 This is the learning outcome for the student and at the end of this session student will be able to explain the basics of repair and rehabilitation. Actually, repair rehabilitation is very vast big topic that is a research area also but student at least they should know the what are the basics of repair and rehabilitation. This is the basic idea behind this video. Now, let us see the introduction why any structure any building is in need of repair or is in need of rehabilitation that is the main thing. First thing is the when the structure structure components are subjected to distress and the distress in the building is common thing or these are the common occurrences. Third thing is when any building element or component is subjected to crack why it is subjected to crack when the stress in it is reaching the limit of its strength then the crack formation is possible. Third thing is buildings are subjected to stresses definitely and that is because of one thing is the gravity loads first is dead load lie load and second is the lateral load that is a seismic load or wind load. So gravity load as well as seismic load or wind load these two are the causes of stresses which are arising in the building components and one more last reason the thermal movements may be expansion or contraction due to temperature changes, moisture changes, chemical action, weathering action these are also causing deformations internally in the material of building. So let us see distress how it can be classified there are two ways to classify the distress one is structural second is non-structural. Let us see what is mean by structural distress if the distress is due to the faulty design faulty design calculations consideration of the loads or due to the faulty construction practices in appropriate practices or last is overloading you will find structural distress in the building. Next is these types of distresses structural distress can endanger the safety of the building also. Now let us see the example for example when overloading is done on any flanger or beam RC beam member definitely extensive cracking you will observe for that beam and that is due to the overloading. Now in case of non-structural cracks or the cracks which are not for the structural component of because of the crack is forming instead of these reasons these are not end danger to the safety of the building but this may look unsightly and it create an impression of faulty work also in proper practice also. Let us see what is mean by non-structural distresses these types of distresses are induced because of stresses in the building components. These generally do not directly resulting structural weakening but the cracks which are non-structural cracks are subjected to the weathering actions atmospheric actions may enter into these cracks and the reinforcement rebar may be subjected to the corrosion and this render to the structure unsafe and finally it may need to collapse also. Now one question is for you you just pause the video and see this question and try to answer this there are two fill in the blanks this is dash dash crack do not directly result into structural weakening and faulty construction and overloading leads to dash dash crack. Now which types of cracks are due to these reasons that you have to answer pause the video think over that and give the answer. The answer is first is non-structural crack do not directly result in structural weakening and faulty construction overloading leads to structural crack this is the answer. Now we are talking about the distress then overloading all those things now finally what is the effect of all those that is the cracking that we are talking about and let us see what are what is the nature of crack and what are the causes of the crack. Now in building components which are subjected to the stresses if the stress tend to move the building away from the steep portion of the buildings which acts as a fixed point due to dimensional changes this is one reason second is in symmetrical structures the center of structure or whatever we can call as the center of resistance acts as a fixed point and movement of the symmetrical building takes place away from the center on either side this is the second reason third is a building as a whole can move easily in a vertical direction but it is horizontal movement in horizontal direction is restricted by the action of substructure and its foundation. So deflection of the building is possible deformations are possible but in horizontal direction its movement or translation is difficult that is why there may be reason of arising vertical cracks on walls and this is more frequent phenomena. The stresses in building components are of three natures one is tensile type of nature compressive nature or having shear stresses or shear nature. Now these cracks once these are forming then this will spoil the internal finish of the building by allowing moisture to percolate and this will increase the maintenance cost of your building the maintenance may be in the form of painting repetitive painting again plaster some repair and this will increase your maintenance cost. Now it is necessary to stitch or seal or stitching or sealing of the cracks is required this is necessary and need where the cracks are formed. Now most of the material in the building it may be mortar concrete it may be masonry all these are very strong in compression but these are weak in shear and tension. So forces of small magnitude of tension or shear type may cause tension tensile or shear stresses and will result into cracking. So the cracking phenomena is very often in the building this is because of this reason. So let us see what is the classification of the cracks and this depends upon based on its width of crack. Now thin crack it is always less than 1 mm in width medium crack it is having width of 1 to 2 mm and wide crack is called as when the width is more than 2 mm. Now this is explaining the nature of the crack or even the type pattern of the crack. Cracks may be of uniform width throughout or may be narrow at 1 n and gradually gets wider at the other end. This is entirely complex phenomena what is the type of crack how it is developed. Next is cracks may be straight tapered to the map pattern random direction wise it is vertical horizontal or diagonal this may be the different patterns of the cracks. Crack may be at the surface or it may extend to the full depth of the member also it may be beam column or it may be a walls closely fine cracks at surface of material is called as grazing. So this phenomena is called as grazing when very fine cracks are on the surface of the plaster basically mapping we can call. Cracks due to different causes have different characteristics and by careful observation only of these characteristics we can diagnosis or we can diagnose the causes of cracking and the adopt we can adopt appropriate remedial treatment for that type of crack. Now what is the way to understand this entire problem first is a visual investigation of the concrete. So this investigation technique can be broadly classified as destructive or non-destructive now how that can be decided we should first visualize visual investigation and walk around the survey we should carry out and it should be taken to decide what type of technique is to be used for that type of cracking. Next is photography and notes should be taken from the site concrete site concrete. Digital photography of large area is helpful in documenting overall condition. So overall condition of the building then afterward they will whenever the photograph is taken in detail you can see very closely you can see what is overall condition of that concrete. Now close-up views can be used to check details such as crack width and its direction. So based on the crack formation and its direction the diagnosis can be made. Now these are the binoculars, telephoto lenses which are used to get the more accurate information and record the same for further use. Visual investigation involves looking for and analyzing cracks. So different phenomena are also explained here spalling of concrete or fine cracks or any other call such defense which can be seen without digging or scratching the surface of the structure or its element. Now to aid this visual examination the following checklist is made and the information which shall be sure should be collected in this checklist this just be as follows. First is the details of owner and occupier next thing is the type of occupancy also. So this detail must be taken first on site then the type of the structure whether this is RC structure, load bearing structure, stone masonry structure, brick masonry structure the type of structure is important. Next the dimensions, dimensions of the structure or structure element in case of building it must be taken at the length level it must be taken at the floor level. In case of the members the exact member irrespective of its extent the member shall be measured as it is which is actual on site. Now the interconnection of element that is also important the interconnection is the connection between walls, connection between the wall to rope, connection between wall to foundation also this is possible only in load bearing wall to foundation. Now material information what is brick masonry, what type of mortar is used plastering, internal plastering, external plastering then the material like concrete, grade of the concrete what was considered during the design and execution this material information is required. Now orientation of the building or building component with respect to north that is also important. Most important is the climatic condition prevailing and wind direction. So the climatic condition prevailing that is very important and based on that the what weathering actions have taken place and what damage that is made to the structure structure component because of weathering action that can be also. The science of the deterioration age of the building and details of the maintenance and previous repair of this. These details are also important. Now these are the equipment and accessories that will helpful in visual examination first is building drawing, layout plan, camera, binoculars, magnifying glass, flashlight, a compass, tape record. These are the references for this video. Thank you.