Public art structures

A report has been received from two engineers who have noticed a trend for more works of ‘Public Art’ being placed near to highways and in cities. The works may be large and warrant a significant engineering input but may be driven forward by persons without sufficient appreciation of the technical issues involved.

On occasions due to the, often complicated, contracts and agreements that are in place – especially on larger regeneration projects – the procurers of the art have no contact with those who will be responsible for its long term inspection and maintenance. By their very nature public art tends to be one off and may, for example, be conceived and created by – say a sculptor.

For public art structures the familiar codes and standards for highway situations from the Design Manual for Roads and Bridges may not be directly applicable. The reporters give several examples including three that are particularly relevant.

This is of a spectacular lighting scheme with unusually shaped steel columns that was developed for a square in a city centre. It was felt necessary by the reporters to have a structural engineer modify the proposals to improve basic stability and to facilitate fabrication of the complicated shapes, and to redesign the foundations.

The lighting has been in use for a few years and there are issues as to the long term maintenance - for example changing the lamp or the special casings. Vibration is a significant consideration as it is unpredictable how such features will oscillate under wind loading and the magnitudes of the deflections.

This is a sculpture of a larger than life size animal in a busy city centre street. The original design did not have a structural frame, and by virtue of its shape would have been unstable. Engineers from the reporters’ organisation had to design an internal space frame and devise unobtrusive ways of tying down the sculpture to resist loads, including those from persons who might want to climb on the animal. The reporters believe that designers of art works may fail to foresee how their creation may be misused by some members of the public.

This was a tall landmark feature adjacent to a major road and was intended to sway in the wind. Unfortunately, the amplitudes were so large that, even at relatively low wind velocities, the authorities were worried about motorists being distracted and there were structural safety concerns. The feature had to be dismantled. Aerodynamic modelling was then carried out and significant modifications were made to the structure before re-erection in a different location.

Engineers should be more proactive in using their authority and expertise in explaining to others the necessity for appropriate technical input. Cantilevers and complex or slender shapes with unusual load paths may lead to dynamic problems, vibration and fatigue. Also, in general these types of structure will be much more difficult to erect, the part erected components becoming stable only in the completed situation.

Meaningful dialogue is required between designer and erector. Planning authorities (as well as other local authority departments) need to be more aware of the potential pitfalls when issuing permissions for works of art on and adjacent to the public highway. Prior to a project proceeding too far, a complete risk assessment needs to be carried out, covering not only hard technical matters but softer issues such as public reaction to an unusual object.

At this stage the basic concepts may need to be amended. An approval in principle should then be agreed between the designer and the approving authority, making clear which standards of design and control apply.

Proper inspection regimes need to be set up and funded. Where the design is non standard, it is vital that the maintaining organisation understands how to do its work and procure any necessary spare parts. In this respect, an up to date and accurate Health & Safety File can greatly assist. In practice, it is often the experience of the reporters that those who would most benefit from seeing the Health & Safety file do not have ready access to it. Funds may not have been allocated for the file’s upkeep or storage due to a lack of recognition of its importance by decision makers.

Durability and fixing details are often overlooked and need to be carefully thought through at design stage. There should not be features that are difficult to uncover and inspect. Corrosion protection and behaviour in the event of vehicle impact and fatigue are difficult to predict in these one off structures. Assumptions as to design life and frequency of inspection and maintenance need to be discussed and agreed in advance between the Designer and Adopting Authority.