Chapter 4 (16-30)

26 A concrete cylinder specimen is tested by loading it in compression from its top. The cylinder is restrained from expanding laterally (not allowed to bulge horizontally under the load). A second identical cylinder is tested in compression similarly but without any lateral restraint, i.e., this cylinder is allowed to bulge laterally. Will both cylinders fail at the same or a different value of load? Explain your answer.

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24 Explain why shear strength of brittle materials is low.

Brittle materials have low strength in shear because of the tension created by the shear, which brittle materials are weak in.

27 What is the difference between bearing strength and compressive strength?

Compressive strength is the resistance of a material to breaking under compression, while bearing strength is the maximum amount of weight or pressure that the structure can hold before collapsing.

21 What is meant by a "structurally efficient" cross sectional shape in bending? Note: "in bending" means that the member is used as beam or slab.

Something that is "structurally efficient" is a shape that can withstand a greater load for the same amount of material. For example, the I-beam is a structure that is structurally efficient to resist bending because it puts the most material where the most stresses are.

18 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 regardless of strength of steel. the modulus of elasticity of steel is 29.0 psi (x10^6).

25 Being a brittle material, concrete is weak in shear. Therefore, shear reinforcement is used in concrete beams. Sketch the profile of this reinforcement and provide the term by which it is identified.

Steel stirrups in a reinforced concrete beams are used to increase the beam's shear strength

22 Why is an I-section beam structurally more efficient than a beam of rectangular cross section whose cross sectional area is the same as that of an I-section beam?

The I-section beam is more structurally efficient than a rectangular beam because the configuration puts the most material at the top and bottom of the beam where the stresses are the greatest.

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

The difference is that bending is produced by loads that are perpendicular to the axis of the member while buckling is caused by axial loads.

17 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.

The material that creates a vertical line in the diagram is a rigid material.

20 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?

The neutral axis of a structural member is a line on the beam's cross section where the stresses are zero.

23 What is the difference between an I-section beam and an open-web I-section beam, called a castellated beam?

The open web I section beam has more efficiency on bending with removed material in the central region.

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

They use diamond tipped steel because it has the greatest stiffness

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

We could prevent buckling by reducing the slenderness of the material or brace the material at the intermediate points along the width or height.

28 Why do we use the term "bearing strength of soil" and not "compressive strength of soil" when, in reality, the soil is under compression from the load of the structure being supported.

We use this phrasing because the soil directly under a footing is confined by a large mass of the surrounding ground.

16 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?

Wood has the lowest modulus of elasticity, while steel has the highest modulus of elasticity.