土木工程概论(英文版)Chapter-9-Introduction-to-Design-of-Civ课件

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 EIntroduction to Design of Civil EngineeringWhat is Introduction to Design of Civil Engineering ? It provides the students with the necessary background on terminology

2、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

3、Design of CiviIntroduction to Design of Civil EngineeringClassification 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 re

4、main 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

5、工程概论(英文版)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 EngineeringTypes of stresses and strainsIntroduction to Design of CiviIntroduction to Design of Civil EngineeringTRUSS BRIDGE LABORATORYBridges are essential to our n

6、ations 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 b

7、ends as shown below. Lines are drawn on the beam for illustration. Introduction to Design of CiviIntroduction to Design of Civil EngineeringTRUSS BRIDGE LABORATORYIntroduction to Design of CiviIntroduction to Design of Civil EngineeringTRUSS BRIDGE LABORATORYA close-up view of a short segment of the

8、 beam is 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

9、in compression 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 CiviIntroduction to Design of Civil EngineeringTRUSS BRIDGE LABORATORYIntroduction to Design of CiviIntroduction to Design of

10、Civil EngineeringTRUSS 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 resista

11、nce. So the moment, 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 C

12、iviIntroduction to Design of Civil EngineeringTRUSS 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

13、 as much in the upright orientation. This is because of a property called moment of inertia. The basic principle of moment of inertia follows. Introduction to Design of CiviIntroduction to Design of Civil EngineeringTRUSS BRIDGE LABORATORYAs we saw before, the highest compression and tension occur i

14、n the very top and the very 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 be

15、low show some beams to illustrate moment of inertia. Introduction to Design of CiviIntroduction to Design of Civil EngineeringTRUSS BRIDGE LABORATORYLow Moment of Inertia Use this for a diving board which you want to bend a lotHigh Moment of Inertia Use this for support beams which you want to be st

16、iffIntroduction to Design of CiviIntroduction to Design of Civil EngineeringTRUSS 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 CiviIntr

17、oduction to Design of Civil EngineeringTRUSS BRIDGE LABORATORYThese show how material is concentrated at the top and bottom of the beam. Introduction to Design of CiviIntroduction to Design of Civil EngineeringTRUSS BRIDGE LABORATORYThe more material and the farther away from the center it is, the h

18、igher the moment of inertia, 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 CiviIntroduction to Design

19、 of Civil EngineeringTRUSS 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

20、 more efficient way to focus material at the top and bottom and provide resistance to shear. Introduction to Design of CiviIntroduction to Design of Civil EngineeringTRUSS BRIDGE LABORATORYThe middle part of the beam does not need to be solid and continuous, but can instead be made up of thin rods.

21、This is shown in the figure below. Introduction to Design of CiviIntroduction to Design of Civil EngineeringTRUSS 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

22、 building one today. A truss is 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 CiviIntroduction to Design of Civil EngineeringTRUSS BRIDGE LABORATORYThe links are called members, and in your cas

23、e, they are craft sticks with drilled 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 CiviIn

24、troduction to Design of Civil EngineeringSome 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 CiviIntroduction to Design of Civil Engine

25、eringSTRESS: A measure of force per unit of 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 materi

26、al fails. Introduction to Design of CiviIntroduction to Design of Civil EngineeringMODULUS 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 st

27、ress-strain curve for a specific material. ELASTIC RANGE: 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

28、Introduction to Design of Civil EngineeringNEUTRAL AXIS: 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 majo

29、rity of the area is located to the ease in which the beam is bent. Introduction to Design of CiviIntroduction to Design of Civil EngineeringExample: 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 i

30、s bending) supported, or fixed, at only one end. i.e. an overhang or a diving board configuration. Introduction to Design of CiviIntroduction to Design of Civil EngineeringSTABILITY AND SIMPLE TRUSSESThere is an important characteristic of a useful truss: it must be stable, which is to say that it s

31、hould not move freely in any direction. Below are some configurations 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,

32、because there is no motion which can freely occur. Introduction to Design of CiviIntroduction to Design of Civil EngineeringSTABILITY 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

33、 long as the angle of the arch is other than 180. A truss which can be assembled in this manner is called a simple truss. Introduction to Design of CiviIntroduction to Design of Civil EngineeringSTABILITY AND SIMPLE TRUSSESLastly, we see that a pentagonal configuration is also unstable, because as p

34、oints A and B move apart, point C is free to move down. What is the smallest 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 CiviIntroduction to Design of Civi

35、l EngineeringTHE LONG AND SHORT OF IT Another special feature of trusses is 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. Th

36、is does not mean the bridge will stay straight, though. As heavier loads are put on the 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 CiviInt

37、roduction to Design of Civil EngineeringA BELT ISNT THE ONLY THING THAT BUCKLESMany materials, 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) toge

38、ther, it doesnt simply stay straight and get shorter, but instead it bends out to the side. This is called buckling, which is the way that most tall, skinny things break when compressed end-to-end. Introduction to Design of CiviIntroduction to Design of Civil EngineeringHOW CAN MY TRUSS FAIL? There

39、are three ways your truss can fail. If a member buckles enough, it will bend and break in the direction 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

40、the middle in tension. The third type of failure possible is joint break-out. This is when the craft stick breaks right where the bolt is connected. Introduction to Design of CiviIntroduction to Design of Civil EngineeringStudents in the Structures lab Introduction to Design of CiviBuilding Envelope

41、PerformanceLaboratoryFull scale wall thermal resistanceexperimentIntroduction to Design of Civil EngineeringBuilding EnvelopeFull scale waStructures LaboratoryIntroduction to Design of Civil EngineeringStructures LaboratoryIntroductEnvironmental LaboratoryIntroduction to Design of Civil EngineeringE

42、nvironmental LaboratoryIntrodWaterResourcesLaboratoryIntroduction to Design of Civil EngineeringWaterIntroduction to Design ofBuildingAerodynamicLaboratoryIntroduction to Design of Civil EngineeringBuildingIntroduction to DesignAcoustics LaboratoryIntroduction to Design of Civil EngineeringAcoustics

43、 LaboratoryIntroductiIndoor AirQuality andVentilationLaboratoryIntroduction to Design of Civil EngineeringIndoor AirIntroduction to DesiThermalEnvironmentand ControlsLaboratoryIntroduction to Design of Civil EngineeringThermalIntroduction to Design ComputerLaboratoriesIntroduction to Design of Civil

44、 EngineeringComputerIntroduction to DesignIntroduction to Design of Civil EngineeringENGINEERING 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

45、computer is essential; computer languages such as FORTRAN and C+ aid the research engineer in completing projects. Students can start early as a student assistant for a professor in the undergraduate major.Introduction to Design of CiviIntroduction to Design of Civil EngineeringENGINEERING RESEARCH Most of the skills necessary to work in the field, however, will come with research completed in graduate studies. Most colleges and universities do