Glazier Challenges
Glazier challenges in vertical movement are effecting glazing contractors, architects, manufactures and engineers.
There seems to be a large gap between what architects require to accommodate vertical movement of the building system, interfacing with glazed systems and what the manufacture provides to accommodate for those movements.
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The gap between Architects and Manufactures in Vertical Movement?
Carrie Jeske JEI Structural Engineering – Glazing Design Calcs
Seems to be a large gap between what architects require to accommodate vertical movement of the building system. Interfacing with glazed systems and what the manufacture provides to accommodate for those movements. Any answers?
Reyad Abu Diab TECHNICAL MANAGER at ALHAMAD
Many senior consultant architects they know nothings about the glazing and aluminum systems. So we suggest to be the specialist consultant for glazing and aluminum works in the area. Chuck Knickerbocker Curtain Wall Manager at Technical Glass Products
Define vertical movement: Are we talking about thermal, or building frame movements (including column foreshortening, concrete shrinkage, and drift, either from wind or seismic)? Or all of the above? The more sophisticated designs / manufacturers are often left to educate the architect through the shop drawing process. Certainly, if / when the specs lay out all these performance requirements, the framing has to address them. The specs are often the first clue that the architects understand the design issues. Their details ought to reflect those constraints, and how they envision the curtain wall system being able to absorb or work within those parameters. If the drawings and specs don’t address all of those issues, then let the c/wall provider beware – or “caveat emptor” in reverse: The architect probably doesn’t have a clue as to what’s coming.
Richard Araw, Façade Design Supervisor at ALT Cladding Inc.
Commonly,
The vertical movement are accommodated by the STACK JOINT – ranging from 25mm to 45mm. But most architects prefer 25mm to 30mm. You do not want to see thick black line across their building. Or , if thick line is necessary, this can be hidden by an aluminum capture instead of the trim on the glass.
And that is where the Curtain wall consultant and curtain wall manufacturer comes in. We need to educate the architects how important vertical movement to the façade.
Stewart Jeske President at JEI Structural Engineering
On virtually all of the small and medium jobs it is a major issue. A general CW or storefront manufacturer is selected by the glazing contractor after receiving quotes. The architect has specified that the system must accommodate the building structural movement. The building structural engineer has designed perimeter/ spandrel beams for L/360 LL (typically between 1/2″ to 3/4″ vertical movement). So, for instance, if it is a head joint, thermal movement (say 1/4″) and the vertical live load (say 3/4″) adds up to a joint required at the head of 2″ (for sealant properly designed). Its ridiculous. The manufacturer’s don’t design standard anchors or receptors for this type of movement.
The breakdown is on the part of the building code – So we need something standardized that requires the structural engineer designing the buildings to design for something reasonable that the manufacturer’s can accommodate – Say 1/4″ vertical LL movement at the perimeter beams. Then, everyone would be on the same page.
Chuck Knickerbocker Curtain Wall Manager at Technical Glass Products
Richard:
if they did a masonry wall instead of curtain wall, wouldn’t there also be a “thick black line across their building” for the very same reason? The floor carrying the dead load deflects, the exterior skin has to accommodate the deflection somehow and / or somewhere, right? In unitized walls, there’s a little more forgiveness, in that the gaskets can compress, and the joints can often be smaller, not having to account for sealant capacity to take movement.
Peter Karsai Associate Director at AECOM
This is a complex issue, and is probably one of the area’s most at risk of poor performance, dispute, and litigation. It is not an issue that can be addressed by a simple “rule of thumb” approach. Coordination between cladding and structure needs to address 3 key aspects:
1) Location of any movement joints in the superstructure (usually vertical joints in long buildings). Cladding needs to mirror a joint over the building joints (common sense, but I’ve often seen cladding installed without joint, always with disastrous results).
2) Deflection of structure at cladding fixing points at time of installation (most cladding is installed level, most structures are not level, cladding brackets need to make up the mis-match).
3) Deflection of the structure after the cladding has been installed (live load deflections, wind load/sway, and creep/settlement movements).
After this, the cladding contractor still has to accommodate his fabrication and erection tolerances.
So, quite complex, and it gets worse if the structure has long spans or cantilevers. Many projects (large and small) have tripped on this issue.
This is not something that can safely be covered by the architect’s specification. It is also beyond the understanding of the structural engineer (structural people and cladding people speak a different “language”, and need an middle-man to help them understand each other). It really needs a specialist cladding consultant to sort it all out, either during the design stage (for a small fee), or during the dispute/rectification/litigation stage (for a very BIG fee). From an industry perspective, the first approach is obviously better.
David Altenhofen East Coast Director at The Facade Group
Good architects figure this out with their structural engineers all of the time. A good consultants can also help but is far from essential on every job. Good structural engineers will frequently bring up the topic just from their own experience.
It is not that big of a deal to ask the structural engineer to limit live load deflection to 1/4″ at the spandrel. On projects with masonry veneers the beams supporting the veneer is frequently designed for L/600 or less. Maximum 3/16″ live load deflection (half of a typical joint width). On large buildings the live load can be a small amount of the total load, so perimeter beams might only have to get a bit bigger.
That L/360 criteria is usually for total load. Sometimes we have introduced extra columns on the perimeter to keep live load deflection down. Sometimes we introduce an extra beam or HSS at the window head to carry only the dead load of the wall and then there is no live load deflection at the head at all. Sometime the spandrel panel is designed to act like a truss and that reduces the deflection. I have worked with many architects over the years who were aware of how to do this coordination.
Peter Karsai Associate Director at AECOM
20 years ago (when I was a structural engineer) I would have agreed. Life has become much more complex since then, with a multitude of different cladding systems, innovative structural systems, and the desire to constantly push things to the limit.
As a result,
Today we often need a 3-way dialogue (architect/structural engineer/cladding contractor)
Also a cladding consultant is well placed to facilitate that conversation.
Lastly,
if the status quo was satisfactory, then this discussion thread wouldn’t be taking place 🙂
Bruce Keeler, PE Principal at Drafting & Engineering
Well stated Stewart. We run up against this issue day in and day out.
I don’t know the answer,
but it does take multiple conversations during the shop drawing and architectural review process.
Along with some RFI’s to get everyone comfortable with the specific requirements on any given project, large or small.
Stewart Jeske President at JEI Structural Engineering
Agree, Agree and Agree. Peter, you point out that there is definitely a need for the cladding consultant in the middle. I think this is essential also, to help bring the limitations of the manufactured systems in to the reality of the design. So i think this will be needed well into the future. David, I agree with you too. If only there were more projects where the Architect would do this with the Structural Engineer – Too many of them do not.
Again, I’m hammering on the Building Code. This is the central area where information and restriction can be communicated. So limitations for spandrel deflections at curtain walls and glazing systems need to be small to work with current off the self manufactured glazing systems.
Fluelenne Duenas Structural Engineer at Vistawall International/ Oldcastle Building Envelope
I agree with you Peter, a curtain wall consultant would resolve these issues before commencing the cladding design and construction phase. But before agreeing with everything the cladding consultant’s figure. A discussion between consultant, manufacturer, Architect and main contractors Structural Engineers should still take place. They need to resolve the floor to floor design vertical movement. The most common mistake happen during the design stage is catering the maximum vertical movement the cladding consultant issued. This is not correct. Intermediate floors should only be design to differential floor slab/beam movement. Its floor having vertical movement depending on live load. All parties must agree on a common figure. Rather than designing the frames/systems to huge movement which in reality not needed at all.
Carrie Jeske JEI Structural Engineering – Glazing Design Calculations
Discussions on the front end of the design process between all parties are rare.
It’s not till after a project is awarded to a glazing contractor that the problem is found.
Forcing everyone into scramble mode.
So our goal is to save glazing contractors money and add value to manufactures designs. It’s conversations like these, with people like each of us, that have to lead the way to better communication and higher quality outcomes. Good leadership requires making tough decisions early on for the good of everyone. Let’s start in our own circle of influence and move out from there.
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