OBJ 3.2 Flashcards
Put the following in order from weakest to strongest material in terms of tensile strength: wood, structural steel, foam, reinforced concrete, graphene.
Foam, wood, reinforced concrete, structural steel, and graphene.
Moment-resisting frame
A moment-resisting frame provides lateral stiffness through a rectilinear assemblage of beams and columns, with the beams rigidly connected to the columns. The connections of the beams and columns are designed to resist moment, or rotation.
Shear wall
A shear wall, or shear panel, is a panel component of a building’s structural system designed to carry lateral loads.
Braced frame
A braced frame is a lateral force-resisting structure that uses diagonal bracing members that work in both tension and compression.
Equilibrium
In statics, equilibrium refers to all net forces acting on an object equaling zero.
P-delta effect
In structural engineering, the P-Δ, or P-delta, effect refers to the abrupt changes in ground shear, overturning moment, and/or the axial force distribution at the base of a sufficiently tall structure or structural component when it is subject to a critical lateral displacement.
Ultimate tensile strength
The ultimate strength of a material is the capacity of a material or structure to resist tension.
Put the following timber components in order from the shortest span to the longest span: joists, trusses, laminated beams, decking.
The correct order is decking, joists, laminated beams, and trusses.
First steel-framed skyscraper
Home Insurance Building, Chicago, Illinois.
Architect: William Le Baron Jenney.
Completed 1884.
Metal gauge thickness
A number that indicates the thickness of a piece of metal; the higher the number, the thinner the metal. (For example, among 3 gauge, 10 gauge, and 14 gauge, 14 gauge is the thinnest.)
Standard metal stud sizes
2-1/2 inches, 3-1/2 inches, 3-5/8 inches, 5-1/2 inches , 6 inches, 8 inches, 10 inches, 12 inches, and 14 inches. Larger stud sizes (8+ inches) are typically used where tall spans (10′0″+) must be achieved.
Deflection header/track
Located at the top track of a wall assembly and designed to allow the top of the wall stud to float within the top track. This connection allows for vertical live load movement of the primary structure by creating room for movement.
Flexible walkway
Designated walking surface on membrane rooftops to protect roof from dishing or puncturing due to foot traffic. Can be made with nonskid surface to enable sure footing.
Lintel
A horizontal structural support across the top of an opening in a wall. Can be made of concrete, steel, wood, or stone.
Topping slab
Thin concrete mix applied to the top of a new or existing floor to create a new and/or level surface.
Precast structural concrete
Concrete that is poured on top of pre-stressed steel cables, which are then cut from the formwork after the concrete cures to transfer compressive stresses. It is poured off-site and transported to the site, which is good for minimal on-site erection time.
Cast-in-place concrete
Concrete that is poured on-site using formwork, with steel rebar used for reinforcement. Good for irregular grids and forms and minimizes off-site fabrication time.
Post-tensioned concrete
Concrete that is formed with steel tendons laid out in the required positions when the concrete is poured. After the concrete has cured, the tendons are tensioned with end anchors for the desired strength. Used to decrease slab thickness and eliminate most slab contraction joints.
Flat-plate structural system
A reinforced concrete slab that does not have beams and is supported directly by columns. This system is often more expensive, but it allows for smaller depths, flat soffits, and flexibility in design.
Drop panel structural system
Like a flat-plate system, this is a reinforced concrete slab that does not have beams and is supported directly by columns. The slab thickness is increased at the columns for greater shear strength.
One-way concrete joist system
Prefabricated concrete structural system in which concrete joists are formed spanning one direction; are spaced 24 to 36 inches apart; and allow for shorter spans of 20 to 30 feet, with depths of 1 to 2 feet.
Two-way concrete joist system
Prefabricated concrete structural system in which concrete joists are formed in two directions. This system is often used in rectangular bays where the distance between columns is equal.
Beam and girder structural system
Structural framing system in which large girders support intermediate beams to hold a slab with 15- to 30-foot spans. Economical system that is easy to form and allows slabs to be penetrated for other systems.
Waffle slab
Ribs formed equally in both directions, creating a grid-like system that allows for the longest spans of conventional concrete floor systems, spanning up to 40 feet.
Structural tee concrete system
Pre-stressed ribs with a 2-inch topping slab integrally connected. Good for long spans. Can be either single or double tee.
Open web steel joists
Lightweight steel truss with parallel top and bottom chords and a triangulated web system between. Lightweight and efficient system that can be used for both long and short spans (depending on depth) that allow for ductwork to pass through.
Tributary area
Tributary area in structural engineering refers to the plan area of a building that loads onto a particular structural member. For example, the tributary area of a beam is half the distance to the next beam in each direction.
Influence area
Influence area is the tributary area plus the area that will impact the load on a structural member.
Impact load
A dynamic load in a building that occurs quickly. Examples include moving elevators or a vehicle hitting a structure. Building codes account for impact loads by adding a safety factor.
Determinate structure
Can use the principles of statics to determine forces and reactions.
Indeterminate structure
Cannot use the principles of statics to determine forces and reactions.
Moment of inertia
A measure of resistance to bending and buckling.
Camber
A vertical curve that is built into a beam to counteract the deflection imposed by any added dead load.
Cement Type I
Normal cement used for most construction.
Cement Type IA
Normal cement, which is air entraining.
Cement Type II
Moderate resistance to sulfate attack (used when in contact with water with high concentrations of sulfates).
Cement Type IIA
Moderate resistance, air entraining.
Cement Type III
High early strength (hardens more quickly; used when reduced curing time is required).
Cement Type IIIA
High early strength, air entraining.
Cement Type IV
Low heat of hydration (used in massive structures such as dams, where emitted heat might raise thetemperature of the concrete to damaging levels).
Cement Type V
High resistance to sulfate attack (used when in contact with water with a high concentration of sulfates).
Admixtures
Admixtures are ingredients other than cement, aggregates, and water that are added to the mix to alter it in various ways.
Air entraining admixtures
Increase the workability of wet concrete, reduce freeze/thaw damage, and (when a lot is used) create very lightweight nonstructural concretes with thermal insulating properties.
Water reducing admixtures
Allow a reduction in the amount of mixing water whileretaining the same workability; results in a higher-strength concrete.
Superplasticizer
Organic compounds that transform a stiff concrete mix into one that flows freely into forms; used to help place concrete in challenging circumstances or to reduce the water content in a mix in order to increase its strength.
Accelerating admixtures
Concrete cures more rapidly.
Retarding admixture
Slow curing to allow more time to work with wet concrete.
Fly ash
A fine powder that is a waste product from coal-fired power plants. It increases concrete strength, decreases permeability, increases sulfate resistance, reduces temperature rise during curing, reduces mixing water requirements, and improves workability.
Blast furnace slag
Byproduct of iron manufacturing that improves workability,increases strength, reduces permeability, reduces temperature rise during curing, and improves sulfate resistance.
Pozzolans
Varicose natural/artificial material that reacts with calcium hydroxide in wet concrete to form cementing compounds.
Workability agents
Improve the plasticity of wet concrete to make it easier to place in forms and finishes.
Corrosion inhibitors
Used to reduce rusting of rebar in structures that are exposed to road deicing salts or other corrosion-causing chemicals.
Fibrous admixtures
Short fibers of glass or steel added to a concrete mix to act as microreinforcers.
Freeze protection admixtures
Allow concrete to cure at temperatures as low as 20°F.
Extend set control admixtures
Used to delay the curing reaction in concrete for up to seven days.
Coloring agents
Dyes and pigments used to alter the color of concrete.
Concrete
A rocklike material produced by mixing coarse and fine aggregates, portland cement, and water, and by allowing the mixture to harden.
Coarse aggregate
Gravel or crushed rock.
Fine aggregates
Sand.
Hydration
Chemical reaction between water and cement that creates heat.
Cement
A product of lime, iron, silica, and alumina that is crushed, ground, proportioned, and blended and then sent through a kiln, cooled, and pulverized to a powder.
Vermiculite
A mineral that expands upon being heated; used in the expanded state for heat/sound insulation and fireproofing.
Perlite
A form of obsidian formed by cracking of cooling volcanic glass; used as insulation.
ASTM A992 steel
A steel alloy typically used for the production of wide flange shapes. A992 steel has an Fy of 50 ksi and an Fu of 65 ksi.
Stress
Stress is the intensity of a force. It is force per unit area, or f = P/A, where f is stress, P is force, and A is cross-sectional area. There are two kinds of stresses: normal (perpendicular) and tangential. Shearing stresses are tangential and axial stresses are normal. Bending stresses result in both normal and tangential stresses.
Strain
Strain is the physical change in a body from the result of stress. Under stress, the size or shape of the body changes. Tensile stress strains a body by elongation and compressive stress shortens a body. Strain has no units because it is a ratio.
Overturning
Lateral forces such as wind and seismic loads act on entire buildings, causing them to want to turn over. Buildings must resist the tendency to overturn due to the moment caused by the lateral force.
Drift
Lateral or story drift is the amount of horizontal displacement or sway in a building due to lateral loading such as wind or seismic activity.
Lally column
A telescoping, adjustable, thin-walled round steel column. Often found in basements or crawl spaces of homes. Can be temporary or filled with concrete to remain in place.
Podium building
Buildings that are multiple stories of wood over an elevated concrete podium or deck. An example is a four-story wood-framed apartment building over a two-story concrete parking structure.
Preliminary span estimates for wood floor I-joists
Estimate depth at 1/18th of their span.
Preliminary span estimates for wood floor joists
2 x 6 = 9 feet; 2 x 8 = 11 feet; 2 x 10 = 14 feet
2 x 12 = 17 feet (for estimating only).
Preliminary span estimates for roof rafters
2 x 4 = 7 feet; 2 x 6 = 10 feet; 2 x 8 = 14 feet
2 x 10 = 17 feet (for estimating only).
CLT
Cross laminated timber. An engineered wood building system of solid, prefabricated structural panels made from lumber that is stacked in alternating directions and bonded with adhesives. They are lightweight, structurally efficient, and gaining in popularity in the United States.
Tensegrity
A closed structural system with compression struts within a network of tension tendons.
What is the difference between control joints and expansion joints in concrete?
Control joints are placed every 5 feet, and expansion joints are placed every 20 feet.
What is the minimum slope required to drain an exterior concrete surface?
A 1 percent slope minimum.
What is the diameter of no. 3 rebar?
The diameter is 3/8 inches. Generally, the number size is always the numerator in a ?/8-inch fraction because rebar comes in 1/8 of an inch increments.
What would the letter S denote on rebar?
This is the type of steel and will always be the third marking down on the rebar. S = carbon steel, W = low alloy steel, SS = stainless steel, R = rail steel, A = axle steel, CS = low-carbon chromium.
Pre-tensioning and post-tensioning are used in what type of concrete?
Pre-stressed concrete is constructed with pre-tensioned or post-tensioned cables.
Sources of loads within buildings
Gravity (the building itself, its contents, snow, ice, and water on the roof); wind, seismic, and hydraulic pressure (groundwater); soil pressure; thermal changes; shrinkage within building materials (similar to thermal changes); internal forces (for example, warping or loosening of the building components and settling); and vibrations (from machinery, for example).
Forces during production, shipping, handling, storage, and erection of building materials and equipment
These forces are not always apparent to the building designer, but they must be considered.
Live loads
Anything that is not a permanent load in a building. Includes people, contents, snow, ice, and wind. Live loads are usually dynamic.
Dead loads
The weight of the permanent parts of a building. They are static loads that are relatively constant.
Static forces
A force that does not change in magnitude or position. They are relatively independent of time. Dead loads are static forces. Static forces have mass and potential energy.
Dynamic forces
A force that changes in magnitude or position over time. Live loads are dynamic forces. Dynamic forces have mass and inertia.
Point load
Loads that are concentrated; for example, a column on a footing is a point load. Also called concentrated load.
Distributed load
Loads that are dispersed across a structure; for example, the dead load of a roof transferred to a bearing wall.
Unbalanced load
Randomly dispersed live loads.
Eccentric load
A load imposed on a column that is located a short distance away from the centroid.
Combining loads
Generally, it is not required to design for both earthquakes and high wind velocities occurring simultaneously, nor is it required to design for high wind velocities blowing from more than one direction simultaneously.
Reactions
A structural member must have sufficient strength and stiffness to resist displacement, deformation, and fracturing. A reaction is the term given to these forces of a structural member that resists the forces acting on it. A reactive force must be equal to the force acting on it in magnitude and opposite in sense (direction), leading to a state of static equilibrium.
Shear force
Shear forces are those that pull a body apart through an internal, parallel, opposing, or sliding action. Scissors cutting paper is a shear force.
Punching shear
Occurs at column footings and in slabs supported by columns. Punching shear is a localized force characterized by the column’s tendency to want to “punch through” the footing or slab.
Rotational force
When a force acts on a body, causing it to want to rotate. For example, a cantilever beam that is supported at one end must resist rotational force. Rotational force is also called moment and is a function of force times distance.
External force
Any forces applied to a structure from outside the system. Dead loads, live loads, uniform loads, point loads, and moments are all external forces. External forces cause internal forces.
Internal force
A force generated within a structure in response to resisting external forces. Includes normal (axial) forces, shear forces, and bending moments.
Properties to consider when selecting structural systems
Appearance, weight, fire resistance, thermal properties of expansion and contraction, durability to weathering and wear, availability, cost, and constructability.
Load
Any force applied to a body.
Space frame
A two-way truss-like system that can span large areas with few supports.
Membrane roof
A membrane roof is a thin fabric sheet that cannot resist compression, bending, or shear but can resist tension. It is a “tent” structure. Examples: Munich Olympic Stadium and Denver International Airport.
Air-supported structure
When a membrane roof is supported by air pressure. Commonly used for sports arenas.
Folded-plate roof
Assemblies of flat plates that are inclined and joined to create a roof structure. Eliminates the need for beams.
In _______ (short-span/long-span) construction, a specific construction sequence is often necessary.
Long-span.
The architect/engineer must practice _______ (more/less) observation of long-span structures.
More.
A two-way structural system is efficient when spans in each direction are ______ (close to equal/far from equal).
Close to equal.
A one-way structural system is ______(easier/more difficult) to design and build.
Easier.
Stressed skin panels
Manufactured panels of glued and nailed plywood skins to both sides of a wood frame, resulting in a unit that performs like an I-beam. Not necessarily insulated.
Two types of structural foam core panels
Sandwich panels and unfaced panels. Skins of panels resist tension and compression, whereas the wood frame or core resists shear and prevents buckling of skins.
Sandwich panel (structural foam core panel)
Rigid-foam panels faced with two structural grade skins; usually made of oriented strand board or plywood.
Unfaced panel (structural foam core panel)
Looks like panels of stick framing with thermal insulation between the members, instead of blanket insulation.
Filigree slabs
Slabs combine desirable characteristics of cast-in-place precast concrete. The panels act as permanent forms for the field-placed reinforcing and cast-in-place topping. The underside is smooth and can be left exposed.
Bored piles
Include auger cast grout, bored and socketed, bored concrete, drilled caissons, drilled concrete piers and shafts, and drilled micropiles. Conditions that make bored piles advantageous include: cohesive soils, obstructions that can be tolerated with the right size drill, and dense reliable bearing surface.
Driven piles
Include concrete, steel, timber, and composite piles that are driven into the ground with a mechanical hammer. Conditions that make driven piles advantageous include cohesionless soils with few boulders.
Pile cap
This element is used when more than one deep foundation element is required to resist gravity and lateral loads to distribute the loads from a single point column to multiple foundation elements.
What is the design strength of concrete?
Design strength is the assumed value of strength for concrete and the yield stress of steel. For concrete, the maximum compressive strength is reached after curing for 28 days and is typically in the range of 3,000–6,000 psi.
Regarding the strength characteristics of wood, it is the weakest in ___________ shear.
Horizontal. Wood is stronger perpendicularly, or across the grain, rather than parallel to the grain direction.
List the differences between lumber and timber.
Lumber is wood that has been milled and is ready to be used as a construction member. Timber is standing or felled trees that have yet to be shaped. Rough stock wood is also referred to as timber. Structural timber is timber machined for use in structural applications and is at least 5 inches or greater in the least nominal direction.
____________ is added to steel to make it stronger and harder.
Carbon. It is important to note that, with an increase in the carbon content of steel, ductility and welding capabilities are reduced.
True or False? The most important cost implication of a structural system is the cost of the structural members themselves and, therefore, savings must be maximized by designing structures with the most efficient sections.
False. The cost of the entire building must be considered, because savings in designing with more efficient structural members can mean deeper sections, which increases the floor-to-floor and overall building height. The resulting increases in all the extra costs of the building in the stairs, elevators, cladding, and MEP systems may offset the cost savings of the structural sections. The most cost-efficient structural system is often one that produces a major cost savings of another system.
Advantages of precast concrete
- Faster erection at the site
- Economy of formwork
- Higher quality can be achieved in the factory, including tighter dimensions, a more uniform look, and higher strengths through pre-stressing
- Allows shortcuts in design efforts by using standardized components
Disadvantages of precast concrete
- Handling and transporting is burdensome
- Costly
- Connections (probably the single biggest disadvantage)
- Coordination with other systems, such as MEP systems
- Lack of performance during seismic events
The principle advantage of shell or folded-plate structures?
Weight reduction due to the form’s response to the development of forces.
True or False? Most masonry in buildings constructed today is load bearing.
False.
True or False? In an arch, the less rise there is, the greater the horizontal thrust.
True.
