Design of steel structures

 

Design of steel structures  

 methods for designing of steel structures are as follows .

(1)- Working stress method or Elastic method.

Note - working stress method  is the oldest method for designing of steel structures 

(2)- Ultimate load Design or Plastic design method (ULD)

(3)-Limit state methods.

It is new design procedure

(1)- Working stress method or Elastic method.(WSM)

In this method  working stress should be less or equal to permissible stress.

i.e 

[Working stress ≤ Permissible stress.] 

Disadvantages of working stress.(WSM)

(1)- It fails to provide a uniform overload capacity of all parts and types of structure.

(2)-It does not take into account the non- linear relationship between stress and strain and the ability of structural members to resist loads even after local yielding.

(3) It is un economical method

(4) It is considered linear elastic behaviour.

 

(2)- Ultimate load Design or Plastic design method (ULD)

 In this method of design failure implies collapse or extremely large deformations, thus the structure fails at a much higher load, called the collapse loads,than the working load.in the plastic design method,the working loads are multiplied by the load factor and the cross sections of members are selected and designed on the basis of the collapse strength.

(3) Limit state method .

In the limit state method, the structure shall be designed to withstand safely all loads likely to act on it throughout its life 

It shall not suffer total collapse under accidental loads such as from  impact , human error or exploration to an extent beyond the local damages.

The structure should be designed on the basis of the most critical limit state and should be checked for other limit state. A structure should be designed to withstand safely all loads likely to act on it.

 

Stress- Strain curve for mild steel 

The stress strain curve for mild steel presents a lot of information necessary to understand how it will behave in a given situation . 

OAB_  OAB line represent a straight line curve - 

It means that the strain produced is proportional to the stress producing it i.e obeys Hooke's law.

A- represent the limit of proportionality.

B- represent the elastic limit- the maximum stress upto which a specimen regains its original length on removal of the applied load.

CD- represent plasting yielding.

DE- represent strain yielding.

E- represent the ultimate stress.

......... Detailed of structural steel.