BEAMS AND COLUMNS

SPECIFICATIONS AND ESTIMATIONS

COLUMNS

RCC ColumnsReinforced Concrete Column is a structural member designed to carry compressive loads, composed of concrete with an embedded steel frame to provide reinforcement. For design purposes, the columns are separated into two categories: short columns and slender columns.

Types of Columns based on height-width ratio

Short ColumnsThe strength of short columns is controlled by the strength of the material and the geometry of the cross section. Reinforcing rebar is placed axially in the column to provide additional axial stiffness

Long ColumnsLong columns are those which have a height and cross sectional dimension ratio more than 1:12. these columns are usually weaker than short columns of same cross sectional area and are not generally preferred.

Types of Columnsbased on their shape

• Spiral ColumnsSpiral columns are cylindrical columns with a continuous helical bar wrapping around the column. The spiral acts to provide support in the transverse direction and prevent the column from barrelling. The amount of reinforcement is required to provide additional load-carrying capacity greater than or equal to that attributed from the shell as to compensate for the strength lost when the shell spalls off. With further thickening of the spiral rebar, the axially loaded concrete becomes the weakest link in the system and the strength contribution from the additional rebar does not take effect until the column has failed axially. At that point, the additional strength from spiral comes into play and prevents catastrophic failure, instead giving rise to a much slower ductile failure.

• Tied ColumnsTied columns have closed lateral ties spaced approximately uniformly across the column. The spacing of the ties is limited in that they must be close enough to prevent barrelling failure between them, and far enough apart that they do not interfere with the setting of the concrete. The ACI codebook puts an upward limit on the spacing between ties.If the ties are spaced too far apart, the column will experience shear failure and barrel in between the ties

Process of Construction

RCC (Reinforced Cement Concrete) column is a structural member of RCC frame structured building. It's a vertical member which transfers loads from slab and beam directly to subsequent soil.

A whole building stands on columns. Most of the building failure happens due to column failure. And most of the column failure happens not for design fault but for the poor construction practice. So, it is very important to know the construction process of the RCC column properly.

General Steps Constructing RCC (Reinforced Cement Concrete) Column involves following four stages of works -

• Column layout work• Column reinforcement work• Column formwork, and• Pouring concrete into column.

STEP 1.Column layout work: In this stage of works the location of columns are determined practically in field. It is done by laying rope according to grids shown in the drawing and then mark the location of columns related to rope.

In drawing, column locations are shown related to grid-line with dimension. Practically, in field, ropes are our grid-line. So we place columns related to rope-line by measuring dimension shown in the drawing.

STEP 2.Column Reinforcement work: After marking the column locations, we then start to place reinforcement as instructed in the structural drawing.

This is normally described in the drawing like -

C1-12#16 mm and stirrup-10 mm @ 4" c/c.⌀ ⌀That means column C1 will have 12 numbers of 16 mm diameter bar as vertical bar and 10 mm diameter steel should be placed 4 inch center to center as stirrup.orC2-8#20 mm + 10#16 mm and stirrup-10 mm @ (4"+6”) c/c.⌀ ⌀ ⌀

SPECIFICATIONS

This is normally described in the drawing like -

C1-12#16 mm and stirrup-10 mm @ 4" c/c.⌀ ⌀That means column C1 will have 12 numbers of 16 mm diameter bar as vertical bar and 10 mm diameter steel should be placed 4 inch centre to centre as stirrup.orC2-8#20 mm + 10#16 mm and stirrup-10 mm @ ⌀ ⌀ ⌀(4"+6”) c/c.

This C2 column's reinforcement specification means that it'll have 8 numbers of 20 mm diameter bar as well as 10 numbers of 16 mm diameter bar as vertical reinforcement and (4"+6") centre to centre of stirrups placement means middle-half portion of clear height of column will have 6" centre to centre spacing of stirrups and upper one-fourth as well as bottom one-fourth height of column's clear height will hold stirrups at 4" centre to centre spacing.

STEP 3. Column formwork: In building, floor height is normally kept 10 feet. If the slab has beam then we have to pour concrete up to beam bottom level. Suppose, beam height specified in drawing is 1'-6". So, the casting height of our column will be 8'-6". And our formwork height will be 8'-6". But one thing should be considered here is that dropping concrete from above 5' height isn't suggested during pouring. Because it leads concrete segregation. So we should make one-side of column formwork within 5 feet height range. After casting 5 feet of column, we just lift the short side up to full-casting height of column next day.

Another way to cast column without segregation is to keep a small window at 5 feet level of full-height formwork. After casting up to that level, close the window and cast the rest of the column.STEP 4.

Pouring concrete into column: Casting column is easy. For small quantity of concrete volume normally constructors depend on machine-mix concrete and for large concrete quantity and order ready-mix concrete.Because, if moving pump with ready-mix concrete is used to not exceed 5 feet height range for dropping concrete that would be difficult.

Leave it to dry for 3-4 days by regularly watering the freshly casted column.

BEAMS

RCC BeamsA beam is a structural elements that is capable of withstanding load primarily by resisting against bending. The bending force induced into the material of the beam as a result of the external loads, own weight, span and external reactions to these loads is called a bending moment. Beams are characterized by their profile (shape of cross-section), their length, and their material.Concrete can provide a cost effective solution offering a composite beam and floor solution which will reduce overall depth and weight with connections developed to your requirements.Beams are traditionally descriptions of building or civil engineering structural elements, but smaller structures such as truck or automobile frames, machine frames, and other mechanical or structural systems contain beam structures that are designed and analysed in a similar fashion.

Introduction to Beams

Historically beams were squared timbers but are also metal, stone, or combinations of wood and metal such as a flitch beam. Beams generally carry vertical gravitational forces but can also be used to carry horizontal loads (e.g., loads due to an earthquake or wind or in tension to resist rafter thrust as a tie beam or (usually) compression as a collar beam). The loads carried by a beam are transferred to columns, walls, or girders, which then transfer the force to adjacent structural compression members. In light frame construction joists may rest on beams.

Classification of beams on the basis of supports

Classification of beams based on supports:

• Simply supported - a beam supported on the ends which are free to rotate and have no moment resistance.

• Fixed - a beam supported on both ends and restrained from rotation.• Over hanging - a simple beam extending beyond its support on one end.• Double overhanging - a simple beam with both ends extending beyond its supports on

both ends.• Continuous - a beam extending over more than two supports.• Cantilever - a projecting beam fixed only at one end.• Trussed - a beam strengthened by adding a cable or rod to form a truss

SIMPLE BEAM CONTINUOUS BEAM

CANTILEVER BEAM

SEMI CONTINUOUS

Types of beams

• Edge/Spandrel Beams – span around perimeter to provide a bearing edge on one side for flooring slabs and structure above.

• Spine Beams - Provide a bearing edge on two sides for flooring slabs.• Lintel Beams - Span over door or window opens, to provide bearing for structure above.• Balcony Beams - These are beams cast with an integral balcony.• Raker Beams – Can be designed and supplied with required bearing for terracing units.

Thin walled beamsA thin walled beam is a very useful type of beam (structure). The cross section of thin walled beams is made up from thin panels connected among themselves to create closed or open cross sections of a beam (structure). Typical closed sections include round, square, and rectangular tubes. Open sections include I-beams, T-beams, L-beams, and so on. Thin walled beams exist because their bending stiffness per unit cross sectional area is much higher than that for solid cross sections such a rod or bar. In this way, stiff beams can be achieved with minimum weight. Thin walled beams are particularly useful when the material is a composite laminates.

Construction of Beams• Lay down the steel beam - as the adjacent picture shows beams are the core of the plinth

beam. Beams have a loop every 6" that holds it together. • Setup re-inforcement - before concrete is poured, re-inforcement has to be established to provide

rectangular shape to the beam. This takes majority of effort as planks have to be nailed properly in place and once concrete is poured they need to be removed.

• Pour the concrete - next step is to pour the concrete. As concrete is poured, mason ensures that it is evenly spread and smoothens out any edges. He also needs to ensure the height of the beam is consistent throughout the periphery.

• Remove re-inforcement - concrete turns solid within 24-hour and final step is to remove the planks leaving the beam intact.