Pp08_ Asep_ Nscp 2015 Update on Ch5 Structural Steel Part 1 Asd

ASSOCIATION OF STRUCTURAL ENGINEERS OF THE PHILIPPINES INC.

UPDATES ON CHAPTER 5: STRUCTURAL STEEL NSCP 2015 Mark Elson C. Lucio ASEP Treasurer (2015-2017) PART 1: ASD Member (Chapter 5 NSCP v1 2015)

NSCP National Structural Code of the Philippines NSCP had evolved from: Edition

Year

∞

First

1972

∞

Second

1981

∞

Third

1987

∞

Fourth

1992

∞

Fifth

2001

∞

Sixth

2010

∞

Seventh

2015

AISC American Institute of Steel Construction AISC Specifications and Manuals had evolve from:

*Year indicated are first printing versions/revisions

Edition

Year

∞

First

1927

∞

Second

1934

∞

Third

1937

∞

Fourth

1941

∞

Fifth

1946

∞

Sixth

1963

∞

Seventh

1970

∞

Eight

1980

∞

Ninth

1989

AISC American Institute of Steel Construction AISC Code of Standard Practice for Steel Buildings and Bridges: Title

Year

∞

Code of Standard Practice

1924, 1928, &1934

∞

Code of Standard Practice for Steel Structures Other Than Bridges

1937

∞

Code of Standard Practice for Steel Buildings and Bridges

1945, 1952, 1959, 1963, 1970, 1972, 1976, 1986, 1992 & 2000

∞

AISC 303-05: Code of Standard Practice for Steel Buildings and Bridges

2005

∞

AISC 303-10: Code of Standard Practice for Steel Buildings and Bridges

2010

AISC American Institute of Steel Construction AISC Seismic Provisions for Structural Steel Buildings: Title

Year

∞

Seismic Provisions for Structural Steel Buildings

1990, 1992, 1997,

∞

Seismic Provisions for Structural Steel Buildings (1997) Supplement No. 1

1999

∞

Seismic Provisions for Structural Steel Buildings (1997) Supplement No. 2

2000

∞

ANSI/AISC 341-02: Seismic Provisions for Structural Steel Buildings

2002

∞

ANSI/AISC 341-05: Seismic Provisions for Structural Steel Buildings, including Supplement No. 1 dated Nov. 16, 2005

2005

∞

ANSI/AISC 341-10: Seismic Provisions for Structural Steel Buildings

2010

NSCP 2001, 2010 and 2015 Comparisons of the previous NSCP editions References of NSCP: 2001

2010

2015

AISC Code

1989

AISC 303-05

AISC 303-10

ASCE

ANSI A58.1-82

SEI/ASCE 7-02

ASCE/SEI 7-10

Other References of NSCP : 2001

2010

2015

ANSI/AISC 341-05 Seismic ANSI/AISC 341-10 Seismic Seismic Provisions for Structural Provisions for Structural Steel Provisions for Structural Steel Steel Buildings (1997) Buildings Buildings n/a

n/a

ACI 349-06 Code Requirements for Nuclear Safety-related Concrete Structures and Commentary

NSCP 2001, 2010 and 2015 Comparisons of the previous NSCP editions Other References of NSCP: 2001

2010

2015

n/a

ASCE/SFPE 29-99 Standard ASCE/SFPE 29-05 Standard Calculation Methods for Structural Calculation Methods for Structural Fire Protection Fire Protection

n/a

ASME b18.2.6-96 Fasteners for ASME b18.2.6-06 Fasteners for Use in Structural Applications Use in Structural Applications

n/a

ASME B46.1-95 Surface Texture, ASME B46.1-02 Surface Texture, Surface Roughness, Waviness Surface Roughness, Waviness and Lay and Lay

NSCP 2001, 2010 and 2015 Comparisons of the previous NSCP editions Revisions of NSCP Manual: 2001

2010

2015

Appendix A‐3.4 Bolts and Threaded Parts (Net Tensile Areaa) n/a

n/a

9382 0.9382 4 4 511.2.2.3 Branches with Axial loads in K‐connections 1

0.24 . 0.5 1.33

.

1

1



0.24 .

.

.



1

510.8 (Design of Connections) Column Bases and Bearing on Concrete n/a

∅ Ω

0.60 2.5

∅ Ω

0.65 2.31

NSCP 2001, 2010 and 2015 Comparisons of the previous NSCP editions Comparison of Load Combinations (LRFD) 2001

2010

2015

1.4D 1.2D + 1.6L + 0.5Lr 1.2D + 1.6Lr + (f1L or 0.8W) 1.2D + 1.3W + f1L + 0.5Lr 1.2D + 1.0E + f1L 0.9D ± (1.0E or 1.3W)

1.4(D + F) 1.2(D + F + T) + 1.6(L + H) + 0.5(Lr or R) 0.9D + 1.6W + 1.6H 0.9D + 1.0E + 1.6H

1.4(D + F) 1.2(D + F + T) + 1.6(L + H) + 0.5(Lr or R) 1.2D + 1.6(Lr or R) + (f1L or 0.5W) 1.2D + 1.0W + f1L + 0.5(Lr or R) 1.2D + 1.0E + f1L 0.9D + 1.0W + 1.6H 0.9D + 1.0E + 1.6H

NSCP 2001, 2010 and 2015 Comparisons of the previous NSCP editions Comparison of Load Combinations (ASD) 2001 D D + L + Lr D + [W or (E/1.4)] 0.9D ± (E/1.4) D + 0.75[L + Lr + [W or (E/1.4)]

2010 D+F D+H+F+L+T D + H + F + (Lr or R) D + H + F + 0.75(Lr or R) D + H + F + [W or (E/1.4)]

2015 D+F D+H+F+L+T D + H + F + (Lr or R) D + H + F + 0.75[L + T + (Lr or R)] D + H + F + [0.6W or (E/1.4)]

ASD Allowable Strength Design The fundamental requirement of structural design is that the required strength not exceed the available strength. Required Strength ≤ Available Strength In Allowable Strength Design (ASD), the available strength value is obtained by dividing the nominal, or theoretical strength by a factor of safety. This can be expressed as:

In AISC 2005, ASD was modified from Allowable Stress Design to Allowable Strength Design. This minor modification changed the equations from a stress equation to strength (axial force, shear, and flexure) equation.

ASD Allowable Strength Design Required strength

where:

Ra

= Required Strength (applied loads) =

Rn

Available strength or Allowable strength

summation of service loads (demand)

= Rnominal strength =

can be solved using the properties of structural material (cross‐sectional area, depth, width, thickness, etc)

Rn / Ω

= Allowable Strength = maximum strength allowed to be applied on a structural material

Ω

= factor of safety to accommodate uncertainties in material properties, design theory,   workmanship and loading

Old ASD vs New ASD Difference between the old and new ASD TENSION

Allowable Stress Design (old)

Yielding of Gross Section











0.60



Allowable Strength Design (new)







Fracture of Net Section





0.50





.

.



Ω Ω



.









. Ω Ω





.

1.67

.

2.00

Sample Problem  Tension Member  A single‐angle tension member, an L90 × 90 × 10, is connected to a gusset plate with 22 mm‐diameter bolts as shown. A36 steel is used. The service loads are 155 kN dead load and 67 kN live load. Investigate this member for compliance with the AISC Specification. Assume that the effective net area is 85% of the computed net area. Use New ASD *See Section 504 of NSCP 2015

L90 x 90 x 10

Sample Problem Tension Member Solution: First, compute the nominal strengths. Gross section: Ag = 1713 mm2 (from the Manual) Pn = FyAg

Eqn. 504.2-1

Net section: An = 1713 – (10)(22 + 3) = 1463 mm2 Ae = 85% (An) = 0.85 (1463) = 1244 mm2

= 250 MPa (1713 mm2) = 428.25 kN

Pn = FuAe = 400 MPa (1244 mm2) = 497.60 kN

Eqn. 504.2-2

Sample Problem Tension Member a)

For the gross section, the allowable strength is

b)

428.25 1.67

.



.



For the net section, the allowable strength is

497.60 2.00



The smaller value controls; the allowable strength is 248.80 kN

Sample Problem Tension Member Solution: c) Solve for the required strength, Pa Pa = D+L = 155 kN + 67 kN = 222 kN Answer: The member is satisfactory since 222 kN Cc (old) or KL/r > 4.71√(E/Fy) (new)





Allowable Strength Design (new)

12 ⁄ 23



:

⁄



.



Ω Ω 1.67 0.877

.

Sample Problem  Compression Member A W14 × 74 of A992 steel has a length of 6.0 m and pinned ends. Compute the allowable compressive strength for ASD. *See Section 505 of NSCP 2015 Solution: Slenderness Ratio: Maximum KL / r



.

.



95.25

4.71

200



OK!

113.4

Since 95.25 < 113.4, it is an inelastic column.

Sample Problem  Compression Member Solution:



200000 95.25

.

217.57 MPa



0.658

The Nominal Strength is:



The Allowable Stress is:



The Allowable Strength is:

.

Eqn. 505.3-4

345



177.66

177.66 14,064

. . .

.

.

.

,

.





,

Eqn. 505.3-2

.



Eqn. 505.3-1

Old ASD vs New ASD Difference between the old and new ASD SHEAR

Allowable Stress Design (old)

h/tw ≤ 998/√(Fy)



0.40

.

h/tw ˃ 998/√(Fy)













2.89

0.40



0.6





.











Allowable Strength Design (new)

Ω

.





Ω

.

.

1.50

Old ASD vs New ASD Difference between the old and new ASD FLEXURE

Allowable Stress Design (old)

Laterally Supported Beams



Compact sections



Allowable Strength Design (new)





0.66





.

Ω



.

Non-compact sections





0.79

.



0.000762

0.7 2



1.67

.

.

*Bending about major axis.

Ω

.

1.67

Old ASD vs New ASD Difference between the old and new ASD FLEXURE

Allowable Stress Design (old)

Allowable Strength Design (new)

(Lp