Designing Resilient Structures 2015-12-27_Draft 2.31

7/26/2019 Designing Resilient Structures 2015-12-27_Draft 2.31

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User HandbookDesigning Resilient Structures

Mainstreaming Disaster Risk Reduction and Climate

Change Adaptation in Local Design Practices

(Draft Version 2.3)


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[Insert ISBN or ISSN and cataloguing-in-publication (CiP) information if required]

Citation

Wang X, Wang C-H, Khoo Y B, Morga C and Stewart M G (2015). Designing Resilient Structures

for the Local Government in the Philippines. Australia.

Copyright

Commonwealth Scientific and Industrial Research Organisation 20XX. To the extent permitted

by law, all rights are reserved and no part of this publication covered by copyright may be

reproduced or copied in any form or by any means except with the written permission of CSIRO.

Important disclaimer

CSIRO advises that the information contained in this publication comprises general statements

based on scientific research. The reader is advised and needs to be aware that such information may

be incomplete or unable to be used in any specific situation. No reliance or actions must therefore

be made on that information without seeking prior expert professional, scientific and technical

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mailto:[email protected]:[email protected]:[email protected]:[email protected]


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Background

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The Build Back Better (BBB)

principle has been introduced by the

Government of the Philippines (GOP)

in the Reconstruction Assistance on

Yolanda (RAY) to prevent the

unending cycle of destruction and

reconstruction. For the RAY

Infrastructure Cluster, BBB means

upgrading of minimum performance

standards and specifications for the

design and structural components as

well as materials for public

infrastructure such as schools, public

markets, municipal/city and

community halls, bridges, etc (OPARR,

2014).

Recovery Assistance on Yolanda

(RAY)-DILG Fund has been used to

support efforts for the rehabilitationand/ or reconstructions of LGU-owned

buildings and facilities that are

essential to reinstate the regular local

government operations and services

in the 171 cities and municipalities in

14 provinces in 6 regions identified as

the most affected areas.

Under the RAY-DILG Fund, the

LGUs shall implement the subprojects

under rehabilitation/ repair of

partially-damaged LGU-owned

facilities/structures. Over the years,

the DILG has supported the LGUs in

the construction of

facilities/structures that are essential

in local government operations,

provision of social services to the

public and socio-economic activities in

their localities through its various

projects namely Payapa at

Masaganang Pamayanan (PAMANA),

Bottom-Up-Budgeting (BUB) and

Performance Challenge Fund (PCF).

The challenge in rehabilitation and

building of new public infrastructure is

to give due consideration to Build

Back Better by making them disaster

resilient. The Comprehensive LandUse Plan is a vital tool that has been

guiding LGUs in local development

and public infrastructure planning.

With the inclusion of the

Supplemental Guidelines on the

Mainstreaming Climate Change and

Disaster Risk in the latest

Comprehensive Land Use PlanGuidebook (2014), the LGUs are

guided in the task of analysing the

implication of hazards and climate

change in the various development

sectors/ subsectors including public

infrastructure. The information

generated from those analyses

becomes the basis not only of theoptimization of land allocation to

various uses but of sound information

for spatial planning and more

specifically in locating public facilities/

structures.


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TABLE OF CONTENTS 1

.

Contents

Contents i

Figures iv

Tables vii

Acronyms 12

1 Principles and Approaches for Resilient Structure Design 13

1.1.Risk Management Principles for Resilience ...................................................................... 13

1.2.Risk Management for Adaptation and Resilience Development ..................................... 17

1.2.1 Risk Measurement........................................................................................... 17

1.2.2 Development of Resilience through CCA and DRR Integration ...................... 19

1.2.3 Option Appraisals for Cost-Effective Resilience Development ....................... 20

2 Risk-Based Resilient Structure Design 22

2.1.Structural Classifications and Performance Requirement ............................................... 22

2.2.Risk Assessment ................................................................................................................ 23

2.2.1 Hazard Assessment ......................................................................................... 25

2.2.2 Exposure Assessment ...................................................................................... 27

2.2.3 Vulnerability Assessment ................................................................................ 28

2.2.4 Risk Evaluation ................................................................................................ 30

2.3.Capacity gap assessment - Examples ................................................................................ 31

2.3.1 Structures Subject to Wind Hazard and Its Increase Due to Climate Change 32

2.3.2 Structures Subject to Earthquake ................................................................... 35

2.3.3 Structures Subject to Flood Hazards and Sea Level Rise................................. 38

2.4.Development of Resilient Design Options - Examples ..................................................... 40

2.4.1 Design Options for Resilience to Wind Hazards .............................................. 41

2.4.2 Design Options for Resilience to Wind Hazards .............................................. 41

2.5.Option Appraisal ............................................................................................................... 43

3 Introduction of Structural Design in National Structural Code of the Philippines 45


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TABLE OF CONTENTS 2

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3.1.Classification of structures................................................................................................ 45

3.2.Wind loads ........................................................................................................................ 47

3.2.1 Basic Wind Speed ............................................................................................ 47

3.3.Earthquake Loads ............................................................................................................. 48

3.3.1 Seismic Zone and Source Type ........................................................................ 49

3.4.Flood Loads ....................................................................................................................... 51

3.5.Structural Concrete ........................................................................................................... 51

3.5.1 Flexure and axial loads .................................................................................... 51

3.5.2 Shear and Torsion ............................................................................................ 53

3.5.3 Development and Splices of Reinforcement ................................................... 54

3.5.4 Walls ................................................................................................................ 55

3.5.5 Earthquake-Resistant Structures..................................................................... 56

3.6.Structural Steel ................................................................................................................. 58

3.7.Wood 59

3.8.Masonry ............................................................................................................................ 60

3.8.1 Special Provisions in Areas Subjected to Seismic Risk .................................... 61

4 Guidance for Resilience Design 63

4.1.Design Guidance Structures .............................................................................................. 65

4.1.1 Objectives ........................................................................................................ 65

4.1.2 Functional Statements .................................................................................... 65

4.1.3 Performance Requirements ............................................................................ 66

4.1.4 Solutions .......................................................................................................... 66

4.1.5 Assessment Methods ...................................................................................... 66

4.1.6 Deemed-to-Satisfy Solution ............................................................................ 66

4.1.7 Alternative Solutions ....................................................................................... 66

4.2.Resilient LGU Hub Facilities .............................................................................................. 67

4.2.1 Objectives ........................................................................................................ 67

4.2.2 Function Statements ....................................................................................... 67

4.2.3 Performance-Based Design Requirement ....................................................... 67

4.3.Resilience-Performance-Based Verification Methods ...................................................... 68

4.3.1 Design Targets for the Wind Hazard ............................................................... 69


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TABLE OF CONTENTS 4

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Figures

Figure 1-1 Three steps of risk management for climate adaptation and disaster risk

mitigation to enhance resilience .................................................................................................. 13

Figure 1-2 Approaches in risk minimisation and the focus of the current policies ................ 14

Figure 1-3 Risk Sharing ............................................................................................................ 15

Figure 1-4 Impact management for both short and long terms ............................................. 16

Figure 1-5 Approaches in climate adaptation and natural disaster risk reduction at multiple

levels ............................................................................................................................................. 17

Figure 1-6 Risk assessment for climate change and natural disasters .................................... 18

Figure 1-7 Impacts of other drivers (e.g. population and land use) ....................................... 19

Figure 1-8 Identification of climate adaptation and disaster risk reduction options for

resilience development ................................................................................................................. 20

Figure 1-9 Identification of climate adaptation and disaster risk reduction options ............. 21

Figure 2-1 A risk-based framework for the guidelines to design resilient structures ............. 23

Figure 2-2 Illustrative description of quantitative representation of hazard through statistical

modelling....................................................................................................................................... 26

Figure 2-3 Illustrative maps of hazard magnitude at a high occurrence frequency (left) andlow occurrence frequency (right). Red and blue colour indicates high and low intensity,

respectively. .................................................................................................................................. 27

Figure 2-4 An illustrative exposure map of roads to flooding as highlighted by the red

colour ............................................................................................................................................ 27

Figure 2-5 Vulnerability curve that gives the relation between damage or loss ratio and

hazard severity .............................................................................................................................. 30

Figure 2-6 Vulnerability curves of four typical structures to wind ......................................... 33

Figure 2-7 Flood hazard at Great Manila Metropolitan Area ................................................. 38

Figure 2-8 Vulnerability curves of four typical structures to flood ......................................... 39

Figure 2-9 Illustration of a triple-grip connection for wood roof structures .......................... 42

Figure 3-1 Wind zone map of the Philippines (source: NSCP 2010). ..................................... 48

Figure 3-2 Seismic zones ......................................................................................................... 50

Figure 3-3 Assumed strains for reinforced concrete and reinforcement (a) ordinary flexural

members, (b) deep beams. ........................................................................................................... 52

Figure 3-4 Maximum spacing of lateral supports of a beam .................................................. 52

Figure 3-5 Maximum spacing for the shear reinforcement .................................................... 53


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Apx Figure B-2 Peak ground motion hazard curves for Zones 4 and 2 ................................. 154

Apx Figure B-3 Flood hazard at Great Manila Metropolitan Area ........................................ 155

Apx Figure B-4 Susceptibility of earthquake induced landslides .......................................... 157

Apx Figure C-1 Vulnerability curves of four typical structures to wind ................................ 160

Apx Figure C-2 Vulnerability curves of four typical structures to earthquake ...................... 162

Apx Figure C-3 Vulnerability curves of four typical structures to flood ................................ 163


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Table 4-5 Performance requirement of the design target of wind pressure on roofs to meet

the requirement 3 for three wind zones (kPa) - Class 3 Buildings (Class 3 - I: Essential Facilities,

III: Special Occupancy Structures) ................................................................................................. 71

Table 4-6 Wind resilience loading factor for the wind design load in three wind zones -

Class 2 Buildings ............................................................................................................................ 71

Table 4-7 Wind resilience loading factor for the wind design load in three wind zonesClass

3 Buildings ..................................................................................................................................... 72

Table 4-8 The average reoccurrence interval of flood height considered for the design

target ............................................................................................................................................. 73

Table 4-9 Design flood height target without consideration of sea level rise (unit: m) ......... 73

Table 4-10 Design flood height target considering sea level rise of 10cm (unit: m) .............. 74



Table 4-13 IPCC-AR5 projected sea level rise (20152100) relative to the sea level of 1986

2005. Low and High correspond to the 5th- and 95th-percentile values. ...................................... 75

Table 4-14 Peak ground acceleration targets (g) to meet the requirement 3 in two

earthquake zonesClass 2 Buildings ........................................................................................... 76

Table 4-15 Peak ground acceleration targets (g) to meet the requirement 3 in two


Table 4-16 Earthquake resilience loading factor to meet the requirement 3 in two


Table 4-17 Earthquake resilience loading factor to meet the requirement 3 in two


Table 4-18 Cost ratio of subassembly (or structural components) of a facility ...................... 78

Table 5-1 Capacity multipliers for triple grips required for CHB-L-W to meet the uplift

capacity avoiding a total loss with a damage ratio large than 50% .............................................. 86


capacity and ensure the damage ratio no more than 40%........................................................... 87






capacity and ensure the damage ratio no more than 10%........................................................... 90Table 5-6 Capacity multipliers for triple grips required for C1L-W to meet the uplift capacity

avoiding a total loss with damage larger than 50% ...................................................................... 91


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Table 5-7 Capacity multipliers for triple grips required for C1L-W to meet the uplift capacity

and ensure the damage ratio no more than 40% ......................................................................... 92







Table 5-11 Capacity multipliers for triple grips required for W1-L to meet the uplift capacity

avoiding a total loss with a damage ratio larger than 50%........................................................... 96








and ensure the damage ratio no more than 10% ....................................................................... 100

Table 5-16 Capacity multipliers for triple grips required for S1-L to meet the uplift capacityavoiding a total loss with a damage ratio larger than 50%......................................................... 101

Table 5-17 Capacity multipliers for triple grips required for S1-L to meet the uplift capacity






Table 5-20 Capacity multipliers for triple grips required for S1-L to meet the uplift capacityand ensure the damage ratio no more than 10% ....................................................................... 105

Table 5-21 Capacity multipliers for nails required for CHB-L-W to meet the uplift capacity

avoiding a total loss with damage large than 50% ..................................................................... 108








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Table 5-26 Capacity multipliers for nails required for C1L-W to meet the uplift capacity

avoiding a total loss with a damage ratio larger than 50%......................................................... 113

Table 5-27 Capacity multipliers for nails required for C1L-W to meet the uplift capacity and

ensure the damage ratio no more than 40% .............................................................................. 114







Table 5-31 Capacity multipliers for nails required for W1-L to meet the uplift capacity


Table 5-32 Capacity multipliers for nails required for W1-L to meet the uplift capacity and




Table 5-34 Capacity multipliers for nails required for W1-L to meet the uplift capacity andensure the damage ratio no more than 20% .............................................................................. 121



Table 5-36 Capacity multipliers for nails required for S1-L to meet the uplift capacity


Table 5-37 Capacity multipliers for nails required for S1-L to meet the uplift capacity and


Table 5-38 Capacity multipliers for nails required for S1-L to meet the uplift capacity andensure the damage ratio no more than 30% .............................................................................. 125





Table 5-41 Capacity multipliers for nails required per square metre for roof-to-purlin

connections to meet the uplift capacity ..................................................................................... 130

Table 5-42 Capacity multipliers for metal screws required per square metre for roof-to-

purlin connections to meet the uplift capacity ........................................................................... 132


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Table 5-43 Capacity multipliers for wood screws required per square metre for roof-to-

purlin connections to meet the uplift capacity ........................................................................... 133

Table 5-44 Class 3 performance requirement for Column C-1 to meet the relative life-saving

costs requirements in earthquake zones 2 and 4 (Class 3 - I: Essential Facilities, III: Special

Occupancy Structures) ................................................................................................................ 139

Table 5-45 Class 3 performance requirement for Column C-2 to meet the relative life-saving

costs requirements in earthquake zones 2 and 4 ....................................................................... 140

Apx Table A-1 Description of Earthquake Intensity Scales (PEIS) ......................................... 143

Apx Table B-1 Basic wind speed given ARI in three wind zones ........................................... 153



Apx Table C-1 Number of building structure types in GMMA .............................................. 158

Apx Table C-2 Typical building types in the Philippines ........................................................ 159

Apx Table C-3 Structural vulnerability to extreme winds (kph) ............................................ 160

Apx Table C-4 Structural vulnerability to earthquake (cm/s-2) ............................................. 162

Apx Table C-5 Structural vulnerability to flood ..................................................................... 163


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PRINCIPLES AND APPROACHES FOR RESILIENT

STRUCTURE DESIGN 12

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Acronyms

ARI Average Recurrence Interval

BBB Build Back Better

CCA Climate Change Adaptation

DRR Disaster Risk Reduction

NDRRM National Disaster Risk Reduction and Management

NSCP National Structural Code of the Philippines

PCF Performance Challenge Fund

PGA Peak Ground Acceleration

CLUP Comprehensive Land Use Plan


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STRUCTURE DESIGN 13

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1

Principles and Approaches for ResilientStructure Design

1.1

Risk Management Principles for Resilience

Climate adaptation and disaster risk mitigation for resilience are implemented fundamentally

on three risk-reduction-based principles,

Reduce the vulnerability of all relevant institutional levels to hazards at relevant spatial and

temporal scales, and

Reduce the likelihood of the occurrence of and exposure to hazards, but be aware that

reducing the occurrence likelihood of natural hazards is in most cases unachievable.

Reduce any residual adverse consequences as a result of the impact of hazards

More specifically, it could be implemented through three steps as shown inFigure 1-1:

Figure 1-1 Three steps of risk management for climate adaptation and disaster risk mitigation to enhance

resilience

(1)Risk minimisation: reduce/avoid the manageable adverse consequence as a result of

climatic hazard impacts.

As shown inFigure 1-2,four strategies to minimise risks to climatic change and disasters can

be summarised as,

Risk Sharing

Risk Minimisation

Impact

Management


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STRUCTURE DESIGN 14

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Mitigate climate change by reducing carbon emission to minimise the likelihood of

increasing climate extremes;

Mitigate the impact consequences of climate hazards through hazard exposure

management of cities. Although the reduction in hazard is not always possible, in

some cases, the hazard could also be reduced such as heatwaves by green

infrastructure development ;

Reduce the likelihood/extent of exposure to climate hazards by land use planning,

protection and retreat, and reduce the consequence by improving the fragility or

reducing the vulnerability of urban built asset and population to hazards;

Reduce the likelihood of indirect loss as a result of direct damage impact by building

urban community capacity, and reduce the consequence by immunizing coastal

infrastructure systems from cascading effects, and developing emergencymanagement and better relief and recovery plan

Figure 1-2 Approaches in risk minimisation and the focus of the current policies

Figure 1-2 also illustrates the focus of current policies and regulations, including The National

Climate Change Action Plan, Comprehensive Land Use Planning (CLUP), The National Disaster Risk

Reduction and Management (NDRRM) Framework, National Disaster Risk Reduction and

Management Plan (NDRRMP), The National Security Policy, and Building Code as well as

Performance Challenge Fund (PCF), which are able to address different parts in risk mitigation.

Mitigate Climate Change

Reduce Likelihood:

Carbon Emission MitigationReduce Consequence

Mitigate Climate Hazards

Reduce Likelihood Reduce Consequence

Reduce Exposure to Climate Hazards

Reduce Likelihood:

eg. Protection, retreat,

land use planning

Reduce Consequence

Reduce Direct and Indirect Loss due to Damage

Reduce fragility:

eg. Asset design

Reduce Likelihood:

eg. Community capacity

building

Reduce Consequence:

eg. emergency management,

recovery relief

CLUP

Building Code

PCF

The National

Climate ChangeAction Plan

The National

Security PolicyTheNationalDRRMF

ramework

N

DRRMP


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STRUCTURE DESIGN 15

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(2) Risk sharing: share the inevitable (residual) impacts as a result of climatic hazard

attacks, to reduce the corresponding adverse consequences incurring on each of

individuals.

Risk sharing can be implemented by distributing the consequence of impacts among

multiple parties, such as private and public, individuals and institutions, communities and

government, as shown as inFigure 1-3,through instruments such as insurance, regulation

and government incentives, to redistribute climate risks. It is particularly important to

balance the needs of socially disadvantaged groups who disproportionally incur high risks

to the climate impacts

Figure 1-3 Risk Sharing

(3) Impact management: manage the inevitable adverse consequence as a result of hazard

impacts for recovery.

The impact management is implemented to minimise the hazard-induced adverse

consequence, particularly to reduce those post-disaster impacts caused by the direct hazard

impacts. It normally covers the short-term emergency responses and humanitarian disaster

recovery, but it is also associated with long-term reconstruction and recovery of, not only

physical assets and services, but also local/regional economy, social systems, environment

and community livelihood etc, as shown inFigure 1-4.It should be pointed out, in the National

Disaster Risk and Management Plan, the immediate short term, short term, medium term,

long term are defined as 1 year, 1-3 years, 3-6 years and greater than 6 years.

Risk


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STRUCTURE DESIGN 16

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Figure 1-4 Impact management for both short and long terms

It should be particularly emphasised, while there are many approaches aiming to reduce or

mitigate disaster risks as already indicated inFigure 1-2,Building Back Betterare indeed can be

advanced in several means, as shown inFigure 1-5,in climate adaptation and disaster risk

reduction. It could be implemented through a range of options, from information, enforcing

practices and governance, such as BBB Operation Manual, NSCP and UCLP, respectively. The

current resilient structure design handbook aims to enforce the resilient design practices in

addition to the requirement by NSCP.

Emergency

Responses

Humanitarian

Disaster

Recovery

Infrastructure

and Service

Reconstruction

Recovery of

Economy,

Social Systems,

Environment,

Livelihood

Short Term

Medium Term

Long Term


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STRUCTURE DESIGN 17

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Figure 1-5 Approaches in climate adaptation and natural disaster risk reduction at multiple levels

1.2

Risk Management for Adaptation and Resilience Development

A risk-based approach can provide an effective tool to develop adaptation and resilience options

for infrastructure exposed to various hazards and subsequent disasters. It generally includes risk

assessment, climate adaptation and disaster reduction option development, and option appraisals

and optimisation.

1.2.1

Risk Measurement

Risk can be considered as the combined effect of hazards (H), exposures (E), and vulnerability

(V) of the assets or infrastructure of interest, as shown inFigure 1-6,or

Measuring risk in Equation (2-1) can be carried out in either qualitative or quantitative

approaches. It can be measured in terms of a distribution of potential loss against hazards

considering various uncertainties. Quantitatively, it is often expressed as an average loss as a result

of impacts of the hazards. The loss is normally related to economic loss, but it could also be

described in association with more broad socioeconomic and environmental loss.

Hazard is generally considered to be an adverse external stimulus that exerts stresses or

pressures, specifically to a system of interests, leading to disasters. For cities, it can be in the form

General practicalguidance, which are thesolutions easily

understood and adopted,often descriptive andqualitative, and carriedout in a less rigorousmanner

Standards, whichstandardise thepractical solutions and

processes byenhanced knowledgeand scientific

evidences , and applydefined criteria toenforce itsimplementation.

Policies, whichprovide overallprinciples and

governance to guideall levels of decision-making, and areoften considered asprotocols that allother relevantdecisions have to

follow.

NDRRMP

BBB Manual

NSCP, NBC

Zoning Ordinance

Information

EnforcedPractices

Governance

C

CA+DRR

Integration


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STRUCTURE DESIGN 18

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of extreme climate events such as heatwaves, cyclones, storms, drought, hails and lightening, and

can also be subsequent extreme events such as flooding, inundation, fire and pollution, which are

caused by weather events together with other factors.

Figure 1-6 Risk assessment for climate change and natural disasters

Vulnerability is deemed as susceptibility of a system of interest and measured as a likely loss, to

a given degree of a hazard. Vulnerability can be described by the loss of functionality, serviceability

or/and integrity of the system, and often represented by a monetary measure, although other

measures may be used. For example, mortality or morbidity to heatwave, house damage to wind

speed or flood depth, water supply to annual precipitation. Vulnerability assessment is the key step

to understand how city would function given different scenarios of its exposure to hazards.

The degree of vulnerability is closely related to the adaptive capacity of a system of interest.

Adaptive capacity is considered as an inherent system property that enables adjustments of its

capacity or capability threshold to accommodate expected (future) adverse hazard impacts without

loss of its functionality and integrity, which may lead to disasters. It can generally be described by

social, human, financial, environmental and physical capitals though there are many other

representations. Enhancement of the adaptive capacity could also be beneficial to immediate

disaster mitigation.

Climate Change

and Variability

Hazard (H)

Exposure (E)

Risk (H*E*V)

Socioeconomic

Environmental

Economic

Loss

Vulnerability (V)

Socioeconomic,

Environmental,

Institutional, Physical


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STRUCTURE DESIGN 19

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1.2.2 Development of Resilience through CCA and DRR Integration

As discussed early, CCA and DRR options are developed to reduce hazards (if possible), exposure

and vulnerability, an important approach to resilience. This can be done by developing new policies,

planning and designs, which are normally dealt with by different levels of jurisdictions ranging from

national, provincial, to various levels of local governments. Integration of CCA and DRR options at

all jurisdictional levels, or called vertical integration should be considered in developing those

options. It has to be mentioned that the CCA and DRR integration for those options that are dealt

with at the same jurisdictional level, or horizontal integration, should also be considered too.

As shown inFigure 1-7,this step will require the understanding of compounding future outlook

factors that affects exposure and vulnerability. The development of CCA and DRR options could be

developed by affecting the future vision and outlooks, such as population growth, demographic and

land use change and resource development, to reduce the exposure and vulnerability.

Figure 1-7 Impacts of other drivers (e.g. population and land use)

Having said that, this handbook aims to address the engineering design approach to develop

CCA and DRR options, in particular, for building structures.

More specifically, the CCA and DRR options for resilience are identified as shown inFigure 1-8.

It is essentially to identify design options for structures that could reduce the residual risk, which is

the remaining risk after implementing climate adaptation or/and disaster risk reduction, below an

acceptable level or a threshold. In many cases, the threshold is defined in or can be estimated fromdesign standards or development guidelines. If the residual risk is not expected to increase as a

result of climate change, the option is considered for climate adaptation. Otherwise, it will be

Climate Change

and Variability

Hazard (H)

Exposure (E)

Vulnerability (V)

Socioeconomic,

Environmental,


Risk (H*E*V)Horizonta

l/Vertical

Integrationo

fCCA

an

dDRROptions

Socioeconomic

Environmental

Economic

Loss

Design

Planning

Policies H

V

Future Outlooks

(population growth,

demography/land use change

resource availability)

Current/Future Visions


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STRUCTURE DESIGN 20

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further assessed to investigate if the option could maintain the residual risks below the acceptable

level in the future considering the effect of climate change. The subsequent outputs will then be

considered for the integration of climate adaptation and disaster risk reduction.

Figure 1-8 Identification of climate adaptation and disaster risk reduction options for resilience development

1.2.3

Option Appraisals for Cost-Effective Resilience Development

The appraisals of options and their comparisons leads to the completion of comprehensive risk

management to develop climate adaptation and disaster risk reduction development, as shown in

Figure 1-9.

The appraisals should be based on broad economic, social and environmental loss and benefit

assessment, with a requirement of the better options that should lead to the high likelihood of thetotal benefit larger than the total cost.

While there have been many discussions on how to properly quantify the benefit and loss, they

could be generally described as,

Benefit = Avoided Loss + Additional Benefit

Loss = Option Investment + Opportunity Loss + Additional Loss

The avoided loss is considered as the reduction in risks as a result of the investment in CCA

or/and DRR options. Additional benefits are more related to indirect benefit as a result of

implementing the options. Opportunity loss is associated with the loss of benefit that could havebeen achieved by investment in others rather than the CCA and DRR options. Additional loss could

Options

Current

Hazards

Do they meet

the Acceptable

Risk Threshold?

Modify

options

Is their service

life long enough

to consider

climate changeimpacts?

Future

Hazards

Do they meet

the Acceptable

Risk Threshold?

Options

for DRR

Modify

options

Options

for

DRR/CCA

Climate Change

Scenarios

No

Yes Yes

NoNo

Yes


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STRUCTURE DESIGN 21

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be considered as the adverse impact due to the implementation of the options, such as the

construction of wave barrier could lead to the impact on nearby environment.

Figure 1-9 Identification of climate adaptation and disaster risk reduction options

Often, the benefit and loss are described in monetary terms. When both benefit and loss are

measurable, an approach similar to cost-benefit assessment is effective for the CCA and DRR

option appraisals. In this case, the option is preferable if one or more of the following criteria are

met,

Higher positive net benefit , which is equal to the benefit subtracted by the loss;

Higher benefit-loss ratio that is larger than one;

Higher likelihood that the benefit is larger than the loss.

However, when it is difficult to quantify the benefit in monetary terms, an approach similar to

cost-effectiveness assessment can be more effective for the option appraisals. In this case the

option is more preferable if the criteria is to be met, i.e., a lower option investment to achieve the

same CCA and/or DRR objectives, or the same level of investment, but more likely to achieve the

same CCA and/or DRR objectives.

Climate Change

and Variability

Hazard (H)

Exposure (E)

Vulnerability (V)

Socioeconomic,

Environmental,


Risk (H*E*V)Horizonta

l/Vertica

l

Integrationo

fCCA

an

dDRROptio

ns

Socioeconomic

Environmental

Economic

Loss

Design

Planning

PoliciesH

V

Future Outlooks

(population growth,

demography/land use change

resource availability)

Current/Future Visions

(Avoided Loss +Additional

Benefit) (Option Investment +

Opportunity Loss in Adaptation

+ Additional Loss)

Decision-Making


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RISK-BASED RESILIENT STRUCTURE DESIGN 23

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Figure 2-1 A risk-based framework for the guidelines to design resilient structures

Class 4: the expected consequence is represented by disastrous events causing severe

damages and losses leading to interruption and delay at a nationalscale;

Class 5: the expected consequence is represented by catastrophic events causingsevere damages and losses beyond a national scale.

Buildings and structures with different levels of criticality or importance has different requirement

of safety or reliability performance. For highly critical and important structures, there is a need to

have a more strict performance requirement, especially on its safety.

2.2

Risk Assessment

As indicated previously, risk assessment normally has steps including hazard assessment,

exposure assessment, and vulnerability assessment followed by the final risk evaluation. Moredetails about the steps in the assessment are shown inTable 2-1.

Structure

Types

Hazard

Severity &

Frequency

Structure

Criticality

Acceptable

RiskThreshold

Failure

ConsequenceExposure

Capacity

Requirement

Maintenanc

e Options

DesignOptions

Vulnerability

Risk

OptionsAppraisal


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Table 2-1 Steps of risk assessment

Assessment Types Assessment Steps

I: Hazard Assessment

Hazard identification: identify hazards that could cause damages and

losses at different scales, such as individual, local (regional) and

national scales;

Hazard information acquisition: acquire historical hazard information,

and if future outlook is considered, projection information from

modelling given different scenarios, such as climate and landscape

changes;

Hazard modelling

o Qualitative approach: Rank hazards into a class, such as

severe, strong, medium, weak, very weak, and describe thelikelihood of the hazard

o Quantitative approach: model the hazard in terms of severity

at different average recurrence interval (ARI) or return

periods, which can be depend on location and time. For

example, wind speed of 1 in 100 years, which could change

as a result of climate change. The hazard could be converted

into more engineering terms such as external loading on

structures.

Hazard mapping: if required, map the hazards of differentaverage recurrence or return periods across a scale as required,

such as local, regional and national scales, at different time

horizons (if future environmental changes are considered);

II: ExposureAssessment

Identification of points of interest (POIs): identify points of interests,

such as physical assets, communities and natural resources, which

distribution generally has the nature of spatiality and temporality, for

example, urban sprawl and population growth;

Hazard Exposure Analysis: analyse the exposure of POIs to the hazards

in association with the severity of hazards, for example, the housesmay not be exposed to the low-depth of flooding, but exposed to

severe flooding.

III: VulnerabilityAssessment

Qualitative Approach

oRank the vulnerability to different level of hazard (if exposed)

in terms of consequences, such as catastrophe, significant,

moderate, small, and very small.

Simplified Vulnerability Curve Approach (Quantitative Approach)

o Develop damage/loss data inventory in association with the

severity of hazards;


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Assessment Types Assessment Steps

o Develop collective performance of POIs subject to the

impacts of identified hazards at different severity, or fragilitycurves that give a distribution of four physical damage states

(slight, moderate, extensive and complete) in relation to

hazard severity;

o Develop vulnerability curves based on fragility curves

Detailed Structural Analysis (Quantitative Approach)

Model structures of building envelop, including roof, wall and

foundation etc.;

Model resistance or capacity of building structures to

loading; Model the loading including permanent loading and dynamic

loading including occupants and hazards (wind, earthquake

etc.);

Implement structural reliability analysis

IV: Risk Evaluation

Qualitative approach

o Rank the risk based on hazard severity and likelihood

together with its consequence

Quantitative Approach

o

Estimate the risk based on the hazard, exposure and

vulnerability quantified in other assessment.

2.2.1

Hazard Assessment

While qualitative hazard assessment is basically based on the perceptions, the quantitative

assessment is using the annual maxima of hazard variables from the collected historical data or

observations. By applying statistical extreme value theory, the annual maxima can be converted

into the relationship of hazard severity and Average Reoccurrence Interval (ARI) or return period,as shown inFigure 2-2.


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Figure 2-2 Illustrative description of quantitative representation of hazard through statistical modelling

It could also be represented similar toTable 2-2,which lists the hazard magnitude and its

occurrence frequency. If the magnitude is spatially dependent, hazard maps can be developed foreach occurrence frequency, as shown inFigure 2-3.The high frequency hazard event shows less

magnitude than the low frequency event. A rare hazard event has a large magnitude.

Table 2-2 Descriptive examples of hazard magnitude and frequency

ARI (years) DescriptionsHazard Magnitude

(eg. severe, strong, medium, weak, very weak)

1Average occurrence of

once every year


once every ten years


once every a hundred of

years


once every five hundreds

of years


once every a thousand of

years

ARI or Return Period (years)

HazardSeverity

1 10 100 1000

Model

Observation

Confidence interval


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Figure 2-3 Illustrative maps of hazard magnitude at a high occurrence frequency (left) and low occurrence frequency(right). Red and blue colour indicates high and low intensity, respectively.

2.2.2

Exposure Assessment

Exposure assessment involves the POIs that could be at the risk of hazard impacts, such as

physical assets and communities. It is often related to the severity or magnitude of hazards. For

example, roads may not be exposed to low tides, but exposed to high tides. The exposure level can

often be described by spatial mapping as shown inFigure 2-4.

Figure 2-4 An illustrative exposure map of roads to flooding as highlighted by the red colour


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Table 2-4 Damage states (developed based on Hazus)

Damage States Descriptions Illustration Mechanism

Slight

Small cracks or damages

appeared on building

envelop, such the corner of

window and door

Yielding point of structural

capacity

Moderate

Large cracks or

damages appeared on

building envelop, for

example, across wall

Ultimate point of

structural capacity

Extensive

Multiple cracks or

damages and

permanent

deformation ormovement, involving

key structure

components.

Exceed the ultimate

capacity point

Complete

Significant permanent

structural damages

with large

deformation and

movement in

imminent collapse

Significantly exceed the

ultimate capacity point

Hazard Loading

Structura

lResponse

Hazard Loading

StructuralResponse

Hazard Loading

StructuralR

esponse

Hazard Loading

StructuralResponse


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Figure 2-5 Vulnerability curve that gives the relation between damage or loss ratio and hazard severity

2.2.4

Risk Evaluation

Measuring the risk can be done either qualitatively or quantitatively. For the qualitative

approach, the risk to a specific severity of hazard can be measured on the basis ofTable 2-5.Formultiple hazards or hazard at various severities, the overall risk is considered as the highest among

all risks.

Table 2-5Qualitative measurement of risks based on hazard likelihood and corresponding consequences

HazardLikelihood

Consequences (Damage or Loss)

Minor Small ModerateSignificant

(extensive)

Catastrophic

(complete)Very often Moderate High High

Extreme

High

Extreme

High

Often Moderate Moderate High HighExtreme

High

Occasional Low Medium Moderate High High

Rare Low Low Moderate Moderate High

Very rareLow Low Low Moderate Moderate

Hazard Severity

Vulnerability

(RatioofDamageorLoss)

0%

100%

H1 H2 H3 H4


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For example,

Hazard 1, its likelihood is very often and the consequence is small, hence the risk is high.

Hazard 2, its likelihood rare and its consequence is moderate, hence the corresponding riskis moderate.

Therefore, the overall risk is the highest among them, which is high.

The risk assessment using quantitative approaches is more complicated based on probabilistic

modelling and simulation, the quantitative measurement of risks is given by a probabilistic

distribution

2.3

Capacity gap assessment - Examples

Capacity gap assessment essentially compares the overall risks with the threshold

(performance requirements) defined in accordance with the criticality or importance of assets, to

identify what structural capacity should be enhanced to meet the performance requirement.

Several examples are here to demonstrate the capacity gap assessment.

Considering that four structure types, including concrete hollow block, concrete moment

frame, wood and steel structure have a significant proportion of building stocks in the Philippines,

they would be mainly considered in the handbook.

W1-L: Wood Frame with Area 500 sq. m (1-2 storeys) - These are typically single- or

multiple-family dwellings. The essential structural feature of these buildings is repetitive

framing by wood rafters or joists on wood stud walls. Loads are light and spans are small.Most of these buildings, especially the single-family residences, are not engineered but

constructed in accordance with conventional construction provisions of building codes.

CHB-L-W: Concrete Hollow Blocks (1-2 storeys) - These are low-rise structures with walls

made of concrete hollow blocks interlocked at the corners, and have no reinforced

concrete frame. The floors consist of either plywood or board sheathing, supported by

wood sub-framing. The roofs are corrugated galvanized iron sheets attached to wooden or

light metal roof trusses.

C1-L-W: Reinforced Concrete Moment Frame (1-2 storeys) - These buildings are similar to

steel moment frame buildings except that the frames are reinforced concrete.

S1-L: Steel Moment Frame (1-2 storeys) - These buildings have a frame of steel columns

and beams. In some cases, the beam-column connections have very small moment

resisting capacity, but some of the beams and columns have in other cases.

For buildings and structures with different levels of criticality or importance, there should be

different requirement of safety or reliability performance. For highly critical and important

structures, there is a need to have a more strict performance requirement, especially on its safety.

The international standard of General Principles on Reliability for Structures (ISO 2394:2015)

defines the risk threshold as shown inTable 2-6.The thresholds not only depends on the criticallyor importance of the structures, but also depends on the costs that would be incurred to address

the cost-effectiveness of risk mitigation measures. To balance between the cost and the


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achievement of a level of reliability, when a high cost is involved to ensure the structural safety,

the reliability requirement could be reasonably reduced (i.e. a risk threshold could be increased).

Based on the requirement of a design to meet a risk threshold from high to low, the corresponding

resilience is considered to be low to high.

Table 2-6 Thresholds of Annual Risks

Relative Life-SavingCosts1

ResilienceRequirement

Class 2(individual

impact)

Class 3(regionalimpact)

Class 4(nationalimpact)

Large Low 0.1% 0.05% 0.01%

Medium Medium 0.01% 0.001% 0.0005%

Small High 0.001% 0.0005% 0.0001%

2.3.1 Structures Subject to Wind Hazard and Its Increase Due to Climate Change

The wind gust hazards in the three wind zones specified in NSCP (2010) are modelled as

generalized extreme-value distribution, with the model parameters being chosen such that the 50-

year gust speeds given by the models match the ones specified in NSCP (2010).

The vulnerability curve of four types of structures subject to wind hazard is based on the study

by Pacheco et al2, as shown inFigure 2-6 and Table 2-7. It highlights the vulnerability of current

timber structures to winds, and shows that the timber structure could be damaged quickly around

50m/s or 180kph.In contrast to the timber structures, other three types of structures display much

less vulnerability, especially the concrete hollow block.

Based on the wind hazard and vulnerability, the risk of four types of structures can be

estimated and given in Table 2-8. As illustrated, there is a significant gap for wood structure in

comparison with all level of thresholds defined in Table 2-6. The highest annual total loss risk of

near 17% for timber framed housing (W1-L) in Zone 1 implies that buildings would experience

total loss (destruction) almost every 5 years on average. This is an unacceptably high risk. As

expected, for all zones the annual risks for concrete hollow block, RC and steel construction are

much lower than timber framed housing, but steel structures in zone 1 has a gap to meet

requirement for evacuation centres classified as Class 3 in Table 2-6.

1The classification as defined by ISO 2394 should be further clarified. Discussion should be undertaken on what thresholds could be accepted

considering cost-effectiveness in the region.

2Pacheco BM, Hernandez Jr. JY, Castro PPM et al (2013). Development of vulnerability curves of key building types in the Greater Metro

Manila Area, Philippines


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Figure 2-6 Vulnerability curves of four typical structures to wind

Table 2-7 Structural vulnerability to extreme winds (kph)

DamageRatio

Wind Speed (kph)

CHB-L-W C1L-W W1-L S1-L

0.05 172 177 152 139

0.10 214 214 157 173

0.15 247 243 160 201

0.20 277 269 163 227

0.25 306 293 166 251

0.30 334 317 168 275

0.35 362 340 170 300

0 50 100 1500

0.2

0.4

0.6

0.8

1

CHB-L-W

C1-L-W

W1-L

S1-L

Gust speed (m/s)

Damageratio


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0.40 392 365 172 325

0.45 422 390 174 351

0.50 455 416 176 379

0.55 490 444 178 409

0.60 528 475 180 442

0.65 571 508 182 479

0.70 620 546 185 522

0.75 677 591 187 572

0.80 748 644 190 633

0.85 839 713 193 713

0.90 969 810 198 828

0.95 1201 978 204 1034

Table 2-8 Annual risk of four types of structures subject to wind hazards

Structures Zone 1 Zone 2 Zone 3

W1-L 16.88% 4.83% 0.65%

CHB-L-W ~0% ~0% ~0%

C1-L-W ~0% ~0% ~0%

S1-L 0.01% ~0% ~0%

Table 2-9, Table 2-10 andTable 2-11 show the effect of 5%, 10% and 20% increases in wind

speed on annual risks. While the increase in wind speed would make the existing high total loss

risk of wood structure to the wind in all zones even worse, a 5% increase in wind speed can double

existing total loss risk of steel structures, and a 10% and 20% increase in wind speed can more

significantly increase their existing risk in Zone 1. This suggests that the total loss of buildings is

very sensitive to increases in wind speed as a result of climate change in Zone 1. The increase inwind speed would further increase the gap of total loss risks in comparison with the defined

thresholds.


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Table 2-9 Annual risk of four types of structures subject to 5% increase in wind hazards


W1-L 20.64% 6.44% 0.95%

CHB-L-W ~0% ~0% ~0%

C1-L-W ~0% ~0% ~0%

S1-L 0.02% ~0% ~0%



W1-L 24.57% 8.30% 1.32%

CHB-L-W ~0% ~0% ~0%

C1-L-W ~0% ~0% ~0%

S1-L 0.04% ~0% ~0%



W1-L 32.67% 12.63% 2.27%

CHB-L-W 0.01% ~0% ~0%

C1-L-W 0.04% ~0% ~0%

S1-L 0.16% ~0% ~0%

2.3.2 Structures Subject to Earthquake

Ground motion caused by earthquake generates impacts on the structural safety. Structures

should be designed to resist the seismic ground motion. In the structural design as defined by

NSCP, the design basis ground motion, representing the ground motion that has a 10% chance of

being exceeded in 50 years (or annual exceedance probability of 0.2%), is applied.


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As described in NSCP, seismic hazard are characterised by the seismic zone, proximity of the

site to active seismic sources, site soil profile characteristics, and the structure importance factor.

NSCP defines two seismic zones (see the review in chapter 4).

NSCP specifies a seismic zone factor of 0.4 and 0.2 for Zones 4 and 2, respectively. This means

that the peak ground accelerations (PGAs) with 10 % probability of being exceeded in 50-year are

0.4 g and 0.2 g for the two zones. The seismic hazard in the Manila region (located in Zone 4) has

been investigated and the spectral accelerations for 50%, 10%, and 2% exceedance probabilities

(or equivalent of average reoccurrence interval of 72, 475 and 2475 years, respectively) have been

estimated. The earthquake hazard can also be represented byTable 2-12.

Table 2-12 Peak ground acceleration given ARI in two earthquake zones

ARI (year) Zone 4 (cm/s2) Zone 2 (cm/s2)

5 41 21

10 67 35

20 101 52

25 113 59

50 159 82

100 215 112

200 285 148

250 310 161

500 399 207

1000 506 263

2000 633 329

2500 679 353

5000 837 435

10000 1022 531

The concrete hollow block structures show relatively high vulnerability to earthquake incomparison with other three types. The vulnerability of four types of structures can be described

as a damage ratio in relation to peak ground acceleration as shown inTable 2-13.


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Table 2-13 Structural vulnerability to earthquake (cm/s-2)

DamageRatio

Peal Ground Acceleration (cm/s2)


0.05 15 36 20 26

0.10 20 49 30 38

0.15 25 62 39 50

0.20 30 75 50 63

0.25 36 89 62 77

0.30 41 103 76 93

0.35 48 120 93 112

0.40 55 138 112 135

0.45 63 159 136 161

0.50 73 183 165 193

0.55 84 212 201 234

0.60 98 247 248 284

0.65 115 290 310 351

0.70 138 344 396 440

0.75 167 417 520 568

0.80 209 519 713 762

0.85 274 676 1048 1088

0.90 392 956 1748 1746

0.95 689 1642 3967 3699

Based on the earthquake hazard and vulnerability, the total loss risk of four types of structurescan be estimated and given inTable 2-14.(It shows the earthquake risks for all building types is


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higher than the threshold defined early. As expected, annual total loss risks are highest for

concrete hollow block construction and lowest for steel and RC construction.

Table 2-14 Annual risk of four types of structures subject to earthquake

Structures Zone 2 Zone 4

W1-L 0.38% 1.84%

CHB-L-W 2.46% 8.70%

C1-L-W 0.25% 1.45%

S1-L 0.22% 1.28%

2.3.3 Structures Subject to Flood Hazards and Sea Level Rise

There are no particular flood hazard zones specified for design purpose. In fact, the flood is

more location specific. As shown inFigure 2-7andTable 2-15,it is the flood hazard for the Manila

city.

Figure 2-7 Flood hazard at Great Manila Metropolitan Area

The study by Pacheco et al3gave the vulnerability of four types of structures to flood, as shown

inFigure 2-8 andTable 2-16.As a result, the annual risk can be assessed as shown inTable 2-17.In

3Pacheco BM, Hernandez Jr. JY, Castro PPM et al (2013). Development of vulnerability curves of key building types in the Greater Metro

Manila Area, Philippines


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fact, the flood would cause little damage to structure, but it would lead to the problem in

accessibility, mostly on the aspect of loss of functions.

Table 2-15 Storm tide height given average reoccurrence intervals

ARI (year)Extractions

from PAGASAdata (m)

Modelling (m)

5 0.12923 0.09860

10 0.16550 0.19335

25 0.25267 0.32170

50 0.48615 0.42358

100 0.56875 0.53069

200 0.60929 0.64367

Figure 2-8Vulnerability curves of four typical structures to flood

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 5 10 15

DamageRatio

Inundation Depth (m)

CHB-L-1

C1-L-1

W1-L-1

S1-L-1


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Table 2-16Structural vulnerability to flood

Water

Depth (m)

Damage Ratio


0.0 0 0 0 0

0.1 0 0.02 0.01 0.02

0.5 0.07 0.09 0.08 0.05

1.0 0.11 0.14 0.18 0.08

2.0 0.14 0.16 0.25 0.09

3.0 0.24 0.21 0.55 0.16

4.0 0.24 0.21 0.6 0.16

6.0 0.24 0.21 0.6 0.16

10.0 0.24 0.21 0.6 0.16

Table 2-17 Annual risk of four types of structures subject to flood

Structures Annual Risk

W1-L ~0%

CHB-L-W ~0%

C1-L-W ~0%

S1-L ~0%

2.4

Development of Resilient Design Options - Examples

The resilient design options should be identified to enhance the structural capacity or reduce vulnerability,

and ultimately reduce the risk to hazards. Examples are here to demonstrate how to assess different

options reduce risk to various hazards.


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2.4.1 Design Options for Resilience to Wind Hazards

The resilient design options aims to enhance the structural capacity or reduce vulnerability, and ultimately

reduce the risk to hazards. Examples are here to demonstrate how to assess the options and quantify thescale of risk.

2.4.2

Design Options for Resilience to Wind Hazards

Triple Grip Connection

Historical field surveys after severe wind events and laboratory tests show that the uplift

capacity of roof-to-wall connection is a critical property for the extent of damage sustained by

buildings after severe events. With about 90% of the US residential construction being of wood-

framed structures, the failures of pre-1994 structures were often found to be a result of an

insufficient number of nails in roof-to-wall and sheathing-to-rafter connections. While these types

of connection are simple to install, they were not designed to resist significant uplift loads.

In view of the historical failure background, Shanmugam et al. (2009)4tested the uplift

capacities of four identical houses. Their purpose was to account for and quantify the variability in

the structural behaviour of the nailed roof-to-wall connections and the roof sheathing in their as-

built condition. Satheeskumar et al. (2015) tested the uplift capacity of triple grips anchored

either by gun-nails or by hand-nails to timber of Australian radiate pine or spruce pine.

Human errors are recognised to be a source for poor uplift capacity. Hong and He (2015)5

investigated the effect of missing nails on the reliability of roof sheathing under uplift windpressure. They conclude that if the missing nail effect is ignored, an overestimation of the mean

of the panel uplift capacity by about 4% is observed. On the other hand, Satheeskumar et al.

(2015)6tested triple-grip connections with 2 missing nails and found it to have significantly

reduced the uplift capacity.

If the roof failure is caused by lift capacity, the application of triple grip connection, as shown

inFigure 2-9 could increase the structure resilience considerably. When triple grip connection is

applied to wood structure, the risk is almost reduced to zero for all zones as shown inTable 2-18.

4Shanmugam B, Nielson BG, Prevatt DO (2009). Statistical and analytical models for roof components in existing light-framed wood structures.

Engineering Structures, 31, 26072616.

5Hong HP and He WX (2015). Effect of human error on the reliability of roof panel under uplift wind pressure. Structural Safety, 52, 5465.

6Satheeskumer N, Henderson D, Ginger J, Wang C-H (2015). Wind uplift strength capacity variation in roof to wall connections of timber

framed houses. Submitted to Journal of Architectural Engineering.


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Table 2-19 Annual risk analysis of wood structure (W1-L) with screw fasteners 8

Zone 1 Zone 2 Zone 3

Existing Risk 16.88% 4.83% 0.65%

Screw fasteners ~0% ~0% ~0%

Risk Reduction ~100% ~100% ~100%

Benefit (reduced risk) ~16.88% ~4.83% ~0.65%

2.5 Option Appraisal

The selection of better resilience design options for structures can be based on the economic

cost and benefit9, more specifically, cost/benefit or cost effectives, as mentioned in Section1.2.3.

The cost or more specifically, the capital cost, would involve

Design

Procurement

Construction

Maintenance/operating cost should also be considered from the lifecycle management aspect.

The benefit is considered as saving in resource use, in this case, due to reduced risks. In general,

the option appraisal follows the steps as shown inTable 2-20.

At the moment, the social discount rate, or the rate at which a society would be willing to

trade present for future consumption, is applied for the discount rate to estimate the future

benefits and costs in the present value. The social discount rate is currently 15%9.However, the

discount rate has been applied at various levels. The International Monetary Fund and the World

Bank has set the discount rate at 5% for Debt Sustainability Analysis since 201310. The review by

ADB indicated that the discount rate can be 8-15% in developing countries and 3-7% in developed

8screw fasteners have an increase in capacity of 4300/1200 = 3.58 compared to nails. Revised median wind speed at failure = 89% increase or

v=92.4 m/s (lamda = 4.53). COV of screw fastener failure is stated in HAZUS to be 10-15% (p. 6-93). Lets assume COV(P)=0.125, then

COV(v)=0.0625, so zeta = 0.0625.

9NEDA, ICC Project Evaluation Procedures and Guidelines. Available onhttp://www.neda.gov.ph/wp-content/uploads/2013/10/ICC-Project-

Evaluation-Procedures-and-Guidelines-as-of-24-June-2004.pdf

10IMF (2013). Unification of Discount Rates Used in External Debt Analysis for Low-Income Countries. Available on

https://www.imf.org/external/np/pp/eng/2013/100413.pdf
http://www.neda.gov.ph/wp-content/uploads/2013/10/ICC-Project-Evaluation-Procedures-and-Guidelines-as-of-24-June-2004.pdfhttp://www.neda.gov.ph/wp-content/uploads/2013/10/ICC-Project-Evaluation-Procedures-and-Guidelines-as-of-24-June-2004.pdfhttp://www.neda.gov.ph/wp-content/uploads/2013/10/ICC-Project-Evaluation-Procedures-and-Guidelines-as-of-24-June-2004.pdfhttp://www.neda.gov.ph/wp-content/uploads/2013/10/ICC-Project-Evaluation-Procedures-and-Guidelines-as-of-24-June-2004.pdfhttps://www.imf.org/external/np/pp/eng/2013/100413.pdfhttps://www.imf.org/external/np/pp/eng/2013/100413.pdfhttps://www.imf.org/external/np/pp/eng/2013/100413.pdfhttp://www.neda.gov.ph/wp-content/uploads/2013/10/ICC-Project-Evaluation-Procedures-and-Guidelines-as-of-24-June-2004.pdfhttp://www.neda.gov.ph/wp-content/uploads/2013/10/ICC-Project-Evaluation-Procedures-and-Guidelines-as-of-24-June-2004.pdf


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countries11. In this regard, a discount rate as low as 3% may be considered for sensitivity

assessment. This is particularly important for climate adaptation project with long-term goals.

While the option is acceptable as long as the net present value or benefit/cost ratio is greaterthan 1, It is desirable to have a high benefit/cost ratio, while it should be great than 1 for

consideration in the design. In general, a better option should have a higher benefit/cost ratio. It

should be mentioned, although it is reasonable to some extent to estimate the benefit purely on

the reduced risks as a result of structural damage or failure, a broad assessment of environmental

and social benefit should be considered. It is also true when cost is estimated.

Table 2-20 Steps in option appraisal

Steps Costs/BenefitsStep 1 (A) Design Cost

Step 2 (B) Procurement

Step 3 (C) Construction

Step 4 (D)* Maintenance at year 1, 2, , N

Step 5 (E) Reduced Risk

Step 6 Benefit/Cost E/[A+B+C+D]

*D=D1/(1+r)+D2/(1+r)2++DN/(1+r)N, where D1, D2, , DN

are the maintenance cost in year 1, 2, , N, and r is the

discount rate.

11ADB (2013). Cost-benefit Analysis for Development: A Practical Guide.


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INTRODUCTION OF STRUCTURAL DESIGN IN NATIONAL STRUCTURALCODE OF THE PHILIPPINES 45

.

3

Introduction of Structural Design in NationalStructural Code of the Philippines

The National Structural Code of the Philippines (NSCP) referred to in this document is the 6th

Edition, 4thPrinting, published in 2013 by the Association of Structural Engineers of the

Philippines. The purpose of NSCP is to provide minimum requirements for the design of buildings,

towers and other vertical structures, and minimum standards and guidelines to safeguard life or

limb, property and public welfare by regulating and controlling the design, construction, quality of

materials pertaining to the structural aspects of all buildings and structures.

More specifically, the NSCP provides minimum design load requirements for the design ofstructures under dead loads, live loads, wind loads, earthquake loads, soil lateral loads, rain loads,

and flood loads. It also develops appropriate load combinations to be used together for strength

design and allowable stress design.

In addition to NSCP, all concrete materials and workmanship shall conform to the latest

building code of American Concrete Institute (ACI-318) and all steel construction shall be based on

AISC Manual.

This is only a brief introduction, and more details should be sought from NSCP.

3.1

Classification of structures

Buildings and other structures shall be classified, based on the nature of occupancy, for

purpose of applying different wind and earthquake design loads, in another word, exert different

design standards. More critical are the structures, stricter the design requirements.

Each building or other structures shall be assigned to the highest applicable occupancy

category or categories. Assignment of the same structure to multiple occupancy categories based

on use and the type of loading condition being evaluated (e.g. wind or seismic) shall be

permissible. Table 3-1 lists the NSCP structural classifications in column 2 and the municipalbuildings and structures in column 3.


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Table 3-1 Occupancy category (source of columns 1 and 2: Table 103-1, NSCP)

OCCUPANCY

CATEGORY

OCCUPANCY OR FUNCTION OF STRUCTURE

NSCP SPECIFICATION MUNICIPAL STRUCTURE

I EssentialFacilities

Occupancies having surgery and emergency treatmentareas,

Fire and police stations,

Garages and shelters for emergency vehicles and

emergency aircraft,

Structures and shelters in emergency preparedness

centers,

Aviation control towers,

Structures and equipment in communication centers and

other facilities required for emergency response,

Facilities for standby power-generating equipment for

Category I structures,

Thanks or other structures containing housing or

supporting water or other fire-suppression material or

equipment required for the protection of Category I, II or

III structures,

Public school buildings,

Hospitals and

Designated evacuation centers.

Public school buildings(except shingle-story

buildings), hospital,

designated evacuation

centers (including gyms,

covered courts, multi-

purpose buildings if used as

such).

II HazardousFacilities Occupancies and structures housing orsupporting toxic or explosive chemicals orsubstances,

Non-building structures storing, supporting

or containing quantities of toxic or explosive

substances.

III SpecialOccupancyStructures

Single-story school buildings,

Buildings with an assembly room with an

occupant capacity of 1,000 or more,

Educational buildings such as museums

libraries, auditorium with a capacity of 300or more students,

Buildings used for college or adult

education with a capacity of 500 or more

students,

Institutional buildings with 50 or more

incapacitated patients, but not included in

Category I,

Mental hospitals, sanitariums, jails, prison

and other buildings where personal liberties

of inmates are similarly restrained,

All structures with an occupancy of 5,000 or

more persons,


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Figure 3-1 Wind zone map of the Philippines (source: NSCP 2010).

3.3

Earthquake Loads

The purpose of the earthquake provisions is primarily to design seismic-resistant structures to

safeguard against major structural damage that may lead to loss of life and property. These

provisions are not intended to assure zero-damage to structures nor maintain their functionality

after a severe earthquake.

The design of structures shall consider seismic zoning, site characteristics, occupancy,configuration, structural system and height. Structures shall be designed to withstand the lateral


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Figure 3-2 Seismic zones


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flexural beams an analysis that considers a nonlinear distribution of strain shall be used.

Maximum usable strain at extreme concrete compression fibre shall be assumed equal to 0.003, as

shown inFigure 3-3. Stress in reinforcement below specified yield strength shall be taken as the

modulus of elasticity times steel strain. For strains grea

Documents

Designing Resilient Structures 2015-12-27_Draft 2.31