What is a Framed structure?

It is a rigid and stable framework of structures that consists of structural members like slabs, beams, and columns that can resist the deformation due to the self-weight and high external loads and transfer the applied loads safely to the substructure and consecutively to the ground. It is made of different materials, such as reinforced concrete, steel, and wood. In ancient days, load-bearing structures were used to build houses and houses were built using load-bearing walls.

Rigid frame structure

A structural frame that can resist the deformation caused due to applied vertical and lateral loads using the rigidly connected joints. In this frame, the moments are transferred through the joints.

Pin ended rigid frame structure

This type of frame has pinned end conditions and if these pinned supports are removed, the frame behaves like a non-rigid structure.

Fixed ended rigid frame structure

This type of framed structure has its support ends fixed.

Braced Frame Structure

In this type of framed structure, bracing (diagonal support) is provided between the structural elements to resist lateral and seismic loads.

Portal frame structure

This framed structure has its vertical supports connected with its horizontal supports using fixed joints to increase the moment-resisting capacity.

Gable frame structure

This framed structure has a triangular extension at the top of the roof and is used for single-story frame construction. Also, this frame is employed in places where heavy rain and snow are common occurrences.

Structural components of frame structure

Columns

A column is a vertical structural element that is designed to take up the downward or axial compressive load acting on the framed structure and transmit it to the foundation. In reinforced concrete structures, the slabs, beams, and columns are cast monolithically.

The columns are classified based on the loading, slenderness ratio, and cross-section.

Based on Loading

(a) Axially loaded column

If the load is applied directly along the longitudinal axis of the column, it is called an axially loaded column.

(b) Uniaxially loaded column (Eccentrically loaded column)

When the load acts away from the centroid of the column, it is called an eccentrically loaded column. In the uniaxially loaded column, the eccentricity will be along with any one of the axes (either X-axis or Y-axis) and cause a moment along that particular axis.

(c) Biaxially loaded column (Eccentrically loaded column)

In the biaxially loaded column, the loads are applied at points other than the axes of the column resulting in moments acting about both the X-axis and Y-axis simultaneously.

Based on the slenderness ratio

(a) Short column

For a short column, the ratio of the effective length of the column to its least lateral dimension (LLD) is equal to or less than 12. The short column usually fails due to direct compression or crushing.

(b) Long column

For a long column, the ratio of the effective length of the column to its LLD is greater than 12. The failure of the long column takes place by buckling.

Based on cross-section

The columns are classified as rectangular, square, circular, L-shaped, and T-shaped columns based on their cross-section.

Beams

Beams are horizontal structural members that run horizontally between columns and transfer the applied load to the column. It takes up the load that is laterally applied to its axis. Beams are classified based on the type of support, material, cross-section of the beam, and based on function.

Based on the type of support

(a) Simply supported beam

It is a beam in which both of its ends are supported, one of the ends has pin support and the other end has roller support. This type of beam gets subjected to both bending moment and shear force depending on the loading condition.

(b) Fixed beam

This type of beam has its ends fixed into the column to provide more stability. Generally, beams of the general building area of fixed beam type.

(c) Overhanging beam

When the length of the beam exceeds the support on its side, it is called an overhanging beam. It is employed to construct balconies in buildings.

(d) Double overhanging beam

It has overhanging on both sides of the beam.

(e) Continuous beam

The beam which has supports at intermediate points in addition to the supports at the end is called a continuous beam. This type of beam has more than one span and is generally employed in the construction of bridges.

(f) Cantilever beam

This beam has one end fixed and the other end free. This beam is employed in bridge construction and balconies.

Based on Materials

Timber, steel, and reinforced concrete are the different materials used for the construction of beams. If different materials are combined to form a single beam element, it is termed a composite beam.

Based on cross-section

Rectangular, L-shaped, T-shaped, C-shaped and I-shaped beams are different types of beams based on cross-section.

Based on function

Main or primary beams

It is the horizontal beam that will directly transfer the load applied to it to the columns.

Secondary beams

These beams transfer the applied load to the main beams.

Slab

Slabs are constructed to provide flat surfaces to act as a floor or roof in structures. Slabs are supported by beams and slabs are cast monolithically with the beam. Based on the supports, the slabs are classified as one-way and two-way slabs.

One-way slab

The slab which is supported by beams on only two of its sides is called a one-way slab. The length to breadth ratio is equal to or greater than 2 and loads are transferred along the shorter span. Main reinforcement steel bars are provided along the direction of a shorter span and distribution reinforcement steel bars are provided along the direction of a longer span.

Two-way slab

This type of slab is supported by beams on all four sides and carries the load in all directions. The length to breadth ratio is less than 2. Main reinforcement steel bars are provided in both directions of the slab.

Foundation

Foundation is the bottom-most structural element of a structure that rests under the ground, it takes the load from the superstructure and transfers it safely to the ground such that the safe bearing capacity of the soil is not exceeded. The soil on which the foundation rests is called a foundation bed.

The foundations are classified as shallow and deep foundations depending on the depth of foundation.

Shallow foundation

When the depth to width of the foundation is less than 1, it is termed as a shallow foundation. This foundation transfers the load near to the ground surface. This type of foundation is used when the soil has a high bearing capacity. The shallow foundation is classified as cantilever or strap footings, mat/raft footings, column footings, and wall footings.

Deep foundation

When the load from the superstructure is heavy and the bearing capacity of the soil is less, deep foundations are used. This type of foundation is used when the top surface soil is unsuitable and deeper soil strata are more stable. It is further classified as pile, pier, and wall foundation.

Shear walls

It is a panel, like a vertical structural element which is designed to resist the lateral loads (wind and seismic forces). It is usually constructed with concrete or braced steel frames or masonry. It is generally employed in large and high-rise building construction. Shear wall is placed either on the perimeter of the building or is designed to form a shear core (structure of shear walls) to encase stairwell or lift shaft.

Context and Applications

Structural components of Framed structure are a vital part of the following courses:

• Bachelors of Technology in Civil Engineering
• Masters of Technology in Structural Engineering

Practice Problems

1. What are ceiling joists?

1. Ceiling joists are another name of shear walls.
2. Ceiling joists provide a surface to fix rafters.
3. It acts as a stairway in concrete structures.
4. It supports load-bearing walls.

Answer: Option b

Explanation: Ceiling joists are structures that are placed above the wall frame in a direction perpendicular to it, to provide a surface to fix the rafters to increase the strength of the structure.

2. After how many days formwork of sides of beams and columns are removed in the Concrete Frame Structure?

1. 72 hours
2. 86 hours
3. 48 hours
4. 12 hours

Answer: Option c

Explanation: The Formwork of the sides of beams and columns is usually removed after 48 hours of concrete casting.

3. Which of the following cross-sectional shape is best for concrete column construction?

1. Circular
2. Rectangular
3. Hexagonal
4. Square

Answer: Option a

Explanation: Circular columns are best preferred for columns as their resistance to buckling is more compared to other cross-sections of the column.

4. What are the bottom plates in framing?

1. A plate that supports the exterior wall.
2. Bottom plates are used to connect the wall stud to the floor.
3. It connects exterior wall with interior walls.
4. Another name of floor joists.

Answer: Option b

Explanation: Bottom plates are provided for the wall stud of partition to rest upon.

5. What is the function of the top plate in the Structural Frame?

1. Top plate connects interior walls with floor joists
2. Provides surface to support the roof/floor
3. Similar to steel bars in light-frame structures
4. Helps to transfer the load in light-frame structures

Answer: Option b

Explanation: It supports the roof or floor of the next level