Chapter 9

NBC 2016 (SP 7:2016) Volume 1

2016 · PDF page 972

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9.1 Basis for Design

9.1.1 Design Objective

The objective of design is the achievement of an acceptable probability that structures will perform

satisfactorily for the intended purpose during the design life. With an appropriate degree of safety, they should sustain all the loads and deformations, during construction and use and have adequate resistance to certain expected accidental loads and fire. Structure should be stable and have alternate load paths to prevent disproportionate overall collapse under accidental loading.

9.1.2 Methods of Design

9.1.2.1 Structure and its elements shall normally, be designed by the limit state method. Account should be taken of accepted theories, experimental information and experience and the need to design for durability. Calculations alone may not produce safe, serviceable and durable structures. Suitable materials, quality control, adequate detailing and good supervision are equally important.

9.1.2.2 Where the limit states method cannot be conveniently adopted; the working stress design [see Section 6(m)] may be used.

9.1.3 Design Process

Structural design, including design for durability, construction and use should be considered as a whole. The realization of design objectives requires compliance with clearly defined standards for materials, fabrication, erection and in-service maintenance.

9.2Loads and Forces

9.2.1 For the purpose of designing any element, member or a structure, the following loads (actions) and their effects shall be taken into account, where applicable, with partial safety factors and combinations (see 11.3.3).

a) Dead loads;

b) Imposed loads (live load, crane load, snow load, dust load, wave load, earth pressures, etc);

c) Wind loads;

d) Earthquake loads;

e) Erection loads;

f) Accidental loads such as those due to blast, impact of vehicles, etc; and

g) Secondary effects due to contraction or expansion resulting from temperature changes, differential settlements of the structure as a whole or of its components, eccentric connections, rigidity of joints differing from design assumptions.

9.2.1.1 Dead loads should be assumed in design as specified in 2 of Part 6 ‘Structural Design, Section 1 Loads, Forces and Effects’ of the Code.

PART 6 STRUCTURAL DESIGN — SECTION 6 STEEL

Table 1Tensile Properties of Structural Steel Products (Clauses 2.113, 2.119 and 8.2.4.2)

Sl No.	Accepted Standard	Grade / Classification		Properties
				Yield Stress MPa Min (4)			Ultimate Tensile Stress MPa Min (5)			Elongation Percent Min (6)
(1)	(2)	(3)
i)	[6-6(24)]	O		—			—			—
		D		280			270-410			28
		DD		250			270-370			32
		EDD		220			270-350			35
ii)	[6-6(18)]	Ex40xx		330			410-540			16
		Ex41xx		330			410-540			20
		Ex42xx		330			410-540			22
		Ex43xx		330			410-540			24
		Ex44xx		330			410-540			24
		Ex50xx		360			510-610			16
		Ex51xx		360			510-610			18
		Ex52xx		360			510-610			18
		Ex53xx		360			510-610			20
		Ex54xx		360			510-610			20
		Ex55xx		360			510-610			20
		Ex56xx		360			510-610			20
iii)	[6-6(25)]	O		—			—			—
		D		—			240-400			25
		DD		—			260-390			28
		EDD		—			260-380			32
iv)	[6-6(26)]	3.6		180			330			25
		4.6		240			400			22
		4.8		320			420			—
		5.6		300			500			20
		5.8		400			520			—
		6.8		480			600			—
		$8.8 (d \leq 16mm)$		$640^{1)}$			800			12
		$8.8 (d >16mm)$		$660^{1)}$			830			12
		9.8		$720^{1)}$			900			10
		10.9		$940^{1)}$			1040			9
		12.9		$1100^{1)}$			1220			8
v)	[6-6(27)]	1		200			370			26
		1A		220			410			25
		2		230			430			24
		2A		250			460			22
		3		270			490			21
		3A		280			540			20
		4		320			620			15
		5		350			710			13
		6		370			740			10
vi)	[6-6(28)]	$S_137$ $S_142$		$\begin{array}{c} \leq 20 & >20 \\ 220 & 200 \\ 250 & 240 \end{array}$			360-440			26
							410-500			23
				$t$			$t$			$t$
				$\leq 16$	>16 and $\leq 40$	>40 and $\leq 60$	>60 and $\leq 100$	>100 and $\leq 350$	$\leq 60$	>60 and $\leq 350$
vii)	[6-6(29)]	1	235	225	215	200	185	360-480	360-480	350-480
		2	265	255	245	215	200	410-530	410-530	400-530
		3	290	285	280	255	230	460-580	450-570	440-570

Table 1 — (Concluded)
(1)	(2)	(3)	(4)			(5)	(6)
			d or t
			<20	20-40	>40	410	23
		E250 (A, BR, B0, C)	250	240	230	430	22
viii)	[6-6(6)]	E275 (A, BR, B0, C)	275	265	255	440	22
		E300 (A, BR, B0, C)	300	290	280	490	22
		E350 (A, BR, B0, C)	350	330	320	540	20
		E410 (A, BR, B0, C)	410	390	380	570	20
		E450 (A, BR)	450	430	420
			d or t
			≤ 25	>25 and ≤ 50
ix)	[6-6(30)]	I	230	220		400-490	22
		II	235	235		400-490	22
		III	235	235		400-490	22
x)	[6-6(31)]	Grade 1		240		350-450	25
x)	[6-6(31)]	Grade 2		245		360-450	34
xi)	[6-6(10)]	Annealed Condition		160		330 - 410	30
xi)	[6-6(10)]	As-Drawn Condition		190		410 - 490	20
xii)	[6-6(32)]	HFC 210/CDS 210/ERW210		210		330	20
		HFC 240/CDS 240/ERW240		240		410	18
		HFC 310/CDS 310/ERW310		310		450	15
xiii)	[6-6(33)]	1		170		290	30
		2		210		330	28
		3		240		410	25
		4		275		430	20
		5		310		490	15
NOTES
1 Percentage of elongation shall be taken over the gauge length of 5.65 $\sqrt{S_0}$ , where $S_0$ = original cross-sectional area of the test specimen.2 Abbreviations: O = Ordinary, D = Drawing, DD = Deep Drawing, EDD = Extra Deep Drawing.

$^{1)}$ Stress at 0.2 percent non-proportional elongation, Min.

9.2.1.2 Imposed loads for different types of occupancy and function of structures shall be taken as recommended in 3 of Part 6 ‘Structural Design, Section 1 Loads, Forces and Effects’ of the Code. Imposed loads arising from equipment, such as cranes and machines should be assumed in design as per manufacturers/suppliers data (see 9.5.4). Snow load shall be taken as per in 6 of Part 6 ‘Structural Design, Section 1 Loads, Forces and Effects’ of the Code.

9.2.1.3 Wind loads on structures shall be taken as per the provisions of 4 of Part 6 ‘Structural Design, Section 1 Loads, Forces and Effects’ of the Code.

9.2.1.3.1 Wind pressure

In calculating the effective wind pressure on exposed circular tube members of a structure, the effective area

shall be taken as 0.6 times the projected area of the member (see 4 of Part 6 ‘Structural Design, Section 1 Loads, Forces and Effects’).

9.2.1.4 Earthquake loads shall be assumed as per the recommendations of 5 of Part 6 ‘Structural Design, Section 1 Loads, Forces and Effects’ of the Code.

9.2.1.5 The erection loads and temperature effects shall be considered as specified in 9.3 and 9.4, respectively.

9.3Erection Loads

All loads required to be carried by the structure or any part of it due to storage or positioning of construction material and erection equipment, including all loads due to operation of such equipment shall be considered as erection loads. Proper provision shall be made,

PART 6 STRUCTURAL DESIGN — SECTION 6 STEEL

including temporary bracings, to take care of all stresses developed during erection. Dead load, wind load and also such parts of the imposed load as would be imposed on the structure during the period of erection shall be taken as acting together with the erection loads. The structure as a whole and all parts of the structure in conjunction with the temporary bracings shall be capable of sustaining these loads during erection.