EN2400 Structural Analysis and Design DESIGN SHORT 3 - INDETERMINATE STRUCTURAL ANALYSIS AND STEEL STRUT DESIGN The land owner (introduced in Design Short 2) is planning on significant renovations to part of their estate and they wish to use the reinstated bridge as access for construction plant and materials. The variable load capacity of the beams you identified in Design Short 2 is significantly lower than that required for the new intended use of the bridge. The land owner has suggested placing steel struts under the mid-point of each beam of each span to enhance their variable load carrying capacity. Using LUSAS and the design guidance provided in Design Short 2 determine the maximum variable load (per m2) that the deck can now support, based on the capacity of the beams in bending and shear. You are also asked to design the steel struts (HINT: try the smallest universal column section first). For this you will need to apply the appropriate ULS partial factors to the permanent and variable loads. Please provide full calculations to support your answers. You may assume the following; . The 125mm thick deck plate is formed from timber and has the capacity to withstand a greater variable load than the beams; · The beams are continuous over pinned supports; . The struts are partially restrained in direction at both ends. The elevation and cross section of the bridge structure are shown below (Figures DS3.1 and DS3.2) together with the beam dimensions (Figure DS3.3). All dimensions are in mm. 6000 5000 3000 > 2500 -- 'S 2000 V 2000 Figure DS3.1 Elevation of bridge structure I I I I 130 160 :130 : Figure DS3.3 I beam dimensions DESIGN DATA Plastic Lumber Beams Elastic (short term) modulus = 2.4 GPa Density, Pbeams = 8.7 kN/m3 Flexural Strength, Øy = 4.1 N/mm2 Shear Strength, Tv = 2.4 N/mm2 (this is an average shear stress capacity) Note: The strengths are serviceability stress limits, therefore you undertake the calculations with serviceability load factors (i.e. partial factors = 1.0) * 500 Figure DS3.2 Cross section through bridge structure 1 500 1000 1000 Timber deck plate Density, Pdeck = 8 kN/m3