004 Loading 12-04-14

Course # CE-5120

03 Credit Hours

Lecture # 04

Introduction to Bridge Engineering

Bridge EngineeringLecture # 04 Email: [email protected] 2Dr. Syed Mohammad Ali

Sequence of Presentation

• Bridge Site & Investigations– Reccy Survey

– Selection of Bridge Site

– Survey

– Geotechnical Studies

– Hydrological & Hydraulic Studies

– Geological & Seismological Studies

• Loads

– Gravity, Lateral, Deformation, Collision

– AASHTO LRFD HL-93

mailto:[email protected]


Bridge Site & Investigations

• Reccy Survey– Done by Client and Designer (consultant) combined

– Ideas are shared

– Constructability is important (workmanship, materials and equipment)

– First hand information is gathered

• Selection of Bridge Site– Shortest span (span = total length of the bridge)

– Feasible approach

– Stable foundation

– Environmentally less affecting

– Hydraulic disturbances are least

• Survey– Selection of instrument

– Selection of contour interval

– Capturing maximum details (poles, tress, boulders, HFL. Existing road/track etc.)

– L-section and X-section locations




• Geotechnical Studies– Bore logs are required

– Drilling for various reasons (bore logs, SPT etc.)

– Drilling types (percussion type, rotary type, diamond drilling)

– How many locations?

– Refraction Surveys


Waqas Ahmed

Sticky Note

The methods depend on the fact that seismic waves have differing velocities in different types of soil (or rock): in addition, the waves are refracted when they cross the boundary between different types (or conditions) of soil or rock. The methods enable the general soil types and the approximate depth to strata boundaries, or to bedrock, to be determined.



The 3 types of drilling methods commonly used in the northeastern U.S. are illustrated. Left to right:1. A hollow stem auger used for drilling in

unconsolidated material, primarily on environmental and geotechnical projects

2. a mud/air rotary drilling in overburden using a tri-cone roller bit

3. a down-the-hole hammer bit used in rotary percussion (air rotary) drilling in bedrock
















Advantages




Disadvantages




• Hydrological & Hydraulic Studies– Rainfall data

– Catchment area

– Flood calculations (probability based e.g. 50-yr & 100-yr return period)

– Type of piers/abutment

• Shape

• Number

• placement/location in flow)

• Geological & Seismological Studies– Geological features

• types of rocks,

• folds,

• faults etc.




• Geological & Seismological Studies– Seismological aspects

• potential of slip i.e. hazard

• quantification of hazard i.e. PGA

• mechanics of fault rupture

• directivity effects

• potential assessment of seismic hazard from multiple sources e.g. Hindu Kush Vs MBT in AJK/NWFP region


Waqas Ahmed

Sticky Note

Directivity is an effect of a fault rupturing whereby earthquake ground motion in the direction of rupture propagation is more severe than that in other directions from the earthquake source.


Loads

• “If there were No Loads, Every Body Could Have been a Bridge Engineer!”

• What is Load?

• Load Categories– Gravity Loads

– Lateral Loads

– Forces due to deformation

– Collision Loads

• Force Effects:

A deformation or a stress resultant, i.e. thrust, shear, torque/or moment, caused by applied loads, imposed deformation or volumetric changes



Loads

• Why to Quantify Reasonable Magnitude of each Load?

– The loads that a structure will be called upon to sustain, cannot be predicted with certainty.

– The strength of the various components cannot be assessed with full assertion.

– The condition of a structure may deteriorate with time causing it to loose strength.

• Gravity Loads– These are results of weight

– Act in downward direction toward the center of the earth. Such loads may be:

• Permanent Gravity Loads

• Transient Gravity Loads



Loads

• Gravity Loads– Permanent gravity loads are the loads that remain on the bridge for an extended period of time or

for the whole service life.

– Such loads include:

• Dead load of structural components and non structural attachments - DC

• Dead load of wearing surfaces and utilities – DW

• Dead load of earth fill –EV

• Earth pressure load -EH

• Earth Surcharge load-ES

• Downdrag-DD

• DC– In bridges, structural components are the elements that are part of load resistance system.

– Nonstructural attachments refer to such items as curbs, parapets, barriers, rails, signs , illuminators, etc.

– Load factors will be discussed in following slides



Loads

• Gravity Loads– Permanent gravity loads are the loads that remain on the bridge for an extended period of time or

for the whole service life.

• Down Drag (DD)

– It is the force exerted on a piles or drilled shaft due to the soil movement around the element. Such a force is permanent and typically increases with time.

– For details refer to AASHTO (LRFD) Section 10, Foundations.

• Gravity Loads : Transient Loads

– These loads change with time and may be applied from several directions

– Highly variable

– Loads include vehicular, rail or pedestrian traffic

• Engineer should be able to foresee

– which of these loads are appropriate for the bridge under consideration

– magnitude of the loads

– how these loads are applied for the most critical load effect.



AASHTO LRFD Loading

• Traffic Lane vs Design Lane– For design the Designer MUST fix the number of lanes that a bridge may carry

– Two such terms are used in the design of a bridge:

• Traffic lane

• Design Lane.

– Traffic Lane:

The traffic lane is the number of lanes of traffic that the Traffic Engineer plans for the bridge. Typically it is 3.6 m (12 ft)

– Design Lane:

Design lane is the lane designation used by the bridge engineer for the live load placement, equals 3m (10 ft)



AASHTO LRFD Loading

– Reference to figure:

PhD Thesis Dr. Akhtar Naeem Khan 1996 “Development of Design Criteria for Continuous Composite I-Beam Bridges with Skew & Right Alignment”



AASHTO LRFD Loading

• AASHTO LRFD uses a 3m (10 ft) Lane for design in which the vehicle is positioned 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 3.6m.[A3.6.1.1.1]

• The clear width is the distance between the curbs and/or barriers.

• The direction of traffic in the present and future design scenarios should be considered and the most critical cases should be used for design

• Additionally, there may be construction and/or detour plans that cause traffic patterns to be significantly restricted or altered. Such situations may control some aspects of the design loading

• Transverse positioning of trucks is automatically accounted for in the live-load distribution factors outlined in AASHTO


Waqas Ahmed

Sticky Note

If ratio=2.5 we will take 2 if = 2.9 we will wake 2 if =3.1 we will take 3 always take INTEGER part


AASHTO LRFD Loading

HL-93 Loading

• Highway Load developed in 1993

• The objective of this model is to prescribe a set of loads such that the sameextreme load effects of the HL- 93 model are approximately the same as theexclusion vehicles

• Some vehicles although above “legal” limits, were allowed to operate routinelydue to “grandfathering” provisions in state statutes. These vehicles are referred toas exclusion vehicles.

• Typically, these loads are short-haul vehicles such as solid waste trucks andconcrete mixers



AASHTO LRFD Loading

• This model consists of three distinctly different live loads:

❑ Design truck

❑ Design tandem

❑ Design lane load


Waqas Ahmed

Sticky Note

if we want to calculate the moment the distance between the load 32kips is kept to 14ft. 14 to 30ft variability in the spacing is to accommodate fatigue.


AASHTO LRFD Loading

• The design truck is the same configuration that has been used by AASHTO (2002) Standard Specifications since 1944 and is commonly referred to as HS20

• The H denotes highway, the S denotes semitrailer, and the 20 is the weight of the tractor in tons

❑ Design tandem

• The second is the design tandem

• It consists of two axles weighing 25 kips (110 kN) each spaced at 4 ft (1200 mm), which is similar to the tandem axle used in previous AASHTO Standard Specifications except the load is changed from 24 to 25 kips (110 kN)



AASHTO LRFD Loading

❑ Design lane

• The third load is the design lane load that consists of a uniformly distributed load of 0.64 kips/ft (9.3 N/mm) and is assumed to occupy a region 10 ft (3000 mm) transversely

• This load is the same as a uniform pressure of 64 lb/sft (3.1 kPa) applied in a 10-ft (3000-mm) design lane



AASHTO LRFD Loading

❑ HL-93

• The load effects of the design truck and the design tandem must each be superimposed with the load effects of the design lane load.

• This combination of lane and axle loads is a major deviation from the requirements of the earlier AASHTO Standard Specifications, where the loads were considered separately.

• These loads are not designed to model any one vehicle or combination of vehicles, but rather the spectra of loads and their associated load effects.



Q & A

Thanks!


004 Loading 12-04-14

Documents

types of drilling methods

mudair rotary drilling

diamond drilling

types percussion type

different types of soil

rotary type

general soil types

geotechnical projects2