CIVL3310 Structural AnalysisCIVL3310 Structural AnalysisProfessor CC ChangProfessor CC Chang

Chapter 1: Chapter 1: Types of Structures and LoadsTypes of Structures and Loads

Introduction

• Structures refer to a system of connected Structures refer to a system of connected parts used to support a loadparts used to support a load• Tallest buildings• Long-span bridgesLong-span bridges

Structures

• Classification of structuresClassification of structures• Beam structuresBeam structures• Arch structuresArch structures• Truss structuresTruss structures• Domes and shellsDomes and shells• Columns and framesColumns and frames

• Structural elementsStructural elements• Tie rodsTie rods• BeamsBeams• ColumnsColumns

IssuesIssues

• How are they designed?How are they designed?

• How are they built?How are they built?

• How safe are they under earthquake, How safe are they under earthquake, typhoon, or terrorist attack?typhoon, or terrorist attack?

A typical structural engineering A typical structural engineering projectproject

Revisedstructural

design

No

Planning

Preliminary structural design

Structural analysis

Load estimation

Safety/serviceability

Construction

Yes

Government

Consultant

Contractor

Structural AnalysisStructural Analysis

Planning

Preliminary structural design

Structural analysis

Load estimation

Safety/serviceability

Construction

Yes

Structure

Factors:Load, Temperature, etc.

PerformanceDeformation, Stress, etc.

Objective of this CourseObjective of this Course

• To analyze, comprehend and present the behavior of structural systems under external effects

• Design loading for a structure is often Design loading for a structure is often specified in codesspecified in codes• General building codesGeneral building codes• Design codesDesign codes

Loads

• Types of loadTypes of load• Dead loadsDead loads

•Weights of various structural membersWeights of various structural members•Weights of any objects that are Weights of any objects that are

attached to the structureattached to the structure

Loads

The floor beam is used to support the 1.83m width of The floor beam is used to support the 1.83m width of lightweight plain concrete slab having a thickness of lightweight plain concrete slab having a thickness of 102mm. The slab serves as a portion of the ceiling for the 102mm. The slab serves as a portion of the ceiling for the floor below & its bottom coated with plaster. A 2.44m floor below & its bottom coated with plaster. A 2.44m high, 305mm thick lightweight solid concrete block wall is high, 305mm thick lightweight solid concrete block wall is directly over the top flange of the beam. Determine the directly over the top flange of the beam. Determine the loading on the beam measured per m length of the beam.loading on the beam measured per m length of the beam.

Example 1.1Example 1.1

• Live loads (Imposed loads)Live loads (Imposed loads)•Varies in magnitude & locationVaries in magnitude & location•Building loads Building loads

• Depends on the purpose for which the building Depends on the purpose for which the building is designedis designed

• These loadings are generally tabulated in local, These loadings are generally tabulated in local, state or national codestate or national code

Loads

LoadsLoads

• Live loads (Imposed loads)Live loads (Imposed loads)

• Highway Bridge loadsHighway Bridge loads•Primary live loads are those due to trafficPrimary live loads are those due to traffic•Specifications for truck loadings are reported Specifications for truck loadings are reported

in AASHTOin AASHTO•For 2-axle truck, these loads are designated For 2-axle truck, these loads are designated

with H followed by the weight of truck in tons with H followed by the weight of truck in tons and another no. gives the year of the and another no. gives the year of the specifications that the load was reportedspecifications that the load was reported

Loads

2-axle truck with semi-trailer

• Railway Bridge loadsRailway Bridge loads

Loads

• Wind loadsWind loads•Kinetic energy wind Kinetic energy wind potential energy of potential energy of

pressurepressure•Depends on density & flow of air, angle of Depends on density & flow of air, angle of

incidence, shape/stiffness of structure & incidence, shape/stiffness of structure & roughness of surfaceroughness of surface

•Can be treated as static or dynamicCan be treated as static or dynamic

Loads

• Earthquake loadsEarthquake loads•Earthquake produce loadings through its Earthquake produce loadings through its

interaction with the ground & its response interaction with the ground & its response characteristicscharacteristics

•Their magnitude depends on amount & type of Their magnitude depends on amount & type of ground acceleration, mass & stiffness of ground acceleration, mass & stiffness of structurestructure

•During earthquake, the ground During earthquake, the ground vibrates both horizontally & verticallyvibrates both horizontally & vertically

Loads

• Hydrostatic & Soil PressureHydrostatic & Soil Pressure•The pressure developed by these loadings The pressure developed by these loadings

when the structures are used to retain water when the structures are used to retain water or soil or granular materialsor soil or granular materials

•E.g. tanks, dams, ships, bulkheads & retaining E.g. tanks, dams, ships, bulkheads & retaining wallswalls

• Other natural loadsOther natural loads•Effect of blastEffect of blast•Temperature changesTemperature changes•Differential settlement of foundationDifferential settlement of foundation

Loads

• Material uncertainties occur due toMaterial uncertainties occur due to•variability in material propertiesvariability in material properties•residual stress in materialsresidual stress in materials•intended measurements being different from intended measurements being different from

fabricated sizesfabricated sizes•material corrosion or decaymaterial corrosion or decay

• Many types of loads can occur Many types of loads can occur simultaneously on a structuresimultaneously on a structure

Structural Design

• In working-stress design, the computed In working-stress design, the computed elastic stress in the material must not elastic stress in the material must not exceed the allowable stress along with the exceed the allowable stress along with the following typical load combinations as following typical load combinations as specified by the ASCE 7-02 Standardspecified by the ASCE 7-02 Standard

•Dead loadDead load•0.6 (dead load) + wind load0.6 (dead load) + wind load•0.6 (dead load) + 0.7(earthquake load)0.6 (dead load) + 0.7(earthquake load)

Structural Design

• Ultimate strength design is based on Ultimate strength design is based on designing the ultimate strength of critical designing the ultimate strength of critical sectionssections

• This method uses load factors to the loads or This method uses load factors to the loads or combination of loadscombination of loads

• 1.4 (Dead load)1.4 (Dead load)• 1.2 (dead load) + 1.6 (live load) + 0.5 (snow 1.2 (dead load) + 1.6 (live load) + 0.5 (snow

load)load)• 1.2 (dead load) + 1.5(earthquake load)+ 0.5 1.2 (dead load) + 1.5(earthquake load)+ 0.5

(live load)(live load)

Structural Design