5/8 inches or 4 inches in diameter and are flat plates
flange extending from the face of plate
shear plates are particularly suited for construction that must be
Bolting and welding are the two most common methods in use today for
making steel connections.
Bearing type connections resist the shear load on the bolt
through friction between surfaces.
critical connections are those where any amount of slip
would be detrimental to the serviceability of the s
as joints subject to fatigue loading or joints with oversized holes.
The entire load is carried by fricton
Bolts are further classified as to whether the bolt threads are
included or excluded from the shear plane.
The strength of conn
ection is affected because there is less area to
resist the load through the threaded portion.
Bolts may be in either single shear or double shear.
There are three basic types of bolts used in modern steel
Bolts designated with ASTM #A30
Called unfinished bolts
Have the lowest load
Used only for bearing type connections
Bolts Designated A325 & A490
May be used in bearing
Must be used in slip
The nuts are tightened to develop a high tensile stress in
the bolt which causes the connected members to develop a
high friction between them which resists the shear.
Bolts range in diameter from 5/8 inch to 1
1/2 inch in 1/8 inch
pically used diameters are 3/4 inch and 7/8 inch
Standard codes for the condition of use:
type connection with threads included in the
type connection with threads excluded from the
S: bolt in single shear
D: bolt in double shear
Factors in bolt selection
Diameter of bolt
Type of hole being used
Standard round holes
larger than diameter of bolt
5/16” larger than diameter of bolt
and may only be used with slip
Short slotted holes
1/16” wider than the bolt diameter
and have a length that does not exceed the oversize ho
dimension by more than 1/16”. May be used in either
bearing or slip
Long slotted holes
1/16” wider than the bolt diameter
and a length not exceeding 2
1/2 times the bolt diameter.
Slotted holes are used where some amount of
is needed. Long slotted holes can only be used in one of
the connected parts of a joint. The other part must use
standard round holes or be welded.
One of the most important considerations in bolted ste
connections is the spacing of bolts and the edge distance from
the last bolt to the edge of the members.
Absolute minimum spacing is 2
2/3 times the diameter of
the bolt being used with 3 times the diameter being the
ge distances varies with the diameter of he
bolt being used. Typically, a dimension of 1.25 inches is
often used for all bolts up to 1 inch in diameter.
Welds are quite frequently used in lieu of bolts for several reasons:
The gross cross section of the members can be used instead of
the net section
Construction is often more efficint because there are no angles,
bolts, or washers to deal with and no clearance problems with
Welding is more practical for moment
Since members must be held in place until welding is completed,
welding is often used in combination with bolting.
The most common type of welding process used in building
construction is the electric arc process.
Penetration refers to t
he depth from the surface of the base metal to
the point where fusion stops.
Two types of electrodes are used commonly today:
E60: allowable shear stress is 18 kips per square inch
E70: allowable shear stress is 21 kips per square inch
ode to use depends on the configuration of the joint, the
magnitude and direction of load, the cost of preparing the joint, and
what the erection process will be.
The three most common types of welded joints are the lap, the butt,
and the tee.
slot welds are frequently used to join two pieces. In these
welds, a hole is cut or punched in one of the members and the area
filled with the weld.
The fillet weld is one of the most common types.
The perpendicular distance from the 90 degree corner
hypotenuse of the triangle is called the throat.
Because the angles are 45 degrees, the dimension of the throat is
0.707 times the leg dimension.
For a butt joint, the throat dimension is the thickness of the material
if both pieces are the same
thickness, or the size of the thinner of two
materials if they are unequal.
There are common symbols used for welding. The full rage of
symbols gives information regarding the type, size, location, finish,
welding process, angle of grooves, and other i
The type of weld is indicated with one of the standard symbols
and placed below the line if the weld is on the side near the arrow
and above the line if it is on the side away from the arrow.
If the members are to be welded on both sides, the symbol is
repeated above and below the line.
Other data placed with the weld symbol are size, weld symbol,
length of weld, and spacing, in that order from left to right.
Field welds are indicated with a flag placed at the junction of the
horizontal line and the arrow line and pointing to the tail of the
A circle at the same point indicates that the weld should be made
The perpendicular legs
of the filled, bevel, J, and flare bevel
welds must be at the left.
Loads in weld design:
For fillet welds, the stress is considered as shear on the throat
regardless of the direction of the load.
For butt welds, the allowable stress is the same as f
or the base
The maximum size of a fillet weld is 1/16 inch less than the
nominal thickness of the material being joined if it is 1/4 inch
thick or more. If the material is less than 1/4 inch thick, the
maximum size is the sam
e as the material.
The minimum size of fillet welds:
material thickness of the
minimum size of
thicker part joined, inches
to 1/4 inclusive
over 1/4 to 1/2
over 1/2 to 3/4
inimum length of fillet welds must not be less than 4 times
the weld size plus 1/4 inch for starting and stopping the arc.
Or two or more welds parallel to each other, the length must be at
least equal to the perpendicular distance between them.
termittent welds, the length must be at least 1
In most cast
place concrete construction there are generally no
connectors as with wood or steel.
Different pours of concrete are tied together with reinforcing bars
cast concrete construction
there must be some way of rigidly
attaching one piece to another. This is accomplished with weld plates.
Rebars and keyed sections:
The most typical type of cast
place concrete joint is one
reinforcing bars are allowed to extend past the formwork to become
part of the next pour.
These types of joints are found in many situations:
Footing to foundation wall
Walls to slabs
Beams to beams
Columns to beams
Reinforcing is only for the purpose of tying two pours of concrete
together rather than transmitting large loads, they are called dowels.
The length of the dowels or extensions of rebar from one section of
concrete to the next is determined by the minimu
m development length
required to transmit the loads or by the ACI code.
Keyed sections are used either alone or with rebars to provide a
stronger joint between teo pours of concrete. Keyed sections are often
used in footings and floor slabs.
Precast structures are built in sections require a way to transmit
horizontal, vertical, and moment forces from one piece to the next.
This is usually accomplished by casting weld plates, angles, and other
types of steel pieces into the concrete memb
ers at the factory.
At the site, the members are placed in position and corresponding plates
are welded together.
Shear connectors are not really conn
ectors in the usual sense, but are
use to tie steel and concrete together in composite sections so forces are
transmitted from one to the other.
One of the typical applications of shear connectors is with concrete slab
/ steel beam composite sections.
Connectors are welded to the top of the steel beam in the fabricating
shop at a fairly close spacing which is determined by engineering
calculations to transmit the forces created by the applied loads.
These are often called headed anchor studs and abbre
viated HAS on the
Building Code Requirements on Structural Design
Th code requires that any construction method be based on a rational analysis
in accordance with well
established principles of mechanics, and that such an
analysis provides a
path for all loads and forces from their point of origin to
the load resisting elements.
The analysis must include distribution of horizontal shear, horizontal
torsional moments, stability against overturning, and anchorage.
Horizontal torsional moment results from torsion due to eccentricity between
the center of application of a lateral force and the center of rigidity of the
Anchorage resists the uplift and sliding forces on a structure.
building design is based on allowable stress or working stress
design, each component must be designed to resist the most critical effect
resulting from the combination of loads listed.
Some reductions in live loads are permitted by code.
Designing floors to accommodate concentrated loads. If these loads,
acting on any space 2
1/2 feet square on an otherwise unloaded floor,
would result in stresses greater than those caused by the uniform load,
then the floor must b de
Practice Examination Answers
Long Spans do not provide better resistance to lateral loads
Long spans are not economical when compared to short spans
Modulus of Elasticity (E)
Ratio of unit stress to unit strain
Unit stress i
s the stress per unit area measured in psi
Unit strain is the total shortening or lengthening of a member divided
by its length
The higher the E value, the greater its stiffness or resistance to deformation
Simple Beams vs. Continuous Beams
beams have more deflection than continuous beams
Continuous beams require more complex calculations and connections
Simple beams generally have more maximum moment
Continuous beams usually have more maximum shear.
Continuous beams deflect less than simple beams.
Continuous beams are subject to negative bending moment over its
Simple beams never have negative moment.
For equal spans and loads, the maximum positive bending moment is
greater in the end spans of a continuous beam than in the center spans.
The full allowable unit bending stress is used in glulams up to 12 inches
Beams more than 12 inches
deep must reduce the allowable unit bending
stress by a size factor related to their depth.
Redwood is usually used when the structure will be exposed to the weather
and durability is the main consideration.
Douglas fir is the strongest
species and is commonly used in construction
Spruce is light weight with low strength
Cedar is durable when exposed to the weather, light weight and low in
strength, and is mainly used for siding and trim.
Deformation = PL/AE
P = the concentrated
L = the length
A = cross
E = modulus of elasticity
Is used to measure the consistency of concrete
Less slump means the mix is stiffer
More slump means the mix is wetter
4 inches of slump is the maximum accepta
ble for concrete used in
Deflection = KwL3/EI
K = load factor
W = the total uniform load
L = length
E = the modulus of elasticity
I = the moment of inertia
Dirt, oil, or other non
metalic coating must be removed before concrete is
placed so that the bond between the steel and concrete is not adversely
Rust and scale, often removed during the handling and placement of the
steel, actually improve th
Wood shrinks the most in the direction of the annual growth rings
Wood shrinks less across the rings (radially)
Wood shrinks the least along the grain (longitudinally)
Studs and logs shrink very little compare
d with the shrinking of joists
across their depth
Glulams are made with seasoned lumber and are designed for very little
Braced Frames (K
Are constructed with steel members forming diagonal braces to act in both
tension and compress
ion between beams and columns.
Concrete is not used for braced frames because it is so weak in tension
Braced frames usually have bolted connections which are not rigid like
Braced frames are designed to create a triangulated syst
em of connections
to resist lateral shear and bending moments.
Since they effectively resist both vertical and lateral (seismic) loadings,
they are employed in both low
rise and high
Concrete slab with reinforcement in t
wo directions and brings its load
directly to the supporting columns, generally without any beams or
Relatively thin and not economical in reiforcement, but economical in
For heavy live loads and bays which are approximately square,
construction is often economical.
In the design of columns, the ratio of the effective length, l, to its least radius
of gyration, r, is known as the slenderness ratio.
Stirrups have a structural design purpose
to reinforce he concrete in areas
where shear stresses exceed the capability of concrete.
Simply supported beams deflect more than fixed
Concentrated loads cause more deflection than uniformly distributed loads
For a given load and span, the deflection of a beam varies inversely with its
moment of inertia (I).
The greater the I value of the beam, the lower its deflection.
Since I = bd3/12 for a rectangular section, the beam with the greatest
depth has the gre
atest I value and therfore will deflect the least.
Amount of deflection is determined by four factors:
The loads acting on the beams
The stiffness of the beam material (measured by its modulus of
The beam’s moment of Inertia (I)
he span of the beam
Inelastic material (wood and concrete) deflect when the load is intially
applied and continues to deflect through time (without an increase in load)
Elastic Material (steel) does not deflect more than its initial deflection
he load is increased.
All steel regardless of strength has the same stiffness as measured by its
modulus of elasticity (E).
The section modulus of a beam section is a measure of its ability to
resist flexural stress, not deflection.
ly supported beam will deflect more than a fixed
end beam with
the same span and load.
A concentrated load at mid
span will produce more deflection than the
same load uniformly distributed.
Summary of reinforced concrete beam design:
Select the speci
fied concrete compressive strength (f’c) and reinforcing
steel yield strength (fy). These values are constant for all the beams in the
For the given beam, determine the maximum bending moment (Mu) and
vertical shear (Vu), using the load factors 1.4 for the dead load and 1.7 for
the live load.
Select the width (b) and the effective depth (d) of the beam; these must be
adequate to resist
the maximum bending moment (Mu). In general, the
value of d should be about 1.5 times b. if the size of the beam is
predetermined, verify that it is adequate. Use T
beam action when
Compute the required area of tensile reinforcement (As) and
bars. Verify that the steel area is at least the minimum required by the
If the depth of the beam is insufficient to resist the maximum moment,
provide compressive reinforcement.
Check the shear capacity and provide stirrups if neces
Verify that all reinforcing bars are extended at least their developmental
length beyond the point of peak stress.
Be sure that the beam is adequately sized for deflection.
Locate centroids of individual
pieces that make up the whole
Select one of the bases as the X
X axis for the whole unit
Set up a chart
Area of each piece
distance from each individual pieces centroid to the X
All the areas together
All the Area(Y) together
The Centroidal Axis will be the result of dividing the total Area(Y) by
total Area. The distance is measured from the X
Moment of Inertia around the centroidal axis (I)
Set up a chart
Area of each piece
Moment of inertia around each pieces own centroidal axis (bd3)/12
Y’ (Y prime) distance from each pieces own centroid to the
centroidal axis of the whole.
Io + Area(Y’squared)
Add up the “Io + Area(Y’squared)” for
the moment of inertia for the
After cutting a free
body diagram of a structure, if the calculated internal
forces are negative, then the internal forces act in the opposite direction
from that assumed.
If a load acts through a body’s center of
gravity, then the body
Has no tendency to rotate
Tends to translate in the direction of the applied force.
The yield point is the unit stress at which the material continues to
deform with no increase in load.
depends on a column’s unbraced length and radius of
The flexural stress in a beam is maximum at the extreme fibers and is
a function of the beam’s section modulus.
The shear stress in a beam is maximum at the
The carbon content of steel affects its strength and ductility.
The modulus of elasticity of steel:
Has a constant value
Is higher than that of any other structural material
Is a measure of the stiffness of steel
a series of parallel arches which are skewed with respect to
the axes of a building and which intersect another series of skewed
a series of arches placed side by side to form a continuous
of trusses which intersect another series of
perpendicular trusses to form a grid.
a series of inclined trusses which intersect another series
of inclined trusses.
Water weighs 62.4 pcf.
Thin Shell Structures
Is able to resist shear,
tension, and compression.
Too thin to have any significant resistance to bending moment, or
William LeBaron Jenney designed the Home Insurance Co. Building, the
first skyscraper in 1883.
Robert Maillart was a swiss engineer who des
igned arched concrete
Pier Luigi Nervi italian contractor and engineer who created soaring
concrete shell roofs of unusual elegance and refinement
Gustav Eiffel designed structures of great strength using steel and iron.
Fazlur Kahn designed
Sear’s Tower and John Hancock Building.
Skyscrapers were made possible by the invention of the elevator by Elisha
Louis Sullivan cast ironed framed buildings were among the first
Thermae were Roman public bathing establishme
Basilica was a Roman rectangular building used as a hall of justice and
public meeting place.
Amphitheater was a Roman oval arena surrounded by tiers of seats and
used in Rome for gladiatorial contests.
Stoa was a Greek colonnade used to provide
access to law courts,
Joseph Paxton’s Crystal Palace (1851) was an immense prefabricated
glass and cast iron structure.
William LaBaron Jenney’
s Home Insurance company Building (1883) is
generally considered to be the first building completely framed in steel.
Burnham & Root’s Reliance Building (1890
95) completely expressed the
aesthetics of its steel skeleton.
H. H. Richardson’s Marshall Fi
eld Wholesale Store (1885
87) floors were
supported by timber framing and its exterior walls were largely of stone
French architect Perret was the first to use the reinforced concrete frame in
rise construction and to express it archit
One of Perret’s pioneering efforts was the Rue Franklin Apartment
Building (1903) in Paris, France.
Eiffel designed the Eiffel tower and several other steel structures as well as
the framework of the Statue of Liberty.
Freyssinet was one o
f the first engineers to develop and make use of
Torroja was a Spanish engineer best known for his shell structures.
Pantheon (123 AD) is one of the greatest achievements in Roman
architecture. Its immense concrete dome is so thi
ck at its bottom that
tensile hoop stresses are resisted by the concrete, without any need for iron
reinforcing. The opening at the crown of the dome was desgned to act as a
masterpiec of GREEK architecture
Adapted from the wood construction of early Greek temples to marble.
Subtle visual adjustments were made to the Parthenon to correct for
a slight convexity of the columns so that they would not
used arches in great profusion and for a variety of reasons.
Roman arches were always semi
They were constructed with scaffolding or centering which was
removed after the keystone was installed
the upper most masonry
The maximm span
of a Roman arch was about 100 feet.
Moment of Inertia, I: measure of the stiffness of a beam, its resistance to
Section Modulus, S: measure of the bending or flexural strength of a
Modulus of Elasticity
, E: determines stiffness of a material, or its
resistance to deformation.
Ductility: materials ability to deform without rupture.
Typically, structural systems in a building represent 25% of the total
If the spans of the structural bays are doubled, the costs for the structural
system would probably increase by about 20
In a solid sawn wood beam, the flexural stress is maximum at the top and
bottom fibers, and it passes through the neutral axis w
here it is zero.
Standard engineering practice calls for the resisting moment of the dead load
to be at least 1.5 times the overturning moment.
Widening the footing of a retaining wall is the simplest solution for
increasing the dead load and the resis
Several factors are used to determine the load bearing capacity of a wood
sectional area of the column is used and is calculated by the
dimensions of the column section
The ratio l/d is another factor, where l is the un
braced length of the column
and d is the smallest dimension in the column plan.
The modulus of elasticity is also considered, which is dictated by the
species of wood used.
The radius of gyration is used in determining the load bearing capacity of
l columns, NOT wood columns.
Open Web Steel Joists
Standardized, lightweight steel trusses which generally support uniform
loads from floor or roof decks
Steel joists ma have parallel chords or single or double pitched top chords
to provide roof drai
Joists have no fire
resistive ratings by themselves but ratings of one hour
or more may be obtained by using he proper floor or roof deck and ceiling.
Open web steel joists are always fabricated in the shop.
Glue Laminated Beams
e laminated beams are manufactured from more than one
The individual laminations are not required to be of the same species and
The higher grades are generally used at the top and bottom cross
where the flexural
(bending) stresses are maximum. Shear failure of a
beam is most likely to occur where the vertical shear is maximum, which is
adjacent to a support.
Horizontal shear stress in a beam varies from zero at the outermost fibers
to a maximum value at the mid
height of the beam.
Since the glue is generally stronger than the wood, failure is more likely to
occur within a lamination than between laminations.
laminated member is 12 inches or less in depth, the full
allowable stress may be used for d
For depths greater than 12 inches, a size factor is used, which has the effect
of reducing the allowable stress that may be used.
Plane scarf joints and finger joints can be made with adequate strength
Butt joints are not permitted for glue
laminated members because they
usually cannot transmit tensile stress and can transmit compressive
stress only after considerable deformation.
Camber is often built into glued laminated beams for the following
To avoid the appearance of sag
To eliminate the ponding of water
To compensate for deflection
The capacity of a wood column is determined by several factors
The modulus of elasticity (E) of the wood, which depends on its species
The allowable compressive strength (Fc), which also depends on the
species and grade of the wood.
The ratio l/d, where l is the unbraced height of the column and d is t
least lateral dimension of the column.
The formulas used to design columns are based on idealized pin
conditions, where the end of the column are free to rotate, but not move
Actual building columns do not alwa
ys meet these conditions.
Their ends may be free to rotate
Or, they may permit no rotation
Their ends may be free to translate
Or, they may be fixed against translation.
To allow the column formulas to be used for all end conditions, the K
This factor is multiplied by the actual unbraced length (l) to arrive at the
effective length (Kl), which is then used to design the column.
The shear stress in a column pad is essentially a function of the column
load, the column size, a
nd the thickness of the pad. It is not at all related to
the reinforcing steel, and only slightly affected by the pad size.
Increasing the pad thickness provides more area of concrete to resist the
shear load, and hence decreases shear stress.
The axial load carrying capacity of a steel column is determined by the
strength of the steel used in the column, and the tendency of the column to
The buckling tendency is a function of the length (l) of the column,
its radius of gyration ( r),
and the effective length factor (K).
In designing steel columns, the larger slenderness ratio is used because it
results in a smaller allowable axial stress.
Eccentrically loaded columns are columns which support vertical loads
applied at some distance from its centerline.
There are two types of concrete columns that differ in the kind of lateral
reinforcing they use:
lose the longitudinal reinforcing bars with a
spaced continuous steel spiral, which braces the longitudinal
bars and confines the concrete.
have separate lateral ties which hold the longitudinal
bars in position, prevent them from
buckling outward, and also,
somewhat, confine the concrete.
Building codes require that reinforcement for shrinkage and temperature
stresses normal to the principal reinforcement must be provided in structural
floor and roof slabs, where the principal re
inforcement extends in one
direction. Such reinforcement is often called temperature steel.
Structural Steel Connections
The connections used in structural steel systems comprise a significant
part of the cost of these systems, and can even influence
the type of
structural steel system selected.
In some cases, bolted connections are more economical and in other cases,
welded connections are.
Usually shop connections are preferred over field because they are less
According to the building
code requirements for reinforced concrete, the
minimum concrete coverages are:
Maximum moment occurs where the vertical shear is equal to zero.
e ultimate tensile capacity of a reinforcing bar is the product of its area
and yield strength.
Grade 40 reinforcing steel has a yield strength of 40 ksi.
Grade 60 reinforcing steel has a yield strength of 60 ksi.
Splicing reinforcement bars:
One common method is the lap bars a sufficient amount; such lapped
bars are often wired together.
Welded butt and lap splices are acceptable.
Newer methods include mechanical couplers and end bearing, which is
acceptable for compression only.
cing bars are furnished with rolled
Identify the producing mill
The bar size
Type of steel
Additional marking for higher
Bolts joining wood members have their greatest capacity when the load acts
parallel to the grain a
nd their least when the load acts perpendicular to the
When load acts at any other angle to the grain, the bolt capacity may be
determined by Hankinson’s formula, and the value thus obtained is less
than that parallel to the grain and greater than
that perpendicular to the
A concrete slab is connected to a steel beam with shear connectors
Shear connectors can develop the ultimate capacity of the concrete or
steel, whichever is less
Because the concrete and steel work together, a smaller size steel beam
may be used than in conventional steel framing, which generally results
in a more economical system.
When smaller steel beams are used, deflections tend to become greater,,
more critical, in composite design than in conventional steel
Conventional steel framing can always be designed to carry the required
Shear Stress in a steel beam:
The unit shear stress f(v) is equal to V/dt.
stress should be checked for beams with a short span and a
The shear stress should be checked for beams with a large concentrated
load near the support.
Strength Design Method
the internal stresses and strains in a r
concrete beam which is about to fail are used to determine the ultimate
moment capacity of the member.
crushing of the concrete and yielding of the
reinforcement steel take place simultaneously.
It is desirable to keep the a
mount of reinforcing steel relatively small,
so that if the member were ever to be overstressed, it will fail gradually
by yielding of the steel, rather than the crushing of the concrete.
For this reason, the amount of reinforcing is limited to 75% of th
which would produce balanced design.
The principle factor that determines the strength of concrete is the
Concrete strength increases as the water
cement ratio decreases
Less water relative to cement results in stronger concret
More water relative to cement results in weaker concrete
Formwork (the following is the usual order for removal of concrete
formwork, from first removal to last):
Beam Side Forms
Slab Bottom Forms
Beam Bottom Forms
Wood Joists / Beams
narrow beams which tend to be laterally unstable
Bridging or blocking is used to prevent rotation or lateral displacement
Bridging and blocking also helps to distribute concentrated loads to the
Horizontal shear is critical for wood b
eams with short spans and large
The following are generally ignored in the design and detailing of strctural
Notching wood beams
A notch near the middle of a beam
’s span has practically no effect on its
The loss of shear strength caused by a gradual change in a beam’s cross
section is not as great as that caused by a square notch.
If the allowable concrete shear stress is exceeded, t
he shear capacity of the
beam ma be increased by adding shear reinforcing such as stirrups.
Other ways of increasing a beams shear capacity include increasing the
concrete strength, and increasing the width or depth of the beam.
Ways to reduce deflecti
on in concrete beams
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the beam wider or deeper.
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In fillet welds, the stress is always considered to be shear stress on the
minimum throat area,
regardless of the direction of the applied load.
The throat area is assumed to be equal to 0.707 times the weld size.
Maximum size of aggregate that can be used depends on the size of
concrete members and the spacing of reinforcing b
Maximum size of aggregate should not exceed 1/5 of the dimension
between sides of forms or 3/4 of the clear spacing between reinforcing bars
Obtaining and handling aggregates larger than 2 or 2.5 inches is usually
The amount of water and cement required for concrete of a given
consistency decreases as the maximum size of coarse aggregate increases.
Reinforcing steel opposite the tension side of a reinforced concrete beam is
called compressive reinforcement, since it is located in the compression
side of the beam and resists compression.
The deflection of concrete members increases with time, beyond
deflection. This additional deflection, caused by shrinkage and creep, can
be reduced by using compressive reinforcement.
As with tensile longitudinal reinforcing, the compressive reinforcement
does not resist shear stress.
Belled caissons are frequently used when the soils near the surface are
relatively poor, but are underlain by dense soils having a high bearing
A special belling attachment is used to enlarge the hole to form a bell
having a diameter of up to
three times that of the drilled shaft.
The purpose of the bell is to provide sufficient bearing area to resist the
applied vertical load.
Is concrete which is permanently loaded so as to cause stresses opposite in
those caused by dead and live loads.
The entire cross
section becomes effective in resisting stress.
Two basic prestressing methods are used
high strength steel is stressed before the concrete is cast
the steel is st
ressed after the concrete is cast
Pretensioned members transfer the prestress force from the steel to the
concrete by bond and therefore require no end anchorages.
Shrinkage of the concrete and creep of the concrete and steel reduce the
rce and must be considered in the design.
Tension / Compression
When a material is stressed in tension or compression, it deforms laterally
as well as longitudinaly.
Under tension, the member increases in length and its cross
Under compression, the length of the member decreases and the
sectional area increases.
The ratio of the unit lateral strain to the unit longitudinal strain is called
Poisson’s ratio. For structural steel, the value of Poisson’s ratio is about
ability of a material to deform non
refers to the capacity of a material to be molded or worked
into a shape.
the ability of a material to return to its original shape after
refers to a material’s resistance to deformation.
Unit stress versus unit strain
Hooke’s Law states that up to the elastic limit, u
nit stress is directly
proportional to unit strain and the diagram will yield a straight line.
The constant ratio of unit stress to unit strain can also be expressed as the
tangent of angle theta
is called the modulus of elasticity.
The point in whic
h the sample continues to increase with no increase in
load is called the yield point.
Increasing the load on the sample will eventually reach the maximum unit
stress which develops before fracture. This is called ultimate strength.
Completely standardized, selected from a catalog, and factory built with
all the necessary components
Often used for single story industrial and warehouse occupancies.
engineered building is likely to be lower in cost than a custom
Factory labor is generally less expensive than field labor.
Quality may be better because greater control is possible under factory
engineered buildings can also be built quicker.
pressure exerted by retained earth against a retaining
lateral pressure exerted by a fluid.
resistance to the movement of a retaining wall
provided by the earth in front of the wall and footin
is the increased lateral earth pressure caused by a
vertical load behind the wall or sloping ground surface.
A retaining wall is necessary whenever the ground elevation changes
The total earth pressure on the stem, for a one foot length of wall, is equal
Hurricane wind speeds usually vary between 30 and 120 mph, with gusts
up to 180 mph.
Rotational speeds of a tornado is estimated
to be nearly 250 mph, and may
occasionally exceed 500 mph.
Measurement of Winds
Wind speed is measured by a device called a revolving cup anemometer.
The maximum average wind speed is called the fastest mile speed.
All wind speed data has been sta
ndardized to a height of 10 meters or 33
When using the wind speed contour map, great attention must be paid to
local wind records and conditions, which may indicate higher basic wind
Areas shown on the map as “special wind regions” have
basic wind speeds so different from those of the surrounding
geographic areas that they are specifically excluded from the map.
Wind speeds in “special wind regions” must be determined from local
A mean recurrence interval of 50 y
ears: means that the fastest mile wind
speed has a two percent probability of occurring in any one year.
Tornados, however, are NOT accounted for on the wind speed map.
Building Response to Wind
Wind creates a negative pressure, or suction, on the le
eward side of the
building, which is the side opposite the windward side, and the side walls
parallel to the wind direction.
The direct wind pressure is also called the stagnation pressure (in psf).
Formula: p = 0.00256(V)2
Doubling the wind velocity
increases the wind pressure four fold.
The terrain surrounding the building has an affect on wind velocity and
Building size and shape also affect wind velocity and pressure.
Buildings of unusual shape, such as domes, o
r with unusual site
conditions, such as at the mouth of a canyon, are not covered by UBC
requirements. Wind tunnel testing may have to be done to determine the
applicable design loads.
The structure must be designed to resist the forces caused by EITHER
wind or earthquake, whichever is greater, in each direction, but not in both
directions acting at the same time.
Basic Formula for Static Analysis: wind pressure on the building (p)=
accounts for the height of the building, the
roughness of the terrain at the building site, and an increase to account
for the gusting effect.
Site exposure is classified as Exposure B, C, or D.
has terrain with buildings, forest, or surface
irregularities, covering at l
east 20% of the ground level area
extending one mile or more from the site.
has terrain which is flat and generally open, extending
half mile or more from the site in any full quadrant.
represents the most severe exposure
in areas with
basic wind speeds of 80 mph or greater and has terrain which is flat
and unobstructed facing large bodies of water over one mile or more
in width relative to any quadrant of the building site. Exposure D
extends inland from the shoreline 1/4
mile or 10 times the building
height, whichever is greater.
is a pressure coefficient for the structure or portion of the
structure under consideration.
The direct pressure on a windward wall is not the same as the suction or
uplift pressure on the roof.
Normal Force Method, the wind pressures normal
(perpendicular) to all external surfaces are determined and are
assumed to act simultaneously.
May be used for any building, and must be used for gabled rigid
For windward walls, the pressure varies with the height.
For inward or outward pressures on roofs and leeward walls, the
factor (Ce) is evaluated at the mean roof height and results in
Projected Area Method, the wind pressures acting on the full
projected horizontal and vertical a
reas of the building are
determined and are assumed to act simultaneously.
Method 2 is limited to buildings less than 200 feet in height,
except those using gabled rigid frames.
(Ce) Factor includes the effects of external pressure or suction,
pressure or suction, and wind drag on the surfaces parallel
to the wind direction.
) factor is the wind stagnation pressure or direct wind pressure at a
standard height of 33 feet, determined from the basic wind speed, or
fastest mile speed, at that
) can be calculated = 0.00256V
(I) factor is the importance factor
similar to that used in earthquake
Dependant on the occupancy category.
Vertical Projected Area = Wall
Horizontal Projected Area = Roof / Floor
d Resisting Systems
Same as those used in earthquake design
Moment resisting frames
The concept of ductility, or the ability of a system to absorb energy in the
inelastic range, is less important for wind design than for earthquake
The stresses in wind design are expected to be in the elastic range, below
the yield point.
Dead load resisting moment must be at least 1
1/2 times the wind
The wind overturning moment may not exceed 2/3 of the dead load
If the columns are adequately anchored to the foundation, the weight of
foundation may be used to increase the dead load resisting moment.
Buildings with a high height
width ratio are most critical for
overturning from wind forces.
Deflection and Drift
The drift between adjacent stories is generally limited to 0.0025 times
the story height.
Diaphragms, collectors, and torsion
Torsion occurs in a rigid diaphragm when the center of mass does not
coincide with the center of rigidity.
Elements and comp
onents of Structures
Higher values for C
factor are used in the design of elements,
components, and discontinuities.