SANA'A UNIVERSITY

FACULTY OF ENGINEERING

DEPT. OF CIVIL ENGINEERING

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Supervisors /

Dr. Muhammad Al-Gurafi

Dr. Fu'ad Sufian

Done By /

Muhammad Jamal AbuBakr AbdRabbih Ali

AC. No. 39/2007

Muhammad Jamal

Classification of Bridges :

1- Types by Kinds of Traffic :

- Highway bridge (trucks, cars)

- Pedestrian bridge (pedestrians, bicycles)

- Railway bridge (trains)

- Transit guideway (city trains, monorail)

- Other types (pipelines, utilities, industrial, aqueduct, airport structure)

2- Types by Traffic Position :

- Deck type :

1- Structural components under the deck

2- Preferred by drivers (can clearly see the view)

3- Requires space under the bridge

- Through type :

1- Structural components above the deck

2- Obstructed view (not a problem for railway bridges)

3- No structure under the bridge

- Half-through type :

3- Types by Material & Fabrications :

- Materials :

1- Masonry (brick, rock)

2- Timber

3- Reinforced Concrete (RC)

4- Prestressed Concrete (PC)

5- Iron

6- Steel

7- Aluminum

8- Composites

9- Plastics

- Fabrications :

1- Precast

2- Cast-in-place (RC/PC)

3- Pretensioned (PC)

4- Posttensioned (PC)

5- Prefabricated ( steel)

6- Rivet (steel)

7- Bolted (steel/ timber)

8- Composites

9- Welded (steel)

1- What are the classifications of bridges? Is there any relationship between them?

Give an example ?

4- Types by Structural System :

- Arch

- Beam (Girder)

- Truss

- Cantilever

- Cable-Stayed

- Suspension

- Others

Yes, there is a relationship between the type and classification of bridges

for example : Beam(Girder) Bridges

1- Widely constructed

2- Usually used for Short and Medium spans

3- Carry load in Shear and Flexural bending

4- Efficient distribution of material is not possible

5- Stability concerns limits the stresses and associated economy

6- Economical and long lasting solution for vast majority of bridges

7- Decks and girder usually act together to support the entire load in highway bridges

8- Common Materials :

- RC Beam

- Steel Plate Girder/ Box Girder

- Steel Truss Girder

- Prestressed Concrete Girders :

- I-Beam, U-Beam, T-Beam

- Segmentally Prestressed Box Beam

Simple

Cantilever

Continuous

9- Currently, most of the beam bridges are precast (in case of RC and PC) or prefabricated

10- Most are simply-supported

11- Some are made continuous on site

Components of Bridge : - Substructure

- Foundation Pile/ Spread Footing)

- Pier (Column)

- Abutment

- Superstructure

Any structures above bearing which support the roadway Wearing Surface.

- Common bridge components

- Bridge Bearings : carry the weight of the bridge and control the movements at

the bridge supports, including the temperature expansion and contraction.

- Bridge Dampers and Isolators : devices that absorb energy generated by

earthquake waves and lateral load.

- Bridge Pier : A wide column or short wall of masonry or plain or reinforced

concrete for carrying loads as a support.

- Bridge Cap : The highest part of a bridge pier on which the bridge bearings or

rollers are seated.

- Abutment : The load bearing floor of a bridge which carries and spreads the

loads to the main beams.

- Expansion Joints : accommodate the translations due to possible shrinkage and

expansions due to temperature changes.

2- What are the components of the bridge ?

Permanent Loads : - DD - Downdrag

- DC - Structural Components and Attachments

- DW - Wearing Surfaces and Utilities

- EH - Horizontal Earth Pressure

- EL - Locked-In Force Effects including Pretension

- ES - Earth Surcharge Load

- EV - Vertical Pressure of Earth Fill

Transient Loads : - BR - Veh. Braking Force

- CE - Veh. Centrifugal Force

- CR - Creep

- CT - Veh. Collision Force

- CV - Vessel Collision Force

- EQ - Earthquake

- FR - Friction

- IC - Ice Load

- LL - Veh. Live Load

- IM - Dynamic Load Allowance

- LS - Live Load Surcharge

- PL - Pedestrian Live Load

- SE - Settlement

- SH - Shrinkage

- TG - Temperature Gradient

- TU - Uniform Temperature

- WA - Water Load

- WL - Wind on Live Load

- WS - Wind Load on Structure

The number of lanes a bridge may accommodate must be established and is an important design

criterion. Two terms are used in the lane design of a bridge:

- Traffic lane

- Design lane

3- Complete the defination of these terms for type of loading ?

4- How to calculate the numbers of lanes ?

The traffic lane is the number of lanes of traffic that the traffic engineer plans to route across the

bridge. A lane width is associated with a traffic lane and is typically 12 ft (3600 mm). The design lane

is the lane designation used by the bridge engineer for live-load placement. The design lane width

and location may or may not be the same as the traffic lane. Here AASHTO uses a 10-ft (3000-mm)

design lane, and the vehicle is to be positioned within that lane for extreme effect.

The number of design lanes is defined by taking the integer part of the ratio of the clear roadway

width divided by 12 ft (3600 mm) [A3.6.1.1.1]. The clear width is the distance between the curbs

and/or barriers. In cases where the traffic lanes are less than 12 ft (3600 mm) wide, the number of

design lanes shall be equal to the number of traffic lanes, and the width of the design lane is taken

as the width of traffic lanes. For roadway widths from 20 to 24 ft (6000 to 7200 mm), two design

lanes should be used, and the design lane width should be one-half the roadway width.

AASHTO has 3 basic types of LL called the HL-93 loading (stands for Highway Loading, year 1993):

- Design truck

- Design tandem

- Design Lane

Live Load Combinations : 1- HL-93 Truck + Lane Load

2- Tandem + Lane Load

3- 90% of 2 Trucks and Lane Load (for negative moments at interior supports of continuous

beams) place two HS20 design truck, one on each adjacent span but not less than 15 m

apart (measure from front axle of one truck to the rear axle of another truck), with

uniform lane load.

- The loads in each case must be positioned such that they produce maximum effects

(max M or max V).

- The maximum effect of these 3 cases is used for the design.

5- What the basic types of LL according to AASHTO ? and What are the LL

comainations ?

Dynamic Load Allowance IM - Sources of Dynamic Effects :

1- Hammering effect when wheels hit the discontinuities on the road surface such as

joints, cracks, and potholes.

2- Dynamic response of the bridge due to vibrations induced by traffic.

- Actual calculation of dynamic effects is very difficult and involves alot of unknowns.

- To make life simpler, we account for the dynamic effect of moving vehicles by

multiplying the static effect with a factor.

IM

- Add dynamic effect to the following loads:

1- Design Truck

2- Design Tandem

- But NOT to these loads:

1- Pedestrian Load

2- Design Lane Load

Table 3.6.2.1-1 Dynamic Load Allowance, IM.

6- Why we need to calculate the Dynamic Load Allowance IM and Mutiple Presence ?

And How much ?

Effect due to Static Load Load

Effect due to Dynamic Load Load

Multiple Presence of LL - We’ve considered the effect of load placement in ONE lane

- But bridges has more than one lane

- It’s almost impossible to have maximum load effect on ALL lanes at the same time

- The more lanes you have, the lesser chance that all will be loaded to maximum at the

same time

- We take care of this by using Multiple Presence Factor

- 1.0 for two lanes and less for 3 or more lanes

- This is already included (indirectly) into the GDF Tables in AASHTO code so we do not

need to multiply this again

- Use this only when GDF is determined from other analysis (such as from the lever

rule, computer model, or FEM)

Table 3.6.1.1.2-1 Multiple Presence Factors m

Simplified Analysis : - AASHTO Distribution Factor

Refined Analysis : - Grillage Method

- Finite Element Modeling

The simplified distribution factors may be used if :

1- Width of the slab is constant

2- Number of beams, Nb > 4

3- Beams are parallel and of similar stiffness

4- Roadway overhang de < 3 ft*

5- Cross section conforms to AASHTO Table 4.6.2.2.1-1

7- What are the methods of analysis the girders ?

8- What are the requirements to use simplified distribution factor ?

Table 4.6.2.2.1-1 Common Deck Superstructure Covered in Articles 4.6.2.2.2 and 4.6.2.2.3

Vehicles per girder for concrete deck on steel or concrete beams; concrete t-beams; t- and doubl

t-sections transversely posttensioned together (SI units)

9- What are the equations to calculate the moment / shear distribution factor for

concrete deck with reinforced beams ( exterior / interior ) ?

a See Table 4.6.2.2.1-1 for applicable cross sections.

b Equations include multiple presence factor; for lever rule and the rigid method engineer must

perform factoring by m.

c Not applicable =N/A.

Where :

S = girder spacing (mm)

L = span length (mm)

ts = slab thickness (mm)

Kg = longitudinal stiffness parameter (mm4)

Kg = n(Ig + Aeg2), where

n = modular ratio (Egirder/Edeck)

Ig = moment of inertia of the girder (mm4)

eg = girder eccentricity, which is the distance from the girder centroid to the middle centroid of the

slab (mm)

A = girder area (mm2)

de = distance from the center of the exterior beam and the inside edge of the curb or barrier (mm)

θ = angle between the centerline of the support and a line normal to the roadway centerline

Modeling Steps : 1- Layout Lines

2- Deck Sections

3- Abutments

4- Bents

5- Diaphragms

6- Bearings

7- Foundation Springs

8- Restrainers

9- Parametric Variations

10- Bridge Object definitions

11- Update of linked model

12- Lanes

13- Vehicles/Vehicle Classes

14- Analysis Cases

10- What are the steps to model the bridge using SAP2000 ?

To account for the variability on both sides of the inequality in the Eq.

Resistance ≥ effect of the loads

the resistance side is multiplied by a statistically based resistance factor φ, whose value is usually

less than one, and the load side is multiplied by a statistically based load factor γ , whose value is

usually greater than one. Because the load effect at a particular limit state involves a combination of

different load types (Qi) that have different degrees of predictability, the load effect is represented

by a summation of γiQi values. If the nominal resistance is given by Rn, the safety criterion is

Because this equation involves both load factors and resistance factors, the design method is called

load and resistance factor design (LRFD). The resistance factor φ for a particular limit state must

account for the uncertainties in

- Material properties.

- Equations that predict strength.

- Workmanship

- Quality control

- Consequence of a failure

The load factor γi chosen for a particular load type must consider the uncertainties in

- Magnitudes of loads

- Arrangement (positions) of loads

- Possible combinations of loads

In selecting resistance factors and load factors for bridges, probability theory has been applied to

data on strength of materials, and statistics on weights of materials and vehicular loads. Some of

the pros and cons of the LRFD method can be summarized as follows:

Advantages of LRFD Method:

1- Accounts for variability in both resistance and load.

2- Achieves fairly uniform levels of safety for different limit states and bridge types

without involving probability or statistical analysis.

3- Provides a rational and consistent method of design.

4- Provides consistency with other design specifications (e.g., ACI and AISC) that are

familiar to engineers and new graduates.

11- Define the LRFD ( Load and Resistance Factor Design ) ? And What are the

types of limit states ?

Disadvantages of LRFD Method:

1- Requires a change in design philosophy (from previous AASHTO methods).

2- Requires an understanding of the basic concepts of probability and statistics.

3- Requires availability of sufficient statistical data and probabilistic design algorithms to

make adjustments in resistance factors.

Limit States : 1- Service :

- Deals with restrictions on stress, deformation, and crack width under regular service

conditions.

- Intended to ensure that the bridge performs acceptably during its design life.

2- Strength :

- Intended to ensure that strength and stability are provided to resist statistically

significant load combinations that a bridge will experience during its design life.

- Extensive distress and structural damage may occur at strength limit state conditions,

but overall structural integrity is expected to be maintained.

3- Extreme Event :

- Intended to ensure structural survival of a bridge during an earthquake, vehicle

collision, ice flow, or foundation scour.

4- Fatigue :

- Deals with restrictions on stress range under regular service conditions reflecting the

number of expected cycles.

- 1.25DC + 1.50DW + 1.75(LL+IM) ( STRENGTH I )

- 1.00DC + 1.00DW + 1.00(LL+IM) ( SERVICE I )

12- Write the combination equation for these states (STRENGTH I and SERVICE I)