Why is it necessary to apply the partial safety coefficient to ensure regulatory compliance of a railing?

As defined by the standard UNE 85237-91, a railing is a construction or work specifically designed to protect people or objects from the risk of accidental falls.

This protective feature makes it a security element, and as such, its resistance must be designed and verified in accordance with the requirements set out in the Technical Building Code (CTE), which is the regulatory framework that establishes the basic quality requirements that buildings must meet in relation to the essential safety and habitability requirements set out in Law 38/1999 of 5th November, on Building Regulation (LOE).

And it is in the CTE where compliance with the safety coefficient is required, as a method of verification of ultimate limit state. This would be the resistance verification method established in the regulations, hence its importance.

What are Limit States?

The term "limit states" refers to "those situations which, if exceeded, mean that the building cannot be considered to meet one of the structural requirements for which it has been designed." According to the Technical Building Code (CTE), there are two types of limit states:

• Ultimate Limit States: These are the ones that, if exceeded, pose a risk to people, either because they cause the building to be taken out of service or result in the total or partial collapse of the building.
• Serviceability Limit States: These are the ones that, if exceeded, affect the comfort and well-being of users or third parties, the correct functioning of the building, or the appearance of the construction.

To perform a strength check for a serviceability limit state (SLS), it would be carried out through movements; however, throughout the entire technical building code, there is no specified displacement for this verification, and there is no value to verify that the handrail complies with the TBC. Consequently, the SLS check would be ruled out, and it would not be possible to verify it under the technical building code.

The state left for us to validate a handrail system would be the ultimate limit state (ULS), applying the partial safety factors.

What does the regulation say about this?

In the Basic Security Document for Use and Accessibility DB-SUA, in section SUA 1 Safety Against Risk of Falls, a resistance requirement for railings is established, indicating that they will be considered as protective barriers as long as they guard a height difference of 55 cm. It is established that protective barriers will have a minimum height of 900 mm when safeguarding a level difference of 55 cm up to 6 metres. From 6 metres onwards, the minimum height will be 1100 mm.

The Basic Document of Actions in Building DB-SE-AE defines the action on railings as a variable action, and these must withstand a uniformly distributed horizontal force, applied at a height of 1.2 m or on the top edge of the element if it is at a lower height. In Table 3.3 Actions on railings and other partition elements, the characteristic value of this horizontal force is defined in kN/m according to the usage category of the railing (these categories are defined in Table 3.1. Characteristic values of usage overloads).

To perform the resistance verification for the variable action type in a railing, according to the CTE, it will be done using partial safety factors, this corresponds to an ultimate limit state (ULS) check.

Such coefficients are defined in Table 4.1 Partial safety coefficients (γ) for the actions of the Basic Document of Structural Safety DB-SE.

As the Basic Document for Building Actions DB-SE-AE defines the action on railings as a variable action, the partial safety factor of 1.5 must be applied, which will be used to multiply the characteristic value from table 3.3. Thus, if a railing is used in a stadium, for example, it must withstand a horizontal force of 3 kN/m multiplied by 1.5, which means the railing must resist 4.5 kN/m. The same applies to the rest of the usage categories, where resistance to 0.8 kN/m must be 1.2 kN/m, resulting from multiplying the force by 1.5, and also for usage categories subject to 1.6 kN/m the resistance value will be 2.4 kN/m.

Furthermore, in case there are doubts about the obligation to use the safety factor, both the blog of the Architects of Public Administrations of Spain, an entity linked to the Higher Council of the Colleges of Architects of Spain, and the website of the General Council of Official Associations of Industrial Engineers mention the enquiry raised on this matter.

All the railing systems by Comenza are tested by applying the partial safety factor.

In the railing sector in our country, there is still a way to go in terms of safety, but at Comenza, we have made a fundamental commitment to the users of our railing systems. For this reason, our R&D+I department specialises in the development of industrialised and innovative railing systems that comply with building regulations, thereby guaranteeing the required level of safety.

COMENZA's railing systems are tested, according to the requirements of the CTE, to define the characteristics of their composition, such as the base or support, the glass, the anchorage, and the handrail, to ensure the safety of end users, verifying that they pass the static and dynamic load tests, taking into account the safety coefficients to be applied.

To achieve this, COMENZA has its own climate-controlled testing laboratory to carry out both static and dynamic load tests, which allows us to launch products on the market that have been tested under the most demanding conditions and conduct tests in accordance with the specific standards. In addition, we work closely with the most prestigious international certification companies (CSTB, Applus, SINTEF, TUV, etc.) to ensure that our railing systems adapt to and comply with the building code specifications of each country in which they are sold.

We offer bespoke services for each project through our technical office, providing professionals with: FEM simulations tailored to the project, railing anchorage study, wind static pressure review, BIM objects, or material certificates, among others.

If you need advice on your project or want to know more about our systems, contact us at [email protected] or through our contact form. Let’s get started!