CHAPTER 1: INTRODUCTION part B BFC 43003 Structural Steel and Timber Design Assoc. Prof. Dr DYeoh david@uthm.edu.my 2014

Course content Assoc. Prof. Dr DYeoh david@uthm.edu.my 2014

Outline of lecture Design concept and design process Stability of structure Actions on structure Quantifying the “effects” on structure How to determine the worst load combination for design? Assoc. Prof. Dr DYeoh david@uthm.edu.my 2014

Design Philosophy LIMIT STATE DESIGN (LSD) Ultimate Limit State (ULS) Serviceability Limit State (SLS) Assoc. Prof. Dr DYeoh david@uthm.edu.my 2014

ULS Conditions considered: Strength Stability Collapse Assoc. Prof. Dr DYeoh david@uthm.edu.my 2014

SLS Conditions considered: Deflections Vibration Assoc. Prof. Dr DYeoh david@uthm.edu.my 2014

Limiting deflection Assoc. Prof. Dr DYeoh david@uthm.edu.my 2014

Design process Flow diagram in structural design: Define problem Site survey and investigation Assess loads Analyse Investigate alternatives Element design and detail design Detailed development Assoc. Prof. Dr DYeoh david@uthm.edu.my 2014

Design concept A structure (e.g. a building/ bridge) is a 3D solid made of: 1D members (beams/columns, cables) 2D members (floors/walls, shells, membranes) Those elements are assembled in order to make the 3D structure. Assoc. Prof. Dr DYeoh david@uthm.edu.my 2014

Design concept The connections between members and with the foundation can be pinned or rigid Assoc. Prof. Dr DYeoh david@uthm.edu.my 2014

Stability The structure must be stable (i.e. at least statically determinate). Any type of instability, in-plane and out-of-plane, must be avoided! IN-PLANE STABILITY NO! YES YES Assoc. Prof. Dr DYeoh david@uthm.edu.my 2014

Stability IN-PLANE STABLE OUT-OF-PLANE UNSTABLE! OUT-OF-PLANE STABLE z x IN-PLANE STABLE OUT-OF-PLANE UNSTABLE! OUT-OF-PLANE STABLE Assoc. Prof. Dr DYeoh david@uthm.edu.my 2014

Important features of Stability in a Structure Static equilibrium Resistance to horizontal forces Sway stiffness – second order or P-delta effect Assoc. Prof. Dr DYeoh david@uthm.edu.my 2014

Lateral resistance for stability Assoc. Prof. Dr DYeoh david@uthm.edu.my 2014

Actions (Loads) on structure Actions – things that produce stresses Loads Settlements Accelerations (earthquake) Fire Loads – forces Self-weight You and me Wind Snow etc etc All loads are actions Not all actions are loads! Assoc. Prof. Dr DYeoh david@uthm.edu.my 2014

Will My Structure Work? Design for limit states Ultimate limit states (life safety) Strength – must not collapse under applied actions* Stability – must not buckle, overturn or move* Cyclic plasticity And others Serviceability limit states (use-ability) Deflections* Comfort Appearance Also others – accidental, fatigue, vibration etc. etc Assoc. Prof. Dr DYeoh david@uthm.edu.my 2014

Will My Structure Work? E<R The BIG PICTURE – design inequalities R=Resistance of structure Need to know size of actions to calculate this side E<R Need theory of structures to calculate this side E= Effect of actions E determined from size of pt load and self-weight R given by bending resistance of beam Assoc. Prof. Dr DYeoh david@uthm.edu.my 2014

Design Values of Actions Design value, Fd Typical distribution of permanent loads Characteristic Value, Fk Design value, Fd Typical distribution of imposed loads Probability density Narrow distribution design load, Fd=γFk γ =partial safety factor γ, large for variable loads γ, small for permanent loads Characteristic Value, Fk Wide distribution Value of Load Assoc. Prof. Dr DYeoh david@uthm.edu.my 2014

Classification of Actions Permanent Self-weight* Settlements Variable Imposed loads* Wind loads* Snow loads* Accidental Fire Blast Impact Assoc. Prof. Dr DYeoh david@uthm.edu.my 2014

LOAD PATH – THE SHORTEST ROUTE DOWN Assoc. Prof. Dr DYeoh david@uthm.edu.my 2014

ACTIONS - Variable Assoc. Prof. Dr DYeoh david@uthm.edu.my 2014

ACTIONS - Variable Assoc. Prof. Dr DYeoh david@uthm.edu.my 2014

ACTIONS - Variable 1.5 kPa = 1.5 kN/m2 = 150 kgf/m2 floor live load 1 Assoc. Prof. Dr DYeoh david@uthm.edu.my 2014

Wind actions This actions is variable and beyond human control. Wind loads are the positive or negative pressures exerted on a building when it obstructs the flow of moving air. Assoc. Prof. Dr DYeoh david@uthm.edu.my 2014

Will all Loads Occur Together? Unlikely to have huge crowd, hurricane, 3m snow and blast altogether therefore consider realistic combinations of loads apply reduced values of some loads Full permanent load and imposed load with 70% wind load Or permanent and 70% imposed plus fire Also unlikely to have full imposed load over a large area – reductions sometimes used. Assoc. Prof. Dr DYeoh david@uthm.edu.my 2014

Recap what have been said... Obtain “characteristic” values for actions Apply appropriate partial safety factors Possibly apply reductions as worst case for each action will not occur together in time in space Use actions to estimate stresses, forces, moments etc. that must be resisted Check “resistance” great than “load effect” Repeat for each limit state Assoc. Prof. Dr DYeoh david@uthm.edu.my 2014

Eurocode 0 and 1 Eurocode 0 (EN 1990) – Basis for Design Design philosophy Safety factors Eurocode 1 (EN 1991)– Actions on Structures Part 1: General actions – self-weight, imposed loads etc Part 3: Snow loads Part 4: Wind loads (later) Other parts deal with fire, bridges, accidental loads etc. etc. Assoc. Prof. Dr DYeoh david@uthm.edu.my 2014

Assoc. Prof. Dr DYeoh david@uthm.edu.my 2014

Characteristic Loads Also known as Working Loads It is not a factored load Statistically, working loads have a 95% chance of not being exceeded Assoc. Prof. Dr DYeoh david@uthm.edu.my 2014

Characteristic Permanent Loads Self-weight – look it up in Section 4 of Eurocode 1 Annex A Eurocode 1 Assoc. Prof. Dr DYeoh david@uthm.edu.my 2014

Example 1 – Permanent Loads Structure supporting a hotel balcony Frames at 6m centres Require vertical reaction at supports Cross-section=75cm2 Self-weight (EN1991-1-1 Table A4) Beam: 75/1002*10*78.5= 5.9kN Columns: 100/1002*(5*2)*78.5= 7.8kN Load per support 6.9kN Note: Section masses normally obtained directly from section tables. Cross- Section =100cm2 5m 10m Assoc. Prof. Dr DYeoh david@uthm.edu.my 2014

Characteristic Variable Loads Imposed loads Given in Section 6 of Eurocode 1 May differ for each country – take care Need to determine category and then look up load Reduction allowed to account for large areas and multiple storeys ( 6.2.1, NA.2.5 and NA.2.6) Some complications for roofs and car-parks Assoc. Prof. Dr DYeoh david@uthm.edu.my 2014

Example 2 – Variable Loads Structure supporting a hotel balcony Frames at 6m centres Require vertical reaction at supports Imposed loads from occupants, furniture etc. Imposed Load (EN1991-1-1) Category A7 Table NA.2 Load intensity 4kN/m2 Table NA.3 Total load: 4*10*6=240kN Load per support =120kN Assume no reduction factor 6.2.1(4) 5m 10m Assoc. Prof. Dr DYeoh david@uthm.edu.my 2014

Partial Safety Factors Section 6 and Annex A1 of Eurocode 0 Apply appropriate partial safety factors and combination factors to account for possible variability in loads Example for the ultimate limit state (Eqn 6.10): Sum of permanent actions Sum of accompanying variable actions Leading variable action Design effect Prestressing action (not relevant for this course) Assoc. Prof. Dr DYeoh david@uthm.edu.my 2014

Unfavourable means action that results in greater effect / load resultant Favourable means action that results in smaller effect / load resultant Assoc. Prof. Dr DYeoh david@uthm.edu.my 2014

Example 3 – Counting design effect For the example there is only one Permanent action (self-weight) and only one variable action (imposed Load) so this simplifies to Partial factor on self-weight Partial factor on imposed load Characteristic Dead load = Permanent action = Gk =6.9kN from before Characteristic Imposed load= Variable action=Qk =120kN from before Partial factor on permanent action=γG =1.35 A1.3.1(5) and Table NA.A1.2(B) Partial factor on variable action= γQ =1.5 A1.3.1(5) and Total load per support for this condition= 1.35*6.9+1.5*120 =189kN Assoc. Prof. Dr DYeoh david@uthm.edu.my 2014

Wind Loads Wind loading complex – many details See separate part of EN1991 For now we assume characteristic values Assoc. Prof. Dr DYeoh david@uthm.edu.my 2014

Example 4 – Wind Wind loads mainly horizontal Some vertical component Assume acting on cladding and transferred to “nodes” Assume characteristic value of 1kPa Resultant force 5m Wind load of 1kPa Acts over surface Characteristic Wind Load Resultant force = 1*6*5=30kN 10m Assoc. Prof. Dr DYeoh david@uthm.edu.my 2014

Other Actions or Loads Snow Earthquake Assoc. Prof. Dr DYeoh david@uthm.edu.my 2014

Example 5 – Loads Cases or Combinations A roof has the following loads applied: Permanent load, Gk = 1.0 kN/m2 Variable actions, Qk = 0.5 kN/m2 Wind load: Wuplift = 1.25 kN/m2 Wdown = 0.4 kN/m2 Snow, S = 0.6 kN/m2 Determine the most critical load combination. Assoc. Prof. Dr DYeoh david@uthm.edu.my 2014

Assoc. Prof. Dr DYeoh david@uthm.edu.my 2014

Assoc. Prof. Dr DYeoh david@uthm.edu.my 2014

Assoc. Prof. Dr DYeoh david@uthm.edu.my 2014

Assoc. Prof. Dr DYeoh david@uthm.edu.my 2014

Assoc. Prof. Dr DYeoh david@uthm.edu.my 2014

End of Introduction part B Assoc. Prof. Dr. DYeoh david@uthm.edu.my 2014

Recap what have we learned? Assoc. Prof. Dr DYeoh david@uthm.edu.my 2014

Recap what have we learned? Design concept and design process Stability of structure Actions on structure Quantifying the “effects” on structure How to find the worst load combinations? Assoc. Prof. Dr DYeoh david@uthm.edu.my 2014