Only axial compressive loads are applied at the initial neutral axis at both ends (no shift due to eccentric load, etc。 is assumed)。 Deadweight is not considered and a uniform temperature is assumed。

Material properties

The material is assumed isotropic with a Poisson's ratio of 0。3 and a Young Modulus of 70,475 N/mm2。 The material properties were taken from the Aalberg experiments [Aalberg et al。, 2001]。 The same material properties are considered for the transverse frames。

The aluminium material strength in the HAZ is reduced by the high temperature during weld thermal  cycle (MIG welded)。

True stresses versus true strain properties derived from engineering values were implemented by each user into his FE model for plate, stiffeners and HAZ。

Fig。 2: ISSC procedure to define the initial imperfections

Additional analyses were performed with the Standard model using as initial imperfections the first buckling mode (m = 4) from eigenvalue buckling analysis scaled so that the maximum deformation remains 2 mm (Standard procedure)。

HAZ modelling

According to several standards, one shall consider the width of the reduced strength zone (noted 1 and in the following) to extend 25 mm at each side of the weld (note that 20 mm is proposed in Eurocode 9 [Eurocode 9, 1998])。 In the present study (Fig。 3), this means 2 1

= 50 mm in the plate and = 25 mm in the stiffener web (measured from the mid-plate and not from the plate surface)。 The extension (width) of the HAZ is mainly affected by the applied welding process and the welding parameters, as well as the material properties。

Fig。 3: Standard HAZ width (2 1 in plate = 50 mm, 2 in stiffener web = 25 mm)

Therefore, the following weld zones were considered in the mesh model (Fig。 4):

five longitudinal welds at the junction between the transverse plate and the five stiffeners,

four longitudinal welds at the intersection between the five extruded elements,

two transverse welds between plates。



Weld types (longitudinal, transversal,  extruded and no extruded components)。  Several  configurations are studied–Phase B1,

HAZ width (2 1 =25–100 mm)–Phase B2,

Initial panel deflection (amplitude and shape)–Phase B3,

Residual stresses––Phase B4,

Yield stress in the HAZ––Phase B5。

Phase B1–weld types

The influence of weld types was studied in this phase。 Fig。5, Fig。6 and Table 1 show the results of the analyses that are compared to the reference case (without HAZ)。

0。000       0。050       0。100       0。150       0。200       0。250       0。300       0。350         0。400

Average strain [%]

Fig。5: Effect of the HAZ

(ISSC model and ISSC initial imperfections)

Fig。 4: Weld positions

It was assumed that the HAZ does not affect the transverse frames material (T1,。。。,T4)。

If not specified, the numerical analyses were conducted with a HAZ width of 50 mm, i。e。 2 1  =  50 mm (2×25 mm in the plate) and = 25 mm in the   stiffener

0。000        0。050        0。100        0。150        0。200        0。250        0。300        0。350    0。400

Average strain [%]

Fig。6: Effect of the HAZ

(Standard model and Standard initial imperfections)