General and Seismic Provisions

8/12/2019 General and Seismic Provisions

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General And Seismic Provisions


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I. DESIGN DATA

A. BRIDGE SITE TOPOGRAPHIC MAP

Drawn to scale of 1:500 to 1:1000 depending on the width of the river

The topo-map should be extended at least 200m upstream anddownstreamfrom the centerline of the proposed bridge

Location plan showing the existing public and private structures/ utilitiesthatmaybe affected by the project.

Cross-section at the approaches at 20m interval

B. PROFILE ALONG THE CENTERLINE OF THE PROPOSED BRIDGE

Showing the elevations of ordinary water level (OWL) andmaximum flood level MFL


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C. RIVER CROSS-SECTIONS

@ 50m interval 100 to 200 meters upstream and downstream from theproposed bridge indicating the experienced high and ordinary waterelevations.

D. HYDRAULIS / HYDROLOGIC ANALYSIS

Topographic map showing the watershed area and the point ofinterest Calculation of required waterway opening

Scour Analysis Calculation of Design Flood Level


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E. BORING DATA WITH SPT and GEOTECHNICAL REPORT

Minimum of two deep borings shall be made at each abutment andpreferably

an additional boring at each pier for multi-span bridges.

Boreholes shall have minimum depth of 20 meters below the riverbed

in ordinary soil or at least 3.0m in bedrock.

Standard Penetration Test at maximum interval of 1.50 m and at everychange

in soil stratum.

Analysis for liquefaction potential.


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The subsurface exploration should define the following, where applicable :

Soil Strata- Depth, thickness and variability- Identification and classification- Relevant engineering properties (i.e., shear strength, unit weight,compressibility, stiffness, permeability, expansion or collapse potential)

Rock Strata- Depth of rock- Identification and classification- Quality (i.e., soundness, hardness, jointing, resistance to weathering if

exposed, and solutioning )

- Compressive strength (e.g.,uniaxial compression, point load index)- Expansion potential

Ground water elevation

Ground surface topography


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II. DESIGN CRITERIA & STANDARDS

A. DESIGN SPECIFICATIONS

AASHTO Standard Specifications for Highway Bridges, 16th Edition, 1996

Department Order No. 75, Series of 1992,Re: DPWH Advisory for Seismic Design of Bridges.

DPWH Design Guidelines, Criteria and Standards, Volumes 1 & 2(currently being updated)

DPWH Standard Specifications, Vol. II, Highways, Bridges & Airports,1995 ed.


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B. LOADING SPECIFICATIONS

(1) DEAD LOAD

Selfweight plus allowance for future superimposed dead loads suchas wearing surface and weight of public utilities.

(2) LIVE LOAD

Six Classes of Highway Loadings :

(Standard Designations)

M 13.5 equivalent to H 15-44 M 18 equivalent to H 20-44 M 22.5 equivalent to H 25 MS 13.5 equivalent to HS 15-44 MS 18 equivalent to HS 20-44 MS 22.5 equivalent to HS 25


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M 13.5 27 kN (3 tons) 108 kN (12 tons) 15 tons GVW

M 18 36 kN (4 tons) 144 kN (16 tons) 20 tons GVW

M 22.5 45 kN (5 tons) 180 kN (20 tons) 25 tons GVW

MS 13.5 27 kN 108 kN 108 kN 27 tons GVW

MS 18 36 kN 144 kN 144 kN 36 tons GVW

MS 22.5 45 kN 180 kN 180 kN 45 tons GVW

ST

D

D

T

UC

LO

NG

4.27 m

4.27 m 4.27 to 9.14 m


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Clearance andLoad Lane Width

3.04m (10)

0.60 m

(2)

0.60 m

(2)

1.84 m

(6)

0.10 W

0.10 W 0.40 W 0.40 W

0.40 W0.40 W

14 (4.27m) Variable

6 ( 1

. 8 4 m

)

W = the combined weight of the first two axles

V = variable length 4.27 ~ 9.15 m. Spacing to beused is that which produces max. stresses.


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4.80 1.37 1.371.374.11 4.11 meters

Permit Design Live Load *

* P Loads (permit design live loads) are special vehicular loads that shall be appliedat the factored level in the Load Factor Design and at service level for fatigue considerationin steel structures.

116 107107107107107 107 kN

13 tons 12 tons 85 tons GVW


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Concentrated Load = 80 kN for Moment= 116 kN for Shear

Uniform Load = 9.40 kN per meter of load lane



L NELO

NG

M 13.5 and MS 13.5 Loading

M 18 and MS 18 Loading


M 22.5 and MS 22.5 Loading



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A heavy vehicle such as truck, trailer or vanoperated on any road or bridge violates the

law if it:

1. Exceeds the permissible single axle load of

13,500 kg. or 13.5 metric tons.2. Exceeds the maximum allowed gross vehicleweight as stipulated in Republic Act 8794 (Anti-Overloading Law) and its regulations publishedin 2001.


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MAXIMUM ALLOWABLE GROSS VEHICLE WEIGHT (GVW) PER R.A. 8794

TRUCKS / TRAILER DESCRIPTION MAX. ALLOWABLEGROSS WEIGHT

TRUCK WITH 2

AXLE (6 WHEELS)16,880

TRUCK WITHTANDEM REAR

AXLE 3 AXLES (10WHEELS)

27,250

TRUCK WITHTANDEM REAR

AXLE 4 AXLES (14WHEELS)

29,700

CODE 1-1

Based on the maximum allowable axle load of 13,500Kgs.

CODE 1-2

CODE 1-3


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TRUCKS / TRAILER DESCRIPTION MAX. ALLOWABLEGROSS WEIGHT

TRUCK SEMI-TRAILER WITH 3

AXLE (10 WHEELS)

30,380

TRUCK SEMI-TRAILER 4 AXLE

(14 WHEELS)30,380

TRUCK SEMI-TRAILER 4 AXLE

(14 WHEELS) 30,380


CODE 11-1

CODE 11-2

CODE 12-1


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MAXIMUM ALLOWABLE GROSS VEHICLE WEIGHT (GVW) PER R.A. 8794 Based on the maximum allowable axle load of 13,500Kgs.

CODE 11-11

CODE 12-2

CODE 11-3

TRUCKS / TRAILER DESCRIPTIONMAX. ALLOWABLE

GROSS WEIGHT

TRUCK SEMI-TRAILERWITH 5 AXLE (18

WHEELS)37,800

TRUCK TRAILER WITH 2AXLE AT MOTOR

VEHICLE AND 3 AXLE ATTRAILER (18 WHEELS)

30,378

TRUCK TRAILER WITH 2AXLE AT MOTOR

VEHICLE AND 2 AXLE ATTRAILER (14 WHEELS)

30,380


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GROSS WEIGHT

TRUCK TRAILERWITH 2 AXLE AT

MOTOR VEHICLEAND 3 AXLE AT

TRAILER (18

WHEELS)

36,900



TRAILER (22WHEELS)

41,000



TRAILER (18WHEELS

37,800


CODE 11-12

CODE 12-3

CODE 12-11


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GROSS WEIGHT



TRAILER (22WHEELS)

36,900


CODE 12-12


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(3) IMPACT

Impact , I = 15.24 / ( L + 38)

where : I = impact fraction (maximum of 30%)L = span length in meters

(4) SIDEWALK LOADING

For spans up to 7.92 m .4070 Pa

For spans 7.92 to 30.5 m...2870 Pa

For spans > 30.5 m ..p =[ 1435 + 43800 / L ] [ (1.67 - W) / 15.2] Pa

L = span length, m W = sidewalk width, m


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(5) WIND LOAD

Superstructure Design

For trusses and arches : 3.59 kPa

For girders and beams : 2.39 kPa

Based on 160 km per hour wind velocity.

Substructure Design

Force transmitted to the substructure by the superstructure plus the forces applieddirectly

to the substructure by wind load :

WLSUBSTRUCTURE

= 1.92 kPa ( 40 psf )

(6) THERMAL FORCE

Provisions shall be made for stresses or movements resulting from variation in temp.Under local condition the range of temperature rise and fall could be taken as : + 12.5 oC


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20

Elevation of Passage

Deck Type

Through Type


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21

Alignment

Curved Type

Straight Type


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22

Structural Type

Girder Type

Rigid Frame Type

Arch Type


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23

Structural Type

Cable Stay

Suspension Type


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24

2. BRIDGE ENGINEERINGTERMINOLOGY


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25

Bridge Composition

Superstructure


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27

Superstructure


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28

Superstructure


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29

Substructure


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30

Substructure


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DEPARTMENT OF PUBLIC WORKS AND HIGHWAYS

BRIDGE PLANNING &

DESIGN

GENERAL PROVISIONS


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1. Navigable river At least 3.75 meters from the designflood level (DFL)

2. Hydraulic At least 1.50 meters for streams

carrying debris At least 1.00 meters for others

3. Highway/Underpass/Tunnel At least 4.88 meters

VerticalClearances


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A. Bridge Alignment

1. Normal bridge A transverse structureperpendicular to the bank of the riveror creek.

2. Skew bridge A transverse structurehaving an angle of less than 90 0 fromthe bank of the river creek.

3. Curved bridge When the structure orportion of the structure is within andfollowing the horizontal curvealignment of the road.

GEOMETRICS


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No. of Lanes Min. RoadwayWidth

Min. No. of Girders

1 Lane

2 Lanes2 LanesMore than 2lanes

4.00 meters

6.70 meters7.30 metersvariable

3 girders

4 girder (rural)4 girders(urban)Not less than 6

girders

B. Span of Bridges

Odd number of spans shall be preferably usedto avoid a pier at the center of river or creek.

NUMBER OF GIRDERS IN RELATION TO NUMBER OF

LANES


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C. Determination of Length of Bridge

1. Sketch the proposed slopes of thegrouted riprap following the slope of thebanks as close as possible (1:1 for cut, 1-1/2:1 for fill).

2. Determine the top of roadway elevationbased on the maximum flood waterlevel, freeboard and depth of girders.

3. The intersections of the slopes of groutedriprap and the top of the roadwayelevation represent the length of bridge

required.


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D. Types/Classification of Superstructure

According to Materials Used

1. Timber Bridge

2. Concrete Bridge

a. Reinforced Concreteb. Prestressed Concrete

3. Steel Bridge

a. Steel Plate Girderb. Steel I-Beamc. Steel Trussd. Steel Box Girder


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According to Usage

1. Temporary a bridge designed for a short

life span2. Permanent a bridge with a designed life

span of at least fifty (50) years before it iscompletely replaced

According to System of Design

1. Simple Spans

2. Continuous Spans3. Cantilever Span4. Suspension Bridge5. Cabled Stayed


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E. Recommended Limits of Span of DifferentSuperstructure in the Philippines

1. Timber Trestle Bridge For span not morethan 6.00 meters

2. Concrete Bridge

a) Reinforced Concrete Precast Slab orReinforced Flat Slab Span from 6.00mto 12.00m.b) Reinforced Concrete Deck Girder(RCDG) span from 8.00m to 24.00m.c) Reinforced Concrete Box Girder span

from 22.00m to 30.00m.


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d) Reinforced Concrete Hollow Slab Bridge

span from 10.0m to 20.0m.

e) Prestressed Concrete Bridge

- Channel Beams

span from 11.00mto 14.0m.- Tee Beams span from 15.00m to

18.00m.- I-Beams span from 15.00m to45.00m.- Box Girders span over 30.00m.


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3. Steel Bridges

a) Steel I-Beam span from 15.00 to 30.00m.

b) Steel Plate Girder span from 20.00m to50.00m.c) Steel Box Girder span from 30.0m to 100m.d) Bailey Bridge span from 9.00m. to 30.00m.

e) Steel Truss span from 40.00m to130.00m.4. Suspension Bridge span from 70.00m and over.

5. Cable Stayed Bridge For span from 70.00m and

over.


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SUBSTRUCTURE

A. Factors in Selecting the Type ofSubstructure

1. Abutment

a) Height of fill at the approaches.b) Kinds of superstructure to be used.

c) Scouring character of river bank.d) Soil encountered at the abutment

foundation.


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2. Pier

a) Velocity of current and nature of drift.b) Kinds of superstructure to be used.

c) Soil encountered at the pierfoundation.d) Direction of flow of the river with

respect to the longitudinal axis of the

bridge.e) Profile along the centerline of thebridge.


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B. SubstructureElements

1. Abutment

Two Basic Categories:

a. Open End Abutments- Diaphragm or integral

type- Seat type- Spill through type


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b. Closed Type Abutments

- Cantilever type

- Restrained type.

- Rigid frame type

- Cellular or vaulted type

- Gravity or semi-gravity type

- Reinforced earth type

Types of Abutment Commonly Used:- Abutments on pile bent- Abutments on two columns- Cantilever type


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2. Piers

Types of Piers Commonly Used- Piers with solid shaft- Piers with two columns- Piers with single column

- Piers on pile bentC. Foundation

Factors in Selecting the Type of

Foundationa. The height of the substructure

b. Characteristics of the foundation soil

at bridge site.


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Requirements for the Use of the DifferentTypes of Piles

Piling shall be considered when footingscannot be founded on rock or other solid

foundation material. Penetration for any pile shall be not lessthan 3.00m in hard cohesive or densegranular material nor less than 6.00m in

soft cohesive or loose granular material.


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Type of Piles

1. Timber Pile

used for temporary construction,revetments, fender and similar work.2. Reinforced Concrete Piles used as foundation

piles (Precast or Cast-in-Place) for bridges.3. Steel Piles used where hard driving is

expected.4. Composite Steel/Concrete Piles used if the

portion of the pile is exposed to corrosiveenvironment and hard driving is expected

5. Prestressed Concrete Piles

used as foundationpiles for bridges where larger bearing capacityand longer piles are required.

PORTAL STRUT


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STEEL TRUSS BRIDGE

TOP CHORD

BOTTOM CHORD

END POST

DIAGONAL MEMBER

VERTICAL MEMBER

PORTAL STRUT

PORTAL BRACING


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STEEL TRUSS BRIDGE


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STEEL EXPANSION

JOINT


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NORMAL BRIDGE ALIGNMENT


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REINFORCED CONCRETE GIRDER

MAIN GIRDER

INTERIOR DIAPHRAGM


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PRESTRESSED CONCRETE GIRDER BRIDGEPROVIDED W/SHEAR BLOCKS


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EXPANSION DAM


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CABLE RESTRAINER


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SOLID SHAFT

FOOTING

COPING

PIER ELEMENTS


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PEDESTAL

SHEAR

BLOCK


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ARCH BRIDGE


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DIAPHRAGM WALL


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BOD SEMINAR PRESENTATION


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SEISMIC DESIGN OF BRIDGES

COURSE OUTLINE :

1. HISTORICAL BACKGROUND

2. DESIGN PHILOSOPHY

3. GOVERNING REGULATION

4. AASHTO 1996 SEISMIC DESIGN PROVISIONS

5. ANALYSIS PROCEDURE

6. BRIDGE RETROFITTING


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SEISMIC DESIGN


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YEAR CRITERIA /SPECIFICATION

PROVISIONS

1987NSCP VOL.II, 1ST EDITION (BASED ONAASHTO 13TH EDITION, 1983)

(a) Equivalent Static Force MethodEQ = CFWC = Response Coefficient (not less than 0.10) for

various depths of alluvium to rocklike material)F = Framing factor, (1.0 for single column, 0.80 for

structures with continuous frames)(b) EQ = 0.10(DL +0.50LL)(c) For complex structures, Response Dynamic

Approach is recommended.

1992

DPWH Department

Order No. 75 Seriesof 1992.DPWHAdvisory for SeismicDesign of Bridges

Amended all existing guidelines on seismic design.

Prescribed the 1991 AASHTO 1991 or latest editionas the reference specification Recommended new design concepts for seismicresistant design of bridges.

SEISMIC DESIGN PHILOSOPHY


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It is not economically practical to proportion bridge members so that they will remainundamaged after a severe earthquake, but a failure that leads to collapse of the

structure must not be allowed to occur. For this reason it is essential to design bridgestructures with sufficient ductility to dissipate the energy of earthquake motions withoutreducing the strength of the bridge to the point of collapse.

The basic philosophy in seismic design of bridges is to design a bridge to resist smallto moderate earthquakes in the elastic range without significant damage. In the event ofa large earthquake, bridges and their components may suffer damage but should notcause collapse of all or any part of the bridge. Where possible, the damages that doesoccur should be readily detectable and accessible for inspection and repair.

The bridge should be designed so as to be usable by emergency traffic after simple and

very rapid repairs and should be capable of permanent repair to an acceptable level forboth vehicular and seismic loading.

Essential bridges are required to function during and immediately after an earthquakeand must meet additional requirements. These are bridges designated as essential onthe basis of criteria such as social/survival and security / defense.

Definition for importance of a bridge structure is subjective influenced by factors


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such as: ADT, available detour, use for emergency vehicles, replacement cost, andthe nature and importance of the route being crossed by the bridge.

DESIGN APPROACH

The analytic approach in seismic design of bridges includes the determination ofthe member forces from an elastic design response spectrum coefficient.The design forces for each bridge component are then obtained by dividing the

elastic forces by a Response Modification Factor (R). Well confined, ductilecolumns are designed for lower-than-expected forces obtained from the analysis.Columns joints are designed and detailed to deform in a plastic manner when theseismic forces exceeds the lower design forces. This approach is completelydifferent than the procedures used in the earlier AASHTO Standard Specifications.

Design displacements are considered as important because of many loss-of-spantype failures in the past earthquakes attributed in part to relative displacementeffects. Thus minimum support lengths at abutments, piers and hinge seats arespecified to prevent this type of failure.

Anchors and connections are important elements in maintaining the overall integrityf b id Th f bl i d i f ifi d


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of a bridge structure. Therefore reasonably conservative design forces are specifieduse in their design. An additional requirement to prevent significant relativedisplacement is to provide horizontal linkages between adjacent sections of the

superstructures using cables or an equivalent mechanism. Deck continuity can alsobe utilized to provide for continuity.

Current design and analysis of bridges to resist earthquakes now include:

+ Force level defined as seismic design spectra+ Abutment stiffness effects are considered

+ The effects of ductility are considered

+ Modal dynamic elastic analysis is used as a routine design tool

+ Introduction of continuity to mobilize the maximum number of bridge components

+ Consideration of soil-structure interaction effects.

GOVERNING REGULATION


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DEPARTMENT ORDER NO. 75, Series of 1992SUBJECT : DPWH Advisory for Seismic Design of BridgesJuly 17, 1992

The threat of earthquakes occurring in the Philippines can no longer bediscounted. Past and recent events have shown devastating effects ofearthquakes not only on buildings but also on highways and bridges. In

addition to the loss of lives, the recent Cabanatuan and Baguioearthquakes caused the closure of many highways and the collapse ofmany bridges which are designed based on older AASHTO StandardSpecifications resulting in millions of pesos in repair and/or replacements.

Considering that highways and bridges are the main arteries in bringingrelief to victims of earthquakes and other calamities, they should beserviceable at all times especially during emergencies.

GOVERNING REGULATION

DEPT ORDER NO 75 cont


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In modern seismic design of bridges, the basic design philosophy is for thebridge to resist small to moderate earthquakes in the elastic range withoutsignificant damage. In case of large earthquakes, a bridge may suffer damagebut this should not cause collapse of all or any of its parts and such damageshould readily be detectable and accessible for inspection and repair.

Therefore, to mitigate, if not prevent damage/s to bridges due to earthquakes,and for the guidance of engineering professionals and DPWH engineersparticularly those undertaking the design of bridges, the DPWH is issuing thisADVISORY :

1. As a minimum requirement, the design of bridges shall conform with

the current AASHTO Standard Specifications for Highway Bridges, 14thEdition, and the Guide Specifications for Seismic Design (1989 or latestedition) or the 1991 AASHTO Standard Specifications adopting the GuideSpecifications for Seismic Design (AASHTO Interim Specifications - Bridges)

DEPT ORDER NO.75 cont..


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DEPT ORDER NO.75 cont..

2. Design Concept to be adopted shall be as follows :

a) Continuous bridges with monolithic multi-column bents have highdegree of redundancy and are the preferred type of bridge structureto resist seismic shaking. Deck discontinuities such as expansion joints

and hinges should be kept to an absolute minimum . Suspended spans,brackets, rollers, etc are not recommended.

b) Where multi-span simple span bridges are justified, decks should becontinuous.

c) Restrainers (horizontal linkage between adjacent span) are required at

all joints in accordance with the AASHTO Guide Specifications forSeismic Design and generous seat widths at piers and abutmentsshould be provided to prevent loss-of-span failures.

DEPT ORDER NO. 75 cont... d) Transverse reinforcements in the zones of yielding is essential to the

successful performance of reinforced concrete columns during


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successful performance of reinforced concrete columns duringearthquqkes. Transverse reinforcement serves to confine the mainlongitudinal reinforcement and the concrete within the core of the

column, thus preventing buckling of the main reinforcements.e) Plastic hinging should be forced to occur in ductile column regions of

the pier rather than in the foundation unit. A scheme to protect theabutment piles from failure is often accomplished by designing thebackwall to shear-off when subjected to the design seismic lateral

force that would otherwise fail the abutment piles.f) The stiffness of the bridge as a whole should be considered in the analysis.

In irregular structures, it is particularly important to include the soil-structure interaction.

This Advisory amends the existing DPWH Guidelines on the SeismicDesign of Bridges and shall take effect immediately.

(Sgd) JOSE P. DE JESUSSecretary

FIG. 2A ILLUSTRATING THE PROVISIONSOF DPWH D.O. No. 75


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MONOLITHICABUTMENT

CONTINUITYMINIMUMJOINTS

GENEROUSSEAT WIDTH

RESTRAINERS

PLASTICHINGES

MULTI-COLUMN BENT IS PREFERRED OVER SINGLE COLUMN PIERS THE STIFFNESS OF THE WHOLE BRIDGE SHOULD BE COSIDERED IN THE ANALYSIS TRANVERSE REINFORCEMENT AT REGIONS OF YIELDING (PLASTIC HINGES)


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Deck continuity


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Assessment of Seismic Deficiencies


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& Retrofitting TechniquesI. Continuity & Restrainers

Deficiencies with respect to continuity often result in totalloss of support and falling of a span

Bridges having deficiencies include:

Simply-supported spans on sliding bearings withinadequate seat width

Continuous spans with sliding supports within the span

Pinned or fixed bearings with very low lateral orlongitudinal load capacity

Sliding supports that have to be guided in the slidingdirection. Guides may be unable to resist transverseload or structure can jump out of guides that are toosmall

Solution


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Restrainers

Solution

Seat type piers (R.C. Superstructures)

The main purpose of restrainers is to prevent spans fromfalling off their supports during the maximum credible EQ.

Restrainer Cable

TYPICAL RESTRAINER DETAILS


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Restrainer at Pier With

Positive Tie to Pier

Restrainer Cable

Restrainer at Pier Without

Positive Tie to Pier


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RestrainerCable

Vertical Motion Restrainer


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C bl R i

Solution


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Cable Restrainers


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TYPICAL SHEAR BLOCK (restrainer) DETAILS


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A

A SHEARBLOCKS

END DIAPHRAGMS

SHEAR

BLOCK

Additional SlabReinforcement

Induced Cra ck

ENDDIAPHRAGMS

SHEAR

BLOCKS

2. @ Expansion Ends1. Continuous Deck Slab

SECTION AA SECTION AA

Solution:


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PROVISION OF CONCRETE SHEAR BLOCKS(restrains both longitudinal and transversemovement of the superstructure)

Steel Longitudinal Shear Keys


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Transverse shear keys


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II. Bearings

Usually a loss-of-support failure results in thecollapse of the span and is considered to beunacceptable while less drastic failures may beconsidered as possibly acceptable

The most common modern bearing is theelastomeric bearing pad consisting of steel platesin layers alternating with rubber or anotherelastomer

Assessment of Seismic Deficiencies &Retrofitting Techniques

Luzon 1990Damage


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Toppling of bearings

Solution


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Bearing embedment in concrete

This will prevent shear failure and toppling of the bearings.

In addition, if spans become displaced from the bearings, theconcrete cap will prevent collapse.

New concrete cap


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Kobe 1995Damage


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Loss of support failure

Solution


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Supplementalsupport

Seat widening

Assessment of Seismic Deficiencies &


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III. Columns and Piers

Key considerations for column & piers:

For bridges designed to most codes,columns will almost always be expected toyield during strong seismic shaking.Sudden loss of flexural or shear strengththat result in structural collapse must beavoided. In the case of existing bridges,such conditions must be corrected.

All possible modes of column failure mustbe assessed in terms of their effects on theglobal stability of the structure.

Retrofitting Techniques



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Common column & pier deficiencies:

Inadequate development of vertical steel due to inadequatelap splice between vertical bars and dowels.

Splicing of column bars and dowels at column sectionswhere the development of plastic moments are required,thus limiting the length of hinging.

Insufficient amount of transverse reinforcement resulting inpoor confinement of the concrete core and insufficient shearstrength to permit the development of flexural hinging inthe column.

Poor detailing of confinement reinforcement, including largespacing of transverse & longitudinal bars, inadequate endanchorage of transverse reinforcement, and lack ofsufficient supplementary core ties in larger rectangularcolumn sections.

Insufficient flexural strength and ductility.

Retrofitting Techniques


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Damage


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DamageColumn failure - lack of ductility

San FernandoEarthquake 1971


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Solution


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Steel Jackets for Columns & Piers

An effective solution to column failure problems is pre-fabricatedsteel jackets to provide passive confinement

Characteristics of column jacketing are: Prefabricated steel jacket is usually circular or elliptical in shape

and annular space is grouted. A short gap at the end(s) isprovided to avoid crushing failure.Decreases tendency for buckling of the column longitudinal bars.Improves column ductility.Increases shear resistance of columnFull height or partial height jackets may be utilized asappropriate.

Caution : Improperly detailed jacketing scheme may force flexural orshear failure into foundations or cap beam creatingunfavourable failure mode.

Solution


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Steel Jackets

Solution

Solution


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Concrete Jackets

Column Steel Jacket


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Extended column spiralsinto coping, min. = D/2


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. . . . . . . . . . . . .

. . . . . . . . . . . .

Column Section

D

d

H

Extended columnspirals intofooting, min.=D/2

Column End RegionH/6, D, or 1 8

Column End RegionH/6, D, or 18

dd

TYPICAL PIER DETAILS

16mm f @300 o.c .

Extended Pile Reinf.w/ hoops or ties



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VI. Foundations

Seismic retrofitting of foundations is one of the most difficultand costly aspects of retrofitting works and often involves adisruption of service

Deficiencies in foundations include:

Undersize footings or inadequate number of pilesInsufficient flexural and shear strength of footings or pilecapsLack of top steel in footings or pile capsInadequate anchorage of piles into capsInsufficient horizontal shear capacity of column-footingdue to insufficient vertical reinforcement at interfaceInadequate anchorage of vertical column bars in footingsExcessive movements due to liquefaction.

Modes of failure for spread footingsDamage


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Modes of failure for pile footingsDamage


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Footing Retrofit

Solution


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g


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III DESIGN PROCEDURE


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III. DESIGN PROCEDURE

1. Preliminary layout of the proposed bridge.(General Plan and Elevation)

- Review hydraulic/hydrologic analyses to determine the

required waterway opening and bridge elevation.

- Survey data (topographic map of bridge site, profiles, rivercross sections, water elevations)

- Bridge geometric requirements such as vertical/ horizontalalignments, roadway width, sidewalk/ shoulder width, medianwidth and vertical clearance.

- Preliminary selection of the types of superstructures,substructures and foundations.

TOTAL BRIDGE LENGTHBased on Required Waterway Width, Minimum Vertical Clearance, etc


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OWL

MFL

MINIMUM CLEARANCE :1.0 m (no debris)1.5 mor as required for navigation TOP OF ROADWAY

ELEVATION

BOTTOM OFGIRDER EL..

SLOPE

SLOPE

(PROFILE ALONG THE CENTERLINE OF BRIDGE)

Fig. 4 PRELIMINARY LAYOUT OF A PROPOSEDBRIDGE

2. Establish the design criteria andspecifications


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(General Notes)

- Design Specifications / Standards

- Design Live Load

- Design Stresses

- Seismic design criteria :

Ground acceleration coefficient., AImportance classification, ICSeismic Performance Category, SPC

- Materials specifications

- Construction specifications

Agas-Agas Bridge ProjectContract PackageV


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Contract Package VPhilippine-Japan Friendship Highway Rehabilitation Project(Visayas Section, Phase II)

3. Final selection of the type of structures.

Superstructures & substructures :


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Superstructures & substructures :

- Span Lengths

- Height of Substructures

- Size Limitations

Foundations :

- depth of scour

- depth of hard strata

- liquefaction potential of foundation materials

- magnitude of loads from superstructure


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5. Design of Substructures


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- Check for depth of scour.

- Check for liquefaction potential.

- Create a stick model of the bridge for structural analyses (see Fig.5)

- Analyze for various combination of loads(see AASHTO Table 3.22.1A for load combinations)(see Fig. 6 & 7, Seismic Design Flow Charts)

- Design pier coping and columns.

- Design pier footings and foundations.

- Detailing


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Documents

General and Seismic Provisions