Dr. Naveed Anwar

Performance Based Design, Value Engineering and Peer Review

Design of Tall Buildings: Trends and Advancements for Structural Performance

Bangkok-Thailand

November 7-11, 2016

Naveed Anwar, PhD

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Is this acceptable?(For the people who purchased apartment and lived here)

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Who are the stakeholders

Developers(Rely on designers and

contractors to make profit)

Designers(Satisfying building codes and

regulations and developer)

Owners(Ultimate StakeholderPays/owns and uses)

Building Officials(enforce the building codes and responsible for public safety)

Bu

ildin

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od

es(P

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equ

irem

sfo

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)

Contractors(Carry out the construction based instructions of Designers

and developers and work for a profit)

Residents and Public(Uses the space)

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Make buildings as primary business

Care about reputation, brandand continued business

Main focus on profit

Own/use the building for living or making living

Care about livability, safety, comfort

Focus on value for money

Developers Buyers/Residents

Willing to spend more to increase profit and

reputation

Willing to pay more for higher value

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How can we increase the value sothe buyers are willing to pay more

And the developer gets higher profit

Public gets a better building

Everyone wins!

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What “Value” are we considering

• Structural Safety is of prime concern and has a high value

• Other value may be in location, brand, finishes, design quality etc.

• Additional value may be “Green” and sustainability

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• A safer and high performance building is more environmentally sustainable

• People pay more for higher sustainability so should pay more for higher and performance

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• Compare Value Engineering and PBD

• What the developers want• Increase profit

• Reputation/ branding

• Reducing cost is one way > Value Engineering

• PBD - increasing safety, value, selling price and branding is another

• Give example of cost /Sq m and cost of review, PBD etc

• How PBD Works

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• Explicit confirmation of higher or expected performance level

Performance Based Design

• Get the best “value” for resourcesValue Engineering

• Provide an independent view and confirmation

Peer Review

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Ensuring Explicit Safety Performance(Specially for extreme events)

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How does CTBUH look at Tall Buildings

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Relatively Tall. Both for public and the professions who design and construct

ProportionSlenderness, in plan and in elevations

Systems and TechnologiesUses something “different” than ordinary buildings

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How modern codes intent to ensure “Safety”

• Define appropriate/estimated hazard or load levels

• Prescribe limits on structural systems, members, materials

• Define procedures for analysis and design

• Provide rules for detailing

• Provide specifications for construction and monitoring

•Hope that all of this will lead to safe structures …

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The Modern Codes – With “intent” to make buildings safe for public

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(ACI 318 – 11)

Extremely Detailed prescriptions and equations using

seemingly arbitrary, rounded limits with

implicit meaning

(IS 456-2000)

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The General Code Families

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UBC, IBC

ACI, PCI, CRSI, ASCE, AISI,

AASHTO

British, CP and BS

Euro-codesChina, USSR,

Japan

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Are All Buildings Codes Correct ?

• If they differ, can all of them be correct ?

• Did we inform the structures to follow which code when earthquake or hurricane strikes ?

• Codes change every 3 or years, should we upgrade our structures every 3 or 5 years to conform ?

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Concerns

• Public

Will the building be safe?

• Owner

Will the building collapse/ will it be damaged ?

Can I use the building after a given earthquake? (blast,

hurricane..)

How much will repair cost?

How long will it take to repair?

Can I make building that will not be damaged and will not

collapse

• Public Officials

Who is responsible if loss of life occurs

Who should have all the answers?

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Structural Engineer’s Dilemma

• Can not answer most of the these questions explicitly

• Answers are always qualified

• There is no warranty for the structure

• There are too many unknowns

• Public understanding and engineers understanding of safety is

different

• Has to hide behind the design codes

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Prescriptive Codes – A Shelter

• Public: • Is my structure safe ?

• Structural Engineer:• Not sure, but I did follow the “Code”

As long as engineers follow the code, they can be sheltered by its provisions

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Shortcomings of Code Based Design for Tall Buildings

• Traditional codes govern design of general, normal buildings Over 95% buildings are covered, which are less than about 50 m

• Not specifically developed for tall buildings > 50 m tall

• Prescriptive in nature, no explicit check on outcome

• Permit a limited number of structural systems

• Do not include framing systems appropriate for high-rise

• Based on elastic methods of analysis

• Enforce uniform detailing rules on all members

• Enforce unreasonable demand distribution rules

• Do not take advantage of recent computing tools

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Motivation for PBD

• Lack of explicit performance in design codes is primary motivation

for performance based design

• Performance based methods require the designer to assess how a

building is likely perform under earthquake shaking and other

extreme events and their correct application will help to identify

unsafe designs.

• At the same time this approach enables arbitrary restrictions to be

lifted and provides scope for the development of safer and more

cost-effective structural solutions

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Performance Based Design (PBD)

• An approach in which structural design criteria are expressed in terms of achieving a set of performance objectives or levels.

• Ensures structures reaches specified demands level in both service and strength design levels.

• Why it was needed?• Traditional codes not suitable/adequate

• Explicit verification not specified or required in most codes

• Public does not care about the code, or theories or procedures, they care about “safety” and ‘performance”

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Performance based design

can be applied to any type

of loads, but is typically

suitable and targeted for

earthquake loads

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Explicit Performance Objective in PBD

Performance based design investigates at least two

performance objectives explicitly

Service-level Assessment

Negligible damage with frequent hazards

(Earthquake having a return period of about 50)

Collapse-level Assessment

Collapse prevention under extreme hazards

(the largest earthquake with a return period of 2500 years)

Codes arbitrary “Design Level”

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Performance Level Definitions

Owner

Will the building be safe?

Can I use the building after the hazard?

How much will repair cost in case of damage?

How long will it take to repair?

Engineer

amount of yielding, buckling, cracking, permanent deformation,

acceleration, that structure, members and materials

experiences

Need a third party to ensure public safety and realistic Performance

GuidelinesPeer Review

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Typical Review Objectives

Enhance Structural Performance

• Improved serviceability, safety and reliability

• Explicit check on various performance indicators

Improve Cost Effectiveness

• Achieve efficient use of materials, resources and time

• Direct reduction cost through reduction of structural material quantities

Objectives to be achieved through

• Better structural system selection and its proportions

• Use of advanced design methodologies and tools

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Typical Review Objectives

Enhancement of Performance

• Dynamic response parameters

• Lateral load response

• Vertical load response

• Demand and capacity ratios

• Response irregularity, discontinuity

• Explicit Performance Evaluation at Service, DBE and MCE

Cost Effectiveness

• Capacity utilization ratio

• Reinforcement ratios

• Reinforcement volume ratios

• Concrete strength and quantity

• Rebar quantity

• Constructability, time and accommodation of other constraints

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Performance Objectives

Level of Earthquake Seismic Performance Objective

Frequent/Service (SLE): 50% probability of

exceedance in 30 years (43-year return

period)

Serviceability: Structure to remain

essentially elastic with minor damage to

structural and non-structural elements

Design Basis Earthquake (DBE): 10%

probability of exceedance in 50 years

(475-year return period)

Code Level: Moderate structural

damage; extensive repairs may be

required

Maximum Considered Earthquake (MCE):

2% probability of exceedance in 50 years

(2475-year return period)

Collapse Prevention: Extensive structural

damage; repairs are required and may

not be economically feasible

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Site Specific Ground Motions

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Seismic Hazard Spectrum, SLE, DBE. MCE

MCE Level

Service Level

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Standard Structural Performance Levels

Restaurant Restaurant

Resta

uran

t

Operational Immediate Occupancy

Life Safety Collapse Prevention

0 % Damage or Loss 99 %

Ref: FEMA 451 B

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Judging Performance Acceptability

• Acceptance criteria are indicators of whether the predicted

performance is adequate for

• Local (component based)

Example: Drift ratio, structural component deformation

• Global (overall structure-based)

Example: Roof drift , base shear

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Performance Based Design Process

Acceptance Criteria for Primary Components

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Performance Based Design Process

Acceptance Criteria for Secondary Components

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Classification of Actions

Element Action Type Classification Expected

Behavior

RC column Axial-flexure

Shear

Ductile

Brittle

Linear

Linear

RC shear wall Flexure

Shear

Ductile

Brittle

Nonlinear

Linear

RC coupling beams

(Deep beam, ln/d<4.0)

Shear Ductile Nonlinear

RC coupling beams

(slender beam, ln/d≥4.0

Flexure

Shear

Ductile

Brittle

Nonlinear

Linear

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How to Work with PBD

Architect

Structural Engineer

PBD Specialist

PBD Peer Reviewer

Site Specific Consultant

Performance Based DesignClient

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Value EngineeringBalancing Cost and Performance

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Cost and Performance

PCC

Cost Effective

Design

Can be done PC

General Belief

Easy to do !

PC

Highly Innovative

Design

Hard to do!

PC

High

Performance

Design

Can be done

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What is the Cost of a Project?

• Cost may include– Financial Cost (loan, interest, etc)

– Planning and Design Cost

– Direct Construction Cost

– Maintenance Cost

– Incidental Cost

– Liquidated Cost (lost profit etc)

– Opportunistic Cost

– Environmental Cost

– Emotional Cost

– Non-determinist Resources

Cost may be:“Consumption of Particular Resources, at Particular Time”

Sustainability may be:<Consumption of all resources, and their impacts through throughout the life cycle>

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Cost and Performance

• Enhancement of Performance• Dynamic response parameters

• Lateral load response

• Vertical load response

• Demand and capacity ratios

• Response irregularity, discontinuity

• Explicit Performance Evaluation at Service, DBE and MCE

• Cost Effectiveness• Capacity utilization ratio

• Reinforcement ratios

• Reinforcement volume ratios

• Concrete strength and quantity

• Rebar quantity

• Constructability, time and accommodation of other constraints

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Optimization

• Need to define What to optimize? And what are the parameters that can be changes?

• Optimizing one or two items may “un-optimize” others

• Optimizing everything is a “Holy Grail”– …. and “Holy Grail” doesn't exist

• Tools– Genetic Algorithms (GA)

– Artificial Neural Networks (ANN)

– Linear and Nonlinear programing

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Levels of Optimization

Levels of Optimization

Micro-Micro Level

One part of a component, “Steel”

Micro Level

One Component, “Column”

Local

One part or aspect

Global

Entire Problem, Project

Universal

Entire System

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• Simple Example of a Column Stack – What and how can we optimize ?• Concrete Strength

• Steel Strength

• Column Size

• Rebar Amount

• Composite Section

• Material Cost, Labor Cost, Formwork Cost, Management and operations Cost, Time ??

Local Vs Global Optimization

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Cost and Performance

(Base Cost and Performance)

(Increased Performance, Same Cost)

(Base Cost and Performance)

(Reduced Cost for Same Performance)

P

M

P

M

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Demand Capacity (DC Ratio)

• Definition of D/C: It is an index that gives an overall relationshipbetween affects of load and ability of member to resists thoseaffects.

• This is a normalized factor that means D/C ratio value of 1 indicatesthat the capacity (strength, deformation etc) member is justenough to fulfill the load demand.

• Two types of D/C ratio Members with brittle behavior D/C is checked by Strength (Elastic) Members with ductile behavior D/C is checked by deformation (Inelastic)

• Total D/C ratio of the member is combined of these two.

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Cost Effectiveness > Utilization Ratio

• Utilization Ratio• Compare, What is

Needed against What is Required

• One measure • The Demand/

Capacity Ratio (D/C)

Demand/ CapacityColumns

No. %

D/C<0.5 178 16%

0.5<D/C<0.7 534 49%

0.7<D/C<1 346 31%

1<D/C<1.5 30 3%

1.5<D/C<2.5 12 1%

D/C>2.5 0 0%

Total 1100 100.00%

Ideal

Not Cost Effective

Not Safe

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Focus should be

“Maximum Value for Resources”

Cost effective, not Low Cost

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Peer ReviewTo ensure Basic Design the Performance Evaluation and Value Enginering are done right

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The Responsibility

Building Officials

Structural Designer

Architect Structural Design Codes

General Building Codes

Legal and Justice System

Public/ Users/ Occupants

Client/Owner

Law Makers

Builder/Contractor

Peer Reviewer

Geotech Consultants

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Peer Review

• What exactly is design peer review?• It is a process whereby a design project (or aspect of) is reviewed and

evaluated by a person, or team, not directly involved with the project, but appropriately qualified to provide input that will either reinforce a design solution, or provide a route to an improved alternative.

• Why is it so important?• Very few can claim to be all-encompassing experts. The invaluable input from

broad base and independent experience at each stage of a design project will often result in technical improvements, lower costs, avoidance of sourcing issues, and improved performance.

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When is Peer Review needed

• Structural Peer Review is required for: • Buildings included in Structural Occupancy Category

IV as defined in the Building Code.

• Buildings with aspect ratios of seven or greater.

• Buildings greater than 500 feet (160 m) in height or more than 1,000,000 square feet (100,000 Sqm) in gross floor area.

• Buildings taller than seven stories where any element supports in aggregate more than 15 percent of the building area.

• Buildings designed using nonlinear time history analysis, pushover analysis or progressive loading techniques.

New York Building Code, adopted by many cities

Important

Slender

Tall or large

Critical

Use NLA

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Responsibility

• Structural Engineer of Record (SER). • The structural engineer of record shall retain

sole responsibility for the structural design. The activities and reports of the Reviewing Engineer shall not relieve the structural engineer of record of this responsibility.

• Reviewing Engineer. • The Reviewing Engineer’s report states his or her

opinion regarding the design by the engineer of record.

• The standard of care to which the Reviewing Engineer shall be consistent with Structural Peer Review services performed by professional engineers licensed/approved

Retains Responsibility

Evaluates, and gives opinion that may or may not be accepted by

Client or SER

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Typical Scope of Work for Review

• Check structural engineering concepts

• Potential behavioral or value improvement suggestions

• Constructability review

• Presentation of peer review findings and peer review report writing

• Review and confirmation of the owner’s seismic performance objectives

• Meeting(s) with the design team to review the project assumptions and the project approach

• Review structural design criteria and analysis/design methodology

• Review available geotechnical and site seismicity reports

• Review all available relevant documents as the design progresses, including drawings, and specifications

• Review of analysis results. This may require implementation of one or more parallel verification models for comparison purposes

• Technical review of the design and details of the proposed structural system

• Preparation of peer review report and comment list

• Meeting(s) with the design team to review and reconcile the peer review comment

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Client

PBDValue

Engineering

Peer Review

Basic Design

Public Officials

Design Codes and Guidelines

High performance, Higher safetyhigher value, cost effectiveSustainable

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