Construction Tech

Question 1

Bonded Screeds

Answer 1

which are laid on to a ready prepared rough, cleaned concrete base.

Question 2

Unbonded Screeds

Answer 2

which are laid on to a sound clean bitumen damp proof membrane.

Question 3

Floated Screed

Answer 3

which is laid with steel or fibre reinforcements on to the insulating board, which in turn can be laid on to a suitable damp proof membrane.

Question 4

Resin bonded screed

Answer 4

which is laid on to a clean, rough pre-prepared concrete base. The resin acts as a ready installed damp proof membrane to the top screed.

Question 5

Sheet piles

Answer 5

a. Deep trench is excavated and concrete is poured in situ
b. Piles can be used to form basement walls or act as retaining walls

Question 6

Secant Piles

Answer 6

a. Interlocking piles provide a combination of foundations and basement walls
b. Support in providing a waterproof structure and are often seen when top down construction methods are used

Question 7

Bored piles

Answer 7

3. Bored piles
   a. An auger is used to excavate the soil and then concrete is poured once complete

Question 8

Pre-cast piles

Answer 8

4. Pre-cast piles
   a. Hammered into the ground (not often favoured due to high noise and lack of flexibility in depth)

Question 9

What are the different ways that the piles transfer their load to the surrounding ground?

Answer 9

• End bearing piles - transfer load through low bearing capacity soil to a strong stratum such as rock or very dense sand.
• Friction piles - bear on frictional resistance between their outer surface and the soil in contact.
• Settlement reducing piles - usually incorporated beneath the central part of a raft foundation in order to reduce differential settlement to an acceptable level.
• Tension piles - resist uplifting forces that might otherwise cause the structure to be extracted from the ground due to uplifting forces such as hydrostatic pressure, seismic activity or overturning movement.

Question 10

What is the difference between bored vs. pre-cast piles?

Answer 10

• Bored piles are defined when the process for removing the spoil to form the hole for the pile is carried out by a boring technique.
• They are used primarily in cohesive subsoils for the formation of friction piles and when forming pile foundations close to existing buildings where the allowable amount of noise and/or vibration is limited.
• Pre-cast Concrete piles are generally used where soft soil deposits overlie firmer strata. These piles are usually driven using a drop or single action hammer.
• Issues can arise due to the noise levels associated with the installation method of pre-cast piles.

Question 11

What is a raft foundation

Answer 11

• Raft foundations spread the load of the superstructure over a large base and reduce the load per m2 of the area.
• Raft foundation solutions are useful in low bearing capacity soils.
• They can be a solid raft slab or beam and slab raft such as a ground beam system and suspended PC concrete ground floor.

Question 12

When would raft foundations be used?

Answer 12

• A raft can be used for lightly loaded buildings on sites with poor soils.
• Heavy loads to the raft have the potential to cause the raft to move sideways as a result of raft foundations not being very deep.

Question 13

What is a strip foundation?

Answer 13

• Strip foundations are formed by creating a shallow continuous excavation to support the perimeter and internal walls.
• They are also referred to as strip footings and are suitable for most subsoils and a light structural design.

Question 14

What are pad foundations?

Answer 14

• Pad foundations provide a base for reinforced concrete or steel columns.
• They are usually formed by making an isolated excavation in the shape of a square or rectangle.
• They often have reinforcement mesh as part of the construction and spread the load to a layer of bearing soil or rock below.

Question 15

What is powder coating?

Answer 15

• A durable factory applied coating on metals, such as aluminum or galvanized steel which is available in many colours.
• This application is sprayed on and is followed by heat curing to give a film thickness of 50 to 100 microns.
• Any holes and cutting should be carried out before the coating is applied.

Question 16

What is post tensioned concrete?

Answer 16

• This method is usually employed where stressing is to be carried out on site after casting an insitu component or where a series of pre-cast concrete units are to be joined together to form the required member.
• In post-tensioning, concrete is cast around ducts or sheathing in which the tendons are to be housed.
• Stressing is carried out after the concrete has cured by means of hydraulic jacks operating from one of both ends of the member.

Question 17

What is the purpose of a threshold strip?

Answer 17

• A lightly rounded metal strip over the joint between the floor finishes or coverings that meet under the door leaf.
• They prevent fraying and provide an aesthetic finish which also interrupt combustible flooring under fire doors.

Question 18

What are the elements of a flat roof?

Answer 18

• Joists which are fixed to wall plates to act as the main support.
• Furrings which are fixed to the top of joists to provide the required gradient of incline.
• Particle board is fixed to top of the furrings to provide a flat surface.
• Felt is applied usually made up of 3 layers and bonded with bitumen to provide a waterproof covering.
• Stone chippings provide protection to the felt and also reflect sunlight.

Question 19

What items would you expect to find on a timber or part glazed FD30 door?

Answer 19

• 3 hinges.
• Intumescent strip on door or edge of frame.
• A self-closing devise.
• If a glazing panel is present it must be 6mm thick, wired glass to a max of 1.2m2 with 13mm x 13mm wood beads encased with non-combustible materials.

Question 20

Explain how power is distributed to floor boxes in a raised access floor?

Answer 20

• The incoming power supply connects to a low voltage switchboard, which in turn connects to a distribution board.
• The distribution board will have an under floor busbar connected to it. The busbar has a number of sockets to which the floor box plugs into via a flexible lead. The floor box has sockets to which the appliances can plug into.