Offsite expert Trevor Richards, Operations Director for Cogent Consulting, discusses logistics and the crucial factors with the design and manufacture of volumetric modules and shares his perspective on the journey from factory to site.
Due to its positive impact on cost, programme, quality and safety, modular construction has gained considerable momentum. For many, volumetric modular is the ultimate expression of offsite manufacture. The more that can be achieved in the factory, the better and safer the process becomes overall, but transportation parameters must be factored into the equation.
Volumetric module sizes must be determined by balancing the width, length and height with transport restrictions and the cost of haulage and installation. The size of any load classed as ‘abnormal’ can be exceeded, however this brings in to play further regulations. This will result in either notifications to the authorities or an escort vehicle accompanying deliveries.
An abnormal load is a vehicle that has any of the following characteristics – weight of more than 44,000 kilograms (43.3 ton), an axle load of more than 10,000 kilograms (9.85 ton) for a single non-driving axle and 11,500 kilograms (11.32 ton) for a single driving axle, a width of more than 2.9m and/or a rigid length of more than 18.65 metres. Loads may overhang the end of a trailer, but once this exceeds 2m, additional notifications are required.
In relation to transport specification, a standard UK flat-bed trailer is 13.5m long. It is generally accepted that a load should not extend beyond 1.5m from the end of the trailer bed and an allowance needs to be made between the load and the trailer headboard to ensure adequate manoeuvrability can be achieved. Any transportable load with a width exceeding 2.9m up to 4.3m, requires two clear days notice to the police in order to be moved. For a width exceeding 5.0m up to 6.1m, in addition to two days notice to the police, a report form needs to be sent to the Highways Agency. Depending on the load being moved and the route taken, in addition to the notifying the Police and Highways, advance warning may also need to be given to bridge and structure owners such as Network Rail.
UK Legislation does not contain any requirement for an abnormal load to be escorted. However, legally enforceable standards exist for the notification of abnormal load movement to both Chief Constables and the Highway Authorities. The police are not responsible for ensuring the safe operational passage of abnormal loads on the roads – this is the role of the operator. General rules for escort vehicles are: up to 4.3m wide, no escort vehicle, over 4.3m but not exceeding 5m, a private escort and for loads over 5m, a police escort is required. In addition, any abnormal load travelling within the Metropolitan Police area, that is within the M25 – has further time restrictions.
Traffic Management and Installation
Routes must be planned to take into consideration road sizes and contours together with height restrictions, including natural and man-made barriers such as trees and bridges. Due to the nature and location of some sites, there may be a requirement for a professional level of traffic management to control both vehicles and pedestrians in and around the area.
The crane selection is calculated on exact structural sizes and module component make-up which will affect the overall gross weight. For some the installation process of modular units can seem complicated and expensive. However, small units can be delivered to site quite easily and offloaded into position using a truck mounted crane. The distance a truck mounted crane can lift a unit, depends very much on the weight. The heavier the unit, the less reach capability of the crane. So therefore, all lifting capabilities are very site specific.
Depending on site conditions, mobile cranes may be required to lift the unit into hard to reach places.
As volumetric and modular buildings get taller, tower cranes are playing a greater role in the installation. The use of mobile tower cranes is prominent on city sites with tight footprints, as they are far quicker to mobilise and more cost effective for a short duration, as well as being quicker than a small telescopic boom crane.
The success and appeal of module manufacture rests in the repeatability of units. Load-bearing modules can be steel or timber-based and are pre-fitted with electrics, plumbing, heating, doors and windows, together with finishes. The modules are commissioned prior to leaving the factory, ensuring that defects are minimised, and quality control is very high. By assembling modules in a precision-controlled factory environment, the production line techniques that drive module assembly bring speed of delivery, enhance the quality of the end product and dramatically improve productivity. Yes, module selection can be significantly influenced by logistics but this ultimate expression of offsite manufacture, brings a wealth of benefits to any building sector.
About the Author
As an offsite manufacturing expert and engineer with over 20 years’ experience developing offsite businesses, processes and products, Trevor Richards, Operations Director of Cogent Consulting, has a wealth of experience in the offsite arena.