Following on from one of our previous posts, we will finish talking about edge protection guardrails. We will focus on the calculations and test methods that the standard establishes to ensure a design and strength suited to the physical demands they will be subjected to.
When calculating the guardrail we must bear in mind that it has to be guaranteed to correctly withstand:
- The main loads it will be subjected to, such as load-bearing capacity and stability against sliding, overturning, and uplift.
- Point loads or infrequent loads, such as a person climbing on the edge protection as if it were a ladder.
In addition to these considerations, it is important to stress that when calculating edge protection, the calculations must be performed on the guardrail as a whole and comply globally.
But it must also be verified separately that the individual load requirements are met. Each element that makes up the guardrail is suitable for the requirements of the applicable standard.
Test Calculations for Edge Protection Guardrails
The calculation must take into account the combination of the structure, the system and its components, and the fixing method. If in any case it is not possible to verify the static load requirements by calculation, verification must be done by testing.
What we are looking to verify is that:
Ed < Rd
Where,
Ed is the design value of the effect of actions, for example, bending resistance, an internal force, or a moment;
Rd is the corresponding design value of resistance
The value of Ed must be established from the design value of the actions Qd .
The value of the action Qd will be calculated using the following formula:
Qd,i = gf,i x Qk,i
Where,
Qd,i is the design value of action i
Qk,i is the characteristic value of action i and must be taken from the table included in the standard
gf,i is the partial safety factor of the resistance Rd,i which will depend on the material used.
Regarding static loads, they must be calculated for any part of the system, that is, they may be assumed to act on the post or between posts.
The structural calculation must include the analysis of different loads:
- Point loads
- Wind loads
The load combination may result in:
- Parallel
- Accidental
Lastly, we will briefly discuss the tests that must be performed on edge protection systems.
Test Methods for Edge Protection Guardrails
The tests will depend on the type of system involved (A, B, or C) and the corresponding requirements.
As we can see in the table above, a section of the standard applies to each type of edge protection system. It describes how the load must be applied in the test, the sample required for the test to be valid, and the procedure to follow to carry out the test, along with the evaluation of the results obtained.
The procedure to follow for the test requires an explanation of the test apparatus. Section 7.5 describes how this apparatus must be built for dynamic loads.
Dynamic loads will be simulated with a spheroconical bag dropped in a controlled fall under the action of gravity and directed at one of the most unfavorable positions of the edge protection system, so that the system retains the bag. Two types of tests must be performed:
- Type 1: the bag must strike the highest part of the post, 500 J, and then the lowest possible part of the post with 1,100 J.
- Type 2: The bag must first strike the upper part of the edge protection, 500 J, and then the lowest possible part of the edge protection, 1,100 J.
No component may be replaced between the two types of test.
Class B Test
Both the 500 J and the 1,100 J tests must be carried out. For class C, only the 500 J test must be carried out.
The impact is produced by the pendulum fall of the spheroconical bag, which is approximately vertical at the point of impact. The bag must be held to prevent a second impact and must comply with standard EN 596.
A typical test apparatus is shown below.
The test ends with the measurement and recording of the instantaneous deflection produced. This is compared with the requirements set out in standard UNE EN 13374 to verify whether or not the manufactured edge system complies.
Class C Test
The standard establishes a specific test for class C, separate from the one explained above. It consists of the test impactor rolling down a ramp toward the edge protection system, at two critical points:
- On the post
- At the center between the posts.
The test impactor will consist of:
- A cylindrical body with a mass of approximately 75 kg,
- A length of 1000 mm
- A diameter of 300 mm
The cylindrical body must be made with a minimum of 25 mm of rubber with a soft surface and no sharp edges.
Finally, remember that the standard requires the edge protection system to be marked on all its components, identifying:
- The type of system
- The manufacturer’s name
- The year of manufacture
- The counterweights
The marking must be clearly visible and must remain visible throughout the product’s service life.
Together with the system marking, the manufacturer must include an instruction manual that complies with section 10 of standard UNE EN 13374.