Beam model static analysis

A. CatinaccioPH-DT Engineering Office, CERN

Page 1

CERN, May 27th 2015

FEA beam model

• Standard beam model of the main portal frames,

• Loading corresponding to the unit cell equivalent loads (1.6 m pitch)

• Capability to implement the rotational stiffness at the corner joints as

extracted from the analytical models ref. 6.4.1 and the FEA sub-models ref

6.4.2.It allows as well to simulate different joint conditions, such as pinned,

and fully moment constrained.

• The FEA model is built parametrically through and ANSYS APDL script.

• BEAM189 provides a linearized stress output as part of its output record.

• The internal stainless steel membrane and supporting grid are explicitly

neglected.

• The load conditions as described in ref. 6.2.1 and 6.2.2 are combined

according to section 6.1. Material and section properties are described in

sections 3.2 - Member size and availability and 4.1 - Material characteristics

and availability.

Page 2

APDL main parameters

Page 3

Main Model Parameters:

parameter Value / units description

w 18.058 m Portal beam neutral axis width

h 16.958 m Portal beam neutral axis height

gap 0.91+1.138/2 m load offset top and bottom

lockbottom 3.8 m +/- 3.8 m vertical support from portal symmetry axis (to

avoid no pulling reaction from the floor)

po 350 mbar Gas overpressure on the top of the LAr

pitch

1.6 m Pitch between main transversal portal frames

ro

1400 kg/m3 Lar density

rotstiff 1.25E9 N m Imperfect joint rotational stiffness

ymbeam 2E11 N/m2 Material Young Modulus

wf11 0.410 m Width flange HL1100-607

wf21 0.410 m Width flange HL1100-607

hb1 1.138 m Section height HL1100-607

thf11 0.055 m Flange thickness HL1100-607

thf21 0.055 m Flange thickness HL1100-607

thw1 0.031 m Web thickness HL1100-607

Model dimensions

Page 4

The support structure (after the 10mm SS plates) shall starts at:

Internal dimensions of warm structure

Length Width Height

[mm] 63’820 16’920 15’820

Dimensions of the main transversal portal frame

Model loads

Page 5

Model boundary Conditions

Page 6

Model loading and boundary conditions

Results

Page 7

Total displacement [m]Vertical displacement [m]

Results

Page 8

Max long stress on beams [Pa]

Bending Moment diagram [N m]

Results

Page 9

Shear force diagram [N]

Normal force diagram [N]

Results

Page 10

Linearized membrane stress on beams [Pa]

Linearized membrane stress on vertical beams [Pa]

Linearized bending stress on beams [Pa]

Calculation model: portal beam

Page 11

Summary of results from the above runs:

Pressure [mbar] Vertical Deflection [mm] Lateral Deflection [mm]

350 -14.6 39

20 -17.5 30

Stresses at 350 mbar top Max VM equivalent stress Max VM equivalent stress

Value [MPa] 160 1.4

ASME verification of results from the above runs:

Stresses at 350 mbar top Max VM equivalent stress Max VM equivalent stress

Value [MPa] 160 1.4

Location Vertical beam top flange Vertical beam web

Linearized stress category Pm+Pb Pm

ASME allowable (ref. 6.1) < 1.5 S = 331 MPa < S = 220 MPa

Factor 2.06 157

It should also be mentioned that the condition Pm < S is verified in all points of the main members of the frame, where the maximum membrane stress, detected on the bottom beam is Pm = 24.4 MPa.

• Sag conservative but in favour of safety: due to extra span in modelling beam length and

height to centroid axis and from rotational stiffness treatment for corner connections.

• Selected following EC3 to obtain conservative predictions.

• Moment & force results used to design and check connections

• ASME verification OK with minimum safety factor of 2

• Eurocode 3 verification on beam bending, shear, normal force capacity OK – buckling

verification OK (with bracings).

𝑃𝑚 < 𝑆𝑃𝑚 + 𝑃𝑏 < 1.5 ∙ 𝑆

𝑃𝐿 < 1.5 ∙ 𝑆𝑃𝐿 + 𝑃𝑏 < 1.5 ∙ 𝑆 √

Material

Page 12

A note on the moment transition• The transition point of M along the vertical beam is highly affected by:

– The rotational stiffness of the bottom joint

– The position of the bottom support (or contact point)

– (The behaviour of the floor beam)

• The top pressure 20, 120, 350 mbar does not influence the transition point

• The splice joint (seen these effects) must be capable of taking Moments

and Shear with some good safety factors

Page 13