Civ 4208 Assignment 1

UNIVERSITY OF GUYANA

FACULTY OF TECHNOLOGY

DEPARTMENT OF CIVIL ENGINEERING

Name: Registration #: Date: Lecturer:

Joash Joseph 12/0933/2333 April 16, 2015 Mr. R. Kansinally

CIV 4208 STRUCTURAL DESIGN III (STEEL) Assignment One

1

CONTENTS Propeities of steel .................................................................................................................................. 2

Strength ............................................................................................................................................... 2

Tensile Strength .............................................................................................................................. 2

Yield Strength ................................................................................................................................. 2

Steel Grades ........................................................................................................................................ 2

Ductility .............................................................................................................................................. 3

Toughness ........................................................................................................................................... 3

Notch Toughness ............................................................................................................................ 3

Fracture Toughness ......................................................................................................................... 4

Durability ............................................................................................................................................ 4

Metal Forming ....................................................................................................................................... 5

Cold forming ....................................................................................................................................... 5

Hot forming ......................................................................................................................................... 5

Rolling ................................................................................................................................................ 6

Structural forms .................................................................................................................................... 7

Frames ................................................................................................................................................. 7

Trusses ................................................................................................................................................ 7

Design Methods .................................................................................................................................. 7

The elastic design method ............................................................................................................... 7

Plastic Design Method .................................................................................................................... 7

Simple and Rigid Deign Methods ....................................................................................................... 8

Modes of failure within elements........................................................................................................ 9

Bending ........................................................................................................................................... 9

Local buckling ................................................................................................................................ 9

Shear ............................................................................................................................................... 9

Shear buckling ................................................................................................................................ 9

Web bearing and buckling .............................................................................................................. 9

Lateral torsional buckling ............................................................................................................... 9

Failure in frames ................................................................................................................................. 9

References ............................................................................................................................................ 12

2

PROPEITIES OF STEEL

Strength

Tensile Strength

The ultimate tensile strength (UTS) is the maximum resistance to fracture. It is equivalent to

the maximum load that can be carried by one square inch of cross-sectional area when the load

is applied as simple tension. It is expressed in pounds per square inch.

Yield Strength

A number of terms have been defined for the purpose of identifying the stress at which plastic

deformation begins. The value most commonly used for this purpose is the yield strength. The

yield strength is defined as the stress at which a predetermined amount of permanent

deformationoccurs. The graphical portion of the early stages of a tension test is used

to evaluate yield strength. To find yield strength, the predetermined amount of permanent

strain is set along the strain axis of the graph, to the right of the origin. (Integrated Publishing,

Inc., 2011)

Steel Grades

Steel grades to classify various steels by their composition and physical properties have been

developed by a number of standards organizations. (Wikipedia The Free Encyclopedia, 2015)

According to the World Steel Association, there are over 3,500 different grades of steel,

encompassing unique physical, chemical and environmental properties. In essence, steel is

composed of iron and carbon, although it is the amount of carbon, as well as the level of

impurities and additional alloying elements that determines the properties of each steel grade.

The carbon content in steel can range from 0.1-1.5%, but the most widely used grades of steel

contain only 0.1-0.25% carbon. Elements such as manganese, phosphorus and sulphur are

found in all grades of steel, but, whereas manganese provides beneficial effects, phosphorus

and sulphur are deleterious to steel's strength and durability.

Different types of steel are produced according to the properties required for their application,

and various grading systems are used to distinguish steels based on these properties. According

to the American Iron and Steel Institute (AISI), steels can be broadly categorized into four

groups based on their chemical compositions:

Carbon Steel

Alloy Steels

Stainless Steels

3

Tool Steels

(About.com, 2015)

Ductility

Ductility is a measure of the degree to which a material can strain or elongate between the onset

of yield and eventual fracture under tensile loading as demonstrated in the figure below. The

designer relies on ductility for a number of aspects of design, including redistribution of stress

at the ultimate limit state, bolt group design, reduced risk of fatigue crack propagation and in

the fabrication processes of welding, bending and straightening. The various standards for the

grades of steel in the above table insist on a minimum value for ductility so the design

assumptions are valid and if these are specified correctly the designer can be assured of their

adequate performance. (Steelconstruction.info, 2014)

Toughness

The ability of a metal to deform plastically and to absorb energy in the process before fracture

is termed toughness. The emphasis of this definition should be placed on the ability to absorb

energy before fracture. Recall that ductility is a measure of how much something deforms

plastically before fracture, but just because a material is ductile does not make it tough. The

key to toughness is a good combination of strength and ductility. A material with high strength

and high ductility will have more toughness than a material with low strength and high

ductility. Therefore, one way to measure toughness is by calculating the area under the stress

strain curve from a tensile test. This value is simply called material toughness and it has units

of energy per volume. Material toughness equates to a slow absorption of energy by the

material. (NDT Education Resource Center, 2014)

Notch Toughness

Notch toughness is the ability that a material possesses to absorb energy in the presence of a

flaw. As mentioned previously, in the presence of a flaw, such as a notch or crack, a material

will likely exhibit a lower level of toughness. When a flaw is present in a material, loading

induces a triaxial tension stress state adjacent to the flaw. The material develops plastic strains

as the yield stress is exceeded in the region near the crack tip. However, the amount of plastic

deformation is restricted by the surrounding material, which remains elastic. When a material

is prevented from deforming plastically, it fails in a brittle manner. (NDT Education Resource

Center, 2014)

4

Fracture Toughness

Fracture toughness is an indication of the amount of stress required to propagate a pre-existing

flaw. It is a very important material property since the occurrence of flaws is not completely

avoidable in the processing, fabrication, or service of a material/component. Flaws may appear

as cracks, voids, metallurgical inclusions, weld defects, design discontinuities, or some

combination thereof. Since engineers can never be totally sure that a material is flaw free, it is

common practice to assume that a flaw of some chosen size will be present in some number of

components and use the linear elastic fracture mechanics (LEFM) approach to design critical

components. This approach uses the flaw size and features, component geometry, loading

conditions and the material property called fracture toughness to evaluate the ability of a

component containing a flaw to resist fracture. (NDT Education Resource Center, 2014)

Durability

A further important property is that of corrosion prevention. Although special corrosion

resistant steels are available these are not normally used in building construction. The exception

to this is weathering steel .

The most common means of providing corrosion protection to construction steel is by painting

or galvanizing. The type and degree of coating protection required depends on the degree of

exposure, location, design life, etc. In many cases, under internal dry situations no corrosion

protection coatings are required other than appropriate fire protection. Detailed information on

the corrosion protection of structural steel is available.

5

METAL FORMING Metal forming is a general term for a large group that includes a wide variety of manufacturing

processes which include, hot rolled and cold formed steel. Metal forming processes are

characteristic in that the metal being processed is plastically deformed to shape it into a desired

geometry. In order to plastically deform a metal, a force must be applied that will exceed the

yield strength of the material. When low amounts of stress are applied to a metal it will change

its geometry slightly, in correspondence to the force that is exerted. That is it will compress,

stretch, and/or bend a small amount. The magnitude of the amount will be directly proportional

to the force applied. A force greater than the yield strength of the material must be applied for

permanent deformation. (thelibraryofmanufacturing.com, 2015)

Cold forming

Cold working, (or cold forming), is a metal forming process that is carried out at room

temperature or a little above it. In cold working, plastic deformation of the work causes strain

hardening. The yield point of a metal is also higher at the lower temperature range of cold

forming. Hence, the force required to shape a part is greater in cold working than for warm

working or hot working. At cold working temperatures, the ductility of a metal is limited, and

only a certain amount of shape change may be produced. Surface preparation is important in

cold forming. Fracture of the material can be a problem, limiting the amount of deformation

possible. In fact, some metals will fracture from a small amount of cold forming and must be

hot formed. One main disadvantage of this type of process is a decrease in the ductility of the

part's material, but there are many advantages. The part will be stronger and harder due to strain

hardening. Cold forming causes directional grain orientation, which can be controlled to

produce desired directional strength properties. Also, work manufactured by cold forming can

be created with more accurate geometric tolerances and a better surface finish. Since low

temperature metal forming processes do not require the heating of the material, a large amount

of energy can be saved and faster production is possible. Despite the higher force requirements,

the total amount of energy expended is much lower in cold working than in hot working.

(thelibraryofmanufacturing.com, 2015)

Hot forming

Hot working, (or hot forming), is a metal forming process that is carried out at a temperature

range that is higher than the recrystallization temperature of the metal being formed. The

behavior of the metal is significantly altered, due to the fact that it is above its recrystallization

6

temperature. Utilization of different qualities of the metal at this temperature is the

characteristic of hot working.

In hot working I is necessary to maintain constant temperature as decreases or increases in

temperature can cause the metal to have defects and flaws.

When above its recrystallization temperature a metal has a reduced yield strength, also no strain

hardening will occur as the material is plastically deformed. Shaping a metal at the hot working

temperature range requires much less force and power than in cold working. Above its

recrystallization temperature, a metal also possesses far greater ductility than at its cold worked

temperature. The much greater ductility allows for massive shape changes that would not be

possible in cold worked parts. The ability to perform these massive shape changes is a very

important characteristic of these high temperature metal forming processes.

The work metal will recrystallize, after the process, as the part cools. In general, hot metal

forming will close up vacancies and porosity in the metal, break up inclusions and eliminate

them by distributing their material throughout the work piece, destroy old weaker cast grain

structures and produce a wrought isotropic grain structure in the part. These high temperature

forming processes do not strain harden or reduce the ductility of the formed material. Strain

hardening of a part may or may not be wanted, depending upon the application. Qualities of

hot forming that are considered disadvantageous are poorer surface finish, increased scale and

oxides, decarburization, (steels), lower dimensional accuracy, and the need to heat parts. The

heating of parts reduces tool life, results in a lower productivity, and a higher energy

requirement than in cold working. (thelibraryofmanufacturing.com, 2015)

Rolling

Rolling is a bulk deformation metal forming process that deforms the work by the use of rolls.

Rolling processes include flat rolling, shape rolling, ring rolling, thread rolling, gear rolling,

and the production of seamless tube and pipe by rotary tube piercing or roll piercing.

(thelibraryofmanufacturing.com, 2015)

7

STRUCTURAL FORMS

Frames

Frame structures are the structures having the combination of beam, column and slab to resist

the lateral and gravity loads. These structures are usually used to overcome the large moments

developing due to the applied loading. (Web Tech Tix, 2014)

Trusses

A truss is an assemblage of long, slender structural elements that are connected at their ends.

Trusses find substantial use in modern construction, for instance as towers bridges, scaffolding,

etc. In addition to their practical importance as useful structures, truss elements have a

dimensional simplicity that will help us extend further the concepts of mechanics introduced

in the modules dealing with uniaxial response. (Roylance, 2000)

Design Methods

The elastic design method

The elastic design method, also termed as allowable stress method (or Working stress method),

is a conventional method of design based on the elastic properties of steel. This method of

design limits the structural usefulness of the material up to a certain allowable stress, which is

well below the elastic limit. The stresses due to working loads do not exceed the specified

allowable stresses, which are obtained by applying an adequate factor of safety to the yield

stress of steel. The elastic design does not take into account the strength of the material beyond

the elastic stress. Therefore the structure designed according to this method will be heavier than

that designed by plastic methods, but in many cases, elastic design will also require less

stability bracing. (INSTITUTE FOR STEEL DEVELOPMENT & GROWTH, 2014)

Elastic analysis programs are the most widely used for structural analysis and are based on the

assumption that the material which is being modelled is linear-elastic., therefore the limiting

stress is the value corresponding to the strain of 0.002, up to which steel behaves as a linear

material. The appropriate value of the elastic modulus has to be provided in the analysis.

(Steelconstruction.info, 2014)

Plastic Design Method

In the method of plastic design of a structure, the ultimate load rather than the yield stress is

regarded as the design criterion. The term plastic has occurred due to the fact that the ultimate

load is found from the strength of steel in the plastic range. This method is also known as

method of load factor design or ultimate load design. The strength of steel beyond the yield

stress is fully utilised in this method. This method is rapid and provides a rational approach for

8

the analysis of the structure. This method also provides striking economy as regards the weight

of steel since the sections designed by this method are smaller in size than those designed by

the method of elastic design. Plastic design method has its main application in the analysis and

design of statically indeterminate framed structures. (INSTITUTE FOR STEEL

DEVELOPMENT & GROWTH, 2014)

Simple and Rigid Deign Methods

Simple and rigid design relates to simple frames and rigid structures, that is, statically

determinate and statically indeterminate structures, having simple or rigid joints.

Simple joints may be defined as being those that will not develop restraining moments which

adversely affect the members and the structure as a whole, in which case the structure may be

designed as if pin-jointed. It is usually assumed, therefore, that no moment is transmitted

through a simple joint, and that the members connected to the joint may rotate. The joint should

therefore have sufficient rotation capacity to permit member end rotations to occur without

causing failure of the joint or its elements.

If there are a sufficient number of pin-joints to make the structure statically determinate, then

each member will act independently of the others, and may be designed as an isolated tension

member, compression member, beam, or beam-column. However, if the pin-jointed structure

is indeterminate, then some part of it may act as a rigid-jointed frame.

Arigid joint may be defined as a joint which has sufficient rigidity to virtually prevent relative

rotation between the members connected. Properly arranged welded and high-strength friction

grip bolted joints are usually assumed to be rigid (tensioned high strength friction grip bolts

are referred to as preloaded bolts). An example of a typical rigid joint between a beam and

column. There are important interactions between the members of frames with rigid joints,

which are generally stiffer and stronger than frames with simple or semi-rigid joints. Because

of this, rigid frames offer significant economies, while many difficulties associated with their

analysis have been greatly reduced by the widespread availability of standard computer

programs. (N.S. Trahair, 2008)

9

Modes of failure within elements

Bending

The vertical loading gives rise to bending of the beam. This results in longitudinal stresses

being set up in the beam. These stresses are tensile in one half of the beam and compressive in

the other.

As the bending moment increases, more and more of the steel reaches its yield stress.

Eventually, all the steel yields in tension and/or compression across the entire cross section of

the beam. At this point the beam cross-section has become plastic and it fails by formation of

a plastic hinge at the point of maximum moment induced by the loading. (Arya, 2009)

Local buckling

During the bending process outlined above, if the compression flange or the part of the web

subject to compression is too thin, the plate may actually fail by buckling or rippling before the

full plastic moment is reached. (Arya, 2009)

Shear

Due to excessive shear forces, usually adjacent to supports, the beam may fail in shear. The

beam web, which resists shear forces, may fail as steel yields in tension and compression in the

shaded zones. The formation of plastic hinges in the flanges accompanies this process. (Arya,

2009)

Shear buckling

During the shearing process described above, if the web is too thin it will fail by buckling or

rippling in the shear zone (Arya, 2009)

Web bearing and buckling

Due to high vertical stresses directly over a support or under a concentrated load, the beam web

may actually crush, or buckle as a result of these stresses (Arya, 2009)

Lateral torsional buckling

When the beam has a higher bending stiffness in the vertical plane compared to the horizontal

plane, the beam can twist sideways under the load. This is perhaps best visualised by loading

a scale rule on its edge, as it is held as a cantilever it will tend to twist and deflect sideways.

Nominal torsional restraint may be assumed to exist if web cleats, partial depth end plates or

fin plates (Arya, 2009)

Failure in frames

The primary actions in triangulated frames whose members are concentrically connected and

whose loads act concentrically through the joints are those of axial compression or tension in

10

the members, and any bending actions are secondary only. These bending actions are usually

ignored, in which case the member forces may be determined by a simple analysis for which

the member connections are assumed to be made through frictionless pin-joints.

If the assumed pin-jointed frame is statically determinate, then each member force can be

determined by statics alone, and is independent of the behaviour of the remaining members.

Because of this, the frame may be assumed to fail when its weakest member fails. Thus, each

member may be designed independently of the. (N.S. Trahair, 2008)

Figure 1: Colapes in Trusses

Figure 2: Beam Type Collapse

11

Figure 3: Sway Collapse

Figure 4: Combination Collapse

12

REFERENCES About.com, 2015. Steel Types & Properties. [Online]

Available at: http://metals.about.com/od/properties/a/Steel-Types-And-Properties.htm

[Accessed April 2015].

Arya, C., 2009. Design of Structural Elements. Third ed. New York: Taylor & Francis.

INSTITUTE FOR STEEL DEVELOPMENT & GROWTH, 2014. [Online]

Available at: http://www.steel-insdag.org/TeachingMaterial/chapter35.pdf


Integrated Publishing, Inc., 2011. Ultimate Tensile Strength. [Online]

Available at: http://nuclearpowertraining.tpub.com/h1017v1/css/h1017v1_73.htm

N.S. Trahair, M. B. D. N. a. L. G., 2008. The Behaviour and Design. Fourth ed. New York Aand London:

Taylor & Francis Group.

NDT Education Resource Center, 2014. Frcture Toughness. [Online]

Available at: https://www.nde-

ed.org/EducationResources/CommunityCollege/Materials/Mechanical/FractureToughness.htm2015


NDT Education Resource Center, 2014. Notch Toughness. [Online]


ed.org/EducationResources/CommunityCollege/Materials/Mechanical/NotchToughness.htm


NDT Education Resource Center, 2014. Toughness. [Online]


ed.org/EducationResources/CommunityCollege/Materials/Mechanical/Toughness.htm


Roylance, D., 2000. [Online]

Available at: http://ocw.mit.edu/courses/materials-science-and-engineering/3-11-mechanics-of-

materials-fall-1999/modules/truss.pdf


Steelconstruction.info, 2014. Steel material properties - Steelconstruction.info. [Online]

Available at: http://www.steelconstruction.info/Steel_material_properties


thelibraryofmanufacturing.com, 2015. Metal Forming. [Online]

Available at: http://thelibraryofmanufacturing.com/forming_basics.html


Web Tech Tix, 2014. Frame Structures - Definition, Types of Frame Structures. [Online]

Available at: http://www.aboutcivil.org/frame-structures-definition-types.html


Wikipedia The Free Encyclopedia, 2015. Steel grades - Wikipedia, the free encyclopedia. [Online]

Available at: http://en.wikipedia.org/wiki/Steel_grades


13

Wikipedia, the free encyclopedia, 2014. Weldability - Wikipedia, the free encyclopedia. [Online]

Available at: http://en.wikipedia.org/wiki/Weldability


Documents

Civ 4208 Assignment 1