What Is Spandrel Beam?
The spandrel beam is the exterior beam that runs horizontally from one column to the next in steel or concrete constructions. These are also referred to as edge beams.
Spandrel beams are provided on each floor, which aids in the differentiation of floor levels in high-rise buildings. Because masonry walls cannot carry self-weight and slab weight totally, these are used to support the load of a building’s peripheral walls and, in some situations, roof loads.
How Is Load Distributed In Spandrel Beam?
Spandrel beams are intended to support both external wall loads and slab loads from slabs to outer columns. The entire load is then transferred to the footings via the columns.
Because of their interaction with the floor beams, these beams experience axial compression, torsion, bending moment, and shear loads all at the same time in RCC structures. Torsion is the primary means of transmitting slab load from beam to columns.
As a result, it generates a complex load distribution system. Beams built as flanged floor beams, such as T-Beams and L-Beams, are more torsional load resistant than rectangular floor beams.
As a result, spandrel beams or edge beams are constructed as flanged floor beams in order to maximize the overall load capacity of the high-rise building.
Types Of Load Applied
- Gravity Load-General Beam Load,
- Horizontal Loads,
- Beam End Connections,
- Spandrel Ledges,
- Volume Change Forces,
- Frame Moment Forces.
General Design Requirements
When building a spandrel beam, it is important to understand how the applied load will be transferred from the point of application to the beam and then to the structural member. The following are some of the fundamental design requirements:
- Beam flexure,
- Internal torsion and shear,
- Beam end torsion,
- Ledge attachment to the web,
- Ledge load transfer,
- Web flexure resulting from torsion equilibrium ,
- At the beam end reaction, the ledge acts as a corbel.
1. Internal Torsion And Shear
Torsion occurs when vertical and horizontal loads are applied that do not pass through the shear center of the beam. The developed torsion to the beam at any cross-section is the sum of the torques (shear force times distance from the shear center) operating at that cross-section.
The loads applied to the beam may differ from the time of erection until the time when all time-dependent volume change loads act. Each loading case must be monitored to determine which controls the design.
Once the applied torsion and shear are known, the internal torsion and shear reinforcement can be calculated according to the ACT 3183 standards for reinforced members or by utilizing it.
2. Torsion At The Beam End
Torsion at the beam’s end, within the distance “d” or “d/2,” is defined as the torsion caused by the torsion equilibrium end connections.
Torsion of beam ends generated by the top and bottom connections is often characterized by a single crack.
This crack is inclined at an angle of about 45 degrees and has a nominal width of 0.015 in. (0.38 mm) or greater.
3. Ledge Attachment
Depending on the beam dimensions, concrete strength, and magnitude of the ledge load, the spandrel beam ledge can be attached to the web using either plain concrete or reinforcing steel. The horizontal connection of the ledge to the web is compared to the action of two hard bodies, where separation would occur throughout the full length of the beam’s web on the attachment plane.
4. Ledge Load Transfer
The ledge of the spandrel beam transfers uniform and focused loads to the web via shear and flexure. The engineering processes described for ledge load transmission are based on the PCI Design Handbook, with certain modifications. The ledge load transfer must satisfy concrete punching shear if no shear reinforcement is used.
5. Web Flexure Resulting From Torsion Equilibrium
If the spandrel beam’s overall torsion equilibrium is formed by the beam web working against the tops of the members it supports and the bottom connections at the spandrel’s end vertical reaction, two types of web flexure can occur.
When horizontal loads are applied to the beam web, a similar loading state can develop, except that the forces are directed in the opposite direction as those resulting from vertical load torsion equilibrium.
6. Ledge Acting As A Corbel At Beam End Reaction
When a spandrel beam’s end support reaction coincides with the applied ledge loads, the ledge behaves like an upside-down corbel. The upside-down ledge corbel can be constructed to sustain the end reaction by modifying the processes in the PCI Design Handbook for corbels.
7. Beam Flexure
Two distinct loading conditions are necessary for general spandrel beam flexure, one at the service level and one in the final state. The techniques of analysis can be essentially the same or substantially different depending on the cross-sectional dimensions of the beam and whether or not the spandrel includes reinforcing bars or prestressing strands.
If the connections between the spandrel beam and the structural units supported by the spandrel do not preclude torsional rotations, the influence of principal axes of inertia relative to service loads must be considered. Spandrel beams typically lack symmetry about either axis.
Furthermore, if the depth of the beam is shallow, the orientation of the principle axes may be significant when evaluating elastic stresses at the service level for reinforcing bars or prestressed reinforcement.
Features Of Spandrel Beam
The properties of the Spandrel beam are strongly influenced by the characteristics of the floor beam. Beams attached to flange floor beams rather than rectangular floor beams have a higher resistance to torsional loads.
As a result, the ultimate load capacity of the high-rise building is increased. Torsion of the Spandrel beam is a crucial feature because torsion is used to transport slab load from beam to column.
Since torsion is used to transfer the weight from the slab to the columns in a spandrel beam structure more reinforcement is required for the beam to prevent torsional failure.
As a result, when constructing the beam, extra care must be taken to avoid torsional failure. ACI Committee 318, Building Code Requirements for Structural Concrete and Commentary, is the most recent design code used for this beam (ACI 318-19).
In flat slab designs, spandrel beams are employed to reinforce the connections between the slabs and the edge columns.
Advantages Of Spandrel Beam
1. Spandrel beams add strength to the outside walls of a multi-story building.
2. The lateral stiffness of steel and concrete constructions is increased by using these beams. In large beam-column connections, spandrel beams with both longitudinal and transverse reinforcements are preferred. This enhances the building’s seismic performance.
3. Spandrel beams are used in coupled shear walls to provide enough stiffness and ductility to withstand earthquakes. Along with shear walls and lintels, these also offer support for exterior side openings such as windows.
Disadvantages Of Spandrel Beam
1. Because Spandrel beams are positioned on the exterior of a building, they are more likely to come into contact with moisture than floor beams, resulting in rot. Hence, reinforcement steel deterioration or corrosion occurs.
2. Concrete cracking and spalling. As a result, a significant amount of money is spent on restoration.
Also Read –
How To Prevent Cracks In Concrete
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