CHAPTER 1: INTRODUCTION part C BFC 43003 Structural Steel and Timber Design Assoc Prof Dr DYeoh david@uthm.edu.my

Course content Assoc Prof Dr DYeoh david@uthm.edu.my

Outline of this Lecture Notations and symbols in EC3 Recap of common structural steel sections Local buckling Understanding failure modes Section classification Assoc Prof Dr DYeoh david@uthm.edu.my

Recognizing important notations and symbols used in EC3 Assoc Prof Dr DYeoh david@uthm.edu.my

Section Assoc Prof Dr DYeoh david@uthm.edu.my

Elastic section modulus Area Elastic section modulus Plastic section modulus Second moment of area major axis Second moment of area minor axis Assoc Prof Dr DYeoh david@uthm.edu.my

Subscripts Ed = design value of an effect eg: MEd = design bending moment NEd = axial force Rd = deign resistance eg: MRd = design resistance for bending NRd = resistance to axial force el = elastic property eg: Wel = elastic section modulus pl = plastic property eg: Wpl = plastic section modulus Assoc Prof Dr DYeoh david@uthm.edu.my

ULS – Equation 6.10 Assoc Prof Dr DYeoh david@uthm.edu.my

SLS Assoc Prof Dr DYeoh david@uthm.edu.my

Recap of common structural steel section Assoc Prof Dr DYeoh david@uthm.edu.my

Rolled and formed sections Assoc Prof Dr DYeoh david@uthm.edu.my

Built-up sections Assoc Prof Dr DYeoh david@uthm.edu.my

Cold rolled sections Assoc Prof Dr DYeoh david@uthm.edu.my

Local buckling failure Assoc Prof Dr DYeoh david@uthm.edu.my

Some basic knowledge when designing with structural steel Structural steel members are made of thin elements These thin elements are slender, as a result causing local instabilities (known as local buckling in flange and web) even before achieving yield strength. As such, cross section classification is important to account for such local instabilities. Assoc Prof Dr DYeoh david@uthm.edu.my

Assoc Prof Dr DYeoh david@uthm.edu.my

Understanding failure modes Assoc Prof Dr DYeoh david@uthm.edu.my

Fundamental modes of failure in Universal Column under compression Overall yielding in compression Overall buckling as a strut Local buckling in flange toes Assoc Prof Dr DYeoh david@uthm.edu.my

Overall yielding in compression Fundamental modes of failure in Universal Beam under compression (UB as column) Overall yielding in compression Overall buckling as a strut (about minor axis) Local buckling in flange toes and web Assoc Prof Dr DYeoh david@uthm.edu.my

Fundamental modes of failure in Universal Beam under flexure (UB as beam) Overall yielding in flexure Overall lateral / torsional buckling Local buckling in compression flange under high strains Local buckling in web UB in flexure behaves differently to UB in axial compression Assoc Prof Dr DYeoh david@uthm.edu.my

Section Classification Assoc Prof Dr DYeoh david@uthm.edu.my

What? CLASS 1 CLASS 2 CLASS 3 CLASS 4 Assoc Prof Dr DYeoh david@uthm.edu.my

What does it mean? Think of plasticity Think of ductility Think of rotational capacity in the whole section Assoc Prof Dr DYeoh david@uthm.edu.my

Assoc Prof Dr DYeoh david@uthm.edu.my

Assoc Prof Dr DYeoh david@uthm.edu.my

Assoc Prof Dr DYeoh david@uthm.edu.my

Why classify? What is the implication of different CLASS? CLASS 1 PLASTIC – able to sustain high strain and achieve plastic moment capacity and full plastic hinge in the whole cross-section; no restrictions in normal design. CLASS 2 COMPACT – achieve plastic moment capacity but with limited plastic hinge; apply plastic modulus under bending for design; elastic analysis only. CLASS 3 SEMI-COMPACT – plastic capacity not achieved; only elastic capacity; apply elastic modulus for design. CLASS 4 SLENDER – local buckling failure appear even before yield strength is achieved; apply effective section properties. Assoc Prof Dr DYeoh david@uthm.edu.my

EC3 – 6.2.4 Compression The design resistance for Class 1, 2 and 3: Assoc Prof Dr DYeoh david@uthm.edu.my

EC3 – 6.2.5 Bending moment The design resistance for Class 1 & 2: We will revisit this later. The design resistance for Class 4: Assoc Prof Dr DYeoh david@uthm.edu.my

How? Table 5.2 EC3 What is the type of cross-section? What kind of stress is the section subjected to? For UB, UC or built-up sections, classify each part separately (ie. Flange and web) Calculate e factor Choose worst classification as CLASS for the section. Assoc Prof Dr DYeoh david@uthm.edu.my

Example – pure compression Assoc Prof Dr DYeoh david@uthm.edu.my

3. Substitute ε into the class limits in Table 5.2 1. Determine fy fy = 355N/mm2 2. Determine ε 3. Substitute ε into the class limits in Table 5.2 Outstand flanges (Table 5.2, sheet 2): cf = (b – tw – 2r)/2 = 110.3 mm cf / tf = 110.3/14.2 = 7.77 9ε = 7.29, 10ε = 8.10, 14ε = 11.34 Limit for Class 2 flange = 10  = 8.10 > 7.77 Hence flanges are Class 2 Assoc Prof Dr DYeoh david@uthm.edu.my

Web – internal compression part (Table 5.2, sheet 1): cw = h – 2tf – 2r = 200.3 mm cw / tw = 200.3/8.6 = 23.29 33ε = 26.73, 38ε = 30.78, 42ε = 34.02 Limit for Class 1 web = 33  = 26.73 > 23.29 , Hence web is Class 1 4. Therefore, overall cross-section classification is Class 2. Assoc Prof Dr DYeoh david@uthm.edu.my

Cross-section compression resistance (clause 6.2.4): Therefore, the design compression resistance of the cross-section is: Assoc Prof Dr DYeoh david@uthm.edu.my

Classification under combined bending and axial force Classify based on the actual stress distribution of the combined loadings. STEP 1 For simplicity, classify using most severe loading condition of pure axial compression. If the section classified as Class 1 or 2, no further works are needed. STEP 2 But if the resulting section classification is Class 3 or 4, it is advisable for economy to conduct a more precise classification under the combined loading. Assoc Prof Dr DYeoh david@uthm.edu.my

Example – combined bending and axial force Assoc Prof Dr DYeoh david@uthm.edu.my

Assoc Prof Dr DYeoh david@uthm.edu.my

Assoc Prof Dr DYeoh david@uthm.edu.my

Assoc Prof Dr DYeoh david@uthm.edu.my

Comparison Separate load condition Combined load condition Flange = CLASS 1 Web = CLASS 4 Overall = CLASS 4 Resisting capacity uses effective sectional area Flange = CLASS 1 Web = CLASS 2 Overall = CLASS 2 Resisting capacity uses whole sectional area MORE ECONOMICAL DESIGN Assoc Prof Dr DYeoh david@uthm.edu.my

End of Introduction part C Assoc Prof Dr DYeoh david@uthm.edu.my

Recap what have we learned? Assoc Prof Dr DYeoh david@uthm.edu.my

Recap what have we learned? Notations and symbols in EC3 Recap of common structural steel sections Local buckling Understanding failure modes Section classification Assoc Prof Dr DYeoh david@uthm.edu.my