BE2S71 Construction Technology 2 Framed Buildings Ref; Civil Engineering Construction Design and Management; D R Warren CORUS British Cement Association

Superstructures Defined as: -“construction of buildings above ground level” Before the turn of the 20th century buildings were restricted in height due to the required thickness of load bearing brickwork The development of the lift in 1880 has been seen as the catalyst to high rise frame construction i.e. not limited by the means of stairs to access higher storeys. Meant building could extend upwards.; lighter in weight and have greater window area

Conventional Superstructure Is now a framed structure using: - Long Span / Medium Rise Structures Beams / Columns to support roof; floor and cladding Competition between steel and concrete and popularity depends upon variations in price

Floor Space Client; Architect usually want as much uninterrupted floor price as possible Because buildings are priced on floor area and must be flexible enough to accommodate varying internal partition arrangements as the use may change many times throughout their design life But they do have the disadvantage of internal columns which reduce and dictate layout

Composite Construction One step to overcoming these disadvantages is by using composite construction of steel and concrete that will assist in achieving long spans

Functional Requirements The main functional requirements are: - Strength Stability Durability Fire safety

Long Span Low Rise Buildings One or Two Storey 15m – 20m in height

Construction Portal Frames Trusses Latticed Portals Space Frames Shell Roofs

Portal Frame Connections Provides a clear open space Spans 12 – 45m

Stability The designer should consider the stability of the structure in all directions Each joint in the framed structure must be systematically considered i.e. x, y and z directions north; south and up

Trusses Often used instead of portal construction as they can span large distances Trusses can carry a huge variety of loading patterns ideal for industrial applications Difficult to prefabricate and transport and can cost up to 20 – 30% more than a portal frame

Medium Rise Structures Defined as up to four storeys medium rise structures are the most common form of construction in the UK Such structures are usually framed structures and can be constructed of concrete and or steel

Concrete Flexible in form; Robust structure Capable of carrying a wide variety of loadings ideal for a change of use Noise insulation from both internal and external sources Provides fire insulation Slower to construct Either pre-cast or cast in-situ Expensive?

High profile failures Alkaline Aggregate Reaction (AAR); Lafarge has been selling RMC from Sept 2002 – Dec 2004 across the South East of England with excessive levels of Alkaline which has been linked to the development of concrete cancer Poor workmanship may lead to carbonisation

Concrete Three materials used in production of concrete Cement Aggregate Sand and Water

Cement Portland Ordinary Rapid Hardening Sulphate resisting White Low heat Blast furnace Water repellent

Aggregates Natural Artificial Fine and Coarse Grading Particle size and shape Water

Reinforcement

Reinforcement

Pre-cast Concrete Is fast to erect and cheaper than in situ Manufactured off site in factory controlled conditions High Quality But usually provides thick floor slabs due to down stand beams to provide support But can be inflexible if design on construction errors occur

In-situ Concrete Requires intensive on site labour operations Weather can dictate on site operations Space requirements = storage; cleaning lifting off loading areas Formwork – Falsework Reinforcement Curing of concrete Slow follow on for trades

Formwork

Steel Frame “Meccano Concept” So called because it requires small number of repetitive parts and is assembled on site in what is basically a “Kit” construction. Pre-fabrication is rigorously controlled and accuracy and quality is guaranteed (nearly always) highly skilled factory workforce with quality control checks at all stages of production.

Skeletal Steel Framed Buildings

Steel Framed Essential that factory and site are in possession of correct and updated drawings and specifications, setting out of stanchion base must be accurate as components are accurately produced to specification Most of the work is undertaken during production. Specialist teams assemble frame on site. Uses modular and dimensional co-ordination for success.

Structural Steel Frames Skeleton frames support and transmit all loadings Economics generally dictate member arrangement. Columns are arranged on a rectangular grid layout. Typically they may be 3 ‑ 4 metres apart and parallel to the span of the floors. Floor beams may be up to 7.5 metres. The floors are designed to span one way. Should greater clear spans be necessary secondary beams may be introduced. Greater span is attained by an increase in structural depth of the floor support structure hence increasing floor to floor height and hence construction costs.

Steel Frames Controlled factory workshop environment all year good conditions enables high productivity Ideal material for fast prefabricated construction Utilises stock of Pre-Made sections cut to length, fixing cleats welded and bolt holes drilled for site assembly of finished components Most work pre- fabricated off site in workshop Little or no on-site storing of component Prefabricated can be installed same time as foundations Little on site work and easily carried out Light members with low cross sectional areas require only mobile crane for installation :-

Steel Frames Factory made high accuracy close tolerance. Pre-fabricated components enables quick and relative ease of on site installation Swift assembly by bolting of few large pre-fabricated parts Allows quick follow on of trades Loaded on back of lorry by use of mobile crane for transport. Reduces hire period of mobile crane due to ease of loading. Enables use of large pre-fabricated cladding and partition panels which further supports the “Meccano” concept Well suited to Multi Storey construction on confined sites. Particularly when supported by programmed sequence of deliveries and direct incorporation of parts into building There are drawbacks, needs protection from fire and corrosion

Hot Rolled Structural Steel Sections

Connections

Fire Protection of Steel Frames Why is it important to protect steel against fire? Loses its bearing capacity At what temperature does steel lose its strength? 5500c When does fire become a problem? After the frame is erected List two types of fire protection Sprayed; Board Casings; Blocks; Concrete; Paint How does the insulating barrier work? Slows down the transfer of heat How does the size of the section of steel affect its capacity to resist fire Larger sections absorb more heat than smaller sections before reaching the critical temperature

Corrosion Protection of Structural Steel To assist in the prevention of corrosion to steel what should be kept away from the surface: - Oxygen Water Alternatively what can be used: - Sacrificial metal such as Zinc or aluminium to discourage corrosion by an electrochemical reaction[ Name two methods of excluding moisture from the surface of steel Put steel inside building where it will not get wet Cover steel with a protective coating

Fire Protection of Steel

Corrosion Protection of Structural Steel Protective coatings differ in their effectiveness in the following ways: - Exclude water from the surface of the steel Adhering to the surface Resisting attack from Chemicals Resisting degradation by exposure to sunlight What are the two important factors that should be considered if maximum life is to be achieved along with minimum life cycle costs: - Surface preparation Design to avoid water collection What dictates the choice of corrosion system? Environment Location

Composite Steel profiled decking

Composite Steel profiled decking

Composite Steel profiled decking