Port planning and design is an interdisciplinary effort where several topics related to economy, commerce, maritime trade, strategy and policy need to be brought together. Design of ports is carried out according to the modern procedures for design in engineering. Design may be articulated into the following phases:
- Planning and consultation with stakeholders;
- Preliminary load estimation and preliminary design of structures;
- Environmental impact assessment;
- Approval of the preliminary design;
- Final detailed design.
Planning is a truly interdisciplinary phase, which involves consideration on the commercial and touristic value of the port, the societal implications in general and the economic impact in particular. Environmental impact is also considered in the planning phase which includes impact on the land, sea and atmosphere.
Many ports all over the world are faced with a lack of available space as a result of increased traffic or environmental regulations. One possible solution to this problem is optimisation of logistic, which explains why port logistic has become a central discipline in harbour engineering. Well in advance of the implementation of city/port development or redevelopment projects, plans for improving access to the port must always take into account the state of the local urban mobility. This must include plans for the transport of both people and goods, as well as all different solutions for transportation. Revising the layout for the transportation to the port is one way of improving port competitiveness and reducing environmental impact. Promoting environmental friendly transportation, by also using waterways from the city to the port, should be the primary target.
We will not discuss port planning in detail here, as we will focus on some aspects of port structure design.
A berth is a structure in ports and harbors where a vessel may be moored, usually for the purposes of loading and unloading goods and passengers. Berths are managed by a responsible body like for instance a port authority.
A berth structure is exposed to a high number of loads for its design life, which have to be properly estimated by engineers. Figure 1 reports a description of the loads that frequently occur.
There are three main categories of characteristic loads or forces acting on a berth structure (Figure 1):
- loads from the sea side;
- loads on the berth structure;
- loads from the land side.
They have to be estimated by also focusing on their extreme values. Other loads may occur which are not considered here. Like for any design in engineering, loads have to be assessed in detail in their diversity and magnitude, by considering the local features and forcings. Some of the loads - like for instance those due to ice - presented in Figure 1 may be discarded, while other loads may have to be considered.
It is common practice that vertical loads are taken by the foundation of the berth (piles or columns), and that all horizontal loads are taken by the friction forces between berth and soil, and passive earth pressure from landslide.
Loads can be divided into normal loads and extreme loads (also called accidental loads or live loads), where normal loads refer to any load that may reasonably be expected to occur during the design life of the structure under normal operating conditions, like for instance self-weight and operating loads. Extreme loads may occur in exceptional situations, they are infrequent and unlikely to occur at the same time unless there is dependence. Extreme loads may be due to unexpected impacts from vessels, seismic activity, heavy storms and so forth. Therefore reduction factors (concurrency factors) that take into account the likelihood of exteme loads to occur simultaneously are usually introduced, so that the extreme forcings are not merely summed up. Reduction factors are also used for normal loads when they are unlikely to occur at the same time. Safety factors, which amplify the load, are introduced to account for uncertainty in load estimation. Guidance on how to estimate extreme loads, normal loads and concurrency/safety factors are given by standards and guidelines and sometimes by local regulations in force. National standards are considered the straightforward way to provide documentation in order to satisfy the demands of legislation.
Authorities managing seaports are increasingly devoting substantial resources to address risks associated with extreme weather events. Flooding is one of the most significant risks as it has the potential to damage electrical substations, as well as electrical motors on wharf cranes and ground level electric pumps.
Figure 1. Forces acting on a berth structure. Redrawn and modified from Thoresen (2010).
Thoresen (2010) writes that:
"Different countries have different regulations. All constructions have to be in accordance with the legislation in the country in which it is built. Many countries have their own standards for marine and coastal construction, but some do not. The designer has to find out whether or not there are national standards or guidelines that have to be used for design. If such national standards exist, they have to be used, and if national guidelines exist, it is recommended to use them. If no national legislation, standard or guideline exists, the designer is not required to use specific design manuals, but it is highly recommended to use internationally accepted standards and guidelines instead of trying to create a specific guideline for the project."
In particular, international rules such as the Eurocodes and National regulations may give orders of magnitude for safety/concurrency factors and individual loads. Analogously, design procedures are often regulated by international and national terms of reference that have to respected (like, for instance, the limit state a structure has to be designed with). Again, the design procedure suggested by National authorities is to be adopted.
Figure 2. Cranes on a berth. By M.Minderhoud / CC BY-SA (http://creativecommons.org/licenses/by-sa/3.0/)
A load combination results when more than one load type acts on the structure. Codes usually specify which load combinations together with load factors (weightings) should be used for each load type in order to ensure safety under expected loading scenarios. The dead load includes loads that are relatively constant over time, including the weight of the structure itself, and immovable fixtures such as walls. Live loads, or accidental loads, are temporary, of short duration, or a moving load.
To find the most critical combination of factors the following guidelines may be considered:
- Although the number of different loads is relatively high, experience suggests that live loads do not occur at the same time. In general it is unlikely that more than two different accidental loads occur together, unless they are dependent each other.
- The seismic load is considered an accidental load when designing berths.
Further details on load combination and load weights can be found in Spanish standard ROM 0.2-90 (Ministerio de Obras Públicas y Transportes, 1990).
The design life of a port is frequently assumed as the operational time that is foreseen for it. A general design rule is that ordinary berth structures in commercial ports should have a design life of 50 years or more. For berths serving special industries, container traffic, oil traffic, etc., a period around 30 years is often adopted, as it it is predicted that industrial traffic may undergo significant changes in a relatively short time. For flood protection works a design life of more than 100 years may be appropriate. It should be considered that berth structures are highly exposed to corrosion which may decrease their operative life. A general rule suggests that the design life should be adopted by considering the impact of a failure. If there is risk for human life the design life should be increased accordingly.
As a rule of thumb the following design life may be adopted as a first estimate for a given type of structure:
- Breakwater: 100 years;
- Reinforced open berth structures: 50-100 years;
- Steel sheet pile berth structure: 50 years;
- Rubber fenders: 10 years;
- Concrete aprons and roads: 20 years.
Finally, it should be considered that safety guidelines are imposed at the national and international level for both the construction and operational phases. They should be adequately considered by the engineer.
Figure 3. Sheet piles in a port in Germany (Recklinghausen). By Frank Vincentz - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=15665298
The purpose of a berth structure is mainly to provide a vertical front where ships can safely dock. Berths can be subdivided into two main categories basing on their shape: wharfs and piers. The wharf is aligned with the coastline while the pier is protruding into the sea. Basing on their structure berths may be classified into two main categories:
- Solid structure berth;
- Open structure berth.
In the first category a solid vertical structure is created to contain fill material which is brought all the way from the land to the structure. The vertical structure is built where the depth of the sea is large enough to allow the considered ship to dock. Solid structure berths can be divided into two main subcategories:
- Gravity-wall structure: the front wall of the structure with its own deadweight and bottom friction is self-sufficient to resist the design loadings;
- Sheet pile structure: the front wall is made by sheet piles - in steel or concrete - which are anchored to an anchoring plate or another structure like a wall behind the berth.
The open berth structures are usually standing over piles set offshore from the natural extent of the land or the farthest extent of fill dirt. This type of berth can offer more flexibility and more space for docking but limits the amount of weight the berth is able to resist.
Figure 4. Open structure berth at the Torridge estuary (UK). By Jonathan Billinger, CC BY-SA 2.0, https://commons.wikimedia.org/w/index.php?curid=13420310
The most appropriate berth structure is usually selected basing on:
- Soil conditions;
- Underwater work;
- Wave action;
- Future extension;
Reliable and complete soil investigations must be carried out at the construction site with consultation of a geotechnical engineer. If the soil is loose and has a low bearing capacity a solid block wall-type structure may be not appropriate as it might be unstable. In such a case, it would be better to consider an open type berth founded on piles.
It is also advisable to avoid massive underwater works which would increase the construction cost and time. The capacity for work under water is often limited compared with the situation above water. Sheet pile structures and structures founded on steel pipe piles are an ideal alternative.
Open berth structures are normally more favourable than solid ones in respect of the reflection of incoming waves against the berth front. At an open structure the waves will be damped to a great extent against the rough rubble-covered slope. At the vertical wall of a solid berth wave reflections and other disturbances can induce undesired impacts.
When designing a berth structure, as well as any other engineering structure, thought should be given to which types of construction plant and machinery can reasonably be procured for the site in question. Piles usually involve heavy equipment and high transportation and installation costs. Therefore, the use of gravity walls may be recommended when the construction material can be easily found locally.
As for the material, a berth structure can be constructed out of timber, steel or concrete or a combination of these materials. The general choice of construction materials to be adopted will depend on the berth use and economic considerations. The durability under marine environmental conditions is of particular importance for marine structures.
Construction time is also a relevant aspect to be considered, especially if the service of an existing berth is impeded during the construction works. The literature suggests rules of thumb for estimating construction time for different berth structures (Thoresen, 2010).
It is also important to consider the possibility that the berth may need to be extended in the future, for increased traffic, increased ship size or other justified needs. Therefore it is important, at the time of design, to predict in which way the berth may be extended and to design the berth structure accordingly.
Finally, construction costs are another important driver, to be considered within a rigorous cost benefit analysis. They considerably vary from country to country. As a rule of thumb one should consider that open berth structures are relatively cheaper than solid structures especially in the presence of high water depth at the front.
The dimension of berth structures should be designed by considering port planning and in particular the traffic plans and related ship size. As a rule of thumb, the following guidelines may be considered:
- The length of the berths is varying from 5–10 m for a small boat in a marina to over 400 m for the large ships. The rule of thumb is that the length of a berth should be roughly 10% longer than the longest vessel to be moored at the berth itself;
- The width of small docks should be at least 2 meters for a ship length up to 10 meters and a length of the pier or wharf up to 100 meters;
- The width should be increased to a minimum of 2.5 meters for ship length between 10 and 20 meters and dock length between 100 and 150 meters;
- The width should be minimum 3 meters for ship and width length exceeding the above limits.
When possible the berths should be aligned with the dominant wind and dominant current.
In terms of structural loads, berths should be designed against a live vertical load of at least 4 kN/m2. Higher loads may result from a detailed analysis.
In terms of vertical positioning of the berth floor, meaning vertical difference between mean sea level and floor, it is recommended to make a specific assessment which should take into account tide dynamics, type of ship and so forth. A difference of at least 1 meter should be adopted.
Port construction and port activities entail a relevant environmental impact on land, sea and air. For large ports the impact is often extended at the regional level for increased traffic, urban expansion and so forth. Environmental impact need to be considered in planning phase and carefully evaluated in the design phase. Local law and regulations, as well international directives and guidelines, suggest how environmental impact assessment is to be carried out. Assessment of environmental impact is becoming a matter of major concern today for the increasing attention that is devoted to sustainable development. Several of the UNESCO's sustainable development goals are directly (SDG #14) related to sea and port activities (SDG #7, SDG #8, SDG #11, SDG #13).
Environmental impact includes emission of fine dust by ships and road traffic, emission of CO
The environmental impact of ports may be divided into four categories:
- impact by port activity itself;
- impact on the sea caused by ships and human induced pollution;
- impact from emissions from transport networks;
- impact induced by land use change and in particular urban expansion supported by the presence of the port.
Local and international authorities have set up coordinated actions and guidelines to reduce the impact of ports and mitigate its consequences. For instance, the European Union recently promoted an integrated maritime policy termed blue growth. It is a long term strategy to support sustainable growth in the marine and maritime sectors as a whole, in consideration that seas and oceans are drivers for the European economy and have great potential for innovation and growth.
The types of strategies to reduce environmental impact are diverse and may include “soft” instruments like information provision, investments to reduce the traffic flow of to promote clean traffic, limitation to environmentally risky activities, the use of clean and safe technologies and policies to reduce emissions. Economic incentives are also an interesting option to promote the use of clean energy and the restoration of the sea environment. Actually, incentives have been proved to be more successful than bans in several case studies. One limitation is the lack of a global framework for addressing environmental impacts of international shipping, making it difficult for individual countries to take an effective action.
An interesting option to reduce the impact of sea activities and to re-use offshore platform is the production of marine energy. It mainly refers to the energy carried by ocean waves and tides. The movement of water in the world’s oceans creates a vast store of kinetic energy, or energy in motion. Some of this energy can be harnessed to generate electricity to power port activities and other civil uses.
Figure 5. Wave energy floaters at the Gibraltar Wave Farm. By Clairemartin96 / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0).
Port activities cause the deposition of contaminated muds over the sea bed. Regular dredging is required to remove contaminants and keep the port in full operational mode. A relevant problem is the displacement of the dredging mud that is contaminated by highly toxic pollutants, including chemicals like heavy metals.
Inland disposal is a possible solution to displace contaminated muds. However, it is not sustainable and often not accepted by population living close to landfill sites. To reduce the volume, dredge muds may be reduced to dry solids via dewatering. Dewatering techniques employ either centrifuges, geotube containers, large textile based filters or polymer flocculant/congealant based apparatus. Research activities is being carried out on the possibility to use dewatered muds for the production of concretes and construction block, although their high organic content may imply limited durability.
I am quoting from Wikipedia:
"The proper management of contaminated sediments is a modern-day issue of significant concern. Because of a variety of maintenance activities, thousands of tonnes of contaminated sediment are dredged worldwide from commercial ports and other aquatic areas at high level of industrialization. Dredged material can be reused after appropriate decontamination. A variety of processes has been proposed and tested at different scales of application (technologies for environmental remediation). Once decontaminated, the material could well suit the building industry, or could be used for beach nourishment."
Figure 6. Grab (clamshell) dredging in process in Port Canaveral, Florida. CC BY 3.0, https://en.wikipedia.org/w/index.php?curid=14370430.
Spanish standard ROM 0.2-90 (Ministerio de Obras Públicas y Transportes, 1990). Thoresen, C. A. (2010). Port designer's handbook. Thomas Telford.
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Last change on Feb 22, 2023.
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