Construction Systems Test 1
concrete Stats
- 2nd most consumed material after water -largest portion of cement is consumed by ready-mixed concrete
right-of-way
legal right granted to a single party or the public to traverse anothers land
easement
legal right held by one party to make limited use of the land of another
spandrel beam
load bearing beams that span column to column
precast concrete connections
precast slabs -> welded steel plates precast structural tees -> structural steel angle welded into plates cast into tees precast beams-> steel angle welded welded into steel plates cast into beam and column is used
excavation
-necessary to reach undisturbed firm soil
foundation wall
-provide support for superstructure above and enclose a basement/crawl space -also must resist active earth pressure, penetration of water and soil gases -concrete foundation walls: require formwork and access to place the concrete -concrete masonry wall: utilize easily handled small units and do not require formwork
Why is europe winning?
Europeans use collaboration with the different fields (engineering) to achieve the best results whereas Americans use competition
methods to reduce cracking in concrete
Joints -Shrinkage reducing admixtures (flyash) -result in a finished concrete that is stronger
precast framing elements (4 types)
1) solid slabs -for short spans and minimum slab depths -reinforced with horizontal strands 2) Hallow-core slabs -intermediate spans, repetitive, rectangular bays with modular widths -internal longitudinal voids replace non-working concrete -economic and -reinforced with horizontal strands -Solid slabs and hallow core slabs save an overall building height in multi story structures 3) double and single tees - for long spans- > double tees are preferred bc they do not need to be supported against tipping -reinforced with depressed strands 4)Topping - bonds elements together -usually 2" thick poured over rough precast top surface and smoothed
insulating concrete forms
Contain a concrete core with insulation on either side that acts as the form work and a permanent part of the wall -is lightweight, can be assembled quickly and is usually assembled as blocks
two-way waffle slab
Two way equivalent to the one way joist system, metal or plastic pans use for formwork to eliminate nonworking concrete from the slab, allowing considerably longer spans, - one of the most expensive site cast framing systems
slip forming
Useful for tall wall structures such as elevator shafts; stairwells -A ring of formwork is pulled steadily upward by jacks supported on a vertical reinforcing bars, while workers add concrete and reinforcing in a continuous process
soil pores
spaces in between soil particles
material features
- materials have undergone a rapid transformation -no longer passive -using traditional techniques means the material and craft is known to everyone thus repairs can be made easily -anna herringer is using mud to build structures as an example of readily available global resource -> venice biencale installation -Kasper Guldager explored bio-based materials produced from seaweed and agriculltural waste like tomato stems
precast concrete wall panels ???
-architectural precast concrete is non-load bearing - solid panels range from 3.5"-10" in thickness +insulation and can span 1-2 stories in height -3 fundamental ways of supporting precast slabs - on a precast concrete skeleton - on precast loadbearing panels -combo -contain properly sealed joints thus reduce heating/cooling costs
joining precast concrete members
-bolting, welding, and grouting is common -simplest joints are those that rely on gravity by placing one element above the other -column-to-column/footing -> usually grouted -with spanning members, bearing pads are usually inserted at points of contact to avoid grinding
designing foundations (donts)
-building below the water table-> more expensive because u must dewater site and take extra precautions to waterproof AVOID! -building close to structure: temp. bracing or underpinning may be required to prevent disturbance -increasing column/ wall load from beyond what can be supported by shallow foundation
formwork ties
-coil ties are medium-heavy duty, fabricated to accept threaded bolt and pass through formwork -flat ties: light duty -taper ties: heavy duty
designing economical site cast concrete building
-concrete-> least expensive -framework -> most expensive -simplification and standardization of framework is important -flat plate construction most economical
flying framework
-fabricated in large sections supported on deep metal trusses and can be can be moved from one section to another
two-way flat plate
-for lightly loaded buildings -> is not thickened around column -building heights can be kept to a minimum
2-way flat slab
-formwork is completely flat except for thickening of concrete to resist shear forces around the top of each column -slabs/plates should be cantilevered 30% of interior span or additional reinforcing must be added to edges -reinforcing is laid in both directions, in half way wide strips -column strips: designed to carry higher bending force with slab crosses column -middle strips: light reinforcing pattern
beam to column frame work (economical)
-most economical design is to form columns with same or narrower width as beams so beams can be cast continuously -very costly to cast a column with a greater depth beam
casting bed
-precast concrete elements are produced in permanent forms called casting beds -> average in 400' in length
sydney opera house
-precasting operation was on site -super expensive and took super long -precast elements were post tensioned to make them behave as a continous structure
sequential vs fast track construction
-sequential construction: each major phase in the design and construction of a building is completed before the next one begins -Fast track (phase) construction: compresses the project schedule by running design and construction together -frequently associated with design/build -economic decision, but final costs are unknown during construction - fixed fee
carbon fiber reinforcing
-substitute for mild steel reinforcing - less concrete cover is required -reduces overall thickness and weight -low thermal conductivity
new ways to build faster and cheaper
-technology transfer: passing on information/ prototypes -architecture is a passive recipient -KTA studied the seembly line production is the automotive industry and found that it produced better quality - tried this method with building: melvin and claire levine hall -walls is comprised of panels assembled in the factory of separate componets "unionized construction"-> allows for more work to be done at a shop resulting in higher quality - higher intial costs but lower long term costs w less repairs
Site cast post-tensioned framing system
-used in beams, girders, 1-way and 2-way slabs to reduce deflection and extend spanning capaibility -used in 2-way flat plate BUT as draped tendons evenly distributed in one direction, and banded closely together over line of columns in other direction - balances upward and downward forces
two-way concrete framing system
-used when column slabs can be arranged in square bays -slabs rarely seen, used to support heavy industrial floors -slab is reinforced with uniform thickness of concrete
Advantages and disadvantages of precast over sitecast
Advantages -mixing and pouring= highly mechanized= more uniform = stronger -operations carried out under shelter -quality is better -formwork can be reused -> sustainable -fast curing-> usually steam cured-> 24 hours - errection is faster on site Disadvantages -more expensive - transportation restricts size and porportion
selecting site cast concrete framing system
Bay shape oblong: 1-way system square -> 2-way system Span? Short = flat plate/slab Long= 1-way/ 2-way joist system how heavy are load? will there be finish ceiling beneath slab? flat plate + slab can act as ceiling lateral stability have to be provided by concrete frame? -> favors one-way joist w deep beam to column connections
worker consideration (on site vs factory)
Factory: capital intensive - process is designed for optimal production and quality workers -specialized skill/division of labor -safer workplace On site : labor intensive -process is not optimized -workers have broad skills -not repetitive -workplace is more hazardous -wages are 30% higher than factory workers -factory based tech is replacing on site labor
Precast concrete beams
Rectangular beam, L-shaped beam, inverted tee beam, aashto beam - projecting ledges on L-shaped and Inverted tee beam provide direct support for precast elements -reinforced with top reinforcing bars
fireproofing
concrete is inherently fire resistant -depends on slab thickness -highest fire Resistance achieved by joist+ waffle systems by increasing thickness and applying fireproofing
secant wall
constricted site drill holes around the perimeter of the site , then you fill them w concrete - formed by constructing intersecting reinforced concrete piles
Lift-slab construction
floor and roof cast in ground and lifted up to final elevations -typically used with 2-way flat plate -virtually eliminates formwork
Tilt-up Construction
reinforced concrete wall panels cast lying down -when panels are strengthened they are tilted vertically and grouted together
gang form
several unit forms attached together, or a single large form, usually moved into position by crane because sections are too heavy to set by hand
backfilling
specifically replacing soil materials at an excavation to restore it to its finished level -occurs at foundations and behind retaining walls
critical path
the sequence of activities that determine the earliest date by which the project can be completed
preconsolidation
-both sand and clays soils have a "built in memory" of previous loads -pre-consolidation pressure of the soil may be far in excess of the pressures induced by current soil profile -when soil has not been preconsolidated, the addition of any new load may result in excessive settlement
Deep foundations (caissons, piles)
-caisson: constructed by drilling a hole, belling the bottom and filling it with concrete -> belted and socketed -more expensive than piles Piles: forcibly driven into the earth instead of drilled and poured -more slender than cassions
concrete- admixtures
-can be added to change the setting rate, water demand, work ability, and freeze-thaw durability
settlement
-foundations of bedrock settle a negligible amount which is why it is good to build on -no settlement -uniform settlement: settling occurs at roughly the same rate throughout building -differential settlement: different parts of the building settle at different rates -occurs where soil types, or building loads are different throughout the building
underpinning
-process of rebuilding/strengthening the foundation of an existing building, or extending it -to provide temp support while an existing foundation is being repaired, needle beams are passed through foundation and carried by hydraulic jacks
diminishing materials
-should be reused/ recycled - aluminum, lead, gold, copper, titanium
slope protection
-slopes are subject to erosion from runoff and require stabilization ex. 1) create terraces to reduce the velocity of runoff 2)riprap: layers of stone placed at slope of embankment 3) cribbing or bin walls 4) gabions: wire baskets filled with stone and stacked to form a retaining structure 5) soil binder: plant materials that prevent erosion by providing a ground cover
basement insulation (purpose, attachment)
-thermally insulated to reduce heat loss -on the inside of a basement wall, insulation may be attached directly to wall, or between furring strips, or in a separately framed wall
Loblolly house
- KieranTimberlake Assoicates -hybrid version of a prefab house, where its components can be unbolted and reconfigured at another site -KTA used revit to 3d model the aluminum frame structure with a tight design tolerance and they embed supply-chain information into the model -house can be divided into a series of major elements (uniform cartridges of floors and walls, aluminum structure, exterior panels, bathroom and kitchen modules) -smart cartridges: radiant heating pipes, electrical, cooling and insulation -Dumb cartridges: insulation -mechanical block rooms and bathrooms arrive on site fully assembled -House needs little area for staging materials, quick to assemble (<month), needs fewer field laborers -good example of a prefab house because it has standardized components and connections
reinforced concrete retaining walls
- gravity wall: <10' -resists overturning by shear weight and volume of its mass -T-type cantelver wall: <20' -counter fort wall: >20 -uses triangular shaped cross walls on backside to stiffen the vertical slab and add weight to the base -L-type cantilver wall: used when a wall abuts a property line
rule of thumb about excavation
-1 story of excavated soil weighs the same as 5-8 stories of super structure
Steps of Concrete wall
-Construct the wall reinforcing and the vertical dowels of footing, connecting the two -construct the form work panels of one side of wall, and then place the form ties in. -erect the form work for the other side of wall, and add walers and braces -surveyor uses laser leveling device to establish exact height concrete will be poured -Slump test: check the consistency/ workability of concrete -concrete is poured into formwork, consolidating it with a vibrator to eliminate air pockets -top of form is covered with plastic sheet and left to cure
bearing capacity
-ability of a soil to support a load without experiencing failure -failure results in movement of the soil and supporting foundation
-coarse grain soil
-ability of these soils to support buildings depends on shear strength: friction between particles to keep particles from sliding past one another -densely packed: high strength -loosely packed: can support less load
Concrete Workability
-ability to place and finish concrete -concrete should be capable of being molded and placed hand -if its too stiff it is difficult to work with -work ability is influenced by: -aggregate ratios -% of cement/ water -entrained air content -tempterature -admixtures
concrete- water
-activator for cement-> water causes cement to undergo hydration (non-reversible exothermic reaction) -hydrated cement particles grow into a dense network of interlocking crystalline structures and this is where the strength comes from
Dr. Mika Kuisma
-any construction system will follow these general trends and it may take decades for change to occur -construction is expensive and is capital intensive -changes involving expensive tools/tech will be very slow -the most reluctant to embrace innovation and change are the developers and investors in construction because they don't want to lose money -architects and engineers are open to change
ada guidelines
-avoid surface irregularities that can impede wheel chair traffic -provide tactile warning strips for visually impaired at grade changes and hazardous vehicular areas
seismic base isolation
-base isolators are used in places where strong earthquakes are common -when movement occurs, they flex or yield to absorb significant % of movement -multilayered sandwich of rubber and steel and a lead core
earth materials (bedrock vs. soil)
-bedrock: dense continuous mass of materials -strongest/ most stable material on which a building can be founded - NYC-> bedrock is closest to surface and massive foundations needed for these tall buildings can be constructed easily -soil: refers to any earth material that is particulate (cobble, gravel, sand, clay)
concrete- cement
-binder the glues aggregate together -ideal quantity should be enough to coat each aggregate particle -provides greatest influence on compressive strength of final product -reaches almost full strength after 28 days -may include supplementary cementious materials (SCMs) -> flyash, slag -often acquired as industrial by-products -offer performance benefits, reduce overall environmental impact of concrete, and remove materials from waste
concrete uniformity (bleeding, crazing)
-bleeding: development of a layer of water at the surface of freshly placed concrete -normal and does not reduce quality of concrete -after water evaporates, a window is available for contractor to achieve the desired effect -however, finishing the concrete while bleed water is still on surface can cause surface durability issues -crazing
caissons
-caisson: constructed by drilling a hole, belling the bottom and filling it with concrete -belted and socketed -more expensive than piles -similar to column footing, spreads load from column over a large enough area of soil so that the allowable pressure is not exceeded -differs from column footing in that it extends beneath substructure until is reaches suitable stratum -if soil conditions are poor, the hole may be temporarily supported by slurry or a casing -belted caissons are practical only where soil is able to retain its shape until concrete is poured -socketed caissons are drilled into rock at bottom and not belted-> its bearing capacity comes from end bearing and friction
generalized solution- pre-engineered metal building
-client preference for off-the shelf solution - acceptance of a general solution, not a custom solution ( mitten vs glove) -increased certainty of time and cost -standardized simple details -compatibility with all parts
Design-build
-clients holds only one contract with the entity that will design and build the structure as opposed to 2 contracts, one with the firm that designs the project and one with the builder -clients prefer design-build because it saves time,/ money and reduces conflict -many decisions are made in the field thus it makes sense that the architect be the contractor as well
proper proportion/ mixing and transportation
-consistency between batches is essential for ensuring uniformity in finishing, color, and durability -typically produced in quantities up to 10 cubic yards for transportation -consider issues such as delivery time, weather, and placement techniques
Designing for disassembly and deconstruction
-construction activities generate 30-40% of all waste -instead of demolishing a building and dumping the remains, we should reuse and recycle old building materials -economic cons: building components are difficult to separate w/o damaging them -> then they are not worth as much, buildings have hazardous materials thus disassembly time and labor are costly -design for dissemble-> individual products should produce little waste and have high value for reuse -randy croxton: materials minimization -do not build fully enclosed spaces -avoid situations the require destructive demolition -avoid glued and composite systems -Chartwell School in Seaside -structural frame is done with wood and has high economical value -windows are detailed for disassembly and minimum waste -wood siding is fastened with clips for ease of disassembly -structure and system are separated
Loads that must be transferred from building
-dead loads: weight of permanent components/ weight of building elements -live loads: not permanent loads (occupants, movable furnishings) -rain/snow loads: act downwards -wind loads: act laterally -seismic loads: horizontal and vertical forces caused during earthquake -horizontal thrust: from long span structural components (arches, rigid frame etc
domino housing system, Finland
-developed because house building season is short in Finland because of cold climate -panelized, interchangeable kit of parts -detailed for easy assembly and disassembly
innovations in materials
-dramatic increase in the # of construction materials that are man made -> greater dependence on industrial production - now we have the ability to design materials so they have the properties we want them to have -new materials are often initially used in familiar forms -use of wood is projected to decline because we can't plant enough trees (still popular in europe though)
constricted site
-during excavation, soil must be held back using some kind of support
special types of settlement (elastic compression, lowering of water table, vibrations)
-elastic compression: pressure is applied, soil will deform elastically to a certain point -For instance, in excavating for a large basement, the weight of the soil removed will relieve pressure on the underlying soil, and the soil will immediately expand vertically upward in an elastic manner because of the stress relief. If the excavation is filled back in with soil or a building, the underlying soil will experience elastic recompression. -lowering of water table: can occur naturally(drought) or by human activities -increases the effective stress and weight on the underlying soil. -can adversely effect adjoining properties -vibration: occurs when soils are subjected to vibrations from machinery, traffic, pile drilling etc. -causes particles to rearrange themselves and can cause settlement -granular soils are more susceptible than clay
concrete curing
-final step for ensuring quality concrete -concrete does not cure by drying but through hydration which requires water -curing requires the maintenance of a satisfactory moisture content and temperature -moisture is retained through plastic sheeting or burlap -supplemental heat may be required where cold temps, slow/halt hyrdration process -> below 14 degrees F or 80% humidity
concrete column (footing, dowels, formwork, formties)
-footing is usually an isolated column footing, a pile cap or a caisson -dowels are sized and spaced in footing to match the vertical bars in column -column form may be a rectangular box of plywood, cylinder steel of plastic tube bolted in halves, or a waxed cardboard tube -form ties are usually required
waterproofing, drainage, damnproofing, waterstops
-ground water must be kept out!! -waterproofing: acts as a barrier between water and the foundation, preventing it from reaching interior -drainage: consists of porous backfill material, drainage mat, and perforated drain piping to draw ground water away from foundations -damproofing: water resistant cement plaster or asphalt is compound applied to walls where waterproofing is not critical -waterstops: material that swells when in contact with water -casted in joints of foundation construction
Tropical forest conservatory, IKM architects
-highest preforming greenhouse -orientation/shape is designed so wind creates low pressure and opening windows allow for ventilation -no heat, no air conditioning -no leed rating because it is better than leed
retaining wall (purpose, failure, material, geotextiles)
-holds back mass of earth on the uphill side of the grade change -must be designed to resist the lateral pressure of the soil being retained -may fail by overturning, sliding or settling. undermining -timber, concrete, brick or stone masonry may be used for low wall, and reinforced concrete can be used for tall walls -geotextiles: fabrics made of plastics that are resistant to deterioration of soil -support earth embankments and retaining walls in forms of grids
prestress concrete
-in reinforced concrete, less than 1/2 of concrete is in compression, thus cracks will appear at full load -when concrete is prestressed, all the concrete acts in compression and the off-center location of the steel causes a chamber (arch) the beam -this chamber will flatten when a load is applied -net effects of post tensioning and pretensioning is equal -wires= 0.5" diameter - subject to creep, becuase concrete is always in compression
greenhouse effect
-infrared radiation is trapped by green house gases (co2, methane), raising the temperature of the earths atmosphere -buildings are responsible for 1/2 of GHG emissions -> comes from operational processes (heating/cooling, lighting) -necessary to incorporate natural heating/cooling/lighting
unconstricted site (angle of repose)
-large construction site -edge of excation can be sloped back/ benched at a low enough angle so that the soil does not slide back : angle of repose -can be steeper for cohesive soils (clay) and shallower for frictional soils
concrete slabs on grade (what? process of pouring)
-may be placed near grade level to serve as a combined floor and foundation system -require the support of a level, stable, uniformly dense soil base containing no organic matter 1) attach a slab edge form to a supporting stake around the perimeter of area to be poured 2) add a layer of 1.5" crushed stone to act as a drainage layer 3) 3/4" thick fiberboard used to form an isolation joint where slab edge abuts walls - add a moisture barrier 4) using a motorized screed, strike off the surface of concrete after pouring to get a level surface 5) floating (bull float -> flattening and consolidating) (by hand) brings cement paste to surface and produces a smoother, denser finish 6) steel troweling produces a hard, dense, smooth finish 7) damp curing of slab with plastic sheet cover so the surface does not crack
concrete permeability
-migration of water and substances through the hardened concrete -decreased permeability improves concretes resistance to corrosion, freeze/thaw degradation, sulfate attacks -reduction strategies include low water/cement ratio, use of SCM,
exterior walks
-minimum of 3 risers per run of stair -handrails required for stairs w 4+ risers
proper placing and consolidation (+ bugholes)
-most common discharge: from chute mounted on back of concrete truck -placement may employ pumps, cranes, etc. -consolidation: physical vibration of concrete which enables pockets of air trapped in the mix to rise to surface -bugholes: voids on surface of concrete walls -> can be minimized by consolidation
concrete- aggregates
-natural/ man-made crushed sand/gravel -a mixture of fine and coarse aggregates produces stronger concrete as there are no voids -typically locally sourced w/ low energy footprint
abundant material examples
-preferred materials! - sand, clay, gravel, lime, stone, earth
Ultra-high performance concrete (properties, strength, maintenance, price, installation today)
-produces thin, lightweight, durable, precast elements with simple/complex shapes -designers can create thin sections with long spans -extremely moldable and can replicate textures, and form with great precision -comprised of common concrete materials with the addition of ground quartz or PVA/ metallic fibers -significantly stronger than conventional concrete (10x denser) -> can be smaller with refined details and no reinforcing steel needed -PVA fiber compressive strength: 17,000 psi -requires less maintenance -typically expensive because precasters need to develop special molds for complex shapes -> however developing a repetitive design allows for use of single mold -very consistent in its formulation and can be cast successfully in repeated scenarios easily -easy to install -largest panel at 0.5" thickness -> 4'x8' -> largest size two ppl can place safely by hand - most economical panel is 3'x5' -custom project =$$$ - custom molds are better on large projects
paving (purpose, layers, types)
-provides a wearing surface for traffic -pavement: receives traffic wear, protects base and transfers loads to the base structure -base: foundation of well-graded aggregate that transfers the pavement load to the subgrade -subgrade: undistributed soil or compacted fill, ultimately carries the pavement load -flexible pavements: laid on sand setting bed and distribute loads in radiating manner (concrete, brick, pavers) -rigid pavements: mortared over a concrete slab and distributes loads internally (reinforced concrete slabs)
foundation (purpose, shallow/deep)
-purpose is to transfer structural loads from the building into ground, and prevent building collapse -shallow foundations: transfer loads close to the base -used when adequate stable soil occurs near ground surface -Deep foundations: piles/ caissons that extend downward though weak layers to reach more component soil/rock
soil consolidation
-reduction of volume of soil caused when the void spaces in soil compress -foundations on under consolidated soils can expect large settlement
concrete wall (footing, key, vertical dowels, wall reinforcing, formwork, formties,
-reinforced concrete wall at ground level rests on a poured concrete strip foot -formwork panels may be custom built but it is more common to use reusable prefab panels -Key: groove that will form a mechanical connection to the wall -> formed on top of the footing w/ strips of wood that are temporarily embedded in the wet concrete -vertical dowels: steel reinforced bars that are usually installed in a footing. Will later be overlapped with bars in the wall to form a structural connection -wall reinforcing: layers of horizontal and vertical bars either at the center or near the faces. The vertical dowels will be overlapped with the dowels projecting from the footing -form ties: steel rods specially shaped to hold the form work together under the pressure of the wet concrete -the ties pass straight through the wall with all but the walls remaining permanently embedded
concrete setting and hardening
-setting: transition period between fluid and solid -hydration: forms crystalline network that forms together
concrete joints (why? expansion, isolation, control, construction)
-slabs on grade are prone to cracking due to shrinkage, thermal expansion, contraction, movement of abut buildings - expansion joints: allow movement to occur between a concrete slab and adjoining columns and walls of a building -formed by casting full depth joint material into the slab, completely separating it from adjacent elements -Isolation joint: expansion joint used when a column goes through a slab -fiberboard is used to separate the two parts -control joints (contraction joints) : intentionally weakened sections created through the concrete slab where tensile forces caused by concrete drying are released -> cracking occurs along predetermined lines -made by running a trowel while concrete in still plastic or by sawing partially through after concrete begins to harden -thinner slabs require closer joint spacing than thicker ones -arranged in roughly square proportion -post-tensioning eliminates need for control joints -construction: provide a place for construction to stop and continue at a later time
frictional/cohesionless soils
-soils that rely on internal friction for strength (gravel, sand) -formed from mechanical weathering of bedrock
cohesive (charateristics, liquid limit)
-soils that stick together (ex. clay) -tend to be hard when dry and mold able when wet -higher liquid limit: sustain higher moisture content before arrive at flowable consistency -expansive: prone to expand/contract w/ changes in moisture content -> can cause damage to building
one-way solid slab steps (forming, reinforcing, pouring and stripping)
-spans across lines of support by walls/beams -walls+ columns are poured before frame work is erected -girders, beams and slab are poured as a single slab, although form work for slab is erected last -forms are supported on temporary shores -edges of concrete structural elements are rounded bc sharp edges are easily damaged/ dangerous -top of slab is finished in a similar manner as slab on grade -when slabs and beams have enough strength to support themselves, formwork is stripped and slabs and beams are reshored for a couple more weeks to cure -cycle of forming, reinforcing, pouring and stripping is repeated floor by floor
posttensioning
-steel strands (tendons) are tensioned after concrete cures -draped strands are better than straight ones becuase using draped strands more nearly approximates the flow of tensile forces in the beams -done on building sites 1) tendons are covered with steel/plastic so the concrete is not allowed to bond to the tendons while curing 2) after concrete cures, tendons are tensioned w/ hydraulic jacks and anchored to ends of beam. Jack applies a large tensile force to the tendon while compressing the concrete w/ equal and opposite force
pretensioning
-steel strands (tendons) are tensioned before concrete cures 1) stretch steel prestressing strands tightly across casting bed 2) concrete is cast around the stretched strands and is cured. Concrete bonds to the strands 3)when the strands are cut/released from tension, the concrete goes into compression and the beam takes on a chamber which will disappear after loads are implemented -strong abutments are needed to hold tensioned strands prior to pouring concrete
innovations in concrete
-structural light wight concretes are being used more to reduce dead load -shrinkage compensating cements for structures that cannot be allowed to shrink -UHPC- casting thin elements -pervious concrete- allows water to pass through -light transmitting concrete: precast blocks made w/ embedded fabrics to allow light to pass through
concrete proper finishing
-surface manipulation of flatwork (striking, floating, troweling) -control and expansion joints mitigate cracking that results from shrinkage and water loss
soil testing (test pit, boring, )
-test pits can be dug when the foundation will not extend deeper than 16' -when a greater depth is required, test boring is preformed with portable drilling rigs -bearing capacity is evaluated by counting hammer blows on open ended hallow tube
sustainability
-the ability of a building to meet the needs of the present generation without compormising the abibilty of the future generation to meet thier needs -sustinable buildings use less energy, consume fewer resources, cause less air pollution, reduce waste etc
piles
Piles: forcibly driven into the earth instead of drilled and poured -driven with pile hammers, compressed hydraulic fluid, heavy weights etc. -more slender than cassions -used where non-cohesive soils, subsurface water or excessive depth of bearing strata make caissons impractical -usually driven close together in clusters consisting of 2-25 piles each joined at the top by reinforced concrete pile cap which distributes loads from superstructure to piles evenly -where piles support load bearing walls, reinforced concrete grade beams are constructed to transmit wall load to pile -end-bearing pile: driven until tip encounters suitable bearing stratum -frictional pile: no bearing layer is reached, it has load carrying capacity through frictional resistance -can be made of wood, steel, concrete -Steel H-pile, Steel pipe pile, Precast concrete pile, wood pile
other excavation supports (shot crete, soil mixing, slurry wall)
Shotcrete: where soil is cohesive enough to hold an adequate slope, excavations can be stabilized w/ pneumatically applied concrete - the hardened concrete reinforces the slope and protects against erosion -Soil mixing: sides of an excavation are strengthened by blending Portland cement and water w/ existing soil -> remains in place and becomes permanent part of construction -slurry wall: complete, steel reinforced concrete wall in the ground before excavation begins - preformed w a narrow clamshell bucket -slurry: (mix of water and bentonite clay) is poured to keep the trench full/ prevent collapse at all times and is displaced by concrete when it is poured using a tremie
shallow foundations (Spread footings)
Spread footing: shallow, simple -take concentrated loads from above and spread them out across an area of soil large enough so that the allowable soil pressure is not exceeded -must be placed below the frost line -footings can not extend past property lines -column footing: square block of concrete w/ or w/o steel reinforcement that distributes load of column to soil -if required, column footings may be linked together with reinforced concrete tie beams -Mat foundation: used when column footings becomes so closely spaced together it is more effective to merge them -wall/strip footing: do the same thing but for a load bearing wall -when building on slopes, strip footings are stepped
Bracing (cross lot, sloping raker, tiebacks)
as excavation deepens, its support system must be braced against earth and water pressure -cross lots: uses steel wide flange columns that are driven into the earth at points where the braces will cross -sloping rakers: used when the excavation is too wide for cross lot bracing -usually placed at a 45 angle and transfers the rotational load of the wall into ground * both are a hindrance to the excavation process as their presence limits earth removal -tie backs: can be used instead of bracing to support the shoring while maintaining a fully open excavation -works well if you know there is nothing but soil on the other side
2020 challenge + reducing buildings GHG emisson
by 2030, all new buildings will be carbon neutral -employ passive heating/ cooling techniques or have building capture its own energy from renewable sources (solar, wind etc)
vehicle dimensions/ parking spaces
compact car: 5'8 x 16' p: 8'x 16' standard car:6'6" x 18' p: ?
water table
elevation at which soil is normally fully saturated
dewatering (most common method, well points)
excavations must be kept free of standing water -most common method is by pumping water as it accumulates in pits -well points: vertical pipes inserted into the ground w/ screen openings at bottom that keep out soil particles while allowing water to enter -used to depress water table
cost to change a building feature..
increases exponentially as you move from the design stage to construction to occupancy
closed loop environmental system
one where every material has an on going useful life and waste is diverted from landfills
double tee
precast, prestressed concrete framing system -can span long distances -deliver alot of load wherever they land -> bearing plate
radon gas control
radon: cancer causing gas that occurs naturally in soils. -concentrations vary by region where radon levels are high, buildings are built with passive radon methods designed to minimize gas flirtation - layer of gravel under concrete slab with a gas imperable plastic sheet -properly sealing joints after pouring -coating walls with waterproofing -a vent pipe extending vertically from gravel through roof of building active: small electrical fans in vertical vent pipes
gradation
range of particle sizes present -well graded: broad range of particle sizes-> less empty space (gap graded soil) -poorly graded: limited size range -uniformly graded: composed of particles within a limited, narrow size range -> maximum possible volume of empty space within a building
one-way concrete joist system (rational)
rational: as the span of a one-way solid slab increases, a thicker slab is required and the slab becomes so thick its own weight is a burden -A one-way concrete joist can span longer efficiently and economically -joists are formed w/ metal/ plastic pans supported on a temp. plywood deck -sides of pans taper from bottom to top to allow them to drop easily from hardened concrete -pans come in widths or 20" or 30", with depths ranging up to 20" -Joists are supported on joist bands which are broad beams that are only as deep as the joists -bottom steel is concentrated in joists
zoning ordinance
regulates the type of activities that can occur on the site and the location of the buildings constructed, and how tall the building can be
excavation supports (shoring)
shoring: soldier beams+lagging, sheet piling -soldier beams: H-piles driven vertically into ground at close interval around excavation before digging begins - lagging: heavy wooden planks are placed against the soldier beams to retain the soil after digging begins -sheet piling: vertical sheets that are aligned against one another edge-to-edge and are driven into the earth to form a solid wall -usually steel, but wood and concrete may be used
Layers of structure
superstructure: structure above ground substructure: habitable portion below ground (basement) -primary purpose is to support and anchor the super structure above foundation: below ground component devoted to the transfer of loads
effects of soil types
when loads are applied to .... -granular soils -> grains are able to respond immediately and will densify as packing becomes tighter Clay soils-> time dependent relationship associated with the consolidation of clay soil -90% of consolidation may vary from a few months to years
bed rock
-unbroken hardrock that is not over any other material -can withstand extremely high bearing pressure and is desirable for foundations supporting high loads
up-down construction
-used when multiple basement/substructures are needed and will take time to construct -begin with installation of a perimeter slurry wall, internal steel columns are lowered into drilled, slurry filled holes and concrete footings are tremied beneath them -ground floor slab is placed and connected to substructure columns, then superstruture may begin
creep
-when placed under sustained compressive strength, concrete will gradually shorten over a period of months/years -at the rate of 1/16" for every 10' of building height
clay (size, charateristics)
0.0002" diameter -inorganic -exhibit cohesion and plasticity -can be stiff, medium or soft depending on moisture content (dry= stiff) -excavations can have steep slopes for short periods of time
sand
0.003"-0.079" -fine-> coarse -adequately compacted sand makes ideal bearing material -the coarser the sand, the higher allowable bearing pressure -may liquefy when they are saturated or subject to seismic forces -settlement is immediate
gravel
0.75"-3" -fine-> coarse -good foundation material-> very high bearing pressures are allowed depending on compactness
you should select materials that are...
1) reusable, renewable, abundant, local 2) durable 3) age gracefully w/ minimum maintence 4) safe to manufacture+ construct 5) minimize waste 6) minimize energy consumption 7) resist environmental deterioration (wood rots) 8) resist deterioration due to human contact (fire) 9) simple and attractive 10) safely disposable
concrete components %
8% air 7-15% cement 14-21% water 60-75% aggregates
boulders
>10" -part of a fill mass (voids are filled with finer grain sands) -not considered suitable for direct foundations
Topography/ ground slopes
>25% -> erosion, difficult to build on >10% -> challenging and expensive 5-10% suitable and can be built on without difficultly -site development should minimize disrupting natural drainage patterns -equalize amount of cut and fill -avoid building on steep slopes
