Structural Design Flashcards
What is a Dead Load?
“Vertical Load” type
Any permenant part of the building construction or system, including:
- building structure
- assemblies, finishes, ETC
- mechanical equipment
What is a Live Load?
“Vertical Load” type
Loads imposed on the building by its use or occupants, including
- people
- furniture
- movable equipment
Does NOT include snow loads, which are considered a special transient load.
Distincts from anything can be considered a “concentrated load”.
What is a Concentrated Load?
Any load that would produce a stress on the floor structure which it is unloaded than the stress on the same floor under the uniform load it is designed for.
What are the four major aspects that effect wind load?
Wind Velocity
Either a code-prescribed value or based on climatic data for the region.
Height of Building
The wind velocity is higher at greater height**.
Surroundings
Prescence of nearby buildings, topography, or trees can reduce or alter the wind velocity. Buildings that are out in the open experience higher wind loads.
Configuration of the Building
Including size, shape, orientation, and surface articulation.
What are the two fundamental methods of determining earthquake load on a building?
Static Analysis
Use a prescriptive formulas to determine the shear at various points in the building.
Dynamic Structural Analysis
Use a computer model to determine the precise shear (and other loads) at any point on the building. Use for my complex buildings or when the code-prescribed values make the design impossible or burdonsome.
What are some of the less common types or sources of structural load?
Dynamic Load
- A load that changes radidly and/or is applied suddenly.*
- Automobiles in a parking garage
- Elevator moving through a shaft*
Impact Load
A dynamic that is only applied suddenly.
Resonant Load
A type of dynamic load that occurs rhythmicly. Usually a comparatively small load, but can build over time if the frequency of the force and the load line up.
Temperature Load
A difference in the thermal expansion of two materials that are fixed to each other causes a load.
Soil Load
Pressue of the soil on a foundation or retaining wall. Soil pressue is greater the lower below ground level.
What are some of the unnique code requirements on wood construction to maintain structural strength?
- All wood within 6” of the earth must be treated or of a species that resists decay
- Joists must be at least 18” above exposed ground (or treated or of a species that resists decay)
- Girders entering masonry or concrete must have a 1/2” airspace on the top, sides, and end (or be treated or of a species that resists decay)
- Foundation plates and sills must be treated
- Under-floor areas must be ventillated with not less that 1-SqFt of vent area per 150-SqFt of plan area which are placed to provide cross-ventillation
- All wood members must be protected from exposure to weather
- Firestops are required in walls at ceiling and floors, and at the intersection of any vertical and horizontal space
- Firestops are required at 10ft vertically and horizontally
- Firestops are required concealed spaces, such as at stairways and vertical openings between floors and the roof
What are some of the unique code requirements on concrete to maintain structural strength?
- Formwork and shoring may not be removed until the concrete has reached a strength where it can support all loads on it
- The amount of conduit or other pipes in concrete may not reduce the effective load-resisting volume beyond a certain amount
- Aluminum conduit can only be used when it is treated to prevent electrolytic reaction between Al and concrete or Al and steel.
- Minimum coverage of reinforcement by conceret is specified for exposure to weather and exposure to earth
What are the three fundamental goals of code-imposed requirements for earthquake resistance?
- The building should not collapse during a major seismic event
- Components of the building should not cause damage or personal injury, even if those components are themselved damaged by the seismic event
- The building and its components should not be damaged by minor seismic events
What are the three types of seismic analysis allowed by cuilding code? When, generally, is each allowed to be used?
Simplified Analysis
Use code-prescribed forces and formulas to determine the forces that must be accounted for
- Only allowed in:
- Seismic Design Cat A*
- Seismic Design Cat B for 3-story, light-framed buildings
- Seismic Design Cat B and Use Group I for any 2-story buildings*
Equivalent Lateral Force
Used the shear at the base of the building to get the equivalent lateral force at each level of the building.
- Only allowed in:
- Seismic Design Cat A, B, and C
- Seismic Design Cat D, E, and F if :
- the building is of a regular shape and has fundamental period meeting certain requirements
- the building is of an irregular shape, has a fundamental period meeting certain requirements, and only has certain allowable types of plan and vertical irregularities*
Dynamic Analysis
Uses a 3D model and computation to accurately model the seismic forces on the building
May be used in any Seismic Design Cat or Seismic Use Group.
What is “ductility” when it comes to a building’s seismic strength?
The ability of a building to absorb seismic energy. This energy absorption occurs when the buiding deflects elastically without failing.
What are the four categories of seismic-resisting systems that the code allows?
Bearing Wall System
Lateral forces are resisted by shear walls. Not (distinct from) a space frame, in which the entire vertical space of the buliding is encompassed. Instead, bearing walls are strategically placed within the building.
Building Frame System
Lateral forces are resisted by space frames. Lateral forces are converted into axial forces on the members of the frames, either one-diagonal compression members or two-diagonal tension members.
Moment-Resisting Frame System
Lateral forces are resisted by moments frames in which the members and connections are rigidly attached. Lateral forces are converted into bending in the members. The code has different requirements on when different classes of moment frames can be used, their detailing requirements, and whether they can be steel or concrete, all depending on the Seismic Design Cat.
Dual System
Gravity loads are resisted by a typical frame system, and lateral loads are resited by strategic placement of shear walls, brace frames, and/or moment frames.
What is a “re-entrant” in building configuration? What is it’s implication on seismic design? How, generally, can these implication be mitigated?
Any plan configuration that results in a ‘corner’.
In can both concentrate lateral and shear forces as well as generate major torsional forces.
General ways to mitigate these concentrations and torsions:
- place seismic isolation joints between ‘arms’ of the building
- over-run the structural systems of both ‘arms’
- splay the corner to and tie the structural across
What are the Seismic Design Categories and the Seismic Use Groups?
Design Categories
Basically a ‘risk category’ based on a building’s geopraghic location. Based on the frequency and intensity of earthquakes in an area. The US is divided into categories A-F, with F being the highest risk.
Use Groups
- Classification of a building based on potential risk to inhabitants and importance during a seismic event.*
- Group III: buildings that has must remain habitable and functional after a seismic event. Includes building with essential functions (EG, hospitals) or buildings that house hazardous substances or functions.*
- Group II: buildings that pose significant risk to inbahitants if they were to fail (EG, housing, power plants, ETC).
- Group I: buildings not included in the other two groups*
