§7.5 Technical Standards and §7.5 Technical Standards and Selection of Building SteelsSelection of Building Steels

Steels of Steel StructureSteels of Steel Structure carbon structural steelcarbon structural steel low-alloy and high- tensile steellow-alloy and high- tensile steel

Steels of Reinforced Concrete Steels of Reinforced Concrete StructureStructure hot rolled steelhot rolled steel cold rolled ribbed steel wires and barscold rolled ribbed steel wires and bars cold rolled twisted steelcold rolled twisted steel

steels of reinforced concrete steels of reinforced concrete structurestructure

It can be classified into:

hot-rolled steelhot-rolled steel

cold rolled twisted steelcold rolled twisted steel

cold-drawing steelcold-drawing steel

steel strandsteel strand

It includes It includes hot-rolled round hot-rolled round bars(Tab.7.5.6)bars(Tab.7.5.6) and and hot rolled ribbed hot rolled ribbed steel barssteel bars..

Hot rolled Hot rolled steelsteel bars have 3 grades by bars have 3 grades by yield strength and tensile strength.yield strength and tensile strength.

Its types, code names, mechanical Its types, code names, mechanical properties and application are shown in properties and application are shown in the following table(Tab.7.5.7).the following table(Tab.7.5.7).

Hot-rolled SteelHot-rolled Steel

Tab.7.5.6 Tab.7.5.6 The mechanical and technical properties of hot rolled round bars

code namescode names

mechanical properties

bending test

180℃d ＝ elbow diameter

a ＝ specimen diameter

σσss

(MPa)(MPa)

σσbb

(MPa)(MPa)

δδ1010

(( ％％ ))

≥≥

Q215Q215

Q235Q235

215215

235235

375375

410410

2727

2323

dd ＝＝ 00

dd ＝＝ 0.5a0.5a

Tab.7.5.7 The mechanical and technical properties Tab.7.5.7 The mechanical and technical properties of hot rolled ribbed steel barsof hot rolled ribbed steel bars

((GB/T701-1997GB/T701-1997 、、 GB1499-1998GB1499-1998))

Code

names

Nominal diameter

（ mm）

Yield pointσs (MPa)

Tensile strength σb

(MPa)

Percentage elongationδ5

(%)

Bending test 180℃dd ＝＝ elbow elbow diameterdiameter

aa ＝＝specimen specimen diameterdiameter

≥

HRB335 6 ～ 25

28 ～ 50 335 490 16

d ＝ 3a

d ＝ 4a

HRB4006 ～ 25

28 ～ 50 400 570 14

d ＝ 4a

d ＝ 5a

HRB5006 ～ 25

28 ～ 50 500 630 12

d ＝ 6a

d ＝ 7a

ApplicationApplicationApplicationApplication

HRB335 and HRB400 apply mainly to non-HRB335 and HRB400 apply mainly to non-prestressed and prestressed concrete.prestressed and prestressed concrete.HRB500 appliess mainly to prestressed coHRB500 appliess mainly to prestressed concrete.ncrete.

Cold rolled ribbed steelCold rolled ribbed steel wires and bars wires and bars

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

Code

names

Tensile strength σb

(MPa)

elongation (%) ≥

Bending

180° D － elbow elbow diameterdiameter

d －nominal diameter

Stress relaxation

σcom=0.7σb

Times of ben

d-ingδ10 δ100

1000h

≮(%)

10h

≮(%)

CRB550

CRB650

CRB800

CRB970

CRB1270

550

650

800

970

1170

8

－－－－

－4

4

4

4

D=3d

D=3d

D=3d

D=3d

D=3d

－8

8

8

8

－5

5

5

5

－3

3

3

3

Tab.7.5.8 The mechanical property of Cold Tab.7.5.8 The mechanical property of Cold rolled ribbed steel wires and bars rolled ribbed steel wires and bars

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 steelCold rolled twisted steel

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 steelCold rolled twisted steel

Tab.7.5.9 The mechanical property of cold rolled Tab.7.5.9 The mechanical property of cold rolled twisted steeltwisted steel ((GBJ204-83GBJ204-83))

level of steel steel

wirewire

Diame

-ter（ mm ）

tensile strength N/mm2

（ Kgf/cm2 ） percentage elongation

（ 100mm ）

（ % ）

repeat bend

(180°)Applica

-tionⅠ Ⅱ

≥

first level

5

4

650 （ 65 ）

700 （ 70 ）

600 （ 60 ）

650 （ 65 ）

3

2.54

PrestrePrestre

-ssed ste-ssed steel el

second level

3 ～ 5 550 （ 55 ） 2 4

non-presprestretre

-ssed ste-ssed steel el