CIV204 MATERIALS OF CONSTRUCTION (2+2 ECTS 6)

Transcription

1 CIV204 MATERIALS OF CONSTRUCTION Aims of the Course (2+2 ECTS 6) To provide students comprehensive information on the basic engineering properties of most common construction materials. To introduce technologies of basic construction materials such as concrete, steel, and composite materials. To provide information about the structure of construction materials.

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3 No cell-phone during class. Do not be late for the class! Regular class and lab application attendance is mandotory. 3

4 Materials for Civil and Construction Engineers CHAPTER 1 Materials Engineering Concepts

5 INTRODUCTION Common civil engineering materials: steel mineral aggregates concrete masonry asphalt wood soil for geotechnical engineers Less common materials aluminum glass plastic Fiber-reinforced composites Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 5

6 New Materials Advances in polymers adhesives composites geotextiles coatings synthetics High performance materials higher strength to weight ratio improved durability lower costs Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 6

7 Material Selection Considerations Economic factors Mechanical properties Non-mechanical properties Production/construction considerations Aesthetic properties Sustainable considerations Emphasis client s needs facility s function Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 7

8 1.1 Economic Factors Factors to be considered availability and cost of raw materials manufacturing costs transportation placing maintenance Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 8

9 1.2 Mechanical Properties Response of material to external loads All materials deform under load depending on: material properties magnitude and type of load geometry of the material element Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 9

10 Loading Conditions Static (Dead) Loads long term applied and removed slowly so no vibrations usually due to gravity Dynamic (Live) Loads short term shock or vibration periodic repeating wave form (rotating equipment) transient quick impulse that decays back to resting (vehicles) random never repeats (earthquake) Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 10

11 Static loading implies a sustained loading of the structure over a period of time. Generally, static loads are slowly applied such that no shock or vibration is generated in the structure. Loads that remain in place for an extended period of time are called sustained (dead) loads. In civil engineering, much of the load the materials must carry is due to the weight of the structure and equipment in the structure. Loads that generate a shock or vibration in the structure are dynamic loads. Dynamic loads can be classified as periodic, random, or transient Periodic loading Random loading Transient loading Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 11

12 Stress-Strain Relations All solid materials deform under load stress is like force (or load) with the size factored out so that we can directly compare different sizes stress = force / area s = F / A (psi, ksi, kpa, MPa, GPa) strain is like deformation with the size factored out strain = deformation / original length e = DL / L 0 (%, in/in, mm/mm) Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 12

13 Typical Stress-Strain Diagrams s e is usually linear in the low stress range but transforms into non-linear Glass and chalk Steel Aluminum alloys Concrete Soft rubber Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 13

14 Elastic Behavior Instantaneous response to load Returns to its original shape upon unloading stretches bonds between atoms without rearranging them Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 14

15 Linear & Non-Linear Behavior A linear material has a straight line stress-strain graph An elastic material returns to its original shape Non-linear elastic Linear elastic Non-linear inelastic Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 15

16 Properties of an Elastic Material Modulus of Elasticity or Young s Modulus E = Ds / De slope (rise over run) of the linear portion of stress-strain curve Poisson s Ratio n = -e l / e a relates lateral strain, e l, to axial strain, e a as material is stretched the cross section shrinks and vice versa for compression Range = 0 to 0.5 (practically 0.1 to 0.45) Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 16

17 Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 17 Generalized Hooke's Law For three directions (3D = triaxial) E z y x x s s n s e E x z y y s s n s e E y x z z s s n s e y x z E E E A F z z y z z y x z ns s n e n s e s s s For axially loaded members, no stresses in the x and y directions

18 Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 18

19 Stress What if response is not linear? How do we find the slope (Modulus of Elasticity)? Initial Tangent Modulus Tangent Modulus Chord Modulus Secant Modulus Strain Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 19

20 Typical E Moduli and Poisson s Ratios Material Modulus of Elasticity (GPa) Poisson s Ratio Aluminum Brick Concrete Limestone ~58 Steel Wood Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 20

21 Elastoplastic Behavior Most materials are linear elastic in small stress range and then plastic the transition point is elastic limit Elastic stretches bonds between atoms without rearranging them recoverable deformations (springs back) Plastic atomic bonds slip past each other and rearrange permanent deformations (doesn t spring all the way back) Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 21

22 Stress Elastic Limit New elastic limit Response to further loading follows original stress-strain behavior Force is applied resulting in stress and strain When force is removed, stress returns to zero. Path is parallel to the initial slope of the curve. Part of the strain is recovered, this is elastic behavior. Part of the strain is permanent, this is plastic behavior. Plastic Strain Elastic Strain Total Strain Strain Reloading will resume to the highest previous stress level. Elastic limit is reset to the previous highest stress level. Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 23

23 What if there s no clear transition point? Offset method Extension method Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 24

24 Elements of Stress-Strain Diagram Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 25

25 Definitions Proportional Limit transition between linear and non-linear behavior Elastic Limit (Yield Point) transition between elastic and plastic behavior maximum stress with full recovery Yielding strain continues with little or no increase in stress (after elastic limit) Ultimate Stress maximum stress on the curve (tensile or compressive strength) Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 26

26 Definitions (Cont.) Rupture Stress point where specimen fractures or ruptures Brittle Material has little plastic deformation before failure (glass, concrete) Ductile Material has lots of plastic deformation before failure (structural steel, rubber) Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 27

27 Viscoelastic Behavior Strain is an instantaneous response to stress in elastic and elasto-plastic materials. In some cases, materials exhibit both viscous and elastic responses, which are known as viscoelastic. Viscosity: Resistance to flow (i.e., to shear force) for linear materials: = shear stress/rate of shear strain, unit Pa.s or cp Viscoelastic materials have both elastic and viscous response have delayed response to load application. Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 28

28 Time dependent response of viscoelastic materials (a good example is asphalt or some plastics) Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 29

29 Deformation in Viscoelastic materials depends on o Duration of load o Rate of loading A quick shock or pulse may cause little deformation, while a sustained (or slowly increasing) load can cause much deformation o Temperature Deformation increases with an increase in temperature (i.e.viscosity decreases). Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 30

30 Mechanisms associated with time-dependent deformation Creep Creep is the long-term deformation of the materials under sustained load. It can occur in metals, ionic and covalent cystals and amorphous materials. In order to observe a creep deformation on the materials, the load needs to be applied for a long time. For example, concrete, can creep over a period of decades. Viscous flow It is the other time-dependent behavior of materials under sustained loads. Viscous flow is associated only with amorphous materials and can occur under short term load duration. For example, asphalt pavements can deform under traffic loads with a load duration of only a fraction of a second. Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 31

31 Creep Behavior of time-dependent materials Relaxation Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 32

32 Rheological models used to model mechanically the time-dependent behavior of materials basic rheological elements Spring Dashpot St. Venant Rheological models are combinations of elements Prandtl Maxwell Kelvin Burgers Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 33

33 Rheological Models Rheological models are used to model mechanically the time-dependent behavior of materials. Rheology uses three basic elements, combined in either series or parallel to form models that define complex material behaviors. Linear spring Linear elastic material (Hook element) Dashpot (absorber) Perfectly viscous materials (Newtonian element) Sliding block Shows the threshold stress for movement Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 34

34 Rheological Models Maxwell Model Kelvin Model Prandtl Model Burgers Model (Standard solid body) Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 35

35 Temperature & Time Effects Temperature affects mechanical behavior of all materials high temp = ductile low temp = brittle Impact fracture test measures toughness at different temperatures Viscoelastic materials like asphalt and polymers are greatly influenced by a change of only a few degrees Metals require a much greater temperature change but are similarly affected Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 36

36 Work & Energy Work (or Energy) = force x distance Modulus of Resilience: energy required to reach yield point Toughness: energy required to fracture Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 37

37 Several ways to fail fracture or breakage fatigue (repeated stress) general yielding buckling excessive deformation Failure and Safety For safety, structures are designed to carry loads greater than anticipated Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 38

38 Endurance Limit Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 39

39 Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 40

40 Factor of Safety FS = (allowable stress / actual stress) FS = s s FS is proportional to cost and is chosen by: cost failure allowable > 1 material variability accuracy in considering all loads possible misuse The factor of safety (FS) is defined as the ratio of the stress at failure to the allowable stress for design (maximum anticipated stress): accuracy in measuring material response (good testing?) Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 41

41 1.3 Non-Mechanical Properties Other than load responses: Density and Unit Weight Thermal Expansion Surface Properties Abrasion & Wear Resistance Surface Texture Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 42

42 density = r = m / V Density and Unit Weight unit weight = g = W / V specific gravity G r r w Specific gravity is the ratio of the mass of a substance relative to the mass of an equal volume of the water. Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 43

43 Specific Gravity Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 44

44 Thermal Expansion All materials expand and contract with temperature Linear Coeff. of Thermal Expansion a L = (DL / DT) / L 0 Volumetric Coeff. of Thermal Expansion a V = (DV / DT) / V 0 for isotropic materials a V = 3a L Stresses develop because of different rates of thermal expansion and contraction for different materials that are connected together use expansion joints Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 45

45 Expansion joint Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 46

46 Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 47

47 Surface Characteristics Corrosion and Degradation Abrasion and Wear Resistance Surface Texture Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 48

48 1.4 Production and Construction Production availability and ability to fabricate material into desired shapes Construction ability to build the structure on site (trained work force) o High early strength concrete used for early traffic opening in pavement Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 49

49 1.5 Aesthetic Characteristics The civil engineer is responsible for working with the architect The mix of artistic and technical design skills makes the project acceptable to the community Engineers should understand that there are many factors beyond the technical needs that must be considered Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 50

50 1.6 Sustainable Design Sustainable design in the philosophy of designing physical objects, the built environment and services to comply with the principles of economic, social, and ecological sustainability. The materials used for CE projects are important to the sustainability of the project. The Green Building Council developed the Leadership in Environment and Energy Design, LEED, building rating system to evaluate the sustainability of the project. Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 51

51 Sustainable Design (Cont.) For new construction and major renovations the rating areas include: Sustainable sites Water efficiency Energy and atmosphere Materials and resources Indoor environmental quality Innovation in design Regional priority Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 52

52 1.7 Material Variability All materials have variability Some materials are more uniform than others o Steel vs. concrete vs. wood Three sources of variance: Material Sampling Testing Use good sampling and testing techniques to minimize those variabilities Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 53

53 Exactness of measurements Precision: measure many times and get same result Bias: tendency to deviate in one direction from true value Accuracy: close to true value; absence of bias Precise but not accurate Accurate but not precise Accurate and precise Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 54

54 Sampling Proper sampling must ensure that a random and representative sample is taken from the population (e.g., stockpile, lot, etc.) Random: have an equal chance of being selected Representative: perfect average of the entire stockpile Sample size: depends on materials variability & tolerance level of results more variability dictates a larger sample Rigorous statistical evaluations required for special applications: high quality asphalt and Portland cement concrete Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 55

55 Normal Distribution Describes many populations that occur in nature, including material properties Area under the curve between any two values represents the probability of occurrence Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 56

56 Control Charts Decrease inspection frequency Early detection of troubles Provide a record of quality Basis of acceptance Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 57

57 Caused by 3 factors: Procedural errors Experimental Error Are often undiscovered Machine errors (bias) If known and constant can be easily corrected Human errors Minimize by repetition, double-checking, etc. o Always do more than one test Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 58

58 1.8 Laboratory Measuring Devices Direct Ruler, dial gauge, calipers Physical & material properties are usually measured (time, deformation, force, etc.) Indirect LVDT, strain gauge, load cell measuring changes in electric voltage and relating to deformation, stress, or strain must be calibrated Electronic sensors can be easily connected to digital devices or computers: CDAS (computerized data acquisition system) Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 59

59 LVDT Strain Gauge Dial Gauge Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 60

60 Extensometer Non-Contact Extensometer Load Cell Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. Proving Ring 61

61 Important considerations: Sensitivity Accuracy Calibration Sensitivity of measuring devices: the smallest value that can be read on the device s scale sensitivity is not accuracy or precision accuracy cannot be better than the sensitivity When choosing a device, sensitivity depends on the required accuracy, which depends on the type of test. Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 62

62 Laboratory Experiment List Experiment 1: Tension Test of Steel Experiment 2: Sieve Analysis of Aggregates Experiment 3: Specific Gravity and Absorption of Coarse Aggregate Experiment 4: Specific Gravity and Absorption of Fine Aggregate Experiment 5: Bulk Unit Weight and Voids in Aggregate Experiment 6: Slump of Freshly Mixed Portland Cement Concrete Experiment 7: Unit Weight And Air Content of Fresh Concrete Experiment 8: Making and Curing Concrete Cylinders and Beams Experiment 9: Compressive Strength of Cylindrical and Cubic Concrete Specimens Experiment 10: Flexural Strength of Concrete Experiment 11: Rebound Number of Hardened Concrete (Nondestructive test on concrete. Mamlouk/Zaniewski, Materials for Civil and Construction Engineers, Third Edition. Copyright 2011 Pearson Education, Inc. 63