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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