Common causes of downfalls of Dam Structures

A dam is a block across flowing water that opposes, directs or slows down the flow, often creating a store, lake or captivities. Most dams have a section named a spillway or weir over or through which the water passes and have some hydroelectric power generation systems installed.

Dams are like ‘installations containing dangerous forces’ due to the huge impact of a possible destruction on the normal population and the environment.

Generally dam failures are happen rarely but can do huge damage and loss of life, it happens as the dam structures are constrained to horizontal loading from the water head behind. The pressure comes from the water to the dam materials such as the adjoining geology and size of the reservoir which are very new in the case of dam structures.

Common reasons of downfalls of Dam Structures: The most known reason of the downfall of the dam structures is overtopping which is happen either for exceeding that is something concerned with the design of the spillway.

• Overtopping: It is happen when water slopping over the top of a dam and become a reason of dam failure. The two major factors of the overtopping failure are one id created due to surface elevation exceeds the total structural elevation profile and the other one is the over washes of the waves.
• Foundation defects and Slope instability: Foundation defects with settlement and slope instability causes most of the dam failures.

• Cracking: happens by the movements like the natural setting of a dam.
• Water Violating.
• Piping.
• Subsidence and the movement of the foundation.
• Uplift form the ground and sliding of the structure.
• Variation in temperature.
• Dynamic blasting in the nearby areas.

• Seismic load action.
• Wave action on the structure and weak energy absorption.
• Higher amount of silting.
• Loosing shear capacity of the concrete.

Reasons of downfalls of Earth Dam Structures: In case of earth dam, that unique materials that are used for the structure is made from the earth materials is nearby the side and makes the structure to be mixed in nature showing different properties in different conditions of weather and bring variations in the physical properties. There are other reasons of the earth dam failure are: insufficient spillways, piping, failure of the structure etc. and many more.

Reasons of downfalls of Gravity Dam Structures: Gravity dams are made from concrete and masonry and the major causes of failures of these structures are: soil erosion, failed construction joints, poor material etc.

Reasons of downfalls of Arch Dam Structures: This dam is different as it has plane stresses existing and thrust and these factors are caused for the design of the structure and completely dependent on the conditions of soil and rock. The failure happens for lack of structure, penstock vibration and insufficient grouting action.

Reasons of downfalls of Buttress Dam Structures: They have the horizontal forces transferred to the rock foundation and carried out by water pressure which is analyzed for the sliding and overturning failure of dam structure. The main reasons of failure are: alternate freeze and thraw cycles, masonry etc.

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Rajib Dey
www.constructioncost.co
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An exclusive course on structural analysis for civil engineering students

This is an exclusive structural analysis course that sheds light on an extensive series of materials which will be a great resource for civil engineering students. To get clear ideas on the topics covered in the course, you should have sound knowledge in mechanics of materials.

The course covers the following topics :-


Shear Force and Bending Moment Diagram Review - If the beam is loaded at random manner, the internal forces and moments are produced and the terms shear force and bending moments appear which are useful to analyze the beams furthermore.

Double Integration Method - The double integration method refers to a robust tool that can be used for resolving deflection and slope of a beam at any point to obtain the equation of the elastic curve.

Method of Superposition – Superposition method is used to determine the deflection. Fundamentally, a complex beam along with its loading is streamlined to a wide array of basic beams (one span) and with only one load.

So, the slope and deflection of a beam owning to various loads is equivalent to the sum of those as a result of the individual loads.

Moment Area Method - The moment-area method is mostly recognized for finding out the bending displacement in beams and frames. Under this method, the area of the bending moment diagrams is applied for working out the slope and or deflections at specific points along the axis of the beam or frame.

Slope Deflection Method - The slope deflection method stands for a structural analysis method for beams and frames. The method is very effective at the time of analyzing indeterminate structures. This method is normally used to determine what reactions exist on indeterminate structures.

Moment Equation - Bending Moment Equations provide a rapid and easy analysis to determine the maximum bending moment in a beam.

Force Method - The force method (also known as the flexibility method or method of consistent deformation) is applied to compute reactions and internal forces in statically indeterminate structures owing to to loads and imposed deformations.



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More about design drawings and model planning

Planning: Building plans can be somehow difficult to get as the planning for every kind of building is not same and they upgrades and changes every day.

Plans are like a set of drawings or two-dimensional diagrams that are used to narrate a place or object or to communicate building or fabrication instructions which are drawn or printed on paper and can take the form of a digital file.

Planning are generally made for different technical purposes like architecture, engineering or construction etc. and those capture all the geometric features of a site, building, product or component in an accurate and clear way so that it can display a clear information to the builder or manufacturer to help in design.

Generally this process of making plans and producing them is known as technical drawing and a working drawing is a kind of technical drawing where documentation has to be done to build any engineering product or architecture such as civil, architectural, structural, mechanical, electrical and plumbing etc. In the same way there is some software that helps to plan the models for building purpose or designing in other way such as BIM describes the process of creating and managing digital information about a building or other facility like bridge, highway, tunnel etc. and many more. BIM ensures that actual information should be created in a right format at the appropriate time so that better decisions can be taken in throughout the design, construction and operation of built assets.

At the beginning of a project, the BIM is known as Project Information model might include previous information like site reviews, condition reviews, information about previous services and many more and all those information should be generated from a previous Asset Information Model or Aim to operate and maintain a built asset.

A design intent model is developed in the time of design stages going in a project and it gets more detailed with the growth of the project and at last it will become a Virtual Construction Model with all other objects in the model to be manufactures, installed or constructed.

Design Drawings: they are used to develop and communicate ideas about a developing design and in the beginning stage of designing them only demonstrate to the client the capacity of a particular design team to grasp the design.

These designs are used in developing and communicating the detail, examine potential sites and assess options and develop the approved idea into a consistent and co-ordinate design and communicate the developed design to the local planning authority, contractors and suppliers.

Besides that it also keeps the track of the completed construction and constant changes in completing the construction project. But it is also true that some of these are not always known as design drawings as sometimes they has not started well or completed early. But all of them have some things of investigation or development of the design or sometimes they are good for nothing.

So these design drawings can be categorized as:

• Feasibility studies.
• Option appraisals.
• Concept drawings.
• Detailed or developed design.
• Technical design.
• Tender drawings.
• Shop, installation and construction drawings.

Design drawings are developed in a detailed way from block and massing drawings, sketches to detailed technical drawings etc. but while developing it are important to know the purpose and about the information the designs can narrate through them. They must determine their actual format, size, scale and every little detail that will be useful for the drawings suppliers to use in fabrication. These drawings can be prepared by architects, technicians, structural engineers, civil engineers and so on other different practitioners; but they must be carefully integrated and co-ordinated to give security about the right level of design in all the elements. These drawings has been revolutionized at first by CAD and then by BIM.




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Published By
Rajib Dey
www.constructioncost.co
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Post-tensioning and its phases

The ducts for the tendons (or strands) are arranged together with the reinforcement prior to the casting of concrete in post-tensioning systems.

The tendons are arranged in the ducts as soon as the casting of concrete is completed. The objective of duct is to avoid connection among concrete and the tendons throughout the tensioning operation.

Contrary to pre-tensioning, the tendons are pulled with the reaction that operates against the hardened concrete. It is defined as bonded post-tensioning when the ducts are filled with grout. The grout belongs to a neat cement paste or a sand-cement mortar that comprises of proper admixture.

In unbonded post-tensioning, the ducts are not at all grouted and the tendon is set in tension individually with the end anchorages. In the sketch given below, there is a schematic illustration of a grouted post-tensioned member. The profile of the duct is based on the support conditions. For a simply supported member, the duct contains a sagging profile among the ends. For a continuous member, the duct bends in the space and hogs over the support.

The following figures demonstrate the assessment of ducts in a box girder of a simply supported bridge. The second image demonstrates the end of the box girder as soon as the post-tensioning of some tendons is completed.

Given below, the different phases of the post-tensioning operation :-

1) Casting of concrete.
2) Arrangement of the tendons.
3) Arrangement of the anchorage block and jack.

4) Use tension to the tendons.
5) Seating of the wedges.
6) Cutting of the tendons.

The stages are demonstrates schematically in the following figures. Once a tendon is anchored at one end, the tension is employed at the other end with a jack.

The tensioning of tendons and pre-compression of concrete happen concurrently. A system of self-equilibrating forces forms once the tendons are expanded.

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Published By
Rajib Dey
www.constructioncost.co
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Why RC Structural Slabs and Beams are provided in plinth level

Given below, the detailed information on the importance of arranging RC structural slabs and beams at plinth level (GF-Finished Floor Level).

Wherever low/poor bearing capacity soils met with, the Architects and also certain Builders think and believe that If the bearing strength of soils become weak or low, RC Structural slabs & Beams may be arranged at plinth level (GF-Finished floor level) with the purpose of preventing settlement of foundation and subsequent development of cracks in walls.

By applying your own experience and expertise in foundation structure, it is possible to have clear idea on the behavior of weak bearing soil if loaded heavily. The foundation cost is raised by 50% with the inclusion of the cost of setting up RC Structural Slabs & Beams.

But the provision of RC structural slabs and Beams at plinth level may not be considered as useful solution to get rid of foundation settlement and subsequent cracks. Rather it will be treated as extra expenses that is incurred on the construction of structure.

It is recommended to apply the following measures to resist the settlement of foundation systems and wall cracks efficiently.

The foundation soil at a depth of 00 m to 2.70m (if it belongs to a weak bearing soil like soft/medium clay) should be artificially reinforced with Geogrids/Geotex layers supported with Quarry dust:Gravel Mix 1:3 or cement.

Quarry dust 1:10 mix in 4 or 5 layers of 200 mm thick will enhance the SBC of soil at 2.00m/1.80m level to 200kN/m2 from 100kN/m2.

Arrange an extra layer of Geogrid/Geotex over and then apply the PCC 1:5:10 for 100 mm. Over which the foundation system should be provided as designed-combined strip Raft/combined/isolated footings as per situation. Inspite, under reamed piles with pile cap may be arranged directly.

To get more details, go through the following link onlinecivilforum.com


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Published By
Rajib Dey
www.constructioncost.co
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Benefits of precast concrete construction

Precast concrete is one type of construction under which casting is done in a recyclable mould or “form” and cured in a controlled surrounding as well as transmitted to the construction site and hoisted into place.

As precast concrete is developed in a controlled surroundings (precast plant), it becomes easier for plant employers to cure it perfectly and supervise carefully. Various types of precast concrete forming systems are available for architectural applications which vary in size, function and cost.

The precast concrete provides huge benefits due to the superior quality of the material formed in controlled conditions, as well as the lower cost of developing large forms utilized with concrete poured on site. It is primarily applied in the erection of buildings with repetitive design and components, like schools and apartments.

Given below, a wide array of benefits for utilizing precast concrete construction:

• Reduced Construction Time and Cost
With precast concrete construction, it is possible to save significant time as well as minimize the risk associated with loiter of project and prospective financial losses. Precast design and fabrication of elements begin when the construction site is under survey or earthworks. Because of the controlled surrounding of the casting area, production is not impacted with weather conditions. With the application of large precast panels, the time is curtailed significantly for the completion of the structural works so that other trades like painting and electrical wiring can be started quickly.

In traditional construction method, various laborious works like formworks, scaffoldings and curing are required to form a structural element. In precast concrete construction method, structural elements are formed in manufacturing plants whereas other activities are started at the construction site. At the time of requiring structural elements, they are delivered to the site right away and accumulated on regular basis, to build up the structural frame and encircle the building. In precast concrete manufacturing plants, there are modern machineries controlled by various technicians to look after specific production process.

• Superior quality and aesthetical value of products
Precast products are fabricated in a casting area where some vital factors like temperature, mix design and stripping time should be closely monitored and managed to make sure that the quality of precast products are superior as compared to cast-in-situ concrete. Significant amount of money will be saved as no rectification works are required. Because of factory-controlled prefabrication environment, various combinations of colours and textures are employed easily to the architectural or structural pieces. An extensive range of sizes and shapes of precast components are developed to offer good flexibility and fresher appearance to the structures.

• Cleaner and safer construction sites
The precast elements can significantly minimize traditional formworks and props. Precast construction also reduces the problem of site wastages and the associated environmental issues. A secure working platform is created for workers to act on with the prefabricated products. Requirements for workers and materials are also significantly minimized at the construction sites. By following just-in-time principles, the precast elements are preserved at the factory yard unless the site gets prepared for installation. There will be less wastage at both factory and construction sites because the elements are developed in the plant and mostly designed to be redundant.

• Superior unobstructed span
With the application of pre-stressed precast solutions like the Hollow Core slabs and Double-T beams, superior unobstructed span is obtained as compared to the traditional reinforced concrete elements. Bigger open space is created with fewer beams and columns. It is mostly suitable for the construction of places of worship, warehouses, halls, car parks, shops and offices.

For more information, go through the following link ukessays.com



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www.constructioncost.co
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The fundamentals of setting up Post-Tensioning Slabs

Construction of post-tensioned slabs on grade is equivalent to apply reinforcing steel, devoid of the tensioning step.

Cables are set up as per instructions of the engineer and placed to go over the center of the slab. For residential construction, tendons at 48 inches on center are generally accepted. Commercial foundations will contain much more steel. Tendons are routed around obstructions smoothly.

Generally, a residential post-tensioned concrete slab should have been 8 inches thick with 3000 psi concrete. As soon as the concrete achieves strength to 2000 psi, normally within the 3 to 10 days as suggested by PTI, the tendons are stressed.

Now-a-days, tendons are seven high-strength steel wires wound together and arranged inside a plastic duct. A PT anchor is situated at each end and these are found in pockets which are implanted into the slab edge. As soon as the strands are stressed, the wires are expanded —about 4 inches for a 50 foot strand—to employ 33,000 pounds of load.

The qualified workers should be appointed for doing stressing. Once the stressing is completed, the tendon is cut off and the pocket in which the anchors are situated is filled with grout to defend then against corrosion.

Bigger structural concrete members may also be post-tensioned, particularly in bridges and floors and beams in parking structures. The process is equivalent to that applied for slabs, with the exception of a bigger scale. The tendons will frequently be "draped" in order that they are low at the midpoint of a beam and high at the supports—this arranges the steel at the point of highest tension where it can retain the concrete to be remained together firmly.

With structural members the duct is frequently grouted full following stressing to tie the strand to the concrete along its entire length—these are known as bonded tendons. Unbonded tendons are mostly found in residential slabs and stay free to progress within the duct and are safeguarded from corrosion with grease.

The position of PT tendon and stressing is normally performed with companies with certified workers having expertise in this type of work.

For more information, read the following construction article concretenetwork.com



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www.constructioncost.co
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