High Rise Design High Rise Design (Notes prepared by A. Hira – modified by N. Haritos) Department of Civil and Environmental Engineering, The University of Melbourne FINITE ELEMENT MODELLING

Introduction Exponential growth in computer applications over last 20 yrs. FEA - Powerful tool for complex structures requiring minimum input and time. Time and expertise is usually the major hindrance for this competitive industry.

The Challenge Apply this powerful tool with confidence. Understanding of limitations. The more refined the FEA the lower the analytical margin of error, adding further pressure for the designer for accurate modelling. Designer must be fully conversant with the software. Fully appreciate the structural behaviour of the structure investigated, both locally and globally. Modelling correct boundary conditions. Correct selection of sectional and material properties.

Finite Element Modelling Finite element applications are now commonly applied as:  Form of the structure is far too complex for application of traditional type analysis and/or code guidelines. Traditional analysis and codes are typically conservative.  Accurate results are desirable due to the economical benefits, ideal for high volumes of identical structural components.  High level of structural accuracy is required.

Comment on F.E.A.  Some structures are so complex that even an elaborate model will be a gross over-simplification,  Results will always be approximate (being at best only as good as the chosen model.)  Computer modelling should be treated as an evolutionary process.

Typically there is no justification for a sophisticated analysis on a simplified model or an approximate analysis for a complex model. FEA is rarely used for overall design of civil engineering structures but can be used effectively to investigate the structural behaviour of sub-structural systems Comment on F.E.A.

The Challenges for Structural Engineers for F.E.A. Theoretical aspects of FEA are well established. Guidance to its application to structural analysis is inadequate. Designer must have a clear understanding of the overall structural behaviour, behaviour of the individual structural components and the form of interaction between them. Model should be kept simple.

The Challenges for Structural Engineers for F.E.A. Model may be progressively refined to achieve the desired accuracy. Accuracy of the results is dependent on the accuracy of the input data, particularly the stiffness parameters formulated from the geometrical and material properties. Where deflections and accelerations dictate, parametric studies requiring engineering skill and judgement are essential.

The Challenges for Structural Engineers for F.E.A. Awareness of the deviations from linear elastic behaviour (eg RC). With good engineering skills non- linearity can be modelled. The designer must not loose sight of the fact that an elastic FEA of complex shapes produces an elastic solution. The designer needs to ensure that all possible load cases are considered and to incorporate redundancies in the system at their own discretion.

Stages to be Adopted for F.E. Analysis For use of FEA the following stages are recommended: a)FEA analysis is an approximate analysis and is relatively expensive in terms of modelling time and interpretation of results (cf with frame analysis) therefore should only be used as a last resort. b)Gain appreciation of the structure to be analysed, identify the main concerns and identify the regions of high stress level and most importantly identify the objective of the study.

Stages To Be Adopted For F.E.A. Analysis c)Identify the boundary conditions and check if model can be simplified. d)Draw/sketch the model with the objective of keeping the model simple. e)Feed model into computer and analyse. f)Study results and confirm whether the behaviour is what you expected. There should be no surprises.

Stages To Be Adopted For F.E.A. Analysis g)Carry out some parametric studies. h)Check whether there is a further requirement to refine the model. (Finer mesh)

Slab with penetration supported on 4 sides

LOADING

DISPLACEMENTS

BENDING MOMENTS

Underground Concrete Pit with Ribs

SOIL LOADING

Underground Concrete Pit with Ribs DISPLACEMENTS

Model Bridge Decks – Influence of Kerbs

Model Bridge Decks – Influence of Kerbs FEA Model

Model Bridge Decks – Influence of Kerbs DISPLACEMENTS

BENDING MOMENTS

Foundation Mat For 14 Storey Building FEA MODEL Soil represented by springs Loading from lift core Column loads

Foundation Mat For 14 Storey Building FEA MODEL

Foundation Mat For 14 Storey Building BENDING MOMENT IN X DIRECTION – Vertical Loading

Foundation Mat For 14 Storey Building BENDING MOMENT IN X DIRECTION – Wind Load

Bench For Art Gallery FRAME

FRAME WITH SKIN SUBJECTED TO SEATING LOAD

Bench For Art Gallery DEFLECTIONS