Term
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Definition
| A structure is in static equilibrium if under the action of a set of external forces (gravity, wind, etc.) it remains at rest relative to the earth |
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Term
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Definition
| Ability or capacity to resist external or internal forces, dependent on material |
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Term
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Definition
| Ability of a structural system to resist gross deformation (overturning, sliding, buckling, slenderness ratio) |
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Term
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Definition
| Quality of resistance to deformation (deflection, stress/strain relationship, drift, deformation, compatibility, pounding, etc.) |
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Definition
| The integral attachment of the individual structural members acts to reduce deflections, stress intensities and to preclude failures (tie everything together!) |
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Term
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Definition
| The ability of a system or element to dissipate energy beyond the elastic limit (i.e. not brittle-- example: steel is ductile and concrete is brittle) |
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Term
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Definition
| The concept of multiple load paths providing more than one alternate load path for every load to travel from its point of application to the ultimate point of resistance (as defined by 2000 IBC) |
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Term
| Single-most leading cause of collapse |
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Definition
| Lack of continuous load path |
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Term
| Cardinal principle of structural design |
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Definition
| Providing a continuous load path |
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Term
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Definition
| What establishes how loads (vertical and horizontal) are transferred from their source to various components and cladding, then to main load-carrying systems, and finally to foundation and supporting ground |
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Term
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Definition
| Having defined limits; definite. The condition of having the exact sufficiency of stability externally and internally, therefore being determinable by resolution of forces alone. Em=0, Ex=0, Ey=0 |
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Term
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Definition
| Characterized by an excess of stability conditions. An element or system in which there are not enough equations of equilibrium to solve for the number of unknown reactions. Example: continuous concrete beams because they are monolithic |
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Term
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Definition
| A structure that does not satisfy equations of equilibrium |
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Term
| Determinate/indeterminate vs Stability |
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Definition
| A determinate or indeterminate structure is not necessarily stable. The reactions and/or geometry may not be properly arranged to ensure stability |
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Term
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Definition
| Can only provide resistance in X and Y directions. Can NOT provide resistance to moment or rotation |
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Term
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Definition
| Can provide resistance to forces perpendicular (normal) to the roller. Can NOT provide resistance to moment or rotation or forces that are parallel to the roller |
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Term
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Definition
Provides resistance in X and Y direction as well as to moment and rotation, due to its strength, continuity, and rigidity
Use fixed bases for smaller drifting, especially with brittle surface like curtain wall |
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Term
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Definition
| Provides resistance in X and Y direction as well as to moment and rotation, due to its strength, continuity, and rigidity. *MUST BE CONTINUITY BETWEEN THE COMPONENTS OF THE SYSTEM THAT RESIST BENDING* |
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Term
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Definition
| For steel memebers flanges and beams resist bending, and for concrete members steel resist tensile stresses due to bending |
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Term
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Definition
Can transfer X and Y forces across the splice to adjoining members, cannot transfer moment (no continuity between flanges of members). Example: cantilever beam systems.
Used for *economic* sizing of members and transforms statically indeterminate structure into determinate system
Typically used in roofs since expensive to span length with one member |
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Term
| Advantages of Indeterminate systems |
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Definition
- Greater stiffness
- Lower stress intensities
- Allows for more economical design
- Redundant (which adds safety)
^ The above all due to continuity |
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Term
| Disadvantages of Indeterminate System |
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Definition
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Term
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Definition
| Forces or other actions that result from the weight of all building materials, occupants, and their possessions, environment effects, differential movement, and restrained dimensional changes. |
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Term
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Definition
| Loads in which variations over time are rare or of small magnitude |
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Term
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Definition
| Consist of the weight of all materials of construction incorporated into the bldg including walls, floors, roofs, ceilings, stairways, built-in-partitions, finishes, cladding, and other incorporated architectural and structural items as well as fixed service equipment (including cranes, stacks and rises, HVAC systems, etc) |
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Term
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Definition
Produced during maintenence by workers, equipment and material; AND during life of the structure by moveable objects such as planters and decorative appurtenances not related to occupancy
Typ. 20psf, NEVER less than 12psf |
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Term
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Definition
| Produced by the use and occupancy of the building and DO NOT include dead load, construction load, or environmental loads (wind, snow, rain, eq, or flood) |
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Term
| Two types of load distribution |
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Definition
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Term
| Critical distribution of Loads |
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Definition
| Where structural members are arranged to create continuity, members shall be designed using the loading condtions which would cause max. shear and bending moments |
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Term
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Definition
Floor live loads are permitted to be reduced (for slabs, beams, girders, columns, piers, walls and foundations):
1. No reduction for Group A occupancy (Assembly)
2. No reduction when LL exceeds 100psf [except for columns which can be reduced by 20%]
3. If under 100psf, if trib. area is > 150sf must use equation: R=r(A-150) where r=0.8 for floors |
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Term
| Edge beams vs Interior Beams |
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Definition
Edge Beams: Support less load. Must be rigid since controlled by deflection since often support exterior envelope and need adequate stiffness for brittle finishes
Interior beams: Must be strong enough to support loads |
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Term
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Definition
Considered "true" forces on structure. They increase in magnitude from bottom to top of structure
If wind design produces greater effects than seismic, wind design governs |
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Term
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Definition
Considered pseudo-forces. Forces are considered imparted onto the structure's base. The forces applied to each level are those that if applied to the structure would cause the same displacement of the structure as the ground motion
Displacement-based design |
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Term
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Definition
| Total design lateral force at the base of the structure (V=Cs*w) (base shear=acceleration*mass) |
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Term
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Definition
Provisions shall be made whether or not shown on the CD's and shall not be less than a uniformly distributed live load of 20psf (2003 IBC)
ASCE 7.05: 15psf. Not require'd where min. LL exceeds 80psf *USE THIS ONE*
UBC 1997: uniformly distributed DEAD load of 20psf *DON'T USE THIS ONE* |
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Term
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Definition
Basement, foundation and retaining walls shall be designed to resist these.
Loads increased if soils with expansion potential are present
Surcharge loads are added to lateral earth pressure load.
Loads in pcf or psf/f
Typ. a triangular load |
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Term
| Active vs At Rest Pressure |
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Definition
Basement walls designed for AT REST pressure (restricted at top)
Retaining walls designed for ACTIVE pressure (free at top) |
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Term
| Retaining wall Components and Loads |
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Definition
[image]
Retaining walls should be designed to resist sliding by at least 1.5x lateral forces and 1.5x overturning moment (using allowable stress design loads) |
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Term
| Active Vs. At Rest Pressures |
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Definition
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Term
| Retaining Wall Reinforcement |
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Definition
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Term
| 3 types of concrete beams |
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Definition
Overreinforced [concrete crushes prior to steel yielding]
Balanced [crush and yield simultaneously]
Underreinforced [steel yields before concrete crushes WANT THIS!] |
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Term
| Fixed end Vs Moment connection |
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Definition
Fixed end: restrains translation
Moment: translation is free |
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Term
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Definition
2 hinges: indeterminate and stable
3 hinges: determinate and stable |
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Term
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Definition
| Never used together (only used one at a time) |
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Term
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Definition
Residential: 40psf
Office: 50 psf
Roof: (12-)20 psf
Light storage: 125 psf
Heavy storage: 250 psf
Assembly: 100psf
Egress: 100psf |
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Term
| Tributary Area vs Influence Area |
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Definition
| A point load outside of a column's tributary area can still influence the column loads |
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Term
| Ranking of horizontal members (smallest to largest) |
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Definition
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Term
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Definition
Caused by:
1. un-uniform loads
2. geometry of structure
3. arching action |
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Term
| One-way vs Two-way Construction |
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Definition
Two-way: even lengths on both sides
One-way: loads want to span shorter distance |
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Term
| Retaining walls: Overturning vs Sliding Resistance |
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Definition
Overturning Resistance: self weight of structure and weight of soil
Sliding resistance: passive pressure, friction, and shear key |
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Term
| Factor of Safety for Retaining Walls |
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Definition
1.5
Resistance Moment / Overturning Moment
(RM/OTM) |
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Term
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Definition
| Loads caused by water above or below ground surface, free or confined, stagnant or moving less than 5ft/sec. Loads are equal to water pressure * surface area |
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Term
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Definition
| All new construction within flood hazard areas shall be designed and constructed to resist the effects of flood hazards and flood loads (2003 IBC) |
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Term
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Definition
Any type of wall subject to flooding that is not req'd to provide structural support to a building or other structure that is designed and constructed to collapse under base floor (or less) conditions so that
1. Floodwaters can pass freely
2. It does not damage the structure or foundation |
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Term
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Definition
For roofs less than 5 degrees
Pf= snow load
Ce= exposure factor related to terrain and exposure of roof to wind
Ct= thermal factor
I= importance factor
Pg= ground snow load |
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Term
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Definition
| Leeward typically controls (behind parapet) |
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Term
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Definition
| Each portion of a roof shall be designed to sustain a load of rainwater that will accumulate on it if the primary drainage is blocked, plus the uniform load of water that rises above the inlet of the second draing |
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Term
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Definition
The retention of water due solely to the deflection of relatively flat roofs.
Roofs with less than 1/4" slopes must have adequate stiffness to preclude progressive deflection as rain or snow accumulates.
*Issue of rigidity, not strength* |
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Term
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Definition
V (mi/hr)
3 sec gust at 33ft above ground at Exposure C |
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Term
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Definition
| Cladding, roofing, exterior walls, glazing, door assemblies, window assemblies, skylights, and other enclosure components |
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Term
| Components & Cladding (C&C) |
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Definition
Elements of the building envelope that do not qualify as part of the MWFRS
With trib areas > 700sf use MWFRS |
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Term
| Main Wind-Force Resisting System (MWFRS) |
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Definition
| An assemblage of structural elements assigned to provide stability for the overall structure. The system generally receives wind loading from more than one surface |
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Term
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Definition
The average of the roof eave height and the height of the highest point on the roof surface
If less than 10 degrees, just the roof eave height |
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Term
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Definition
| Based on ground surface roughness determined from topography, vegetation, and constructed facilities. |
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Term
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Definition
US Atlantic OCean and Gulf of Mexico
Hawaii
Puerto Rico
Guam
Virgin Islands
American Samoa |
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Term
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Definition
| Urban and suburban areas, wooded areas, or other terrain with numerous closely spaced obstructions having the size of a single-family dwellings or larger |
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Term
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Definition
| Open terrain with scattered obstructions having heights less than 30'. Includes flat open country, grasslands, and water surfaces in hurriance regions |
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Term
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Definition
| Flat unobstructed areas and water surfaces outside hurricane regions. Includes smooth mud flats, salt flats, and ice |
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Term
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Definition
At isolated hills, ridges and enscarpments constituting abrupt changes in topography, located in any exposure category.
Kzt=1.0 if does not meet conditions |
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Term
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Definition
Shielding: No reductions due to apparent shielding of buildings by other buildings or terrain
Openings: Apertures or holes that allow air to flow through bldg envelope
Building, Simple Diaphragm: Bldg in which windward and leeward wind loads are transmitted through floor and roof diaphragms to same vertical MWFRS (no structural separations)
Building, Low-Rise: enclosed or partially enclosed bldgs where Mean Roof Ht < 60 feet and does not exceed least horizontal dimension |
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Term
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Definition
Enclosed: not following req's for others
Open: at least 80% of wall is open
Ao > .8Ag where Ao=total area of openings that receive positive pressure and Ag=gross area of wall where Ao is
Partially Enclosed: total area of openings receiving pressure exceeds sum of openings in balance of building (walls and roof) by more than 10%
Ao > 1.1Aoi where Aoi=areas of openings not including Ao
AND
Total area of openings that receive positive pressure exceeds 4'2" or 1% of area of wall (whichever smaller) and % of openings doesn't exceed 20%
MULTIPLE CLASSIFICATIONS: If a bldg complies with both open and partial, classified as open |
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Term
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Definition
| Glazing in wind-borne debris regions shall be protected with impact resistance covering or be impact-resistant glazing |
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Term
| Flexible vs Rigid Building |
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Definition
Flexible: slender buildings that have fundamental natural frequency less than 1Hz
Rigid: fundamental frequency greater than or equal to 1Hz
F=1/Tn where Tn is natural period of vibration |
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Term
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Definition
Approximate Building Period=Ta
Ta=Ct*Hn^x
where Hn is height in feet above base to highest level of structure |
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Term
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Definition
q=pressure
Kz=Velocity Pressure
Kzt=Topographic Factor
Kd=Wind directionality factor
V=velocity
I=importance factor
q=.00256*Kz*Kzt*Kd*V^2*I |
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Term
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Definition
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Term
| When to use wind tunnel testing |
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Definition
1. Bldg has shape significantly different than box/rectangular prism
2. Flexible with natural frequencies below 1Hz
3. Subject to buffeting by wake of upwind buildings
4. Subject to accelerated dlow cause by channeling or local topography |
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Term
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Definition
Strike slip (left lateral)
Strike slip (right lateral)
Normal
Reverse (Thrust |
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Term
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Definition
- Compression (P wave) (slinky-like)
- Shear (S wave) (up and down like jump rope, most concerning)
- Love wave
- Rayleigh wave (circular motion under surface) |
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Term
| Seismic Concepts of Damage |
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Definition
Resist minor eq. without damage
Resist moderate eq. without structural damage, possibly some non-structural damage
Resist major eq. without collapse, probably structural and non-structural damage |
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Term
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Definition
Modified Mercalli Intensity Scale
Based on damage and other observed effects on people, buildings and other features. |
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Term
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Definition
Modified Mercalli Intensity Scale
Based on damage and other observed effects on people, buildings and other features. |
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Term
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Definition
Richter Magnitude Scale
Measurement of earthquake strength, based on logarithm to base 10, recorded by seismometer |
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Term
| Response Spectrum Concept |
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Definition
| A practical means of characterizing ground motions and their effects on structures. The response of a building to earthquake ground motion depends on the dynamic characteristics of the building, *specifically the natural period and damping ratio* |
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Term
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Definition
The process by which vibration steadily diminishes in amplitude
Mechanisms that contribute to energy dissipation:
- Friction at steel connections
- Opening and closing of micro-cracks in concrete
- Friction between structures itself and non-structural elements like partition walls
Damping coefficient: Ccr = critical damping coefficient - the smallest value of c that inhibits oscillation completely
Architects typ. only deal with underdamped structures |
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Term
| Static Force Procedure (V=CsW) |
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Definition
W - the effective seismic weight of the structure including dead load and:
1. min. 25% of LL in storage areas
2. Partition loads (min. 10psf)
3. Operating weight of permenant equipment
4. 20% flat roof snow load where snow load > 30psf
Cs=the seismic response coefficient (>0.01)
Cs=Sds/(R/I) and < Cs=Sd1/[T(R/I)] |
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Term
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Definition
Design spectral response acceleration in SHORT PERIOD RANGE
Sds= 2/3 Sms |
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Term
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Definition
Maximum considered earthquake spectral response for short periods, adjusted for site class effects
Sms=FaSs
Fa=coefficient
Ss=mapped maximum considered earthquake spectral response acceleration at short periods |
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Term
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Definition
Design spectral response acceleration at period of 1 second
Sd1=2/3 Sm1 |
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Term
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Definition
Maximum considered earthquake spectral response at periods of 1sec, adjusted for site class effects
Sm1=FvS1 |
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Term
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Definition
A. Hard rock
B. Rock
C. Very dense soil or soft rock
D. Stiff soil
E. Vs < 600ft/sec
F. Site specific reqs
Without geotech report, MUST USE SITE CLASS D |
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Term
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Definition
| Due to vibration and soil pore water pressure, the soil looses is cohesive properties and bearing capabilities |
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Term
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Definition
| Due to vibration and soil pore water pressure, the soil looses is cohesive properties and bearing capabilities |
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Term
| Response Modification Factor "R" |
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Definition
A measure of a system's ductility and overstrength. The greater the value, the more ductile it is and the more drift it will experience
Accounts for:
-ductility
-overstrength
-redundancy
-damping
-past behavior
1.5 (masonry shear walls) to 8 (special moment frames, eccentrically braced frames with welds)
Bearing wall:
-metal/wood wall supporting 100lb/ft + own weight
-concrete/masonry wall supporting 200lbs/ft + own weight |
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Term
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Definition
Load resulting from moving machinery, elevators, craneways, vehicles, or other similar forces and kinetic loads, pressure or surcharge
*All elevator loads shall by increased by 100% for impact |
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Term
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Definition
3 types of unserviceability:
1. Excessive deflections or rotations
2. Excessive vibrations
3. Deterioration
*Lateral deflection from wind does not impair serviceability, though they are concerning
Drift limits usually 1/600 to 1/400 of height |
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Term
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Definition
The design story drift (delta) shall not exceed allowable story drift (delta a)
Delta mx = Cd * delta xe / I
Cd= deflection amplification factor
Delta xe= deflections determined by elastic analysis
I= importance factor
Delta mx < delta a |
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Term
| Allowable Stress Design (ASD) |
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Definition
Loads are NOT factored, conservative
Calculated stresses do not exceed predesignated allowable values (general method for wood, steel, masonry) |
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Term
| Allowable Strength Design (ASD) |
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Definition
Loads are NOT factored, conservative
Used for steel, similar to other ASD |
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Term
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Definition
Factored loads, economical
Multiplying actual loads by desired safety (mostly for concrete)
1.2DL + 1.6LL |
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Term
| Load and Resistance Factor Design (LRFD) |
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Definition
Factored loads, economical
Multiplying actual loads by safety factor (mostly steel)
Strength provided > strength required |
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Term
| Strength Reduction Factor (phi) |
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Definition
Reduce the amount of strength provided for a factor of safety.
Seriousness of failure either to human or goods
Importance of the member in the sturcture
Chance of warning prior to failure
.9 for bending (phi Mn > Mu)
.75 for shear (phi Vn > Vu)
.65 for axial (phi Pn > Pu) |
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