Learning Outcome Lesson Objective Understand the techniques used in the construction of superstructures for low-rise domestic and commercial buildings Lesson Objective To be able to explain the techniques used for construction of floors in domestic and commercial construction

Recap What is the purpose of site investigation? What are its key stages? What is the difference between a trenchfill foundation and a traditional strip foundation? When is a wide strip foundation required? In what situations are strip foundations not suitable? Why is piling becoming more common? What is the function of the ground beam which sits on top of the piles? When are rafts sometimes used?

Industrial/Commercial flooring What are the Functional Requirements of a floor slab? Provide a flat surface Strength and stability Durability and freedom from maintenance To support load Fire safety Resistance to passage of heat Resistance to passage of sound Act as a divider (privacy) for the occupants Upper slab became the ceiling for the storey below Space between slab and ceiling /floor finish can be used to place building facilities

Industrial/Commercial flooring

Industrial/Commercial flooring

Floor construction: Ground Bearing Lightweight block DPC 1. Cavity fill & backfill 2. Hardcore and blinding 3. Damp Proof membrane 4. Insulation & slab 5. Build walls 6. Floor screed

Ground Floors The hardcore fills and levels out the sub floor void, reduces capillary action and provides a level stable base for the concrete. A thin layer of sand called blinding can then be spread over the hardcore to provide a smooth bed for the polythene damp proof membrane.

Floor construction: Ground Bearing Ground bearing floor – Insulation under slab, DPC above insulation

Floor construction: Ground Bearing Ground bearing floor – Insulation under slab, DPC under insulation

Floor construction: Ground Bearing Ground bearing floor – Insulation above slab, with screed

Floor construction: Ground Bearing Ground bearing floor – Insulation above slab, with chipboard

Floor construction: Beam & Block 7. Insulation 8. Vapour check and chipboard 6. Build Wall 1. Cavity fill & backfill 2. Level earth 3. DPC 4. Position beams 5. Block infill and grout

Floor construction: Beam & Block Precast Ground Floors When do you think pre-cast ground floors may be specified? the water table is high there are aggressive chemicals in the ground the ground is likely to heave the ground quality is poor and large volumes of hardcore might be required the site slopes steeply

Floor construction: Beam & Block Modern pre-cast floors require sub floor ventilation Periscopic vents are common

Floor construction: Beam & Block Polystyrene insulation Polythene vapour check Chipboard with glued joints

Floor construction: Beam & Block Beam & Block Floor - alternative example Pre-cast beams on DPCs Polystyrene infill blocks

Floor construction: Beam & Block Insitu concrete – optional reinforcement using lightweight mesh or glass fibre Powerfloat concrete

Floor construction: Beam & Block Advantages

Floor construction Suspended timber ground floor

Floor construction Upper floor: traditional construction In modern construction joists are supported on joist hangers. The joists should be a good fit in the hangers and must have a good bearing to ensure structural stability. They should be nailed to the hangers. In all but the shortest of spans strutting is required to prevent the floor joists from twisting and cracking the ceiling below

Simple first-floor joist plan This house has cavity walls with mineral wool cavity batts Joists are built-in to internal leaf 100mm aerated block 50mm mineral wool batt 100mm face brick

Lounge Hall Approx 5 metres Kitchen/Diner Approx 9 metres

1st joist about 50mm from wall Internal load-bearing walls Joists usually @ 400mm centres Extra joists to avoid gaps

Trimming Trimmer

Strapping Strutting

Photographs

Floor construction

Floor construction In any modern house cables and water pipes will have to run through the floor. To prevent the floor from being weakened the Building Regulation lay down strict rules for the positioning of cables and pipes. As a general rule cables run through holes drilled in the centre-line of the joists, pipes lie in notches cut in the top of the joists.

Floor construction Timber framed construction: Intermediate floors The construction of the first floor is very similar to that used in more traditional houses. The joists are usually at 400 or 600mm centres and are secured in position by nailing to the head binder. A header joist is nailed round the perimeter of the floor and, besides providing a firm base for the upper floor panels, prevents fire from entering the floor cavities. Once the joists are in position, the chipboard or plywood deck is laid right across the joists, and this forms the platform for the next lift of wall panel

Floor construction Timber framed construction: Intermediate floors Most systems in the UK use the platform method of construction. This means that the upper floor panels sit on the chipboard decking. If this chipboard gets wet for any reason and needs renewing, there are obvious problems

Floor construction Timber framed construction

Floor construction Concrete Intermediate floors In modern construction low-rise purpose-built flats, usually have upper floors made from precast concrete. The floors in flats separate dwellings and, as such, require higher levels of fire protection and sound insulation than their timber counterparts in houses. Concrete floors are also capable of greater spans than timber floors and are ideally suited to flats where large floor areas may be required without the complication of unnecessary internal load bearing walls.

To investigate industrial and commercial floor construction Lecture Objective To investigate industrial and commercial floor construction

Classification of Slabs Industrial/Commercial flooring Classification of Slabs UPPER FLOOR GROUND FLOOR TIMBER FLOOR PRECAST FLOOR SOLID FLOOR REINFORCED CONCRETE FLOOR SUSPENDED GROUND FLOOR

Industrial/Commercial flooring Materials Steel and concrete; These two materials complete one another. Why? Concrete is efficient in compression and steel in tension Concrete encasement restrain steel against buckling Protection against corrosion and fire Steel bring ductility into the structure

Industrial/Commercial flooring Rebar Used For Slab Construction

Industrial/Commercial flooring Joints Why are joints required in concrete floor slabs? All concrete floor slabs are subject to stress. Causes include drying shrinkage, settlement, temperature changes, and applied loads. When stresses acting on concrete exceed its tensile strength, cracking will occur. That’s why joints —planned breaks in concrete — are important. They relieve stress by allowing concrete to move.

Industrial/Commercial flooring Joints Most concrete floors require three types of joints: Isolation Contraction Construction Though each type of joint is installed differently, they all work together to help minimize cracking.

Industrial/Commercial flooring Composite slabs Reinforced concrete slab In-situ concrete on shuttering Partially prefabricated slabs Fully prefabricated slabs

Industrial/Commercial flooring In situ cast concrete floors The principal types of reinforced in situ cast concrete floor construction:- Beam and slab Waffle grid slab Drop beam and slab Flat slab

Industrial/Commercial flooring Flat plate system Waffle Slab One Way Slab /Two Way Slab

Industrial/Commercial flooring What are the reasons for using composite slabs? Architectural Structural Economical Functionality Service and Flexibility Assembly

Industrial/Commercial flooring What are the Architectural reasons for using composite slabs? Longer spans Thinner slabs More slender columns More generous design solutions

Industrial/Commercial flooring What are the economical reasons for using composite slabs? Reduction in building height - saves area of cladding Loner spans with the same height –column free spaces Additional storeys with the same total building height Quicker time of erection Saving costs, earlier completion of building Lower financing costs Ready for use earlier - increasing rental income

Industrial/Commercial flooring What are the functional reasons for using composite slabs? Fire protection by using principles of reinforced concrete in which the concrete protects the steel Against Internal fire spread Resistance to collapse (loadbearing capacity) Resistance to fire penetration (integrity) Resistance to the transfer of excessive heat (insulation)

Industrial/Commercial flooring What are the service and flexibility reasons for using composite slabs? Adaptable structures Modification during the life of the building Modify services without violating the privacy of other occupants Accommodation of service facilities in the ceiling within a false floor in a coffer box running along the walls

Industrial/Commercial flooring What are the assembly reasons for using composite decking slabs? Working platforms of steel decking Permanent shuttering Reinforcement of profiled steel sheetings Speed and simplicity of construction Quality controlled products ensure greater accuracy

Industrial/Commercial flooring Precast Hollow Floors Prestressed Slabs

Industrial/Commercial flooring Precast Flooring There are many types of precast concrete floor such as : Precast Hollow Floors Precast hollow floor units are available in a variety of sections such as box planks / beams, tee section, I beam sections and channel sections. Composite floors Composite floors are combination of steel sheet, precast units and in situ concrete.

Industrial/Commercial flooring Precast floor What are the advantages of Precast Concrete floors? Doesn’t need formwork Time taken for concrete to cure in the formwork can be eliminated Better quality control Doesn’t need many workers as in in-situ concrete construction Fast completion of construction project Long spans available with precast concrete flooring systems reduce the number of secondary beam required and maximize the column free space. Fire resistance ratings normally between 1 & 2 hours