Foundations Flashcards
what are the four entities involved in a building?
-client, designers/archtiects, consultants (E), contractors
site selection
building’s structural integrity depends on the soil type and its strength under loading
the measure of a soil’s strength is its bearing capacity in kg per centimeter square.
site preparation
- excavation
- very important before designing to divide the area by the weight = soil strength
wind pressures - a structural system
the stress of the wind on buildings
annual prevailing wind conditions
impact loads - structural system
vertical and horizontal analysis
vibration and earthquakes - structural system
- three modes in motion : first, second and thrid modes
- fixed-base vs. base-isolated structure: preventing modes to occur
5 main criteria when selecting a structural system
- stability - most stable based on location
- function - does it fix its function structure
- economy - can i afford it?
- image - aesthetic
- environmental design attributes - efficient + sustainable
difference between bearing wall system vs post and beam system
bearing wall system = untilizes rigid vertical planes to support building loads and transmit them down to its foundation
- secondary axes penetrate through the wall perpendicular to the primary axes
- looks heavy in form
post and beam system = transmits forces laterally along its length to its supports. beam carries load experience bending stresses
-looks light in form
3 foundation requirements
- failure: safe against collapsing
- settlement: must not damage the structure or impair its function
- feasibility: both technically and economically
Foundation settlement
uniform settlement vs. differential settlement
-differential settlement = parts of the foundation of a building may suffer different magnitudes of settlements due to variation in load on the foundation or soil conditions
weak link
weak link is implemented to connect low and high ruse buildings to prevent any cracking
structural joints
expansion joints and construction joints
- built-type construction joint
- built-type construction joint with dowels
- built type construction joint with tie bars
settlement joints
two separate joints because of the high and low rise buildings
stability of soil
soils abiliting to retain its structual propterties under varying conditions
- most stable - rock, gravel, and sand tend to be most stable soils
- least stable - clays the least stable soil
site selection steps
- renovating an existing building
- building in an urban area with existing infrastructure
- building on a damaged or polluted site
- avoiding construction on prime agriculture land
- avoiding construction on undeveloped land that is environmentally sensitive protects the wildlife and natural habitats
- avoiding construction on public parkland or land adjacent to bodies of water that support recreational use
- selecting a building that is well connected to existing networks of public transportation, and to pedestrian and bicycle paths
site design steps
- minimize the building footprint
- designing an appropriate landscape
- using of captured rainwater, recycled wastewater, or other nonpotable sources of water
- minimizing impervious ground surface
- providing a surface drainage system
- grading the site to approriate slopes and planting vegetation to hold soil in place will prevent erosion
- large existing trees can not be replaced
- providing shade - reducing heat island effect
- minimize nighttime light pollution
- siting building for best exposure to sun and wind
construction process steps
- complying with local conservation laws related to soil, wetlands, and stormwater
- topsoil should be stockpiled carefully
- guard against soil reosion, sedimentattion of streams and sewers, pollution of air with dust or particulates
- develop minimal well-marked access routes
- construction machinery should be selected for less pollution
- reusing surplus excavated soils onsite or nearby
- recycling construction wastes
excavation
- benched excavation (w/ angle repose)
- sheeted excavation (w/ bracing) - bracing required to resist soil pressure (timber sheet, steel sheet, precast concrete sheet)
slurry wall
- excavating the trench through a bentonite clay surry
- the trench is drug to the desired depth
- the welded cage of steel reinforcing bars is inserted
- the trench is concreted from bottom up
- the reinforced concrete wall is tied back as excavation progresses
bracing
three methods of bracing
- crosslot bracing
- rakers (removable)
- tiebacks (not removable)
factors that affect the choice of type - foundation
- subsurface soil and groundwater conditions
2. structural requirements, including: foundation, loads, buildings configuration, and depth
secondary factors that may be important - foundation
- construction methods, including access and working space.
- environmental factors, including noise, traffic, and disposal of earth and water
- building codes and regulation
- proximity of adjacent property and potential impacts on that property
- time available for construction
- construction risks
two types of foundation
shallow foundation (footing) = strip, pad, and raft (solids slab raft, beam and slab raft, and cellular raft)
deep foundation = caissons, piles, selamic base isolation (for high rise building)
strip - shallow foundation
the formation is in a strip of linear structure that ultimately serves to spread the weight across the total area of the soil (UPSIDE DOWN T)
pad - shallow foundation
rectangular, square, or sometimes circular concrete ‘pads’ that support localized single-point loads such as structural columns, groups of columns, or framed structures.
raft - shallow foundation
A raft foundation is a reinforced concrete slab under the whole of a building or extension, ‘floating’ on the ground as a raft floats on water. This type of foundation spreads the load of the building over a larger area than other foundations, lowering the pressure on the ground
- solif slab raft
- beam and slab raft
- cellular raft foundation
3 substructures with shallow foundations
- slab on grade (GARAGE)
- crawlspace (BETWEEN GROUND AND FIRST FLOOR)
- basement
tie beams vs grade beams
tie beams = columns connected with reinforced concrete tie beams to reduce differential movement between columns (CONNECT COLUMNS TOGETHER)
grade beam = it is reinforced to distribute the continuous load from bearing wall to separate foundations (CARRY WALL AND OTHER LOADS)
difference between caissons and piles
width is the difference
seismic base isolation
in areas where strong earthquakes are common, building are sometimes placed on base isolators
-site between base and building
retaining walls
- enforces the soil
- holds soil back to create an abrupt change in the elevation of the ground
footing is shaped to resist sliding and overturning
drainage behind the wall reduces the likelihood of undermining
3 types of retaining walls
- stone gravity wall
- vertical timber cantilevered wall
- horizontal timber wall with deadmen
waterproofing and drainage
- the gravel drain - hard to do well - gravel is key material for water to go through
- the drainage mat - is easier and more economical to install - cheaper + easier
shallow frost-protection foundation
foam insultation boards can be used in cold climates
to trap enough geothermal heat
foundation cost jumps
- building below the water table
- building close to an existing structure
- increasing the column or wall load from a building beyond what can be supported by shallow foundation. mandating a deep foundation due to adding extra stories
