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