Friday, March 12, 2021

What is the creep of concrete?

If the load is maintained for a considerable period of time, concrete undergoes additional deformations even without any increase in the load. This time-dependent strain is termed as creep.

The reversal of creep is not fully complete, continuous use of load over period of time results in a residual deformation or permanent deformation or irreversible creep. 

In creep, loss is due to sustained applied stress. They increase with higher cement content, higher water content, lower aggregate content, low relative humidity, high temperature, small thickness of the member, etc.

If the load is removed, only the instantaneous elastic deformation will recover- the plastic deformation will not.

Creep is factored in when concrete structures are designed.

Wednesday, March 03, 2021

What is the difference between a steel lintel and an RCC lintel?

A lintel is a horizontal load bearing member in construction. Lintels support wall or wall cladding above window and door openings.

Steel Lintel

Steel lintels are generally made from pre-galvanised steel which is cut and either roll-formed or pressed into the required shape. Steel has the advantage over concrete in that the lintels are usually lighter and are easier to handle on site.

These are used when the superimposed loads are heavy and openings are large. These consist of channel sections or rolled steel joists. We can use one single section or in combinations depending up on the requirement. When used singly, the steel joist is either embedded in concrete or cladded with stone facing to keep the width same as width of wall. When more than one units are placed side by side, they are kept in position by tube separators.

Reinforced Cement Concrete Lintel

At present, the lintel made of reinforced concrete are widely used to span the openings for doors, windows, etc. in a structure because of their strength, rigidity, fire resistance, economy and ease in construction. These are suitable for all the loads and for any span. The width is equal to width of wall and depth depends on length of span and magnitude of loading. RCC lintels can have a finish matching other components and details of the fa├žade, unifying the entire design. Rebar's in RCC lintels can be epoxy coated to prevent corrosion.


Tuesday, March 02, 2021

What is the difference between trapezoidal load and hydrostatic load?

Slab pressure loads (Kn/m2) are transferred to supporting beams as line load (kn/m) which can be triangular, trapezoidal, or partially distributed. Slab having two unequal sides distribute trapezoidal load on longer side beam.

Hydrostatic load: The pressure exerted by a fluid at equilibrium at a given point within the fluid, due to the force of gravity. Hydrostatic pressure increases in proportion to depth measured from the surface because of the increasing weight of fluid exerting downward force from above. Hydrostatic load can be trapezoidal but trapezoidal load cannot be hydrostatic. Because hydrostatic load occur due to water.