steel fixing

Outlines

• why put steel in concrete?
• detailing
• reinforcement schedule
• fabrication
• safety considerations
• reflection

Why reinforcement in concrete?

(混凝体中为什么加入钢筋)

• concrete is the material of choice for designs based on the skeletal
  and cellular concepts;
• however, concrete is brittle(脆的) while steel is ductile(延性);
• reinforcement concrete offers economic & technical advantages;
• expansion rate(膨胀率) of concrete proportional to steel;
• composite action(复合效果) depends on bonding between concrete and steel;

Purpose of steel reinforcement

concrete is weak in tension, rebars required to resist tension and shear;

Applications

• structural concrete reinforced:

• foundation-wide trip, pad, raft & piles
• columns
• beams
• walls
• slabs & stairs
  structural designer specifies the type, size & shape & layout of rebars for detailer;

Design varianles

• structural engineer:
  • calculates area of steel for desired capacity;
  • steel grade(钢种)( mild or high yield);
  • nubber of bars, size and pitch(间距)( to achieve area);
  • cover to reinforcement(钢筋保护层)( fire and durability requirement)

Structural Layout

Detailing of reinforcement

• details must be read in conjunction(一致); be consistene-adopt an order of
  working;
• graphical representation(图示) of reinforcement layout;
  • arrangement of bars(钢筋排列) depends on structural element
  • mesh(钢筋网)–array of longitudinal & cross bars; tied together;
  • fabric(编网钢筋)–factory made welded mesh; bar size<=10mm;
  • links-bent bars used to resist shear;
    
• detailing must provide sufficient information for fabrication and
  construction; clarity, understand language
• structural elements detailed on plan and section- must be read
  together; query if necessary;
• BS-8666- reinforcement bar shape coding-Tab3;
• standard shape(杆的形状), guide for determining length of bars and template(模板) for preparing schedule;

Notation of steel reinforcement

BS 4449 classification of steel reinforcement

BS 8666–reinforcement shape code(1-99);
bars avaiable 12-32m;
extract of of BS8666:2005 – shape codes:

General structural layout

slab

beam

column & foundation

Reinforcement (bending) schedule

required for pricing, fabrication & construction;
preparation-- can be elemental & activity e.g. individual foundation or one for all groundworks;
dimensions measured according to BS 8666

calculate length of bars form:

dimensions of concrete less the cover to rebars(钢筋);
allow for bends using standard or applicable values;
count numbers(数一数) if spacing rather than quantity given;

Fabrication

• slab reinforcement installed directly on formwork;
• mesh or reinforcement cages, fabricated & installed;
• bar cut, bent and tied together or welded;
  

Safety considerations

• hazards;
• fabrication–cutting(切割), welding(焊接), tying(捆扎), trips(脱扣),working at heights(高空作业) etc;
• construction: lifting, exposed ends, protrusions;

summary

steel reinforcement plays a major role in construction–effcient combination with concrete;
reinforcement detailing and schedule have been considered;
the fabrication of reinforcement for some structural elements discussed;
steel reinforcement presents high risk on site(在现场);