Hammersmith Bridge underside and steelwork – May 2020

The Society’s committee is of the view that as part of the renovation work, there is a great opportunity to improve the Bridge to make it better suited to future needs, requiring more space for pedestrians and cyclists, as mentioned in our last article.  Our proposal is to widen the pathways to allow safe and satisfactory bidirectional walking on one side, and bidirectional cycling on the other, so that cyclists no longer need to compete with road traffic, significantly improving safety.  Currently, because of the somewhat narrow walkways, it’s not possible to safely cycle or even pass easily when walking, certainly not in a wheelchair or buggy.  We think this can be done both at modest cost (certainly compared with the Garden Bridge!) and largely independently of the planned repair works, so as not to lengthen the closure.  We have a brief update on repair works at the foot of this article.

The bridge’s narrow pathways for most of the span measure approximately 1.6m, widening at the pillars to approximately 1.8m, but still too narrow for bikes to pass safely (one of the reasons cyclists have to dismount currently), let alone to support social distancing needed now, and possibly in the future.  We’ve now looked at the structure in a little detail, and, as shown on the photos here, the pathways are supported by simple cantilevers, apparently bolted on.

Hammersmith Bridge – historical repairs (photo: Keepingthingslocal)

Steelwork underneath the bridge was repaired section by section in the 1970’s, and a new grid of substantial longitudinal girders replaced the originals (pierced where bridge hangers meet the deck). Historic photos (right) show the original, very much less substantial steelwork.  Given the scope of the repair works, and amount of money and time to be spent on repairs, there seems little reason not to now consider the attached pathways in more detail, especially if the planned temporary bridge removes the need to keep it open during the works.

Interventions over the years have added weight, helping push the bridge into its current parlous state, and rather the opposite of modern engineering design. The replacement girders are one example, but the significant weight of the roadway could, with modern design and materials, be reduced to invisibly reduce the load on the bridge to the point that it could handle heavier buses.  Currently some or all of the roadway support is in the form of large wooden beams – possibly railway sleepers – which must be very heavy indeed.  The life-expired roadway surface is planned to be replaced in any case.

Pathway supports (recent replacement)

As can be seen from the photos, having used the decoration budget on the highly visible upper parts of the bridge, the cantilevers are from the ‘Bazalgette functional’ school of design, and the same can be said of much of the underside of the bridge which has suffered a fair number of inventions and additions of maintenance cradles and similar artefacts over the years. The existing cantilevers may be strong enough already, especially if a replacement pathway were made of a lighter yet stronger modern material or different design, and the recent heavier wooden supports (shown left) replaced.  Alternatively, the photo below shows that Bazalgette designed matching extended cantilevers for the bridge-ends – copies of these could be used throughout if longer ones are calculated to be necessary.

Extended cantilever – Barnes side

Wider pathways would retain the existing handrail and associated heritage structures, such that the appearance would be substantially unchanged.  The width should be increased to a minimum 2m following DfT guidance, or better 2.6m to meet TfL guidance for moderate capacity, or whatever is practically achievable, given all the constraints.  The DfT dimension allows 2 wheelchairs to pass, and is a minimum for bidirectional cycle lanes.

To argue that the it should be left as is for heritage reasons flies in the face of the many recent and already planned interventions, not least the 1970’s steelwork, and pathway changes shown photographically here.  The bridge can be fairly straightforwardly updated to better handle 21st century needs, without damaging its aesthetic or heritage value, and we think Bazalgette would approve on the basis of public health alone.

Update on repair works

• The exploratory works are expected to be completed this week. No further issues of substance were found. The results have been used to help inform the finalisation of the concept design for the bridge repairs, as well as the detailed design for the stabilisation works.
• Thames Tideway Tunnel passed the bridge without incident recently.
• There are currently over 300 sensors and strain gauges on the bridge which provide a continuous alert monitoring system.
• Concept design for the main bridge solution is being finalised by consultants in the next couple of weeks.
• Temporary Bridge design is complete and TfL are consulting and expecting to have planning permission submitted within the next couple of weeks,  however approval from key stakeholders is subject to having funding in place for the main bridge works.