department of civil and environmental engineering, the university of melbourne finite element...

Department of Civil and Environmental Engineering,

The University of Melbourne

Finite Element Modelling Finite Element Modelling ApplicationsApplications

(Notes prepared by A. Hira – modified by N. Haritos)

IntroductionIntroduction

• FEA is a powerful tool.

•  Analyses structural behaviour of complex problems.

• Must be used with full confidence.

• Understanding of the structural problem.

•  Knowledge on the limitations and features of the

FEA.

• This lecture will illustrate some examples of FEA

applications identifying the key problem to be

investigated and some of the difficulties.

Transfer StructureTransfer Structure

• New 27 storey hotel structure built over an existing

10 storey department store

•     Challenge in the project was to design the transfer

structures at the base

•     Typically store has a large column spacing for flexibility

in retail space and Hotel has small column spacing

FEA Required for the FEA Required for the Following ReasonsFollowing Reasons

• The structure is highly irregular.

• The load paths were sensitive to the door openings.

•  Identify regions where tension prevailed. (Important

for RC structure)

•  Required to have clear understanding on the

secondary stresses due to prestressing.

•  Parametric studies needed to be carried out quickly,

efficiently and accurately in a fast track program.

Stages for FEA ApplicationStages for FEA Application

 Conceptual Stage

  Required for sizing purposes.

Manual structural assessment using

a simple strut-tie model.

   Identify level of stresses and critical

regions.

   Formulate finite element model

(FEM)

Stages for FEA ApplicationStages for FEA Application

Preliminary Stage

  FEA was extensively applied to fine

tune suitable locations for door openings.

   Geometry of the wall was finalised

and prestressing procedure was

determined.

Detailed Analysis StageDetailed Analysis Stage

• Detailed analysis carried out for all load

combinations.

• Typical stress distributions determined.

• Correct interpretation of FEA results for RC

elements is important. 

• FEA determines regions of high tensile stresses

under serviceability

Detailed Analysis StageDetailed Analysis Stage

• Enables designer to evaluate prestressing required

for crack free environment.

• Considerable time was allocated to checking the

results.

•    The most effective and efficient method of checking FEA

results is by inspecting graphical outputs.

• Simple equilibrium checks and checking of the load

cases is essential.

Detailed Design StageDetailed Design Stage

• Interpreting the results of FEA is a critical phase.

• Converting to Reinforcement drawings is a most

important phase.

• This stage deserves greater attention as it is often

overshadowed by the glamour associated with the

analytical modelling and analysis phase.

Detailed Design StageDetailed Design Stage

• For reinforced concrete the designer must have a

thorough understanding of the two dimensional stress

state.

•  Skilful use of the powerful graphical post-processing

capabilities,

Structural OptimisationStructural Optimisation

• Spectacular progress over the last two decades.

• Obvious imbalance between the extraordinary

growth of structural optimisation theory and its minimal

application to structural design of engineering structures.

• Readily applied in the areas of space and

aeronautical industries and in the automobile industry.

Structural OptimisationStructural Optimisation

• Currently optimisation process is carried out by trial

and error involving engineering judgement by the

designer.

•  Systematic procedures to arrive at optimal solutions

is desirable.

•  Closer collaboration between research and industry

is required.

Optimisation of WallOptimisation of Wall

• Cantilever Wall system for tall building.

•  Governing Criteria is Stiffness (governed by lateral

deflection at top of building)

•  The objective of the optimisation process is to obtain

the optimum solution. minimum volume of material. maintaining a target stiffness in terms

of the lateral displacement at the top of the

structure.

Optimisation of WallOptimisation of Wall

• Optimal solution = wall thickness profile up the

height of the building will continually change.

•  Solution not practical. Minimise the # of transitions

in wall thick for practical and economic reasons.     

• The procedure involves a systematic sizing-

analysing and resizing process.

Coupled Cantilever WallCoupled Cantilever Wall

Typical Highrise BuildingTypical Highrise Building

Complex Slab ShapeComplex Slab Shape

The reasons for using FEA design of flat slab for a High-

Rise Slab:

• The project consists of 17 buildings ranging from 30

to 38 storeys with similar slab layout. (optimisation

results in economy). 

• The slab is highly irregular.      

• The support system is not in a recti-linear grid. 

• Further studies in the inelastic areas were required

to investigate the slab behaviour under severe

earthquake conditions.

Complex SlabsComplex Slabs

FEA analysis appropriate for:

• Bending moments and shear forces.

• Deflection characteristics.

• Dynamic characteristics including natural

frequencies and deflections due to heel-drop loadings.