Which DEFLECTION METHOD to use in which case in structures?

INTRODUCTION

•  Whenever a structure got affected from any external sources, then there may be a chance of having deflection in the structures.
• The external sources mentioned above may be anything such as loading applied (axial force, shear force, bending moment, torsion), self weight, change in temperature (increase/decrease),fabrication or misfits errors, support settlements, etc.
• The calculations of  these deflections in the structures are very important to know. 
• The deflections of structures must be within permissible limit as per design to prevent cracking or even failure of structure. So, it is very much necessary to calculate deflection at all critical points of the structure so that the structure should be designed as such deflection in structure remains within the permissible limit as per the design.
• The calculation of deflection is also very much necessary in case of analysis of indeterminate structures, where deflection is required to write compatibility equation.

 TYPES OF DEFLECTION METHOD

There are so many different types of method which are used to find deflection in any structure. 

1. Double integration method
2. Method of superposition
3. Moment area method
4. Conjugate beam method
5. Castigliano's method
6. Method of virtual work/ unit load method

DOUBLE INTEGRATION METHOD

• This method is also sometimes known as Macaulay's method/Singularity function method/ Discontinuity function method.
• This method of finding deflection is very much used in case of beams.
• This method is only used for finding deflection for bending.
• This method gives the equation of deflected elastic curve of whole beam at once.
• This method can't be applied directly for the structures having some kind of discontinuity in the elastic deflected curve. By discontinuity we mean to say presence of any hinge or slider.
• This method can also be not applied directly for the non-prismatic beams.
• This deflection method is best for the case when deflection or slope is required to be found at too many points.  

METHOD OF SUPERPOSITION

• In this method of finding deflection, deflection at any point on the structure can be calculated by summing up the effects of each load acting on the structure one by one.
• This method of superposition is only helpful in the case if deflection/slope at any point is already known for the given applied loading. And so, the limitation of this method is that this method can only be used for standard types of loading or supports present in the beams.

MOMENT AREA METHOD

• This method of finding deflection is only used to find bending deflections.
• This method is generally used to find deflection for beams subjected to a series of concentrated loads and for non-prismatic beams.
• This method can't be applied directly for the structures having some kind of discontinuity as hinge or slider.

CONJUGATE BEAM METHOD

• This method of finding deflection is only used to find bending deflections.
• This method is generally used to find deflection for beams subjected to a series of concentrated loads and for non-prismatic beams.
• This method of finding deflection can be even applied directly for the structures having any discontinuity like hinge or slider.

 CASTIGLIANO'S METHOD

• This method of finding deflection can be used for all types of external loading.
• This method of finding deflection can also be applied for ant discontinuity case or even in non-prismatic case.
• The limitation of the castigliano method is that it can't be applied for support settlement case(can be applied for support settlement in case of self  restraining structure) and in temperature change case.

METHOD OF VIRTUAL WORK/ UNIT LOAD METHOD

• This method of finding deflection can be applied for all types of external loadings.
• This method of finding deflection can also be applied for ant discontinuity case or even in non-prismatic case.
• This method can also be applied for support settlement case or in case of temperature change also.

You can also check for some extra details Types of loading a structure resist in civil engineering/ Different types of structure

TYPES OF CONTRACT IN CIVIL ENGINEERING

 What is CONTRACT

The most broad and simple definition of contract is that " A contract is an agreement enforceable by a law".

Now as per Civil Engineering, a contract is an agreement between two or more firms/individuals based on which, one agrees to do some work for other under the given terms and conditions. Now this work mentioned above can be anything like construction or maintenance or repairs of any structures, supply of labour or materials, transportation of materials, storage of materials, etc.

Types of CONTRACT IN CIVIL ENGINEERING   

By the term types of contract in Civil engineering , we mean to say different methods of payments which are used to reimburse contractors for the construction or other services they provide.

1. ITEM RATE CONTRACT

• This types of contract in Civil engineering is also known as Unit price contract or Schedule contract.

TYPES OF STRUCTURES USED IN CIVIL ENGINEERING

In civil engineering, a structure is defined as anything which is made up of various components which will resists external loading applied on them without  affecting the functions for which  the particular structure is designed.

 It is a very important task  for a structural engineers to select the type of structure which will be used in supporting or transmitting loads. On the basis of types of primary stresses which can be developed in a structure on the application of load, structures are classified in to five types:-

1. Tension carrying structures

2. Compression carrying structures

3. Trusses

4. Shear structures

5. Bending structures

The above mentioned structures can be considered as a basic types of structures. A single structure may be composed of combination of above mentioned structures.

TENSION STRUCTURES

These types of structures supports loading applied on them by generating tensile forces.

Some of the common types of tension structures we usually see are Cables, Vertical rods, etc.

Cables are usually used in supporting bridges. Vertical rods are used as hangers.

COMPRESSION STRUCTURES

These types of structures supports loading applied on them by generating compressive forces.

Some of the most common types of compressive structures we usually see are Columns and Arches.

Column is a straight member subjected to axially compressive loads while Arch is a curved structure. Column and Arches develops mainly compressive stresses on application of loads.

TRUSSES

These types of structures supports loading applied on them by developing axial forces. The axial forces generated can either be tensile or compressive in nature.

Trusses are generally composed of straight members with a pin connections at the ends. In real life , the trusses are generally constructed by connecting members to gusset plates by bolted or welded connections. This makes connections at the ends somewhat fixed and so induces some bending in the members of trusses. But as these secondary stresses are so small in magnitude, so that they can be neglected in design, and so the assumptions of pinned connections at the ends holds good.

Loading on trusses are only subjected to joints.

SHEAR STRUCTURES

These types of structures supports loading applied on them by developing mainly in-plane shear.

e.g. Reinforced concrete shear wall in multistorey buildings. This shear wall helps in reducing lateral movements of building due to wind loads and earthquake loads.

BENDING STRUCTURES

These types of structures supports external loadings applied on them by developing bending stresses.

Some of the most common types of  bending structures which we usually see are Beams, Rigid frames, Slabs. Beam is a straight member which is usually loaded perpendicular to its longitudional axes. Frames are composed of straight members connected together to support external loads applied on them. Unlike trusses , the loading on frames may be applied on joints as well as on members. In general a rigid frame develops bending moment, shear force and axial force also. But the design of horizontal members or beams of frames  is generally governed by bending and shear stresses only.