of concrete embedded underneath the slab floor. The design of these footings for the steel portal framed structure was completed by the following steps: Concrete Pad Footing Design Bolt Selection Base Plate Design Concrete Pad Footing Design The process for the pad foot was as follows: 1. Find concrete volume to resist uplift 2. Find footing area to withstand bearing pressure 3. Derive pad foot dimensions 4. Determine steel reinforcement requirements Step 1: Concrete Volume Neglecting friction between the wall and soil, the dead weight of concrete ( ) required to resist the uplift force ( ) was found as follows: Step 2: Footing Area To find the area ( ) to correctly transfer the downwards force ( ) without surpassing bearing pressure, assuming a square pad shape ( ) and allowable bearing pressure = :
(the combined weight of concrete and downwards) Step 3: Foot Pad Dimensions Thickness of the pad footing ( ) was then found as follows: this is acceptable as minimum depth for HD bolts is 900mm Therefore, final dimensions are , refer to Appendix drawings for detail. Step 4: Steel Reinforcement To determine steel reinforcement requirements as follows: Try N32 reo bars ( ) take 40 mm cover as work will be conducted on the surface for construction purposes. Assume U/R where T=C,
steel yields U/R To check bending moment, therefore O.K Find reinforcement bar spacing, Determine development length, Therefore the reinforcement bars will fully develop their yield stress Bolt Selection While 2 bolts may be sufficient for small portal frame structures, a 4 bolt design was chosen with the initial assumption of 4-M20 4.6/S to be checked for shear and tension 4-M20 4.6/S bolts
Tension check: therefore O.K Shear check: therefore O.K Development length: This is not correct as the minimum development length is not achieved. Therefore in design the bolts must run to the bottom reo bars, so bolts will run 1900mm in length . Base Plate Design The process of design of the base plate to attach a column to the footing was based as follows. Some of the steps have been completed above, as in the reactions at the footing and the bolt size requirements. The remainder of the design was in the selection of the type of welding to secure the base plate to the column and checking the plate is sufficient in tension and compression. This can be used to design the dimensions for the base plate. Welding Selection SP grade welding quality will be used for base plate welding, with Try 8mm E41XX/W40X SP Fillet Welds
Therefore, capacity is O.K. for the design forces imposed on the plate now to check compression and tension at the plate. Plate Capacity Checks Tension Check therefore, this is O.K. for tension on the plate. Compression Check For compression of the base plate, the uplift for on the footing will be the governing force as this as already been checked in the pad footing design, axial compression can be ignored.
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