Design rolling shear strength is greater than the mean shear stress in the web across glue line; therefore OK. Also, there is clearly no requirement to check the rolling shear strength of the bottom flange/web connection.

4 m3

Example 7.5.3 The roof structure of an office building is formed by steel beams supporting thin flanged box beam panels as shown in Figure E7.5.3. Each panel comprises 4 No 47 mm thick by 120 mm deep timber webs at 400 mm centre to centre with plywood panels glued to the top and bottom faces and has an effective span of 4000 mm. The plywood is Canadian Douglas fir and is 15.5 mm thick on the top face and 12.5 mm thick on the bottom face and is aligned with the face grain parallel to the direction of span of the panel. To allow roof light structures to be fitted, areas of the plywood flanges between the central ribs in each panel are cut out and this occurs at three positions along the length of each panel as shown in Figure E7.5.3. Each box beam panel is 1272 mm wide and is detailed to fit against adjacent panels, being connected on site by nailing as shown in Figure E7.5.3. Each panel supports a characteristic permanent load, including self-weight, of 0.81 kN/m2 and a characteristic variable medium-duration load of 0.75 kN/m2. The timber used for the panel ribs is strength class C24 in accordance with BS EN 338:2003, and the properties of the plywood are given below.

The structure functions in service class 2 conditions and the cross-section of a box beam panel is shown in section A-A in Figure E7.5.3.

Check that the panel will comply with the strength rules in EC5 at the ULS and calculate the final deformation of a panel at the SLS when subjected to the combined permanent and variable loading.

1. Panel geometric properties

Distance between the beam centre bcc = 400 mm lines, bcc

(a) Plan on a box beam panel

Top and bottom flanges nailed to the adjacent thin flanged box beam web in the 25-mm zone

Open area to allow roof light to be fitted

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