4.

STRUCTURAL DESIGN
4.1 General Provisions
Codes and References
• National Structural Code of the
Philippines (NSCP 2010)

• Referral Code of RA 6541 National

Building Code of the Philippines (NBCP)

• Code Basis: UBC 1997, IBC 2009, ASCE7-

05, ACI Code 318-08M, AISC-05
4.2 Design Load
Load Combinations
• Strength Design or Load and Resistance Factor
Design (LRFD)
1.4(D+F)
1.2(D+F+T) + 1.6(L+H) +0.5(Lr or R)
1.2D + 1.6(Lr or R) + (f1L or 0.8W)
1.2D + 1.6W + f1L + 0.5(Lr or R)
1.2D + 1.0E + f1L
0.9D + 1.6W + 1.6H
0.9D + 1.0E + 1.6H
Load Combinations
Where:
D = dead load
E = earthquake load
F = load due to fluids
H = lateral earth pressure of soil and water
L = live load
Lr = roof live load
T = loads due to temperature change
W = wind load
f1 = 1.0 for floors in places of public assembly, for live
load exceeding 4.8 Kpa, and for garage live load
= 0.5 for other live loads
Load Combinations
• Allowable Stress Design (ASD)
D+F
D+H+F+L+T
D + H + F + ( Lr or R)
D + H + F + 0.75 [L + T + (Lr or R) ]
D + H + F + ( W or E/1.4)
Loadings
• Dead Loads: weight of the structure and permanent
attachments
• Live Loads: maximum loads expected due to
intended use or occupancy
• Wind Load
• Seismic Load
• Other Loads: impact, crane loads, heliport landing
areas, soil load
Dead Load
• Weight of structure
• Self weight

• Weight of permanent attachments

• Roofing materials
• Ceiling
• Plumbing and electrical fixtures
• Finishes
• Fixed equipment
Dead Load
Table 4-1 Minimum Densities for Design Loads from Materials (kN/m3)
Dead Load
Table 4-2 Minimum Design Dead Loads (kPa)
Live Load
• Determined by the function and occupancy of the building

• Weights of temporarily placed items

• Furnishings
• Human occupants
• Construction activities
Live Load
Table 4-3 Minimum Uniform and Concentrated Live Loads
Roof Live Load
Table 4-5 Minimum Roof Live Loads
Wind Load
• Every building and every portion thereof shall be
designed and constructed to resist the effects of
wind

• Design wind load for the Main Wind Force

Resisting System (MWFRS)
1. Simplified Procedure
2. Analytical Procedure
3. Wind Tunnel Procedure
Important Parameters for
Wind• Load Calculations
Geometric Properties of the building (length, width, height, etc.)

• Location of Building/ Wind Zone -> Wind Speed

• Structural Type ->Wind Directionality factor

• Importance Category

• Exposure Category ->Velocity Pressure Exposure Coefficient

• Topographic factor

• Enclosure Category: Enclosed, Partially Enclosed, Open Building

Wind Zone Map of the Philippines

V=200kph
V=250kph

V=125kph
Table 4-7 Wind Zone for the Different Provinces of the Philippines
Table 4-8 Wind Directionality Factor
Table 4-6 Occupancy Category
 Table 4-9 Importance Factor

-a magnifier that increases or reduces the wind load.

Table 4-10 Velocity Pressure Exposure Coefficients, Kh and Kz
Table 4-11 Terrain Exposure Constants, Kzt
Other Factors to be determined in accordance
with NSCP
• Gust Effect Factor, G

• Enclosure classification

• Internal and External Pressure Coefficients, GCpi and

GCpf

• Velocity Pressure, qz
Design Wind Pressure
• For rigid buildings of all heights

• For flexible buildings

• For low-rise buildings

Seismic Load
Structures and portions thereof shall, as a minimum, be
designed and constructed to resist the effects of seismic
ground motions
Analysis due to Earthquake
• Lateral force Procedures:
1. Simplified Static
2. Static
3. Dynamic

• Earthquake design is SITE SPECIFIC

Simplified Static Analysis
• Single family dwellings not more than three floors

• Other structures not more than two floors

• Design Base Shear

Static Analysis
• For regular structures

• Simplified Design Base Shear

Ft Static Lateral
Force Procedure
Fn
Vn Vx = Fx +…Fn +Ft
x=1…n ; x ≈ n

Fx+1 Fx – design seismic

force at level x
Vx+1
Ft – portion of base
shear conc. at
Fx the top
Vx Vx= story shear

V
Dynamic Analysis

• Pertinent parameters are enumerated in 3D modeling of

structures with irregular configuration (NSCP Section 208.6)
Table 4-23 Vertical Structural Irregularities
Vertical Irregularities
Table 4-24 Horizontal Structural Irregularities
Horizontal Irregularities
Important Seismic Parameters in Building
Design
• Seismic Zone
• Site Characteristics
• Soil Profile Type & Zone -> Seismic Coefficient
• Seismic Source Type & Distance from Fault Line-> Near
Source Factor Na & Nv
• Occupancy
• Importance factor
• Building Configuration
• Regular or irregular
• Earthquake Force Resisting Structural Systems
• Rw, Rx
Seismic Zone Map

Zone 2 4
Philippine Earthquake Distribution
Zone
0.2 0.4 from 1970 to 2008 (PHIVOLCS)
Factor
Table 4-12 Seismic Importance Factor
Table 4-13 Soil Profile Type
Seismic Source
Type
Type Max. M
A ‫ ≥ ܯ‬7.0
B 6.5 ≤ ‫ < ܯ‬7.0
C ‫ < ܯ‬6.5
Table 4-14 Seismic Source Type
Table 4-15 Seismic Coefficient, Ca
Table 4-16 Seismic Coefficient, Cv
 Table 4-17 Near-Source Factor, Na

Table 4-17 Near-Source Factor, Na

Table 4-21 Earthquake Force Resisting Structural Systems of Steel, R
4.3 Geotechnical Works
Flowchart for Foundation Selection
Comprehensive Building
and Project Requirements

Preliminary (Off) Site

Review

Subsurface
Investigations

Laboratory Tests

Data Analysis

Foundation Design

Shallow Foundation Deep Foundation

Ground Improvement
Design Design
+
Project Requirements
• Structure type
Commercial, industrial, residential

• Location and geographical features

Slope, near-shore

• Site development plans

Site accesibility, adjacent structures

• Basement provisions

• Natural hazards
Seismicity, flood susceptibility

• Government provisions
+
Site Investigation
Subsoil Condition
• Soil Boring Tests is
required for buildings two
(2) stories and above

TestPit is done to gather

in-situ soil parameters for
foundation design
+
Site Investigation
Subsoil Condition
• A minimum of two (2) bore holes for less than 300m2
building footprint and three (3) bore holes for 300m2 and
above building footprint.
+
Site Investigation
Subsoil Condition
• One bore hole for every 200m2 building footprint.
+
Site Investigation
Subsoil Condition
• Adequate soil investigation for lower buildings located on
soils with geological/geotechnical problems

• Expansive soils
• Unknown GWT
• Cavities
• Liquefaction

• Further information is provided in DGCS Volume 2A:

GeoHazard Assessment
+
Sub-
Sub-surface Investigation

• Should extend beyond basement

• When hard strata is encountered (SPT N

value>50), coring is executed 3-5m into hard
stratum
+
Subsoil Failures
Laboratory Tests
Table 4-25 Geotechnical Laboratory Tests and Corresponding Standards
Allowable Soil Bearing Capacity
௤ೠ೗೟
• ‫ݍ‬௔௟௟௢௪ ൌ
ி..

• Factory of safety between 2.0 and 3.0

• The Geotechnical Engineer should use any widely

accepted method (Methods of Terzaghi, Meyerhof,
etc.) to calculate for the ultimate soil bearing capacity,
qult
Allowable Soil Bearing Capacity

• Further information is provided in DGCS Volume 2C:

Geotechnical and Geological Investigation

• For standard school buildings, assumed allowable soil

bearing capacity, qallow = 96kPa
Foundation Design
• Shallow Foundations (Footing Design)

• Deep Foundations (Pile Design)

• Driven piles
• Bored piles
• Micropiles
Pile Design
Types:

1. Driven Piles
- Installation of precast piles on-site
- Causes significant noise and vibration
- May cause structural damage to adjacent structures
Pile Design
Types:
2. Bored Piles
- Cast in place
- Mobilizes end-bearing more than skin friction
- Longer time to install than driven piles

3. Micropiles
- Bored mini piles with diameter not exceeding 300 mm
Pile Design
• Pile Geotechnical Capacity

• Relies on end-bearing resistance, Qp and skin friction, Qs

Qu = Q p + Q s
Pile Design
• Pile Geotechnical Capacity

• End-bearing
capacity
Pile Design
• Pile Geotechnical Capacity

• Skin friction
Pile Design
• Micropile Structural Capacity

• Based on Micropile Design and Construction Reference

Manual, US Department of Transportation, Federal Highway
Administration
Pile Design
• Micropile Structural Capacity

Allowable compression load

Allowable tension load

Pile Design
• Micropile Structural Capacity

Combined stresses

-subjected to lateral loads or overturning moments

Pile Design
• Pile Adequacy

Qactual < Q allowable (Geotechnical and Structural)

4.4 Concrete Design
Governing Laws and Applicable
Codes and Standards

• National Structural Code of the Philippines (NSCP) 2010 Chapter 4

• American Concrete Institute (ACI) 318-08M

Structural Detailing
• Spacing Limits for Reinforcement
• NSCP Section 407.7

• Concrete Protection for Reinforcement

• NSCP Section 407.8

• Shrinkage and Temperature Reinforcement

• NSCP Section 407.13

• ACI Detailing Manual 2004

Structural Detailing

Moment Resisting Frames

• Lateral force resisting system from the flexural
characteristics of the members and joints.
• Commonly used in the Philippines.
• Types: Special (SMRF), Intermediate (IMRF), Ordinary
(OMRF)
 Moment Resisting Frames
• Transverse Reinforcements for Concrete
COLUMNS as per ACI Code

Zone 4 is under Special Moment Resisting Frame (SMRF).

 Moment Resisting Frames
• Transverse Reinforcements for Concrete BEAMS
as per ACI Code

First hoop is located no more than 50mm from the face of the support
Concrete Columns
• Steel ratio: 1-6% (as per NSCP for EQ resistance)

Avoid over-crowded reinforcements! (especially on the beam-column

connection)
Take note of the ties, splicing and anchored bars.
Beam to Column Connection
Confinement at beam-
column joint

77
Splicing on Beams
Splicing for continuous beams:

For cantilever beams:

Splicing on Columns

Splice
Location for
Columns

79
Analysis and Design
• Design Strength (NSCP Section 409.4)

• Deflection Control (NSCP Section 409.6)

• Flexure and Axial Load (NSCP Section 410)

• Shear and Torsion (NSCP Section 411)

Analysis and Design
• Development and Splice Legnth (NSCP Section 412)

• Two Way Slab (NSCP Section 413)

• Walls (NSCP Section 414)

• Footings (NSCP Section 415)

Analysis and Design
• Precast Concrete (NSCP Section 416)

• Prestressed Concrete (NSCP Section 418)

• Strength Evaluation of Existing Structures

(NSCP Section 420)

• Earthquake Resistant Structures (NSCP Section 421)

Design Principles
• Flexure
Design Principles

• Shear (NSCP Section 411.6.6)

Design Principles

• Slab (NSCP Section 413.6.1)

• One way Slab (NSCP Table 409-1)

• Two way Slab (NSCP Section 409.6.3)

Design Principles
• Columns (NSCP Section 410)

• Tied Column
ØPn = 0.85Ø[.85f'c(Ag-Ast) + Astfy]

• Spiral Column
ØPn = 0.80Ø[.85f'c(Ag-Ast) + Astfy]

• Slenderness Effect (NSCP 410.11)

Design Principles
• Footings

• Isolated footing
• Cantilever footing
• Wall footing
• Combined footing
• Strip footing
• Strap footing
• Mat or Raft foundation
• Footing on Piles
Design Principles

• Footing Design Considerations

1. Area of footing = design load / soil bearing capacity

Figure 4-3 Concentrically loaded footing

Design Principles

• Footing Design Considerations

Case 1: e ≤ L/6

Figure 4-4 Eccentrically loaded footing

Design Principles

• Footing Design Considerations

Case 2: e > L/6

Figure 4-5 Eccentrically loaded footing e>L/6

Design Principles

• Footing Design Considerations

2. Check for shear

Beam Shear
Design Principles

• Footing Design Considerations

2. Check for shear

Punching Shear

3. Design for Flexural stress to determine reinforcement

4.5 Structural Steel Design
Governing Laws and Applicable
Codes and Standards

• National Structural Code of the Philippines (NSCP) 2010 Chapter 5

• Uniform Building Code (UBC) 1997

• American Institute of Steel Construction (AISC) 360-10 (13th Edition

for LRFD)
Design for Tension Members

• Slenderness Limitation (NSCP 504.1)

• L/r should not exceed 300
• Bracing members
• Tension chords
• Internal ties
• (except for rods or hangers in tension)
Design for Tension Members
• Tensile Strength (NSCP 504.2)
• Design strength and allowable tensile strength based on lower value of two
limit states:
• Tensile yield strength, Fy
• Tensile rupture strength, Fu

• Members fail by:

• Excessive deformation if stress on gross section > Fy
• Fracture if stress on net section > Fu
Design for Tension Members
• Effective Net Area (NSCP 504.3)
• U values provided in NSCP Table 504.3.1

• Built-up Members (NSCP 504.4)

Design for Tension Members
• Pin-connected Members (NSCP 504.5)
• Design strength and allowable tensile strength based on:
• Tensile rupture
• Shear rupture
• Bearing
• Yielding
Design for Tension Members
• Pin-connected Members (NSCP 504.5)

• Tension on net effective area

• Shear on effective area

• Tension on gross section

• Bearing
Design for Tension Members
• Eyebars (NSCP 504.6)
Example: Eyebar Tension Members

1. Determine geometric and material properties, Fy and Fu

(AISC Table 2-4)
2. Check dimensional requirements such as t, w, d, dh
(NSCP 504.6.2)
3. Calculate required tensile strength, Pu
Design for Tension Members
• Eyebars (NSCP 504.6)

4. Calculate available tensile yielding strength at the eyebar

body (at w). Determine An and Pn
Pn = FyAg
5. Determine the tensile yield strength.
Using LRFD Φ = 0.90 ]
ΦPn > P

The structural engineer shall take note that the pin should
also be checked for shear yielding and bearing.
Examples provided in DGCS
• Flexural Member Design in Strong-Axis Bending, Continuously
Braced

• Flexural Member in Minor-Axis Bending

• Flexural Member with Noncompact Flanges

• Flexural Member with Slender Flanges

• Member Subject to Combined Axial Tension and Flexure

• All-Bolted Double Angle Connection

• All-Welded Double Angle Connection

Examples provided in DGCS
• Pin-Connected and Eyebar Tension Members

• Plate with Staggered Bolts

• Column Design Pinned Ends

• Column Design with Intermediate Bracing

• Column Member with a Slender Web

• Compression Member without Slender Elements

• Design of Compression Member with Slender Elements

4.6 Timber Design
Governing Laws and Applicable
Codes and Standards
• National Structural Code of the Philippines (NSCP)
2010 Chapter 6
• Stresses
• Densities
• Nailing Information
• Wood Screw Load Capacity
• Bolt Load
• Horizontal Member Design
• Column Design
• Flexure and axially loaded members
• Connectors and fasteners
Table 4-30 Working Stresses for Visually Stress-Graded Unseasoned
Structural Timber of Philippines Woods
4.7 Masonry Design
Governing Laws and Applicable
Codes and Standards
• National Structural Code of the Philippines (NSCP)
2010 Chapter 7

• General Design Requirements

• Seismic Analysis
• Similar to RC bearing wall system
4.8 Evaluation of Existing
Structures
Governing Laws and Applicable
Codes and Standards
• National Structural Code of the Philippines (NSCP)
2010 Chapter 1, Section 108

• Earthquake Engineering: From Engineering

Seismology to Performance Based Engineering
(Bozorgnia and Bertero, 2004)

• Fundamentals of Earthquake Engineering (Sarno,

2008)
• Reasons for evaluation
• Material Wear and Tear
• Functional Change
• Quality of Construction

• Test procedures
• Rebound hammer
• PUNDIT (Portable Ultrasonic Nondestructive Digital
Indicating Tester)
• Rebar locator
• Corrosion and carbonation test
• Load testing
• Structural Analysis

• Code based
• To bring the existing structure into a design level consistent with
the latest NSCP

• Performance based
• Uses as an objective the “degree of acceptable risk”
Publication of the Association of Structural Engineers of the Philippines
4.9 Peer Review
4.10 Design Flow Charts
Process for design of beams, compression members and tension members
4.11 Minimum Content of
Structural Plans
• General Notes
• Excavation Notes including soil bearing capacity
• Construction notes and design criteria
• Notes on rebars and structural steel
• Notes requiring shop drawings

• Masonry
• Wall footings, CHB wall reinforcements
• CHB wall opening details, lintel beam location and details,
stiffener details
• Rebar splice, development length, hook schedule
• Slab opening
• Pipe sleeve on beam, change in elevation of beams
• Foundation Plan
• Property line, footing and column designations
• Location of walls with wall footings, slab on fill thickness
and rebar spacing
• Scale consistent with floor plan scale

• Floor Framing Plan

• Beam and slab designation
• Columns terminated at a particular floor should be hatched

• Roof Framing Plan

• Roof beams, truss, rafters, bracings designations
• Purlin size and spacing call out
• Schedule and Typical Details
• Slabs, beams, footings showing all necessary
dimensions and rebar size and number
• Detailed column section and typical column elevation
showing splice
• Truss and rafter schematic diagrams with sizes and
connection detail
• Purlin, sagrod, bracing connection details
• Stair details
• Shear wall and footing details, ramp details
• Elevated water tank detail including concrete saddles
• Cistern, septic tank details