3.1 Test Phenomena

The phenomena of the two specimens is approximately the same, the sequence of specimen failure were as follows: First, the yield appeared at the ends of column between slits; Then, obvious tensile strip appeared along the overall diagonal, and buckling appeared in the middle of the specimen; The out-of-plane deformation of specimen increased sharply, until the instability appeared at corner; At this moment, the bolts had rather obvious slip phenomenon. Finally, larger outward deformation appeared in specimen and T plate, even the tearing of welding seam appeared. Meanwhile, during the overall instability of specimen, it is be accompanied by the local torsion instability of column (Figure 5, Figure 6). Refer to Figure 9 and Figure 10 for the curves of load vs. shift. (δT here is the horizontal relative displacement between the upper and lower T plate, and it is defined as inter-lamination displacement in the test).

1) Specimen SPSWS 1

Before loading to δ= ±6 mm , no obvious deformation of specimen appeared.

During the first round of loading to δ= ±60mm, the obvious out-of-plane drum-like buckle appears in the sheet, and the obvious tensile strip appeared. No obvious column instability appeared. During the second round of loading to δ= ±60 mm, crevices began to appear in T plate and specimen, and the obvious deformation outside plane appeared. During the loading to δ= ±70 mm, the deformation out-of-plane further aggravated in sheet and T plate (Figure 7), and there appeared obviously the overall instability.

2) Specimen SPSWS 2

Before loading to δ= ±6 mm , no obvious deformation of specimen appears. During the loading to δ= ±30 mm, obvious out-of-plane deformation appears in steel sheet wall, and the middle bulged slantly outward. There is a little deformation at the corners on both ends in the joint of steel sheet bottom and T plate. During the loading to δ= 40 mm, the steel sheet had more obvious deformation outside plane, and near the zero displacement, a sudden change of north and south direction occurs in the out-of-plane bulging direction of the steel sheet, thus, it brings about a leaping phenomena appearing near the zero displacement in the curve of Figure 10. During the loading to δ= 60 mm, large flexural southward deformation is found at the lower west corner of the steel sheet bottom and the T plate web (Figure 8). Meanwhile the phenomena of overall instability were obvious.

3.2 The Stress Form of Column between Slits

To study the stress form of the column between slits, a column in the specimen is specially chosen as an analytic object (as shown in Figure 11), and the relational graph of strain at each measuring point in Figure 11 and the distribution height h is thus obtained after or by comparing the measured data of two loads P =200.6 kN and P=300 kN (elastic stage) (In the figure, the horizontal ordinate h is the distance from each measuring point to the lower end of silt, in mm. and T-1, T-2, T-3 is the strain of measuring point in vertical, slant and horizontal direction. S is the strain of single direction sheet).

It is observed that from Figure 11, the strain at column end is mainly the vertical strain, and it essentially shows a dissymmetry distribution along cross-section, it is obvious that the stress form at end is mainly the bending force; The vertical strain in the column middle is close to zero, which is similarly identical to the inflection point of lower beam under the bending moment action, so it is obvious that the stress form of the middle is mainly the shearing force.

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