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Educational Basic Civil Engineering

Discussion in 'Education' started by Tazul Islam, Jun 15, 2016. Replies: 62 | Views: 3808

  1. Tazul Islam
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    Last edited: Aug 10, 2016
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    Advantages of Prestressed Concrete



    The prestressing of concrete has several advantages as compared to traditional reinforced concrete (RC) without prestressing. A fully prestressed concrete member is usually subjected to compression during service life. This rectifies several deficiencies of concrete. The following text broadly mentions the advantages of a pre-stressed concrete member with an equivalent RC member. For each effect, the benefits are listed.


    A) Section remains un-cracked under service loads


    1. Reduction of steel corrosion
      • Increase in durability.
    2. Full section is utilized
      • Higher moment of inertia (higher stiffness)
    3. Less deformations (improved serviceability).
    4. Increase in shear capacity
    5. Suitable for use in pressure vessels, liquid retaining structures.
      • Improved performance (resilience) under dynamic and fatigue loading.

    B) High span-to-depth ratios


    1. Larger spans possible with prestressing (bridges, buildings with large column-free spaces)
    2. Typical values of span-to-depth ratios in slabs are given below.

    For the same span, less depth compared to RC member.


    • Reduction in self weight
    • More esthetic appeal due to slender sections
    • More economical sections.
     
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    C) Suitable for precast construction The advantages of precast construction are as follows.


    • Rapid construction
    • Better quality control
    • Reduced maintenance
    • Suitable for repetitive construction
    • Multiple use of formwork

    1. Reduction of formwork

    • Availability of standard shapes.

    Limitations of Prestressing
    Although prestressing has advantages, some aspects need to be carefully addressed.

    • Prestressing needs skilled technology. Hence, it is not as common as reinforced concrete.
    • The use of high strength materials is costly.
    • There is additional cost in auxiliary equipments.
    • There is need for quality control and inspection.
     
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    Factors to be considered in the design of steel structures


    All the members in the structure should have adequate strength, stiffness and toughness to ensure proper funtioning during service life. Members should have adequate strength, stiffness and toughness to ensure propoer functioning during service life.


    Reserved strength must be available to cater for:


    • Occasional overloads - underestimated loads
    • Variability of strebgth of materials from those specified.
    • Variation in strength due to workmanship, construction practices.

    Goal is to prevent limit state from being reached.


    1. Adaptations to site:

    If the structure is a building, for instance, the designer must create a plan that has suitable arrangement for rooms, corridors, stairways, windows, elevators, emergency exits etc and all this plan should be adapted to site so that it is feasible, accepted aesthetically and at a reasonable cost. This is called funtional planning.


    2. Structural scheme:

    structural scheme is dependent on funtional planning. Structural scheme includes the location of columns in the buildings, it is to be worked out with the funtional plan and sufficent space must be anticipated between finished ceiling and finished floor for location of columns.


    3. Structural analysis:

    Once loads are defined and design is laid out, structural analysis must be performed to determine internal forces that will be produced in various members of the framework. Assumptions must be made and it should be ensured that structure in reality also behaves as it is supposed to (and as it was assumed to behave).


    4. Proportionality of members:

    Members must be proportioned with factor of safety in mind.


    5. Factor of safety:

    The development of design specifications to provide suitable values of the margin of safety, reliability and probability of failure must take into consideration the following factors.


    1. Variability of the material with respect to strength and other physical properties
    2. Uncertainity in the expected loads
    3. Precision with which internal forces are calculated
    4. Possibility of corrosion
    5. Extent of damage, loss of life
    6. Operational importance
    7. Quality of workmanship

    The design safety of structures may be evaluated in either of the two ways:


    1. Allowable Stress Design
    2. Load and resistance factor design
     
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    What we study in Hydrology

    In hydrology we study Hydrologic cycle, its processes, water balance, precipitation types, estimation of precipitation, and analysis of precipitation data. We also study infiltration phenomena, solution of the Richard’s equation and approximate infiltration models. Methods of measurement of stream flow, stage discharge relation, unit hydrograph theory, Transposition of Hydrograph, Synthesis of hydrograph from basin characteristics, stream flow routing, flood frequency analysis and attenuation of flood flows are also studied in Hydrology.


    Definition of hydrology:

    The study of water in all its forms (rain, snow and water on the earth’s surface), and from its origins to all its destinations on the earth is called hydrology.


    Scope of Hydrology

    1. Water is one the most valuable natural resources essential for human and animal life, industry and agriculture.
    2. It is also used for Power generation, navigation and fisheries.
    3. Tremendous importance is given to the hydrology all over the world in the development and management of water resources for irrigation, water supply, flood control, water-logging and salinity control, Hydro power and navigation.

    Engineering Hydrology

    It uses hydrologic principles in the solution of engineering problems arising from human exploitation of water resources of the earth. The engineering hydrologist, or water resources engineer, is involved in the planning, analysis, design, construction and operation of projects for the control, utilization and management of water resources.
    Hydrologic calculations are estimates because mostly the empirical and approximate methods are used to describe various hydrological processes.
     
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    Uses & Applications of Hydrology in Engineering


    In hydrology we apply scientific knowledge and mathematical principles to solve water-related problems in society: problems of quantity, quality and availability. Mathematical models of all Hydrological phenomena are made.


    They may be concerned with finding water supplies for cities or irrigated farms, or controlling river flooding or soil erosion. Or, they may work in environmental protection: preventing or cleaning up pollution or locating sites for safe disposal of hazardous wastes.


    Applications of Engineering Hydrology

    • [​IMG]Hydrology is used to find out maximum probable flood at proposed sites e.g. Dams.
    • [​IMG]The variation of water production from catchments can be calculated and described by hydrology.
    • [​IMG]Engineering hydrology enables us to find out the relationship between a catchments’s surface water and groundwater resources
    • [​IMG]The expected flood flows over a spillway, at a highway Culvert, or in an urban storm drainage system can be known by this very subject.

    • [​IMG]It helps us to know the required reservoir capacity to assure adequate water for irrigation or municipal water supply in droughts condition.
    • [​IMG]It tells us what hydrologic hardware (e.g. rain gauges, stream gauges etc) and software (computer models) are needed for real-time flood forecasting
    • [​IMG]Used in connection with design and operations of hydraulic structure
    • [​IMG]Used in prediction of flood over a spillway, at highway culvert or in urban storm drainage
    • [​IMG]Used to assess the reservoir capacity required to assure adequate water for irrigation or municipal water supply during drought
    • [​IMG]Hydrology is an indispensable tool in planning and building hydraulic structures.
    • [​IMG]Hydrology is used for city water supply design which is based on catchments area, amount of rainfall, dry period, storage capacity, runoff evaporation and transpiration.
     
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    • [​IMG]Dam construction, reservoir capacity, spillway capacity, sizes of water supply pipelines and affect of afforest on water supply schemes, all are designed on basis of hydrological equations.
    • [​IMG]Determining the water balance of a region.
    • [​IMG]Determining the agricultural water balance.
    • [​IMG]Designing riparian restoration projects.
    • [​IMG]Mitigation and predicting floods, landslides and drought risk.
    • [​IMG]Flood forecasting and flood warnings.
    • [​IMG]Designing irrigation schemes and managing agricultural productivity.
    • [​IMG]Designing dams for water supply or hydroelectric power generation.
    • [​IMG]Designing bridges.
    • [​IMG]Designing sewers and urban drainage system.
    • [​IMG]Predicting geomorphologic changes, such as, erosion or sedimentation.
    • [​IMG]Assessing the impact of natural and anthropogenic environmental change.
    • [​IMG]Assessing containment transport risk and establishing environmental policy guidelines
     
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    Precipitation

    What is Precipitation? Defined:
    Water falling in solid or liquid form e.g. rain, snow, and hail.

    Uses of Precipitation Data
    • Runoff estimation analysis
    • Groundwater recharge analysis
    • Water balance studies of catchments
    • Flood analysis for design of hydraulic structures
    • Real-time flood forecasting
    • low flow studies
    Mechanism Producing Precipitation
    Three mechanisms are needed for formation of precipitation.
    1. Lifting and Cooling - Lifting of air mass to higher altitudes causes cooling of air.
    2. Condensation - conversion of water vapor into liquid droplets.
    3. Droplet Formation - Growth of droplets is required if the liquid water present in a cloud is to reach ground against the lifting mechanism of air.

    Precipitation
    Depending upon the way in which the air is lifted and cooled so as to cause precipitation, we have three types of precipitation, as given below:

      • Cyclonic Precipitation
      • Convective Precipitation
      • Orographic Precipitation
    Cyclonic Precipitation:
    Cyclonic precipitation is caused by lifting of an air mass due to the pressure difference. Cyclonic precipitation may be either frontal or non-frontal cyclonic precipitation.

    Frontal precipitation:
    It results from the lifting of warm and moist air on one side of a frontal surface over colder, denser air on the other side. A front may be warm front or cold front depending upon whether there is active or passive accent of warm air mass over cold air mass.

    Non-frontal precipitation:
    If low pressure occurs in an area (called cyclone), air will flow horizontally from the surrounding area (high pressure), causing the air in the low-pressure area to lift. When the lifted warm-air cools down at higher attitude, non-frontal cyclonic precipitation will occur.
     

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