Elements of Skeleton System: Beams

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Questions and Answers

What is a beam?

A horizontal element of a structure that spans between one or more supports.

Which of the following is NOT a common purpose of a beam?

  • Supporting a vertical wall directly (correct)
  • Supporting masonry above
  • Supporting a water tank above
  • Supporting slab above

The most common geometry of a beam is rectangular.

True (A)

In a rectangular beam, which dimension should be larger for optimal strength?

<p>Depth (A)</p> Signup and view all the answers

The depth of a beam should always be ______ than the width.

<p>larger</p> Signup and view all the answers

What are the two primary criteria for beam design?

<p>The maximum stress on the beam should not exceed the safe stress limits for the material, and the deflection should not exceed the specified limits.</p> Signup and view all the answers

What is meant by deflection in a beam?

<p>Deflection refers to the deformation of a beam from its original position when subjected to a load.</p> Signup and view all the answers

What is the main difference between a plinth beam and a coping beam?

<p>A plinth beam is located at the foundation level, supporting the masonry walls, while a coping beam is placed at the top of a parapet wall, protecting the wall from damage.</p> Signup and view all the answers

Match the type of beam with its description:

<p>Tie beam = Supports masonry above the plinth, often in the perimeter of a building Ground beam = Supports the load of the superstructure above the foundation Plinth beam = The first beam constructed in the skeletal structure, usually below the foundation Sill beam = A horizontal support below a window, often used in walls Lintel = Supports the weight above an opening like a door or window Band/Ring beam = Runs continuously around the perimeter of a building, supporting floors and roof loads Roof beams = Support the roof structure and distribute loads to columns Hidden beam = Not visible after the slab is cast, supporting masonry walls Inverted beam = Placed below the slab, often used for sunk slabs or porches Coping beam = Placed at the top of a parapet wall, protecting bricks from damage Simply supported beam = Supported at two points, with a pinned support at one end and a roller support at the other Cantilever beam = Fixed at one end and free at the other, extending outward Overhanging beam = Extending beyond the supports, with one or both ends unsupported Continuous beam = Supported at multiple points, with more than two supports Grid beams = A set of beams in two perpendicular directions, supporting a slab above Portal beam = A structure with an integrated beam and two columns</p> Signup and view all the answers

What is the primary function of a sill beam?

<p>A sill beam supports the load above a window opening, preventing the wall from cracking under stress.</p> Signup and view all the answers

A lintel is a type of beam used to support the weight above door or window openings.

<p>True (A)</p> Signup and view all the answers

What is the main difference between a simply supported beam and a continuous beam?

<p>A simply supported beam has two supports, one pinned and one with a roller, while a continuous beam has more than two supports.</p> Signup and view all the answers

A cantilever beam is fixed at both ends.

<p>False (B)</p> Signup and view all the answers

Which of these is NOT an advantage of using a continuous beam?

<p>Requires more complex design and construction (B)</p> Signup and view all the answers

What is a pergola, and where is it typically found?

<p>A pergola is a structure made of beams with smaller spacing that doesn't have a slab above. It's often found at terrace levels for architectural purposes.</p> Signup and view all the answers

A portal beam is a structure that combines an arch with a beam.

<p>False (B)</p> Signup and view all the answers

What is the main characteristic of an arch beam?

<p>An arch beam is a compression member, meaning it experiences compressive forces along its length.</p> Signup and view all the answers

Flashcards

Beam

A horizontal structural element that spans between supports.

Beam Function

Beams support loads above, below, or between them, or to connect structural elements.

Beam Types (based on function)

Beams are categorized into types, including those in substructures (below plinth) and superstructures (above plinth).

Tie Beam

A beam used to tie columns together in substructure.

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Ground Beam

A beam located at ground level, supporting the structure's load.

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Plinth Beam

Beam laid above the foundation, typically supporting floor or roof loads.

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Sill Beam

A beam placed below a window.

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Band Beam

A beam that spans columns, perimeter and supports loads.

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Lintel

A beam above a door or window opening, supporting a wall or roof.

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Roof Beam

A beam supporting the roof structure.

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Hidden Beam

A beam not visible after the slab is cast. It supports loads from walls.

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Inverted Beam

A beam with the slab below it, commonly in porches or sunken areas.

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Coping Beam

Beam on top of a wall, protecting it from wear.

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Simply Supported Beam

Beam supported at two points.

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Cantilever Beam

Beam fixed at one end, free at the other.

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Continuous Beam

Beam supported at multiple points.

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Overhang Beam

Beam extending past its supports.

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Rectangular Beam

Most common beam shape, with a larger depth than width.

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Pergola

A set of beams with no slab above, typically an architectural feature.

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Grid Beams

Set of beams in perpendicular directions, supporting a slab.

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Portal Beam

Beam and columns that integrate.

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Arch

A curved structural component used as a beam.

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Normal Load Distribution

How loads from occupants and items are transferred through slabs to beams then to columns.

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Study Notes

Elements of Skeleton System: Beams

  • A beam is a horizontal structural element that spans between one or more supports.
  • Beams serve various purposes, including:
    • Connecting columns
    • Supporting masonry above
    • Supporting slabs (both above and below)
    • Supporting secondary beams
    • Holding suspended accessories (e.g., electrical fixtures, cables, ducts, ceilings, water tanks)

Beam Geometry

  • Rectangular geometry is the most common beam shape.
  • Beam depth should always be greater than the width for strength.
  • Width should be 115mm and depth 75mm for RCC framed structures.

Beam Design Criteria

  • Beam depth is determined based on the maximum stress on the beam and deflection limits.
    • Maximum stress must not exceed safe stress limits for the material.
    • Deflection must not exceed specified limits.

Types of Beams

  • Beams are categorized based on their function:

    • Below the plinth/In Substructure:
      • Tie beam
      • Ground beam
      • Plinth beam (beam laid above foundation)
    • Above the plinth/Superstructure:
      • Sill beam (below the window)
      • Band beam
      • Lintel
      • Roof beam

  • Supporting masonry above:

    • Beams are positioned along the perimeter of a building to span the columns, often supporting floor or roof loads.

  • Hidden Beam:

    • Hidden beams are not visible after the slab is cast.
    • They support masonry walls.
    • They transfer wall load to main beams.
    • Common situations for hidden beams include:
      • Sunk slab for toilets
      • Porch beams
      • Staircase mid-landings

  • Coping Beam:

    • Placed at the top of a masonry parapet wall to protect it from wear.
    • Reinforced concrete coping beams have a rectangular shape.
    • There is no component above a coping beam, rather the masonry continues.

Beam Classification

  • Based on support pattern, beams are categorized as:
    • Simply supported: Two supports
    • Cantilever: One fixed support, one free end
    • Continuous: Multiple supports (more than two)
    • Overhanging: One or both ends extend beyond the supports

Simply Supported Beam

  • A simply supported beam has pinned support at one end and roller support at the other.
  • It undergoes shearing and bending depending on the applied load.
  • Commonly seen in bridge decks and precast beams.

Continuous Beam

  • A continuous beam has multiple supports along its entire span.
  • It supports horizontal and vertical forces with zero bending moment at the end support.
  • Used when span is long and building construction in fragments is not economical or plausible.

Beam Shapes

  • Beams can be classified by plan shape into:
    • Straight horizontal
    • Straight inclined
    • Curved

Unique Beams

  • Pergola: Set of beams spaced closely with no slab above (primarily an architectural feature).
  • Grid beams: Perpendicular sets of beams supporting a slab.
  • Portal beam: Integrated beam structure with two columns.
  • Arch: Compression member, often involving pre-stressed concrete.

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