1. §7.5 Technical Standards and Selection of Building Steels Steels of Steel Structure  carbon structural steel  low-alloy and high- tensile steel Steels of Reinforced Concrete Structure  hot rolled steel  cold rolled ribbed steel wires and bars  cold rolled twisted steel

2. steels of reinforced concrete structure It can be classified into: hot-rolled steel cold rolled twisted steel cold-drawing steel steel strand

3. It includes hot-rolled round bars(Tab.7.5.6) and hot rolled ribbed steel bars. Hot rolled steel bars have 3 grades by yield strength and tensile strength. Its types, code names, mechanical properties and application are shown in the following table(Tab.7.5.7). Hot-rolled Steel

4. Tab.7.5.6 Tab.7.5.6 The mechanical and technical properties of hot rolled round bars code names mechanical properties bending test 180 ℃ d ＝ elbow diameter a ＝ specimen diameter σ s (MPa) σ b (MPa) δ 10 ( ％ ) ≥ Q215Q2352152353754102723 d ＝ 0 d ＝ 0.5a

5. Tab.7.5.7 The mechanical and technical properties of hot rolled ribbed steel bars (GB/T701-1997 、 GB1499-1998) Code names Nominal diameter （ mm ） Yield pointσ s (MPa) Tensile strength σ b (MPa) Percentage elongationδ 5 (%) Bending test 180 ℃ d ＝ elbow diameter a ＝ specimen diameter ≥ HRB335 6 ～ 25 28 ～ 50 33549016 d ＝ 3a d ＝ 4a HRB400 6 ～ 25 28 ～ 50 40057014 d ＝ 4a d ＝ 5a HRB500 6 ～ 25 28 ～ 50 50063012 d ＝ 6a d ＝ 7a

6. Application Application HRB335 and HRB400 apply mainly to non-prestressed and prestressed concrete. HRB500 appliess mainly to prestressed concrete.

7. Cold rolled ribbed steel wires and bars The mechanical property of Cold rolled ribbed steel wires and bars are shown in Tab.7.5.8

8. Code names Tensile strength σ b (MPa) elongation (%) ≥ Bending 180° elbow diameter D － elbow diameter d － nominal diameter Stress relaxation σ com =0.7σ b Times of bend -ing δ 10 δ 100 1000h ≮ (%) 10h ≮ ( %) CRB550 CRB650 CRB800 CRB970 CRB1270 550 650 800 970 1170 8－－－－8－－－－ －4444－4444 D=3d －8888－8888 －5555－5555 －3333－3333 Tab.7.5.8 The mechanical property of Cold rolled ribbed steel wires and bars

9. It is one type of cold-working steels. It is formed through repeated cold- drawing of the circled bars of Q235 or Q215 whose diameter is 6.5-8mm by wire stretcher. Cold rolled twisted steel

10. It is classified into first-rate and second- rate. The former is mainly used as prestressed reinforcement. The latter can be used as non-prestressed reinforcement, as well as weld net, weld structure, hoop and constructional steel. The mechanical properties are demonstrated in the following table(Tab.7.5.9). Cold rolled twisted steel

11. Tab.7.5.9 The mechanical property of cold rolled twisted steel (GBJ204-83) steel wire level of steel wire Diam e -ter （ mm ） tensile strength N/mm 2 （ Kgf/cm 2 ） percentage elongation （ 100mm ） （ % ） repeat bend (180°) Applica -tion ⅠⅡ ≥ first level 5454 650 （ 65 ） 700 （ 70 ） 600 （ 60 ） 650 （ 65 ） 3 2.5 4Prestre -ssed steel second level 3～53～5550 （ 55 ） 24 prestre non- prestre -ssed steel