- Spandrel Beam Meaning
- What is Spandrel Beam?
- Spandrel Beam Design
Spandrel Beam Meaning
In frame structures, spandrel beam plays an important role. This beam moves horizontally joining the exterior most columns to another column. Spandrel beam are generally known as “Edge beams”.
What is Spandrel Beam?
In multistory buildings, these beams are generally provided at each floor level to differentiate among the different floor levels. These are generally used to take care of the exterior wall load known as peripheral walls. These are load-bearing members in between load-bearing columns around the perimeter of building.
In case of high-rise buildings, masonry walls are not able to carry self-weight of its own and unable to carry the roof load also. Therefore, these beams are provided along with the external walls at each floor level to bear the wall load.
Now a days, these beams reinforced or prestressed are plays an important role in precast concrete structures. In concrete or steel structures, it is the exterior most beams that mark the floor level between different stories of the multistory buildings.
Properties of Spandrel beam
- The properties of this kind of beam are generally dependent upon the characteristics of floor beam in the building.
- To improve the torsional capacity of these beams, they are generally attached to the flanged floor beams rather than rectangular beams which ultimately enhance the overall load capacity of the multistory buildings.
- As we know that, slab load from beam to column is majorly transferred by torsional forces. Hence, the edge beam torsional behavior plays an important role while transferring the load from one member to another member.
- Due to large transfer of torsion from slab to column through spandrel beam high reinforcement is required in the beam to avoid failure in torsional behavior.
Also Read: Complete Guide on Tie Beam
Let’s discuss about various features of spandrel beam in the construction of RCC and steel structures.
Features of Spandrel Beam
- Spandrel beam are used in high rise building at each floor level.
- Parapets on the roof are generally placed on these beams.
- These beams improve the overall connection strength between column and slab.
- These beams are designed in such a way that they carry the load from slab and external wall load and further passed that load to the column. Therefore, it helps in overall load distribution system of the building.
- These beams are provided between the sill and head of the window.
Advantages of Spandrel Beam
There are number of benefits of spandrel beam which are as follows:
- These beams provide overall strength to the exterior walls of a high-rise building.
- These are generally used to increase the overall lateral stiffness of steel and concrete structures.
- These beams enhance the seismic-resistant of buildings.
- In coupled shear walls, these beams are also used to increase the stiffness and ductility of the structure during the earthquake.
- They act as protection to the windows and lintels.
Disadvantages of Spandrel Beam
As we know, everything has pros and cons the same is the case with spandrel beam. Let’s look at the disadvantages of these beams in the structures.
- As we learnt that these beams are placed on the exterior of the building, they get exposed to environmental conditions such as rain, heat, etc which ultimately degrades the concrete and corrode the reinforcement provided in the beam.
- As a result, restoration work of concrete cracking and concrete spalling demands a huge amount which further added to the list of disadvantages of these beams.
Load Distribution Method in Spandrel Beam
Let’s talk about the load distribution scene of spandrel beam. As we know that, these beams experience axial tension, shear stress, torsion, and bending moment in RCC building as they are connected to the floor beam due to which it creates a dynamic load distribution in the building. These beams are subjected to a variety of loads which are as follows:
- Gravity loads
- Horizontal impact forces
- Volume changes forces
- Frame moments
- Ledges transmitted load
- End connection load
Spandrel Beam Design
The basic design requirements of spandrel beams are as follows:
#1. Internal torsion and shear
As we know, torsion evolves when applied vertical and horizontal forces does not pass through the shear center of the beam. At any cross-section of beam, developed torsion is the total sum of the torques (shear force times distance from the center) operating at that section.
It is known that applied load on the beam may vary from the point of erection to when all time-dependent volume changes happen. Each loading case needs to be finding out which one actually controls the design of the beam.
If loads applied are vertical only, the shear center is assumed to be web vertical centerline.
#2. Beam end torsion
Beam end torsion can also be referred as torsion at end of beam. It is torsion at beam end within the distance ‘d’ or ‘d/2’ from the torsion end equilibrium connections. Generally, the torsion produced in beam is seen by single inclined crack at 45 degree which has width of about 0.015 in (0.38 mm) or greater.
#3. Ledge attachment to the web
The attachment of spandrel beam ledge to the web can be done by plain concrete or using reinforcement that completely depends upon various factors such as dimensions of the beam, strength of concrete, amount of ledge load. The connection of ledge to the web is similar to the motion of two hard bodies in which when separation happens, it will occur along the whole length of the beam.
#4. Ledge load transfer
The spandrel beam’s ledge transmitted uniform and focused loads to the web by flexure and shear. The PCI design handbooks are used to understand the engineering procedures for the transfer of ledge loads. This ledge load transfer must always satisfy the concrete punching shear when no shear reinforcement is used.
#5. Web flexure resulting from torsion equilibrium
Web flexure can come into the picture due to two different conditions which are as follows:
If overall torsion is developed by the beam web acting against the top of the members it supports and bottom connections at the end’s vertical connection.
Same condition may also arise when horizontal loads are applied to the web portion of the beam except that the forces are applied in opposite direction due to vertical load torsion equilibrium.
#6. Beam flexure
In general, the spandrel beam requires two well defined loading conditions one at service level and another one at final level or final state. The method of analysis could be same or different it completely depends upon the cross-sectional dimensions of the beam and the type of reinforcement provided. When the connections between the edge beam and the other structural members are not able to prevent torsional rotations, then it is important to consider the inertia principal axes. These beams are generally lacking in symmetry about the axes.
When the depth of beam is shallow, the direction plays an important role while evaluating the elastic stress at the service level for reinforcement.
#7. Ledge acting as a corbel at beam end reaction
Ledge acting as a corbel at beam end reaction can be referred as “corbel end behavior”. This condition arises when the beam’s end support reaction coincides with the applied ledge loads, the ledge acts as an upside-down corbel. This upside-down corbel can be designed using the PCI design handbook for the engineering procedures.