1.
FOUNDATIONS
Foundation for all equipment and structures shall be designed in
accordance with the recommendations outlined in the geotechnical consultant’s
investigation and recommendations, specifying the following information:
₋
Pipe types, depths,
and foundations for the different structure or equipment classifications.
₋
Pipe or caisson
capacities, if such foundations are used.
₋
Allowable soil
bearing for both vertical and lateral loading.
₋
Active and passive
earth pressures.
₋
The water table
height for buoyancy computations.
₋
Use of passive and
frictional forces to resist active and lateral forces.
₋
Settlement data for
the different equipment classifications.
2.
Foundation for Vibrating Machines
Foundation for vibrating machines must be isolated from neighboring
foundation of buildings, structures, and equipment by a through joint as a
minimum. Vibrating machines directly coupled with each other must be placed on
the same foundation. If the machines are placed on pedestals or raised concrete
plaints, the clearance between external surfaces of concrete shall not be less
than 4 inch to allow access for cleaning and maintenance.
If dynamic analysis will not be performed for block type foundations
placed on the ground, the minimum concrete weight shall be as follow:
₋
3 times the weight of overhanging machineries in
the case of rotating machines or balanced reciprocating compressors.
₋
5 times the weight of overhanging machineries in
the case of unbalanced reciprocating compressors or pumps.
The maximum eccentricity between the center of gravity of the machine
foundation system and the center of gravity of the base surface should not be
more than 3% of the dimension of the base side at that direction.
a.
Avoid Resonance
Resonance on the foundation shall be avoided and the natural frequency
shall be within the limits as specified.
fe/fn < 0.7 or fe/fn > 1.4
where : fe = machine frequent
fn = natural frequency
b.
Allowable Amplitude
Amplitude of vibration is defined as the maximum displacement of a
given point from its resting position. The evaluation shall include for three
components: vertical, parallel to shaft of machineries, and transversal.
Amplitude of vibration shall be calculated on the most representative
points of the foundation, practically at the corners of top foundation where
the machineries is placed. In the case of heavy multistage reciprocating
machines, reference shall be made only to the main block underneath equipment.
3.
Minimum Reinforcement for Block Type Foundation
The minimum reinforcement in a concrete block foundation should
consist of bars D-13 mm (1/2-inch dia.) spaced at 200 mm (8-inch) extending
both vertically and horizontally near all of the faces of the foundation block.
4.
Stability
Stabilizing structures and foundations shall be designed so that the
safety factor shall not be less than the values mentioned below at any
circumstances.
Sliding
:
|
1.5 (friction factor between concrete and
soil is 0.5)
|
Overturning
:
|
1.5 for temporary loading
2.0 for permanent loading
|
Uplift
:
|
1.1 for temporary load
1.2 for permanent load
|
5.
Settlement
For dead load plus imposed load conditions the allowable net bearing
soil capacity shall be based on settlement criteria (by Skempton and Mac
Donald, 1955) with the following maximum settlement (Δmax.) :
Foundation
type
|
Foundation
placed
|
Δmax.
(mm)
|
Footing foundation (isolated foundation)
|
Soil Clay
|
65
|
Sand
|
40
|
|
Raft foundation
|
Soil Clay
|
65~100
|
Sand
|
40~65
|
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