Class Topics & Objectives. Bearings & Substructures. EGCE 406: Bridge Design. Load Transfer. Components of Bridge.

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1 EGCE 406: Bridge Design Bearings & Substructures Class Topics & Objectives Topics Bridge Bearing Bridge Substructures Loads on Substructure Abutment Piers Objective Students can identify and describe types of bridge bearings Students can describe the loads involved in the design of substructures. Students can describe pros and cons for each type of substructure Parts of the topics discussed in this class can be found in: Chapter 1-4 Praveen Chompreda Mahidol University 1 First Semester, Load Transfer Loads on the bridge must find a way to the ground Components of Bridge Superstructure Roadway Deck Live Load on Bridge Deck Slab Superstructure Girder Superstructure Substructure Abutment Abutment Superstructure Substructure Bearing Superstructure Roadway Deck Ground Foundation (Footing/ Pile) Substructure (Abutment/ Pier) Substructure Pier Abutment 3 4

2 Bearing Role of Bearing Forces and Movements Types Selection of Bearing 5 Bearing Bearing is a structural device positioned between bridge superstructure and substructure Roles of Bearing: Transmit load from superstructure to substructure Accommodate relative movements between superstructure and substructure Types: Fixed Bearing Rotational movement only Expansion Bearing Rotational movement Translational movement 6 Forces and Movements on Bearing Types of Bearing Forces on Bearing Vertical forces - from dead loads and live load Horizontal forces - from wind, earthquake Movements on Bearing Horizontal translation caused by creep, shrinkage, and thermal expansions. Rotations caused by traffic, construction tolerances, and uneven settlement of foundations Rocker Bearing Pin Bearing Roller Bearing Slider Bearing Elastomeric Bearing Curved Bearing Pot Bearing Disk Bearing If no movement is allowed, then the bearing must be able to resist the force due to the deformation 7 8

3 Rocker/ Pin/ Roller Bearing Rocker/ Pin/ Roller Bearing Mostly used for steel beams Can carry large loads Requires high clearance Corrosion can be a problem need regular inspections high maintenance cost Source: (2010) 9 10 Elastomeric Bearing Elastomeric Bearing with Slider Made up of natural or synthetic rubber Very flexible in shear but very stiff against volumetric change Can accommodate both rotational and translational movements through the deformation of pad Steel or fiberglass is typically used to reinforced the pad in alternate layers to prevent it from bulging under high load, allowing it to resist higher loads 11 Steel slider with Teflon (PTFE polytetrafluoroethylene) coated surfaces may be used in combination with elastomeric bearing to allow for more translations 12

4 Elastomeric Bearing Curved Bearing Source: (2010) Curved Surface allows for rotation Cylindrical Surface can rotate only about 1 axis Spherical Surface can rotate about any axes Slider surface coated with Teflon must be used to allow for the translation Can resist relatively large loads Curved Bearing Pot Bearing Source: (2010) Pot bearing consists of steel container ( Pot ) with elastomeric pad inside Can resist much larger loads than conventional elastomeric bearing Rotation is accommodated by deformation of the elastomer Sliding surface is used to allow for translation 15 16

5 Pot Bearing Disk Bearing Source: (2010) Hard elastomeric disk is used with metal key inside Metal key is used to resist horizontal loads Rotation is accommodated by deformation of the elastomer Sliding surface is used to allow for translations Which type of bearing should I use? Consider the following factors when selecting a bearing to use: Vertical and Horizontal Loads Translational and Rotational Movements Available Clearance (footprint/ height) Environment (corrosion/ temperature range) Initial Cost Maintenance Cost Availability Owner s Preference Bearing Capacity of Common Bearings 19 20

6 Types of Substructures Substructures Abutment-Type Substructures Abutment and Retaining Walls Anchored Walls Mechanically Stabilized Earth Walls Prefabricated Modular Walls Pier-Type Substructures Concrete Pier Steel Pier Composite Steel & Concrete Pier Types of Substructures Abutment & Pier Loads on Substructures Abutment Pier Loads from Superstructure Loads on Substructure Load Combinations 23 24

7 Loads from Superstructure Vertical Loads from Superstructures Dead Load of Structural and Nonstructural Components (DC) Dead Load of Wearing Surface (DW) Live Load (LL) and Impact (IM) Pedestrian Live Load (PL) Horizontal Loads from Superstructures Wind Load on Structures (WS) Wind Load on Live Load (WL) Earthquake Load (EQ) Vehicular Braking Force (BR), Centrifugal Force (CE), and Collision Force (CT) Creep (CR), Shrinkage (SH), Friction (FR), and Temperature (TG/ TU) 25 Loads on Substructures Vertical load acting on substructure Dead Load of Structural and Nonstructural Components (DC) Vertical Pressure from Dead Load of Earth Fill (EV) Horizontal loads acting on substructure Water Load and Stream Pressure (WA) Ice Load (IC) Wind Load on Structure (WS) Earthquake Load (EQ) Vehicular Collision Force (CT), Vessel Collision Force (CV) Horizontal Earth Pressure Load (EH) Earth Surcharge Load (ES) Live Load Surcharge (LS) 26 Wind Loads (WS, WL) WL WS (on Superstructure) WS (on Substructure) Vehicle Collision Forces (CT) Unless protected, abutments and piers located within a distance of 30.0 FT to the edge of roadway, or within a distance of 50.0 FT to the centerline of a railway track, shall be designed for an equivalent static force of 400 KIP, which is assumed to act in any direction in a horizontal plane, at a distance of 4.0 FT above ground. CT need not be considered for structures which are protected by: An embankment A structurally independent, crashworthy groundmounted 54.0-IN high barrier, located within 10.0 FT from the component being protected; Or a 42.0-IN high barrier located at more than 10.0 FT from the component being protected 27 28

8 Load Combinations Load Combinations Source: AASHTO (2002) 29 Source: AASHTO (2002) 30 Design of Abutment and Retaining Substructures Roles and Types Failure Limit States Loads on Abutment Roles and Types Roles of Abutment Provide support for bridge superstructure at the bridge ends Connect the bridge with the approach roadway Retain the roadway material (soil & rock) from the bridge span Types Abutment Open End Abutment Close End Abutment Retaining Structures Gravity Wall Cantilever Wall Anchored Walls Mechanically Stabilized Earth Walls Prefabricated Modular Walls 31 32

9 Types of Abutment Types of Abutment Open End Abutment Open End Abutment Close End Abutment Types of Abutment Types of Abutment Close End Abutment Open End Abutment Close End Abutment Has some slopes between abutment wall and roadway/ water channel below Requires relatively larger space Requires longer bridge span Allow for some roadway widening below bridge More economical Has no slopes between abutment wall and roadway/ water channel below Requires relatively smaller space (good for urban areas) Requires shorter bridge span No allowance for future widening More expensive to construct 35 36

10 Types of Retaining Structures Types of Retaining Structures Anchored Walls Types of Retaining Structures Types of Retaining Structures Mechanically Stabilized Earth Walls 39 40

11 Types of Retaining Structures Failure Limit States Abutment structures must be checked for: Global Stability Failure: Bearing Capacity (a) Overturning (b) Sliding Failure (c) Deep Seated Failure (d) Local Strength Failures: Compression Failure Bending Moment Failure Shear Deflection Etc Strength Limit States (Global) Loads on Abutment from Superstructure (a) (b) Vertical loads from superstructures Dead Load of Structural and Nonstructural Components (DC) Dead Load of Wearing Surface (DW) Live Load (LL) and Impact (IM) Pedestrian Live Load (PL) Horizontal loads from superstructures Wind Load on Structures (WS) (c) (d) Wind Load on Live Load (WL) Earthquake Load (EQ) Vehicular Braking Force (BR), Centrifugal Force (CE), and Collision Force (CT) T N 43 Creep (CR), Shrinkage (SH), Friction (FR), and Temperature (TG/ TU) 44

12 Loads on Abutment Itself Vertical loads acting on substructure Dead Load of Structural and Nonstructural Components (DC) Vertical Pressure from Dead Load of Earth Fill (EV) Loads on Abutment Horizontal loads acting on substructure Water Load and Stream Pressure (WA) Ice Load (IC) Earthquake Load (EQ) Vehicular Collision Force (CT), Vessel Collision Force (CV) Horizontal Earth Pressure Load (EH) Earth Surcharge Load (ES) Live Load Surcharge (LS) Earth Pressure (EH, ES, LS and DD) Earth pressure is a function of the: Type and unit weight of earth Water content Soil creep characteristics Degree of compaction Location of groundwater table Earth-structure interaction Amount of surcharge Earthquake effects Earth Pressure (EH) Basic earth pressure, p p h s k γ gz k h = coefficient of lateral earth pressure At-rest pressure coefficient, Ko Active pressure coefficient, Ka Passive pressure coefficient, Kp γ s = unit weight of soil z = depth below the surface of earth Force resultant is assumed to act at 0.4H from the base of wall 47 48

13 Earth Pressure (EH) Surcharge Loads (ES and LS) Constant horizontal earth pressure due to surcharge load is added to the basic earth pressure p kq s s k s = coefficient of earth pressure due to surcharge At-rest pressure coefficient, Ko Active pressure coefficient, Ka q s = uniform surcharge applied to the upper surface of the active earth wedge Source: AASHTO (2002) Loads on Abutment Live Load from Superstructure Loads on Abutment Earth Pressure and Surcharge Loads Concrete Approach slab H 51 Passive pressure is O ignored 52

14 Loads on Abutment Loads on Abutment Earth Pressure and Surcharge Loads Earth Pressure: Ph = ½ (EFP h )H 2 Pv = ½ (EFP v )H 2 Location at 0.4H instead of 1/3 EFP = Equivalent Fluid Pressure Concrete Approach slab H Earth Pressure and Surcharge Loads Pressures generated by the Live Load and Dead Load Surcharges: H L = Kw L H H D = Kw D H V L = w L (heel width) V D = w D (heel width) w L = h eq w D = slab thickness c V L V D Live load approach Concrete Approach slab H D W L W D H L H P v P v P h P h 0.5H 0.4H 0.4H Passive pressure is O ignored 53 Passive pressure is O ignored 54 Loads on Abutment Loads on Abutment Earth Pressure and Surcharge Loads Earth Pressure and Surcharge Loads Vertical Loads at the Bearing: DL and LL Horizontal Loads: BR (braking) CR (creep) SH (shrinkage) TU (temperature) BR CR+SH+TU DL LL V L V D Live load approach Concrete Approach slab H D W L W D H L H Dead Load of the abutment BR CR+SH+TU DL LL 3 V L V D 4 Live load approach Concrete Approach slab H D W L W D H L H P v P h 0.5H 2 P v P h 0.5H 0.4H 0.4H Passive pressure is O ignored 55 Passive pressure is O ignored 1 56

15 Design of Pier Substructures Types Failure Limit States Loads Design of RC Columns Piers Pier substructures may be designed using design procedures of columns Steel Concrete Composite Piers Reinforced Concrete Piers Piers Steel Truss Pier Source: (2005) 59 Source: (2005) 60

16 Piers Pier Shapes Piers may be Solid usually for short piers Hollow usually for taller piers to save weight (need large moment of inertia to prevent buckling and provide larger moment capacity for lateral loads) Pier Types Solid Wall Pier Single Pier (Hammer Head Type) Rigid Frame Piers Pier Types Steel Bridges 63 64

17 Pier Types Steel Bridges Pier Types Concrete Bridges Rigid Frame Pier Pier Types Concrete Bridges Pier Selection Factors that influences the selection of pier types includes: Types of superstructures Steel or Concrete Widths Location Over land or water Hydraulics Height (tall piers may be hollow to reduce weight) Space available Aesthetics 67 68

18 Pier Selection Guidelines Strength Limit States Pier structures must be checked for: Global Stability Failure: Overturning Local Strength Failures: Compression Failure Bending Moment Failure Shear Deflection Loads on Piers from Superstructure Vertical loads from superstructures Dead Load of Structural and Nonstructural Components (DC) Dead Load of Wearing Surface (DW) Live Load (LL) and Impact (IM) Pedestrian Live Load (PL) Horizontal loads from superstructures Wind Load on Structures (WS) Wind Load on Live Load (WL) Earthquake Load (EQ) Vehicular Braking Force (BR), Centrifugal Force (CE), and Collision Force (CT) Creep (CR), Shrinkage (SH), Friction (FR), and Temperature (TG/ TU) 71 Loads on Piers Itself Vertical load acting on substructure Dead Load of Structural and Nonstructural Components (DC) Horizontal loads acting on substructure Water Load and Stream Pressure (WA) Ice Load (IC) Wind Load on Structure (WS) Earthquake Load (EQ) Vehicular Collision Force (CT), Vessel Collision Force (CV) 72

19 Pier Load Analysis for Wind Loads Reinforced Concrete Columns Pure Axial (Ø=0.75) WL Sprial φp φ0.85p φ f ' ( A A ) A f n 0 c g st st y WS (on Superstructure) Tie φp φ0.80p φ f ' ( A A ) A f n 0 c g st st y Pure Flexure (beam) (Ø=0.90 for RC) WS (on Substructure) φmn φa ( sfy d a /2) Combined Axial and Flexure in on direction Interaction Diagram Investigate High Compressive Force Investigate High Bending (Low Compression) Reinforced Concrete Columns Axial Loads + Bending Moment Spiral vs. Tie columns Source: Wang et. al. (2006) 75 76

20 Reinforced Concrete Columns Biaxial Bending + Axial For high axial load Factored Axial Resistance when has eccentricity only in Y direction For low axial load P 0.1 φf ' A u c g P P P P M M rxy rx ry ux rx P 0.1 φf ' A u c g Muy 1.0 M ry 0 Factored Axial Resistance when has eccentricity only in X direction Factored Applied Moment in X and Y direction Factored Nominal Moment Capacity in X and Y direction For slender columns, must also determine the secondary moment due to P- Effect 77