Motorway Crash Barriers: Materials and Manufacturing Selection Analysis - Case Study Example

MOTOR WAY CRASH BARRIERS: MATERIALS AND MANUFACTURING SECTION ANALYSIS Introduction Crash barriers also known as traffic barriers are constructed on roads either to prevent accidents or to minimise the loss incurred after the accident occurs. This is by stopping the moving vehicles that have lost control and preventing them from getting off their current lane as this can cause further damage to other road users. Crash barriers are erected in strategic locations on roads, mostly in areas that are most vulnerable to occurrence of accidents. Some of this high risk areas include; Sharp turning points and bends on roads, on bridges or on roads built over large masses of water. To ensure the barrier are in good working conditions before they are erected on roads, they are first tested through simulated crush tests to test the various types of degree of impact and also not to pose any hazard to pedestrians and motorists due to their placement. In addition, they are placed at a specific distance from the road to allow room for the motorcycles to navigate without any difficulty whatsoever. SECTION A 1. FUNCTIONS AND IN SERVICE REQUIREMTNTS OF CRASH BARRIERS Crash barriers are mainly constructed along the road to protect vehicle occupants, cyclists, other road users, useful structures and protected areas along the road from severe damage due to collision by absorbing the impact energy generated. More specifically, the roadside barriers ensure that the vehicles and cycles are kept within the roadway thus preventing them from crushing into buildings, walls, steep slopes, water bodies, and trenches constructed along the road. They are also erected in between the carriageways of a highway to prevent unlawful U- turn that may cause accidents with the oncoming motors. Before the barriers are constructed, a number of conditions have to be observed and taken care of. These include, the height of the barrier, its distance from the protected area or hazard, spared space for pedestrians and cyclists, the thickness of the road left and the clear recovery area for vehicles and motorists 2. JUSTIFICATION AND REVIEW OF THE DESIRED MATERIALS The most common materials used in making crash barriers are the concrete, cables or wire ropes, metal sheets, plastics and wood. Concrete is known to be strong on compression forces and weak in tension forces, therefore, reinforcement bars are provided to counter the weakness. This is necessary since a good percentage of the impact applies tension forces to the barrier. Cables are designed to have some degree of elasticity and reflective property when installed and maintained within a certain tension. Metal sheets are modified to have corrugations that can contain some impact energy. Wood and plastic are finished with a smooth surface and shape that can redirect the impact. Figure 1: Steel Safety Barrier Systems Figure 2: Wire Rope Safety Barrier The figures 1 and 2 above show some of the crash barriers in use. The choice of the material depends on cost, availability and functional requirements of the barrier. For instance, reinforced concrete barriers may not be very effective on roads whose frequent road users are cars with light bodies. In such cases, less rigid materials like corrugated metal sheets play a better role. The fact that the barriers are designed to absorb the impact energy, the best material chosen for a particular place can fall in the two broad categories; materials that responds to energy by redirecting the involved motor vehicle and those that receives it and withstand the whole impact by transmitting it to its neighbourhoods as well as transforming it into another form of energy. SECTION B 1. SELECTION OF THE DESIRABLE MATERIAL All the materials discussed above can be used as traffic barriers but the effectiveness and the cushion property that each one has matters a lot. Concrete barriers and some of the wood barriers are designed to redirect the motor in a direction parallel to their length due to their stiffness end inelasticity. An example is illustrated below; figure 3. In such a case, the body of the motor vehicle gets severe deformation as a result of its inability to fully cushion the motor, although the degree of deformation depends on the approach angle. These barriers are suitable in places where the preserved areas or hazards are situated very close to the guardrail. Materials like cables, metal sheets and plastics are a bit elastic and less deflective to a certain extent, therefore non re-directive; they would contain the impact to a higher percentage than the concrete and bring about little deformations on the motor’s body. Among these materials, metal sheets are the best since they can be easily transformed into shapes that can provide the best degree of shock absorption. Figure 3 2. Perform a material selection The most common metal sheets are steel. They are available in two common types, that is, W beam and three beam barriers. They are prevented from rusting by adding a galvanisation layer that makes them environmental friendly, healthy and safe for the road users. According to Michael (2005), rational selection of materials to meet environmental objectives starts by identifying the phase of product life that causes greatest concern in: production, manufacture, use or disposal. Dealing with all these requirements is not only for eco- attributes such as energy, Carbon II Oxide and others, but also for mechanical, thermal, electrical and chemical properties’. Diagram 1 below shows how materials for a mobile barrier are obtained and selected depending on their strength and how the best candidate materials are finally obtained. Diagram 1 The figure above shows the relationship between different materials i.e. metal, polymer and composites with their respective yield strength when faced with impact. The materials chosen are cast irons an steels. The second diagram below shows the selection of materials for static barriers, the desirable candidate materials CFRP, Mg, Ti alloys and Al alloys. Diagram 2: materials CFRP, Mg, Ti alloys and Al alloys. This diagram shows an advanced selection process that is applied in most manufacturing process to select desirable candidate materials that can be used to make traffic barriers Materials and the Environment (Michael 2005, P. 18). SECTION C 1. POTENTIAL MANUFACTURING METHODS Modern technology is used in the manufacturing process of rolling high rolled coils into steel sheets that are in turn modified into suitable steel barriers. Picking process is done using hydrochloric acid then continuously rinsed by water. This is followed by cold rolling where the red hot coils are reduced to the desired nature of the surface, thickness and shape. This process leads to excessive hardening of steel and loss of structural properties like ductility and formability which are in turn recovered by annealing in presence of Nitrogen Hydrogen. Smoothening and some surface improvements are done by continuous skin passing which also increases the magnetic, strain and stretching properties of the coils. With these properties, the coils are fed into the slitting machine which produces some reasonable thin sheets that are further sheared to the required dimensions for use. The sheets are then galvanized to provide a rust resistant coat. The final process which is corrugating is done by the appropriate machine to required corrugation sizes that are suitable for crash barrier purposes (Anees et. al. 1993). 2. Review the selected manufacturing Steel barriers processing is accompanied by a number of direct and indirect environmental impacts. The process indirectly leads to production of non biodegradable materials that pollutes land if they are not recycled. Mining of the metals leads to depletion of land and vegetation making it inhabitable as well as being a health hazard. Direct environmental impacts include the emission of carbon dioxide gas into the atmosphere which brings about green house effect that increases global warming. The process is also accompanied by emission of harmful radiations and fumes into the atmosphere that affects flora and fauna negatively. Other negative impacts are brought about by disposal of waste water into lakes and rivers that threatens aquatic life. Finally, the process leads to sound pollution by creation of noise that mostly affects human beings. The process produces corrugated steels that are easier to manipulate when designing traffic barriers to suit the intended architectural design. SECTION D 1. INFLUENCE OF THE MANUFACTURING PROCESS TO THE STRUCTURE AND PROPERTIES OF THE MATERIAL SUITABLE FOR ITS FUNCTIONS The manufacturing process reduces the coils into sheets to provide easy working conditions using simple machines. It also removes impurities and rough textures present in the original material that would have made the final finish ugly, un-presentable and weak due little bonding forces caused by incompatibility that results from heterogeneity of the material. The smooth surface achieved in the manufacturing process also reduces frictional force between the vehicle and the barrier leading to low degree of vehicle deformation. This is very effective in cases where the vehicle is deflected along the length of the barrier. The same surface also creates a healthy and safe condition for other road users like pedestrians by reducing the abrasive effect to their bodies, belongings and attires. The corrugations made on the steel sheet gives it a spring-like elastic property that increases the absorption property of the impact energy dissipated on the barrier thereby reducing the resultant impact on the vehicles body and its occupants. The sheets are galvanized with a thin coat that is resistant to rust leading to low maintenance costs of the barrier. This also ensures that the barrier lasts for long. The ductility properties added during the skin passing process gives the steel sheet some strength that enables undergo some degree of strain before breaking, a property that increases some cushioning effects. 2. IMPARTMENT OF RESISTANCE FEATURES TO ENVIRONMENTAL DEGRADATION The major environmental threat is rusting and growth of fungi and moulds. This can be minimized through a number of steps for durability purposes and maintenance of its strength. Coating the barrier with a metallic coat during the manufacturing process is one of the major steps that reduce rusting. Smoothening of the surface ensures that little or no water sticks on its surface thus reducing the rate of rusting which is stimulated by presence of water or moisture. Painting the barrier is also necessary to reduce the rate of rusting. Constant clearing of vegetation underneath reduces moisture in the area, a factor that promotes the growth of moulds and fungi. Conclusion In conclusion, crash barriers are a very important part of roads and their presence indicates safety and minimises the loss in case an accidents occur on roads. They not only protect the motor vehicles, but also they protect other road users such as the pedestrians and motor cycles from the risk of falling of the roads in case of bridges. From the report, we can deduce that in order to manufacture crash barrier that are road worthy, material selection is extremely important. In addition, it can be concluded that the manufacturing methods take into keen consideration the environmental implications of all procedures undergone in the manufacture of Crash barriers. Without crash barrier, accidents on roads would be much more rampant and losses would increase additionally making more lives to be lost. List of references Anees Malik, Saleh Fozan and Mohammad Romiahl (1993) Relevance of corrosion research in the materials selection for desalination plants, Presented in Second Scientific Symposium on Maintenance Planning and Operations, King Saud University, Riyadh, 24-26 April, Ashby, M.F. (2005) “Materials Selection in Mechanical Design”, 3rd edition, Butterworth- Heinemann, Oxford, UK, Chapter 16 Read More