Chapter 4: Short Answer

What is the difference between a ductile material and a brittle material?

A brittle material is one for which ultimate strain is less than or equal to 0.5%. A ductile material is one for which the ultimate strain is more than 0.5%.

What is the shape and dimensions of the specimen typically used for determining the compressive strength of concrete?

A cylinder with a diameter of 6 in. and a length of 12 in. This standard is used to test concrete's compressive strength and make it easier to compare different types of concrete.

What is the yield stress of grade 60 reinforcing steel? Of A-36 structural steel?

A grade 60 would have a yield stress of 60 ksi and a -36 structural steel has a yield stress of 36 ksi.

What is the difference between bearing strength and compressive strength?

Bearing strength is the resistance of the stress at the contact between an element and its supporting element. Compressive strength is just the resistance in an element due to a load.

What does the term "strength" of a material imply and how does it differ from a material's ultimate stress?

Both terms refer to the stress at failure of a material.

What is the relationship between a material's brittleness and its tensile strength?

Brittle materials are strong in compression but weaker in tensile strength.

Explain why shear strength of brittle materials is low.

Brittle materials are weak in tension and therefore are also weak under shear stresses.

When a member buckles, it bends. Explain the difference between buckling and bending.

Buckling happens abruptly unlike bending.

Explain the difference between an elastic and a plastic material.

Elastic materials are completely recoverable after deformation when the load is removed and conversely plastic materials are not recoverable after deformation when the load is removed.

Is low-carbon steel an elastic or a plastic material?

Elastic- plastic

What is the modulus of elasticity of a material whose stress-strain relationship is a vertical straight line? Name the material with such a stress-strain relationship.

Infinity and no material exists with this relationship.

The saw blades used for cutting masonry, concrete and stone are made of diamond-tipped steel. Why is that so?

It has the highest psi value

What is the unit of measure for strain?

No units

Among the commonly used structural materials (steel, concrete, masonry and wood), which has the highest modulus of elasticity and which has the lowest modulus elasticity?

Steel has the highest modulus of elasticity. Wood has the lowest modulus of elasticity.

For most materials, their strength is directly related to their modulus of elasticity, i.e., the greater the strength of the material, the greater its modulus of elasticity. Is there a material whose modulus of elasticity is not related to its strength but is constant, i.e., it has a fixed value regardless of the material's strength? If so, name the material and provide its modulus of elasticity value.

Steel has the same modulus of elasticity no matter its strength.

If a concrete test cylinder measuring 6 in. x 12 in. breaks when the load on it reaches 169.5 k, what is the compressive strength of concrete? In PSI

The compressive strength of concrete that failed at 169.5 k load is 5990 psi. This is found by dividing the load at failure(169.5 k) by the area of the cylinder(28.27 square in.) 1 ksi = 1000 psi

Does the slope of the stress-strain diagram relate to any property of the material? Explain.

The slope of the stress strain diagram gives the magnitude of the modulus of elasticity of the material. The greater the modulus of elasticity the more stiff a material is and the less it will deform under a given stress.

A concrete column 20 ft high shortens to 19 ft 11-1/2 in. under a load. Determine the strain in the column.

The strain in the column is 0.002.

Explain two methods by which the buckling of a member may be prevented

To reduce chance of buckling, you can increase the cross sectional area of a member or brace it at intermediate points.

What is the neutral axis of a structural member and in which situation do we refer to it— when the member is in axial compression, axial tension or bending?

When bending... the neutral axis is the part of the member between the compressive stresses on one side of the member and the tensile stresses on the opposite side of the member.

Explain what yielding of a material means.

Yielding is the excessive deformation that happens after the yield point of a material

What is the unit of measure for modulus of elasticity in U.S. System of units? In SI System of units?

psi or ksi for the US system and pascals in the SI system.

List the following materials (aluminum, concrete, steel, and wood) in terms of their ductility beginning with the most ductile and ending with the least ductile.

steel, aluminum, wood, and concrete.

In the stress-strain diagrams of materials, which axis (X-axis or Y-axis) is typically used for stress and which for strain?

x-axis is used for strain and the y-axis for stress.