The term “hard walls” would seem to encompass steel walls as well as any other type of wall, but in this case, we are talking about masonry or concrete attached to the frame in place of steel panels. While steel wall panels are available in nearly every color, texture and pattern under the sun, there are still times when a hard wall is the better choice.
The owner may have a particular aesthetic appearance in mind, or it is more cost effective to reduce sound issues with a hard wall. Security, stability and lateral load and fire resistance are a few more reasons why hard walls are installed in preference to steel.
In some areas, permitting may be easier if the structure is designed with hard walls in mind. Also, hard walls may increase the value of the completed building.
Types of hard walls, wall bases, wainscoting and direction of the span are all considerations when designing a masonry or concrete building with a steel frame.
When to Use Hard Walls
Hard walls, aside from durability and aesthetic appeal, often withstand incidental impacts from equipment and machinery used within and around the building. Where steel panels may dent, dimple or scratch, a masonry wall will not receive more than a mark or tiny divot. In warehouse and manufacturing conditions, concrete may be the material of choice for durability and aesthetics as the building ages.
For protection against flying and falling debris in the case of earthquake or hurricane, concrete encased steel members can outperform other cladding. Thick masonry walls can muffle noise from the outside to provide a comfortable interior workspace for the building’s occupants. In regions with high traffic, manufacturing or other noise, concrete or masonry added to the steel frame will block a high percentage of the sound waves.
Hard walls come in two common types: single-wythe and cavity walls.
Single-wythe walls are also called barrier walls. They are usually concrete masonry units (CMUs), commonly known as cinderblock. Wall strength depends on the impermeability and solidity of a single layer.
Cavity walls are used when a single layer is insufficient as a moisture barrier. It is built from a masonry veneer, and a structural back-up wall of masonry or steel studs is added.
Hard Wall Challenges
Hard walls have their weaknesses, just like any other material.
- It is critical to design with the movement differential between metal and masonry in mind. Additional lateral support may be required.
- Concrete and masonry are brittle materials that crack and crumble during seismic movement, whereas steel can bend without failure.
- Finding competent designers who are familiar with both steel and concrete construction may be difficult. Often, contractors and owners do not consider the difference in expertise.
- The steel building manufacturer may not be willing to take responsibility for the entire building if it includes concrete or masonry walls.
- Building with concrete cast in place is much slower than assembling a complete pre-manufactured steel building.
Concrete and masonry work require specialized skill sets that steel erectors may not have. The added expense of the longer construction time-line and the need for additional workers may not fit the original budget.
The Need for Hinged Wall Bases
Deformation and stiffness differences between rigid concrete and flexible steel create the need to control the location of cracking in the masonry. Cracks are most likely to occur when a steel frame deflects at the top of the structure, where the movement is greatest.
The answer to the problem is a hinge.
- A hinge is incorporated at the base of the masonry wall to allow for out-of-plane rotation with less damage.
- One hinge type is created with through-wall flashing to break the bond at the base of the wall and provide support that allows for shear transfer but no moment for out-of-plane loading.
- A second hinge type is used when masonry wall sections are used as shear wall segments. Vertical reinforcement continuous into the foundation is required. Flashing at the floor level allows some out-of-plane rotation from building drift.
The building corners must be detailed correctly to accommodate movement allowed by a masonry hinge. A vertical isolation joint placed near the corner and thoughtful design of masonry and steel connections at the corner columns using flexible anchors or slotted connections should resolve the issue.
The full benefits of masonry walls are provided by full height walls, particularly for shear walls. However, partial height walls can be used if designed appropriately. Partial height walls are called wainscots, which vary in height from four to ten feet. They are bordered by metal panels extending from the top of the masonry to the roof.
The concrete provides additional strength and impact resistance for that portion of the wall most exposed to potential damage.
A cantilevered wainscot can be constructed independently of the metal wall, or it can span horizontally between the metal columns of the frame. Another variation is building the masonry span vertically between the ground and a row of girts on the steel frame or a beam constructed along the top of the masonry run between building columns.
Construction Sequence for Hard Walls
Building a masonry wall with a steel frame typically begins with the concrete footing and steel column placement.
- A concrete foundation wall is constructed to grade, and a concrete slab is placed.
- The steel frame is erected.
- The concrete masonry wall is constructed and attached to the frame.
When load-bearing endwalls are required by design, the steel frame is erected after the masonry wall is in place.
Concrete masonry walls may be the best choice when constructing new buildings in an area with certain types of architectural design to maintain the overall aesthetics and ambiance along a street. Concrete is also an excellent material for deadening sound and creating a quiet interior environment.
However, building concrete walls with a steel frame requires specific skill sets, and close coordination is needed to ensure the completed structure meets building codes and the design requirements of the owner. A carefully constructed masonry and steel building will stand for decades.