Wind and Construction Sites

What is the issue?

Higher wind speeds can significantly increase hazards on construction sites. Wind can affect equipment stability, especially for cranes and scaffolding, and can lead to flying debris, making it more dangerous for workers. It’s crucial for construction teams to monitor weather conditions and implement safety protocols, such as securing materials and possibly halting work during high winds to ensure everyone’s safety.

High winds pose several insurance risks for construction sites, including:

Property Damage: Strong winds can damage equipment, materials, and structures, leading to costly claims. This includes damage from flying debris or toppled scaffolding.

Injury Claims: Increased risk of accidents due to falling objects or unstable equipment can result in worker injuries, leading to liability claims and workers’ compensation costs.

Project Delays & Contractual Risks: Wind-related interruptions can extend project timelines, leading to additional costs and potential penalties.  It is recommended to have a record of weather conditions to assist with disputes and any additional liabilities

What are the limits and recommendations

The Health and Safety executive states:Do not consider going on any roof in poor weather conditions such as rain, ice, frost or strong winds (particularly gusting) or if slippery conditions exist on the roof.  Winds in excess of 23mph (Force 5) will affect a persons balance.

The National Federation of roofing contractors has very useful and practical guidance in their Roofing and Cladding in Windy Conditions document.   https://www.nfrc.co.uk/knowledge-hub/NFRC-publications Their recommendations are 23mph as per the HSE guidelines and 17mph where operatives are handling larger materials which will impact the wind load on them.

Crane operations: The safe wind speed for different types of cranes varies. For example, the maximum in-service wind speed for tower cranes is typically 45 mph, while it’s 31 mph for crawler cranes and 22 mph for mobile cranes.

In general, as stated in ISO 4302:2016 Cranes – Wind load assessment, the maximum wind speed for all cranes types installed in the open should be 20 m/s (45 mph), and it’s 31 mph for crawler cranes and 22 mph for mobile cranes. It can be higher or lower, the rule of thumb is to always check the crane manual and follow crane manufacturer’s guidelines accordingly.

Wind load, Average Wind and Gusts

Normally it is average wind speed, which is reported, however it is usually wind gusts (that are often not considered), which is do the most damage and are most hazedous on construction sites.  Here’s a breakdown of the concepts:

Wind load refers to the pressure exerted by wind on structures and objects.

Static Wind Load is calculated based on the average wind speed and it considers factors such as an objects shape and surface area.

Dynamic Wind Load (Gust Load) accounts for sudden increases in wind speed, known as gusts. Gust loads can significantly impact the safety of individuals and stability of structures.

Higher wind speeds increases the wind load with the square of the wind speed (i.e, doubling the wind speed quadruples the wind load).

Gust windspeed can be 1.5 times higher than average windspeed on flat open areas and 2 times higher in urban areas where you have effects of wind funnelling between buildings. 

For the above reasons wind gusts should be measured accurately and recorded.

How to measure to wind gusts

To measure wind, we use an anemometer which come in two types.  We have traditional the mechanical cup design and ultrasonic anemometers.

Sensors:

Cup anemometers work by measuring their rotating speed and using the cup size to calculate the wind velocity.

Ultrasonic wind sensors use transducers to emit and receive ultrasonic sound waves, and then calculate the wind speed from the time it takes for the sound waves to travel between the transducers.

Cup anemometers have the advantage of being lower cost but are prone to wear and damage because of mechanical parts.

Ultrasonic anemometers have no moving parts and require less maintenance.

Quality of data

When averaged over time, ultrasonic and mechanical measurement accuracies are comparable. Mechanical sensors, however, will not always reflect turbulence and gusts due to the physical limitations of its moving parts. If there is a sudden gust of wind it will take several seconds to register and report the change especially where the wind direction is changing.

An ultrasonic sensor, however, will immediately measure a change in wind direction or a high gust. (This is what spurred the National Weather Service to update its 883 Automated Surface Observation Systems from mechanical to ultrasonic sensors).  For these reasons we use ultrasonic sensors.

How we record gusts and average

Wind speed, wind direction and gusts are reported over a 2-minute interval in compliance with World Meteorological Organisation (WMO) recommendations.

Wind speed is averaged over 2 minutes; gusts are the peak value of wind speed over the 2-minute period and reset at the start of the next 2-minute interval. The peak value is calculated from a 3 second moving average in compliance with (WMO) recommendations.

To complement the sensors we have developed a market leading module in the DL40 which is a LPWAN cellular communications device. Specifically, it connects to  LTE-M or NB-IoT networks depending on which is available or which network provides the better connection.  Data is available 24-7 via the supplied Sonitus Cloud Portal.

The system is powered by 230v/ 100v or 12V DC (includes long life 12v battery packs and Solar)

Cloud Data reporting.

The cloud displays wind speed and gusts as standard and with the GMX600 version it will also report temperature, humidity and precipitation. Real time alerts can also be set to advise site management immediately via SMS or email if wind speeds exceed thresholds.