 In today's lecture, we are going to study modes of transportation, bridges and tunnels. Learning outcomes of this video. At the end of this video, the viewers will able to explain the importance of bridges and tunnels and the classification. Importance of bridges. Bridges can connect the difficult ways. It make the transportation easy and good. It reduces the travelling time. It mostly convenient use in military. It has importance regarding political and economical aspect and it gives the less emission due to displacement. Introduction. A bridge is a structure built to span physically obstacles such as a body of water, valley or road. For the purpose of providing passage over the obstacles without closing the gap below. Normally, we will construct the bridges over rivers or at the hilly areas to provide the efficient transportation system without disturbing the natural obstacles. So in this figure, you can see it is the river valley and over this river valley, the bridges constructed. So it provides the good transportation and it provides the less time to transport from one place to another place, any goods or passengers. It is constructed for the purpose of providing passage over the obstacles usually sometimes that can be detrimental to cross otherwise. So these are the common elements of the bridge structure. The bridge is divided in two parts that is substructure and superstructure. The substructure consists of foundation, piers and abetment etc. And the superstructure consists of deck slab, girder, truss etc. As we know in building also we have two structures means one building is divided in two components that is substructure and superstructure. Substructure is mainly consists of foundation below the ground level and the superstructure is constructed whatever building or portion of the building above the ground level. So in bridge also it will have two components that is substructure and superstructure. If you see this figure, in this figure this line shows the original ground level or it may be a water level. So in substructure foundation is there, abetment is there, foundation means it is the main part of the bridge which carry the overall load of the superstructure and it will transfer to the natural soil or the ground below it. So this abetment is also constructed with the help of natural materials or rock pitching. This abetment is provided for the stability at the ends of the bridge. The main purpose of abetment is to provide the stability to the overall bridge structure at the ends or the road connect. Piers are nothing but the columns of the bridge. So it is also comes in substructure. Here you can see the effective span of bridge means it is the centre to centre distance between the two piers. These bearings are provided to reduce the vibrations due to the vehicle traffic and to reduce the damages which are creating or to reduce the stresses which are creating on this deck slab. Deck slab is nothing but the road surface of the bridge. Here this HFL is called as high flood level means whenever it is a river or it will indicate as HFL means this is the maximum level of the water which can increase during the flood level. So it is used for the precautions in rainy seasons to avoid the flood situations. Now these are called as longitudinal girders which are provided throughout the span and these cross girders are provided throughout the width of the bridge. Width of the bridge is nothing but the width of the road pavement which constructed over the bridge. So here again handrails are provided, parapet wall is also provided, handrails and parapet walls are provided for the purpose of safety. These expansion joints are constructed to avoid the expansion or contraction of the material which is used in the construction of the deck slab. Means here you are constructing the deck slab with the concrete. The concrete is consist of cement, sand and aggregate. These materials are having their own properties like shrinkage and expansion due to change in weather conditions. So these expansion joints are provided to reduce the stresses and effects of the stresses due to the temperature effects. Means if temperature changes or now if you observe in summer there is expansion of the material due to the heat. So in that case if this material is trying to expand so this cap will help without damaging the overall structure of the bridge and in winter season these materials or the cement will have the property of shrinkage. So due to that property it will try to contract or compressed. So it will reduce again the effects of the temperature. So expansion joints are provided at each span of the, so these are the normal and common elements of the bridge. Now these are the various types of bridges. Bridges are classified based on material, based on structural use, based on design and based on span. Again this based on material is classified as timber bridge, concrete bridge and steel bridge. The structural use is classified cantilever bridge, suspension bridge, belly bridge and movable bridge. Again based on design it is classified as plate girder bridge, lattice girder bridge and busting bridge. Based on span it is classified as major bridge, minor bridge, other bridges and culverts. So this is the overall classification of the bridges. Based on material it is divided in timber, concrete and steel. It is the material which is used for the construction of the bridge. Normally timber bridges are used for decorating purpose. So we can observe this timber bridges in gardens, restaurants and for the main use of bridge. It is used as concrete and steel bridge. Based on structural bridge means by use of structure of bridge means what purpose you are using, using the bridge. It is cantilever bridge, suspension bridge, belly bridge and movable bridge. These suspension bridges and movable bridges are mostly used where you have to cross the river and those rivers or seas are used for the water transportation by ships or large boats. So in that case you can, without disturbing the construction of bridge you can make the way to pass the boats below that bridge. Again based on design it is plate girder bridge, lattice bridge and busting bridge. These are the types of girders means whatever, whatever beam, girder is nothing but the beam you can see. So these are the types of beams used in the construction. Again based on span it is classified as major bridge, minor bridge, other bridge and culverts. So major bridge is constructed where the span is more than 45 meters, minor bridges are constructed when span is 30 to 45 meters then other types of bridges and where you are having other types of bridges are constructed for the span less than 30 meters and culverts are constructed when you are having span very less or you can say it is more than 6 meters. So it is the overall classification of the bridges. Now tunnels, tunnels are also very important to make the possible way of transportation. So this permits the transportation of passengers and freight or it may be for the transportation of utilities like water, sewage or gas etc. So this figure shows the typical cross section or typical image of the tunnel. So it is the typical cross section of the tunnel. In this cross section you can observe various parts of the tunnel. So first you have to make a drill into the hill or where you have to construct the tunnel and again you have to provide the all facilities for drainage, electricity and you have to provide the stability to the tunneling by providing the lining PCC means PCC means it is plain cement concrete. So it is the typical cross section of the tunnel. Again these tunnels are classified as based on purpose, based on surrounding material and submerged tunnels. Based on purpose means for road and railway utilities, based on surrounding materials means whatever material is actually present at that site and submerged tunnels are mostly used in underground situation. So it is the typical cross section of the construction of the tunnel. Now again we are having the tunnels in different shapes means the tunnel is constructed in circular, egg shaped elliptical cross section, horseshoe vertical wall and box type cross section. So accordingly purpose and condition of the site we have to decide the shape of the tunnel. These are the advantages of the tunnels. We have beyond 18 to 20 meter deep cutting in hills tunnels are economical construction is independently possible without disturbing the surface activities like life and traffic. They serve as underground shelters in case of bombing and enemy attack. The tunnels are cheaper compared to bridges or the surface carriage of water, sewage or gas means by constructing the tunnels you can transport the sewage as well as gas also. Modern technique makes the tunnel construction safe and sound. So these are the disadvantages means the initial cost which is required for the construction of tunnel is more than other constructions like bridges and roads. The special costly equipments and machineries are required and the labor which are required for the construction those are technically skilled. It is the slow construction activity which requires the long duration for completion of the project. Now you pause this video and try to answer this questions. So these are the answers for the questions. These are the references considered for the further study. Thank you.