Structural Engineering Tips for large span buildings like warehouses

Introduction

Large-span structures have unobstructed, column-free spaces that exceed 100 ft (30m) for various functions. This includes operations where flexibility is needed such as warehouses and exhibition halls. Or where visibility is essential for large audiences such as covered stadiums and auditoriums. The same case applies to aircraft hangars where large movable items are stored.

In that regard, durable upper span limits for these types of structures have been established in the 20the century. For instance, the biggest commercial fixed-wing airplane is 224 ft (69.4m) long with a wingspan of 222 ft (66.7m). In that case, this type of aircraft requires a hangar whose span is 250 to 266 ft (75–80m). On the contrary, the biggest exhibition hall has a span of 710 ft (216m), while the span of the biggest covered stadium is 670 ft (204m).

In this guide, we’ll share some structural engineering tips you can use when designing large-span structures!

Design for large span buildings

Every building structure must be constructed in a manner that allows it to last for the desired lifespan. Similarly, it must satisfy the need for efficiency for what it’s intended for. With that in mind, the design of a large span structure can fall into the following categories;

• Structural engineering design

Before the process of design commences, the form of the structure has to be selected. Generally, structural design refers to the art & science of comprehending the action of structural elements subjected to loads. More importantly, it involves designing those structural members with elegance and economy to result in a serviceable, durable, and safe structure.

• Functional design

A structure should be primarily constructed to serve the purpose for which it is intended, yet maintain a pleasing look. Moreover, the building should offer a comfortable environment, both outside and inside. For those reasons, the functional design of a structure must consider the proper organization of spaces to satisfy good lighting, ventilation and meet the client’s needs. On the same note, the design should provide good acoustics as well as an unobstructed view in case of large span structures like cinema theaters and community halls.

Choosing the right foundation design for large span buildings

Before you dive into a new large-span building project, it’s important to determine the best type of foundation for your building. More importantly, you’ve to consider the land the structure will be built on. After determining the location of the structure, evaluate the soil bearing capacity of the area where the foundation will be constructed.

Generally speaking, foundation design for large-span structures can either be permanent or temporary. Temporary options include; driven tube anchor kits, precast concrete, and helical anchors. While permanent options include; I-beam, wood posts, and poured concrete (Piers/ walls).

The best foundation design for the structure should be chosen after relevant considerations with the supporting soil bearing capacity are taken into account. Also, it will be determined by the load that will be carried by the foundation.

Structural systems

Large-span buildings can be categorized into 2 types of structural systems. That is;

• Structures that are susceptible to bending (have both compressive & tensile forces)
• Funicular structures (Either experience pure compression or pure tensile forces)

Bending structures include the 2-way grid, 2-way truss, space truss, girder, and truss. Typically these structures have a varying depth-to-span ratio that ranges from 1:35–1:40 and 1:5–1:15 for the space truss and one-way truss respectively.

Funicular structures, on the other hand, include the dome, tunnel vault, and parabolic arch structures which experience pure compression. Or the bicycle wheel, warped tension surfaces, and cable-stayed roof which are subjected to pure tension forces.

Materials used for large-span structures

Regardless of the structural system for your large-span structure, the labor and materials used to assemble the building are important factors you need to consider. On that regardless, here are the different types of large-span structures based on the material used to erect the building;

• Steel structures

Steel is one of the most commonly used materials in large-span structures, especially bending structures. In that regard, structures like trusses and plate girders that were originally designed for bridges are currently used in large-span buildings. Also, plate girders can be welded from steel plates to create an I-beam with a span of up to 200 ft (60m).

The construction of a cable-stayed roof is another structure derived from bridge construction. It involves bending flat roof structures that are supported by steel cables from above radiating downwards from masts rising above the roof level. Interestingly, such structures with a span of up to 236 ft (72m) have been constructed.

Also, the bicycle-wheel roof is another form of a funicular structural system. It comprises 2 layers of radiating tension steel cables separated by compression struts that connect outer and inner tension rings. The structure is then supported by columns.

• Concrete structures

Due to its inherent compression strength, reinforced concrete is mainly used for funicular large-span structures such as domes, shells, and vaults. As an example, there are thin parabolic shell vaults with spans of up to 300 ft (90m) that are stiffened with ribs. Also, there are more complex concrete shells such as intersecting parabolic vaults and hyperbolic parabolic that have been constructed. A good example is the CNIT Exhibition Hall in France that consists of 6 intersecting parabolic vaults with a span of around 708 ft (216m).

• Timber structures

Another material that can be used to build large-span buildings is glue-laminated timber. When prefabricated with metal connectors, it can be used to make trusses with a span of around 150 ft (45m). However, the most economical form of large-span timber structures is the pure compression shape of the multiple-arch vault that spans up to 305ft (93m). Or ribbed domes that span up to 350 ft (107m).

Glued laminated timber is often used to build large-span industrial storage facilities for materials like potash, salt, or aluminate that can corrode concrete or steel. More notably, these structures are only found near forested areas to reduce the cost of transporting timber.

Final Word

Overall, the design and construction of large-span buildings require serious structural engineering considerations to accomplish these spans. One thing you need to note though is that the process of structural design and planning requires more than conceptual thinking and imagination. Instead, it also needs sound knowledge of practical aspects like recent by-laws and design codes, supported by ample experience, judgment, and institution.

Fortunately, structural engineers at Innodez Design & Engineering offer various design options for large-span structures to give clients plenty of flexibility. In addition, they’re experienced professionals who can help design, recommend and construct large-span structures in California.