LECTURE 1 Flashcards
They decide how the building should look.
Architect
They make sure the building doesn’t fall
Engineer
Collaborate throughout the design process to complete the project in an efficient manner
Engineer and Architect
Roles of an Architect
Overall proportions and dimensions of the supporting framework
Number of Stories
Floor plan
Roles of the Engineer
Selection of the cross-sections of individual members
Serviceability
Economy
Advantages of Steel over Reinforced Concrete
High Strength
Uniformity
Elasticity
Permanence
Ductility
Toughness
Addition to Existing Structures
Adaptation to Prefabrication
Speed of Erection
Ability to be Rolled into a Wide Variety of Sizes and Shapes
Scrap Value
It means that the weight of structures will be small. This fact is of great importance for long-span bridges, tall buildings, and structures situated on poor foundations.
High Strength
The properties of steel do not change appreciably with time, as do those of a reinforced-concrete structure.
Uniformity
Steel behaves closer to design assumptions than most materials because it follows Hooke’s law up to high stresses. The moments of inertia of a steel structure can be accurately calculated, while the values obtained for a reinforced-concrete structure are rather indefinite.
Elasticity
Steel frames that are properly maintained will last indefinitely. Research on some of the newer steels indicates that under certain conditions no painting maintenance whatsoever will be required.
Permanence
The property of a material by which it can withstand extensive deformation without failure under high tensilestresses is ______
Ductility
Structural have both strength and ductility. A steel member loaded until it has large deformations will still be able to withstand large forces.
Toughness
This is a very important characteristic, because it means that steel members can be subjected to large deformations during fabrication and erection without fracture—thus allowing them to be bent, hammered, and sheared, and to have holes punched in them without visible damage.
Toughness
The abilityof a material to absorb energy in large amounts is called ____
toughness
Steel structures are quite well suited to having additions made to them. New bays or even entire new wings can be added to existing steel frame buildings, and steel bridges may often be widened.
Addition of Existing Structures
Disadvantages of Steel over Reinforced-Concrete
Corrosion
Fireproofing Cost
Susceptibility to Buckling
Fatigue
Brittle Fracture
Most steels are susceptible to ___________ when freely exposed to air and water, and therefore must be painted periodically. The use of weathering steels, however, in suitable applications tends to eliminate this cost.
Corrosion
Although structural members are incombustible, their strength is tremendously reduced at temperatures commonly reached in fires when the other materials in a building burn.
Fireproofing Cost
As the length and slenderness of a compression member is increased, its danger of __________ increases.
Buckling
For most structures, the use of steel columns is very economical because of their high _______________. Occasionally, however, some additional steel is needed to stiffen them so they will not buckle. This tends to reduce their economy.
strength-weight ratio
Another undesirable property of steel is that its strength may be reduced if it is subjected to a large number of stress reversals or even to a large number of variations of tensilestress.
Fatigue
Under certain conditions steel may lose its ductility, and brittle fracture may occur at places of stressconcentration. Fatigue-type loadings and very low temperatures aggravate the situation. Triaxial stress conditions can also lead to brittlefracture.
Brittle Fracture
largest stress for which Hooke’s Law applies, or the highest point on the linear portion of the stress-strain diagram
Proportional Limit
Properties of Steel
Proportional Limit
Elastic Limit
Yield Stress
Elastic Strain
Plastic Strain
Strain Hardening
the stress at which there is a significant increase in the elongation, or strain, without a corresponding increase in stress
Yield Stress
largest stress that a material can
withstand without being permanently deformed
Elastic Limit
strain that occurs before the yield stress
Elastic Strain
strain that occurs after the yield stress
with no increase in stress
Plastic Strain
range in which additional stress is
necessary to produce additional strain
Strain Hardening
Steel strength increase; what decreases?
Ductility
Types of Steel
Carbon Steels
High-strength Low-Alloy Steels
Atmospheric-corrosion-resistant-high-strength-low-alloy structural steels
Quenched and Tempred Alloy Steels
Carbon content of Carbon steels
1. Low Carbon
2. Mid Carbon
3. Medium-Carbon Steel
4. High-Carbon Steel
- <0.15 %
- 0.15% to 0.29%
- 0.30% to 0.59%
- 0.60% to 1.70%
In addition to containing carbon and manganese, these steels owe their higher strengths and other properties to the addition of one or more alloying agents such as columbium, vanadium, chromium, silicon, copper and nickel.
High-strength Low-alloy steels
have yield stresses from 480 MPa to 840 MPa.
High-strength Low-alloy steels
When steels are alloyed with small percentages of copper, they
become more corrosion resistant. When exposed to the atmosphere,
the surfaces of these steel oxidize and form a very tightly adherent
film (a tightly bound patina or a crust of rust), which prevents
further oxidizing
ATMOSPHERIC CORROSION-RESISTANT HIGH-STRENGTH LOWALLOY STRUCTURAL STEELS
not satisfactory if frequently subjected to saltwater sprays or fogs, or continually submerged in water or the ground, or where there are severe corrosiveindustrial fumes, very dry areas.
ATMOSPHERIC CORROSION-RESISTANT HIGH-STRENGTH LOWALLOY STRUCTURAL STEELS
have yield stresses of 480 MPa to 690 MPa.
QUENCHED AND
TEMPERED ALLOY
STEELS
These steels of higher strength are obtained by heat treating low-alloy steels.
The heat treatment consists of quenching (rapid cooling) and tempering (reheating).
QUENCHED AND
TEMPERED ALLOY
STEELS
USES OF
HIGH STRENGTH STEEL
- Superior corrosion resistance
- Possible savings in shipping, erection, and foundation costs caused by weight saving.
- Use of shallower beams, permitting smaller floor depths.
- Possible savings in fireproofing because smaller members can be used.
ASTM DESIGNATIONS:
Carbon Steels
A36, A53, A500, A501, A529
ASTM DESIGNATIONS:
High-Strength Low Alloy Steels
A572, A618, A913, A992
ASTM DESIGNATIONS:
Corrosion-Resistant High-Strength Low-Alloy Steel
A242, A588, A847
Governing Bodies/ Agencies / Reference
- ACI - American Concrete Institute
- ASCE - American Society of Civil Engineers
- AISC - American Institute of Steel Construction
- AWS - American Welding Society
- RCSC - Research Council on Structural Connection
6, ASTM International - ASME
- NSCP 2015
Types of Steel Sections
Built-up Shapes
Cold-Formed Plate Shapes
COLD-FORMED LIGHT GAGE SHAPES
Rolled Shapes
Metal Decks
