explains, "the consultants had worked on the project for more than two years before work started on site".