Eurocode Impact Load

[Umbelina Baublitz]

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For information on the dynamic impact design, see Appendix C. This annex distinguishes between a "hard impact," where the energy is mainly dissipated by the impacting body, and a "soft impact," where the structure is designed to deform in order to absorb the impact energy. According to Annex C.2.1(1), calculating with an equivalent static force for a "hard impact" is allowed. In the event of a car crashing into a carport, a hard impact is assumed and the content of this article refers to the determination of the equivalent static force.

If the National Annex of a country does not provide further information, it is worth taking a look at [3], Annex B. In Equation B.1, the horizontal equivalent load for a fall protection is described. This results in:

According to [4], 4.3.1(3), applying the impact force of passenger cars at a height of 50 cm above the top edge of the road is allowed. In [3], Annex B, 37.5 cm are specified for passenger cars with a maximum vehicle mass of 2,500 kg. Since the height of a passenger car's bumpers is not standardized in most countries, the engineer has to decide at which height the equivalent load will be applied. The German Annex [5] recommends a height of 50 cm for passenger cars.

There is also the option to analyze the effects of complete failure of the affected structural component on the entire structure (Image 02). Depending on how the component is fixed, such an analysis can be useful.

For this purpose, a new load case has to be created first where the static equivalent load is defined. If the automatic load combination is used, the "Accidental" action class should be assigned to this load case.

In this example, the distance of the equivalent load from the member start of 37.5 cm is selected, because the fastener (in this case, the height of the column footing) is not taken into account in the structural analysis.

As already explained, it is worth taking a look at the complete failure of the column (Image 02). For this purpose, it is not necessary to consider failure or deletion of the member in a separate file. The column can be easily deactivated for specific load combinations. For the complete failure of the column, a new load combination will be created where only the self-weight is included and the column is deactivated in the calculation parameters.

Furthermore, the fasteners must be checked in case of an impact. Therefore, it is necessary to verify that the column base and the connection of the column to the purlin above are dimensioned sufficiently. The type of the structure governs whether the impact load must be transferred into the foundation or not. In [5], NDP to 4.1 (1), Note 3, the transfer of forces generally does not govern for buildings. This statement is true for the carport mentioned in the example.

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"Impact load" refers to the amount of force or energy that is exerted on a surface when an object collides with it. In the case of falling ice, the impact load is the force that the ice exerts on the surface it falls on.

The size and shape of falling ice can have a significant impact on the amount of force it exerts upon impact. Larger and heavier pieces of ice will generally have a higher impact load than smaller and lighter pieces. Additionally, the shape of the ice can also affect its impact load, as a sharper or more pointed shape will concentrate the force onto a smaller area, resulting in a higher impact load.

Aside from the size and shape of the falling ice, other factors that can influence the impact load include the height at which the ice falls from, the speed at which it is falling, and the angle at which it impacts the surface.

The impact load from falling ice can be measured using various methods, including strain gauges, accelerometers, and high-speed cameras. These tools allow scientists to measure the force and energy exerted by the falling ice upon impact.

High impact loads from falling ice can result in serious damage to structures, vehicles, and even people. They can also cause disruptions to transportation systems, power outages, and damage to natural habitats. Additionally, the repeated impact of falling ice can weaken structures and lead to long-term structural damage.

Bollards are a familiar sight throughout the urban landscape. These short poles are used to protect infrastructure and to serve as a barrier, particularly to vehicles. They are used in design against blast loading, as a first line of defense, and are incorporated into any threat analysis; by keeping vehicles further away from any critical structure the standoff distance is increased, hence the magnitude of any blast loading originating from a vehicle-borne explosive is decreased. Even more common is the use of bollards to prevent the direct impact of vehicles on buildings or sensitive objects. Inside a structure (Figure 1(a)), they may be used to prevent accidental impacts from vehicles in car parks, or forklifts inside warehouses. Outside a structure (Figure 1(b)) their use is to prevent vehicles from access to certain routes or restricted areas, to guard buildings against intentional or accidental impact, and similarly to prevent impacts on equipment, facilities or assets.

Although bollards may be designed to be retractable, removable, or even decorative features (e.g. large concrete boxes containing plants or trees), the most common bollard is a simple, concrete-filled, HSS (Figure 2). Since these members are designed for impact resistance, round HSS are preferable to square HSS as the latter have a reduced Charpy V-notch (CVN) impact resistance in their four corners. ASTM A1085 (ASTM, 2015) would be the preferred HSS material as this requires a minimum CVN value of 25 ft-lb @ 40oF, which corresponds to AASHTO Zone 2. Furthermore, round HSS to ASTM A1085 have a minimum yield stress of 50 ksi. Since most bollards are located outdoors, hot-dip galvanizing is often required for environmental protection (Figure 1(b)), and round HSS are more readily galvanized than square or rectangular HSS too. Tubular bollards can also serve as an architectural complement to other exposed HSS construction (Figure 1(b)). The most common sizes used for bollards are outside diameters of 4.500 in. (which has limited capacity), 6.625 in. and 8.625 in. OD.

HSS bollards are usually designed as cantilever members and hence require fixity at the foundation. If mounted on a hard-finished surface via a bolted base-plate, as shown in Figure 1(a), the lateral load resistance will likely be limited by the baseplate connection. On the other hand, embedment in a foundation (Figure 2) can provide a high lateral load resistance and the member may be designed as a fixed-ended cantilever beam. This article deals with the design of the bollard itself, as a composite member, assuming full fixity at the base.

By considering only the first stage of impact, the vehicle stiffness is used to calculate the equivalent static force. A vehicle equivalent stiffness of 300 kN/m is adopted in Eurocode 1 Part 1.7 (CEN, 2006), for all types of vehicles and velocities at impact. The static equivalent impact force, in SI units, is then given by:

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