Design Awards: 2002: Certificate of Merit

Whatman’s Field Downstream Bridge, Maidstone

Whatman's Field Downstream Bridge, Maidstone

Architect

Studio Bednarski

Structural Engineer

Flint and Neill Partnership

Steelwork Contractor

Fairfield-Mabey Ltd

Main Contractor

Lewin, Fryer and Partners

Client

Maidstone Borough Council

In May 1998 a team of Architects and Engineers were appointed to assist in the concept and design for a Millennium Project at Maidstone River Park.

The concept was to open up Whatman’s Field, a new public park, with the construction of two new foot/cycle bridges spanning the River Medway. By allowing easy access to Whatman’s Field the public are able to take advantage of new nature trails and safe landscaped areas.

The upstream bridge, a cranked concrete stress ribbon, is complemented by a downstream steel bridge inspired more by ‘landscape’ art than bridge engineering aesthetics. Due to unconventional design this bright blue 75m long bridge has a very slender appearance.

The steel box beam bridge is carried by two delicate V shaped piers. The aim was to reduce the visually perceived elevational depth of the box section. The upper, deeper, part of the box section has been set back and ‘camouflaged’ by wire mesh balustrade panels and stainless steel grills along the walking deck of the bridge. A striking blue colour was used for the visible side strip and the bottom of the box section, while the part that is set back was painted grey to make it almost invisible. At night, thanks to the lights which are set on the vertical walls of the set back box, light is shed upwards onto the wire mesh leaving the coloured narrow facia dark, only the glistening wire mesh is visible.

Circular cut outs in the bottom of the box section serve two functions. Firstly, they facilitate inspection access to the inside of the steel box sections. Secondly, they also lighten the overall appearance of the bridge and provide visual relief for the long horizontal underside of the bridge.

The bridge was fabricated in three spans. The centre span is approximately 31m long. The steel box sections were pre-cambered during fabrication. The use of the most advanced 3-D CADCAM techniques enabled the complex geometry to be easily dealt with and provided a good degree of accuracy. The holes in the flanges were profiled using highly automated fabrication machines.

The erection scheme of the bridge was restricted by the river. The Medway is a tidal river and is also navigable, a lock near the bridge allows boats to pass through at restricted times depending on the tide. Erection was only permitted during river possessions, which usually only lasted for four hours.

Two heavy duty trestles were temporarily constructed on each bank to assist in the erection of the bridge. Apart from the bolted edge boxes and parapets, all site splices were fully site welded, with welds then ground flush on all visible surfaces. Welding and subsequent painting of welded areas was carried out in a controlled environment using shelters as required.

At either end of the bridge the steel box sections bear onto concrete abutments which are supported by six piles. Embankments have been built up locally at either end of the bridge to achieve access.

All the parties involved on the project worked together to achieve a successful project outcome. The bridge allows access to rejuvenated areas and gives the local area a unique yet practicable Millennium project that can be admired for many more years to come.

Judges’ Comment

s:

The innovative cross-section with the façade and balustrade supported from the protruding underside of the main box girder, successfully leads to the objective, and the impression of a remarkably shallow structure. Careful detailing and good fabrication contribute to the high quality of this bridge – and it is hoped that the maintenance will be sustained to a corresponding standard.

MPV, Church Walk, Leeds

MPV, Church Walk, Leeds

Architect

Union North

Structural Engineer

Buro Happold

Seelwork Contractor

Merseyside Ship Repairers Ltd

Main Contractor

Simons Construction Ltd

Client

Townhouse Life Ltd

Union North was briefed to develop a set of four railway arches as a bar/club/pavement café, replacing existing retail and light industrial units. Several issues were key to the direction of the design development:

  • Railtrack were to carry out inspection and maintenance of the arches on a two yearly cycle.
  • There was a substantial area of private open space in front of the viaduct available for use as a pavement café suggesting a very outward oriented spatial arrangement and the need for measures to extend the outdoor drinking season.
  • Requirements for emergency escapes and the fact that the arches are blocked to the rear necessitated an open fronted arrangement for rapid evacuation.
  • The project is a significant distance from the main drag of Assembly Street and it therefore had to present itself as a destination in its own right with a distinctive commercial offer and visual identity to match.

The above constraints could not help but drive the design in the direction of four identical mass-produced units each in turn assembled from repeating prefabricated segments. From this starting point key design elements fall into place inevitably: rounded profiles blur floor, wall and roof into a unified all-enveloping skin; the effective legal limit on the upper floor area generates the characteristic section profile of the units fitting the surrounding arch closely at low level, tapering in above with the reduction in floor area; the front flip-up doors double as canopy and security shutter; airlock links connect the pods together through existing jack arches and the narrow alley to the rear of the viaduct becomes a connecting service void.

An industrial aesthetic suggests industrial building techniques and the pods were factory prefabricated in two metre segments, that dimension being set by the available size of mild steel plate and the maximum volume of motorway loads.

Each segment was fully welded and painted in Liverpool before trucking to site for rapid assembly by industrial forklift, necessitated by Railtrack’s restrictions regarding the use of cranes near their track installations. Completed shells were then coated internally with sprayed insulating foam.

Internally the tight fit integrated design philosophy is continued, organically shaped tubes of space snugly interlock with one another, servicing and structure disappear into the intersitial spaces between their wraparound plywood skins. Visible fittings were eliminated or reduced to simple openings in the plywood lining: ventilation grilles are perforations in an otherwise continuous skin; lighting is by concealed fluorescents in coloured voids sunk into the structural depth of the pod and washbasins reduce the slots concealing stainless steel troughs. The door counterweight and opening mechanism are concealed in a void inside the glassfibre nose. Under licensing conditions a protected route was required from upper floor areas direct to the exterior. This was articulated as a sculpted tube sweeping down through the ceiling and out through the glazed external screen terminating in clam-shell exit doors. Access doors to the stairs fold back into flush recesses on alarmed magnetic catches.

Judges’ Comment

s:

There are thousands of railway arches in the UK, and they are put to many uses. This innovative concept, of a steel shell providing surprisingly good space which is secure, whilst affording easy access to the arch for inspection and maintenance, can have wide application.