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