Superstructure

Superstructure

1. Key considerations

   • Stability - Horizontal loads
   • Primary structure - vertical loads

2. Steel frame

   • Skeleton frame
     • Consists of a steel frame building with vertical columns and horizontal beams, often constructed on a rectangular grid layout to support the floors, roofs and walls that are eventually attached to the frame
       • The floor construction usually follows the frame with metal decking which is shot fired to the beams to assist in frame stabalisation
         • The frame is usually further stabilised by tying in the steel to an in-situ concrete vertical lift shaft
         • Floor slabs are precast with insulation, they span up to 12metres
         • Alternatively metal decking is used and shot fired to the beams to add lateral stability, shear bolts are added to tie the floor to the frame
           • Reinforcement is added and then concrete is poured on site
           • Surface slab is usually power float finished
       • Tubular columns verticle
       • Cellular beams horizontal
         • Horizontal stability is improved with additional bracing at either end of the structure in a cross fashion
   • Sometimes a skeleton frame is used with a cantilevered support
     • Often in the form of 500mm diameter steel columns added to the end of the skeleton structure

3. Concrete Frames

   • Column and beam frame
     • Square grid of floor beams or rectangular grid arrangment, downstand beams as integral art of the slab, wide variety of cladding available, maximum span of 5- meters.
   • Flat Slab Frame
     • In this form of consturction the slab is in uniform thickness, column spacing 5-8 meters
   • Crosswall frame
     • Consists of in-situ concrete walls and floor slabs spanning between 5-7 meters.
       • Suitable for buildings with identical floor layouts across each level
       • Walls and slabs could be precast to incorperate wider slab regions, plank floors may be used to reduce formwork and costs
     • Mainly used for multistoreys, hotels, or mid rise residential units
       • Walls can be in-situ or precase at 6-8meters high
         • If precast, the concrete will have connect to the tie bar, the elements will be made so that they slot in and can be attached easily
       • Cladding may be infill panels fitted to the cross walls or a curtain walling system

4. Stability

   • For a framed building there are two main methods of stability enhancement
     • Concrete (lift and stairs) core s or sway frame stability moment connections
   • Schemes with concreted walls or steel structures will gain most of their stability form the verticle walls and horzontal floor fittings
   • Structural steel frames could use a steel cross bracing system on the outsides of the building or install bracing bays at regular intervals along the full height of the building

5. Light modular steel consturuction

   • Involves the steel modules being manufactured offsite and brought to site to be bolted together
     • Quick, economical, less on site waste, suitable where sites are limited for deliveries for more traditional methods, minimum disturbance to locality when consturcting
       • Size of units is limited by transport, usually 3.6m x 8m
         • Usually 4-10 storeys
   • Often inserted into steel frame column and beam structures, this distributed the load and allows for an open plan ground floor below
     • Columns are usually spaced at 6-8m intervals to support 15kN/m load
     • Modules are placed internally so facades can be fitted to the steel frame, bracing usually comes in the form of a central piece such as lifts or stairs
   • All sections are BIM coded for precise drilling, windows are often added and walls are insulated, some utilities and services can also be added to the floors and walls , finishes can also be installed like carpets, wallpaper, paint and for bathroom modules all utilities will be added
   • Key benfits
     • Shorter build times, leading to reduced site management costs and early return on investment
       • Superior quality achieved by factory based construction process and delivery checks
         • Economy of scale in production, particularly in larger projects or repeated modules
           • Excellent building regulations application, fire safety, acoustic and insulation performance
             • Reduced design costs to the client, suppliers do most of the work
               • Lightweight, less materials used and less wasted, more room on site especially if space is restricted
                 • Increased productivity in factories, reduction of on site labour
                   • Safer construction, less chance of accidents, reduced time on risk assesment
                     • Less neighbourhood disturbance to adjacent buildings

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