construction II final
laminated glass
a double layer of glass held together by a middle layer of polyvinyl butyral (plastic); a type of safety glass used for windshields Most codes require laminated glass in overhead glazing such as skylights and glass floors (if glass breaks, fragments adhere to the inter layer)
Spandrel
a panel in a multistory frame building, located between the sill of a window on one level and the head of a window immediately below
load sources and design
all must be considered, codes stipulate that both load sources and form of combinations to be used for design
What is a curtain wall?
an exterior wall supported wholly by the structural frame of a building and carrying no loads other than its own weight and wind loads curtain wall systems are non-structural cladding systems for the external walls of buildings comprise of a lightweight aluminum frame onto which glazed or opaque infill panels can be fixed
load sources - static
applied slowly 1. Settlement or thermal 2. Live Loads (occupancy and snow, water) 3. Dead Load (self weight and fixed elements)
load sources - dynamic
applied suddenly 1. continuous (earthquake) 2. Impact (car or plane)
form action example
armadillo vault, uses tiles that work only in compression to stay together adjustment of forces
semi-rigid connections
assume beam and girder connections possess a limited moment resisting capacity
Pressure-Equalized Design Function
by blocking all external forces that can drive water across a barrier where the inside face of the glass and the inside face of the glazing pocket meet are interconnecting gaskets or wet seals that serve as airtight barriers
clamping glass
can be fastened directly onto bearing substructure or to nodal points of pre tensioned cable structure
tension truss system
can be fishtail
geodesic domes
can withstand very heavy loads because rigid
plate glass
cast glass. rolled in pan, polished
height action
collection and grounding of loads, system of stories that collect load vertically collecting and grounding of forces
cable braces systems
combination of rigid mullions and cables that mostly function as bracing rather than direct structural support
live loads
commonly refers to vertical gravity loading's on roof and floor occupancy, furniture, etc All codes provide minimum live load s
ROT girders
depth: 1/15 width: 1/3 - 1/2
ROT steel beams
depth: 1/20 of span width: 1/3 - 1/2 depth
structural systems
designed and constructed to support and transmit loads - Superstructure is vertical extension above ground - Columns, beams, and walls - Substructure below grade
clamping plate
direct contact, only compressive forces act perpendicular to the contact face may be transmitted via contact
dead load
due to gravity, always included in load combination, produce stabilizing effects that resist uplift and overturn
gravitational force
force by means the mass of earth pulls a solid commensurate to quantity of mass = weight
loads
forces that act on solid form from exterior excepting reactive forces
Fire Considerations on Curtain Walls
- A noncombustible material (safing) must be installed to prevent spread of fire at each floor within column covers and between wall panels - Fire code specifies fire-resistance requirements for structural frame and curtain wall panels
Unit Panel System
-consists entirely of precast concrete, or masonry -wall units may be 1-3 stories high -panel systems offer controlled shop assembly and rapid erection, but are bulky to ship and handle
Glass in Curtain Walls
-most common infill mater
systems of order - conceptual
-scale, proportion -human activities - functional zoning - paths of movement - sensible qualities like light, color - building within natural and built environment
Stick System Characteristics
-standard off the shelf products with low material cost -offer low expense of shipping and handling due to the ability to efficiently package and transport separate components
glass composition
-super cooled liquid with no fixed melting point and an open non crystalline micro structure -69% silicon dioxide (fine sand), 17% soda ash (alkaline), 11% lime, 3% alumina, iron and manganese oxide
components of stick system
1. Aluminum pressure plate exerting pressure through gaskets 2. The plate is separated by a plastic rubber that acts as thermal brake 3. Pressure plate covered by cap on exterior; less pieces
Design Considerations for Curtain Walls
1. How to support the weight of the glass 2. How to support the glass against wind pressure and suction 3. How to isolate glass from structural deflections of the building's structure and the frame from the mullions 4. How to allow independent expansion and contraction of glass and frame 5. How to avoid glass contacting any other materials that could scratch or stress it
Curtain Wall Examples in Buildings
1. Nelson-Atkins Museum of Art by Steven Holl (A custom double-skin system separating an outer wall of translucent sandblasted glass from the inner wall of translucent laminated glass) 2. Skirkanich Hall by Tod Williams Tsien Architects (Customized thermally broken stick system with angled mullions of extruded aluminum supporting clear and translucent glass panels) 3. Torre Cube by Estudio Carme Pinós (Window walls with extruded-aluminum framing and floor to ceiling monolithic glass protected by a brise-soleil system of timber slats) 4.
glass methods of manufacturing
1. Primary process of making large sheets 2. Secondary processes fabricated various products through processes like laminating, insulating, etc
Frame and Panel functions in Curtain Walls
1. Transferring loads back to the primary structure of the building 2. Providing thermal insulation and avoiding cold bridging and condensation 3. Providing fire, smoke and acoustic separation (particularly difficult at joints between the curtain wall system and interior walls and floors) 4. Creating a barrier to water penetration 5. Accomodating differential movement and deflection 6. Preventing panels from falling out of the frame 7. Allowing for opening windows 8. Preventing the accumulation of dirt
components of unit system
1. Two adjacent unit frames that interlock to form vertical member (allows movement between units for expansion, contraction, and assembly) 2. Gaskets as seal where joints meet 3. Silicone glazing (glass is essentially glued onto its frame using tight-strength silicone)
Curtain Wall Hybrids
1. Unit-and Mullion Systems (One or two story high mullions installed before pre-assembled wall units are placed behind mullions) 2. Column-Cover-and-Spandrel Systems (vision glass assemblies and spandrel units supported by spandrel beams between ext. columns clad with cover sections) see images
How can framing panels of a curtain wall be supported
1. by the columns alone 2. by the columns as well as by spandrel beams or the edges of floor slabs depends on whether the primary building structure is: 1. structure steel frame 2. reinforced concrete
ROT triangular steel roof truss
1/4 - 1/5 of span
ROT rectangular girder trusses
1/8 - 1/12 of span
annealed glass
A glass that is cooled slowly to relieve internal stresses.
Fins for glass componenents
A series of clips clamp units of the curtain wall in place, while horizontal laminated glass girts support the curtain wall from lateral forces
ROT open web joists
Depth: 1/20 for heavily loaded, 1/24 for lightly spacing 2-4 ft
Structural glass fin examples
Extension to Glass Museum, Museo Amparo, Four Seasons Center for Performing ARts
Fundamentals in building structures
Formal intent: - exposing the structure - concealing the structure - celebrating the structure
transferring stresses in glass - Friction
Friction: mechanical interlocking of microscopic surface imperfection of both contact faces -elasticity and fatigue strength of the friction cushion are critical to the quality of the friction joint - forces transferred are roughly linear
moment connections
Hold original angle under loading, specific resisting moment, made with plates welded or bolted to beam and column
Types of Cladding Systems
Storefront - inserting glass frame into the building fabric Standard Curtain Wall - engineered system Custom Curtain Wall Structural Glazing - glass walls
bearing
Structures control own weight and additional loads Mechanical action of receiving additional loads called bearing Internal operating process of transmitting loads
Stick system
Tubular metal mullions and rails assembled piece by piece on site 1. primary mullions are anchored to the building's structure 2. intermediate mullions spanning between primary members 3. infill panels with other secondary components such as shading devices or ornament
roof loads
Uniformly distributed live load, accounts for construction and maintenance, added for snow
lateral loads
wind, earthquake, soil pressure on foundation and training walls
Unit system
pre fabricated modules off-site, delivered in panels - assembled under controlled factory conditions and then shipped to the construction site and connected to preinstalled anchors on the building's structure
bolting
pros: easy, cheap Cons: requires drilling or punching
welding
pros: no punching, simplifies complicted joints cons: more skill needed, more expensive, wield inspection
mechanical systems
provide services like water supply, sewage disposal, AC, electrical, vertical transportation, fire fighting, waste disposal and recycling
float glass
pulled horizontally over
drawn glass
pulled through rollers vertically
force
quantity which induces a solid to move or change its state
shear connections
resist only shear, free to rotate, shear wall or diagonal bracing needed for lateral stability
truss
see slides for what is tension and what is compression
form action
single stress condition, either compressive or tensile
resistance
solid withstands deformation or motion by external force
cable braced systems components
spider fastener, tension rods, silicone sealant
lateral reinforcement
stabilizing frame with diagonal brace, diaphragm (filled in) or rigid joint (moment connection, fill in corners)
equilibrium
sum total of forces does not produce motion, equal to 0
cross section action
systems in bending stress condition, sectional forces confinement of forces
vector action
systems in co active stress, compressive and tensile; dissection of forces
surface action
systems in surfce stress condition: membrane forces dispersion of forces
vector action example
throncrown chapel, sainsbury center, IDS center
bow string truss
transmits no tension forces into boundary structure, erects quickly, middle range pricing, middle range transparency
moment
turning motion induced by exerted force of which center of motion lies outside direction of force
Water Considerations on Curtain Walls
-Rain can collect on the wall's surface and be wind-driven under pressure through the smallest openings -Water vapor that condenses within the wall must be drained to the outside
Mullions on Curtain Walls
- Extruded aluminum is most often used as the framing material - Snap-on covers may be used to conceal fasteners, provide uninterrupted profiles, and permit variations in metal finishes - Required size, strength and stiffness of curtain wall frame are determined by the loads the frame must carry
Glass system connections
- Fixings for glass and load carrying connections introduce forces into either the edge or body of glass - To avoid too much stress, a minimum stress transfer zone exists - Local stress peaks must be avoided
Fin support for structural glass
- Glass fins for maximum transparency - Very high facades than don't exert large in-plane loads - The weight of the panels and mullions is carried by connection at head of each fin
tension truss
- Primary truss as metal trusses as support for curtain wall - Secondary rigging can be steel and cable tension structures, which is most rigid, cheap and conventional
wind - lateral stability
- Results from forces exerted by kinetic energy of moving mass of air, produced direct pressure, negative pressure, or suction and drag forces - Produces dynamic loads that create displacement and deflections
earthquake - lateral stability
- Seismic forces from vibration of earth, cause base to move and induce shaking in all directions - Mass of structure tries to resist horizontal ground acceleration, shear force between the building and ground
Possible infill panels for curtain wall systems
- Vision glass (may be double or triple glazed, include low-e coatings, reflective coatings, etc) - Spandrel (non-vision) Glass - Aluminum -Stone or brick veneer -Terracotta -Fibre-reinforced Plastic (FRP) - Louvres or vents
Wind Considerations on Curtain Walls
- Wind can create positive or negative pressure on a curtain wall depending on direction, shape and height of building - The curtain wall must be able to transfer wind loads to the structural frame of the building
Stick System Disadvantages
- derive from the method of assembly on the field (slower pace, higher labor costs, potential precision problems) - generally limited to low or mid-rise applications
Unit System Disadvantages
- include higher shipping cost and necessity for sequential installation - typically selected for high-rise and high-volume curtain walls
Sun (heat) Considerations on Curtain Walls
-Brightness and glare should be controlled with shading devices or reflective/tinted glass -Ultraviolet rays of the sun can cause deterioration of joint and glazing materials
Loads Considerations on Curtain Walls
-Curtain wall panels must be supported by the structural frame - Deflection or deformation of the structural frame should not be transmitted to the curtain wall
Temperature Considerations on Curtain Walls
-Joints and sealants must be able to withstand movement caused by thermal stresses -Thermal insulation may be incorporated into panels
how flow of forces work
Object form follows direction of acting forces, should not accept detours, structure must convert acting forces into new picture , redirection of forces
load types
Point load - small distance, concentrated Distributed load - acts over length (measurable)
cross section exampe
Richards labs, Crown Hall, carpenter center
height actione examples
Seagram, New York Times
Enclosure Systems
Shell or envelope, shelters interior, controls access, light, air, views, security, privacy
transferring stresses in glass - point fixing with perforation
glass panes equipped with bore-holes and fastened with screws
transferring stresses in glass - point fixing no perforation
glass panes fixed by fittings on both sides, no perforation
tempered glass
glass that is strengthened by introducing stress through rapid heating and cooling of the glass surfaces. 4x stronger than annealed
cable truss
highest tensile load onto boundary structure, increased support stiffness, lightweight and max transparent but expense
Pressure-Equalization Chamber
in the glazing pocket reduces water penetration by eliminating (equalizing) the pressure difference across the rain screen (the outside face of the glass, and the outer exposed face of the framing function as a rain screen that directs water away) aka zone-glazed systems
stress
internal resistant force per unit area which is mobilized through external force
surface action examples
kimbell, airforce academy
flow of forces
load reception, transfer, and charge
rigging
manufacturers began as rigging for sail boats
building code requirements
minimum live loads, wind loads (varies on area), seismic, load duration (time span), load combinations, design data for types of structure, fire resistant