In each site, a main contractor was responsible for the overall coordination of the project (the projects were not divided into separate lots). The high fragmentation of the construction sector results in a large number of stakeholders and suggests potentially high benefits in consolidating building materials. The four construction sites involved many trade subcontractors (e.g., electricity and plumbing companies) focused on their own activities and relatively autonomous in the selection of their suppliers. For one of the sites, 66 distinct shippers delivered building materials over eight months. Most of the subcontractors collaborated for the first time with the main contractor who coordinated the activities according to an agreed plan. The construction projects resulted in a temporary collaboration. However, only two of the main contractors (in Luxembourg City and Paris) used framework agreements to work on long-term collaborative arrangements with their subcontractors. The framework agreement allows the construction company to instruct another party to carry out works or provide goods or services, by reference to pre-agreed terms, over a pre-agreed period.
4.3. Handling of Building Materials
In all sites, the cost of materials represented 30–40% of the overall construction costs. Considering the lack of space on site and the dynamic nature of the activities, the logistics of materials on a construction site is challenging. Each subcontractor manages its own materials and the potential storage area increases with the construction progress by using newly erected floors as additional storage. In Paris, considering the high footprint of the building on the site, the sole solution was to store materials in the existing floors (cf. Table 1
). In Verona and Luxembourg City, the storage space increased with the progress of the construction works.
For all four sites, the most frequent loading unit was the pallet, sometimes by a vast majority (82.6% for site 3), sometimes by a lower proportion (39.8%).
The way to handle goods varied depending on the equipment and organisation of each site. One site used mainly its crane to unload the goods in addition to the truck’s crane, while two others used mainly the forklift in combination with either the site crane or a construction lift.
The average weight of deliveries varied from site to site and depending on the delivery vehicle. However, the average weight of materials delivered daily was uniform among the sites: Between 8 and 10 tons per day.
The accessibility of the sites depended strongly on the configuration of the sites themselves and evolved during the construction. The location and number of entrance and exit gates is one of the first logistics issues to solve when planning construction activities. The decision has a direct impact on the frequency and scheduling of deliveries. In Luxembourg City, drivers needed to enter backwards into the site because there was not enough space to do a U-turn. For the same reason, the site could not receive simultaneous deliveries. When there was not enough available space on the site, trucks had to double park and unload directly on the street before 6 am. In Paris, the delivery vehicles accessed the site through one of the two entrances. The limited space on the site obliged the main contractor to rent public space to create the entrance and exit gates. In Verona, the entrance and exit gates were separate. To avoid excessive congestion, a detailed schedule of the entrance slots for the incoming trucks was required. Temporary traffic lights regulated the movement of vehicles when they left the construction site to facilitate reinsertion into the traffic flow. In Valencia, the two entrance/exit gates and the abundance of available space eased the deliveries.
The scheduling of deliveries was the standard for three sites out of four with more than two thirds of deliveries scheduled. One of the three sites even rejected any unscheduled deliveries. The remaining sites used the scheduling only for 13% of deliveries. With regard to the scheduling approach, both fixed and time window scheduling were used.
In three sites out of four, most deliveries occurred in the morning (25% of deliveries occurred before 8:30 am, 50% before 10 am and 75% before 12:15 pm). For the remaining sites, deliveries were more distributed during the day. The distribution of delivery time per site is shown in Figure 1
. The average duration of deliveries ranges from 34 min to 1 h.
For all sites, it was quite usual to see the delivery vehicles stopped either in traffic jams before reaching the site, or before being allowed to enter the construction site, or even inside the construction site, before being allowed to unload (waiting for the unloading equipment to be available). On average, and depending on the site, the vehicles were stopped between 18 and 36 min for each delivery.
The sites received deliveries between two and ten times a day. The number of deliveries was somehow correlated to the size of the construction project but also to the size of the vehicles used. However, as stated before, the average weight of the materials delivered daily was quite homogeneous across the sites.
The location of the unloading area depended on the organisation of the site; deliveries were unloaded on a delivery zone for three sites and at the point of use in the building under construction for one site. It has to be noted that delivering at the point of use makes the delivery duration longer.
Below we report anonymously and in an order that does not refer to the previous table the findings for the four construction sites. The results of the comparison between construction sites are summarized in Table 2
. For conciseness, not all recorded times and durations are reported in the table. For example, the duration of trucks’ stops inside the site was recorded but not reported.
Transport related to the construction UFT generally follows standard transport rules. Close collaboration with the local authorities is requested to put in place, when necessary, signs asking pedestrian to use the opposite pavement, lower speed limits, or traffic lights. Special requests to rent public space, to change weight restrictions or time windows are common. In Luxembourg City and Paris, the main contractor rented public spaces (respectively €7200 for the first six months of the project and €1 million for all the project duration) to create delivery zones, set up a part of living accommodation and offices, and set up the lifts.