Carmarthen Road Sign

Client: Howard Bowcott and Carmarthenshire County Council  Role: Structural engineer

Howard Bowcott is a fantastic artist and sculptor based in the Northern Welsh town of Penrhyndeudraeth. Over the years, we at R Vint Engineering have had the privilege to provide structural advice and design for several of his projects. The Carmarthen Road Sign is the 6th and latest sculpture that I personally have worked on.
These sculptures always present a challenge, which pushes our engineering knowledge in ways our more typical projects do not, and the Carmarthen Road Sign Sculpture is no exception.
For this project, we used Autodesk’s Robot Structural Analysis software to create a model of the sculpture. This was done by taking a 2-D dwg file of the sculpture to act as a template. The plates that make up the sculpture were input as panels in the analysis model with openings made in the panels to spell out the words CAERFYRDDIN and CARMARTHEN. Not a difficult task, but with 61 uniquely shaped panels and 50 openings not a short one either.

Horizontal support bars were introduced to replicate the channels that would support the panels on-site and the appropriate loading was applied. To determine the need for strengthening of the panels, we had to determine the bending moment capacity of the material and determine a deflection limit. The bending moment capacity was a fairly easy process, once determined it was easy to create my own panel mapping scale to show green when below the bending moment capacity and red when above. The deflection limit was a little trickier. Typically, deflection limits are based on the human experience of the structure or if certain brittle finishes are to be used on the structure. If something deflects too much, people will not want to use it or it will crack the finishes. However, we did not really have either of those limitations for this structure. Using our engineering knowledge and even getting colleagues holding tape measures with various lengths from a distance a limit was agreed upon. With these limits in place, it was a simple case of going through the model, panel by panel, checking whether it worked and adding in additional strengthening members or moving the horizontal members if necessary.

The final challenge came from the connections between the horizontal channels and the plates. There were a lot of constraints when it came to deciding on the bolts such as material thickness, allowable space for the bolt and how to counter potential loosening of the bolts from vibration. Although products like Tek-Screws and Hollo-Bolts were looked at they generally were too large for the available space. M6 x 20mm Button Flange Head Screws were suggested by the contractor as a product that was small enough and could be made to be a High Strength Friction Grip (HSFG) connection, but would it have the capacity? With little to no relevant information concerning its capacity from supplier we were tasked with calculating it ourselves. Thankfully, in Eurocode 3: Design of steel structures – Part 1-8: Design of steel joints, we had all the calculations we needed to be able to mathematically prove the suggested screws, and with on-site testing to confirm our findings, we were able to complete the design for this beautiful sculpture. An interesting and rewarding project.

Date: July 22, 2020