PDD 01 Flashcards
(195 cards)
1
Q
What are four material
characteristics that should be
considered when selecting
exterior finishes for a
building?
A
Making sure the material is appropriately
used.
Material can withstand the elements (sun,
wind, rain, etc.)
How often does the material require
maintenance.
How well does the material perform for its
intended use and longevity.
2
Q
How should the performance
of materials be considered
during the design phase?
A
Materials should be tested to assure they
will perform as expected and designed.
The life span of the material should be
evaluated to make sure it will withstand
normal wear and tear.
3
Q
How does building orientation
effect natural daylighting?
A
Windows facing north will not get any
direct sunlight, whereas windows facing
south will receive a fair amount of sunlight
year round.
4
Q
Describe the treatments for a
North-facing window vs. an
East-facing window.
A
North-facing windows: will not get any
direct light but will provide an even glow
from reflected light all day. In hot places
they have almost no heat gain. In cold
climates, a north window will be cold and
grey.
East-facing windows: will receive sunlight
in the morning and are opportunities to
start warming up the building at the
beginning of the day.
5
Q
Describe the treatments for a
South-facing window vs. a
West-facing window.
A
South-facing windows: receive sunlight nearly
all day. In hot climates, use overhangs above
the windows to block the summer sun from
coming in. A 2 foot overhang will shade the
summer sun but allow the winter sun to come
in.
West-facing windows: receive hot afternoon
sun until sunset. The western sun is much
lower in the sky, so overhangs will not prevent
the heat from entering the building. Using
louvers will help control the amount of sun that
enters the building.
6
Q
What is a free body diagram?
A
To analyze forces on and within
structures, we borrow a graphic technique
from physics called a free body diagram,
or FBD. An FBD is a representation of a
body and all forces and moments acting
on it. It does not include internal forces.
7
Q
What structural connection
can resist either x or y forces,
but not moment?
A
Pinned connections
8
Q
This type of structural
connection only resists forces
in the y direction.
A
Roller connections
9
Q
Within any structural member
in bending, _____ is quantified
as the maximum translation
measured perpendicular to its
central axis.
A
deflection, In a beam, deflection is the
vertical distance that the beam sags at
midspan.
It’s usually expressed as a fraction of the
span. Often noted as the Greek letter delta
(Δ).
10
Q
The formula for deflection of a
beam with a uniformly
distributed load is:
A
Δ = 5 wl4 / 384 EI
11
Q
The fibers within a beam
develop an internal moment to
resist the moment caused by
deflection. This resisting
moment is called:
A
bending moment
12
Q
The centroid of an area is
conceptually defined as:
A
The center of gravity of a mass
For simple geometric shapes, like circles
and rectangles, determining the centroid is
easy and simply corresponds to the
geometrical center. For many common
asymmetrical shapes, the centroid is
calculated.
13
Q
A factor relating the shape of
a structural section and the
distribution of its material
relative to a chosen axis is
called:
A
A section’s moment of inertia, usually
denoted “I”.
The units of moment of inertia are, in4 or
inches to the fourth power.
14
Q
The ratio of a sections Moment
of Inertia and the distance
between the neutral surface and
the outermost edge of the
section, “c” is referred to as:
A
The section modulus
The formula for Section Modulus is:
S = I / c
15
Q
The two reasons that column
buckling occurs are:
A
If an applied load is eccentric, or 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 in a
column.
16
Q
Finding this value quantifies a
cross section’s ability to resist
buckling under an axial
compressive load by relating
its moment of inertia and area.
A
Radius of gyration The radius of gyration
is a convenient parameter, providing a
measure of the resistance of a crosssection
to lateral buckling.
17
Q
A load imposed on a
structural member at some
point other than the centroid
of the section is called:
A
Eccentric Load
18
Q
Bending stress is a function
of the section modulus and
the:
A
bending moment
19
Q
Define slenderness ratio:
A
The ratio of a wall or columns
unsupported height/length to its thickness
and measures its ability to resist buckling
when a compressive load is applied.
20
Q
Vertical steel reinforcing
within reinforced concrete
columns essentially are very
slender ______ when
compressive stress is applied.
A
columns
21
Q
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:
A
truss
22
Q
The two methods for manually
analyzing trusses are:
A
the method of joints and the method of
sections
23
Q
In this type of truss analysis, a
cut is made passing through
no more than three members,
and the three equations of
equilibrium are applied:
A
method of sections
24
Q
Forces acting toward a joint
indicate a truss member is in:
A
tension
25
LIQUEFACTION
Liquefaction is a process by which water-saturated
sediment temporarily loses strength and acts as a
fluid.
For liquefaction to be possible, there has to be space
between particles that water can occupy.
Liquefaction can have dramatic and devastating
impacts during an earthquake.
Sites that are prone to liquefaction are said to be
liquefiable or to have liquefiable soils.
Sands, muds, and silts are the soils most vulnerable
to liquefaction. These often occur naturally or as
landfill in coastal areas.
26
SEISMIC WAVES
Seismic waves are oscillations at the molecular level within
the soil.
In an earthquake, sudden relative displacement of very large
masses and energy release results in waves of particle
displacement rushing through the surrounding rock and soil.
Seismic waves project outward from the hypocenter, but
have different velocities and characteristics.
The hypocenter generally occurs at a depth measured in
miles, or kilometers, below the surface.
There are many types of seismic waves. The three of
concern to us are:
P waves or Primary Waves
(also called Pressure Waves)
S waves or Secondary Waves
(also called Shear Waves)
Surface Waves
27
P WAVES
One of the seismic waves produced in
soils by earthquakes
• Have the highest velocity and will arrive
at distant locations first
• therefore, they also called Primary waves
• Cause compression in soil, in the
direction of travel, in an alternating pushpull
fashion
• also called Pressure waves
• can travel through liquid
28
S WAVES
•one of the seismic waves produced in soils by
earthquakes
•have the second highest velocity and will arrive
at distant locations just after the P waves
•therefore, they also called Secondary waves
•cause shear in the soil particles, causing
motion perpendicular to direction of wave travel
•therefore they also called Shear waves
•the shearing forces they transmit cause
damaging sideways and vertical accelerations
at the surface
•cannot travel through liquid
29
SURFACE WAVES
• one of the seismic waves produced in soils by
earthquakes
• have the lowest velocity and will arrive at distant
locations after the P waves and after the S waves
• vertical displacements in the earth's surface
• tend to last longer and have larger amplitudes;
can be very destructive
• restricted to near the earth’s surface.
• analogous to waves in the ocean that do not
disturb the water at depth.
• as depth increases, ground displacements
decrease.
(FEMA 454 Ch. 2)
30
STABILIZING MOMENT
A building's self-weight creates a moment in the opposite
direction of it's overturning moment.
This is it's stabilizing moment.
The building code establishes factors of safety between
stabilizing moment and overturning moment. When overturning
moment results from earthquake loads, the basic loading
combinations in IBC 1605.3.1 (taken from ASCE 7-05 chapter 2)
govern how resisting moment is compared to overturning
moment.
Using LRFD, load and resistance factor design:
compare 0.9D and 1.0E
(90% of dead load * moment arm) and (100% earthquake load *
moment arm)
Using ASD, allowable stress design:
compare 0.6D and 0.7E
(60% of dead load * moment arm) and (70% earthquake load *
moment arm)
31
BASE SHEAR
STORY SHEAR is defined by ASCE 7 as “The
summation of design lateral seismic forces at levels
above the story under consideration.”
Therefore BASE SHEAR is the sum of all STORY
SHEARS at the base.
This is commonly referred to as SEISMIC BASE
SHEAR.
The diaphragms at each story must transfer the force
received at that level, plus those from the levels
above.
The shear forces proceed downward in this additive
fashion until they reach the base.
BASE SHEAR is “Total design lateral force or shear
at the base.” (IBC 2009)
32
What is SDC?
Seismic Design Category. The IBC and
ASCE 7-05 have requirements for
geotechnical investigations relating to
seismic forces likely to be experienced at
a site.
All sites are assigned a Seismic Design
Category which the authority having
jurisdiction will use in evaluating a project.
33
What is "fundamental
period"?
Fundamental period is a measure of the time an
object takes to travel out and back once, when a
force has acted on it.
It is defined in FEMA 454 by the often used
analogy of a child on a swing. When we push a
child on a swing, if we want it to go higher, we
push just as the child starts travelling away from
us.
The fundamental period of a building is the time,
in seconds, that a building takes to sway out and
back again in an earthquake.
In an earthquake, all structures tend to sway back
and forth at their fundamental period.
34
What is a "fault"?
A fault is a plane within rock that forms in
response to stress. Most commonly, though
not always, the stress is induced by movement
of tectonic plates.
A fault can be a vertical plane, a horizontal
plane, or any orientation in between
Stress resulting from movements of masses of
crust accumulates along faults.
When the capacity of the rock is reached,
slippage occurs and energy is released in the
form of an earthquake.
35
An earthquake's depth and its
relative location to a building
is often directly related to its
____?
Destructive power.
An earthquake's depth (vertical distance)
and its relative location to a building
(horizontal distance) is often directly to its
destructive affects.
Earthquakes have complex, immediate,
and often violent effects on the rock and
soil around them, in the form of seismic
waves.
36
THEORY OF PLATE
TECTONICS
The theory of plate tectonics holds that the
earth's crust is made up of masses that
essentially float on molten rock below.
These cooled, solidified chunks of crust ride
around on the molten material below,
somewhat freely.
The exact cause of the movement is debated,
but the movements have been observed.
All plate boundaries, where different plates
meet, have earthquake faults.
However, not all faults occur at plate
boundaries.
37
CRUSTAL CONVEYOR BELT
It's the loop of creating crust at mid-ocean ridges and
destroying it at subduction zones.
It includes fault systems that are great distances from
each other at either end of the loop.
No material is "created" or "destroyed", this is a
shorthand used to describe a change of state from liquid
to solid and back again.
Crust is created at mid-ocean ridges, travels over very
long periods of time to subduction zones, and is pushed
down and "destroyed" or converted back to magma.
It was theorized to exist because the mass of the earth
remains unchanged, yet crust was known to be
destroyed.
The discovery of the system of mid-ocean ridges and
divergent faults confirmed the theory.
38
The amplitude of any wave is
proportional to _____ .
The energy the wave transmits.
True of any wave, including seismic
waves.
Higher amplitude seismic waves means
more energy, more acceleration, more
force on a building.
39
A low ratio of width to height
has what advantage for a
building?
It minimizes tendency the to overturn
when acted on by lateral loads, including
seismic loads.
40
Coefficient of friction
The coefficient of friction describes the ability
to resist sliding, such as a footing transferring
lateral loads to the ground. The higher the
coefficient, the greater that soil's capacity to
resist sliding.
To get the capacity for resisting sliding in a
footing, multiply the coefficient of friction * the
dead load (the vertical load) on the footing.
For certain soil classes, the IBC gives a lateral
sliding resistance value to be multiplied by the
contact area, instead of using a coefficient of
friction.
41
A pendulum clock is an
example of _____ .
Resonance. The pendulum swings back
and forth propelled by its own weight. A
mechanism imparts a very small force to
overcome friction, keeping the pendulum
going at a constant rate. If the timing isn't
exactly right, the pendulum would
eventually stop.
42
The magnitudes of seismic
forces a building will
experience are determined by:
• The building's weight
• The maximum ground acceleration
These dictate the magnitude of the forces.
Once the forces act on the building, it's
overall configuration determine how those
forces will be transferred to the ground.
43
Fundamental periods of
buildings relate primarily to
height. True or false?
True. An approximate rule-of-thumb is to
divide the number of stories by 10 to
estimate the fundamental period in
seconds. Any particular building's
fundamental period can also be influenced
by its structural system and detailing,
especially those of the lateral force
resisting elements.
44
Response Spectrum
Represents a building's range of responses to
ground motion of different frequency.
May be called a Site Response Spectrum when
referring to a specific site.
A graph that plots the maximum response values of
acceleration, velocity, and displacement against
period and frequency
(FEMA 454 Ch. 4)
A Site Response Spectrum enables us to see how
buildings of different fundamental periods will
behave on the same site. It also helps us avoid
resonant loading of a building.
45
One benefit of creating a
Response Spectrum is:
The response spectrum tells us the
resonant frequencies at which a building
will undergo peak accelerations.
The building design can be adjusted, or
tuned, so the building period does not
coincide with the site period of maximum
response.
46
What is SFRS?
Seismic Force-Resisting System
The vertical elements of a building that take seismic load
from the diaphragms and transfer it to the ground.
From ASCE 7-05 Chapter 11 Definitions"
"SEISMIC FORCE-RESISTING SYSTEM: That part of the
structural system that has been considered in the design to
provide the required resistance to the seismic forces
prescribed herein."
In the building code, horizontal elements such as
diaphragms are not included in the SFRS, nor does the code
use that acronym.
However, diaphragms are considered as integrally related
with the vertical SFRS elements. They are designed in
conjunction.
47
Name three basic alternative
types of vertical SFRS and
their essential characteristics.
Shear walls
• receive lateral forces from diaphragms and transmit them to the
ground.
• resists lateral force by developing shear in their planar surfaces
Braced frames
• receive lateral forces from diaphragms and transmit them to the
ground.
• generally less resistance than shear walls, and more ductility
• ductility can be adjusted with detailing of the joints
Moment-resisting frames
• frame without diagonal bracing
• resist lateral forces primarily by bending in beams and columns
• require strong column-beam joints to take moment
( some items summarized from FEMA 454 sec. 5.2.1 )
48
Regardless of group, any
vertical SFRS must continue
from roof to base without
interruption to perform the
best. True or false?
True.
• Decreasing the horizontal dimension of
the SFRS from one story to another
decreases its capacity.
• Eliminating the SFRS from one story to
another breaks the load path.
• Openings in shear walls reduce capacity,
and create stress concentrations.
49
DUCTILITY
Ductility describes a material's or system's
ability to undergo deformation without
breaking, and while still carrying load.
A metal spoon can be bent back and forth
several times before it breaks.
However a plastic spoon breaks almost
instantly, with a sudden snap.
This illustrates metal's ductility, and
plastic's brittleness.
(FEMA 454 Chapter 4.9)
50
Steel and 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 with 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.
51
Ductility in lateral force
resisting systems (or the
SFRS)
• absorbs energy (often desirable)
A building whose lateral force resisting
elements are more ductile will have to
resist smaller seismic forces than its less
ductile counterpart.
52
Are shear walls generally
considered ductile or nonductile?
Non-ductile
Shear walls resist lateral forces by
developing shear in their planar surfaces.
Shear walls are generally the most rigid,
therefore the least ductile, of the three
SFRS groups.
53
Are moment-resisting frames
considered generally ductile
or non- ductile?
Ductile
Moment-resisting frames are, generally,
the most ductile of the three SFRS groups.
They are generally the least rigid, therefore
the most ductile.
54
The San Andreas Fault is what
type of fault?
A transform fault or strike-slip
The movements are primarily horizontal.
The Pacific Plate and the North American Plate are
moving about northwest and southeast,
respectively. The average annual movement
relative to each other is about a couple inches.
Due to friction, the plates get "stuck" against each
other at this boundary zone.
Periodically, enough stress builds up for sudden
slippage to occur. This slippage is an earthquake.
55
A building's configuration:
is a large factor in its ability, or inability, to
survive an earthquake.
56
Stress concentration
"Stress concentration occurs when large
forces are concentrated at one or a few
elements of the building, such as a particular
set of beams, columns, or walls."
( FEMA 454 sec. 5.3.1 )
Reentrant corners (in plan) and offsets (such as
at a setback roof) are examples of building
form likely to cause stress concentrations.
Both can be "irregularities."
57
Idealized "regular" building
configuration:
Identical resistance on both
axes (of a plan)
Identical resistance on both axes of a plan:
"Eliminates eccentricity between the
centers of mass and resistance and
provides balanced resistance in all
directions, thus minimizing torsion. "
( FEMA 454 sec. 5.2.3 )
58
Idealized "regular" building
configuration:
Continuous load path
(vertically and horizontally)
Continuous load path:
This "regular" building configuration is
worth considering, because:
• interruptions in load path always
produce stress concentrations
• a continuous load path minimizes stress
concentrations
( see FEMA 454 ch. 5 )
59
Idealized "regular" building
configuration:
Symmetrical plan shape
Symmetrical plan shape:
This "regular" building configuration is
worth considering, because it:
• minimizes stress concentrations
• minimizes torsion
( see FEMA 454 ch. 5 )
60
"Idealized ""regular"" building
configuration:
Arrangement of vertical SFRS
elements
Symmetrical and parallel arrangement of
vertical SFRS
• SFRS (in plan) arranged in two directions
• SFRS (in plan) in parallel on opposite
sides
• minimizes torsion and stress
concentrations
( see FEMA 454 ch. 5 )
61
Idealized "regular" building
configuration:
Uniform strength and stiffness
at perimeter
Uniform strength and stiffness at
perimeter
• reduces the likelihood of torsion.
( see FEMA 454 ch. 5 )
62
Idealized "regular" building
configuration:
Equal floor heights
This is one aspect of a "regular" building
configuration.
• equalizes column and wall stiffness
• minimizes stress concentrations
( see FEMA 454 ch. 5 )
63
Idealized "regular" building
configuration:
Uniform sections and
elevations
This is one aspect of a "regular" building
configuration.
• eliminates offsets, minimizing stress
concentrations
( see FEMA 454 ch. 5 )
64
Idealized "regular" building
configuration:
Low ratio of width to height
This is one aspect of a "regular" building
configuration.
• minimizes tendency toward overturning
65
Define base shear.
Total design lateral force or shear at the
base.
66
The term that describes the
ability of a structural system
or element to dissipate energy
beyond its elastic limit is:
ductility
67
ELFP
Equivalent Lateral Force Procedure
This procedure in ASCE 7-05, which is
incorporated by the IBC 2009, establishes
how to calculate Seismic Base Shear.
68
Equivalent Lateral Force
Procedure:
Seismic Base Shear:
V = CsW
the formula for seismic base shear is:
V = CsW
V = seismic base shear
It is the sum total of all story shears. In effect, it gives us the
total seismic (lateral) force a building must resist.
The formula is about establishing a reasonable percentage of
the actual force to which we will design.
Cs = seismic response coefficient
It collects factors related to:
• occupancy (Importance)
• soils at the site
• ground acceleration
W = effective seismic weight (of the building)
69
Equivalent Lateral Force
Procedure:
Seismic Response
Coefficient:
Cs
The Seismic Response Coefficient, CS, is used in calculating seismic
base shear.
CS = seismic response coefficient
It collects factors related to:
• occupancy (Importance)
• soils at the site
• ground acceleration
Cs = SDS / ( R / I )
where:
SDS = 2/3 SMS
and:
SMS = FaSs
If you find yourself working with
Cs, it's more useful to rewrite it
as:
2/3 (FaSs) / (R / I )
because you can then more easily
plug in or find Fa, Ss , R and I.
70
Equivalent Lateral Force Procedure:
Design earthquake spectral response
acceleration parameter at short period:
SDS
SDS is used in calculating seismic base shear.
"Design earthquake spectral response acceleration
parameter at short period" This is a fancy way of saying
"acceleration." In this case, it is ground acceleration.
The formula for SDS is:
SDS = 2/3 SMS , where: SMS = FaSs
The formula is about establishing a reasonable percentage of
the actual force to which we will design.
Why is the 2/3 there? It's arbitrary, and knocks a third off the
acceleration to be used in calculating seismic base shear.
Fa is the Site Coefficient; it reduces or increases the
acceleration depending on Site Class (soil characteristics)
Ss is ground acceleration from maps or the USGS web site,
or: "Mapped spectral response acceleration at short periods"
71
Equivalent Lateral Force
Procedure:
Response Modification Coefficient:
R
The Response Modification Coefficient, R, is used in
calculating seismic base shear.
It's given in tables in ASCE 7, which is referenced by
the IBC. Greater ductility translates to a higher R
value. For example, shear walls have low R values
and moment-resisting frames have high R values.
Other systems generally fall in between. That is a
simplified summary, but it's all we need to know.
•greater R = lesser seismic base shear
• lesser R = greater seismic base shear
72
In a basic sense, what must
be considered when
designing the structural
system of a building?
The vast range of physical loads also shape the
elements of the structure: animated and
inanimate objects, as well as resistance to
anticipated and unanticipated loads. Materials,
equipment and other dead loads, and varying
loads - such as snow, ponding of water on the
roof, wind and earthquake - must be calculated
and elements properly sized for. International
and building codes direct structural choices as
well. If conflicting information appears in
building codes, the most stringent one prevails.
73
Equivalent Lateral Force
Procedure:
Site coefficients and adjusted MCE
spectral response and acceleration
parameters:
SMS
SMS is used in calculating seismic base shear.
"Site coefficients and adjusted MCE spectral response and
acceleration parameters" This is a fancy way of saying
"acceleration." In this case, it is ground acceleration.
Essentially, it's acceleration, taken from maps or the
USGS web site, modified by a factor that considers
the soils at the site.
SMS = FaSs
Fa is the Site Coefficient; it reduces or increases the
acceleration depending on Site Class (soil characteristics)
Ss is ground acceleration from maps or the USGS web site,
74
Equivalent Lateral Force
Procedure:
Site Coefficient:
Fa
Fa , Site Coefficient is used in calculating
seismic base shear.
Fa is the Site Coefficient; it reduces or
increases the acceleration depending on
Site Class (soil characteristics)
75
Equivalent Lateral Force
Procedure:
Mapped spectral response
acceleration at short periods:
SS
SS is used in calculating seismic base shear.
"Mapped spectral response acceleration at short
periods"
This is a fancy way of saying ground acceleration that
we get from maps (or the USGS web site.)
SS forms the basis of the "A" or acceleration
remember, when determining seismic base shear, it
really all boils down to Newton's Second Law of Motion:
F=mA
Force = mass * Acceleration
76
Name some of the general
types of luminaries.
Surfaced mounted, recessed, suspended,
freestanding, wall mounted and accessory
lighting.
77
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
78
What is fluid mechanics in
relation to wind design?
The branch of physics that studies
physical properties and behaviors of
fluids, which teaches us about wind
behavior.
79
What is “mean roof height”?
According to ASCE 7 Definitions: The
average of the roof eave height and the
height to the highest point on the roof
surface, except that, for roof angles of less
than or equal to 10◦, the mean roof height
shall be the roof eave height.
80
What is wall wash lighting?
A smooth even distribution of light over a
wall.
81
Wind’s movement is primarily
_______?
Wind’s movement is primarily lateral,
though sometimes there’s a vertical
component.
82
What is an escarpment?
According to the ASCE 7-05 Definitions:
Also known as scarp, with respect to
topographic effects in ASCE 7-05 Section 6.5.7,
a cliff or steep slope generally separating two
levels or gently sloping areas.
Locations with abrupt changes in elevation
cause wind speed-up.
This is accounted for in the Topographic Factor
Kzt in both the Simplified and Analytical
procedures.
83
Locations with abrupt
changes in elevation are
subject to _____
Locations with abrupt changes in
elevation cause wind speed-up.
This is accounted for in the Topographic
Factor Kzt in both the Simplified and
Analytical procedures.
84
What is Design Force, p?
From the ASCE 7-05 Chapter 6 Definitions:
Equivalent static pressure to be used in
the determination of wind loads for
buildings.
It is found by using Method 2 - Analytical
Procedure
85
What is uplift?
Uplift is an upward acting force. It results
from wind passing over a horizontal
surface such as a roof. Due to the
Bernoulli Effect, building roofs tend to act
like airplane wings, producing uplift.
86
What is Basic wind speed?
Basic Wind Speed, V
From the ASCE 7-05 Chapter 6 Definitions:
Three-second gust speed at 33 ft (10 m) above the
ground in Exposure C (see Section 6.5.6.3) as
determined in accordance with Section 6.5.4.
• Older codes used to give Basic Wind Speed as
average speed of a column of air one mile long
• Current code uses 3-second gust at a height of 33
feet in Exposure C
87
What is the MWFRS?
From the ASCE 7-05 Chapter 6 Definitions:
Main Wind-Force Resisting System:
An assemblage of structural elements assigned to
provide support and stability for the overall structure.
The system generally receives wind loading from
more than one surface.
Main Wind-Force Resisting System
• The assemblage of structural elements, considered
as a whole, that resist wind loads. It must resist:
• wind lateral loads
• wind uplift
• overturning
88
What is vortex shedding?
When a tall building is subjected to high
winds, vortices are produced in sequence
over time. This repeated creation of
vortices is called vortex shedding.
For a detailed discussion, see FEMA
Buildings at Risk, Chapter 3
89
What are vortices?
Swirls of air created when wind is forced
around objects, and are most noticeable
when wind flows around taller buildings.
For a detailed discussion, see FEMA
Buildings at Risk, Chapter 3
90
BUILDING AND OTHER
STRUCTURE, FLEXIBLE
“Slender buildings and other structures
that have a fundamental natural frequency
less than 1 Hz.”
( ASCE 7-05 sec. 6.2 )
91
BUILDING OR OTHER
STRUCTURES, RIGID
"A building or other structure whose
fundamental frequency is greater than or
equal to 1 Hz."
92
BUILDING, ENCLOSED
"A building that does not comply with the
requirements for open or partially
enclosed buildings."
93
BUILDING, OPEN
"A building having each wall at least 80
percent open # ."
94
BUILDING, PARTIALLY
ENCLOSED
1. The 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 and roof ) by more than
10 percent.
2. The total area of openings in a wall that
receives positive external pressure exceeds 4 ft2
(0.37 m2) or 1 percent of the area of that wall,
whichever is smaller, and the percentage of
openings in the balance of the building envelope
does not exceed 20 percent. #
( ASCE 7-05 sec. 6.2 )
95
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?
They’re also given in meters per second.
96
Wind produces uplift,
especially on_____?
Roofs and overhangs.
97
As defined in ASCE 7-05
Chapter 6, an open building
has _____?
Each wall at least 80% open.
98
What are components and
cladding?
Elements of the building envelope that do
not qualify as part of the MWFRS.
99
The equivalent static force to
be used in the determination
of wind loads for open
buildings and other structures
is?
Design Force, F
100
Tropical disturbances,
hurricanes and typhoons are
all examples of_________
Tropical cyclones; cyclones that originate
over tropical oceans.
101
Chinooks and Santa Ana
winds are examples of______
Down-slope winds; that occur at the
leeward side of mountain ranges.
102
Buildings at Risk identifies a
total of four damage
mechanisms through which
severe windstorms damage
structures. What are they?
1. Aerodynamic pressures created by flow
of air around a structure.
2. Induced internal pressure fluctuations
die to breach in the building envelope.
3. Impact forces created by wind-borne
debris.
4. Pressures created by rapid atmospheric
pressure fluctuations (associated primarily
with tornadoes).
103
The magnitude of pressure
from wind (a uniformly
distributed load) is directly
related to what?
Wind speed
104
In the most intense
windstorms, debris impacts
represent a significant portion
of the damage caused,
including_____?
Including injuries and loss of life.
105
Fluid dynamics 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 and overhangs.
• In the highest winds, such as those from
severe windstorms, uplift forces on a
building can be significant.
106
What are "special wind
regions"?
Areas requiring detailed study to
determine Basic Wind Speed due to
topographical and climatic conditions.
107
In relationship to design for
wind forces, a building or
structure having no unusual
geometrical irregularity in
spatial form is known as
_____
a regular-shaped building or structure.
From ASCE 7-05 Section 6.2:
BUILDING OR OTHER STRUCTURE,
REGULAR SHAPED:
A building or other structure having no
unusual geometrical irregularity in spatial
form.
108
What is "eave height, h"?
From ASCE 7-05 Definitions:
The distance from the ground surface
adjacent to the building to the roof eave
line at a particular wall. If the height of the
eave varies along the wall, the average
height shall be used
109
How much effect do pressure
fluctuations of the
atmosphere (as opposed to
inside the building) have on
most structures?
Little to no effect.
110
There are three Allowed
Procedures for wind load
analysis established in ASCE
7-05 Chapter 6. What is
Method 1?
• Method 1 – Simplified Procedure
The others are:
• Method 2 – Analytical Procedure
• Method 3 – Wind Tunnel Procedure
Method 1 can be applied to a simple building of regular
shape meeting several listed criteria. It borrows several
important factors from Method 2.
Both methods 1 and 2 incorporate all the concepts we
studied as various coefficients, equations, and tabulated
values. Each of these methods shows how to calculate
wind loads separately on the MWFRS and Components
and Cladding, or C & C.
111
Simplified design wind
pressure is?
Simplified design wind pressure, ρs
• Gives the force per square foot to use in
design of the MWFRS
• Cannot be less than 10# / sq. ft.
• Horizontal pressures combine windward
and leeward
• Method 1 - Simplified Procedure gives us
ρs
112
Internal Pressure Coefficient:
Cpi
Internal pressure coefficient.
• Relates degree of enclosure and resulting
internal pressures on the MWFRS
• Used in Method 2 - Analytical Procedure
A table relating degree of enclosure and
internal pressure
Requires two load cases to be tested : A
positive and a negative Gcpi applied to all
internal surfaces
113
Method 1 - Simplified Procedure
C & C
Net design wind pressure for
Exposure B at 30 foot height from
the ground.
Ρnet30
Net design wind pressure for Exposure B
at 30 foot height from the ground.
Gives the base pressure per square foot to
be used in determining Pnet , the Net
design wind pressure for Components and
Cladding, using Method 1 - Simplified
Procedure.
114
Method 1 - Simplified Procedure
MWFRS
Simplified design wind pressure for
Exposure B at 30 foot height from
the ground.
Ρs30
Simplified design wind pressure for
Exposure B at 30 foot height from the
ground.
Gives the base pressure per square foot to
be used in determining Ps , the Simplified
design wind pressure for MWFRS, using
Method 1 - Simplified Procedure.
115
A unit of illumination based
on the metric system equal to
1 meter-candle or 1 lumen/m2.
Lux.
116
Method 1 - Simplified
Procedure
C & C and MWFRS
Topographic Factor:
KZT
• Considers the topography of the site
• accounts for wind speed-up at
escarpments or ridges and their distance
from building site
• K1 comes from a table on last page of
figureK2 and K3 can be calculated or taken
from a table relating to selected distance
ratios
• Defaults to 1.0 if conditions are not met
117
Method 1 - Simplified Procedure
C & C and MWFRS
Adjustment factor for building
height and exposure:
λ
Adjusts the 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.
( ASCE 7-05 fig. 6.2 last page )
Exposure category
• Exposure B, C, or D is assigned based on the
Surface Roughness of the surroundings
118
What do the acronyms
MWFRS and MSFRS stand
for?
Main Wind Force Resisting System/Main
Seismic Force Resisting System
119
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 and the resultant lateral
wind force, torsion results.
120
When a lateral force acts on a
building, there is a tendency
for it to tip over, this is
referred to as:
Overturning moment
121
Overturning can be an issue
when the lateral force is large,
or the building is ______.
The building’s self-weight counteracts
overturning moment with a stabilizing
moment.
122
The two types of forces that
create overturning moment
have different origins. For
wind what is it? For seismic
what is it?
For wind, it’s a consequence of a pressure
multiplied by an area.
For seismic, it’s a consequence of
accelerated mass, with each story
contributing based on mass and height.
123
In a multistory building, each
story adds to the total
overturning moment in
proportion to what 3 factors?
story shear, height above the base, and
it's weight
124
In seismic design,
vulnerability to overturning is
related to soil conditions.
Name two conditions to look
out for:
Buildings supported on soils subject to
liquefaction can overturn if the ground
subsides.
Buildings that are supported on different
soil types can overturn as a result of
differential settlement.
125
When overturning moment results from
earthquake loads, denoted E, the basic load
combinations in IBC 1605.3.1 (taken from ASCE 7-
05 chapter 2) govern how resisting moment is
compared to overturning moment. Using load and
resistance factor design, equation 16-7 would
apply and we would compare ___D and 1.0E.
Using allowable stress design, Equation 16-15
would apply and we would compare ___D and
0.7E.
0.9D, 0.6D
126
Overturning from wind loads
isn’t usually an issue for
typical buildings. It can be a
major consideration for which
two types of structures.
tall or lightweight
127
Overturning moment can be
calculated in a simplified way
using the _____ design
pressure multiplied by
the____over which it acts.
windward, area
128
Due, in part, to the higher W factors, a
building’s ratio of width to height can
matter more when designing to resist
wind loads, rather than seismic loads.
A ____,____ building, relative to the
direction of wind loading being
considered, has advantages in
moment arm length.
wider, lower
Greater width means a longer moment arm
for the dead load, increasing the resisting
moment. Less height means less area and
a lower magnitude of the lateral force, plus
a shorter moment arm for the overturning
moment.
129
Because their purpose is to
achieve grade changes by
holding back earth, retaining
walls must resist lateral forces
caused by what two factors?
Lateral force in retaining walls comes from
the weight of the soil retained, plus the
weight of ground water if it’s present.
130
The three types of forces a
retaining wall must resist are:
overturning, sliding, and the soil pressure
They are generally categorized by how
they resist these forces.
131
This type of retaining wall:
Uses only its own dead load
to resist forces and can be
built of stone, masonry, or
plain or reinforced concrete.
gravity wall
132
Roofs and floors generally act
as _____ and carry lateral
load.
diaphragms
133
When plywood is used in
wood construction to create
diaphragms, special attention
should be paid to what?
nailing patterns
Building codes prescribe nailing patterns
for plywood diaphragms. Nailing patterns
are described for field and edge
conditions. Nails are generally spaced
closer at the edges.
134
If provision for drainage isn’t made
for a retaining wall, hydrostatic
pressure based on the weight of
water must be added to the soil
load. Such loads in addition to
those from the soil are called:
surcharges
135
This type of retaining wall uses:
perpendicular buttresses, usually
combined with a cantilever wall.
Buttresses usually occur at the
retained side and are buried in backfill
and these usually can be constructed
higher than Cantilever walls.
Counterfort walls
136
This type of retaining wall
combines a wall with tension
ties to the retained rock or
soil:
Tie-back or anchored wall
The rock or soil is drilled and injected with
reinforced concrete, or steel cables
attached to an expanding anchor. The
walls can be of many types, but are
commonly of cantilever design and are
usually used for high loads and tall
heights, such as at highway cuts.
137
______pressures are allowed
to apply where the top of a
wall is free to move, such as
at a retaining wall.
Active
138
______pressures, which are
higher, apply where the top of
the wall is not free to move,
such as at a foundation wall
with a floor structure attached
like a basement.
At-rest
139
For retaining walls the IBC
typically requires a factor of
safety of what?
1.5 for each mode of failure
140
In a cantilevered retaining wall
the _____ resists lateral
pressure by creating moment.
heel
141
How is the soils lateral
pressure distributed on
retaining walls?
triangular pressure with zero at the top
and maximum at the bottom or the stem
Because it’s a triangle, a Resultant force
occurs at 1/3 the height, and creates
overturning moment
142
The edge members or beams
of a diaphragm (roof or floor)
are referred to as:
Chords
Chords receive their load as a uniformly
distributed load per linear foot. They react
with bending moment and shear, just like a
beam.
143
Just as with gravity loads, the
foundation ultimately
transfers all lateral loads to:
the earth.
144
Lateral loads and related uplift
on a foundations ability to
resist these loads depends on
which 2 factors?
coefficient of friction and lateral bearing
capacity
145
This type of wall is required to
resist the lateral pressure of
retained soil:
retaining wall
146
A diagonally braced frame in which
at least one end of each brace
frames into a beam a short
distance from a beam-column or
from another diagonal brace is
known as:
Eccentrically braced frame (EBF)
147
Name three forms of intrusion
detection.
Perimeter protection
Area or room protection
Object protection
148
What are four methods of
perimeter building protection?
Magnetic contacts
Glass break detectors
Window screens with embedded wire
Photoelectric cells
149
How do photoelectric cells
work to protect building
openings?
Photoelectric cells are installed around
building openings, such as doors, and can
detect an intrusion when the light beam is
broken.
150
What is area protection?
Area protection offers security to a space
by alerting of an intruder's presence within
the building. If perimeter systems fail to
activate, sensors placed in rooms can be
triggered by a person moving or making
noise within the space.
151
Which form of area protection
has the least amount of
coverage?
Ultrasonic detectors can be effective by
triggering building alarms when the high
frequency sound wave they produce is
disrupted. However, they are limited to a
space not much larger than a standard two
car garage, about 20 ft by 30ft.
152
What kind of security
protection would a car alarm
be considered?
A car alarm would be considered object
protection as it sounds an alarm when the
car is touched or the handle attempts to be
opened.
153
What is typically required for
building wiring in order to
reduce the risk of fire?
Conduits are used to protect cables and
wiring within building systems. In addition
to fire protection, the conduit limits the
exposure of harmful gases which may be
emitted from the cables.
154
How do you calculate the
elevator speed required based
on the building height?
Elevator speed can be determined by
multiplying 1.6 by the building height and
adding 350. For example, if a building is
50 feet high, the equation would be 1.6 x
50ft = 80 + 350 = 430 feet/minute.
155
What is the difference
between a hydraulic elevator
and a standard electric
elevator?
Hydraulic elevators have a plunger arm
beneath the passenger car that pushes the
up to the correct floor. Electric elevators
use a system of wire cables and pulleys to
move the elevator car to the required floor.
156
What is a general size and
capacity for an elevator car?
Typical elevator cars for low rise building
application are rated at 2,500 pound
capacity and are 5'X7' in area.
157
What is an ionization
detector?
Ionization detectors are able to sense
particles of combustion from a fire in the
early smoldering stage before flames are
present. It is considered an early warning
detector and is not applicable in areas
where fires may produce a lot of smoke as
they do not detect the presence of smoke.
158
What type of fire alarm will
detect the presence of
smoke?
Photoelectric detectors will sense the
presence of smoke when the sensor light
on the device is obstructed by smoke
present within a space. These are
required as life safety devices since
smoke inhalation is usually more lethal
than the actual fire itself.
159
What is a disadvantage of
using a fire detection system
that responds to changes in
temperature within a space?
Rise-in-temperature detection systems can
be set to alert building occupants when
the temperature within a space rises above
a certain limit. However, flames generally
need to be present in order for the
temperature to rise drastically which does
not provide much advanced warning to
building occupants.
160
What are the requirements for
fire detectors according to the
building code?
Fire detection devices, such as smoke
alarms, must be placed in all sleeping
rooms such as hotel rooms or bedrooms
in apartment buildings as well as in places
of public assembly. Fire dampers must
also be located within the mechanical
system so that smoke is not allowed to
circulate throughout the building.
161
Which fire detection system is
most commonly used in
buildings?
A combination of smoke and fire detection
is generally used in most buildings to give
early warning of fire when smoke becomes
present as well as responding to the
presence of flames by triggering an alarm
or sprinkler system within the building.
162
Name 4 types of fire detection
devices:
Ionization, Photoelectric, Rise of
Temperature, Infrared or Ultraviolet
radiation Flame detectors.
163
When architects and
designers use windows and
skylights to bring daylight into
a space it is called:
Daylighting.
164
There are two kinds of lighting
to consider when planning the
lighting of a space:
Natural light and artificial light.
165
A system that uses a shallow pool
of water on the roof during the day
to absorb the sun’s energy. An
insulated covering is placed over
the pond at night – to keep the
absorbed heat from escaping into
the cool night air.
Roof pond system.
166
A massive element capable of
absorbing heat when needed
and providing for later use
when ambient temperatures
are cooler is referred to as:
Thermal mass.
167
The greatest potential for heat
gain and heat loss in a
building (when not
considering infiltration)
comes through where?
The windows.
168
In cold climates (Northern
Hemisphere) in order to take
advantage of low solar angles in
the winter to collect heat in thermal
mass in the building, it is best to
have large windows facing which
direction?
South.
169
This type of light output
points all the light in the
direction of the task.
Direct.
170
This type of light output
throws all the light towards a
reflective
ndirect.
171
The largest likely impacts on
electric lighting requirements
and design for a building are
derived from:
Architectural orientation, ceiling height,
massing, and section profiles which
determine daylight availability in the
building.
172
The calculated amount of
illumination on a surface is
called a:
Footcandle (FC).
173
What is the difference
between luminance and
illuminance?
Luminance: the measurement of how
bright light is (leaving) a surface...it
depends on reflectivity or transmittance.
Illuminance: the density of luminous
energy incident (falling) on a surface:
expressed as lumens per unit area.
174
What is a lumen (l)?
SI unit of luminous flux, a measure of the
total amount of visible light emitted by a
source. One lumen of luminous flux
uniformly cast on 1 square foot of area
creates an illuminate of 1 foot candle.
175
The calculated lumen output
per watt input is called:
Efficacy. An important measure of the
energy efficiency of a light source.
176
When direct lighting is used to
produce clearly defined lighting
levels in accordance with the light
required to complete detailed work
such a reading, writing, paperwork,
or scientific experiments, it is
called:
Task lighting.
177
This type of lighting is generally used for
circulation and general lighting to offer a
“sense of space” throughout the structure.
This type of lighting is similar to outdoor
light experienced on an overcast day.
There are no sharp shadows produced
with this type of lighting, since the light is
coming from all directions.
Ambient lighting.
178
This type of lighting is used to
provide illumination to
pathways for exiting a space
should an emergency arise.
Emergency or egress lighting. The
illuminated “EXIT” sign is an example of
emergency lighting.
179
Define CRI.
Color Rendition Index (CRI) is a measure
of how closely a light source approximates
daylight of the same color temperature
and displays the true color of an object.
180
A unit used in lighting that
comes complete with a lamp,
reflector, refractor, housing,
and electrical connection.
Luminaire.
181
Two types of glare that a
lighting designer should be
aware of:
Direct Glare: a light source in the that
causes interference/distraction with a
visual task.
Reflective Glare: when a light source is
reflected from a viewing surface into the
eye and interferes with a viewing task.
The critical zone for direct glare is in the
area above a 45 angle from the light
source.
182
What does CFL stand for in
lighting?
Compact fluorescent lamp. These lamps
have a self-contained ballast and can be
used in place of incandescents
183
A two-lead semiconductor lighting
device that is gaining in popularity
in the lighting industry due to their
energy efficiency, long life, and
ability to create bright white light
with no heat output are:
Light-emitting diodes (LEDs).
184
The maximum CRI rating is
____.
100
185
What are the 4 types of
electric light sources?
Incandescent, fluorescent, high intensity
discharge (HID), and light-emitting diodes
(LEDs).
186
This type of lamp consists of
a tungsten filament that is
sealed in a glass bulb
containing and inert gas.
Incandescent.
187
A few disadvantages to using
incandescent lamps are:
Low efficacy, short lamp life, and high heat
output.
188
What is a tungsten-halogen?
This is a type of incandescent lamp in
which the filament is located within an
inner quartz “envelope”. This envelope
can tolerate higher operating temperatures
and contains a special halogen gas. The
halogen gas prevents evaporated metal
from the filament from depositing on the
inner surface of the quartz. The tungstenhalogen
is only slightly more efficient than
a regular incandescent bulb.
189
These tubes produce light
when an electrical current
passes through gases inside
the glass tube.
Fluorescent lighting.
190
Name two types of lamps that
have a reflective coating
integrated into the lamp.
Reflector (R), Parabolic Aluminized
Reflector (PAR). This increases the
efficiency of the lamp and allows for more
precise beam control.
191
The three types of fluorescent
lamps are:
Preheat, instant start, and rapid start.
192
A device that limits the
starting and operating
voltages to a lamp and
controls the current once the
lamp is operating is called a:
Ballast.
193
The high intensity discharge,
or HID lamp, is a lamp within a
lamp and is run at very high
voltage. Name 4 types of
lamps in this category.
Mercury vapor, metal halide, high-pressure
sodium, low-pressure sodium.
194
This type of HID lamp is only
considered suitable for street
and security lighting because
it produces a monochromatic
yellow light and no color
rendering.
ow-pressure sodium.
195
Name a few advantages of
using incandescent lamps.
They are inexpensive, compact, dimmable,
and have a warm color rendition. These
typery inefficient and created more heat
than light.
