Aluminium Grandstand

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Aluminium Grandstand
Finite Element Project

• Paul De Palma and Matt Ellis

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Introduction - Project Goals

• To conduct a finite element analysis of the
  grandstand under different loading conditions to
  gauge the suitability of its design.
• The maximum possible loading conditions will be
  used to test the grandstand under extreme
  conditions.
• Microstran and Strand 7 will be used for these
  analyses, with only beam elements mainly required.

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Description

• Constructed of aluminium members.
• Most connections are welds, with minor use of
  bolted connections
• Constructed off site in modular format so that
  different sizes can built.

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Dimensions - Base frame
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Sections

• Eight different cross-section were used
• Understructure beams
• 50 x 50 x 5 mm SHS
• Seats and Footpads
• user defined section (will be talked about in
  the next section)
• Risers
• 150 x 25 x 5 mm RHS
• Railings
• 37.5 x 5 mm CHS

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Sections (continued)

• Side Base Railings
• 87.5 x 62.5 x 5 mm C-Section
• Side Railing Posts
• 50 x 50 x 5 mm SHS
• Back Railing Posts
• 90 x 50 x 5 mm RHS
• Back angle supports / bracing
• 75 x 75 x 5 mm EA

NOTE Some odd dimension were used due to
conversion from imperial to metric.
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Materials

• Aluminium was used for all members, which
  consisted of two grades
• 6061-T6 (For the understructure and the rail
  posts)
• 6063-T6 (For all other members including seat and
  foot boards, risers, angles and railings)

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User defined cross-section

• A custom cross-section had to be created, for the
  seats and foot pads, using Strand 7s Make beam
  section function.
• The following cross-section was entered into
  Strand 7, joined with Quad4 elements and set as a
  beam cross-section.

25
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Stress Analysis

• Stress wasnt critical for any of the grandstand
  members in 2D or 3D.
• Axial stress values were all lower than 10 MPa.
• Highest value for bending stress in planes 1 and
  2 was 100 MPa, whilst the rest were around 50 MPa
  or less.

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Stress Analysis

• Critical 100 MPa case for Rail Loads Case 1, at
  the rail supports at the back.
• Yield stress of 6061-T6 Aluminium is 255 MPa in
  tension (Hibbeler).

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2D Analysis - Back Frame

• Analysis of back frame to see how it performed
  under a uniform distributed load of 2.5kN/m along
  the seat i.e. for a 100kg person of 40cm width of
  seat.

NOTE This 2.5kN/m load is used in further
analyses of the grandstand.
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2D Analysis - Back Frame

• Support nodes were restrained in the X and Y
  planes.

• Critical deflection is Y-Axis deflection 0.3 mm.

• The base frame stays very rigid when load is
  placed.

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2D Analysis - Side Frame

• Analysis of side frame to see how it performed
  under a uniform distributed load of 2.5kN/m at
  each seat and footing.

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2D Analysis - Side Frame

• Support nodes were restrained in the X , Y and Z
  plane.

• Critical deflection is X-Axis deflection 0.07
  mm.

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3D Analysis - Self Weight

• The grandstand was analysed with only its
  self-weight acting on it.

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3D Analysis - Self Weight

• Maximum X-Axis deflection 0.6mm.

• Deflection in side rails fall inwards towards the
  centre of the grandstand.

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3D Analysis - Seating Loads

• A load of 2.5kN/m is applied to the seats and
  footing.

• The grandstand is at maximum capacity and must
  support the weight of people sitting and standing
  at the same time.

• Maximum capacity is approximately 60 people.

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3D Analysis - Seating Loads

• Maximum Y-Axis deflection 2.5mm.

• Maximum Z-Axis deflection 1.3mm.

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3D Analysis Wind Loads

• Three different cases were modelled to simulate
  the forces applied by the wind when the
  grandstand is empty.
• 0.1kN/m the X direction (side)
• 0.1kN/m in the negative Y direction (back)
• 0.1kN/m in the positive Y direction (front)

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3D Analysis Wind Loads (Case 1)

• Load applied from the side.

• Deflection in the X-Axis is critical 3.48 cm.

• Maximum Y and Z Axis deflection was about 1 - 2
  mm.

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3D Analysis Wind Loads (Case 2)

• Load applied from back.

• Deflection in the Y-Axis is critical 2.18cm.

• Maximum X and Z Axis deflection was about 2-6
  mm.

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3D Analysis Wind Loads (Case 3)

• Load applied from front.

• Deflection in the Y-Axis is critical 2.27cm.

• Maximum X and Z Axis deflection was about 2-7
  mm.

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3D Analysis Rail Loads

• Two different cases were modelled to simulate
  other external forces applied to safety rails.
• 1.7kN/m in negative Z direction (people hanging
  from top rail)
• 0.17kN/m in positive Y direction (people leaning
  back from seat on to lower 4 rails)

Assuming weight of 70kg person.
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3D Analysis Rail Loads (Case 1)

• Deflection in Y-Axis is critical 4.2mm.
• X-Axis deflection 1.7mm.
• Z-Axis deflection 1.2mm.

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3D Analysis Rail Loads (Case 2)

• Deflection in Y-Axis is critical 8.6mm.
• X-Axis deflection 3.4mm.
• Z-Axis deflection 0.1mm.

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Need for Base Restraint?

• Tried to simulate rotational effects and sideways
  movement of the whole grandstand from wind and
  rail loads.
• However, this proved very difficult as Strand7
  gave unrealistic values of deflection in the
  direction under consideration (in the billions of
  metres).

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Beam Testing

• Determine the maximum possible distance between
  supports on seat.
• Tested in Strand7 and Microstran
• Unable to create a custom cross-section in
  Microstran, therefore, simple rectangular section
  was modelled.
• Load of 2.5kN/m was applied.
• Supports were placed at different distances to
  find how long the beam may be before the
  deflection in the seat becomes critical.
• Critical deflection determined by aesthetics and
  shape.

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Beam Testing (Strand 7)

• At 8m intervals, deflection still only 70mm at
  the mid section.

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Beam Testing (Microstran)

• Deflection in Microstran at 8m is 38cm.
• Strand7s results seem unrealistic, despite being
  modelled the same way in both programs.
• For aesthetic purposes it is suggested that seat
  lengths should stay around the design value of
  2.5m.

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Increased Grandstand

• Grandstand comes in modular format and can be
  connected together for increased capacity.

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Increased Grandstand

• 2.5kN/m distributed load applied on seats and
  footings.
• Deflection in mid seats were only 2cm
• Deflection in safety rails were 70cm!

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Increased Grandstand - Improvements

• 2cm deflection in seats is acceptable.
• 70cm deflection in rails is due to increased
  height of structure, lack of support in this area
  and thus greater susceptibility to more
  deflection.
• Can be minimised by providing extra support and
  reinforcement in the rear of the grandstand.
• Cross bracing may also be inserted at this
  mid-section of railing.

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Troubles encountered

• Difficulty in finding information for a
  grandstand regarding dimensions and materials.
• Offsetting of beam elements for appearance of the
  structure.
• Difficulty with beam-node connections, as nodes
  were left unconnected.
• Difficulty in determining design details.
• Base rail beam property, which proved very
  critical, had to be changed.
• Deflection then decreased from 89cm to 0.1mm!

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Conclusion

• From our analysis the basic design of the
  grandstand performs quite well under the given
  loading conditions.
• Only basic additions were required when the size
  of the grandstand was changed which is as
  expected.
• Strand 7 proved to be the best program to use,
  but at times its accuracy was questioned, such as
  in the beam testing.