Buildings are often made up of a combination of masonry walls and steel beams, among other things. Those masonry walls function as both bearing and non-bearing components. In steel detailing, beam-to-masonry connections have to account for various factors, such as:
- The type of connection
- The potential for movement between the two systems
- Lateral bracing of the masonry wall(s)
The most common connections between steel beams and masonry are K-series and LH-series steel joists. These open web joists come in various spans and depths, depending on their bearing requirements.
The range of K-series joists is between 8 and 30 inches in depth and has a maximum span of 60 feet. The minimum requirement on masonry is 4 inches, and the joist may be anchored to a steel bearing plate with a minimum width of 6 inches. LH-series joists range from 18-48 inches deep, and span a maximum of 96 feet. Their minimum bearing requirement on masonry is 6 inches, and the anchoring plate (if needed) must have a minimum width of 9 inches.
In some cases, it is necessary for a steel beam to bear on a masonry wall less than the requisite dimensions. This is particularly true for the construction of tall, slender reinforced masonry walls, wherein the structural engineer must design the connection between the steel beam and the masonry with special attention.
Connections to bearing and non-bearing walls
Masonry walls require lateral bracing to resist wind loads. This additional bracing often comes from the roofing and the steel beam connections. The steel beams function as a diaphragm for a constant brace against wind loads.
Bearing walls are braced where the masonry connects to the steel beams. The design of the connection should facilitate easy installation, and it must be adjustable in two directions:
This is to accommodate construction tolerances. Where a welding connection is required, there should be studs on the bearing plate to achieve the necessary adjustability. This can increase the wall’s allowable height without increasing its thickness. The joist’s bottom chord can be extended and connected to the wall once all the roofing dead loads are in place.
The steel beam must have sufficient stiffness to minimise any deflection once live loads are applied. Excessive deflection can cause horizontal cracks to develop in mortar joints.
With non-bearing masonry walls, connection adjustability is less important. You can accomplish the connection by extending an angle over the steel beam’s bottom cord and welding it to the concrete masonry wythe via an anchored angle. The extended bridging angles must be aligned with the horizontal steel beam to prevent crimping due to wind loads.
The beams that are connected to the masonry must have adequate stiffness to resist maximum deflection. Roofs should also have sufficient insulation to avoid joist movement due to variations in temperature. Thermal movement can be accommodated by modifying the camber of the top chord of the steel beam.
A slippage joint can be created at the connection. It must be a slotted connection that is oversized in order to accommodate movement from the steel beam. There should be a washer over the slot and an expansion anchor installed through the slot and tightened.
In order to successfully design masonry and steel connections, one must have a complete understanding of both materials. There are many problems that can arise from improper design and application of the connections, but they can be avoided with well-developed and workable connection details.
Jensen Consulting’s steel connection design and calculation service can ensure your steel beams are connected to masonry in the right way for successful construction. Contact us to enquire about what we do.