5 - PDD Flashcards
what are 4 material characteristics that should be considered when selecting exterior materials for a building?
- properly used
- withstand elements
- how often does it require maintenance?
- how well does it perform for its intended use & longevity?
how should the performance of materials be considered during the design phase?
- tested to assure they will perform as expected
- life span, withstand normal wear & tear
how does building orientation affect natural daylighting?
- north = no direct sunlight
- south = fair amount year round
describe the treatments for a north facing window vs. east facing
- north: no direct light but an even glow from reflected light all day, in hot places they have almost no heat gain, in cold climates almost always cold and grey
- east: receive sunlight in morning, start warming building at beginning of day
describe the treatments for a south facing window vs. west facing
south: receive sunlight nearly all day; in hot climates use overhangs to block summer sun (a 2’ overhang will shade summer, but allow winter in)
west: receive hot afternoon sun until sunset, much lower in sky so overhangs dont help, use louvers to control
what is a free body diagram?
to analyze forces on and within structures, use this technique from physics (FBD)
representation of a body and all forces & moments acting on it - does not include internal forces
what structural connection can resist either x or y forces, but not moment?
pinned connections
this type of structural connection only resists forces in the y direction
roller connections
within any structural member in bending, _____ is quantified as the maximum translation measured perpendicular to its central axis
deflection: vertical distance that the beam sags at midspan
usually expressed as a fraction of the span (often noted as greek letter delta)
the formula for deflection of a beam with a uniformly distributed load is:
delta = 5 wl4 / 384 EI
the fibers within a beam develop an internal moment to resist the moment caused by deflection. this resisting moment is called:
bending moment
the centroid of an area is conceptually defined as:
the center of gravity of a mass
for simple geometric shapes, this is easy… for many common asymmetrical shapes, it is calculated
a factor relating the shape of a structural section and the distribution of its material relative to a chosen axis is called:
a section’s moment of inertia, usually denoted “I”
the units of moment intertia are in4 or inches to the fourth power
ratio of a sections moment of inertia and the distance between the neutral surface & outermost edge of the section, “c” is referred to as:
the section modulus
S = I / c
the 2 reasons that column buckling occurs are:
- if an applied load is eccentric, or if it doesn’t occur exactly at a column’s centroid, it will impart some degree of moment, causing bending
- no material is truly uniform in its internal composition; any very slight variation of the material will tend to allow buckling
finding this value quantifies a cross section’s ability to resist buckling under an axial compressive load by relating its moment of inertia & area
radius of gyration = convenient parameter, providing measure of the resistance of a cross section to lateral buckling
a load imposed on a structural member at some point other than the centroid of the section is called:
eccentric load
bending stress is a function of the section modulus and the:
bending moment
define slenderness ratio
ratio of a wall or columns unsupported height/length to its thickness (measures ability to resist buckling)
vertical steel reinforcing within reinforced concrete columns essentially are very slender _____ when compressive stress is applied
columns
a special kind of made up beam that uses members efficiently by placing them in pure compression or tension, when loaded properly, to carry loads over a span is called a:
truss
the two methods for manually analyzing trusses are:
- method of joints
- method of sections
in this type of truss analysis, a cut is made passing through no more than 3 members, and the 3 equations of equilibrium are applied
method of sections
forces acting toward a joint indicate a truss member is in:
tension
liquefaction
water saturated sediment temporarily loes strength & acts as a fluid
- must be space between particles that water can occupy
- dramatic impacts during an earthquake
- sands, muds, silts are most vulnerable (coastal)
seismic waves
oscillations at molecular level within the soil
- sudden relative displacement of very large masses & energy release results in waves rushing through surrounding rock & soil
- project outward from hypocenter and have different characteristics
- Primary/pressure waves, Secondary/shear waves, Surface waves
P waves
Primary/pressure seismic wave
- highest velocity, arrive first
- cause compression in soil in the direction of travel in alternating push-pull
- can travel through liquid
S waves
Secondary/shear seismic wave
- second highest velocity, arrive just after P wave
- cause shear in soil particles (motion perpendicular to direction of wave travel)
- damaging sideways & vertical accellerations
- can not travel through liquid
surface waves
- lowest velocity seismic wave, arrive after P & S waves
- veritcal displacement in earth’s surface
- last longer w/ larger amplitudes, can be very destructive
- near surface of earth (similar to ocean wave)
stabilizing moment
a building’s self-weight creates a moment in the opposite direction of its overturning moment
- load & resistance factor design
- allowable stress design
base shear
story shear = summation of design lateral seismic forces at levels above the story under consideration
base shear = sum of all story shears at the base
diaphragms at each story must transfer force received at that level, plus those from the levels above
what is SDC?
seismic design category
req’s for geotechnical investigations relating to seismic forces likely to be experienced at a site
what is fundamental period?
measure of the time an object takes to travel out and back once when a force has acted on it
“child on a swing”
what is a fault?
plane within rock that forms in response to stress, usually induced by tectonic plates
vertical, horizontal, or any orientation in between
slippage creates earthquake
an earthquake’s depth & its relative location to a building is often directly related to its_____
destructive power
theory of plate tectonics
holds that earth’s crust is made up of masses that float on molten rock below
cooled, solidified chunks of crust ride around freely
crustal conveyor belt
loop of creating crust at mid-ocean ridges and destroying it a subduction zones (liquid-to-solid / solid-to-liquid)
fault systems that are great distances from each other at either end of loop
the amplitude of any wave is proportional to ______
the energy the wave transmits
higher amplitude seismic wave = more energy, acceleration, force on building
a low ratio of width to height has what advantage for a building
minimizes tendency to overturn when acted on by lateral loads, including seismic
coefficient of friction
describes the ability to resist sliding, such as a footing transferring lateral loads to the ground
the higher the coefficient, the great the soil’s capacity to resist sliding
capacity to resist = coefficient x dead load (vertical) on the footing
a pendulum clock is an example of _____
resonance
propelled by its own weight; a mechanism imparts very small force to overcome friction, keeping it going at a constant rate
the magnitudes of seismic forces a building will experience are determined by:
- the building’s weight
- the maximum ground acceleration
once forces act on building, its overall configuration determines how the forces will be transferred to the ground
fundamental periods of buildings relate primarily to height. T or F?
true
appx. divide no. of stories by 10 to estimate the fundamental period in seconds
response spectrum
represents a building’s range of responses to ground motion of different frequency
(site response spectrum)
allows us to see how buildings of different fundamental periods will behave on the same site
one benefit of creating a response spectrum is:
- tells us the resonant frequencies at which a building will undergo peak accelerations
- design can be adjusted/tuned so building period does not coincide with site period of maximum response
what is SFRS?
seismic force-resisting system
vertical elements of a building that take seismic load from the diaphragms & transfer it to the ground
name 3 basic alternative types of vertical SFRS and their essential characteristics
shear walls: receive forces from diaphragms & transmit them to the ground
braced frames: receive lateral forces from diaphragms and transmit to ground; generally less resistance than shear walls, more ductility (detailing of joints will help)
moment-resisting frames: frame without diagonal bracing; resist lateral forces primarily by bending in beams & columns; require strong col-beam joints
regardless of group, any vertical SFRS must continue from roof to base without interruption to perform the best. T or F?
true
- decreasing horizontal dimension of SFRS from one story to another decreases its capacity
- eliminating SFRS from one story to another breaks the load path
- openings in shear walls reduce capacity & create stress concentrations
ductility
a material’s or system’s ability to undergo deformation without breaking, and while still carrying load (e.g. a metal spoon can be bent back & forth several times before it breaks, but a plastic spoon breaks almost instantly… metal is ductile, plastic is brittle)
steel & ductility
steel’s capability of withstanding load past the yield point on the stress-strain curve makes it a very ductile material
steel is often combined w/ other materials to add ductility, such as in reinforced concrete
steel is often used in seismic force-resisting systems in ways intended to add ductility
ductility in lateral force resisting systems (or the SFRS)
absorbs energy (desirable)
a building whose lateral force resisting elements are more ductile will have to resist smaller seismic forces than its less ductile counterpart
are shear walls generally considered ductile or non-ductile?
non-ductile - shear walls resist lateral forces by developing shear in their planar surfaces (generally rigid, least ductile of the SFRS groups)
are moment-resisting frames considered generally ductile or non-ductile?
ductile
moment-resisting frames are generally the most ductile of the 3 SFRS groups, least rigid
the san andreas fault is what type of fault?
transom fault or strike-slip
horizontal movements primarily
a building’s configuration:
is a large factor in its ability or inability to survive an earthquake
stress concentration
occurs when large forces are concentrated at one or a few elements of a building, such as a particular set of beams, columns, or walls
reentrant corners & offsets (e.g. setback roof) are examples of building forms likely to cause stress concentrations
idealized “regular” building configuration:
identical resistance on both axes (of a plan):
eliminates eccentricity between the centers of mass & resistance and provides balanced resistance in all directions, thus minimizing torsion
idealized “regular” building configuration:
continuous load path (vertically & horizontally)
- interruptions in load path always produce stress concentrations
- continuous load path minimizes stress concentrations
idealized “regular” building configuration:
symmetrical plan shape
- minimizes stress concentrations
- minimizes torsion
idealized “regular” building configuration:
arrangement of vertical SFRS elements
symmetrical & parallel arrangement of vertical SFRS
- arranged in 2 directions in plan
- in parallel on opposite sides
- minimizes torsion & stress concentrations
idealized “regular” building configuration:
uniform strength & stiffness at perimeter
reduces likelihood of torsion
idealized “regular” building configuration:
equal floor heights
- equalizes column & wall stiffness
- minimizes stress concentrations
idealized “regular” building configuration:
uniform sections & elevations
eliminates offsets, minimizing stress concentrations
idealized “regular” building configuration:
low ration of width to height
minimizes tendency toward overturning
define base shear
total design lateral force or shear at the base
the term that describes the ability of a structural system or element to dissipate energy beyond its elastic limit is:
ductility
ELFP
equivalent lateral force procedure
establishes how to calculate base shear
equivalent lateral force procedure:
seismic base shear:
V = C(s)W
V = seismic base shear
it is the sum total of all story shears - gives us total lateral force a building must resist
C(s) = seismic response coefficient
collects factors related to occupancy, soils at the site, ground acceleration
W = effective seismic weight of the building
equivalent lateral force procedure:
seismic response coefficient:
C(s)
used in calculating base shear
C(s) = S(ds)/(R/I)
S(ds) = 2/3 S(ms)
and
S(ms) = F(a)S(s)
so
C(s) = 2/3 [F(a)S(s)] / (R/I)
equivalent lateral force procedure:
design earthquake spectral response acceleration parameter at short period:
S(ds)
S(ds) is used in calculating seismic base shear w/ ground acceleration
S(ds) = 2/3 S(ms)
and
S(ms) = F(a)S(s)
- establish reasonable percentage of actual force to which we will design
- Fa = site coefficient (depends on site class)
- Ss = ground acceleration from maps or USGS website
equivalent lateral force procedure:
response modification coeffeicient: R
R is used in calculating seismic base shear
- greater ductility translates to a higher R value (shear walls = low; moment resisting frame = high)
- greater R = less seismic base shear
- lesser R = greater seismic base shear
in a basic sense, what must be considered when designing the structural system of a building?
vast range of physical loads also shape the elements of the structure
equivalent lateral force procedure:
site coefficients and adjusted MCE spectral response & acceleration parameters:
Sms
used in calculating seismic base shear (ground acceleration)
Sms = Fa * Ss Fa = site coefficient, reduces or increases acceleration depending on site class (soil characteristic) Ss = ground acceleration
equivalent lateral force procedure:
site coefficient: Fa
site coefficient
reduces or increases acceleration depending on site class
equivalent lateral force procedure:
mapped spectral response acceleration at short periods:
Ss
basis of acceleration
name some of the general types of luminaries
- surface mounted
- recessed
- suspended
- freestanding
- wall mounted
- accessory
per the IBC, if site soil conditions are not known in sufficient detail, what is the best site class category that can be used?
site class D: stiff soil profile
what is fluid mechanics in relation to wind design?
branch of physics that studies physical properties and behaviors of fluids, which teaches us about wind behavior
what is mean roof height?
average of roof eave height & height to the highest point on roof surface (except for roof angles of less than or equal to 10 degrees, the mean roof height shall be the roof eave height)
what is wall wash lighting?
smooth, even distribution of light over a wall
wind’s movement is primarily _____ ?
lateral
sometimes there are vertical components
what is an escarpment?
aka scarp - with respect to topographic effects, a cliff or steep slope generally separating two levels or gently sloping areas
locations w/ abrupt changes in elevation cause wind to speed up
Kzt factor
locations with abrupt changes in elevation are subject to _____
locations w/ abrupt changes in elevation cause wind to speed up
Kzt factor
what is design force, p?
equivalent static pressure to be used in the determination of wind loads for buildings
what is uplift?
upward acting force, results from wind passing over horizontal surface (roof)
what is basic wind speed?
V
3-second gust speed at 33’ above the ground in exposure c
- older codes used to give as average speed of a column of air one mile long
what is the MWFRS?
main wind force resisting system
assemblage of structural elements assigned to provide support & stability for the overall structure; generally receives wind loading from more than one surface:
- wind lateral loads
- wind uplift
- overturning
what is vortex shedding?
when a tall building is subjected to high winds, vortices are produced in sequence over time
what are vortices?
swirls of air created when wind is forced around objects, and are most noticeable when wind flows around taller buildings
building or other structure, flexible
slender buildings & other structures that have a fundamental natural frequency less than 1 hz
building or other structure, rigid
a building or other structure whose fundamental frequency is greater than or equal to 1hz
building, enclosed
a building that does not comply with the requirements for open or partially enclosed buildings
building, open
a building having each wall at least 80% open
building, partially enclosed
- total area of openings in a wall that receives positive external pressure exceeds the sum of the areas of openings in the balance of the building envelope (walls & roof) by more than 10 percent
- total area of openings in a wall that receives positive external pressure exceeds 4 sq.ft. or 1% of area of that wall, whichever is smaller, and the % of openings in the balance of the building envelope does not exceed 20%
basic wind speeds have been mapped and are available to use as a basis for determining wind loads. they’re given in miles per hour or ____?
meters per second
wind produces uplift, especially on ____?
roofs & overhangs
as defined in ASCE 7-05 chapter 6, an open building has____?
each wall at least 80% open
what are components & cladding?
elements of the building envelope that do not qualify as part of the MWFRS
the equivalent static force to be used in the determination of wind loads for open buildings & other structures is ___?
design force, F
tropical disturbances, hurricanes & typhoons, are examples of _____
tropical cyclones; originate over tropical oceans
chinooks & santa ana winds are examples of _____
down-slope winds; occur at leeward side of mountain ranges
buildings at risk identifies a total of 4 damage mechanisms through which severe windstorms damage structures. what are they?
- aerodynamic pressures created by flow of air around a structure
- induced internal pressure fluctuations die to breach in the building envelope
- impact forces created by wind-borne debris
- pressures created by rapid atmospheric pressure fluctuations (associated primarily w/ tornadoes)
the magnitude of pressure from wind (uniformly distributed load) is directly related to ____?
wind speed
in the most intense windstorms, debris impacts represent a significant portion of the damage caused, including _____?
injuries & loss of life
fluid dynmaics shows us that a fluid passing over an obstruction will cause uplift. this is called bernoulli’s principle. it acts on airplane wings and _____.
roofs & overhangs
what are special wind regions?
areas requiring detailed study to determine basic wind speed due to topographical & climatic conditions
in relationship to building design for wind forces, a building or structure having no unusual geometrical irregularity in spatial form is known as _____.
a regular-shaped building or strucutre
what is eave height, h?
the distance from the ground surface adjacent to the building to the roof eave line at a particular wall (average height if it varies)
how much effect do pressure fluctuations of the atmosphere (as opposed to inside building) have on most structures?
little to no effect
there are 3 allowed procedures for wind load analysis established in ASCE 7-05 chapter 6. what is method 1?
- simplified procedure
others are:
- analytical procedure
- wind tunnel procedure
1 & 2 are tabulated values & calculations
simplified design wind pressure is?
ps
- gives force per sq. ft. to use in design of the MWFRS
- cannot be less than 10lb/sqft
- horizontal pressures combine windward & leeward
- method 1: simplified procedure gives us ps
internal pressure coefficient
Cpi
- relates degree of enclosure & resulting internal pressures on the MWFRS
- requires 2 load cases to be tested: a positive & a negative Gcpi applied to all internal surfaces
method 1 = simplified procedure
C & C
net design wind pressure for exposure B at 30’ height from ground
Pnet30
gives base pressure per sq.ft. to be used in determining Pnet, the net design wind pressure for components & cladding, using method 1 - simplified procedure
method 1 - simplified procedure
MWFRS
simplified design wind pressure for exposure B at 30’ height from ground
Ps30
gives the base pressure per sq.ft. to be used in determining Ps, simplified design wind pressure for MWFRS, using method 1 - simplified procedure
a unit of illumination based on the metric system equal to 1 meter-candle or 1 lumen/sq.m.
lux
method 1 - simplified procedure
C & C and MWFRS
topographic factor: Kzt
- considers topography of site
- accounts for wind speed-up at escarpments or ridges & their distance from site
- K1 comes from a table, K2 & K3 can be calculated
- defaults to 1.0 if conditions are not met
method 1 - simplified procedure
C & C and MWFRS
adjustment factor for building height & exposure
adjusts simplified design wind pressure (for MWFRS) or the net design wind pressure (for C&C) based in a table graduated by building height in feet and exposure category
exposure category: B, C, or D is assigned based on surface roughness of the surroundings
what do MWFRS & MSFRS stand for?
main wind force resisting system
main seismic force resisting system
a non-symmetrical building is likely to experience what type of force under wind loads?
torsion
if there’s eccentricity between a building’s center of rigidity & resultant lateral wind force, torsion results
when a lateral force acts on a building, there is a tendency for it to tip over, this is referred to as:
overturning moment
overturning can be an issue when the lateral force is large or the building is _____
rigid
the building’s self-weight counteracts overturning moment w/ stabilizing moment