then steel born - yyardim.com · 2016 then steel born ... higher installation costs and the ......

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Then Steel Born

Assoc. Prof. Yavuz yardim

Some times in 17th Cost iron uses to construct one

bridge in Uk . Latter Wrought iron is used, this iron was

much more reliable for both tension, and compression,.

Wrought iron is an iron alloy with a very low carbon

(less than 0.08%) content in contrast to cast iron (2.1%

to 4%), and has fibrous inclusions known as slag up to

2% by weight.

The bridge is completed. It is opened as the

world's first iron bridge on New Year's Day 1781

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Hope, we can go a steel factory in Oman


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Structure Design II - Fall Semester 2015-2016Structure Design II - Fall Semester 2015-2016

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Management and Control at Steel Construction Site


Erecting structural steelwork for building construction takes

place in a dynamic, changing environment where there are

many hazards and risks. Proper and timely planning and

coordination are the most effective ways to manage those

hazards and risks. Projects involving structural steel

construction have four main stages where risks to health

and safety need to be considered:

• design

• fabrication

• transport

• erection.

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INT

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TO

BS

59

50

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Aims of structural design Cl. 2.1.1.1


�The main aim of structural design is to design a safe

structure that will fulfill its intended purpose.

�The structure should be able to resist the predicted

loading for its entire design life with a sufficient margin of

safety.

� The in-service deflections and behaviour of the structure

must not be such that it is unacceptable for the intended

use.

�Other factors that should also be considered in the design

stage are economy, safety, erection, transport and

sustainability.

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Limit states design


Factors are applied both to the loads and to the materials, to allow for the possibility

that the loads may be greater than the assumed values and that the materials may

be weaker than the assumed values. The design requirement is often expressed as:

F × γ l ≤ R / γm

where:

F is the load effect (e.g. force or

moment)

γ l is the load factor

R is the resistance or capacity of the

member

γm is the material factor

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Limit states design


F × γ l ≤ R / γm

Using the partial factors in Table the design requirement can be

expressed more fully as:

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Limit states design


In BS 5950 the γ factors have been combined to simplify the design.

The performance factor ( γ p ≈ 1.2) has been combined with the load

factors (γ Dead Load ≈ 1.15 and γ Imposed Load ≈ 1.3). The material

factors (γm1 and γm2) are combined into the recommended design

strengths.

Therefore, when designing to BS 5950, the relationship which

has to be satisfied is simply:

F × γ f ≤ R

where: γ f is the product of γ l and γ p and is

given in Table of the Standard.

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Material strength variation


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In practice, because the strength of steel is quoted by the

steel specifications as a “guaranteed minimum”, the curve

for steel strength is similar to that shown in Figure at

previous slide .

The mean strength of the steel is close to 310 N/mm2, but

the 95% confidence limit (i.e. mean minus 2 standard

deviations) is 275 N/mm2.

Material strength variation

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Limit states


BS 5950-1 considers two classes of limit states. The ultimate limit

state (i.e. the point beyond which the structure would be unsafe) and

the serviceability limit state (i.e. the point beyond which the specified

service criteria are no longer met). The principal limit states covered

in BS 5950-1 are shown in Table .

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16 Ultimate limit states


Application of load factorsWhen the structure reaches a limit state of strength or stability it is on the point

of being unsafe or about to collapse. It is necessary to verify that there is an

adequate factor of safety against this limiting condition.

In buildings not subject to loads from travelling cranes, the following load

combinations should be checked:

• Load combination 1: Dead load and imposed load (gravity loads)

plus notional horizontal forces

• Load combination 2: Dead load and wind load

• Load combination 3: Dead load, imposed load and wind load.

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Partial factors for loads

Ultimate limit states

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Stress-strain Behaviour of Steel


The primary characteristics of structural steel include mechanical

and chemical properties, metallurgical structures and weldability.

In the past structural engineers have tended to focus only on the

tensile properties (longitudinal yield stress and ultimate tensile

strength), with some attention paid to the deformability as

measured by the elongation at fracture of a tension specimen.

Since the modulus of elasticity, E, is constant for all practical

purposes for all grades of steel, it has rarely been a consideration

other than for serviceability issues. Weldability was assumed to be

adequate for all such steels. Deformability or ductility was similarly

assumed to be satisfactory, in part because the design

specification has offered only very limited, specific requirements.

The stress-strain curve for steel is

generally obtained from tensile test on

standard

specimens as shown in Fig

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The stress-strain curve for steel is generally obtained

from tensile test on standard

specimens as shown in Fig

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Pro

po

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Stru

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fir Ste

el B

uild

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Connections


Connections form an important part of any structure and are designed more

conservatively than members. This is because, connections are more complex

than members to analyse, and the discrepancy between analysis and actual

behaviour is large. Further, in case of overloading, we prefer the failure confined

to an individual member rather than in connections, which could affect many

members. Connections account for more than half the cost of structural steelwork

and so their design and detailing are of primary importance for the economy of

the structure. The type of connection designed has an influence on member

design and so must be decided even prior to the design of the structural system

and design of members. For example, in the design of bolted tension members,

the net area is calculated assuming a suitable number and diameter of bolts based

on experience. Therefore, it is necessary to verify the net area after designing the

connection.

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The connections provided in steel structures can be classified as 1)

riveted 2) bolted and 3) welded connections.

Riveted connections were once very popular and are still used in

some

cases but will gradually be replaced by bolted connections. This is

due to the low strength of rivets, higher installation costs and the

inherent inefficiency of the connection. Welded connections have

the advantage that no holes need to be drilled in the member and

consequently have higher efficiencies. However, welding in the field

may be difficult, costly, and time consuming. Welded connections

are also susceptible to failure by cracking under repeated cyclic

loads due to fatigue which may be due to working loads such as

trains passing

over a bridge (high-cycle fatigue) or earthquakes (low-cycle fatigue).

A special type of bolted connection using High Strength Friction

Grip (HSFG)

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Bolt Connection


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bolts has been found to perform better under such conditions than

the conventional black bolts used to resist predominantly static

loading. Bolted connections are also easy to inspect and replace. The

choice of using a particular type of connection is entirely that of the

designer and he should take his decision based on a good

understanding of the connection behaviour, economy and speed of

construction.

Type of bolt connections

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Bolt HolesSince HSFG bolts under working loads, do not rely on resistance

from bearing, holes larger than usual can be provided to ease

erection and take care of lack-of-fit. Typical hole types that can be

used are standard, extra large and short or long slotted. These are

shown in Fig.

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The possible limit states or failure modes that may

control the strength of a bolted connection is shown in

Figure


Shear failure of bolt

Shear failure of plate

Bearing failure of bolt

Bearing failure of plate

Tensile failure of bolts

Bending of bolts

Tensile failure of plate

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Connection


Arc Welding Processes

Shielded Metal Arc Welding (SMAW)

In Shielded Metal Arc Welding or SMAW , heating is done by means of electric arc between

a coated electrode and the material being joined. In case bare wire electrode (without

coating) is employed, the molten metal gets exposed to atmosphere and combines

chemically with oxygen and nitrogen forming defective welds. The electrode coating on the

welding rod forms a gaseous shield that helps to exclude oxygen and stabilise the arc.

Submerged Arc Welding (SAW)

Shielded Metal Arc Welding (SMAW)

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Submerged Arc Welding (SAW)

In this arc welding process, the arc is not visible because it is covered

by a blanket of fusible powdered flux. The bare metal electrode is

deposited as a joining material. The flux, which is a special feature of

the method, protects the weld pool against the atmosphere. The arc

once started is at all times covered by the flux

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