As an integral part of frame designs, the Spandrel Beam appears. The focus of this article is on the description and discussion of various aspects of spandrel beams.

What is Spandrel Beam?

Spandrel beams are reinforced important and functional elements of precast concrete structures. The spandrel beam come up as an important part of frame designs. The spandrel beam is the external beam that extends horizontally from one column to another. These beams are also known as edge beam.

On each floor, spandrel beams are provided that help differentiate the floor levels in high-rise buildings. This is used to sustain the load of the peripheral walls, even roof loads of a building in certain instances since masonry walls do normally not completely bear self-weight and slab weight.

Load Distribution Method

Spandrel beams are designed for the transfer to the outer columns of external wall load and slab load from slabs. And the whole load through the columns is carried on to the footings. These beams experience simultaneous axial tension, torsion, bending moment, and shear stress in RCC systems due to their contact with the floor beams. The slab load is fundamentally shifted from the beam to the columns by torsion. Therefore it generates a dynamic load management mechanism.

Types of Loads Applied

• Gravity Load-General Beam Load
• Horizontal Loads
• Beam End Connections
• Spandreal Legdes
• Volume Change Forces
• Frame Moment Forces

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Features of Spandrel Beam

The properties of the Spandrel beam are heavily dependent on the characteristics of the floor beam. Instead of rectangular floor beams, beams attached to flanged floor beams produce improved capacity to withstand torsional stresses. This consequently increases the high-rise building’s ultimate load capacity. The Spandrel beam’s torsional activity is a significant aspect as the slab load is fundamentally transferred by torsion from beam to column. Therefore when building, the beam requires additional exposure to torsional collapse. For this beam, the current construction code adopted is ACI Committee 318, Structural Concrete Building Code Specifications, and Commentary (ACI 318-19).

Uses of Spandrel Beam

Spandrel beams are used at each level of the floor of multi-story buildings. This is connected as a belt to the outside perimeter of floor slabs to reinforce the beams of the floor. It also reinforces the connection between the slab and the columns outside. The parapets above these beams are mounted on the roofs.

General Design Requirements

We have to consider how the applied load is transmitted from the point of application to the beam and then to the structural element while designing a spandrel beam. Some of the basic design requirements are:

• Internal torsion and shear
• Beam end torsion
• Ledge attachment to the web
• Ledge load transfer
• Web flexure reulting from torsion equilibrium
• Ledge acting as a corbel at beam end reaction
• Beam flexure

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Internal Torsion and Shear

When applied vertical and horizontal loads do not pass through the beam’s shear center torsion evolves. At any cross section, the evolved torsion to the beam is the sum of the torques (shear force times distance from the shear center) acting at that particular cross section. It is possible that the loads applied on the beam can differ from the time of erection to when all time-dependent volume change loads act. Each loading case requires monitoring to find out which controls the design.

Once the applied torsion and shear are known, the internal torsion and shear reinforcement can he determined following ACT 3183 requirements for reinforced members or employing other relationships 9′ for prestressed members. If only vertical loads are applied to the spandrel, the shear center can quite conservatively be assumed to align with the beam’s web vertical centerline.

Beam End Torsion

Beam end torsion is defined as the torsion at the beam’s end, within the distance “d” or “d/2,” resulting from the torsion equilibrium end connections. Typically, beam end torsion created by top and bottom connections is characterized by a single crack, inclined at about 45 deg, having a nominal width of 0.015 in. (0,38 mm) or greater.

Ledge Attachment

Attachment of the spandrel beam ledge to the web can be either by the strength of plain concrete or by reinforcing steel depending upon the beam dimensions, concrete strength, and magnitude of the ledge load. The ledge to web horizontal attachment is considered similar to the action of two hard bodies where separation would occur along the entire length of the beam’s web on the attachment plane.

Ledge Load Transfer

The spandrel beam’s ledge transfers uniform and concentrated loads to the web by shear and flexure. The engineering procedures presented for transfer of the ledge loads are based on the PCI Design Handbook with some
variations. The ledge load transfer must satisfy concrete punching shear if special shear reinforcement is not to be used.

Web Flexure Resulting from Torsion Equilibrium

Two instances of web flexure can develop if the spandrel beam’s overall torsion equilibrium is generated by the
beam web acting against the top of the members it supports and bottom connections at the spandrel’s end vertical
reaction. A similar loading condition can occur when horizontal loads are applied to the beam web, except that the forces have a direction opposite of those resulting from vertical load torsion equilibrium.

Ledge acting as a Corbel at Beam End Reaction

When the end support reaction of a spandrel beam aligns with the applied ledge loads, the ledge acts like an upside down corbel The upside down ledge corbel can be designed to support the end reaction by following the procedures of the PCI Design Handbook for corbels with some modifications.

Beam Flexure

General spandrel beam flexure involves two distinct loading conditions -one at service level and the other at ultimate state. Depending upon the beam’s cross-sectional dimensions, and whether or not the spandrel employs reinforcing bars or prestressing strands, the methods of analysis can be basically the same or fundamentally different. If connections between the spandrel beam and the structural units supported by the spandrel do not prevent torsional rotations, then it may be necessary to consider the influence of principle axes of inertia relative to service loads.Spandrel beams usually do not have symmetry about either axis. And, if the depth of the beam is shallow, then when determining elastic stresses at service level, for either reinforcing bars or prestressed reinforcement, the orientation of the principle axes possibly can be critical.

Advantages of Spandrel Beam

• Spandrel beams impart additional power on a multi-story building’s exterior edges.
• The lateral stability of steel and concrete frameworks is improved by these beams. Spandrel beams with both longitudinal and transverse reinforcements are preferred to be used in large beam-column links. This boosts the seismic efficiency of the house.
• To generate adequate stiffness and ductility against earthquake events, spandrel beams are used in coupled shear walls.
• This also provides help with shear walls and lintel for exterior side openings such as windows.

Disadvantages of Spandrel Beam

Spandrel beams are placed on the outside of a house, they come into contact with moisture more frequently than floor beams, resulting in moisture.

• Deterioration or rusting of steel reinforcements.
• Concrete Breaking and Spalling.

A considerable sum of money is also spent on reconstruction.

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