[Canadian Mind]

I've been watching Bentall 5, and now Shangri-la rise in vancouver, and can't help but wonder how they went about attaching the curtain walls to the concrete.

Could someone enlighten me on the process, including such things as how they make it air resistant, sharp corners, etc.

[Kelvin]

The glass itself likely arrives on site as a prefabricated sealed unit which will then be placed inside an aluminium frame which is "hung" from the superstructure. As each window unit is placed it is sealed in place within its individual frame and becomes air tight. Building envelope designers then also need to devise a method for removing and replacing units which fail or break.

The JHT in Boston became famous because, as it was later determined, the building racked under larger wind loads which then cause small deformations in the aluminium frame. Even though the distortions were only small, they were enough to allow some glass panels to dislodge and fall onto the sidewalk below.

There was another building in Ft. Worth TX which had its panes of glass sucked out during a near-direct hit with an F? tornado. Afterward it looked like a giant (texas-sized) corn-cob.

[mthd]

kelvin, in my experience very tall buildings are rarely built with stick-system glazing as you describe. unitized curtain walls are the norm these days.

typically the window 'frame' and glass itself are actually assembled together off site, at the curtain wall fabricators facilities. a typical 'unit' might be one floor high and 5 feet wide with several pieces of glass (although usually just two) already sealed into the aluminum frames.

on a concrete building, curtain wall embeds are typically cast into the edge of the slab. the actual attachment is made mechanically via various types of bolted connections. typically the unit bears on the lower floor and is only connected to the top for general restraint, allowing it to move in and out as the two floors move in different directions under wind or seismic loading.

there are 'stick framed' curtain walls more like kelvin describes, but in these everything usually arrives separately - the vertical mullions, the horizontal mullions, and the glazing. the verticals are attached to embeds in the concrete slab, the horizontals attach to the verticals, and then the glass more or less sits in the glazing pockets of the mullions and the assembly is usually covered by a decorative cap. this requires lots of fairly precise field labor and generally prevents the use of certain kinds of curtain walls - especially those in which there is no exposed metal on any side of the frame.

[BTinSF]

^^^Note the metal brackets for attaching the glass curtain wall:

http://img103.imageshack.us/img103/4919/1909070imgxx9.jpg

The attachment is begionning although the 2nd floor is not galss but some sort of metal screening (all the floors above will be glass):

http://img408.imageshack.us/img408/2084/1909084imgrt6.jpg

Note a panel on the far right being hoisted into place.

[Kelvin]

MTHD - that is interesting. I would assume though that the smaller sections of glazing in each panel unit can still be individually replaced if need be.

You also raise another interesting point - the norm is for 5' widths, which I assume has as much to do with ease of handling as it does for manufacturer's capacity.

[mthd]

MTHD - that is interesting. I would assume though that the smaller sections of glazing in each panel unit can still be individually replaced if need be.

You also raise another interesting point - the norm is for 5' widths, which I assume has as much to do with ease of handling as it does for manufacturer's capacity.

glazing can be replaced, but it's a non-trivial excercise - and has to be done from the outside of the building. usually it's done from the window washing platform.

the 5' module has more to do with the standard office planning modules in the united states than anything else. in metric countries it's often 1.5M. in both cases the smallest office is two modules. for residential buildings you'll see more variation in the unit size, but they almost never go past 7' because glass is hard to come by with both dimensions greater than 7' due to limitations in the tempering, laminating, heat-strengthening, or low-e coating machines. they have an ±7' width that the glass rolls through. since the vertical dimensions of the main lite of glass will almost always be more than 7', that generally dictates a < 7' width.

[snappingturtle]

structural tolerances must also be dealt with.
typically, curtainwall anchor assemblies accommodate between 1 to 2 inches in any direction of tolerance in the building structure. that is, the structure is allowed to be in a 2-4 inch theoretical envelope in each axis.
for large scale unitized curtainwall, each curtainwall company has its own proprietary set of parts that accommodate the required tolerances, in-out, up-down, side-side.

side-side is commonly accomplished by having a bar or angle that the curtainwall panels hook onto. as long as the bar extends a few inches to either side of the mullion, the hooks can go anywhere on the bar.

in-out is sometimes accomplished with shims, other times with slotted holes in a serrated clip angle that can be pulled in or out.

up-down is usually accomplished with "lifting" or "jacking" screws within the assembly. this is usually the final operation in setting curtainwall units.

[Kroy Wen]

I took these pics recently- although this is a steel structure, the process is virtually the same:

http://img84.imageshack.us/img84/3576/bloodknuckle117iq7.jpg

http://img84.imageshack.us/img84/6549/bloodknuckle118dn7.jpg

http://img84.imageshack.us/img84/3505/bloodknuckle119ck7.jpg

http://img139.imageshack.us/img139/7081/bloodknuckle122oe8.jpg

[dericcio]

well you answered in this post to my questions: "looking for images of glass panels facade";
where can I find more pictures or videos about?

[Coldrsx]

^

http://people.cornell.edu/pages/jo24/comments/curtainwall.html

[zawmyonaing]

thanks for your photos with how to prepare for wall cladding,I also like to know
which is economy between using Aluminum panels on R.C.C slab and prefabricated slab.
thanks again,please,share more photo of steel structure buildings construction site,I,m familiar with R.CC buildings.
:)

[zawmyonaing]

thanks for your photos with how to prepare for wall cladding,I also like to know
which is economy between using Aluminum panels on R.C.C slab and prefabricated slab.
thanks again,please,share more photo of steel structure buildings construction site,I,m familiar with R.CC buildings.
:)

[Kelvin]

prefabricated concrete slabs are not normally used in North America (although can be found in generally smaller buildings). The method of (floor) construction seen in the photos above is a "corrugated steel deck" of relatively thin thickness (16 ga, 20 ga etc.). The profile (from top of flute to bottom of flute) though could be between 1.5" (32 mm) and 4" (102 mm) and concrete is later placed to a maximum thickness of 4" to 8" w/ regular rebar.

The steel deck is either spot welded to the steel beam below or a series of studs are welded to the beam (in the field) thus connecting beam, decking, and stud (which allows for some basic anchorage with the concrete).

Precast concrete panels can also be prestressed and/or post-tensioned (bonded or unbonded).

As with all material systems (and structural issues aside), it depends on local market experience, trends, material costs, material supply, labour availability/costs to determine which system may prove most economical for construction on a given project.