Frameless glass spider wall details
Frameless glass spider wall solution
This project is a good example of a frameless glass spider wall to a car showrooms. The structure of this frameless glass spider wall solution is the full height glass fins.
The glass fins 8m high at 2.4m facaeted centres; they are manufactured in two parts, the joint is mechanically clamped at midspan, the glass fin passes in front of the intermediate floor slab with no connection to it. The 12mm tempered HST clear face glass covers an area of 406 sqm; The frameless glass spider wall covers an overall faceted surface of 406 sqm. The frameless glass spider wall is 52m wide by 8m high.
Frameless glass spider wall components
The midspan connection is an intermediate 316 grade stainless steel 20mm flat plate located to either side of the fin. These flat plates are typically 500mm deep by 200mm high predrilled with 20mm diameter holes.
The 4 way spider fittings are cast 316 stainless. The holes in the glass are countersunk so that the head of the bolt is flush.
Inplane movement can be accommodated by the articulation of the stainless steel bolt and fitting. This was an important feature of this project which worked well with the 3 degrees radius.
Each fitting has four holes and typically 2 are designed with traditional dead holes and the other two are live, these transmit the loads to the fin.
The fin is erected is assembled by a specialist glazer on the ground and erected in one piece with the base and midspan brackets in situ. Erection of the glass fins starts at the centre of the opening working to either side to minimise creep. The importance of a method statement can never be understated, it is always recommendable that the façade designer communicates to all members along the cladding supply chain.
The fins are typically 500mm deep by 20mm thick, toughened and laminated, heat soak tested. It is always our policy to carry out a glass risk analysis as part of the design process to guarantee the longevity of the solution in respect of service and warranty life.
The face glass is 12mm toughened, HST, typically which follow the facet in plan and the height is divided into three panes to align to architectural sightlines. The face glass is predrilled with a countersunk hole to an agreed setting out to minimise stress.
Accomodating Movement within a framless glass spider wall solution
The interface detail at the head of the screen is designed to accommodate movement both upwards and downwards.
The face glass is inserted into the horizontal stainless steel channel. This member is designed with an extended leg height to accommodate vertical movement in both directions without inducing any load on the glass.
The fixing brackets at the head and base of the screen are located on either side of the glass fin. The faces of these are machined to follow the line of the facet.
Challenges facing designers of frameless glass spider walls
The vertical leg of the head bracket has elongated slots to enable the roof to move without the fin inducing stress from imposed loads, ie dead, live, snow, access, failing to provide for this at design stage will result in the fin bucking leading to collapse.
The designs of these brackets were of particular importance to the successful installation of this project and worthy of mention.
The primary steelwork beams which ran out radially from the centre were erected to excessive tolerances outside of best practise industry norms.
The level of these beams varied by as much as ±40mm from the agreed design dimension which meant that the holes in the brackets had to be extended vertically and adjusted to suit the localised secondary brackets. It is therefore important in the design of such details that the façade designer takes recognisance of this type of problem, designing interface details which are buildable.
There are a number of distinctive challenges on this type of solution. The radius, levels and construction setting out must be defined at the earliest that requires detail coordination between relevant trades.
Frame glass spider wall work package management at each critical interface must be discussed openly.
This allows the ordering of the face glass and requires very careful coordination of the section vertically particularly the position of the beams.
Agreeing the setting out sizes enables the ordering of faceted members cut to size, drilled and prepared.
On this project all the glass was ordered in advance with the exception of the jambs which were site measured.
Taking this decision is a risk and the designer must be confident.