Paddy Engineering Consultant

A water tank is used to store water to tide over the daily requirements. In general, water tanks can be classified under three heads: (i) tanks resting on ground (ii) elevated tanks supported on staging, and (iii) underground tanks. From the shape point of view, water tanks may be of several types, such as (i) circular tanks (ii) rectangular tanks (iii) spherical tanks (iv) Intze tanks and (v) circular tanks with conical bottoms. In the construction of concrete structures for the storage of water and other liquids, the imperviousness of concrete is most essential. The permeability of any uniform and thoroughly compacted concrete of given mix proportions is mainly dependent on the water-cement ratio. The increase in water-cement ratio results in increase in the permeability. The decrease in water-cement ratio will therefore be desirable to decrease the permeability, but very much reduced water-cement ratio may cause compaction difficulties and prove to be harmfu

Spacing of Reinforcement in reinforced concrete members: Minimum Spacing between Bars in Tension The minimum horizontal spacing between two parallel main bars shall be diameter of larger bar or maximum size of coarse aggregate plus 5 mm. However, where compaction is done by needle vibrator, the spacing may be further reduced to two-third of the nominal maximum size of the coarse aggregate. The minimum vertical distance between two main bars shall be (a) 15 mm, (b) two-third of the nominal size of coarse aggregate, or (c) maximum size of the bar or whichever is greater. Maximum Spacing between Bars in Tension Normally these spacing will be as mentioned below : (a) For beams, these distances are 300 mm, 180 mm and 150 mm for grades of main reinforcement of Fe 250, Fe 415 and Fe 500, respectively. (b) For slabs (i) the maximum spacing between two parallel main reinforcing bars shall be 3dor 300 mm or whichever is less, and (ii) the maximum spacing between t

Requirements of concrete mix design should be known before calculations for concrete mix. Mix design is done in the laboratory and samples from each mix designed is tested for confirmation of result. But before the mix design process is started, the information about available materials, strength of concrete required, workability, site conditions etc. are required to be known. Following are the information required for concrete mix design: 1. Characteristic strength of concrete required: Characteristic strength is the strength of concrete below which not more than 5% of test results of samples are expected to fall. This can also be called as the grade of concrete required for mix design. For example, for M30 grade concrete, the required concrete compressive strength is 30 N/mm2 and characteristic strength is also the same. Fig: Characteristic Strength of Concrete 2. Workability requirement of concrete: The workability of concrete is commonly measured by slump test. The slu

Concrete without cement is possible with the use of flyash as an alternate for cement. Concrete is the most common material used for construction due to its properties such as strength, durability and easy availability. But cement is commonly used in preparation of concrete. Cement has excellent binding property but its production requires large amount of energy which contributes for pollution and global warming. The process of cement production starts from mining for raw materials, crushing, blending and heating these materials at high temperature of 15000C and finally creating cement from heated materials. All the process involved in manufacturing of cement requires large amount of energy, it involves huge costs, contributes to increase in CO2 emissions and other greenhouse gases. The production of cement contributes to 7% of the emissions of greenhouse gases and it is likely to double by the year 2014. As the demand for more and more infrastructures is increasing day by day,

Liquid penetrant inspection is a non-destructive testing method for detection of crack penetration depth in concrete. This method is used when visual inspection is not enough to detect cracks in concrete, especially in the case of liquid retaining structure. In this method, a liquid with high surface wetting characteristics is applied to surface where cracks are appearing. Then excess liquid from the cracks are removed. This is done by applying a developer (powder) to pull out the trapped penetrant liquid from the cracks. This powder is spread on the surface for cracks propagation to be seen. The cracks in concrete are detected by visual inspection process. The penetrant used is often loaded with a fluorescent dye and inspection of cracks is done under ultra-violet light to increase the test sensitivity. Liquid penetrant inspection method is used for location of surface breaking defects in non-porous materials. Based on capillarity action, low surface tension fluid penetrates i

Records to be maintained at construction sites play important role in construction activities. It is a document required to prove any construction activity has taken place at site during billing or any other claims. These records have all the data of various construction activities carried out at site. If any additional work has been carried out and it is claimed during billing, these documents need to be produced as a proof. Maintenance of records also helps during audits of construction projects at any point of time. These documents helps to defend any claims such as liquidated damages or false claims or violations of any guidelines by authorities or clients. Following are the various records that need to be maintained at construction site: 1. Contract Agreement: Contract agreement documents including all sets of drawings, including amendments, a copy of approval of municipality, corporation or urban development authorities need to be maintained at construction sites till

High-Strength versus High Performance Concrete High strength concrete and high-performance concrete are not synonymous because strength and performance of concrete are different properties of concrete. High-strength concrete is defined based on its compressive strength at a given age. During 1970s, any concrete mixtures which showed 40 MPa or more compressive strength at 28 days were designated as high strength concrete. As the time passed, more and more high strength concrete such as 60 – 100 MPa, were developed which were used for the construction of long-span bridges, skyscrapers etc. While high strength concrete is defined purely on the basis of its compressive strength, Mehta and Aitcin defined the high-performance concrete (HPC) as concrete mixtures possessing high workability, high durability and high ultimate strength. ACI defined high-performance concrete as a concrete meeting special combinations of performance and uniformity requirements that cannot always be achi

Types of Drawings prepared by Structural Engineers There are four different types of drawing: 1) Structural Drawings 2) Reinforcement Drawings 3) Standard Details 4) Record Drawings Structural Drawings: Structural Drawings are used to progress the Architect’s concept by specifying the shape and position of all parts of the structure – thus enabling the construction of that structure on site. Structural Drawings are also used for the preparation of the reinforcement drawings. Structural Drawings would typically include the following information: . North Point . Setting out dimensions for the concrete structure on site. . Plans, sections and elevations showing layout, dimensions and levels of all concrete members within the structure. . Location of all holes, chases, pockets, fixings and other items affecting the concreting work. . Notes on specifications, finishes and all cross-references affecting the construction. . Provide the detailer with the layout and sectio

Concrete mix design is defined as the appropriate selection and proportioning of constituents to produce a concrete with pre-defined characteristics in the fresh and hardened states. In general, concrete mixes are designed in order to achieve a defined workability, strength and durability . The selection and proportioning of materials depends on: . The structural requirements of the concrete . The environment to which the structure will be exposed . The job site conditions, especially the methods of concrete production, transport, placement, compaction and finishing . The characteristics of the available raw materials The various factors affecting the choice of concrete mix design are: 1. Compressive strength of concrete: It is one of the most important properties of concrete and influences many other describable properties of the hardened concrete. The mean compressive strength required at a specific age, usually 28 days, determines the nominal water-cement ratio of the

Causes of defects in concrete structures can be broadly categorized as: i) Structural deficiency resulting from errors in design, loading criteria, unexpected overloading, etc. ii) Structural deficiency due to construction defects. iii) Damage due to fire, floods, earthquakes, cyclones etc. iv) Damage due to chemical attack. v) Damage due to marine environments. vi) Damage due to abrasion of granular materials. vii) Movement of concrete due to physical characteristics. Structural Deficiency due to Design and Detailing In such case, the design is required to be reviewed in detail and remedial measures worked out by the design team. Once this is done the methods of carrying out the remedial measures will be similar to those arising out of other defects. Structural Deficiency due to Construction Defects Defective construction methods form the largest segment of source of distress to the beams. Such defects can be broadly subdivided as follows: i) Defects due to t

Factors affecting selection of foundation for a building can be many from the soil conditions to the type of structure and loads from the building. All the factors are considered during selection of foundation for durable building construction. Factors Affecting Selection of Foundation are: 1. Loads from Building: The first factor considered is loads from building on the foundation. This load is a combination of dead load and imposed loads on the buildings. Other loads such as wind loads, earthquake loads, snow loads etc. are also considered based on location. The quantity of loads depends on the type of structure, number of floors and material of construction. As the number of floors increases, the dead load and imposed loads also increase. Choice of material for construction such as reinforced concrete or steel construction also has impacts on foundation. Reinforced concrete buildings exert more loads on the foundation compared to steel structures. Based on the safe beari

Quality assurance of construction materials is the responsibility of the purchase department to assure the quality of purchased materials in consultation with production and engineering department. Proper specifications have to be decided and finally conveyed as part of purchase orders. The characteristics/standards of the construction materials need to be put down in purchase orders in unambiguous items. The technical terms should uniquely be understood by the supplier. The testing and inspection methods/procedures, the type of tests that are required to be conducted; all need to be specified accurately. The purchase department can achieve required quality of incoming construction material by: (a) Conveying correct specifications, (b) Assessing quality capability of supplier before placement of purchase order, (c) Frequent testing and inspection at the supplier’s production facilities, if considered necessary, (d) Insisting on proper certification of dispatched material

The responsibility of project manager to make sure that the customer is satisfied and the work scope is completed in a quality manner, using budget, and on time. The Project Manager has primary responsibility for providing leadership in planning, organizing and controlling the work effort to accomplish the project objectives. In other words, the project manager provides the leadership to project team to accomplish the project objective. The project manager coordinates the activities of various team members to ensure that they perform the right tasks at the proper time, as a cohesive group. The different roles of project manager are as follows: . Planning . Organizing . Controlling . Leading . Communicating . Cognitive functions . Self management functions . Motivational and personal development functions . Customer awareness functions . Organizational savvy functions Planning First, the project manager clearly defines the project objectives and reaches agreem

What is a Green Building? The concept of a green building was developed in the 1970s in response to the energy crisis and people’s growing concerns about the environment. A Green Building, also known as a sustainable building, is a structure that is designed, built, renovated, operated, or re-used in an ecological and resource efficient manner. Sustainable development is maintaining a delicate balance between the human need to improve lifestyles and feeling of well-being on one hand, and preserving natural resources and ecosystems, on which we & future generations depend. Objectives of a green building: . Protecting occupant health . Improving employee productivity . Using energy, water and other resources more efficiently . Reducing overall impact to the environment . Optimal environmental and economic performance . Satisfying and quality indoor spaces Considerations of a green building: . Control erosion to reduce negative impacts on water and air qual

Building materials such as concrete, mortar, bricks, wood etc are porous in nature and expand by absorbing moisture from atmosphere and shrink on drying. These changes in building materials are cyclic in nature and are caused during moisture changes. But building materials undergo irreversible changes due to change in moisture content during its initial conditions. These initial changes cause shrinkage or expansion of materials. For example, irreversible movement in materials are shrinkage of cement and lime based materials on initial drying i.e. initial shrinkage/plastic shrinkage and expansion of burnt clay bricks and other clay products on removal from kilns i.e. initial expansion. Initial Shrinkage in Concrete and Masonry: Initial shrinkage of building materials which is partly irreversible, occurs in all building materials that are cement / lime based such as concrete, mortar, masonry units, masonry and plaster etc. This initial shrinkage is one of the

Contaminated construction sites are those which possess risk to human health and environment. With the increase in demand for infrastructure development around the world and shortage of land available for the same, contaminated sites may be used for new construction projects. The Contaminated construction site can be the result of: . Any industry in the past on current site . Wastes being dumped at site . Contamination through chemicals used for agricultural purposes . Contamination in site filling materials . Soil contamination through demolition of existing structure. The presence of chemical contamination of soil or ground about to subside creates risk of health hazards for construction workmen. Following are the objectives for contaminated construction site investigation: 1. To identify the types of hazards, their extent and importance for assessment of potential risks to human and environment. 2. To identify suitable remedial measures for the existing contam

The reinforcement repair techniques are different for mild steel and prestressing steel. 1. Mild reinforcing steel The damaged bars may either be replaced or supplemented by additional reinforcement based on engineering judgment, the purpose of the reinforcement and the required structural strength of the member. a) Replacement: In case it is decided to replace the bars, splicing of reinforcement with the remaining steel must be done. The lap length must be according to the provision of ACI 318 and the welding (if used) must satisfy ACI 318 and American Welding Society (AWS) D1.4 (or the codal provisions of the respective country). Butt welding is usually avoided due to the high degree of skill required to perform a full penetration weld because the back side of a bar is not usually accessible. Welding of bars larger than 25 mm may cause problems because the embedded bars may get hot enough to expand and crack the surrounding concrete. Mechanical connectors may also be used acc

Poor construction methods and workmanship is responsible for the failure of buildings and structure. The poor construction methods and workmanship is caused due to negligence and inadequate quality control at construction site. The effects of some of the poor construction methods are discussed below: Poor construction methods and workmanship (a) Incorrect placement of steel Incorrect placement of steel can result in insufficient cover, leading to corrosion of the reinforcement. If the bars are placed grossly out of position or in the wrong position, collapse can occur when the element is fully loaded. (b) Inadequate cover to reinforcement Inadequate cover to reinforcement permits ingress of moisture, gases and other substances and leads to corrosion of the reinforcement and cracking and spalling of the concrete. (c) Incorrectly made construction joints The main faults in construction joints are lack of preparation and poor compaction. The old concrete should be washed