Foundation and Retaining Wall Design Presentation 2.pptx
1. PCSP 411 Professional
Course SP1: Foundation
and Retaining Wall
Design
Engr. Raymond Jay G. Severo
Civil Engineer
2. 01
Foundation/ Footing
Footing Foundation
Different types of
Footing foundation
Footing Design
Concepts
Provisions and formula
for design and factors
to consider in
designing foundation
Introduction
NSCP 2015 Provision
(Earthwork,
Foundation and
Footings)
02 03
Topic Overview
3. Introduction: (NSCP 2015 Provisions)
Foundation Investigation (NSCP 2015)
Soil Exploration shall be required for
buildings, towers and other vertical
structures falling under categories I, II, III
and IV in accordance with Table 103-2 of
NSCP 2015 or as required by the Building
Official or if the site-specific conditions
make the foundation investigation
necessary.
4. Introduction: (NSCP 2015 Provisions)
Excavations – Footings:
Existing footing or foundation which may be undermined by any
excavation shall be underpinned adequately or otherwise protected
against settlement and shall be protected against lateral movement.
Chapter 3: Earthworks and Foundation
Section 303: Foundation Investigation:
Foundation investigation shall be conducted and a Professional
Report shall be submitted at each building site. For Structures two
storeys or higher, an exhaustive geotechnical study shall be performed
to evaluate in-situ soil parameters for foundation design and analysis.
The minimum required number of boreholes per structure based on
footprint area is summarized in the table 2 below.
5. Introduction: (NSCP 2015 Provisions)
All these boreholes should fall within the footprint of the structure
and should generally be uniformly distributed throughout the
building footprint. Unless specified by the consulting
Geotechnical Engineer, all boreholes should be drilled to a
depth of at least five meters into hard strata or until a suitable
bearing layer is reached. For buildings with basements, the depth
of boring should extend to twice the least dimension of the
structures footprint (2B) added to the depth of the basement.
6. Introduction: (NSCP 2015 Provisions)
Table 2: Minimum required number of boreholes per structure
Foot print area of
Structure (m2)
Minimum
Required Number
of Boreholes
A ≤ 50 1
50 < A ≤ 500 2
A ≥ 500 2 + (A/100)
*The minimum required number of boreholes should in no way be constructed as
an upper limit value.
** “A” corresponds to the footprint area of the structure in m2
7. Introduction: (NSCP 2015 Provisions)
An exhaustive geotechnical investigation should also be conducted in case of:
1. Questionable soil, expansive soils, or problematic soil (e.g., liquefiable, organic,
compressible, sensitive, etc.);
2. To determine whether the existing groundwater table is above or within 1.5 meter
below the elevation of the lowest floor level;
3. Where such floor is located below the finished ground level adjacent to the
foundation;
4. In case where the use of pile foundation and/or ground improvement are
anticipated;
5. In areas underlain by rock strata where the rock is suspected to be a questionable
characteristic or indicate variations in the structure of the rock or where solution
cavities or voids are expected to be present in the rock; and
6. Other cases deemed necessary by the Geotechnical Engineer.
The Building Official may require that the interpretation and evaluation of the results of the
foundation investigation be made by a geotechnical engineer.
8. Introduction: (NSCP 2015 Provisions)
Section 304 Allowable Foundation and Lateral Pressure
304-1: From Geotechnical Site Investigation and Assessment
The recommended allowable foundation and lateral
pressure shall be estimated from a reasonably exhaustive
geotechnical site investigation and assessment, which shall include
at least the following:
a. Description of Regional geologic characteristics;
b. Characterization of in-situ geotechnical conditions;
c. Factual report on the in-situ and laboratory tests performed to
characterize the site for a list of in-situ and laboratory test
commonly carried out for geotechnical site characterization);
9. Introduction: (NSCP 2015 Provisions)
d. Disclosure of the assumptions and the applicable analytical or
empirical models used in estimating the allowable foundation
and lateral pressures;
e. Calculations carried out and factor of safety (FS) assumed in
arriving at the recommended allowable foundation and lateral
pressure; and
f. Evaluation of existing potential geologic hazards and those
that may be induced or triggered by the construction?
Installation of the structure.
The geological site investigation and assessment shall be
performed by a geotechnical engineer.
10. Introduction: (NSCP 2015 Provisions)
A geotechnical investigation and assessment shall be presented in a report. The
report, together with a brief resume and a sworn statement of accountability of
the geotechnical engineering consultant who prepared it, shall be included in
the submittals to be reviewed and examined by the building official or
government authority in charge of issuing the relevant permits such as
environmental compliance certificate and/or building permit.
11. Introduction: (NSCP 2015 Provisions)
305: Footings:
General:
Footing and foundation shall be constructed of masonry concrete or treated wood in
conformance with chapter 4, 6 and 7. Footing of concrete and masonry shall be of solid
material. Foundation supporting wood shall extend at least 150 mm above the adjacent
finish grade.
Minimum Requirements for foundation (Section 305)
●
The minimum depth of footing is given in Table unless another depth is warranted, as
established by a foundation investigation.
14. Foundation and Footing
What is Footing/ Foundation?
Footing are structural members used to
support columns or walls and transmit
their loads to the underlying soils.
Reinforced concrete is the most suited
materials for footing for reinforced
concrete and structural steel buildings,
walls, towers, bridges and other
structures.
15. Different Types of Foundation:
01 Shallow Foundation
02 Deep Foundation
Shallow foundation transfer the load from the superstructure to a soil
stratum that is relatively close to the ground surface
Deep foundation is generally any type of foundation that extends below
strata of poor soil to a level where the sil is adequate to support the
loads.
16. Types of shallow foundation
Footing and mats are two types of shallow foundation
Isolated spread footing – Carries a single column. (Square or rectangular
footing)
Wall footing – is similar to a spread footing and is usually continuous under
the length of the wall
Combined Footing – is a special type of spread footing that supports
multiple columns or wall on the same footing.
Strap Footing or cantilever footing – consist of an eccentrically loaded
footing connected to an adjacent footing by a strap beam.
Spread Footing - Supports one or more vertical elements (Column).
Mat Foundation – is a large concrete slab that supports some or all of
the columns and/ or walls in the building.
17. Types of deep foundation
The most common types of deep foundations utilized under
building are piles abd drilled piers
Piles – are foundation members that have relatively small-cross sectional dimensions
compared with their length. They are available in various materials and shapes, and
most concrete piles are circular, square, or octagonal in cross-section. Piles are typically
placed vertically into the soil but can be installed at a slight inclination to help resist
lateral loads.
Drilled Pier – is similar to a cast-in-place pile in that it is a shaft that is drilled into
the soil. The shaft may be lined with a casing that may or may not be extracted as the
shaft is filled with concrete. A permanent casing is generally required where unstable
soil conditions are encountered, which could lead to the soil caving into the drilled
shaft. A drilled pier is also referred to as a pier or caisson.
18. Designing a Footing:
Loads and Reaction – design of reinforced concrete member,
footing must be proportioned to resist the effect from the
governing factored loads determined in accordance with the
ACI. The thickness of a footing and the required area of
flexural reinforcement are determined using the strength
design method, which utilizes factored load effects. Shear
requirements must be satisfied using factored shear forces and
design shear strength.
Design Consideration:
19. Designing a Footing:
Design Consideration:
Sizing the base area – the base dimension of a footing are determined using
the unfactored loads and allowable soil bearing capacities
• Allowable Bearing Capacity – bearing capacity of soil or rock can be
obtain from soil borings and tests performed by geotechnical engineer.
• Soil Pressure Distribution - after determining the bearing capacity of
the soil, the next step in designing is to determine the soil pressure
distribution at the base of the footing.
22. Designing a Footing:
Design Consideration:
Sizing the Thickness – Once the required area of the
footing has been established on the basis of the service
loads and the allowable bearing capacity of the soil, the
thickness h of a footing must be determined considering
both flexural and shear.
23. Designing a Footing:
Design Consideration:
Design for Shear – provision for shear strength in footing are the same as those
required for slab and are given by ACI 11.11. Requirements for both one- and two -
way shear must be satisfied.
• One-way shear – the factored shear force at the critical section, based on
the factored pressure at the base of the footing within the tributary area,
must be equal or less than the design shear strength determined in
accordance with ACI 11.11.2.1. Critical section is located a distance “d”
from the face of the column.
• Two-way shear – the factored shear force at the critical section, based on
the factored pressure at the base of the footing within the tributary area,
must be equal to or less than the design shear strength determined in
accordance with ACI 11.11.2.1. Critical section is located a distance “d/2”
from the face of the column perimeter.
25. Designing a Footing:
Design Consideration:
Design for Flexure – after obtaining the dimension and thickness of the footing, it
must be test and check for it shear capacity if the thickness of the footing can resist
the shear and flexure force on the footing.
• Critical Section – a spread footing must be designed for the bending
moments that are induced because of the pressure developed at the
base of the footing from the factored load.
• Determining the required reinforcement - once maximum factored
moment at the critical section has been determined, the required area of
reinforcing steel can be calculated using the strength design
requirements.
28. Designing a Footing:
Design Consideration:
Detailing the Reinforcement – requirements for the distribution of flexural
reinforcement in footing are given in ACI 15.4. For one-way (wall footing) and two
way square footing, reinforcement is to be distributed uniformly across the entire
width of the footing. Flexural reinforcement for two-way rectangular footings must
be distributed in accordance with ACI 15.4.4. Reinforcement in the long direction is
uniformly distributed across the entire width of the footing. In the short direction, a
portion of the total reinforcement must be uniformly distributed over a band width
centered on the column or pedestal that is equal to the length of the short side of
the footing.
Development of Reinforcement - Flexural reinforcement in footing must be fully
developed in accordance with the applicable provision of ACI chap. 12.The bars
must extend at least a tension development length beyond the critical section
defined by ACI 15.4.2.
30. Designing a Footing:
Design Consideration:
Bar Size (No.) Diameter (mm)
Development Length Ld
Inches mm
4 12 mm 19 482.6
5 16 mm 24 609.6
6 20 mm 29 736.6
8 25 mm 48 1219.2
9 28 mm 54 1371.6
10 32 mm 60 1524.0
Minimum Tension Development Length for Flexural Reinforcement in Footings
31. Designing a Footing:
Design Procedure:
The following design procedure can be used in the design of footings.
Included is the information presented in the previous section on analysis,
design and detailing.
Step 1: Determine the area of the footing.
Step 2: Determine the thickness of the footing by shearing stress; one-
way and two-way shear
Step 3: Flexure and steel reinforcement
Step 4: Developmental length of the reinforcement
32. Designing a Footing:
Step 1: Determine the area of the footing.
𝑞𝑎 =
𝑃 (𝐹𝑜𝑟𝑐𝑒)
𝐴(𝐴𝑟𝑒𝑎)
𝑞𝑒 =
𝑃 (𝐹𝑜𝑟𝑐𝑒)
𝐴(𝐴𝑟𝑒𝑎)
Assume thickness of footing to be used in
getting the effective soil pressure
ℎ𝑐 = 20% 𝑙𝑜𝑛𝑔𝑒𝑠𝑡 𝑑𝑖𝑚𝑒𝑛𝑠𝑖𝑜𝑛 + 75𝑚𝑚
𝑞𝑒 = 𝑞𝑎 − 𝛾𝑠ℎ𝑠 − 𝛾𝑐ℎ𝑐
𝐴 = 𝐵2
for square footing
𝐴 = 𝐵𝐿 for rectangular footing
33. Designing a Footing:
Step 2: Determine the thickness of the footing
𝑞𝑢 =
𝑃 (𝑓𝑎𝑐𝑡𝑜𝑟𝑒𝑑 𝐹𝑜𝑟𝑐𝑒)
𝐴(𝐴𝑟𝑒𝑎)
Determining thickness by Shearing; One-way shear and Two-way (punching)
shear which ever is greater
𝑉𝑢 = ∅𝑉𝑐
𝑞𝑢𝐴𝑠ℎ𝑎𝑑𝑒𝑑 = ∅(.17𝜆 𝑓′𝑐𝑏𝑤𝑑)
One-way shear Two-way shear
𝑉𝑢 = ∅𝑉𝑐
𝑞𝑢𝐴𝑠ℎ𝑎𝑑𝑒𝑑 = ∅(.33𝜆 𝑓′𝑐𝑏𝑜𝑑)
36. Spread Footing ( Square Footing)
A squared column footing is to support a 400mm x 400
mm squared tied column with 12 pcs of 25 mmØ bar, the
top of the footing is located 1.5 m below the natural
grade line. The column is to carry a service dead load of
1500 kN and a live load of 1000 kN. Allowable soil pressure
is 300 kPa as per boring test conducted by geotechnical
engineer, also, soil unit weight is determined to be 17.95
kN/m3. The site location is determined to be flood prone
area and there is always an average surcharge pressure
of 25 kN/m2. Assume that the concrete unit weight for
both column and footing is 23.5 kN/m3, also, concrete
cover is located 75 mm from the nearest face of the
reinforcement bar . Design the square footing having
25mm bars. Assume f’c = 27.5 MPa and fy = 275 MPa.
37. Spread Footing ( Square Footing)
A squared column footing is to support a 450mm x 450
mm squared tied column with 16 pcs of 25 mmØ bar,
the bottom of the footing is located 2 m below the
natural grade line. Allowable soil pressure is 300 kPa as
per boring test conducted by geotechnical engineer,
also, soil unit weight is determined to be 18 kN/m3.
Assume that the concrete unit weight for both column
and footing is 23.5 kN/m3, also, concrete cover is
located 80 mm from the centroid of the nearest
reinforcement bar . Design the square footing having
25 mm bars. Assume f’c = 27.5 MPa and fy = 414 MPa.
The column is to carry a service dead load of 1700 kN
and live load of 1100 kN.
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THANKS!
Raymond Jay G. Severo
raymond16severo@gmail.com
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