04 Flashcards
T-Beam Action
In reinforced concrete design with a monolithic beam/slab condition, part of the slab becomes the compressive flange and contributes to the load resistance of the beam.
Force Couple
Two parallel forces of equal magnitude, but opposite sense, that are displaced by distance.
Liquefaction
When soils behave like liquids, losing the ability to support structures.
Effective Span
Clear Span
The distance between the centerlines of the supports of a span.
The distance between the inside faces of the supports of a span.
Zero Force Member
A member in a truss that takes no load.
Woods for Structural Use
Fir, pine, spruce, redwood, cedar, hemlock, and larch.
Larger sections of wood shrink proportionately ________ (less/more) than smaller sections of lumber.
Less.
Wood is strongest when loaded _________ (perpendicular/parallel) to the grain.
Parallel; however, wood is often loaded perpendicular to the grain, as in a beam.
Dressed Lumber
Lumber that has been surfaced by a planar.
Rough Lumber
Lumber that has been cut into board shapes and sizes but has not been planed.
Dimension Lumber
2-by and 4-by lumber; joists, rafters, studs, etc.
Timber
Lumber 5 inches or more in least dimension; beams, posts, purlins, etc.
Section Modulus
A property of a material’s cross-section, it is the moment of inertia divided by the distance from the neutral axis to the extreme fiber.
Engineered Wood
Any of various products manufactured by taking strands, veneers, fibers, or other parts of wood and bonding them together for a composite product; includes plywood, OSB, glulams, paralams, microlams, LVLs, particleboard, and cross-laminated timber.
Mild Steel
Rolled structural steel. Typically referred to as “I beams”.
Principal disadvantages of steel
- Loss of strength when exposed to fire
- Rusting
- Cost
Principal advantages of steel
- Immense strength
- Flexibility (can sway under seismic loads)
- Ductility (deforms before fracturing)
Steel Shapes
Bar, plate, rod, tube (square), pipe (round), structural shapes such as wide-flange, channels, and angles.
Cold Rolled
Steel that has been rolled at room temperature. It has closer dimensional tolerances and smoother surfaces than hot-rolled steel and is more expensive. Cold rolled steel is first hot rolled into a general shape.
Hot Rolled
Steel that has been shaped through a roller at high temperatures and then cooled. It is easier to form and less expensive than cold rolled steel.
Ways to shape metal
Rolling, extruding, casting, forging, stamping, and drawing.
How to read a wide-flange steel shape designation.
For W 12 x 26, W is the shape (W stands for wide-flange), 12 is the depth in nominal inches (actual depth of this section is 12.22 inches), 26 means the steel shape weighs 26 pounds per linear foot.
Steel-Bearing Plates
Steel beams typically sit on steel bearing plates. The plate provides a level surface for bearing, helps distribute the load over a larger area, and helps with setting the beam at the proper bearing height.
Built-Up Section
Forms a structural member by combining two or more structural steel shapes.
Pipe and tube structural steel is best for columns in ______ (single-story/multi-story) buildings.
Single story. This is because the spanning members can sit on top of the columns and not have to connect to the side. Wide-flange beams are most useful for multi-story buildings, where beams are attached to the sides of columns.
Free-Body Diagram
A diagram of a body that shows the external forces with the magnitude and angle of all the forces. Also called a force diagram.
normal
“Normal” means perpendicular in physics.
Area of a Circle
A = π r2.
External loads on a body cause it to elongate or shorten. What is this called?
Deformation or strain.
Resistance to deformation is due to _______.
The modulus of elasticity, which is the measure of a material’s stiffness.
The _______ is the point at which a material continues to stretch with no increase in load.
Yield point.
Hooke’s Law
States that stress is proportional to strain, up to the elastic limit.
Young’s Modulus
A measure of the stiffness of a material; also known as the elastic modulus or modulus of elasticity.
The cable of a uniformly supported suspension bridge hangs in the form of a(n) ________.
Parabola.
Circumference of a Circle
C = 2πr.
Cast Iron
A brittle ferrous metal with large amounts of carbon and impurities. Pipes are sometimes made from cast iron.
Wrought Iron
Ferrous metal with low carbon content. Malleable, ductile, and corrosion resistant. Can be welded. The Eiffel Tower is made of wrought iron.
Area of a Triangle
A = 1/2 x base x height.
Considerations of the effects of wind
Magnitude of sustained velocities; duration of gusts; gust effects such as swirling; and prevailing wind direction.
Resonant Loading
Winds can make buildings oscillate side to side, the forces of which are called resonant or oscillating loads.
Story Drift
Horizontal deflection of a single story relative to the story above or below. Story drift is due to wind or earthquake forces. Not specified in the IBC but often limited to 0.005 or 0.0025 times the story height.
Special Wind Region
Wind is affected by local topography and climate such as that near open water or mountains. These areas often have local wind design considerations.
Restoring Moment
Resists overturning moment
Wind Speeds
10 mph: mild breeze;
25 mph: stiff breeze;
50 mph: strong gale
General effects of wind on objects
Big Three: 1. Direct Positive Pressure
2. Drag
3. Negative Pressure (aka, suction on the leeward side)
Also rocking effects (wind is not a constant velocity), harmonic effects (vibration, flutter, whistling), and clean-off effect (the impact of wind on protruding objects such as equipment, canopies, and signs). Wind damage can be local or total. Damage can be collapse, roll-over, or uplifting. Factors include the nature of the wind, nature of the object (size, shape, period, stiffness of surfaces, and strength of connections), and nature of the environs (sheltering and funneling).
Specific effects of wind on objects
Inward pressure on exterior walls, suction on exterior walls, pressure on roof surfaces (inward and outward), overall horizontal force (the reason we need lateral resistance), horizontal sliding force (the building sliding off the foundation), overturning, wind design for specific building parts such as protruding elements, harmonic effects, effect of openings and “cups” (particularly band shell structures and similar forms), and torsional effects due to asymmetry. In addition to buildings, freestanding exterior walls and signs must be designed for wind resistance.
Simplifying wind design
Most buildings are box-shaped, which results in a typical aerodynamic response. Most buildings have closed, relatively smooth surfaces. Most buildings are snug to the ground where the earth creates drag. Most buildings are relatively stiff, and there is a relatively limited range of building periods.
Wind Exposure A, B, C, and D
Exposure A is legacy.
Exposure B is for sites in urban and suburban areas, wooded areas or other areas where there is terrain with numerous closely spaced obstructions.
Exposure C is for sites of open terrain, such as flatlands and grasslands.
Exposure D is for sites next to open water, unbroken ice or salt flats.
Overturning Effect
Can apply to the building as a whole or parts.
Fastest Mile
The old way of measuring wind speeds (prior to 1998). Now it is the 3-second gust.
3-Second Gust
The 3-second gust speed at 33 feet above the ground in exposure category C is used to determine the basic wind speed (V) for building design.
Highest recorded surface wind speed
About 300 mph (during a tornado).
Most important tables in the code to know for PDD case studies
Table 503 Allowable Building Heights and Areas
Table 601 Fire-Resistance Rating Requirements for Building Elements (hours)
Table 602 Fire-Resistance Rating Requirements for Exterior Walls
Table 716.5 Opening Fire Protection Assemblies, Ratings, and Markings
Most important chapters in the code to know for PDD case studies
Chapter 3 Use and Occupancy Classification
Chapter 4 Special Detailed Requirements Based on Use and Occupancy
Chapter 5 General Building Heights and Areas
Chapter 9 Fire Protection Systems
Chapter 10 Means of Egress
Chapter 11 Accessibility
Chapter 12 Interior Environment
Split Slab
In contrast to a solid slab, which acts as both the structural support and traffic surface for a floor, a split slab separates these two functions into two parts. The lower part is a structural slab, which carries the necessary loads. A waterproofing membrane is placed above this element to separate it from the topping slab. The topping slab is then placed on top of the waterproofing membrane. Split slab construction allows the waterproofing layer to be protected from traffic by the topping slab.
Cold-Formed Metal Framing
Steel metal studs that are manufactured by bending sheet metal at room temperature; contrasts with hot-rolled steel. Cold-formed metal framing, also called light gauge metal framing, is used as a non-combustible alternative to wood studs.
Two main classifications of loads
- Gravity loads 2. Lateral loads
Examples of gravity loads
Dead load, live load, rain load, and snow load.
Examples of lateral loads
Wind load, earthquake load, and other lateral loads.
Design Wind Speed
Used in determining the design wind loads on buildings. If the basic wind speed has a 2% annual probability of being exceeded, this is a 50-year recurring value.
Factors that affect wind loads
- Height above ground
- Exposure classification of the site
- Topography of the site
- Enclosure classification of the building
- Importance of the building’s occupancy
Site Exposure Category B
Urban and suburban areas, wooded areas or other terrain with numerous closely spaced obstructions.
Site Exposure Category C
An open country or grassland location.
Site Exposure Category D
A flat, unobstructed site facing a large water body.
Partially Enclosed Structures
These include buildings in which the area of openings in one wall is much larger than that of the remaining walls, like for airport hangars or warehouses with docks.
Escarpment
A long, steep slope, separating areas of land at different heights. It increases wind speed, and thus wind loads on buildings.
Soil Liquefaction
This occurs in water-saturated, sandy soils where particle sizes of sand are relatively uniform in size. This results in a loss of foundation support for buildings with construction on top.
Richter Scale
Scale most commonly used to measure the intensity of earthquakes.
Tectonic Plates
Tectonic Plates
Earth’s crust is divided into several individual segments and these segments float on a molten mantel below and are constantly in motion relative to each other.
Factors that affect earthquake loads
- Ground motion
- Building mass and ductility of structural frame
- Type of soil
- Importance of buildings
Material weight relative to earthquake loads
Lighter buildings attract smaller earthquake loads; concrete and masonry framed buildings attract larger loads than those made from wood or steel.
True or false? Buildings are designed to resist wind and earthquake loads.
False. Buildings are designed to wind or earthquake loads, whichever causes the greatest effect. In regions with low seismic activities, buildings are designed for wind.
Seismic Risk Category IV
Most important or hazardous buildings including: police stations, water-treatment facilities, and fire stations. Reference IBC Table 1604.5.
Seismic Group II
Important or hazardous buildings: schools, health-care facilities, and power-generating stations.
Seismic Group III
Normal buildings that do not belong in group I or II.
Tributary area of a building component
Area of a building that contributes to a load on a specific component, like a column.
Brittle Material
A material that deforms little before failure. This type of material is generally stronger in compression than in tension.
Buckling
Type of failure that results in the sudden bending of a slender structural member subjected to excessive loading.
Beamless Floor
A reinforced-concrete slab supported directly on columns without supporting beams.
Centering
Temporary framework for constructing an arch, vault, or dome.
Basic Wind Speed
Peak 3-second gust wind speed with a 50-year recurrence interval, used to determine wind loads on a building.
Elevated Slab
An above-ground floor or roof slab, supported on columns and/or beams and forming an integral part of a structural frame.
Insulating Concrete
Lightweight concrete consisting of portland cement, water, and expanded aggregate, primarily used as low-slop roof insulation.
Hollow Structural Section
Square or rectangular tubular steel section used as columns or beams in a steel frame structure or as components of a steel truss.
One-Way Slab
An elevated reinforced concrete slab where most of the load on the slab is carried to the supporting beams in one direction; a four-sided, supported rectangular slab whose length is greater than or equal to twice its width.
Pilaster
A column formed by thickening an area of a masonry or concrete wall.
Primary Reinforcement
Steel reinforcement in a one-way concrete slab oriented in the direction that carries most of the loads.
Secondary Reinforcement
Reinforcement in a one-way concrete slab placed perpendicular to primary reinforcement.
Internally Braced Frame
Shear walls, diagonal bracing, and knee braces that are used to resist lateral loads from within a structure.
Externally Braced Frame
The use of external sources of lateral bracing such as guylines, struts, and buttresses.
Eccentrically Braced Frame
When one or both ends of the lateral bracing for a structure do not join the end points of other members. Eccentric bracing is the opposite of concentric bracing. Knee bracing is an example of eccentric bracing.
Will braced frame members work in tension, compression, or both?
Both
True or false? Roof slabs are typically designed to be stronger than floor slabs because of the added forces of wind and snow.
False. Roof structures are typically lighter construction than floor structures.
Three-Hinged Structure
A gable roof where members are supported only by one another at the top is called a three-hinged structure. It requires additional support, such as collar ties or ceiling joists, to keep the rafters from collapsing.
Collar Tie
In a small, pitched roof formed by two planes of inclined rafters, collar ties are the horizontal framing members that tie the rafter together near the top to reduce outward thrust on the rafters.
Ridge Beam
In a gabled roof, a ridge beam is the horizontal member that the upper end of rafters can be supported on, eliminating the outward thrust of the rafters on the lower walls.
Wind Speed Maps
Published by the American Society of Civil Engineers (ASCE) and incorporated into building codes, wind speed maps are continuously updated. The current version is the ASCE 7-10.
True or false? Concrete and reinforcing steel have similar coefficients of thermal expansion.
True
Effective Length Factor (K Factor)
The effective length factor (K) is a coefficient for approximating the length of a column that will actually buckle based on end conditions. The effective length can be longer, shorter, or the actual length, depending on the rigidity of the supports. If the K factor is below 1.0, then the structure has a greater ability to carry forces, and if the K factor is above 1.0, then the structure has a lesser ability to carry forces. For example, fixing both ends of a long column has a K factor of 0.5, which reduces its effective length by half.
How much does normal weight concrete weigh? Lightweight concrete?
Normal = 150 pcf Lightweight = 90–120 pcf
Lateral Load Resisting System
The structural system responsible for countering wind and seismic loads on a building. The vertical portion is often composed of moment frames, braced frames, shear walls, or a combination of these. A common path of the lateral load is from the façade to the floor plates (which act as diaphragms), to the vertical lateral load resisting system, to the foundations.
