Rod anchors vs. strand anchors: applications and differences explained

Bar anchors and strand anchors are both used for ground anchoring, but differ in construction and load-bearing capacity. In this article, we will explain how both systems work and when to choose a ground anchor or a strand anchor.

In construction projects where stability under tensile load is essential, ground anchoring plays an important role. This includes situations such as cofferdams, sheet piles, or foundations, where forces from the structure need to be transferred to the subsoil. Within this field, various types of anchors are used, including bar anchors and strand anchors. Although these systems are similar, they differ in their operation and scope of application. The correct choice depends heavily on factors such as load, soil structure, and the desired lifespan of the construction.

What is a ground anchor and how does it work?

An ground anchor is a structural element used to transfer tensile forces from a building into the surrounding soil layers. This keeps a structure stable and prevents displacement. In practice, a ground anchor is installed by drilling into the ground, after which the anchor is inserted and secured with grout, a cement-like mixture that creates a strong connection with the soil. For this reason, it is also often referred to as a grout anchor, bored anchor, or tension anchor. 

Ground anchors are widely used in combination with sheet piles, quay walls, and foundations. They also offer an effective solution for applications in concrete structures, such as a ground anchor in concrete.

Een strengenanker is een type verankeringsbout dat wordt gebruikt om materialen aan beton te bevestigen. Het bestaat uit een staaf met schroefdraad, een moer en een ring. De staaf wordt in een geboord gat in het beton gestoken en de moer en ring worden op de staaf geschroefd om het materiaal stevig op zijn plaats te trekken. Strengenankers worden typically gebruikt in situaties waar een hoge mate van sterkte en stabiliteit vereist is, zoals bij het bevestigen van zware apparatuur, steunpilaren of structurele verbindingen. Ze zijn geschikt voor het dragen van zowel trek- als schuifkrachten en worden vaak gebruikt in de bouw, civiele techniek en de industrie.

A strand anchor is a specific variant within ground anchoring and is distinguished by its construction. Instead of a single solid anchor rod, a strand anchor consists of multiple steel strands that are tensioned together. Due to this construction, a strand anchor can withstand significantly higher tensile forces than a standard ground anchor. This makes the system particularly suitable for applications where heavy loads occur or where long-term, permanent anchoring is required. Its operation is similar to that of a ground anchor but offers greater capacity and control in critical structures. Furthermore, a strand anchor comes on a reel, requiring less space to insert the anchor into the borehole. 

Het verschil tussen staafankers en strengenankers is de manier waarop ze zijn opgebouwd. Staafankers bestaan uit een enkele, massieve stalen staaf, terwijl strengenankers bestaan uit meerdere stalen draden die samen zijn gedraaid tot een kabel.

Although both bar anchors and strand anchors are used for ground anchoring, they differ distinctly in construction and application. A bar anchor consists of a single anchor bar and is suitable for a wide range of medium-load projects. A strand anchor is constructed from multiple high-grade steel strands and is used when higher tensile forces and long-term stability are required. This makes the installation more complex, but also more reliable for heavy constructions.

What type of ground anchoring is suitable for your project? (practical checklist)

The choice between a bar anchor and a strand anchor is determined by the project's requirements. For projects with average loads and a relatively short lead time, a ground anchor often suffices as an efficient solution. When the load increases or when the structure needs to remain stable long-term, a strand anchor is more frequently chosen. This is particularly true for deep excavation support and infrastructure works. 

This checklist helps you make the right choice:

A comparison on paper is one thing, making the right choice for a specific project is another. In practice, five factors are weighed: traction, lifespan, safety, ground conditions, and the balance between speed and certainty. The questions below will help to structure that consideration.

What is the maximum tensile force that needs to be accommodated?

The required pulling force often determines the type of anchor. Bar anchors are typically used for loads of approximately 150 kN to 3,500 kN. Strand anchors accommodate higher forces: from 400 kN to 4,600+ kN, by combining multiple steel strands of approximately 200 kN each.

With moderate loads, such as standard Construction pits of Dam anchoring, A ground anchor suffices as an efficient solution. When forces increase, for example in deep excavations or heavy infrastructural constructions, a strand anchor offers more certainty. Furthermore, the capacity per strand is modular: by adjusting the number of strands, you can precisely match the system to the calculated load.

Is the application temporary or permanent?

For temporary applications lasting up to 7 years, ground anchors are often chosen because they are quicker to install and remain flexible in their use. For permanent structures with a lifespan of up to 100 years, such as quay walls, tunnel sections, or railway infrastructure, a strand anchor offers greater certainty through system-level corrosion protection.

At Deepro, that difference has been implemented in the system itself, the PL0 en PL1+ are designed for temporary anchoring for two and seven years respectively. The PL2 offers permanent protection for up to 100 years, with two independent protective layers over the entire anchor length. The PL3 adds electrical insulation to it, essential for projects where stray currents are a factor, such as along or under the track.

How critical is security?

For projects with limited risks and a relatively standard execution situation, a bar anchor is often a suitable solution. However, in urban environments, complex construction sites, or constructions where the consequences of movement or deformation are significant, a strand anchor is more likely to be the preferred choice. This type of anchor offers more control, higher capacity, and thus extra security in situations where a larger safety margin is required.

What is the soil condition?

In stable ground conditions, a bar anchor can function perfectly, whereas in more complex or unpredictable soil conditions, a strand anchor offers greater control and reliability. Therefore, especially in urban projects or situations where risks are higher, a solution with a greater safety margin is often chosen.

What is more important: speed or maximum certainty?

While a bar anchor excels in efficiency and broad applicability, a strand anchor offers the capacity and durability required for heavier and longer-term projects. 

In practice, the higher the load and the longer the service life, the greater the likelihood that a strand anchor is the correct solution.

In practice, when would you choose a strand anchor?

In practice, for a standard excavation pit in sandy soil with a limited excavation depth and relatively low loads, ground anchors are often chosen. This type of anchor is quick to install and offers sufficient capacity for medium-duty applications. 

For an urban project with a deep excavation pit, high ground and water pressure, and limited space for deformation, the choice is different. In such situations, strand anchors are often chosen. Due to their higher load capacity (up to 4,600 kN) and the possibility to combine multiple strands and tension them individually, more control over the behaviour of the structure is achieved. 

In addition, a strand anchor offers greater security for permanent applications, such as quay walls or infra-structureel working, where lifespan and reliability are essential. 

These sorts of practical choices are often seen back in applications such as Sea walls, Grafting en Construction pits.

Standards and certification for ground anchors and strand anchors

When choosing an anchoring system, standards and certifications play an important role. It is not only the capacity, but above all the reliability and lifespan of the system that must be demonstrable. 

For bar anchors and strand anchors, different standards and assessment frameworks apply in Europe. The most important ones are: 

• EAD 160071-00-0102 (2019) European Technical Assessment for ground anchors 

• European Technical Assessment – system certification by manufacturer 

• BS EN 1537 (2013) – installation and proof loading of ground anchors 

• Eurocode 7 / NEN 9997 geotechnical design 

A significant difference lies in the system-level certification. Whereas traditional bar anchors are often assessed per component, strand anchors are tested and certified as a complete system. This means that all parts (strand, anchor head, sheathing, grout, and seals) are evaluated together for performance, durability, and safety. 

Just as is also the case within standardisation, an anchor rarely fails due to one component, but rather due to the weakest link in the whole. It is precisely for this reason that system-level certification offers additional certainty, particularly for permanent and heavily loaded structures.