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1、土木工程概论Introduction to Civil Engineering,第九章土木工程设计概述 Chapter 9 Introduction to Design of Civil Engineering,土木工程概论Introduction to Civil E,Introduction to Design of Civil Engineering,What is Introduction to Design of Civil Engineering?It provides the students with the necessary background on terminolog
2、y used in design.With this chapter,entry-level students of civil engineering will better understand from the outset lectures on detailed subject areas.It will also prove beneficial for newly qualified professionals and others who want a concise guide to everyday design terminology.,Introduction to D
3、esign of Civi,Introduction to Design of Civil Engineering,Classification of loads:According to variation with time:Loads whose magnitude is constant,and not varying with time are called as static loads,and may vary with time are called as dynamic loads.According to occupation:The loads which remain
4、constant in position are called dead loads.According to distribution:The distribution where a heavy load distributed over a small area is called concentrated load.The load which are evenly distributed over a large area is called an uniformly distributed load.,Introduction to Design of Civi,土木工程概论(英文
5、版)Chapter-9-Introduction-to-Design-of-Civ课件,土木工程概论(英文版)Chapter-9-Introduction-to-Design-of-Civ课件,Introduction to Design of Civil Engineering,Types of stresses and strains,Introduction to Design of Civi,Introduction to Design of Civil Engineering,TRUSS BRIDGE LABORATORYBridges are essential to our na
6、tions infrastructure.A simple bridge can be made by spanning a gap with planks.As the gap becomes wider,however,the planks will begin to sag excessively even under the weight of a person.If the bridge is longer still,the planks may break.When one of the planks,called a beam,is loaded,it bends as sho
7、wn below.Lines are drawn on the beam for illustration.,Introduction to Design of Civi,Introduction to Design of Civil Engineering,TRUSS BRIDGE LABORATORY,Introduction to Design of Civi,Introduction to Design of Civil Engineering,TRUSS BRIDGE LABORATORYA close-up view of a short segment of the beam i
8、s shown below.The top part of the beam is being squeezed(in compression)and the bottom part of the beam is being stretched(in tension).The force in the beam actually changes continuously from the top of the beam to the bottom.That means that in the middle(top to bottom),it is neither in compression
9、nor tension.These forces act in a bending manner on the beam.This bending force is referred to as moment,as shown in the diagram.,Introduction to Design of Civi,Introduction to Design of Civil Engineering,TRUSS BRIDGE LABORATORY,Introduction to Design of Civi,Introduction to Design of Civil Engineer
10、ing,TRUSS BRIDGE LABORATORYIf a plank bridge breaks,it is likely to splinter in the middle leaving the rest of the plank undamaged.This is because the center of the plank experiences much more moment than the ends,which experience none,because they are free to rotate without resistance.So the moment
11、,or twisting force,varies continuously from zero at the left end to its highest value in the middle and back to zero again at the right end.The result is that although it is simple to build,a plank bridge does not make very efficient use of material.,Introduction to Design of Civi,Introduction to De
12、sign of Civil Engineering,TRUSS BRIDGE LABORATORYOne way of making more efficient use of wooden beams is to stand them on edge.If you have ever been in an unfinished attic,you may have noticed that the floor beams(and the rafters)are in this configuration.The beams dont bend as much in the upright o
13、rientation.This is because of a property called moment of inertia.The basic principle of moment of inertia follows.,Introduction to Design of Civi,Introduction to Design of Civil Engineering,TRUSS BRIDGE LABORATORYAs we saw before,the highest compression and tension occur in the very top and the ver
14、y bottom of the beam,respectively.We also found out that the middle of the beam(top to bottom)isnt working very hard at all.So what we want is to have as much material at the outer edges as possible and have as little material in the middle as possible.The pictures below show some beams to illustrat
15、e moment of inertia.,Introduction to Design of Civi,Introduction to Design of Civil Engineering,TRUSS BRIDGE LABORATORY,Low Moment of Inertia Use this for a diving board which you want to bend a lot,High Moment of Inertia Use this for support beams which you want to be stiff,Introduction to Design o
16、f Civi,Introduction to Design of Civil Engineering,TRUSS BRIDGE LABORATORYThe two beams above are called I-beams or wide flanges because of their shape(when looked at on end).The left beam would be made of steel and the right of concrete.,Introduction to Design of Civi,Introduction to Design of Civi
17、l Engineering,TRUSS BRIDGE LABORATORYThese show how material is concentrated at the top and bottom of the beam.,Introduction to Design of Civi,Introduction to Design of Civil Engineering,TRUSS BRIDGE LABORATORYThe more material and the farther away from the center it is,the higher the moment of iner
18、tia,and hence the stronger the beam.As nature would have it,achieving greater distance from the center is more beneficial than adding more material,because the moment of inertia increases as the square of that distance.,Introduction to Design of Civi,Introduction to Design of Civil Engineering,TRUSS
19、 BRIDGE LABORATORYObviously,we cannot remove all the material from the middle of the beam,because the top and bottom must be connected.The material in the middle also keeps the top and bottom from sliding with respect to each other in what is called shear.Yet there is a more efficient way to focus m
20、aterial at the top and bottom and provide resistance to shear.,Introduction to Design of Civi,Introduction to Design of Civil Engineering,TRUSS BRIDGE LABORATORYThe middle part of the beam does not need to be solid and continuous,but can instead be made up of thin rods.This is shown in the figure be
21、low.,Introduction to Design of Civi,Introduction to Design of Civil Engineering,TRUSS BRIDGE LABORATORYThis configuration establishes the basis for what is known as a truss.A truss is the oldest and most often used method of making more efficient bridges,and you will be building one today.A truss is
22、 a structure made from straight links connected at joints.The joints are always at the ends of the links,never in the middle.,Introduction to Design of Civi,Introduction to Design of Civil Engineering,TRUSS BRIDGE LABORATORYThe links are called members,and in your case,they are craft sticks with dri
23、lled holes.The joints are assembled with small bolts in your case.If the term members makes you think of a team,you are on the right track.When a load is applied to any joint,the members will share the load,although not equally.,Introduction to Design of Civi,Introduction to Design of Civil Engineer
24、ing,Some Concepts:COMPRESSION:This,as you would expect,describes a squeezing action or force on an object.TENSION:The opposite of compression,or a stretching action or force on an object.,Introduction to Design of Civi,Introduction to Design of Civil Engineering,STRESS:A measure of force per unit of
25、 area,i.e.lb./in2(or psi),kN/m2 STRAIN:A measure of deformation or elongation of a material,its units are inch per inch;it is the ratio of a change in length to the original length of a specimen.STRENGTH:The stress value at which a sample of material fails.,Introduction to Design of Civi,Introductio
26、n to Design of Civil Engineering,MODULUS OF ELASTICITY:Relates stress to strain and visa versa.It is the ratio of the stress on a sample to the amount of stain that level of stress causes.It is also the slope of the straight line portion of the stress-strain curve for a specific material.ELASTIC RAN
27、GE:The portion of the stress-strain relationship for a material where if the specimen loaded and then unloaded,it will return to its original undeformed shape.The straight line portion of the stress strain curve.,Introduction to Design of Civi,Introduction to Design of Civil Engineering,NEUTRAL AXIS
28、:A line which runs along the length of a beam where stress and strain are equal to zero.MOMENT OF INERTIA:This is one measure of the stiffness of a beam.It relates cross sectional area and the distance from the neutral axis at which the majority of the area is located to the ease in which the beam i
29、s bent.,Introduction to Design of Civi,Introduction to Design of Civil Engineering,Example:An I beam has a greater moment of inertia than a flat plate of the exact same cross sectional area.CANTILEVER BEAMA beam(a member whose main action is bending)supported,or fixed,at only one end.i.e.an overhang
30、 or a diving board configuration.,Introduction to Design of Civi,Introduction to Design of Civil Engineering,STABILITY AND SIMPLE TRUSSESThere is an important characteristic of a useful truss:it must be stable,which is to say that it should not move freely in any direction.Below are some configurati
31、ons of members joined at the ends.The first shown is the most basic triangular truss.The left support only allows connected members to rotate.The right support additionally allows horizontal movement.This configuration is stable,because there is no motion which can freely occur.,Introduction to Desi
32、gn of Civi,Introduction to Design of Civil Engineering,STABILITY AND SIMPLE TRUSSESTwo members connected at a joint form a hinged arch,as shown below.A hinged arch may be added to any stable truss to form another stable truss,as long as the angle of the arch is other than 180.A truss which can be as
33、sembled in this manner is called a simple truss.,Introduction to Design of Civi,Introduction to Design of Civil Engineering,STABILITY AND SIMPLE TRUSSESLastly,we see that a pentagonal configuration is also unstable,because as points A and B move apart,point C is free to move down.What is the smalles
34、t number of members required to make this stable?In a similar fashion,all but the triangle will be unstable,so the triangle is basic unit of any truss structure.,Introduction to Design of Civi,Introduction to Design of Civil Engineering,THE LONG AND SHORT OF IT Another special feature of trusses is
35、that the members dont bend.They get pulled apart(in tension)and pushed together(in compression),but they dont bend like the plank does when you stand on it.The members stay straight from end to end until they break.This does not mean the bridge will stay straight,though.As heavier loads are put on t
36、he bridge,it will still sag in the middle.This is because the individual members of the truss are getting longer(if they are in tension)and shorter(if they are in compression).,Introduction to Design of Civi,Introduction to Design of Civil Engineering,A BELT ISNT THE ONLY THING THAT BUCKLESMany mate
37、rials,in theory,have the same strength when being squeezed together(in compression)as they do when pulled apart(in tension).The problem is that if you press the two ends of a thin member(like a ruler)together,it doesnt simply stay straight and get shorter,but instead it bends out to the side.This is
38、 called buckling,which is the way that most tall,skinny things break when compressed end-to-end.,Introduction to Design of Civi,Introduction to Design of Civil Engineering,HOW CAN MY TRUSS FAIL?There are three ways your truss can fail.If a member buckles enough,it will bend and break in the directio
39、n in which the craft sticks have a low moment of inertia.This may be prevented if the loading frame supports partially buckled members.Another type of failure is that a craft stick pulls apart in the middle in tension.The third type of failure possible is joint break-out.This is when the craft stick
40、 breaks right where the bolt is connected.,Introduction to Design of Civi,Introduction to Design of Civil Engineering,Students in the Structures lab,Introduction to Design of Civi,Building EnvelopePerformanceLaboratory,Full scale wall thermal resistanceexperiment,Introduction to Design of Civil Engi
41、neering,Building EnvelopeFull scale wa,Structures Laboratory,Introduction to Design of Civil Engineering,Structures LaboratoryIntroduct,Environmental Laboratory,Introduction to Design of Civil Engineering,Environmental LaboratoryIntrod,WaterResourcesLaboratory,Introduction to Design of Civil Enginee
42、ring,WaterIntroduction to Design of,BuildingAerodynamicLaboratory,Introduction to Design of Civil Engineering,BuildingIntroduction to Design,Acoustics Laboratory,Introduction to Design of Civil Engineering,Acoustics LaboratoryIntroducti,Indoor AirQuality andVentilationLaboratory,Introduction to Desi
43、gn of Civil Engineering,Indoor AirIntroduction to Desi,ThermalEnvironmentand ControlsLaboratory,Introduction to Design of Civil Engineering,ThermalIntroduction to Design,ComputerLaboratories,Introduction to Design of Civil Engineering,ComputerIntroduction to Design,Introduction to Design of Civil En
44、gineering,ENGINEERING RESEARCH The role of the research engineer is achieved after many years of study.Students wishing to pursue this field should take courses that emphasize advanced mathematics and statistics.Use of the computer is essential;computer languages such as FORTRAN and C+aid the resear
45、ch engineer in completing projects.Students can start early as a student assistant for a professor in the undergraduate major.,Introduction to Design of Civi,Introduction to Design of Civil Engineering,ENGINEERING RESEARCH Most of the skills necessary to work in the field,however,will come with rese
46、arch completed in graduate studies.Most colleges and universities do not offer a research sub-discipline in the Civil Engineering major.Students should choose courses which they wish to specialize in.,Introduction to Design of Civi,Introduction to Design of Civil Engineering,STRUCTURAL ENGINEERING A
47、ll structures,regardless of their function,are subjected to forces caused by the natural environment(such as wind and earthquakes)and by man(such as cargo and automobile traffic),and they must be designed to withstand these forces.These structures can be as varied as buildings,bridges,pipelines,mach
48、inery,automobiles and spacecraft.,Introduction to Design of Civi,Introduction to Design of Civil Engineering,STRUCTURAL ENGINEERING The job of the structural engineer is to create these new designs or to evaluate and improve the load resistance capabilities of existing structures which may have been
49、 damaged during an earthquake.In order to accomplish this the structural engineer must be knowledgeable about the behavior of deformable bodies,about the sources,magnitudes and probability of occurrence of applied loads,about material properties,design philosophies and governmental design codes,and
50、about computer programming and usage.,Introduction to Design of Civi,Explain the terms stress and strain.State Hooks Law.Why is a factor of safety provided for a design?What is meant by working stress?Define(i)Poissons ratio(ii)hydrostatic pressure and(iii)volumetric strain.,Introduction to Design o
