CIVIL STRUCTURES

Question 1

Idenity how beam design affects its performance

Answer 1

• height of the beam controls the distance it can span
• increasing the height generates more material to dissipate the load
• material: concrete/steel

Question 2

Identify the advantages of an I-beam

Answer 2

It has great strength as it places the largest amount of material possible away from the neutral axis and is easily manufactured by hot rolling processes at steel mills

Question 3

Identify the advantages of a box beam

Answer 3

The webs give the structure greater resistance to twisting and torsional forces desirable for curved structures where torsional forces play a greater part

Question 4

Explain why Arch bridges were easily constructed

Answer 4

• strength + material availability
• typically made out of timber placed or stone cemented in place
• only small arches could be constructed

Question 5

Explain why Beam bridges were constructed

Answer 5

-allowed stronger and bigger structures due to the post-tensioning of concrete, which could carry greater loads
post-tensioning-> greater strength + lighter

Question 6

Identify how beams can be joined, and outline an advantage and disadvantage of each

Answer 6

-bolts
Advantages: easy to implement if holes are already done, joints are flexible -> suitable for dynamic loads, easy application + less equipment

Disadvantages: requires holes to be accurate-> drilling of holes weaken beams, subject to differential aeration corrosion

-welding
Advantages: less preparation and maintenance is required, less prone to corrosion, easier and less equipment

Disadvantages: some metals require treatment before welding and may be subject to warping due to heat and stress corrosion

Question 7

Describe methods used to protect civil structures against corrosion, support your answer with examples

Answer 7

Steel truss bridges: may be protected by sacrificial anodes which are reactive metal anodes such as zinc and aluminium that make the structure cathodic thus, protecting it as the electrons leave the anodes, thus, dissolving the sacrificial anodes.

underground pipeline+tram rails: protected by impressed current cathodic protection (ICCP) where the structure is made cathodic. By supplying electrons the structure from an outside DC source.

Question 8

Explain how the process of galvanising protects steel from corrosion

Answer 8

Galvanised steel consists of steel with a zinc coating, where the zinc acts like a sacrificial anode to protect the cathodic steel