Chapter 17 Glass and Glazing
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Transcript of Chapter 17 Glass and Glazing
Chapter 17 Glass and Glazing
Glass
Benefits of Using GlassAllows entry of natural lightProvide “views” of exterior environmentEntry of sunlight provides warmth
Disadvantages and/or Design ConsiderationsLimits occupant’s privacy Lower resistance to thermal transmission
heat in the summer & Cold in the winter
Initial & operating costs
Glass HistoryMaterial used for Centuries
Early Processes (10th Century) Crown Glass
Heated glass blown into sphere Reheated & spun on “punty”(rod) Sphere becomes a “disk” Cooled & cut into pieces
Cylinder glass Heated glass blown into sphere Swung like a pendulum Elongated into a cylinder Ends cut off, split lengthwise Reheated, opened, flattened into rectangular
sheet Cut into pieces
Neither had high “optical” quality
Glass History (cont.)
Plate GlassIntroduced in the 17th CenturyProcess
Molten glass cast into frames Spread into sheets by rollers Cooled Each side ground / polished
Larger sheets of High optical qualityCostly (until process was mechanized)
Glass History (cont.)
Drawn GlassReplaced cylinder glass, early 20th centuryFlat sheets of glass drawn directly from a molten glass
container
Production Process Continuous production line - highly mechanized
Drawn glass Ground & Polished (plate) To finished sheets of glass
Glass History (cont.)
Float GlassProcess invented in 1959 in England (produced in US, 1963)
Has become a worldwide standard Largely replaced drawn & plate glass
Production Process (Glass “floated” across a bath of molten tin)
Ribbon of Float Glass
Process Benefits•Surfaces parallel•High Optical Quality
(Comparable to Plate)•Brilliant Surface Finish•Economical •Virtually all flat glass produced
TerminologyGlazing - “...installation of a transparent material (usually glass) into an opening”I.E. “Glass & Glazing”
Glazier A glass installer
Lites (lights)Individual pieces of glass
Glass as a Material
Major ingredient - Sand (silicon dioxide)StrengthIndividual fibers stronger than steel, but less stiffIn larger sheets - microscopic imperfections inherent
with manufacturing process significantly reduce its strength
Cracks propagate from these imperfections near the point of maximum tension
Types of Breakage Thermal Stress Breaks Mechanical Stress Breaks
Glass Thicknesses
Range of Thicknesses 3/32” Single strength 1/8” Double strength Up to 1”+
Thickness Required is Determined by:Size of Glass Lites (span)Maximum Design (Wind) Loading Acceptable Breakage Rate (most always some breakage)
Wind TestingCommon on tall Buildings - Purpose: Establish expected loads
Mockup for a 24 Story Condo
Tempered Glass
Ordinary Glass - Annealed glass cooled slowly under controlled conditions to avoid
internal stresses
Tempered GlassAnnealed glass that is:
Reheated Surfaces cooled rapidly, core cooled more slowly Induces permanent compressive stresses in edges & faces and
tensile stresses in the core Result:
4 times as strong in bending More resistant to thermal stress & impact
Tempered Glass
When Tempered Glass Breaks:The sudden release of the internal stresses:
Produces small square edged particles (as opposed to sharp, jagged pieces)
Strength & breakage characteristics make it well suited for: Exterior Doors Floor to Ceiling Sheets of Glass All-Glass Doors, Glass walls (ex; handball courts), basketball backboards
DisadvantagesMore CostlyProcess may cause noticeable distortionsCutting & Drilling must be prior to tempering
Uses of Tempered Glass
Heat-Strengthened Glass
Substitute for Tempered GlassLower Cost, but Less of the desirable qualities of tempered
Lower strength Less desirable breakage characteristics
Process Similar, howeverLower induced stressesLess strength (only twice annealed)Breakage characteristics more similar to annealed
Laminated Glass
Sandwiching Transparent interlayer (PVB) Between layers of glass (can be multiple layers) Bonded under heat & pressure
PVB - Polyvinyl Butyral Soft interlayer Can be clear, colored, and/or patterned Improves resistance to sound transmission Upon breakage - PVB holds pieces of glass together
Uses? Skylights (overhead glazing) Reduce noise (hospitals, classrooms, etc.) Security glass (typically has multiple layers)
Glass
PVBLayer
Skylight @ the Bellagio Hotel
Hurricane Resistant GlassLarge Missile Impact Test
Laminated and Tempered
Fire Rated Glass
Required for:Fire rated doorsRated Window and wall assemblies
Glass TypesSpecially Tempered Glass (rated for 20 minutes)Wired Glass (mesh of wire in glass, rated for 45min.)
most common, but changes the appearance of the opening
Optical Quality Ceramics (20min. to 3hr)
Wire Glass
Spandrel Glass
Interior faceCeramic based paints w/
pigmented glass particles (frits) applied
Heated / Tempered to form a ceramic coating
Opaque LiteMatch or contrast other glassOften tempered - resist thermal
stresses behind lightPurposeConceal structure behind glass /
curtainwall
Spandrel Glass(view from the inside)
Spandrel Glass(view from the outside)
Spandrel Glass
Tinted & Reflective Glass
Why tint or apply a reflective coating to glass?
Reduce glare from sunlight
Reduce solar heat gain
Architectural look - Aesthetics
Clear Float Glass
Sunlight
Outside InsideReflected
Sunlight
Absorbed & Reradiated as Heat
85% +/-sunlightenters
Tinted Glass
Sunlight
Reflected
14% to 75%
ReradiatedReradiated
Outside Inside
Result: •Lower Cooling Costs•Less “sunlight”
Glare for peopleFading FF&E
Tinted Glass
ProcessChemical elements added to the molten glassColors available
Grays, bronzes, blues, greens, golds, etc.
Clear (untinted) Glass
Lightly tinted glass
Lightly tinted glass
Tinted glass
Reflective Glass
Thin films of metal or metal oxide placed on the surface of the glass
Film purpose:Reflect sunlight
Reduce solar heat gain
Changes Appearance Colored Mirror effect
Can be placed on either face,However, often on the inside face
Glass
ReflectiveFilm
Reflective Glass
Reflective Glass
Reflective Glass
Shading Coefficient
“Ration of total solar heat gain through a particular glass compared to heat gain through double-strength clear glass.”
Shading Coefficient = Heat gain of a Glass type Heat gain thru Clear (double-strength)
Tinted glass range: .5 to .8
Reflective glass range .3 to .7
Visible Transmittance
“Measures the transparency of glass to visible light (rather than solar heat gain)
Ranges:Clear Glass .9Tinted & Reflective < .9
Glazing Luminous Efficacy (Ke)
Ke = Visible Transmittance Shading Coefficient
High KeHigh amount of solar heat blocked whileConsiderable amount of sunlight allowed to enterGreen & blue glass
Low KeSimilar amounts of solar heat & sunlight blocked Darker interior (less light)Bronze, gold, & grays
Glass & Thermal Transmission
Single PaneGlass
1” Polystyrene
“Well”Insulated
Wall
1/5 of Glass
Thermal Transmission
1/20 of Glass
Disadvantage of Glass: Higher Initial & Operating Costs, Reduced Comfort
Insulating Glass
Two or more sheets of glass separated by an air spaceDouble Glazing: Two (2) sheetsTriple Glazing: Three (3) sheets (somewhat uncommon)
Primary purpose of additional sheets of glassImprove insulating value - reduce thermal transmissionTwo (2) sheets - cuts heat loss in half (1/3 for 3 sheets)
Increases initial cost but:Reduces operating costsIncreases comfortProvides additional architectural options
Insulating Glass
Glass
AirSpace
Spacer
Sealant
Spacer (Spline)•Separates the glass•Often Metallic
Air Space•Dry Air or •Inert Gas (such as Argon)
Sealant•“Seals” Unit•Prevent air escape & moisture penetration
Glass•Clear, reflective and/or tinted
Insulated Glass (tinted)
Insulated Glass (tinted)
Metal Spline
Low-Emissivity GlassLow-E Glass
Improves thermal performanceUltra-thin, transparent, metallic coating Generally placed on:
The #2 or #3 position in insulating glass or The #4 position in laminated glass
Reflects selected wavelengths of light & heat radiation Allows entry of most short-wave (sunlight) Reflects most longer-wave infrared radiation from objects and humans
inside the building
Result: Reduced heating & cooling load, increased comfort
inside
4321
Insulated Glass
Thermal Performance Data Obtained from PPG Glass
Clear, insulated, alum. spacer, air filled
Add Low-E Glass
Add “special” spacer
AddArgon
33% Improvement
6% Improvement
13% Improvement
Glass with Changing Properties
Thermochromic glass (darker when warmed by the sun)
Photochromic (darker when exposed to bright light)
Electrochromic (changes transparency with electricity)
Photovoltaic (generates electricity from sunlight)
Self-Cleaning GlassProprietary product w/ coating of titanium
oxideCatalyst allowing sunlight to turn organic dirty
into carbon dioxide and water
Plastic Glazing SheetMaterials – acrylic & polycarbonateMore expensive, higher coefficients of thermal
expansion
Glazing - Small Lights
Design ConsiderationsLow stresses from wind loadingLow stresses from thermal expansion / contraction
Glazier’s points &Putty
WoodStop
Snap-in Glazing Beads &Synthetic Rubber Gaskets
Glazing - Large Lites
Design ConsiderationsGreater spans, Larger wind loadsGreater stresses from thermal expansion / contractionMinor Frame irregularities can induce stresses
Design ObjectivesEffectively support glass weight (w/o inducing abnormal stresses)Support glass against wind pressure (both positive & negative) Isolate glass from from the supporting frame & building structureAllow for independent expansion/contraction (glass & supports)Separate glass from support materials that could induce stress or cause
abrasion
Glass Support &Isolation from Frame
Setting Blocks•Synthetic Rubber•Set @ the bottom edge•Often two/lite @ quarter pts.
Centering Shims•Synthetic Rubber•Center Lite•Isolate Lit from the Frame
Bite
Support against Wind Pressure•Bite
•Too little - pop out•Too much - stress w/ glass deflection
•Supporting Mullion•Support Glass•Transmit loads to structure
Mullion
Gaskets•“Seals” the Glass (1st line of defense)•“Isolates” glass (from abrasion)•Allows for Thermal Expansion/Contraction•Accommodates Structure/Support deflection
Anchorage of Glass to Mullion(s)
‘Dry’ Glazed Lite (using compression)
Mullions being anchored to the structure
Glass being installed
Insulated Glass
Gaskets
Retainer (compression) strips installed
Finished Installation(Snap on Covers applied over the retainer strips)
Lock-Strip Gasket
Structural Silicone Flush Glazing
Mullions onthe “inside” of the
Glass
Glass adheredby SiliconeSealant orRetainer
Structural Silicone Flush Glazing
Structural Silicone Flush Glazing
Butt-Joint Glazing
•Head & Sill with conventional frames•Vertical Mullions eliminated•Vertical joints - caulked
Butt-Joint Glazing
Truss-like Mullions with ‘architectural qualities’ to
support wind loading on a tall entrance
Weeps / “Drainage” System
Sampling
of
Mullion ColorsAluminum & Glass L.C.
Suspended Glazing System
Tempered & Laminated Glass
Glass support & anchorage
Structural Glazing System(exterior)
Structural Glazing System(interior)
Glass Mullion Systemtempered glass
Glass & Design
Methods to compensate for its poor thermal propertiesDouble & triple glazingLow E coatingsLow conductivity gas fills Tinting, reflective coatingsCurtains, shuttersWindow sizing & orientation on the buildingShading or overhangs
Glass & the Building CodesCodes concerned with:
Structural Adequacy wind & impact loads
Providing natural light in habitable rooms may require a certain glass area as a % of floor area
Safety concerns with breakage skylights, overhead glazing, in or near doors, “clear” sheets of glass that could be
mistaken for an opening Use of laminated, tempered, etc.
Prevention of fire maximum glazed area, wire glass
Energy consumption may require double glazing, storm windows, limit the maximum % of glazed area