Quiz Flashcards
What are the two types of methods ASCE uses to calculate pressures on buildings ?
Normal force method - which must be used for gables rigid frames and may be used for any structures
Projected area method - assumes that horizontal pressures act on the full vertical projected area of the structure and that vertical pressures act simultaneously on the full horizontal projected area.
What is a girt
It is a structural wind member similar to a purloin on the roof
Buildings suffer the greatest damage at what frequency ?
Ground motion at a frequency close to or equal to their natural frequency
What is the difference between ASD and LRFD?
ASD uses service loads or loads given from the book
LRFD uses factored loads or loads that have been increased from the service load
It includes an ultimate load:
U: 1.2(dead load) +1.6 (live load)
How is does a two way flat slab work ?
It does not have a grid or beams under the slap and does not need temperature reinforcing. It accommodates large loads such as 30’x30’ and reduces punching shear by incorporating drop panel or a capital at the columns
What are the two irregularities outright banned by code ?
Extreme soft stories and extreme torsion in essential buildings in high seismic zones
Buildings must be designed to resist
wind or earthquake forces but not at the same time
A thin shell structure is able to resist what forces?
Shear, tension and compression but not bending
Where is wind pressure the highest on a building ?
Corners , overhangs, parapets
How does the dead load effect lateral forces ?
The dead load directly is proportional to seismic forces
The dead load does not effect wind forces
Charpy V-notch Test
A ductility test where a piece of material has a v-notch cut into the top. Tests how much energy it takes to make the not good go through the whole piece.
When bending is low shear is?
High
How much more load does a column half the length take then a full size column ?
8 times stiffer ( the stiffness of a column varies by the inverse of the cube of the length
How is a two-way beam slab used ?
A two way reinforced slab between four beans and that spans a square. Usually 40x40 span.
What org gives the allowable unit stresses for wood ?
National design specification for wood construction
What is the maximum drift allowed for a building ?
1/500
What is considered a Risk Catergory IV
These are buildings that are considered essential in that their continuous use is needed. They are usually needed in instances or medical, seismic, or fire emergencies
How is a two way flat plate used ?
Typically found in high rise, residential and light loads. Usually 20x20 and up to 30x30. No need for temperature reinforcing
How do you increase the section modulus of a member?
Increasing the amount of material away from the neutral axis of the member …i.e. make it deeper
What does the IBC require that drift be limited in typical buildings
0.02 and 0.01
What are theee solutions to the soft story?
Add columns,
Add bracing,
Add external buttresses
What are one-way structural systems?
Beam-and-girder system
Concrete joist system
Axial loads are more efficient in use of material in what direction to the load
Perpendicular
What is the minimum concrete coverage for a footing?
3”
The earthquake regulations of the IBC are intended to provided resistance to?
ground shaking
Frequency is the inverse of period
A 20 story building
Period = 2.0
Frequency = 1/2
.5 hertz
What are the benefits of using space frame over one-way parallel trusses?
the space frame tends to deflect less,
the space frame can be shallower
the loads are resisted by all members if the space frame
the space frame spans in two directions
What does the IBC in regards to handrails?
Handrails and guard rails shall be designed to resist a linear load of 50 pounds per linear foot.
What is the duration of the allowable design loads based on normal duration of loads
10 years
What is the natural period of most low-rise buildings ?
The natural period will be relatively short
What is considered a Risk Category II ?
Buildings and other structures except those in I, III, and IV
The wind pressures used in the design of buildings depend on?
wind speed
terrain
occupancy category
the part of the building under consideration
What is the maximum height for buildings in SDC D
no limit
What does the IBC say in terms of landscaped roofs ?
The uniform design live load in unoccupied landscaped areas on roofs shall be 20 psf
space frames are
highly undetermited
What are the effects on a building closer to the fault line ?
It will experience higher frequency and shorter period ground motion
What type of load is post and beam unable to support?
Lateral load
What does the IBC say about partition loads?
The partition load shall not be less than a uniformly distributed live load of 15psf if the uniform live load is 80psf or less
In regards to wind loads when must a building be approved by wind tunnel testing procedures ?
Buildings over 400ft in height
When can you reduce the live load?
The tributary area is greater than 150 sqft
The live load is less than or equal to 100psf ( not an assembly ) or the building does not support one floor of parking garage
The reduced live load must be greater than 50% of the original live load
Can a moment connection be made with wood ?
No
What is sin, cos, tan?
Rise, run, slope
The allowable shear in plywood is based on what?
The plywood grade
Nail size and spacing
Width of framing members
What concepts have been developed for strengthening existing construction ?
Add strength , alter stiffness , add continuity, add containment, rationalize the existing capacity and isolate the building from the ground
The shape that s cable assumes when the only load acting on it is its own weight ?
Catenary
Abrupt changes in topo can cause wind speeds to increase
Don’t locate building on upper half of a hill
What three properties help reduce seismic induced forces?
Damping , ductility , strength and stiffness
What does the IBC say in terms of wood ?
Bottom wood joist at least 18 in above ground
Ends of wood girders provide .5 in air gap
Crawl spaces provide 1ft bet area for ventilation
When can the repetitive use factor (Cr) or 1.15 be used ?
When the members are not over 4 in thick, not spaces more than 24 in oc And must be joined by bridging or decking ( three members in a group)
What are the requirements for columns in Type IV ?
Columns must be at least 8 in in any direction, brand and girders must be at least 6 in wide and 10 in deep and floor decking must be at least 3 in thick.
What is the difference between a connection on the web vs a bolt connection on the flange of steel?
Web = pin connection /shear
Flange = pin connection / moment
What does the IBC say in regards to decks?
Where supported by attachment to an exterior wall, decks shall be positively anchored to the primary structure and designed for north vertical and lateral loads as applicable. There should be no use of toenails or nails subject to withdrawal.
Earthquake damage tends to be more severe in areas of ?
Soft ground
How many reactions in each support ?
Roller = 1 vertical reaction Pin = 2 vertical and horizontal Fixed = 3 vertical, horizontal, and moment/rotation
what type of diagram is the same as a stress diagram?
Maxwell
How does the fundamental period of vibration of a building affect its seismic load?
the longer the period the smaller the seismic load. A longer period means a more flexible building.
What is considered a Risk Category III?
Buildings that represent a substantial hazard to human life in the event of failure. Like schools, colleges, public assemblies
What does the IBC say in terms of interior walls and partitions ?
Interior walls and partitions that exceed 6 ft in height including their finish materials shall have adequate strength to resist the loads to which they are subjected but not less than a horizontal load of 5psf
What is a another name for shear studs ?
Nelson studs
What is considered a Risk Category I?
Low hazard buildings
Is a lamella structure one way or two way ?
One way
An arch supports load by ?
A combination of compression and bending
Where are stirrups in relation to the suppers ?
More stirrups at the support
What is the reference height of the basic wind speed?
33 ft
What does the IBC in terms of dynamic and static lateral forces ?
The dynamic method is always permitted while the static method is only allowed under certain conditions
What does the IBC say in terms of the reduction of live loads?
Live loads that exceeds 100psf shall not be reduced. The live loads for members supporting two or more floors are permitted to be reduced by a max of 20%
What makes a Vierendeel truss different from a regular truss?
It has rigid joints not pinned.
It resists bending movements not axial loads
It resists shear forces.
What does the IBC say about dead loads?
First floors in office buildings where partition locations are subject to change must be designed to support a uniformly distributed load of 20psf. Access floor systems may be designed to support an additional 10psf of uniformly distributed dead load over all other loads
__________ states that up to the elastic limit, unit stress is directly proportional to unit strain.
Hookes Law
What does the IBC require for concrete strength tests?
Samples must be not less than once per day, once per 150 cubed yards, once for each 5000 sqft the result cannot be less than 500psi
What are the various gradient heights for wind speed?
900 ft country
1200 suburban
1500 city
Why are stirrups used in reinforced concrete construction ?
To provide web reinforcement where the concrete is overstressed in shear
What is the difference between a flexible diaphragm and a rigid diaphragm ?
A flexible diaphragm is seen as a simple beam which translates to vertical resisting elements
A rigid diaphragm distributes horizontal forces to the vertical resisting elements in proportion to their rigidities.
How can you make a concrete beam more resistive to deflection?
Increase the moment or inertia by making the beam deeper
Increase the modulus of elasticity by using higher strength concrete or adding more reinforcing steel
Buildings with long periods have what advantage ?
Low accelerations and low seismic forces
What is the most effective way to protect a residential building from structural damage ?
Include anchor bolts between the mud silk and the foundation
What is commonly referred to as ‘shear stress’ is technically a form of ________________.
Diagonal tension stress
What is the basic wind speed in the country? What is the average gust speed to cause damage ?
Basic wind speed 90mph
Peak gust to cause damage 70-80mph
What are some solutions to reentrant corners?
Separate the two building components
Strengthen the notch
Add stiffeners to the ends
What does the IBC say in terms of intermediate rails ?
Intermediate rails, balusters and panel fillers shall be designed to resist a concentrated loss of 50 pounds
At what length of a truss, according to the IBC must steel be cambered ?
80 ft be cambered for the dead load deflection
Irregular configurations cause what type of problems for buildings ?
Torsion
Stress concentration
Which of the following are methods by which pressures for various types of buildings are calculated?
Normal force method
Projected area method
How is a one way Pan joist system used ?
40’-60’ range covering rectangular bays
How is a two way waffle slab system used ?
Most economical 40x40 but up to 60x60 . It is the equivalent of a two way pan system
What are the four serious configuration conditions ?
Soft and weak stories Discontinuous shear walls Variations in perimeter strength and stiffness Reentrant corners Perforated shear walls
How much moment is there at the point of inflection ?
None / zero moment
the basic stress in an arch is?
compression
How much greater is a taller buildings period ?
A factor of 0.8 or an increase by 75 %
What are the reasons for cover in concrete ?
Fire protection Corrosion of rebar Embedment (bonding concrete and rebar) Life safety (concrete and rebar fail simultaneously ) Rebar should yield before concrete fails
A(n) ________ is a structure with a curved surface that supports load by compression, shear, or tension in its own plane, but which is too thin to resist any bending stresses.
Shell
What does the IBC say about concentrated load for railings ?
Handrails and guardrails shall be designed to resist a concentrated loss of 200 lbs
What are the various life load reduction methods ?
No live load reduction on life safety/ assembly
- if tributary area is over 150sqft
- If LL is less than Or equal to 100#/sqft
- Reduced LL must be greater than 50% of original LL
What are the categories of moment-resisting frame?
IMRF – Intermediate moment-resisting frame
OMRF – Ordinary moment-resisting frame
SMRF – Steel moment-resisting frame
Section modulus is a measure of a beams?
Bending strength
What does the IBC say in terms of grab bars, shower seats, and benches?
They should resist a single concentrated load of 250 lbs in any direction
What are the exposure categories ?
Exposure B: buildings with an average height of 30ft / surface roughness b( Urban and suburban)
Exposure C: everything besides B or D
Exposure D: or surface roughness D ( flat, unobstructed )
Steel joists are to meet the deflection limitations in what ?
Steel Joist Institute (SJI)
What is the suggested limit of drift between adjacent stories?
0.0025 times the story height
What is the allowable beam deflection for live loads on roofs and floors?
1/360
What is the allowable beam deflection for dead loads and live loads on roofs and floors?
1/240
How many reactions equal a stable and determinate reaction?
2: unstable
3: stable and determinate
4: indeterminate
What is the minimum hoist bearing requirements on steel beam and masonry/concrete walls?
2.5” for steel beams
4” for masonry / concrete wall
What would be the reasoning for coping a steel beam?
To allow the top of the beams and girders to be flung which allows the steel deck to be level.
What is required according to building code when renovating, remodeling, and additions to existing building ?
Seismic strengthening is required according to the building code.
Ductility of steel is referred to the deformation of ?
Tensile stresses
What is the height limitation for a gravity retaining wall?
8ft
What is the height limitation for a cantilever retaining wall?
20 ft
What is the minimum factor of safety against sliding ?
1.5
What is the role of link beams in eccentric bracing ?
Link beans add ductility to the system. Under earthquake movements the link beam distorts and dissipates the earthquake energy in a controlled manner this protecting the rest of the structure.
What are the three categories of code policies and regulations for the seismic evaluation and retrofit of existing buildings ?
Passive Code Provisions
Active Code Provisions
Post-Earthquake Code Provisions
What is the Passive Code Provision?
They represent the minimum seismic standards for existing buildings. The owners are required to retrofit their buildings as part of the remodeling or addition.
What is the Active Code Provision?
This is a result of a policy decision of a jurisdiction to reduce seismic risk by requiring seismic upgrades in a certain community.
What is the Post-Earthquake Code Provision ?
Following a strong earthquake many buildings can be closed for evaluation and needed repairs. Buildings that get tagged yellow or red are requires to be seismically retrofitted.
What type of existing structures are the most vulnerable to seismic damage?
Unreinforced masonry and tilt up construction
The design earthquake load depends on what factors ?
Site conditions
Building location
Occupancy type
Space frames can be made of what materials?
Steel
Aluminum
Wood
The effective length of a column depends on ?
Rigidity of members connected to the columns ends, columns end conditions, and columns length
What is the design wind pressure based on ?
Building location
Building height
And building importance
What does the IBC say in terms of rebar?
The area of longitudinal reinforcement must be at least 1 percent of the cross sectional area of the column
What are the advantages of continuous beams over simple beams ?
Less deflection
Lower moment
What determines the factor of safety against overturning for a building subjected to wind loads?
Building height
Building width
Building wind pressure
Building weight
What is the percentage of increase in the design live loss of a floor or balcony due to impact ?
33%
What is the maximum factor by which the span of the joist may not exceed the nominal depth ?
L/24
What is the difference between reinforced concrete spiral columns as compared to tied columns ?
Spiral columns have greater allowable axial loads than their ties column counterparts
How does beam deflection relate to moment of inertia?
To reduce deflection, the moment of inertia has to be increased.
What does the wind stagnation pressure (qs) depend on?
Basic wind speed
What is the primary goal of seismic rehabilitation in standard Occupancy?
Provided for safety by minimizing the collapse exposure
Poorly constructed buildings in earthquake prone regions begin to suffer damage at what acceleration ?
10%
What is the typical damping ratio assumed for buildings in earthquake prone regions?
5%
Unreinforced masonry construction was outlawed for high seismic zones starting with which addition of building code?
1933
How often are concrete slump tests performed?
50ft^3
What is the level of earthquake forces considered for the retrofit of existing old buildings in seismic regions?
75% of forces for new buildings
The non-structural components and systems must be seismically retrofitted to at least what level of force as compared to that of the structure?
The same level
________ is the lowest stress that produces a permanent deformation in a material.
yield strength is the material property defined as the stress at which a material begins to deform plastically. Prior to the yield point the material will deform elastically and will return to its original shape when the applied stress is removed.
What does the k in the slenderness ratio stand for?
k is a constant determined by the degree of fixity at the ends of the column
What is the span of different types of open web steel joists ?
K-Series 60 ft span
LH-Series 96 ft span
DLH-Series 144 ft span
What is the difference between the static method and the design method?
The dynamic method is always permitted and the static method is permitted case by case.
How does wind relate to lateral resisting pressures?
Wind is an actual surface applied force.
The dead load does not affect the wind force.
Seismic forces are simulated forces. Seismic forces depend on dead load and the type of lateral resisting system.
Which loads are combined with seismic loads for strength design combinations?
Dead Load
Floor Live Load
Snow Load
What are the advantages of a space frame?
They can be shallower than one way trusses, tend to deflect less, loads are resisted by all members, two way span.
The deflection of a reinforced concrete beam is affected by what?
The load supported by the beam The duration of the load The span of the beam The moment of inertia of the beam section The strength of the concrete
What is the purpose of stirrups?
To resist shear stress
Infilling a moment resistant frame with a nonstructural frame causes what?
A stiffened frame which attracts more load.
The capacity of a wood column is determined by what?
The modulus of elasticity of the wood The species The compression design value the unbraced height of the column The dimension of the column section
What are three methods to splicing reinforcing bars?
Lapped
Welded
Mechanical Connections
How does a shell structure work?
A shell structure resists compression, tension, and shear in its own plane. It is too thin to resist concentrated loads nor substantial bending.
The IBC regulates what for earthquake loads?
Building configurations
Occupancy categories
Soil characteristics
The purpose of earthquake regulations by the IBC is what?
to safeguard against major failures and loss of life.
Which material has the lowest coefficient of thermal expansion out of wood, concrete and steel ?
Wood
The resistance to sliding of a retaining wall should equal what?
1.5 times the total lateral pressure of the retained earth
What is the minimum concrete cover for slabs and walls?
0.75”
Reinforced concrete beams and slab are designed for crushing or yielding first in failure?
They are designed for yielding so that their failure occurs by yielding of steel in tension rather than crushing of concrete in compression. We proportion the beam to be under reinforced. We do not prefer a over reinforced or balanced section.
What is the minimum concrete cover for concrete beams?
1.5” interior
2” exterior
How do you increase the factor of safety against sliding ?
Increase the length of the heel or use a shear key
What does ductility rely on ?
Member proportions, end conditions, and connection details
What are the three techniques for Lateral Load Resistance Enhancements ?
Base Isolation System
Added Damping System
Tuned Mass Damper
What are methods of mitigation for liquefaction ?
Avoid the site
Site compaction
Change soil
Dewater the site
What is the order of qualifiers for the response modification factor,R from high to low
Special
Intermediate
Ordinary
What is included in the seismic importance factor of 1.5 ?
Components used for life-safety after an earthquake (sprinklers)
Components containing hazardous materials
Components in or attached to an essential facility
Non structural components and systems must be seismically retrofitted to what level in comparison to the structure ?
The same level as the structure.
What are the four types of hazards presented by non structural components?
Direct and Indirect hazards (damaged materials )
Loss of critical function (loss of power)
Release of hazardous material
Fire caused by non-structural damage
How can precast panels be seismically retrofitted ?
The use of push-pull connections
How can suspended ceilings be seismically retrofitted ?
With the use of vertical struts made of metal conduit of angles.
What are the three basic categories of measure to retrofit an existing building ?
Decrease drift
Increase deformation capacity
Strengthen the connectivity of elements
What are the five basic issues related to seismic retrofit that are a concern to building owners ?
Seismic performance
Construction costs
Disruption to the building users during construction
Long-term effects on building space planning
Aesthetics
The modulus of elasticity of concrete increases as ?
It’s unit weight increases
It’s strength increases
The change of length that a member undergoes when loaded axially depends on what?
The magnitude of the load
The length of the member
The cross-sectional area of the member
The modulus of elasticity
The wind design regulations in the IBC consider ?
Exposure
Gusting
And hurricanes
What are the advantages of stub girder framing systems ?
Reduced weight of steel
Reduced story height
Simplified steel erection
Ease of providing simulated continuity for floor beams
What is the minimum distance from the top or bottom of joists for a notch according to IBC?
2 inches
What are the regulated Load increases for various structures ?
The weight of elevator machinery to allow for impact: 100%
Light machinery: 20%
Power driven machinery: 50%
Hangers for floors or balconies: 33%
