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 < 248.80 kN
Old ASD vs New ASD Difference between the old and new ASD COMPRESSION
Allowable Stress Design (old)
(inelastic)
1
KL/r ≤ Cc (old) or KL/r ≤ 4.71√(E/Fy) (new)
Allowable Strength Design (new)
3 8
5 3
⁄ 2 ⁄
⁄
8
⁄
⁄
Ω Ω
:
⁄
.
1.67
0.658
.
Old ASD vs New ASD Difference between the old and new ASD COMPRESSION (elastic)
Allowable Stress Design (old)
KL/r > 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
(Lc
0.6
0.7
.
1.67 .
*Bending about major axis.
.
Old ASD vs New ASD Difference between the old and new ASD FLEXURE Laterally Unsupported Beams
Allowable Strength Design (new)
(Lb > Lu)
703270
3516330
Allowable Stress Design (old)
2 3
⁄ 10550 10
0.6
(Lb > Lr)
⁄
3516330
Ω
(Lb > Lu)
Ω
1170 10
*Bending about major axis.
⁄
0.6
.
1.67
Sample Problem Flexure Member The beam shown is a W16 × 31 of A992 steel. It supports a reinforced concrete floor slab that provides continuous lateral support of the compression flange. The service dead load is 6.5 kN/m. This load is superimposed on the beam; it does not include the weight of the beam itself. The service live load is 8 kN/m. Does this beam have adequate moment strength? wD = 6.5 kN/m w = 6.5 kN/m wL =D8 kN/m wL = 8 kN/m 9.0 m 9.0 m
Sample Problem Flexure Member Solution: First, determine the nominal flexural strength. Check for compactness. .
6.28
.
.
0.38
9.15
6.28
*The beam is COMPACT Because the beam is compact and laterally supported, the nominal flexural strength is 345
885 103
.
.
Compute the maximum bending moment
1 6.5 8
0.45
8 9.0
Eqn. 506.2-1
Sample Problem Flexure Member Solution: Compute the allowable strength
Ω
305.33 1.67
.
.
.
Ω
The W16x31 is satisfactory.
Old ASD vs New ASD Difference between the old and new ASD COMBINED AXIAL and BENDING (old)
Allowable Stress Design (old)
0.15
1.0
(new)
⁄
0.15
0.6 (new)
0.2
.
1.0
2 .
0.2
(old)
Allowable Strength Design (new)
⁄ 8 9
1.0 .
⁄
.
⁄
1.0
⁄
⁄
.
References: Segui, W. (2007). Steel Design (4th Edition). Toronto, Canada. Nelson, a division of Thomson Canada Limited Fisher, J. (Oct. 2005). “SPECwise: Don’t Stress Out.” Modern Steel Construction. Retrieved January 29, 2017 from https://www.aisc.org/globalassets/modern-steel/archives/2005/10 Quimby, B. (2014). “ASD vs LRFD”. A beginner’s guide to the Structural Engineering. Retrieved January 29, 2017 from http://www.bgstructuralengineering.com/BGDesign AISC. Historic Steel Construction Manuals. Retrieved January 27, 2017 from https://www.aisc.org/publications/historic-steel-construction-manuals/ AISC. Historic Standards. Retrieved January 27, 2017 fromhttps://www.aisc.org/publications/historicstandards/ (2001). National Structural Code of the Philippines (5th Edition). Quezon City, Philippines. Association of Structural Engineers of the Philippines, Inc. (2010). National Structural Code of the Philippines (6th Edition). Quezon City, Philippines. Association of Structural Engineers of the Philippines, Inc. (2015) National Structural Code of the Philippines (7th Edition). Quezon City, Philippines. Association of Structural Engineers of the Philippines, Inc.
Thank You!
