The Maidenhead canopy was dismantled as part of the Cross Rail project and electrification of the Great Western Line. As one of the few remaining Brunellian sheds attracted the attention of the Railway Heritage Trust (RHT). The RHT an application was successfully submitted to the RHT to fund the restoration and eventual erection at Wallingford.
The work has progressed well and discussion about how extensive the preparation of the wood should be before painting and whether the painting at this stage (ie before erection) should include undercoat(s) and top coat(s).
Careful examination of the remaining pieces of principle rafters has confirmed that those of one side were indeed slightly curved. It will not be possible to reproduce this curvature on the repaired structure as the damaged pieces will be held together by inset metal plates each with 20-22 countersunk bolts which will of course make the principle rafter rigid. In all over 400 such bolts will be added. The solution to this geometrical puzzle will be to allow the spandrels on the wooden upright beams of the wall to be slightly countersunk at their upper end.
Detailed measurements of the position and depth of the culvert were made and to our relief this will not interfere with the foundations needed for the Canopy wall.
Getting one of the tie bar assemblies and principle rafters all laid out on the floor of McCurdys revealed that the geometry of the tubing that makes up the tie bars is unexpected – it is impossible to have the wall and columns vertical when the tie bar is horizontal as the principle rafter on one side is longer than on the other.
This helps to explain why the tie bars on each side of the central triangle are unequal, however it also suggests that the longer principle rafter was put under tension and distorted.
Work continued on the repairs to the major wooden components with all the structures removed from Wallingford to McCurdy’s workshop before Easter running.
Delivery of one large I beam was taken and this was cut on site to generate two T beams that could be used to re-create one of the lattice beams that ran between each pair of columns as one of these failed to make it to Wallingford.
Much of February was spent taking the ironwork to pieces and some interesting discoveries were made for each spandrel had 10 fixing points designed to be secured with a bolt and nut, although on some spandrels the tie bars obscured two of the fixing points and so lugs were provided to help locate the spandrel. However most of the fixings were not a nut and bolt but simply a shortened bolt hammered into the wood! Most spandrels had only two or three proper fixings! The tie bars were held together by an ingenious arrangement of two wedges and two [-shaped pieces, although a very firm way of fixing them a good blow on the end of one of the wedges broke the seal formed by numerous coats of paint and released the arrangement.
By carefully taking the various iron bosses used to hold the principle rafters at the apex and those securing the tie bars it was possible to work out the method of construction.
The first practical step was to layout the eight
panels in order to see just how extensive the repairs needed to be and to make
a start on disassembling the ironwork in readiness for repairs. To do this
McCurdy’s brought in their crane to allow the various parts to correctly