If you ask a structural engineer to design an unsupported wall without a deep foundation, you’ll probably receive one of two answers: a T shape or a Z shape. Both rely on geometry rather than concrete to hold them up. Z-walls simply follow a slightly different path to reach their destination. A true picture of precast Z-walls production and application on UAE projects, and the true meaning of the shape.
The True Purpose of a Z-Wall
A Z-wall is a precast concrete barrier panel which is cast in an off-set cross section, rather than a flat face. Patent literature for barrier systems provides a clear description of the barrier design, which is stable and self-supporting due to the z-shape and without the need for additional structural support columns.
The whole idea is that it’s an offset geometry. A Z-wall is not only wider at base, like the T-wall, but has an angled profile that resists tipping and lateral forces along the length of the wall, instead of focussing the strength in one broad footing.
Students Learn About Why the Zigzag Shape Works
There are basically two types of self-supporting concrete barrier designs—the first being undulating wave-profile walls and the second being offset zigzag walls, both are designed to skip the deep foundation below the ground. The logic for this goes back decades, and it’s just basic structural common sense: A flat, unbroken wall wants to rotate horizontally, but a folded, offset wall offers much better resistance to that force, structurally it’s been braced on itself.
There is a downside here as well. A self-supporting profile wall will generally require significantly more material than an equivalent wall of the same height that is just a flat plate. The added cost of that material is the return you get: No deep foundation, no long site excavation, and the ability to quickly build your wall on a level surface.
What’s the True Difference Between Z-Wall and T-Wall?
The problem is the same for both: Z-walls and T-walls; both provide a barrier that does not require a poured foundation. A T-wall is a wall with one wide, strong footing under each section that forms the wall, and is perpendicular to the vertical panel. In a Z-wall, however, the shape of the offset panels is used to interlock sections end to end to support each other.
In reality, project teams usually are selected based on site size and footprint. T-walls are ideal for straight perimeter runs where space at the base is not limiting. Where the folded profile can also act as a natural visual screen, Z-walls can be effective; because the offset shape disrupts sightlines more effectively than a flat panel of the same height.
The First Step Is Mix Design for Strength and Site Condition
Like all important precast security products, it begins with a concrete mix. Barrier panels are made of high-strength reinforced concrete and range in compressive strength from standard high-strength concrete up to ultra-high performance concrete with over 20,000 PSI for more extreme blast or security situations depending on the threat level the wall is required to withstand.
Mix design also needs to consider local conditions for UAE based manufacturing such as very hot summer temperatures during curing, possible coastal salt exposure and the high life expectancy required of these barriers without any large scale maintenance required. The same mix successful in a mild climate won’t necessarily be successful in the 10 years of Gulf summers.
Reinforcement Cage Is Fabricated During Step 2
Workers will build the steel reinforcement cage to the correct size prior to casting based on the offset geometry of the panel. Since a Z-wall panel is not a flat panel, the reinforcement layout must mirror the fold and the reinforcement needs to be covered at the folds and the areas where adjacent panels will inter-lock.
In barrier grade applications, a mix of primary structural reinforcement and lighter secondary reinforcement that is distributed throughout the panel is generally used to achieve a balance of strength with the overall panel weight, with the heavier panels requiring more to be transported and installed.
The Next Step Is to Prepare the Mold and Cast
The forming process for the zigzag profile of Z-wall panels is more complicated than for a straight flat panel or even a T-wall panel which has a cross-section. The accuracy of the fit directly impacts the accuracy of adjacent panels’ alignment and interlock when installed on site.
Like other precast security barriers, casting is done in a factory, under controlled conditions. The controlled environment also produces a more uniform product than cast in place construction can ensure and this is vital to barrier products where each panel must react in the same way in a crisis.
Step 4: Curing
After casting, Z-wall panels are cured at controlled temperature and humidity to achieve the desired compressive strength. This is a critical step that is essential to the success of the mix design and if the panels are to be tested for barrier performance in the event of barrier impact or blast, under-cured panels will not meet the rated concrete strength.
The 5th Step Is Quality Control and Certification
Barrier panels are tested by reputable manufacturers to meet recognised standards, often in reference to ASTM manufacturing standards for structural quality. Depending on the risk classification of the application and the facility, an additional certification against force protection or anti-terrorism standards can also be required for applications in which higher security requirements are needed.
The dimensional accuracy of the Z-walls is more important than that of the simpler barrier shapes, because the Z-walls must fit together correctly around the entire perimeter run. Even a panel that is slightly misaligned can cause a section of wall to be misaligned.
Step 6: Transport and Installation
A technology like this requires no deep foundation and transfers the shear force to a foundation slab or hard surface, and panels are held in place by mechanical interlocking at the base. Panels are lifted to position with a crane and connected to the adjacent panels with offsets to create a continuous wall with self-bracing.
As with a T-wall system, a Z-wall perimeter can be installed (from delivery to complete) significantly faster than an equivalent cast-in-place wall system.
The Regions in the UAE Where Z-Walls Are Used
Other precast structures that can also be found using z-walls include perimeter walls around industrial or restricted buildings, construction site demarcation walls and semi-permanent walls which provide visual screening benefits in addition to the structural role of the wall.
The offset Z profile is a natural choice in particular for sites in need of both security and sightline obstruction, where there are sensitive pieces of equipment or activity that you want to keep hidden from view.
What to Ask a Z Wall Supplier?
It is better to have a precast manufacturer tell you than just state that he or she has an offset geometry in their panel, and it works! Inquire about the strengths of the standard mix, if there are alternative strengths available for increased security, and what standards their panels are tested against.
Check how the adjoining panels join and what preparation of the foundation surface is truly necessary for a self-supporting design—even one to be self-supporting will need a well-levelling foundation surface to perform engineered. Then seek out project references, preferably including some photographs of weathered walls installed in the UAE, especially after a full summer.
Bringing It Together for Precast Z-Walls
Precast Z-walls overcome the same fundamental issues as T-walls for strength and speed without requiring a wide base, but with a geometry that is folded and offset. Every stage, from the high-strength mix design, to the reinforcement specific to the profile, to the controlled casting, curing and crane-based installation, is designed to support itself in the form it takes. That folded profile is the reason why the Z-wall is a profile worth considering over a simple flat barrier profile, in UAE projects where perimeter security and visual screening are both important.
