Standard structural steels (Europe)

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ELEMENTS OF STEEL STRUCTURAL DESIGN


1.

What is structure steel? What are their requirements?


Structural steel

is

steel

construction

material
, a

profile
, formed with a specific

shape

or

cross
section

and certain standards of

chemical composition

and mechanical properties. Structural
steel

shape, size, composition, strength, storage, etc., is regulated in most industrialized
countries.

Structural steel members, such as

I
-
beams
, have high

second moments of area
, which allow
them to be very stiff in respect to their cross
-
sectional area.

Standard structural steels (Europe)

Most steels used throughout Europe are specified to comply with th
e

European standard

EN
10025
. However, many national standar
ds also remain in force.
[
citation needed
]

Typical grades are described as 'S275J2' or 'S355K2W'. In these examples, 'S' denotes structural
rather than eng
ineering steel; 275 or 355 denotes the

yield strength

in newtons per square
millimetre or the equivalent

megapascals
; J2 or K2 denotes the materials

toughness

by reference
to

Charpy impact test

values;
and the 'W' denotes

weathering steel
. Further letters can be used to
designate fine grain steel ('N' or 'NL');

quenched and tem
pered

steel ('Q' or 'QL'); and
thermomechanically rolled steel ('M' or 'ML').

The normal yield strength grades available are 195, 235, 275, 355, 420, and 460, although some
grades are more commonly used than others e.g. in the UK, almost all structural st
eel is grades
S275 and S355. Higher grades are available in quenched and tempered material (500, 550, 620,
690, 890 and 960
-

although grades above 690 receive little if any use in construction at present).

A set of euronorms define the shape of a set of s
tandard structural profiles:



European I
-
beam: IPE
-

Euronorm 19
-
57



European I
-
beam: IPN
-

DIN 1025
-
1



European flange beams: HE
-

Euronorm 53
-
62



European channels: UPN
-

DIN 10261
-
1

[
edit
]
Standard structural steels (USA)

Steels used for building construction in the US use standard alloys identified and specified
by

ASTM International
. These steels have an alloy identification beginning with

A

and then two,
three, or four numbers. The four
-
number

AISI steel grades

commonly used for mechanical
engineering, machines, and vehicles are a completely different specification series.

The standard commonly used structural steels are:
[1]


2.

What do you understand by indeterminate structure and the degree of
indeterminacy?


Introduction

Indeterminacy was discussed in one of

Jacq
ues Derrida's

early works

Plato's
Pharmacy

(1969),
[1]

a reading of

Plato
's

Phaedrus

and

Phaedo
. Plato writes of a fictionalized
conversation between
Socrates

and a student, in which Socrates tries to convinc
e the student that
writing is inferior to speech.
[2]

Socrates uses the Egyptian myth of Thoth's creation of writing to
illustrate his point. As the story goes, Thoth p
resents his invention to the god
-
king of Upper Egypt
for judgment. Upon its presentation, Thoth offers script as a

pharmakon

for the Egyptian people.
The Greek word

pharmakon
poses a quandary for translators
-

it is both a remedy and a poison. In
the proffer
ing of a pharmakon, Thoth presents it as its true meaning
-

a harm and benefit. The
god
-
king, however, refuses the invention. Through various reasonings, he determines the
pharmakon of writing to be a bad thing for the Egyptian people. The pharmakon, the un
decidable,
has been returned decided. The problem, as Derrida reasons, is this: since the word pharmakon,
in the original Greek, means both a remedy and a poison, it cannot be determined as fully remedy
or fully poison. Amon rejected writing as fully poiso
n in Socrates' retelling of the tale, thus shutting
out the other possibilities.

The problem of indeterminacy arises when one observes the eventual circularity of virtually every
possible definition. It is easy to find loops of definition in any dictionary
, because this seems to be
the only way that certain concepts, and generally very important ones such as that of

existence
,
can be defined in the English language. A definition is a coll
ection of other words, and in any finite
dictionary if one continues to follow the trail of words in search of the precise meaning of any
given term, one will inevitably encounter this linguistic indeterminacy.

Philosophers and scientists generally try to
eliminate indeterminate terms from their arguments,
since any indeterminate thing is unquantifiable and untestable; similarly, any hypothesis which
consists of a statement of the properties of something unquantifiable or indefinable cannot be
falsified and

thus cannot be said to be supported by evidence that does not falsify it. This is
related to

Popper
's discussions of falsifiability in his works on the scientific method.
The

quantifiability

of data collected during an experiment is central to the

scientific method
, since
reliab
le conclusions can only be drawn from replicable experiments, and since in order to
establish observer agreement scientists must be able to quantify experimental evidence.

Immanue
l Kant

unwittingly proposed one answer to this question in his

Critique of Pure
Reason

by stating that there must "exist" a "
thing in itself
"


a thing which is the cause of
phenomena, but not a
phenomenon

itself. But, so to speak, "approximations" of "things
in
themselves" crop up in many models of empirical phenomena: singularities in physics, such
as

gravitational singularities
,

certain aspects of which

(e.g., their unquantifiability)
[
citation needed
]
can
seem

almost

to mirror various "aspects" of the proposed "thing in itself", are generally eliminated
(o
r attempts are made at eliminating them) in newer, more precise models of the universe; and
definitions of various

psychiatric disorders

stem, according to philos
ophers who draw on the work
of

Michel Foucault
, from a belief that something unobservable and indescribable is fundamentally
"wrong" with the mind of whoever suffers from suc
h a disorder: proponents of Foucault's
treatment of the concept of insanity would assert that one need only try to quantify various
characteristics of such disorders as presented in today's

Diagnostic and Statistical Manual



delusion
, one of the diagnostic criteria which must be exhibited by a patient if he or she is to be
considered

schizophrenic
, for example


in order to discover that the field of study known
as

abnormal psychology

relies upon indeterminate concepts in defining virtually each "mental
disorder" it describes. The quality that makes a belief a delusion is indeterminate to the extent to
which it is unquantifiable; arguments that delusion is dete
rmined by popular sentiment (i.e.,
"almost no
-
one believes that he or she is made of cheese, and thus that belief is a delusion")
would lead to the conclusion that, for example,

Alfred Wegener's

assertion of

continental drift

was
a delusion since it was dismissed for decades after it was made.


3.

Explain the different types of riveted joints by m
eans of neat sketch.


A

rivet

is a permanent mechanical

fastener
. Before being installed a rivet consists of a
smooth

cylindrical

shaft with a head on one end. The end opposite the head is called the

buck
-
tail
. On installation the rivet is placed in a punched or pre
-
drilled hole, and the tail is

upset
,
or

bucked

(i.e., deformed), so that it expands to

about 1.5 times the original shaft diameter,
holding the rivet in place. To distinguish between the two ends of the rivet, the original head is
called the

factory head

and the deformed end is called the

shop head

or buck
-
tail.

Because there is effectively

a head on each end of an installed rivet, it can support tension loads
(loads parallel to the axis of the shaft); however, it is much more capable of supporting shear
loads (loads perpendicular to the axis of the shaft). Bolts and screws are better suited

for tension
applications.

Fastenings used in traditional wooden

boat building
, like copper nails and

clinch bolts
, work on
the same principle as the rivet but were in use long before the term

rivet

came about and, where
they are remembered, are usually classified among the nails and bolts resp
ectively.

Solid rivets are used in applications where reliability and safety count. A typical application for
solid rivets can be found within the structural parts of

aircraft
. Hundreds of

thousands of solid
rivets are used to assemble the frame of a modern aircraft. Such rivets come with rounded
(universal) or 100°

countersunk

heads
. Typical

materials

for aircraft rivets
are
aluminium

alloys

(2017, 2024, 2117, 7050, 5056, 55000, V
-
65),

titanium
, and

nickel
-
b
ased
alloys (e.g.

Monel
). Some aluminum alloy rivets are too hard to buck and must be softened
by

a
nnealing

prior to being bucked. "Ice box" aluminum alloy rivets harden with age, and must
likewise be annealed and then kept at sub
-
freezing temperatures (hence the name "ice box") to
slow the age
-
hardening process.

Steel

rivets can be found in static structures such
as

bridges
,

cranes
, and

building

frames.

The setting of these fasteners requires access to both sides of a structure. Solid rivets are driven
using a

hydr
aulically
,

pneumatically
, or

electromagnetically
driven squeezing

tool

or even a
handheld

hammer
. Applications in which only one side is accessible require the use of blind
rivets.

[
edit
]
High strength structural steel rivets

Until relatively recently, structural steel connections were either welded or riveted. High
-
strength
bolts have completely

replaced structural steel rivets. Indeed, the latest steel construction
specifications published by

AISC

(the 13th Edition) no longer covers their installation. The reason
for the change is prima
rily due to the expense of skilled workers required to install high strength
structural steel rivets. Whereas two relatively unskilled workers can install and tighten high
strength bolts, it took a minimum of four highly skilled riveters to install rivets
in one joint at a
time.
[
citation needed
]


4.

Write the merits and demerits of riveted and welded joints


Types

There are many types of butt welds, but all f
all within one of these categories: single welded butt
joints, double welded butt joint, and open or closed butt joints. A single welded butt joint is the
name for a joint that has only been welded from one side. A double welded butt joint is created
when
the weld has been welded from both sides. With double welding, the depths of each weld
can vary slightly. A closed weld is a type of joint in which the two pieces that will be joined are
touching during the welding process. An open weld is the joint type w
here the two pieces have a
small gap in between them during welding.

[
edit
]
Square butt joints

The square
-
groove is a butt w
elding joint with the two pieces being flat and parallel to each other.
This joint is simple to prepare, economical to use, and provides satisfactory strength, but is
limited by joint thickness. The closed square butt weld is a type of square
-
groove joint
with no
spacing in between the pieces. This joint type is common with gas and arc welding.

For thicker joints, the edge of each member of the joint must be prepared to a particular geometry
to provide accessibility for welding and to ensure the desired wel
d soundness and strength. The
opening or gap at the root of the joint and the included angle of the groove should be selected to
require the least weld metal necessary to give needed access and meet strength requirements.

[
edit
]
Bevel butt joints

Single
-
bevel butt welds are welds where one piece in the joint is beveled and the other surface is
perpendicular to the plane of the s
urface. These types of joints are used where adequate
penetration cannot be achieved with a square
-
groove and the metals are to be welded in the
horizontal position

[4]
. Double
-
be
vel butt welds are common in arc and gas welding processes. In
this type both sides of one of the edges in the joint are beveled.

[
edi
t
]
V
-
joints

Single
-
V butt welds are similar to a bevel joint, but instead of only one side having the beveled
edge, both sides of the weld joint are beveled. In thick metals, and when welding can be
performed from both sides of the work piece, a double
-
V j
oint is used. When welding thicker
metals, a double
-
V

joint requires less filler material because there are two narrower V
-
joints
compared to a wider single
-
V joint. Also the double
-
V joint helps compensate for warping forces.
With a single
-
V joint, stress

tends to warp the piece in one direction when the V
-
joint is filled, but
with a double
-
V
-
joint, there are welds on both sides of the material, having opposing stresses,
straightening the material.

[
edit
]
J
-
joints

Single
-
J butt welds are when one piece of the weld is in the shape of a

J

that easily accepts filler
material and the other piece is square. A J
-
groove is formed either with sp
ecial cutting machinery
or by grinding the joint edge into the form of a J. Although a J
-
groove is more difficult and costly
to prepare than a V
-
groove, a single J
-
groove on metal between a half an inch and three quarters
of an inch thick provides a strong
er weld that requires less filler material. Double
-
J butt welds
have one piece that has a

J

shape from both directions and the other piece is square.

[
edit
]
U
-
joints

Single
-
U butt welds are welds that have both edges of the weld surface shaped like a J, but once
they come together, they form a U. Double
-
U joints have a U formation on both the top and
bottom of the prepared joint. U
-
joint
s are the most expensive edge to prepare and weld. They are
usually used on thick base metals where a V
-
groove would be at such a extreme angle, that it
would cost too much to fill.

[
edit
]
Others

Thin sheet metals are often flanged to produce edge
-
flange or corner
-
flange welds. These welds
are typically made without the addition of filler metal because the flange melts and provides all
the

filler needed. Pipes and tubing can be made from rolling and welding together strips, sheets,
or plates of material.
[5]


5.

Explain the various sections used in tension members with

sketch.

6.

Different steps in finding the strength of an axially loaded compression member.

7.

Define plate girder and explain the function of its various element


A

plate girder bridge

is a

brid
ge

supported by two or more

plate

girders
. The plate girders are
typically

I
-
beams

made up from separate

structural steel
plates (rather than rolled as a single
cross
-
section), which are

welded

or, in older bridges,

bolted

or

riveted

together to form the
vertical web and horizontal
flanges

of the

beam
. In some cases, the plate girders may be formed
in a Z
-
shape rather than I
-
shape. The first tubular

wrought iron

plate girder bridge was built in
1846
-
47 by

James Millholland

for the

Baltimore and Ohio Railroad
.
[1]

Plate girder bridges are suitable for short to medium spans and may
support

railroads
,

highways

or other traffic. Plate girders are usually prefabricated, and the length
limit is frequently set by the mode of transportation use
d to move the girder from the bridge shop
to the bridge site.
[2]



Anatomy of a plate girder.

Generally, the depth of the girder is no less than 1/15 the span, and for a given load bearing
capacity, a depth of around 1/12 the span minimizes t
he weight of the girder. Stresses on the
flanges near the centre of the span are greater than near the end of the span, so the top and
bottom flange plates are frequently reinforced in the middle portion of the span. Vertical stiffeners
prevent the web pla
te from buckling under shear stresses. These are typically uniformly spaced
along the girder with additional stiffeners over the supports and wherever the bridge supports
concentrated loads.
[3]

Deck
-
type plate girder bridge

In the deck
-
type bridge, a wood, steel or

reinforced concrete

bridge deck is supported on top of
two or more plate g
irders, and may act

compositely

with them. In the case of railroad bridges,
the

railroad ti
es

themselves may form the bridge deck, or the deck may support

ballast

on which
the track is laid. Additional beams may span across between the main girders, for example in the

form of bridge known as

ladder
-
deck

construction. Also, further elements may be attached to
provide cross
-
bracing and prevent the girders from

buckling
.

In the half
-
through bridge, the br
idge deck is supported between two plate girders, often on top of
the bottom flange. The overall bridge then has a 'U'
-
shape in

cross
-
section
. As cross
-
brac
ing
cannot normally be added, vertical stiffeners on the girders are normally used to prevent buckling
(technically described as 'U
-
frame behaviour'). This form of bridge is most often used
on

railroads

as the construction depth (distance between the underside of the vehicle, and the
underside of the bridge) is much less. This allows obstacles to be cleared with less change in
height.

[
edit
]
Multi
-
span plate girder bridge



Multispan Plate girder bridge: deck type on concrete piers.

Multispan plate
-
girder bridges may be an economical way to span gaps longer than can be
spanned by a single girder.

Piers

serve as intermediate abutments between the end

Abutments

of
bridge. Separate plate girder bridges

span between each pair of abutments in order to allow
for

expansion joints

between the spans.

Concrete

is

commonly used for low piers, while
steel

trestle

work may be used for high bridges.


8.

Explain the structural behaviour of plate girder and deflection shape of web.