DESIGN OF BRIDGES Required Design DataII. Design Criteria and StandardsIII. Design ProcedureIV. Design Revisions

REQUIRED DESIGN DATA : BRIDGE SITE TOPOGRAPHIC MAP Drawn to scale of 1:500 to 1:1000 depending on the width of the riverThe topo-map should be extended at least 200m upstream & downstream from the center line of the proposed bridge to obtain enough information for river control & training works Location plan showing the existing public and private structures that maybe 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, ordinary flood level & maximum flood level.C. RIVER CROSS-SECTIONS @ 50m interval extending 100 to 200 meters upstream and downstream from the pro- posed bridge indicating the experienced high and ordinary water elevations.

D. HYDRAULICS / HYDROLOGIC ANALYSIS

Topographic map showing the watershed area and point of interest Calculation of required waterway opening Scour Analysis Calculation of Design Flood LevelE. BORING DATA WITH SPT and GEOTECHNICAL REPORT Minimum of two deep borings shall be made at each abutment and preferably an additio- nal boring at each pier for multi-span bridges

Boreholes shall have minimum depth of 30m below the riverbed in ordinary soil or at least 3.0m in bedrock

Standard Penetration Test (SPT) at maximum interval of 1.50m and at every change in soil stratum

Analysis for liquefaction potential.

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 elevationGround surface topography

DEPARTMENT OF PUBLIC WORKS AND HIGHWAYS

BRIDGE DESIGN

IA - GENERAL PROVISIONS

1.Navigable riverAt least 3.75 meters from the design flood level (DFL)2.HydraulicAt least 1.50 meters for streams carrying debrisAt least 1.00 meters for others3.Highway/Underpass/TunnelAt least 4.88 meters

Vertical Clearances

A.Bridge Alignment

1.Normal bridge A transverse structure perpendicular to the bank of the river or creek.2.Skew bridge A transverse structure having an angle of less than 900 from the bank of the river creek.3.Curved bridge When the structure or portion of the structure is within and following the horizontal curve alignment of the road.

GEOMETRICS

B.Span of BridgesOdd number of spans shall be preferably used to avoid a pier at the center of river or creek.NUMBER OF GIRDERS IN RELATION TO NUMBER OF LANES

No. of LanesMin. Roadway WidthMin. No. of Girders1 Lane2 Lanes2 LanesMore than 2 lanes4.00 meters6.70 meters7.30 metersvariable3 girders4 girder (rural)4 girders (urban)Not less than 6 girders

C.Determination of Length of Bridge1.Sketch the proposed slopes of the grouted riprap following the slope of the banks as close as possible (1:1 for cut, 1-1/2:1 for fill).

2.Determine the top of roadway elevation based on the maximum flood water level, freeboard and depth of girders.

3.The intersections of the slopes of grouted riprap and the top of the roadway elevation represent the length of bridge required.

D.Types/Classification of SuperstructureAccording to Materials Used

1.Timber Bridge

2.Concrete Bridgea.Reinforced Concrete b.Prestressed Concrete

3.Steel Bridgea.Steel Plate Girder b.Steel I-Beamc.Steel Truss d.Steel Box Girder

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 is completely replaced

According to System of Design

1.Simple Spans 2.Continuous Spans 3.Cantilever Span 4.Suspension Bridge 5.Cabled Stayed

E.Recommended Limits of Span of Different Superstructure in the Philippines 1.Timber Trestle Bridge For span not more than 6.00 meters2.Concrete Bridgea)Reinforced Concrete Precast Slab or Reinforced Flat Slab Span from 6.00m to 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.

Reinforced Concrete Hollow Slab Bridge span from 10.0m to 20.0m.

Prestressed Concrete Bridge

-Channel Beams span from 11.00m to 14.0m.-Tee Beams span from 15.00m to 18.00m.-I-Beams span from 15.00m to 45.00m.-Box Girders span over 30.00m.

3.Steel Bridges

a)Steel I-Beam span from 15.00 to 30.00m.b)Steel Plate Girder span from 20.00m to 50.00m.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.Suspension Bridge span from 70.00m and over.5.Cable Stayed Bridge For span from 70.00m and over.

SUBSTRUCTUREA.Factors in Selecting the Type of Substructure1.Abutmenta)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.

2.Piera)Velocity of current and nature of drift.b)Kinds of superstructure to be used.c)Soil encountered at the pier foundation.d)Direction of flow of the river with respect to the longitudinal axis of the bridge.e)Profile along the centerline of the bridge.

B.Substructure Elements1.Abutment

Two Basic Categories:a.Open End Abutments-Diaphragm or integral type-Seat type-Spill through type

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

2.PiersTypes of Piers Commonly Used -Piers with solid shaft -Piers with two columns -Piers with single column -Piers on pile bentC.FoundationFactors in Selecting the Type of Foundationa.The height of the substructureb.Characteristics of the foundation soil at bridge site.

Requirements for the Use of the Different Types of PilesPiling shall be considered when footings cannot be founded on rock or other solid foundation material.Penetration for any pile shall be not less than 3.00m in hardcohesive or dense granular material nor less than 6.00m in soft cohesive or loose granular material.

Type of Piles1.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 corrosive environment and hard driving is expected 5.Prestressed Concrete Piles used as foundation piles for bridges where larger bearing capacity and longer piles are required.

II. DESIGN CRITERIA & STANDARDS

DESIGN SPECIFICATIONS

AASHTO Standard Specifications for Highway Bridges, Sixteenth 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 (Red Book)

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

B. LOADING SPECIFICATIONS 1) DEAD LOAD

Selfweight plus allowance for future superimposed dead loads such as wearing surface and weight of public utilities. 2) LIVE LOAD FOUR CLASSES OF HIGHWAY LOADINGS : M 13.5 equivalent to H 15-44 M 18 equivalent to H 20-44

FOUR CLASSES OF HIGHWAY LOADINGS : M 22.5 equivalent to H 25MS 13.5 equivalent to HS 15-44MS 18 equivalent to HS 20-44MS 22.5 equivalent to HS 25 M 13.5 27 kN 108 kN

M 18 36 kN 144 kN

M 22.5 45 kN 180 kN4.27 mSTANDARD TRUCK LOADING

MS 13.5 27 kN 108 kN 108 kN

MS 18 36 kN 144 kN 144 kN

MS 22.5 45 kN 180 kN 180 kN4.27 m 4.27 to 9.14 mSTANDARD TRUCK LOADING Concentrated Load = 60 kN for Moment = 87 kN for ShearUniform Load = 7.10 kN per meter of load laneM 13.5 and MS 13.5 LoadingLANE LOADING

Concentrated Load = 80 kN for Moment = 116 kN for ShearUniform Load = 9.40 kN per meter of load laneLANE LOADINGM 18 and MS 18 Loading Concentrated Load = 100 kN for Moment = 145 kN for ShearM 22.5 and MS 22.5 LoadingUniform Load = 11.75 kN per meter of load lane

3) IMPACT

Impact , I = 15.24 / ( L + 38) where: I = impact fraction (max. of 30%) L = span length in meters 4) SIDEWALK LOADING For spans up to 7.92m .4070 Pa For spans 7.92 to 30.5m...2870 Pa For spans > 30.5m ..p = [ 1435 + 43800/L ] [(1.67 - W)/15.2 ] L = span length, m W = sidewalk width, m

5) WIND LOAD

Superstructure Design For trusses and arches : 3.59 kPa For girders and beams : 2.39 kPa Based on 100 miles per hour wind velocity.

Substructure Design Force transmitted to the substructure by the superstructure plus the forces applied directly to the substructure by wind load : WL SUBSTRUCTURE = 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 : +10oC7) UPLIFT 100 % of the calculated uplift caused by any loading or combination of loading in which the live load plus impact load is increased by 100 percent. 150% of the calculated uplift at working load level

8) FORCE FROM STREAM CURRENT P = 515 k V2 where : P = pressure in Pascal (Pa) V = velocity of flow, m/sec k = 1 3/8 for square ends, 2/3 for circular piers or, 1/2 for angle ends where the angles 30o or less

9) BOUYANCY Buoyancy is considered where it affects the design of either substructure, including piling, or the superstructure.

dqbPaHH/3sa = Ka g Hd + 90o - q90oFig. 2 Computation procedure for active earth pressure, Coulomb Analysis Normal Time10) EARTH PRESSURE Calculated using the Rankines formula. However no structure shall be designed for less an equivalent fluid weight of 4.71 kN/m3 (30 pcf). Surcharge due to live load = 0.61m (2 ft) where : g = effective unit weight of soil f = effective angle of friction d = angle of wall friction (Table 5.5.2 B AASHTO)

1 +2Ka =Pa = 1/2 g H2 KaA = sin2 (q + f) B = sin2 q sin (q - d) C = sin (f + d) sin (f - b ) D = sin ( q - d) sin (q + b) ABCD

Fig. 3 Calculation of earth pressure, Mononobe- Okabe Analysis EarthquakeTimeFAILURE SURFACEACTIVE WEDGEGRAVITY WALLKh w(1 - kv ) wFAILURE SURFACEACTIVE WEDGECANTILEVER WALLKh wEAEEAEEAERHhakv wskh wswfidbActive wedge force diagram EARTH PRESSURE (cont.)(1 - kv ) w

EAE = 1/2 g H2 (1 - kv) KAESeismic Active Earth Pressure, EAE ha = 0.60 H EARTH PRESSURE (cont.)A = cos2 (f - q - b)B = cos q cos2 b cos ( d + b + q ) C = sin (f + d) sin (f - q - i)D = cos ( d + b + q ) cos (i - b )1 +2KAE =ABCD

where : H = height of soil face g = effective unit weight of soil f = effective angle of friction q = arctan [ kh / (1 - kv) ] d = angle of wall friction (Table 5.5.2 B AASHTO) kh = horizontal acceleration coeff. kv = vertical acceleration coefficient i = back fill slope angle b = slope of soil face

EPE = 1/2 g H2 (1 - kv) KPEMononobe-Okabe Analysis for Seismic Passive Earth Pressure, EPE EARTH PRESSURE (cont.)A = cos2 (f - q + b)B = cos q cos2 b cos ( d - b + q ) C = sin (f - d) sin (f - q + i)D = cos ( d - b + q ) cos (i - b )1 +2KPE =ABCD

11) SEISMIC LOAD

Specification : AASHTO, 1996 Fifteenth Edition, Division I-A, Seismic Design

Governing Regulation : DPWH Department Order No.75 Series of 1992, re: Seismic Design of Bridges

Design Parameters : Ground motion parameter defined as ground acceleration coefficient, A ( A = 0.40g is pre- sently being adopted for design of bridges throughout the Philippines)

Important Considerations :

- Relationship of the site to active faults. - Seismic response of the soils at the site. - Dynamic response characteristics of the whole structure. Site Effects as defined by site coefficient, Sdepending on soil profile at the bridge site.

ANALYSIS PROCEDURES :

Procedure 1 : Single Mode Spectral Method (Equivalent Static Lateral Force Method) - For regular bridges only.* - The method assumes single mode shape so that a single degree of freedom generalized parameter model can be formulated.

Procedure 2: Multi-mode Spectral Method (Dynamic Analysis) - Required for bridges with irregular geometry. - Performed using a computer program with space frame linear dynamic analysis capabilities. Ex. SAP 2000, STAAD III & STRUDL

* A regular bridge has no abrupt or unusual changes in mass, stiffness or geometry along its span and has no large difference in these parameters between adjacent supports(abutments excluded). For example a bridgemay be considered regular if it is straight or describes the sector of an arc not exceeding 90oand has adjacent columns or piers that do not differ in stiffness by more than 25 %.An irregular bridge is any bridge that does not satisfy the above definition.

DEPARTMENT ORDER NO. 75, Series of 1992 SUBJECT : DPWH Advisory for Seismic Design of Bridges July 17, 1992 The threat of earthquakes occurring in the Philippines can nolonger be discounted. Past and recent events have shown devastating effects of earthquakes not only on buildings butalso on highways and bridges. In addition to the loss of lives, the recent Cabanatuan and Baguio Earthquakes caused the closure of many highways and the collapse of many bridges which are designed based on older AASHTO Standard Specifications resulting in millions of pesos in repair and/or replacements.

Considering that highways and bridges are the main arteriesin calamities, they should be serviceable at all timesespecially during emergencies.

In modern seismic design of bridges, the basic designphilosophy is for the bridge to resist small to moderate earthquakes in the elastic range without significantdamage. In case of large earthquakes, a bridge may suffer damage but this should not cause collapse of allor any of its parts and such damage should readily be detectable and accessible for inspection and repair.

DEPT ORDER NO.75 cont..Therefore, to mitigate, if not prevent damage/s to bridges dueto earthquakes, and for the guidance of engineeringprofessionals and DPWH engineers particularly thoseundertaking the design of bridges, the DPWH is issuingthis ADVISORY : 1. As a minimum requirement, the design of bridges shall conform with the current AASHTO Standard Specifica- tions for Highway Bridges, 14th Edition, and the Guide Specifications for Seismic Design (1989 or latest edition) or the 1991 AASHTO Standard Specifications adopting the Guide Specifications for Seismic Design (AASHTO Interim Specifications Bridges)

2. Design Concept to be adopted shall be as follows : a) Continuous bridges with monolithic multi-column bents have high degree of redundancy and are the preferred type of bridge structure to 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 be continuous.

DEPT ORDER NO. 75 cont... c) Restrainers (horizontal linkage between adjacent span) are required at all joints in accordance with the AASHTO Guide Specifications for Seismic Design and generous seat widths at piers and abutments should be provided to prevent loss-of-span failures. d) Transverse reinforcements in the zones of yielding is essential to the successful performance of reinforced concrete columns during earthquakes. Transverse reinforcement serves to confine the main longitudinal 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 founda- tion unit. A scheme to protect the abutment piles from failure is often accomplished by designing the back- wall 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 Seismic Design of Bridges and shall take effect immediately. (Sgd) SEC. JOSE P. DE JESUS

MONOLITHIC ABUTMENTCONTINUITYMINIMUM JOINTSGENEROUSSEAT WIDTHRESTRAINERSPLASTIC HINGESFIG. 2A ILLUSTRATING THE PROVISIONS OF DPWH D.O. No. 75 for SEISMIC DESIGN OF BRIDGESMULTI-COLUMN BENT IS PREFERRED OVER SINGLE COLUMN PIERSTHE STIFFNESS OF THE WHOLE BRIDGE SHOULD BE COSIDERED IN THE ANALYSISTRANVERSE REINFORCEMENT AT REGIONS OF YIELDING (PLASTIC HINGES)

III. DESIGN PROCEDURE

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, river cross sections, water elevations) - Bridge geometric requirements such as vertical/ horizontal alignments, roadway width, sidewalk/ shoulder width, median width and vertical clearance. - Preliminary selection of the types of superstructures, substructures and foundations.

OWLMFLTOTAL BRIDGE LENGTHBASED ON WATERWAY WIDTH & MIN. VERT. CLEARANCEMINIMUM CLEARANCE :1.0 m (no debris)1.5 m or as required for navigationTOP OF ROADWAY ELEV.BOTTOM OF GIRDER EL.SLOPESLOPE(PROFILE ALONG THE CENTERLINE OF BRIDGE)Fig. 4 PRELIMINARY LAYOUT OF A PROPOSED BRIDGE

2. Establish the design criteria and specifications (General Notes)

- Design Specifications / Standards - Design live load - Design Stresses

- Seismic design criteria : Ground acceleration coefficient., A Importance classification, IC Seismic Performance Category, SPC - Materials specifications

- Construction specifications

3. Final selection of the type of structures. 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

4. Design of superstructures

- Deck slab (interior & exterior slab) Slab thickness Steel reinforcement (main rebars, distribution rebars )

- Design of main girders & cross beams (RCDG, prestressed I-girder, steel or concrete box girder, composite plate girder, etc.) - Design of steel trusses Main members (top & bottom chords, vert. & diag.) Floor system (stringers & floor beams) - Miscellaneous designs Bearings, railings, expansion dams, lighting etc. - Detailing

5. Design of Substructures

- 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) - Design pier coping and columns.

- Design pier footings and foundations.

- Detailing

FIG. 5 STICK MODEL FOR STRUCTURAL ANALYSIS

IV. DESIGN REVISIONS

1. When are revisions of bridge design necessary ? (Revision of Superstructure Design)

- To facilitate construction and/or shorten e.g., Revision from cast-in-place girder construction to precast / prestressed girders. - Change in span length or elevation. - To update the design with current / revised code provisions. - Faulty design sometimes resulting from inaccurate survey data / information. - Non availability of materials / equipment for construction.

(Revision of Substructure and Foundation Design)

- When actual soil conditions do not correspond with the design assumptions. - Insufficient penetration of test piles. - Required bearing capacity at footing elevation could not be attained. - Non-availability of materials / equipment for construction.2. Requirements for approval of revised plans : - Reasons/justifications for the proposed revisions - Revised structural analysis

- Boring Data / Pile Driving Data - Hydraulic analysis - Copy of approved plans - As-staked survey data Other Requirements :

- Redesigns could be done by the original designer/ consultant, the implementing office or the contractor when it is necessary for proper project implementation. - Redesigns shall have the concurrence of the original designer / consultant. - Revised plans should be approved by the official who approved the original plans

Thank YouandGod Bless !!!

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