## LOADS: DEFINITION & TYPES

STATIC LOADING DESIGN

**DEFINITION OF LOADING**

Mechanical resistance against which system acts or reacts.**CLASSIFICATION OF LOADS :**

1. WRT TIME

2. WRT DIRECTION

3. WRT DISTRIBUTION**ELASTIC CONSTANTS**Its types , relationship and equations.

*DEFINITION OF LOADING: External mechanical resistance against which a system acts or reacts.*

**TYPES** : LOAD can be classified on basis on the following

*1)W.R.T TIME :*

**A) STATIC LOADS :** Loads which are constant in magnitude as well as direction.

*a) Dead load* : A constant load acting all the time starting with some initial non zero load value (at t=0).

*b) Gradually applied load (GAL) *: A constant load acting for a constant time starting with some zero load value (at t=0).

**B)DYNAMIC LOADS:** Loads which are variable in either magnitude or direction or both.

*a)Impact load *: Load which acts suddenly or for a very short time interval of time.

b)* Cyclic load* : Load acting variably over a system in a cyclic period of time/ periodic motion. Will be discussed in detail later.

### IMPACT LOADS AND LOADING : CASE STUDY

Loading in which load is suddenly applied over a system in short time interval ( Δt=0).

As per the diagram above ;

**σ _{imp } > σ_{static }** ⇒

**δ**

_{imp }> δ_{static }EMPIRICAL RELATION : *σ _{imp= }(I.F.)σ_{static}*

**Where , I.F = 1+ (1+2h/δ _{static})^{1/2} (I.F.)_{MIN }= 2**

Therefore, impact stresses are more dangerous.

#Less impact stresses, less chances of failure for a material AND VICE VERSA.

*2.W.R.T DIRECTION:*

*1.NORMAL AXIAL LOAD(NAL):* Load acting normal to the area, along the longitudinal axis.

*2.NORMAL ECCENTRIC AXIAL LOAD(NEAL):* Load acting normal to the area , at a distance from longitudinal axis in a direction along longitudinal axis.

*3.TRANSVERSE / DIRECT SHEAR LOAD(TSL/DSL) *: Load acting along the area , perpendicular to the longitudinal axis along transverse axis.

*4.ECCENTRIC TRANSVERSE / DIRECT SHEAR LOAD(ETSL/EDSL) :* Load acting along the area, perpendicular to the longitudinal axis at a distance from transverse axis, in a direction along transverse axis.

**3.W.R.T DISTRIBUTION:**

*1.CONCENTRATED LOADS* : Loads and its effects that occur on a single point. It may be seen as :

a) Concentrated force

b) Concentrated moment

*2.DISTRIBUTED LOADS *: Loads which acts on a body over a particular span/region.

*a)Uniformly distributed loads(UDL) :* Load uniformly spread over a length.

*b)Uniformly varying loads(UVL) :* Load varying at every point over a length.

Same analogy of LOAD for MOMENT ALSO.

**ELASTIC CONSTANTS :**

According to HOOKE’S LAW;

**” STRESS IS DIRECTLY PROPORTIONAL TO STRAIN , WITHIN ELASTIC LIMIT.”**

*THEREFORE,*

**STRESS ∝ STRAIN ⇒ STRESS = A (STRAIN)**

THE CONSTANT **A **CALLED ELASTIC CONSTANT. These usually define the characteristics of an element under loading.

#### TYPES OF ELASTIC CONSTANTS:

**1**.FOR AXIAL LOADING : **σ _{T} ∝ ε ⇒ σ_{T} = Eε**

E = MODULUS OF ELASTICITY/YOUNG’S MODULUS

**2**.FOR SHEAR LOADING : **τ ∝ γ ⇒ ****τ= G****γ**

G = MODULUS OF RIGIDITY

**3.** FOR HYDRO STATIC LOADING : **p∝ Δv/v ⇒ p= k (Δv/v)**

k = BULK MODULUS , p = pressure stress

***POISSON RATIO (μ) μ = ( ΔD/D)/(ΔL/L)**

##### RELATIONSHIP BETWEEN VARIOUS ELASTIC CONSTANTS :

**1.E=2G(1+μ)**

**2.E=3K(1-2μ)**