Materials Science: Low-Alloy Steels

Questions and Answers

What is the maximum tensile stress that can be specified according to ASTM Supplementary Requirement S79?

620 MPa (correct)

515 MPa

480 MPa

550 MPa

Which material specification does not apply to shapes with a flange thickness greater than 50 mm?

A588

A242

A992 (correct)

A847

For which material is a maximum carbon equivalent specified in order to improve weldability?

A847

A913 (correct)

A588

A242

What is the tensile strength range for Low-Alloy Gr. 60?

415-515 MPa Signup and view all the answers

Which of the following is a responsibility of the structural designer when specifying materials?

Confirm availability of other applicable material specifications Signup and view all the answers

What is the yield-to-tensile strength ratio specified for ASTM A992?

0.85 Signup and view all the answers

What is the minimum yield strength for shapes nominally 20 mm thick or under?

345 MPa Signup and view all the answers

What is the preferred material specification for high-strength low-alloy materials?

A588 Signup and view all the answers

What is a primary advantage of using steel as a structural material concerning its weight?

Steel enables the construction of lightweight structures. Signup and view all the answers

Which property of steel allows it to behave predictably under stress?

Elasticity Signup and view all the answers

What does the uniformity of steel imply in structural design?

Steel maintains consistent properties across its lifespan. Signup and view all the answers

How does steel's permanence as a structural material benefit its use?

Steel, when maintained, can last indefinitely. Signup and view all the answers

Which of the following best describes a disadvantage of steel as a structural material?

Steel can experience corrosion without proper treatment. Signup and view all the answers

What is the ductility of steel primarily characterized by?

Its capacity to withstand extensive deformation without failure. Signup and view all the answers

What is one reason why steel is preferred for long-span structures?

Steel's high strength allows for reduced dead load. Signup and view all the answers

Which of the following conditions affects the strength of steel during a fire?

Structural members are incombustible but lose strength at high temperatures. Signup and view all the answers

What characteristic of steel contributes to its long-term performance compared to concrete?

Steel properties remain consistent over time. Signup and view all the answers

What must be considered to prevent buckling in compression members of steel?

The length and slenderness of the member. Signup and view all the answers

Why is steel’s toughness considered an important property in construction?

It allows materials to absorb large amounts of energy. Signup and view all the answers

What is a key responsibility of a structural designer when working with steel?

Ensuring that the structure adheres to applicable codes and specifications. Signup and view all the answers

What is a significant maintenance requirement for most steels exposed to environmental conditions?

They must undergo regular painting to combat corrosion. Signup and view all the answers

What contributes to the phenomenon of fatigue in steel?

Repeated stress reversals and variations in tensile stress. Signup and view all the answers

Which of the following is a disadvantage associated with steel structures?

Vulnerability to brittle fracture under certain conditions. Signup and view all the answers

What characteristic allows for the addition of new structures to existing steel buildings?

The various sizes and shapes it can be rolled into. Signup and view all the answers

Which of the following is classified as a movable load?

Furniture in an office Signup and view all the answers

What type of load is primarily caused by the vibration of moving or movable loads?

Impact loads Signup and view all the answers

Which type of load causes longitudinal forces to be applied on a bridge?

Traffic loads Signup and view all the answers

Which of the following does NOT count as an environmental load?

Soil pressures Signup and view all the answers

What is the result of ponding on a flat roof?

Accumulation of rainwater Signup and view all the answers

Which type of forces are created due to changes in temperature?

Thermal forces Signup and view all the answers

Which of the following is categorized under 'other live loads'?

Hydrostatic pressures Signup and view all the answers

What type of load is primarily caused by explosions or sonic booms?

Blast loads Signup and view all the answers

What is the total dead load ($w_D$) acting on the W460x60 beam?

6.36 kN/m Signup and view all the answers

What is the value of the roof live load ($w_{Lr}$) for the W460x60 beam?

4.32 kN/m Signup and view all the answers

Which load combination yields the governing load for design?

10.68 kN/m Signup and view all the answers

What is the combined load ($w_a$) for the ASD method when considering $D$, $H$, and $L_r$ only?

6.36 kN/m Signup and view all the answers

How is the wind load ($w_W$) characterized for the W460x60 beam?

Positive and negative values Signup and view all the answers

What factor is used to adjust for wind load in the general load formula for load combinations?

0.6 Signup and view all the answers

Using the ASD method, what would the value of $w_a$ be if the wind load was negative?

3.61 kN/m Signup and view all the answers

In analyzing the maximum combined loads, how is the live load ($L$) typically represented?

As a separate entity from the dead load Signup and view all the answers

What happens to the governing load when both upward and downward wind loads are considered?

It depends on the scenario Signup and view all the answers

Which of the following is NOT included in the load combination for ASD method labeled as 203-11?

Tension Load (T) Signup and view all the answers

Study Notes

Structural Steel Materials and Specifications

Low-Alloy Steel grades include Gr. 50 (345 MPa yield, 415 MPa tensile), Gr. 60 (415 MPa yield, 515 MPa tensile), Gr. 65 (450 MPa yield, 550 MPa tensile), and Gr. 70 (480 MPa yield, 620 MPa tensile).
ASTM A913 and A992 specifications indicate yield strengths ranging from 345 MPa to 450 MPa.
Corrosion-resistant steel specifications include A242 and A588, both with a yield strength of 345 MPa and varying tensile strengths.
Use of structural steel should account for responsibilities of designers and material availability as per specifications.

Advantages of Steel as a Structural Material

High strength-to-weight ratio enables lighter structures, beneficial for bridges and buildings on weak foundations.
Steel properties remain consistent over time, unlike reinforced concrete which can change.
Elasticity allows steel to closely follow design assumptions according to Hooke’s law.
Steel structures that are maintained properly have a long lifespan, with some varieties requiring no painting.
Ductility permits steel to deform without failure, providing safety against sudden loads.
Toughness in steel combines strength and ductility, allowing it to absorb significant energy.
Steel allows for easy additions to existing structures and can be prefabricated for quick assembly.
It can be produced in a wide range of shapes and sizes, accommodating various design requirements.

Disadvantages of Steel as a Structural Material

Susceptibility to corrosion necessitates protective coatings, such as paint or copper additives.
Incombustibility doesn’t eliminate the loss of strength at high temperatures typically encountered in fires.
Buckling risk increases with longer and slender compression members, requiring reinforcement.
Fatigue from repeated loading can degrade steel strength, particularly under cyclical stress conditions.
Potential for brittle fracture, especially at stress concentration points, accompanied by loss of ductility.

Types of Loads on Structures

Live loads include moving loads (like trucks) and movable loads (such as furniture).
Specific load classifications encompass floor loads, traffic loads for bridges, impact loads, and thermal forces.
Environmental loads can arise from rainfall, snow accumulation, wind, and seismic activity.

Load Calculations and Combinations

Dead load calculations for the W460x60 beam yield approximately 6.36 kN/m.
Live load calculations for the same beam are about 4.32 kN/m.
Wind load for the W460x60 beam is approximately ±4.59 kN/m depending on direction.
Load combinations for design under ASD involve various criteria, with maximum loads calculated for both service and environmental conditions.
Notable governing load for design determined as 10.68 kN/m, integrating different load effects.

Responsibilities of Structural Designers

Designers must assess and integrate all applicable building codes and specifications, specifically the National Structural Code of the Philippines (NSCP).
Familiarity with various load types and combinations is essential for achieving safety and structural integrity.
Understanding material properties and behaviors under different conditions plays a crucial role in design decisions.

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Description

This quiz covers important aspects of low-alloy steels, including their grades and properties. Test your knowledge on grading standards and corrosion resistance features in materials science. It’s essential for understanding the applications of various steel grades.