smces civil engineering seminar 2016 (yangon)...

SMCES Civil Engineering Seminar 2016 (Yangon)

Seismic Retrofit of Existing Structures

by Dr. Methee ChiewanichakornP.E. (California), S.E. (California), LEED AP BD+C

Meinhardt (Thailand) Ltd.

Yangon Technology University

December 18th, 2016

OVERVIEW

Introduction

Description of Case Study Building

Component Laboratory Testing

Nonlinear Analysis Results

Comparison of Retrofit Schemes

using Conventional vs. Nonlinear

Based Approaches

Conclusions

HISTORY AND BACKGROUND

California has a history of strong

earthquakes.

The most earthquake prone regions

in the state are also the most

heavily populated.

Building design and construction

has evolved as a result of lessons

learned in damaging earthquakes.

1933 LONG BEACH EQ

Magnitude 6.3 earthquake

resulted in loss of 115 lives and $40

million in property damage.

Led to the development of

building code requirements for

seismic resistant design of

buildings, especially schools.

1933 LONG BEACH EQ

1971 SAN FERNANDO EQ

Magnitude 6.5 earthquake

caused 65 deaths and over $500

million in property damage.

Produced an unanticipated

amount of damage to hospitals,

leaving the public in large areas

without medical assistance.

1971 SAN FERNANDO EQ

RESPONSE TO SAN FERNANDO EQ

Hospital Seismic Safety Act (HSSA),

also known as the Alquist Act.

The Alquist Act establishes

hospitals as essential facilities and

defines explicitly their expected

performance.

Acute care hospitals to withstand

and remain operational after a

major earthquake.

1994 NORTHRIDGE EQ

Magnitude 6.8 earthquake caused 57

deaths and over $20 billion in property

damage.

Forced evacuation of several hospital

facilities.

Hospitals constructed in accordance

with the Alquist Act survived the

earthquake with minimal structural

damage.

Non-structural damage impaired

operation of hospitals, even when no

structural damage occurred.

1994 NORTHRIDGE EQ

SENATE BILL (SB 1953)

After the January 17, 1994

Northridge Earthquake, State of

California passed a law (Senate

Bill 1953) that requires hospital

owners to evaluate and possibly

retrofit pre-1973 hospital buildings.

Addresses survivability of both

structural (SPC) and non-structural

(NPC) components.

SB 1953 MAJOR MILESTONES

STRUCTURAL PERFORMANCE CATEGORIES

SPC 3, 4 & 5 Reasonably capable of serving

the public after strong ground

motion.

SPC 2 No risk to life safety

SPC 1 Significant risk to life safety

STRUCTURAL PERFORMANCE CATEGORIES

Current StateSPC-1

Significant Risk of Life Safety

Retrofit StateSPC-2

Life Safety

CODE FRAME WORK

Followed two methodologies

1. Prescriptive (Code Based)

2. Performance Based

CODE BACKGROUND

Prescriptive(Code Based)2001, 2007 CBC

Performance BasedASCE 41-06

CASE STUDY: BUILDING DESCRIPTION

Structural Systems: Lateral Force Resisting

System: Concrete Shear

Walls.

Floor and Roof Framing: Formed Concrete Pan Joist

System.

Foundation: Concrete

Continuous Wall & Spread

Footings.

Number of Stories: 6

Year Constructed: 1961

Weakened Plane

Joint (WPJ)

Weakened Plane Joint (WPJ)

Weakened Plane Joint (WPJ): Half to two-thirds of typical wall

reinforcement at mid-span were cut and

grooves in concrete

ASCE 41-06 MODELING PARAMETERS

Modeling Parameters, Drift % Acceptable Drift %

Performance Level

d e c Immediate Occupancy

Life Safety

Collapse Prevention

0.75 2.0 0.40 0.40 0.60 0.75

CPLSIO

d e - d

Table 6-19: Wall Segments

COMPONENT TESTING

Horizontal Wall

Segment (HWS)

Vertical Wall

Segment (VWS)

TEST SPECIMENS – VERTICAL WALL SEGMENT (VWS)

hp = 62.5”

(1.60 m)

lp = 72” (1.83 m)

tp = 8”

(200 mm)

v = ~0.25%

h = ~0.35%

Prototype (Actual Building)

hp = 62.5”

(1.60 m)

lp = 72” (1.83 m)

tp = 8”

(200 mm)

v = ~0.25%

h = ~0.35%

Prototype (Actual Building)

hp = 48”

(1.20 m)

lp = 54” (1.40 m)

tp = 6”

(150 mm)

v = ~0.25%

h = ~0.35%

¾ Scale Test Specimen

TEST SPECIMENS – VERTICAL WALL SEGMENT (VWS)

Specimen Geometry (inches) Reinforcement3 P/Agf 'c4 Specimens

ID Height Length Thickness Edge1 Vert. Web2 Horiz. Web2 (kips) (#)

(1) (2) (3) (4) (5) (6) (7) (8) (9)

WP1-1-10 48 54 6 2 - #4 0.26% 0.35% 0.10 2

WP2-1-05 48 54 6 2 - #4 0.26% 0.35% 0.05 2

WP3-1-00 48 54 6 2 - #4 0.26% 0.35% 0.00 2

WH1-1-0 60 60 6 1-#4 1-#5 0.35% 0.26% 0.0 2

WH2-1-0 60 60 6 4 - #5 0.35% 0.26% 0.0 2

HORIZONTAL WALL SEGMENT – WEAKENED PLANE JOINT

COMPONENT TESTING SET-UP

Horizontal LoadVertical Load

Vertical Load

Reaction FrameOut-of-plane support

Specimen

P2 ΣP=0

TEST RESULTS – SPANDREL (HWS)

TEST RESULTS – BACKBONE RELATIONSHIP

Results from Test 2

-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0

Lateral Displacement (in)

Full History

Test Based

Test #2

TEST RESULTS – BACKBONE RELATIONSHIP

Results from Test 2

-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0

Lateral Displacement (in)

FEMA Based

Test Based

New ASCE-41 Supplement

Backbone Curve for shear

controlled wall segments

- based on these testsTest #2

PRESCRIPTIVE/CODE BASED: ETABS MODEL

3D model

Fixed base

Elastic wall elements

Elastic diaphragms

ETABS Model

PERFORMANCE BASED: PERFORM-3D MODEL

3D model

Nonlinear soil spring

Nonlinear wall elements

Elastic diaphragms

PERFORM-3D Model

PUSHOVER ANALYSIS

Plastic Hinge

PUSHOVER ANALYSIS

Lateral displacement

CollapseInelastic RangeElastic Range

CODE BASED: ASSESSMENT OF SEISMIC BEHAVIOR

Mechanism• Unclear

CODE BASED: ASSESSMENT OF SEISMIC BEHAVIOR

Mechanism• Unclear

PERFORMANCE BASED: ASSESSMENT OF SEISMIC BEHAVIOR

Not Desirable• Lack of ductility

• Potential loss of vertical load carrying ability

Possible Mechanism: Soft Story

Not Desirable• Lack of ductility

• Potential loss of vertical load carrying ability

Possible Mechanism: Soft Story

Desirable• Ductile response

• No loss of vertical load carrying ability

Possible Mechanism: Segmented Wall Rocking

Desirable• Ductile response

• No loss of vertical load carrying ability

Possible Mechanism: Segmented Wall Rocking

PERFORMANCE BASED: FORMATION OF MECHANISM

Step 1: Undeformed

Step 2: Localized Damage

Step 3: Formation of Rocking

Mechanism

Step 4: Fully Rocking

Mechanism

PERFORMANCE BASED: PUSH-OVER CURVES (LB SOIL)

HOW DO THE METHODOLOGIES COMPARE?

CODE-BASED• Extensive wall

thickening

• Concrete infills at a

multiple openings

• Complete

foundation system

replacement

CODE-BASED• Extensive wall

thickening

multiple openings

• Complete

foundation system

replacement

PERFORMANCE-BASED• Almost no wall

thickening

few openings

• Isolated FRP

strengthening

• Isolated foundation

thickening

• FRP “Catch

Mechanisms” at

hospital

exits/corridors

HOW DO THE METHODOLOGIES COMPARE?

RETROFIT HIGHLIGHTS – PRESCRIPTIVE/CODE BASED

Foundation Retrofit

14’ wide x 5’ deep foundation retrofit

RETROFIT HIGHLIGHTS – PERFORMANCE BASED

Foundation Retrofit

Isolated Foundation Thickening

RETROFIT HIGHLIGHTS – CODE vs. PERFORMANCE BASED

Retrofit Work and Business Disruptions

Isolated concrete infill

FRP “Catch Mechanism”

FRP ”WPJ”strengthening

Performance Based

14’ wide x 5’ deep foundation retrofit

16” thick concrete wall thickening

24” thick concrete wall thickening

Prescriptive/Code Based

FRP Chords

RETROFIT SCHEMES: CONVENTIONAL VS. NONLINEAR

Prescriptive/Code Performance Based

Foundations New foundations below 90% of all perimeter walls

Strengthening of 5% of Existing Foundations

Shear Walls 90% of all perimeter walls need to be thickened 16” (380 mm) or 24” (610 mm) with new reinforced concrete walls

Reinforced concrete infill of 5% of existing openings

Thickening of 1% of existing perimeter walls.

Catch mechanisms in 5% of HWS

Repair of existing weakened plane joints in 2 walls

RETROFIT SCHEMES: CONVENTIONAL VS. NONLINEAR

Prescriptive/Code Performance Based

Diaphragms New interior chords at all levels

Thickening of existing concrete slab in selected locations

New FRP chords at two upper floors (mostly exterior)

Stair Towers Demolish and replace existing stair towers

No action required

Impact on Adjacent Buildings

At least 2 adjacent buildings need to be cut back to accommodate thickening of existing walls

Minimum impact to adjacent buildings

RETROFIT PHOTOS

Concrete Wall Thickening

RETROFIT PHOTOS

Foundation Thickening

RETROFIT PHOTOS

Concrete Wall Opening Infill

Beam/Joist FRP Strengthening

RETROFIT PHOTOS

Gravity Column FRP Strengthening

RETROFIT PHOTOS

FRP Anchors

RETROFIT PHOTOS

FRP Catch Mechanism at Corridor

FRP Anchors

RETROFIT PHOTOS

Diaphragm Strengthening

RETROFIT PHOTOS

Diaphragm Strengthening

Floor Plan

DiaphragmFRP

Collector

Steel Plate

(L-Shape)

RETROFIT PHOTOS

Collector Strengthening

Floor Plan

DiaphragmFRP

Collector

Steel Plate

(L-Shape)

RETROFIT PHOTOS

Floor Plan

DiaphragmFRP

Collector

Steel Plate

(L-Shape)

Test Samples

RETROFIT PHOTOS

BENEFITS OF NONLINEAR ANALYSIS

• Ability to explore actual post-elastic seismic

performance of existing structures

• Better identification of desirable collapse

mechanisms for the existing structure

• Better identification of efficient retrofit

options

• Improved communication of the expected

performance of the buildings

BENEFITS OF NONLINEAR ANALYSIS

• Potential reduction of retrofit costs

• Potential reduction of disruptions due to

retrofit work

BENEFITS FROM THE OWNER’S PERSPECTIVE

• Less retrofit means …

• Less disruption• Happy patients & staffs

• Less cost• Happy hospital

leadership

• More capital for other

• Less cost• Happy hospital

leadership

• More capital for other

• Shorter schedule• Happy patients & staffs

CONCLUSIONS

• A nonlinear model has the potential of

greatly improving the understanding

of the seismic performance of existing

structures.

• Nonlinear based approach leads to

targeted retrofit that provides a higher

level of confidence that the building

will behave as expected and meet

the desired performance.

CONCLUSIONS

• Nonlinear based approach may lead

to a reduced amount of retrofit that is

less invasive than a retrofit based on

conventional code-based methods.

• With nonlinear based retrofit scheme,

cost saving can be maximized while

the disruption of the hospital

operations can be greatly minimized

during the construction.

Source: http://www.bvt.co.nz/faq-seismic-restraint-of-non-structural-building-elements/

NONSTRUCTURAL COMPONENTS

• What is “Nonstructural Components”?

• How important is “Nonstructural Components”?

Types of failure

1. Initial Failures

2. Displacement/Deformation Failures

Inertial failures:

• Excessive shaking

• Component rocking

• Component sliding

Electrical Switchgear

Disruption to Patient Care

Patient Records

Boilers & Chillers

Electrical & Communications Equipment

•Displacement / Deformation failures:

• Excessive building inter-story displacements or drift

• Incompatible stiffness between the building structure and component

• Interaction between adjacent structural systems and nonstructural systems

• Multiple structure connection points

Sprinklers & Water Lines

Design Code / Standard

• International Building Code (IBC)

• ASCE 7

• ASCE 41

Thank you

methee@meinhardt.net

Career Opportunity @ Meinhardt Myanmar

• C&S Site Engineer

• M&E Site Engineer

• Electrical Design Engineer

• Senior Electrical Design Engineer

• Mechanical Design Engineer

• Senior Mechanical Design Engineer

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