I begin this weekend, intending to treat it as a concept design submission. The goal is to have half a dozen sheets of drawings (plans, elevations, sections) several perspective views and a tidied up model with a fairly consistent level of development across the whole building. Let’s see what happens.
Thursday evening found me sketching ideas for vault family strategies on my phone. I knew that the curved ambulatories around the East end would be tricky but I was optimistic.
Friday morning revealed serious issues with the existing setting out. This would have to be resolved before embarking on the vaults. First thing to do is look more carefully. Peel off another layer of the onion. There are radial alignments where the flying buttresses sit. These were not working.
Also there should be curved sections of wall between the arches of the outer row, not free standing columns like the two inner rings. I decided to use a new background image. Maybe this plan was more accurate. Certainly easier to read.
The next detour along my weekend journey was distracting but positive. Conversations with potential collaborators, which I managed to get moved to Slack eventually. Four way conversations in full swing by Saturday.
I realised that there was a double grid at the transition from straight to curved, an offset of about 1.5m This was crucial in getting the radial alignments to work.
Along the sides of the nave I have columns nested into the arch families. This works well, but around the curve the columns need to be independent in order to fine tune their position and alignment.
All this took time. The second pass through the model can be frustrating. Work proceeds more slowly than during the first roughing out. But the complexity of the apse Geometry is quite fascinating. I would love to compare with other cathedrals. I wonder if someone has done this already.
Here there are 5 bays in the inner ring, 10 in the middle ring, and 13 in the outer. The first two rings are evenly spaced. But the third has grouped arches. This allows for the thickness of the hefty walls that anchor the flying buttresses.
So on the outer edge you have vaults that link 3 arches on one side to two on the other. Creating a sort of zigzag pattern. This seemed like a suitable challenge for Saturday.
I tried the swept blend approach that had worked well for the radial vaults high above the altar. Actually, these need to be reworked now because the offset has disturbed their regularity. The Leica TruView site was really helpful in visualising the context here. It really captures the spirit of Gothic architecture: bundles of circular ribs curving upwards. The tricky part of the Swept Blend in this situation is the way the void extrusion cuts at an oblique angle to the second profile.
Couldn’t get the swept blend to work for the zigzag. Too much irregularity. Can’t get the ends of the vaults to match the arches. So I opted for Point World, and lofted surfaces. Took a long time and the fit is still far from perfect. But I learnt a lot about the subtlety of these spaces. This is all manually created with an in-place mass. You could thicken the surface up using wall/roof by surface, but I don’t think the junction at the ridges will work out too well. The alternative would be to use a closed profile for the loft, instead of a line.
Looking from above you get a feel for the nature of the challenge. There are five wedge shaped portions of vaulting between the zigzag of the ribs. The middle one is symmetrical, but the others are skewed. It’s just the way things work when you divide the space up like that. You can see the small gaps down the sides where the vaults meet the ribs.
Of course, it’s always possible to generate a softer image that disguises the minor imperfections that leave me dissatisfied with my efforts so far. “Fake News” you may say, but I think it’s always useful to step back from time to time and view your work from a metaphorical distance. Between the groups of 3 arches there is a wider section of wall. The round column is pushed a little further forward and there is a flat splay leading back to the arch. There should be a horizontal line where the vault meets this splay. Not happening. Something wrong with the geometry but I’m not sure how to fix it.
There are 3 types of zigzag vault. I’ve done one instance of the pink type. One out of three. There are two different types that connect two arches to one (green and blue) Looks like I’m going to pass all these on to Alfredo now. Big sigh of relief.
Alfredo very generously offered to host the model on his BIM360 site. Ideally I would have liked Autodesk to host the model, but those discussions have not yet come to a conclusion and there are several people keen to contribute, so we went ahead. There will need to be discussions about how we coordinate our efforts. From previous experience with Project Soane, a naming system for the various elements will be helpful, so that will probably be my initial focus next weekend.
After uploading the model on Sunday afternoon, I had time for a bit more modelling. Some adjustments to the main vaults over the choir and the apse. Not complete, but enough to establish how the double grid is accommodated. Then I roughly sketched in the intermediate flying buttresses around the apse. This is another example of a “3 bays into 2” situation. So you get two buttresses converging to meet at their highest point. I have made them straight in plan at present, but actually they need to do a bit of a “dog-leg”
So we have a lot of fascinating challenges, and a small team of experienced Reviteers. Let’s see what happens over the next few weeks.
There's nothing like a good collaboration.
There's nothing like a good collaboration.