Sunday, August 30, 2009
Work has been progressing all week on the brickwork corner buttressing as this needs to be in place prior to completing the dome. Work has been slow due to the high number of specials where the brick meets the arches, but we are almost over the hump(s). The dome has arisen in each of the corners but will begin in earnest next week. Thank you to all who have been putting in the hard hours on the brickwork, especially - Carthage, David, Mark, Bruno, Alex, Ian, Elaine, Rae, and Suzy.
Tuesday, August 25, 2009
We've completed the arches and have started work on the dome. The key thing for the coming week is to keep the brick rising walls ahead of the dome, as we cannpt complete the dome until the walls are in place.
We used the lower course of the arches as a test for getting the placement of the slips right for the dome - and so used casting plaster to allow us to perfect the mixing of small amounts of plaster (enough for one slip) to the correct consistancy quickly. This will be critical for the dome as we will be relying on the plaster to set quickly and to hold each slip in place as we work upward.
Thursday, August 20, 2009
Wednesday, August 19, 2009
Laying bricks continued and we passed the 11th course on all piers. This means that the angle of embrace for the arches is now less than 52 degrees for the remainder of the arch. This will allow us to complete the brick slip portion of the arches and get going on the dome. The remainder of the brickwork will follow on over the next few days to its completed state.
The beam across the top of the site is part of a setting out methodology for the dome that we will be testing tomorrow. It replaces our initial idea to use a central pole. Once we have the system working correctly we will document it here.
Tuesday, August 18, 2009
Many thanks to Ecocem who have provided a significant quantity of cement for the project, which we are mixing with Portland cement as required. Ecocem is bascially GGBS, and using this reduces the carbon footprint of our project by substituting a by-product of industrial processes for cement that is made locally and consumes a significant amount of energy in its manufacture.
Monday, August 17, 2009
We continued bricklaying and building the arches today as was the case last Friday. Work was still slow but we managed to get to the 5th course on each pier, so we are getting a bit faster. We're taking tomorrow (Sunday) off and will continue where we left off on Monday.
Dermot Fullam from Dermot Paul construction came back and gave us a very thorough lesson in brick laying. There was a lot of work in getting things going in the correct manner. I think that we all gained an insight into the skill of a good brickie. We are going to take this section of the works very slowly to ensure that we can be accurate. Hopefully as we learn we will get faster.
Our intention is to work each pier up simultaneously with the arch, to brace against the buckling experienced in the earlier arch test. We will have to lay the first 12 courses this way, until we reach the point where the angle of embrace is reduced to less than 52 degrees. Once this is the case we will be able to complete the arches and start work on the dome as the brick walls continue to rise.
Wednesday, August 12, 2009
Wanda W Lau of MIT has a number of very useful tools to assist in the design of masonry arches and domes on her website. Of particular interest is this graphical analysis tool.
Many thanks to Michael Ramage for forwarding this to us. We will use these as part of the ongoing research into the redesign of the space resulting from last weeks work.
Tuesday, August 11, 2009
Following the collapse of the arch we carefully sorted through the broken pieces of the arch to attempt to form a full critique of the problems we had encountered. The following is a synopsis of what we observed:
- Not enough overlap between upper and lower brick courses allowing potential for joints to occasionally pass right through the arch. The cause of this was the rapid work method we had used, where the lower course was frequently completely obscured by plaster. Where good overlap been achieved the arch was very strong and it was difficult to retrieve bricks without breaking them.
- Small air-pockets between both courses. Again this appears to have been a product of the frenetic work method employed.
- The casting plaster was occasionally crumbly and hadn't set to a full strength.
Based on the above we held a design workshop over Skype with Michael Ramage and Peter Brunner.
Michael was incredibly useful and outlined our problems as being primarily geometrical in origin. A Catenary arch would be a far more stable form for a universally loaded arch to take, whereas a taller circular arches need some buttressing to contain the lateral load without buckling. Based on the discussion it appears as if the route forwards is the following:
- Drop the arches slightly (another 100mm or so)
- Build the side piers to the arches at the same time as the arches. This will entail keeping the formwork in place until the end of the project.
- Build the arches by placing the brick slips one by one. Use casting plaster for the lower course. This is not strictly necessary for the construction but will give valuable practice for the dome works.
- Use portland cement for the second course to save casting plaster
- Use bed-joint reinforcement for the bricks to the lower section of the piers.
- The geometry of the dome as designed should be fine - in this he mentioned that a good rule of thumb is to keep the angle from the apex of the dome to the springing point to a maximum of 50degrees.
- As we dismantled the collapsed arch we noticed that occasionally the casting plaster hadn't set hard but rather was biscuity and slightly crumbly. Michael recommended wetting the bricks before laying as this will allow for a greater adhesion between the casting plaster and the bricks, without the bricks taking too much water from the mix.
- Again in dismantling the collapsed arch we were able to pinpoint weaknesses in the pattern of overlapping between the upper and lower levels. Rae prepared new patterns for how to do this to ensure complete cover through the arch. Michael commented that running the second course perpendicular to the first would be adequate for our arches.
Monday, August 10, 2009
We designed the formwork to be easily removable, first dropping the edges from underneath and then pulling away both sides in turn.
As we dropped the formwork it became clear that there was a major problem with the arch, as it dropped with the formwork, eventually completely buckling to one side.
We cleaned up the site, and managed to salvage most of the bricks. Our instinct is that the geometry of the arch is wrong, being too upright where it bears on the pads. We also feel that there were errors in our construction methodology with not enough overlap between the first and second courses of the arch.
Tonight we are going to have a design workshop with Michael Ramage to adjust the design to solve these issues. We meet tomorrow morning to adjust the formwork and begin again.
Today we got the first delivery of brick slips and made our first attempt at constructing a timbrel arch, the first of 4 we need to bear on.
We decided to loose lay the brick slips and work the casting plaster in from the top side.
As we worked we experienced some problems with getting the lower courses to stay in place as the bricks we built up along the formwork. To counter this we ended up working and casting in sections.
As we finished up we noticed that one side of the arch had come away from the formwork. as if the arch had buckled during construction. Propped by the top of the formwork we decided to wait until Monday to strike the formwork to see if the arch is self supporting or not.
Friday, August 7, 2009
Today started out with checking the tolerances of the concrete on site. We were within 5mm accuracy on plan, and about 2mm vertically. Not bad for the first time most of us have worked on site.
As we don't get the first bricks until Friday most of this week will be spent readying ourselves for this. The first thing is to make the formwork for the timbrel arches. We will only make one to begin with, and test this over the weekend. If it is stable we will prepare the rest of the formwork for late next week. Our concerns stem from the fact that our proposed arches are quite upright when they spring from the ground. There is a possibility that this may not work.
The primary design consideration for the formwork is how to remove it afterwards. We are making ours in two halves so that each can be propped and removed independently of the other, and without destabilizing the arch.
Saturday, August 1, 2009
We finished the formwork for the concrete by placing the boxes to cast the upstands on the pads. These up-stands will provide an edge for the arches to spring from. Great care was required to get all the boxes located accurately. This was done using triangulation off the central pole and lots of patience.
The threatened rain didn't materialise, but we were anxious to place the concrete as quickly as we could. With Dermots team working two mixers there was a steady stream of barrowloads of concrete to the site.
Dermot gave further demonstrations as the concrete was poured in using a poker to vibrate it to an even consistency.
By the end of the day 4 all pads and trenches were poured and the site and all tools cleaned. We meet on Tuesday to start work to get ready for making the arches.