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Comparison of Bridging Systems and Joen Reinforcement Bars in Joist Floor Systems (Iran vs Europe & USA)

In joist floor systems, one of the most common technical misunderstandings in Iran is considering Joen reinforcement bars to be equivalent to what is internationally known as Bridging.
Although these elements may appear similar in terms of location, they differ fundamentally in design philosophy, structural behavior, and performance.

What Is Bridging in Joists? (Europe & USA)

Bridging refers to structural members installed between joists in order to:

• Control lateral buckling of joists

• Reduce torsional instability

• Increase local lateral stiffness of the floor system

• Control vibrations before concrete placement or even in non-composite systems

Bridging is commonly installed in two forms:

• X-Bridging (Diagonal Bridging)

• Horizontal Bridging

A critical characteristic of Bridging is that:

❗ Bridging is not embedded in concrete and performs independently of the concrete slab.

This system is widely used in Open Web Steel Joists (OWSJ) designed in accordance with SJI specifications, as well as in timber joist systems in Europe and North America.

What Is Joen Reinforcement? (Common Practice in Iran)

Joen reinforcement bars, also known as transverse ties, are a conventional solution in Iranian joist–block floor systems. These bars:

• Are installed as reinforcing steel bars

• Become fully embedded in concrete after casting

• Rely entirely on concrete hardening for their performance

The primary functions of Joen bars include:

• Post-concrete integration of joists

• Distribution of gravity loads

• Reduction of cracking and service-stage vibrations

Joen reinforcement has no effective structural role before concrete curing and, unlike Bridging, does not control joist lateral buckling.

Key Differences Between Bridging and Joen Bars

Why Is Bridging Less Common in Iran?

The limited use of Bridging in Iran is primarily due to the historical dominance of concrete joist–block systems, where concrete provides the main source of stability.
However, with the introduction of modern systems such as Open Web Steel Joists (OWSJ), the use of Bridging becomes a structural necessity rather than an optional detail.

Bridging Terminology and Its Interpretation in Iran

In international engineering terminology, Bridging means lateral bracing of joists, and conceptually can be interpreted as:

Inter-joist bracing or joist restraint bars

Nevertheless, this concept has not been fully adopted in Iran and is commonly replaced by Joen reinforcement bars.

Current Practice in NIAZIT Joist Systems

At present, in most Iranian projects:

• NIAZIT joists are installed together with Joen reinforcement bars embedded in concrete

• This practice is driven by contractor familiarity and limited awareness of Bridging design principles

From an engineering standpoint, OWSJ systems are inherently intended to use steel Bridging independent of concrete.

Use of Bridging According to SJI Provisions

According to the Steel Joist Institute (SJI):

• Horizontal or X-Bridging is mandatory for controlling joist lateral buckling

• Bridging spacing depends on span length, joist type, and loading conditions

Conceptual SJI Bracing Relationship

SJI provisions conceptually control maximum unbraced length as:

Lb ≤ C × L

Where:

• Lb = Unbraced length (Bridging spacing)

• L = Joist span

• C = Coefficient based on joist type and loading

Typically:

• Bridging is required at mid-span or third points

• Long spans require multiple rows of Bridging

This demonstrates that Bridging in SJI is a designed structural system, not merely a construction practice.

Technical Advantages of Bridging in NIAZIT Joists (Engineering Box)

Design Note – NIAZIT OWSJ

Using properly designed Bridging systems in NIAZIT Open Web Steel Joists in accordance with SJI provides:

• Effective control of joist lateral buckling independent of concrete

• Increased construction-stage safety before concrete placement

• Potential for increased joist spacing under controlled design conditions

• Reduced reliance on embedded Joen reinforcement

• Improved vibration performance in long spans

• Full alignment with OWSJ design philosophy

Final Conclusion

• Bridging refers to inter-joist lateral bracing acting independently of concrete

• Joen reinforcement is a post-concrete solution commonly used in Iran

• NIAZIT joists are currently executed with Joen bars due to local practice

• SJI fully permits and regulates Bridging systems for open web joists

• Implementing Bridging elevates NIAZIT floor systems to international engineering standards