Material Requirements for Steel and Concrete Structures

1 Material Requirements for Steel and Concrete Structures Chiew Sing-Ping School of Civil and Environmental Engineering Nanyang Technological University, Singapore 2 Scope Materials Concrete Reinforcing Steel Structural Steel Seismic Requirements (BC3: 2013) Materials for seismic design Detailing for seismic design 3 Structural Eurocodes SS EN 1990 (EC0): SS EN 1991 (EC1): Basis of structural design Actions on Structures design of Concrete Structures design of Steel Structures design of composite Steel and Concrete Structures design of timber Structures design of masonry Structures design of aluminium Structures Geotechnical design design of Structures for earthquake resistance SS EN 1992 (EC2): SS EN 1993 (EC3): SS EN 1994 (EC4): BS EN 1995 (EC5): BS EN 1996 (EC6): BS EN 1999 (EC9): SS EN 1997 (EC7): SS EN 1998 (EC8): 4 SS EN 1992 design of Concrete Structures BS EN 206-1 Specifying Concrete BS EN 10080 Reinforcing Steel BS EN 13670 Execution of Structures BS EN 10138 Prestressing Steel National Annex BS 8500 Specifying Concrete BS 4449 Reinforcing Steel BS 8666 Reinforcing scheduling Concrete Structures (EC2) 5 Concrete Six density classes of lightweight Concrete are defined in EN206-1.

2 Density class Density (kg/m3) 801-1000 1001-1200 1201-1400 1401-1600 1601-1800 1801-2000 Density (kg/m3) Plain Concrete 1050 1250 1450 1650 1850 2050 Reinforced Concrete 1150 1350 1550 1750 1950 2150 Normal Concrete Strength class C12/15 C90/105 Density 2400 kg/m3 Lightweight Concrete Strength class LC12/13 LC80/88 Density 2200 kg/m3 used in design to calculate self-weight 6 fck (MPa) 12 16 20 25 30 35 40 45 50 55 60 70 80 90 fck,cube (MPa) 15 20 25 30 37 45 50 55 60 67 75 85 95 105 fcm (MPa) 20 24 28 33 38 43 48 53 58 63 68 78 88 98 fctm (MPa) fctk, (MPa) fctk, (MPa) Ecm (GPa) 27 29 30 31 33 34 35 36 37 38 39 41 42 44 c1 ( ) cu1 ( ) c2 ( ) cu2 ( ) n c3 ( ) cu3 ( ) Strength and deformation characteristic for normal Concrete Concrete 7 flck (MPa) 12 16 20 25 30 35 40 45 50 55 60 70 80 flck,cube (MPa) 13 18 22 28 33 38 44 50 55 60 66 77 88 flcm (MPa) 17 22 28 33 38 43 48 53 58 63 68 78 88 flctm (MPa) flctm = fctm 1 flctk, (MPa) flctk, = fctk, 1 flctk, (MPa) flctk, = fctk, 1 Elcm (GPa) Elcm = Ecm E lc1 ( ) kflcm (Ecm E) lcu1 ( ) lc1 lc2 ( ) lcu2 ( ) 1 1 1 1 1 n lc3 ( ) lcu3 ( ) 1 1 1 1 1 Strength and deformation characteristic for lightweight Concrete Concrete 1 = + /2200 E = ( /2200)

3 2 8 Modulus of elasticity Ecm The modulus of elasticity of a Concrete is controlled by the moduli of elasticity of its components. Approximate values for the modulus of elasticity Ecm, for Concrete with quartzite aggregates are given in Table (EC2). For limestone and sandstone aggregates the values should be reduced by 10% and 30% respectively. For basalt aggregates the values should be increased by 20% 9 Creep and Shrinkage Creep coefficient is determined by the following factors: Relative humidity Element geometry Strength class Age at loading Cement class Stress/strength ratio at loading 10 Creep and Shrinkage The total shrinkage is taken as the sum of the autogenous shrinkage and drying shrinkage: cs = ca + cd The autogenous shrinkage is related to Concrete class.

4 The drying shrinkage is estimated by the following factors: Relative humidity Element geometry Strength class Cement class 0501001502002500100200300400C50/60 C45/55 C40/50 C35/45 C30/37 C25/30 C20/25 C55/67 C60/75 C70/85 C80/95 C90/105 Time (days) Autogenous shrinkage 11 Stress-strain relations Parabolic-Rectangular Bi-Linear 90 for for MPafor MPafor MPafor MPafor ffnfnffffff (?)(?)(?) 35 90/10050cu2ckckMPafor MPaff (?) / 35 90/10050c3ckc3ckckcu3ckcu3ckckfor MPafor MPafor MPafor MPaffffff (?)(?)(?)(?)12 Stress-strain relations Higher strength Concrete shows more brittle behavior. Concrete stress-strain relations C45/55 C40/50 C35/45 C30/37 C25/30 C20/25 C55/67 C60/75 C70/85 C80/95 C90/105 c (MPa) 13 EC2 permits a rectangular stress block to be used for section design Rectangular stress distribution = for fck 50 MPa = (fck 50)/400 for 50 < fck 90 MPa = for fck 50 MPa = (fck 50)/200 for 50 < fck 90 MPa fck (MPa) 50 60 70 80 90 Stress-strain relations : defining the effective height of the compression zone : defining the effective strength.

5 14 Reinforcing Steel Reinforcing bars Coils Welded fabric Lattice girders Cold-reduced Steel wires Hot-rolled Wire Rod Dia. to 14mm YS : 300 N/mm2 Profiling Rollers - Dia. Reduction 8mm > 7mm Finished Wire Coils Dia. 5mm to 13mm, YS : 500 N/mm2 15 Welded fabric Resistance Welding Welded Mesh Cold Rolled Wire Straightening & Cutting Computerised Machine Wires in coil / pre-cut form 16 17 Reinforcing Steel EC2 does not cover the use of plain or mild Steel reinforcement. Principles and rules are given for deformed bars, de-coiled rods, welded fabric and lattice girders. There is no technical reason why other types of reinforcement should not be used. Relevant authoritative publications should be consulted when other types reinforcement are used. EN 10080 provides the performance characteristic and testing methods but does not specify the Material properties.

6 These are given in Annex C of EC2. 18 Reinforcing Steel Performance Requirements Strength (fyk or , ft) Ductility ( uk and ft/fyk) Weldability Bendability Bond characteristics (fR) 19 Reinforcing Steel Stress-strain relations for reinforcing Steel Strength Yield strength fyk or and tensile strength ft. Ductility Ratio of tensile strength to yield strength ft/fyk Elongation at maximum force uk. Tensile test Universal Testing Machine Tensile Test Coupon Extensometer Computer and Datalogger Analog Datalogger Analog Datalogger 21 Weldability Weldability is usually defined by two parameters: Carbon equivalent value (CEV) Limitations on the content of certain elements The maximum values of individual elements and the carbon equivalent value are given below.

7 Table Chemical composition (% by mass) Carbon Max. Sulphur Max. Phosphorus Max. Nitrogen Max. Copper Max. CEV Max. Cast analysis Product analysis 22 Properties of reinforcement Product form Bars and De-coiled rods Wire fabrics Class A B C A B C Characteristic yield strength fyk or (MPa) 400 to 600 k = (ft/fy)k < < Characteristic strain at maximum force uk(%) Bendability Bend/Re-bend test - Maximum bar size deviation from 8mm normal mass (%) > 8mm Properties of reinforcement (Annex C EC2) The UK has chosen a maximum value of characteristic yield strength, fyk= 600 MPa, But 500 MPa is the value assumed in BS4449 for normal supply. 23 Reduces congestion Fewer bars needed Increases bar spacing Reduces bar diameter Faster construction Placing/tying bars (labor) Less weight (crane) Concrete placement is easier Higher strength reinforcing Steel Advantage of higher strength reinforcing Steel : There is a push to use reinforcing Steel with higher yield strength of 600 MPa because EC2 permits it.

8 24 Structural Steel (EC3) Performance Requirements Strength able to carry load Ductility able to sustain permanent deformation Weldability able to transfer load Toughness able to absorb damage without fracture 25 High strength Steel (HSS) Normal strength Steel : Steel grades S235 to S460 High strength Steel : Steel grades greater than S460 up to S700 Compared to normal strength Steel , high strength Steel has lower ductility. 26 Why use HSS When strength-to-weight is important, for example, in bridges to facilitate construction and crane Structures . Studies show that the ratio of the tensile residual stress to yield stress of the member seems to decrease with increasing yield strength in hot-rolled sections. More favorable buckling curves may be used for high strength Steel for S460.

9 Higher buckling resistance due to favorable buckling curves. 27 Buckling curves 28 Buckling curves 29 EC3 has additional ductility Requirements compared to BS5950 in terms of stress ratio, elongation and strain ratio. Ductility Requirements Normal strength Steel (fy 460 N/mm2) fu/fy Elongation at failure not less than 15% u 15 y y is the yield stain high strength Steel (460 N/mm2 <fy 700 N/mm2) fu/fy (EC3-1-12) fu/fy ( UK NA to EC3-1-12) Elongation at failure not less than 10% u 15 y 30 Some product standards only have Requirements on nominal yield and tensile strength, or their minimum values. The stress ratio calculated according to these nominal values cannot comply with EC3. Problem Standard Grade Nominal yield strength (MPa) Nominal tensile strength (MPa) Stress ratio AS 1397 G450 450 480 G500 500 520 G550 550 550 AS 1595 CA 500 500 510 EN 10149 S 550MC 550 600 S 600MC 600 650 S 650MC 650 700 S 700MC 700 750 EN 10326 S550GD 550 560 ISO 4997 CH550 550 550 31 Reinforcement Structural Steel A B C Normal strength High strength Yield strength (MPa) 400 to 600 460 > 460 700 Modulus of elasticity (GPa) 200 210 ft/fy or fu/fy < (NA) Elongation (%)

10 15 10 Ultimate strain u 15 y Comparison of structural Steel and reinforcing Steel Structural Steel and reinforcing Steel 32 EC2 EC3 EC4 Concrete Normal C12/15- C90/105 _ C20/25 - C60/75 Light weight LC12/13 LC80/88 LC20/22 - LC60/66 Reinforcing Steel 400 - 600 N/mm2 _ 400 - 600 N/mm2 Structural Steel _ 700 N/mm2 460 N/mm2 Material comparison These ranges in EC4 are narrower than those given in EC2 ( C12/15 C90/105) and EC3 ( 700 N/mm2) because there is limited knowledge and experimental data on composite members with very high strength Concrete and high strength Steel . 33 Material for seismic design Ductility Class DCL (Low) DCM (Medium) DCH (High) Concrete grade No limit C16/20 C20/25 Steel Class (EC2, Table C1) B or C B or C Only C Longitudinal bars only ribbed only ribbed Material limitations for primary seismic members DCL - ductility class low DCM - ductility class medium DCH - ductility class high For secondary seismic members , they do not need to conform to these Requirements .