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Friday01 August 2014

How we cracked it 19: Peepul Centre, Leicester

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The challenge: To create removable, tiered seating for a flexible performance space

The solution: A hinged seating rake
architect:
Andrzej Blonski Architects
Site: Peepul Centre, Leicester
Project type: Arts and community centre

Step 1 Designing a flexible space

Our client, the Belgrave Baheno, a women’s organisation based in Leicester, wanted an arts and community building that included flexible space for both traditional, tiered performances and flat-floor functions.

The brief called for a 350-seat auditorium for drama, music and cinema, and a flat-floor layout for cabaret and assembly functions such as weddings.

The design problem was to provide a flat-floor format where storage for seating did not encroach on the available space. We also wanted to give a feeling of permanence in each configuration. These factors ruled out the traditional method of using retractable, tiered seating, known as “bleacher” seating.

Step 2 Raising the seat rake

During the competition period for this project, we suggested raising the seating rake, similar to the lifting of a steel canal bridge. This solution resolved the problem of lost floor space and also kept the seats permanent and comfortable.

After the competition stage, we developed two options for the movement of the seating rake, with the help of Adams Kara Taylor. Both were based on a “low-tech” approach of balancing the load of the seating rake with a counter-weight, so it could be lifted with relatively little effort.

The first option used a fixed counterweight that is normally seen on a Bascule drawbridge. Two weights on either side of the seating rake would pivot backwards, tilting the rake upwards in response.

The second option used a pulley and counterweight system similar to that used in theatres to raise and lower scenery, where the downwards action of the weight pulls the seating rake upwards.

However, the disadvantage of both options was that the weights would take up space that could otherwise be used for seating, and also restrict the flat-floor area.

Step 3 The built solution

The client opted for a design-and-build procurement method, but the contractor viewed the tilting mechanisms as a risk. Instead, it suggested a retractable, tiered- seating system to save money — the very option we wanted to avoid. However, we convinced the client that we could find a value-engineered solution which would preserve our initial concept. This was achieved by restricting the contractor’s package to steelwork and creating a new package for the lifting elements awarded to a specialist theatre contractor.

In conjunction with Theatre Project Consultants and Adams Kara Taylor, we developed a third solution, which dispenses with the need for moving counterweights. It uses two motorised pulley chains fixed to the auditorium roof trusses, each capable of lifting 12 tonnes.

Chains lowered from the roof are attached to the front of the seating rake. The motors then winch the seating rake into its raised position, where it is locked in place with shoot bolts that are recessed into the steelwork of the rake in the “down” position. To secure the rake in the “up” position, the bolts fit into holes in the auditorium’s concrete walls.

To allow the seating rake to move up, we also designed a piano-hinged, timber flap between the movable rake and the three uppermost, fixed-seating tiers.

The space’s poured-concrete walls were constructed to a tolerance of plus or minus 15mm, so the seating rake had to be far away enough from the walls to ensure it would not be obstructed during its lifting arc. The steelwork on the leading edge of the rake had to be repositioned on site to achieve this.

Step 4 Final touches

The underside of the seating rake has been fitted with recessed light fittings. In the upright position, their light will be filtered through a semi-transparent, coloured canvas permanently fixed to the seating rake. The aim is to create a tented ceiling surface for the auditorium in its flat-floor mode to disguise the exposed steelwork.

At a speed of one metre per minute it takes eight minutes for the seating rake to be lifted. It takes about 15 minutes to alter the configuration.

The auditorium has been in use since October, and the client will be using the flat-floor arrangement for the first time in mid-December.

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