LE 1 CONCEPTS Flashcards
may be defined as a mixture of art and science, combining the engineer’s judgment (experienced engineer’s intuitive feeling for the behavior of a structure) with a sound knowledge of the mechanics (principle of statics, dynamics, mechanics of materials, and structural analysis), to produce a safe, economical structure that will serve its intended purpose.
Structural design
the numerical process of determining the behavior of a structure due to externally applied loads and moments.
Structural Analysis
established to evaluate whether or not an optimum has been achieved.
Design Criteria
Typical Design Criteria
- minimum cost
- minimum weight
- minimum construction time
- minimum labor
- minimum cost of manufacture of owner’s products
- maximum efficiency of operation to owner
ensures that intended results are achieved, such as (a) adequate working areas and clearances; (b) proper ventilation and/or air-conditioning; (c) adequate transportation facilities, such as elevators, stairways and cranes, etc; (d) adequate lighting; and (e) aesthetics.
Functional design
the selection of the arrangement and sizes of structural elements so that service loads may be safely carried, and displacements are within acceptable limits.
Structural framework design
conditions of a structure at which it ceases to fulfill its intended function.
Limit States
maximum ductile strength, buckling, fatigue, fracture, overturning and sliding.
Strength Limit State
deflection, vibration, permanent deformation, cracking
Serviceability Limit State
or uncertainties in material properties, construction tolerances, etc.
Nominal Capacities and Resistance Factors
for uncertainties in variable loads
Load Factors
a single variable is used to handle uncertainty in both load and capacity
Factor of Safety
designing members and connections using loads and resistance factors such that no applicable limit state is reached when subjected to appropriate load combinations.
LRFD (Load and Resistance Factor Design)
designing members and connections such that calculated stresses do not exceed specified material stresses when subjected to appropriate load combinations.
ASD (Allowable Stress Design)
Classification of metal that is the principal element is iron as in cast iron, wrought iron, & steel
Ferrous Metal
Classification of metal with examples such as copper, tin, lead, nickel, aluminum
Non-ferrous Metal
________ - iron alloys containing less than ________ carbon
Iron | 0.008%
_________ - carbon content between _____ & ______. Chemical union of iron & carbon plus other elements
Steel | 0.04% and 2.0%
________ - carbon content between _____ & _____
Ferrous metal composed primarily of iron, carbon, & silicon shaped by being cast in a mold because of brittleness due to large amount of
carbons
Cast Iron | 2% and 4%
Highly refined iron with slag deliberately incorporated but not in chemical union with iron
Wrought Iron
Effect of Carbon on Steel: Up to 0.9%
increases hardness, tensile strength, & responsiveness to heat treatment with corresponding increase in strength & hardness
Effect of Carbon on Steel: Over 0.9%
increases hardness & brittleness
Effect of Carbon on Steel: Over 1.2%
causes loss of malleability
Process of Production of Steel: compressing & shaping an ingot into a useful shape by squeezing it through a succession of rollers, each succeeding set of rollers squeezing the material smaller in cross section and closer to the final shape
Rolling
forcing a billet of hot, plastic steel through a die of the desired shape to produce a continuous length of material
Extrusion
pulling a steel through a small die to form a wire or a small rod of round, square, oval, or other cross section
Drawing
deforming steel by pressure or blows into a desired shape
Forging
Heat Treatments of Steel: heating the steel to a temperature of about 1500 F or higher & cooling several hundred degrees slowly in air to increase uniformity of structure
Normalizing
Heat Treatments of Steel: heating the metal slightly lower than for normalizing, holding it at that temperature for the proper period of time, & then slowly cooling, usually in a furnace
Annealing
Heat Treatments of Steel: cooling steel very rapidly in oil, water, or brine from a temperature about 1500 F to increase hardness and strength (but reduces ductility & toughness); residual stresses are also introduced
Quenching
Heat Treatments of Steel: process of re-heating a hardened steel to a temperature of about 300 to 1200 F, holding it at that point for a time, and cooling it to reduce residual stresses & increase ductility
Tempering
