LOADS – TYPES OF LOADS REINFORCED CONCRETE STRUCTURES

LOADS

The reinforced concrete structures are designed to resist the following types of loads.
(i) Dead loads
(ii) Live loads or Imposed loads
(iii) Wind loads
(iv) Earthquake forces
(v) Snow loads
(vi) Shrinkage, creep and Temperature ellects.
(vii) Other forces and effects

DEAD LOADS
Dead loads mainly due to self weight of structural members, permanent partitions, fixed equipments and fittings. These loads shall be calculated by estimating the quantity of each material and then multiplying it with the unit weight. The unit weights of various materials used in building construction are given in the code IS 875 (Part-1)-1987. The unit weight of commonly used building materials are given in Table

LIVE LOADS (OR) IMPOSED LOADS
These are the loads that changes with respect to ime. Live loads or imposed loads include loads due to the people occupying the floor, weight of movable partitions, weight furniture and materials. The live loads to be taken in design of buildings have been given in IS: 875 (Part-2) – 1987. Some of the common live loads used in the design of buildings
WIND LOADS
It depends up on the velocity of wind and shape and size of the building. Complete details of calculating wind loads on structures are given in IS: 875 (Part-3) – 1987.

(i) Basic wind pressure V_{b} has to be picked up depending upon the locality of the building
(ii) To get the design wind velocity Vz the following expression shall be used.
V_{z} = K_{1}*K_{2}*K_{3}*V_{b}

k₁ =Risk coefficient

k_{2} = Coefficient based on terrain, height and structure size.

k_{3} = Topography factor Where
(iii) The design wind pressure is given by
P(z) = 0.6V²z
Where P{z} is in N / (m²) at height Z and V_{z} is in m/sec.
EARTH QUAKE FORCES
Earthquake shocks cause movement of foundation of structures. Due to inertia additional forces develop on the super structure. The impact of earthquake on structures depends on the stiffness of the structure, stiffness of the soil media, height and location of the structure ete. Accordingly, the country has been divided into several zones depending on the magnitude of the earthquake. following two methods may be used for computing the seismic forces.
(i) Seismic coefficient method.
(ii) Response spectrum method.
The details of these methods are prescribed in IS: 1893 code and also in National Building Code of India.
SHRINKAGE, CREEP AND TEMPERATURE EFFECTS
Shrinkage, creep and temperature (high or low) may produce stresses and cause deformations like other loads and forces. Hence, these are also considered as loads which are time dependent. The safety and serviceability of structures are to be checked following the stipulations of clauses 6.2.4, 5 and 6 of IS: 456 2000 and Part 5 of IS 875
OTHER FORCES AND EFFECTS
• Foundation movement (IS 1904)
Elastic axial shortening
Soil and fluid pressures (IS 875-Part-5)
Vibration
Fatigue
Impact (IS: 875-Part-5)
• Erection loads (IS: 875-Part-2)
Stress concentration effect due to point of application of load and the like.