2020 Steel Course Notes PDF

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Warning: TT: undefined function: 32U N I V E R S I T Y O F S O U T H A U S T R A L I ASteel and Timber Design – CIVE 3013Design of Steel Structures to AS 4100C o u r s e n o t e s - 2020Steelwork erection at Whyalla HospitalDanda LiUniversity of South AustraliaContents How to Use this Study Guide Wh...

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UNIVERSITY OF SOUTH AUSTRALIA

Steel and Timber Design – CIVE 3013 Design of Steel Structures to AS 4100 Course notes - 2020

Steelwork erection at Whyalla Hospital

Danda Li University of South Australia

Contents How to Use this Study Guide .............................................................................................................. 2 What is Structural Steel? .................................................................................................................... 3 Lecture preparation: ................................................................................................................................... 3 Steel – Introduction ..................................................................................................................................... 3 Structural Steel ............................................................................................................................................ 3 Introduction to AS 4100 .............................................................................................................................. 5

Design of Tension Members ............................................................................................................... 6 Lecture preparation and worked examples: ............................................................................................. 6 Design of tension members to AS 4100 ...................................................................................................... 6 Example A1 Design of a tension member .................................................................................................................. 7

Key Points – Tension members................................................................................................................... 8

Design of Compression Members ....................................................................................................... 9 Lecture preparation and worked examples: ............................................................................................. 9 Design of compression members to AS 4100 ............................................................................................. 9 Example A2 Design of a compression member ........................................................................................................ 10 Interpolating.............................................................................................................................................................. 11 Example A3 Design of a structure with tension and compression members ............................................................ 11

Key Points – Compression members ........................................................................................................ 12

Design of Flexural Members (i.e. Beams) ....................................................................................... 13 Lecture preparation and worked examples: ........................................................................................... 13 Serviceability limit state ............................................................................................................................ 13 Strength limit state..................................................................................................................................... 13 Section Capacity ....................................................................................................................................................... 13 Member capacity ...................................................................................................................................................... 14 Effective lengths ....................................................................................................................................................... 15 Example B1 (serviceability and bending) ................................................................................................................. 16 Example B2 (serviceability and bending) ................................................................................................................. 17 Example B3 (serviceability and bending) ................................................................................................................. 19

Key Points – Bending................................................................................................................................. 21 Shear ........................................................................................................................................................... 22 Shear / bending interaction ....................................................................................................................... 22 Example B1 cont. (shear, shear and bending interaction) ......................................................................................... 22 Example B2 cont. (shear, shear and bending interaction) ......................................................................................... 23 Example B3 cont. (shear, shear and bending interaction) ......................................................................................... 24

Bearing ........................................................................................................................................................ 25 Example B4 .............................................................................................................................................................. 25

Key Points – Shear and bearing ............................................................................................................... 26

Design for Combined Actions (i.e. Beam-Columns) ....................................................................... 27 Lecture preparation and worked examples: ........................................................................................... 27 Design of beam-columns to AS 4100 ........................................................................................................ 27 Beam column examples ............................................................................................................................................ 29

Key Points – Combined Actions (Beam-columns) .................................................................................. 32

Connections ....................................................................................................................................... 33

Design of Steel Structures to AS 4100

University of South Australia

Lecture preparation and worked examples: ........................................................................................... 33 Design of connections to AS 4100 ............................................................................................................. 33 Minimum design actions ........................................................................................................................... 33 Bolted connections ..................................................................................................................................... 34 Example C1 Tension splice with bolts in direct shear ............................................................................................. 36 Example C2 Bolts in direct and torsional shear ....................................................................................................... 37 Example C3 Bolts in direct shear and tension .......................................................................................................... 38

Welded connections ................................................................................................................................... 39 Strength of butt welds ............................................................................................................................................... 39 Strength of fillet welds .............................................................................................................................................. 39 Example C4 Welded lap joint ................................................................................................................................... 40 Example C5 Eccentrically loaded welded connection ............................................................................................. 41 Example C6 Welded bracket connection ................................................................................................................. 42

Key Points –Connections ........................................................................................................................... 42

Steel design sizing heuristics (approximations) ............................................................................... 43 Tutorial Questions: ........................................................................................................................... 45 Steel Design Tutorial - Tension and Compression Members................................................................. 45 Steel Design Tutorial – Flexural members .............................................................................................. 46 Steel Design Tutorial - Beam Columns .................................................................................................... 47 Steel Design Tutorial - Connections ......................................................................................................... 48 Appendix A ................................................................................................................................................. 49 Appendix B ................................................................................................................................................. 50

Danda Li

February 2020

1

Design of Steel Structures to AS 4100

University of South Australia

How to Use this Study Guide This study guide provides summary notes and worked examples to guide you through the first half of Steel and Timber Design, which focuses on the concepts of the design of steel structures. In addition, it details the complimentary reading that you need to undertake from the textbook and the design codes. Reading the Study Guide alone will not be sufficient for you to gain the understanding you will need to pass this course. It will also be essential to work through tutorial problems (in class and your own time), PowerPoint slides for each section, attend lectures and in particular to work through the Design Project to gain that understanding. Each section of the Study Guide refers to a section of the course. Each section opens with the Lecture preparation and worked examples that you should do before attending the lecture. The reading and examples will come from the textbook or the design codes, which are referred to as follows: • SDH = Gorenc, B., Tinyou, R. and Syam, A., Steel Designers’ Handbook, 8th Edition, 2012 • AS1170.0: 2002, Structural design actions Part 0: General principles Standards Australia • AS1170.1: 2002, Structural design actions Part 1: Permanent, imposed and other actions Standards Australia • AS1170.2: 2011, Structural design actions Part 2: Wind actions Standards Australia • AS4100: 1998, Steel structures Standards Australia Each section then continues with some summary notes and worked example(s), and concludes with the Key points for the section.

Danda Li

February 2020

2

Design of Steel Structures to AS 4100

University of South Australia

What is Structural Steel? Lecture preparation: • SDH Chapter 1, Chapter 3 • AS4100 Skim through and get a feel of what they involve. You will be using some parts of this standard in the design project and the exam. • Lecture on the course homepage under Week 1B - Steel - Introduction Steel – Introduction Steel is made from a combination of iron ore, coal and oxygen plus smaller amounts of several other metals. Steel is strong, ductile, flexible, malleable and versatile and can be connected using rivets (Titanic, Sydney Harbour Bridge but rarely used any more) but more commonly using bolts or screws and by welding. The following two youtube videos will give you an indication of the steel making process. The first is American and the second is Australian. YouTube - Traditional Steel Making Process YouTube - Whyalla Steel Works - Onesteel / Arrium Structural Steel Structural steel is any steel member that forms part of the building frame of a building or carries a load such as a sign post. These can take many different cross sections or profiles including Universal Beams UB (I beams), Universal Columns UC (H beams), Parallel Flange Channels PFC (C beam), Square Hollow Sections SHS, Rectangular Hollow Sections RHS, Circular Hollow Sections CHS, Equal Angles EA, Unequal Angles UA and various plates (thin rectangular elements), rods (solid round bars), billets (solid large rectangular and square cross sections).

PFC

UC

UB

EA

SHS

RHS

CHS

UA

Steel is available in various strengths and is described by a ‘Grade’. The Grade number is the approximate yield strength of the material in MegaPascals (MPa). Common grades for Australian Steel are Grade 250, 300 and 350. The yield strength (denoted fy) varies slightly for each grade and is dependent on the thickness of the material. The thicker the material, the lower the yield strength. For example, the most common steel grade is Grade 300 steel. The yield strength (fy) varies from 280MPa to 320MPa.

Danda Li

February 2020

3

Design of Steel Structures to AS 4100

University of South Australia

There are 4 main types of basic elements in a structural frame. These elements are: • Beams – normally horizontal elements • Columns – normally vertical elements • Braces – can be at any angle • Struts – can be at any angle Each element can be constructed of different profiles dependent on how visible these elements are (aesthetical consideration) and how much loads they need to carry. The table below gives an indication of the elements, their main design action and the typical profiles that are common to be used for these elements as well as some naming conventions used (Nomenclature). Element

Main Design Action

Typical Profile Used

Beam

Bending moment

UB, PFC

Column

Axial Load (Compression or Tension) + Bending moment

UC, SHS, CHS, RHS

Brace

Axial Load – Tension

EA, UA, plates, rods

Strut

Axial Load - Compression

SHS, RHS, CHS, UC

Typical Nomenclature Rafter, roof beam, floor beam, joists, purlin Column, Mullion, Post Roof Brace, Cross Brace, Wall Brace Ridge Strut, Eaves Strut

Below is a typical structural frame of a building. This shows the locations of the different elements. We will be using this nomenclature (names) during this course.

Danda Li

February 2020

4

Design of Steel Structures to AS 4100

University of South Australia

Introduction to AS 4100 AS 4100-1998 (with Amendment 1 - 2012) is the current code of practice for the design of steel structures in Australia. This standard was re-confirmed in 2016 with no further amendments since 2012. The main feature of AS4100 is that it uses the limit state design approach as opposed to allowable stress design previously used in Australia. It should also be noted that the USA allows both limit states and working stress design methods to be used for steel design, with working stress design commonly used in practice, but all European codes are limit state. AS 4100 gives a procedure to calculate the design resistance for steel structures subject to various internal stress combinations. The capacity reduction factor, , that is applied to the design resistance calculated for steel structures is given in Table 3.4 of AS 4100 and is 0.9 for everything except connections.

Danda Li

February 2020

5

Design of Steel Structures to AS 4100

University of South Australia

Design of Tension Members Lecture preparation and worked examples: • SDH Chapter 7, Sections 7.1 to 7.4.1; Example 7.2 • AS4100 Section 7.1 to 7.4 • Lecture on the course homepage Week 1B - Steel - Tension Design of tension members to AS 4100 Design for members subject to axial tension is contained in Section 7 of AS 4100. These members have two failure modes and may reach the strength limit state either by: •

Yielding of the gross cross-section – ductile failure, expressed as

N t = Ag f y •

Fracture through the weakest point of the cross-section – sudden failure, expressed as

N t = 0.85k t An f u

Yield Failure through cleat plate – smallest cross section

Fracture Failure – through the cross section at the bolts

Both possibilities must be checked, and the lower value adopted as the ultimate tensile load capacity. The first formula is fairly self-explanatory with a cross sectional area Ag * strength fy to give a maximum failure load. However, in the fracture formula: • • • •

0.85 is an additional “safety factor” against a sudden, non-ductile failure mode kt is used to account for eccentrically applied axial load and is given in Table 7.3.2 for most common situations. This is of particular relevance to angle design where connections usually apply the load eccentrically. An is the net cross-section area allowing for bolt holes, including allowance for staggered holes to Clause 9.1.10 if applicable fu is the ultimate tensile strength

Danda Li

February 2020

6

Design of Steel Structures to AS 4100

University of South Australia

Example A1 Design of a tension member A single angle cross-bracing system is to be used in the end wall bay of an industrial building. The ultimate design tensile force, N*t, in the brace from the ultimate wind loads has been determined as 200 kN. It is proposed that the angle will be connected to a cleat plate from the column through one of its legs with 4 – M16 8.8/S bolts in 2 rows of 2. Determine a suitable angle size. N*

N*

Note:

A “row” of bolts is defined as the perpendicular direction to the force. For example if we had 6 bolts on this connection in 3 columns each with 2 bolts in the column as indicated below, that would still be calculated as having 2 bolts per row. + +

+ +

+ +

Solution

To fit sufficient bolts, a minimum angle leg width of 125 mm will be required. Hence try a 125 x 125 x 8 EA (Grade 300) Check yielding failure:

N t = Ag f y where Ag = 1900 mm2, fy = 320 MPa, hence Nt = 0.9 x 1900 x 320 / 1000 = 547 kN > N*t OK (For  values, refer to Table 3.4, AS 4100) Check fracture failure:

N t = 0.85k t An f u where • kt = 0.85 (Table 7.3.2) for an equal angle • An = 1900 – 2 x 18 x 7.8 = 1619 mm2 (i.e. subtract 2 holes of 18 mm width x 7.8 mm thick; bolt holes are 2 mm greater in diameter than the bolt itself) • fu = 440 MPa hence Nt = 0.9 x 0.85 x 0.85 x 1619 x 440 / 1000 = 463 kN > N*t OK and fracture failure governs. Adopt 125 x 125 x 8 EA (Grade 300) Hence the capacity of the member Nt = 463kN >> N*t = 200kN. We should try a smaller angle – maybe an unequal angle. Try a 125 x 75 x 6 UA (Grade 300) Check yielding failure:

N ...