REBOUND HAMMER TEST

 The Schmidt rebound hammer is principally a surface hardness tester with little apparent theoretical relationship between the strength of concrete and the rebound number of the hammer.

However, within limits, empirical correlations have been established between strength properties and the rebound number. Further, scientist has attempted to establish a correlation between the hammer rebound number and the hardness as measured by the Brinell method.

The rebound hammer method could be used for:

1. Assessing the likely compressive strength of concrete with the help of suitable correlations between rebound index and compressive strength
2. Assessing the uniformity of concrete,
3. Assessing the quality of the concrete in relation to standard requirements, and
4. Assessing the quality of one element of concrete in relation to another.

Rebound hammer test

FACTORS INFLUENCING REBOUND HAMMER TEST

The rebound numbers are influenced by a number of factors like types of cement and aggregate, surface condition and moisture content, age of concrete and extent of carbonation of concrete.

1. TYPE OF CEMENT

Influence of Type of Cement Concretes made with high alumina cement can give strengths 100 percent higher than that with ordinary Portland cement. Concretes made with supersulphated cement can give 50 percent lower strength than that with ordinary Portland cement.

2. TYPE OF AGGREGATE

Influence of Type of Aggregate Different types of aggregate used in concrete give different correlations between compressive strength and rebound numbers. Normal aggregates such as gravels and crushed rock aggregates give similar correlations, but concrete made with lightweight aggregates require special calibration.

3. SURFACE CONDITION & MOISTURE CONTENT

Influence of Surface Condition and Moisture Content of Concrete The rebound hammer method is suitable only for close texture concrete. Open texture concrete typical of masonry blocks, honeycombed concrete or no-fines concrete are unsuitable for this test. All correlations assume full compaction, as the strength of partially compacted concrete bears no unique relationship to the rebound numbers. Trowelled and floated surfaces are harder than moulded surfaces, and tend to overestimate the strength of concrete. A wet surface will give rise to underestimation of the strength of concrete calibrated under dry conditions. In structural concrete, this can be about 20 percent lower than in an equivalent dry concrete.

4. CURING AND AGE OF CONCRETE

Influence of Curing and Age of Concrete The relationship between hardness and strength varies as a function of time. Variations in initial rate of hardening, subsequent curing and conditions of exposure also influence the relationship. The effect of age can be ignored for concrete above 14 days old.

5. CARBONATION OF CONCRETE

Influence of Carbonation of Concrete Surface The influence of carbonation of concrete surface on the rebound number is very significant. Carbonated concrete gives an overestimate of strength which in extreme cases can be up to 50 percent. The carbonation depth shall be checked in cases where the age of concrete is more than six months. It is possible to establish correction factors by removing the carbonated layer and testing the concrete with the rebound hammer on the uncarbonated concrete.

6. TEST POSITION

Influence of vertical distance from the bottom of concrete placement. The influence of vertical distance from the bottom of concrete placement on the rebound number is very significant. Generally, a higher rebound number is observed near the bottom of concrete placement as during compaction concentration of aggregates will be higher at the bottom.

7. STRENGTH CORRELATIONS

Influence of surface conditions used in development of correlation between compressive strength and Rebound Number. The direct correlation between rebound numbers and strength of wet cured and wet tested cubes is not recommended. It is necessary to establish a correlation between the strength of wet tested cubes and the strength of dry tested cubes on which rebound readings are taken. The ratio of dry tested cube to wet tested cube in compression is generally about 1.05

Analysis & design of RC structures

Analysis & design of RC structures

Analysis & design of RC structures is one of the modes in graphical user environment of the program. It is possible to assign arbitrary properties of concrete and reinforcement that is useful for analyses of reconstruction. In this mode you can unite several elements of the same type into one structural element (STE) and arrange reinforcement along the whole length of this element. Drawing of beams and columns are presented after analysis and can be saved as DXF files.

Working stress design

This design concept is based on elastic theory, assuming a straight line stress distribution along the depth of the concrete. The actual loads or working loads acting on the structure are estimated and members are proportioned on the basis of certain allowable stresses in concrete and steel. The allowable stresses are fractions of the crushing strength of concrete (fc') and the yield strength (fy). Because of the differences in realism and reliability over the past several decades, the strength design method has displaced the older stress design method

Limit state design

It is a further step in the strength design method. It indicates the state of the member in which it ceases to meet the service requirements, such as, loosing its ability to withstand external loads or local damage. According to limit state design, reinforced concrete members have to be analyzed with regard to three limit states:

1. Load carrying capacity (involves safety, stability and durability)
2. Deformation (deflection, vibrations, and impact)
3. The formation of cracks

The aim of this analysis is to ensure that no limiting sate will appear in the structural member during its service life.

Dead Loads:

Dead loads are those that are constant in magnitude and fixed in location throughout the lifetime of the structure. It includes the weight of the structure and any permanent material placed on the structure, such as roofing, tiles, walls etc. They can be determined with a high degree of accuracy from the dimensions of the elements and the unit weight of the material.

Live loads:

Live loads are those that may vary in magnitude and may also change in location. Live loads consists chiefly occupancy loads in buildings and traffic loads in bridges. Live loads at any given time are uncertain, both in magnitude and distribution.

Environmental loads:

Consists mainly of snow loads, wind pressure and suction, earthquake loads (i.e inertial forces) caused by earthquake motions. Soil pressure on subsurface portion of structures, loads from possible ponding of rainwater on flat surfaces and forces caused by temperature differences. Like live loads, environmental loads at any given time are uncertain both in magnitude and distribution.

Strucural Concrete elements

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Slab:

Slabs are horizontal slab elements in building floors and roof. They may carry gravity loads as well as lateral loads. The depth of the slab is usually very small relatively to its length and width.

Beams:

Long horizontal or inclined members with limited width and height are called beams. Their main function is to transfer loads from the slab to the columns.

Column:

Columns are vertical members that support loads from the beam or slabs. They may be subjected to axial loads or moments.

Frames:

Frames are structural members that consists of combination of slab, beams and columns

Footings:

Footings are pads or strips that support columns and spread their load directly to the soil.

Walls:

Walls are vertical plate elements resisting gravity as well as lateral loads e.g retaining walls, basement walls. etc

Maximum reinforcement ratios for singly reinforced beams

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ACI code limits the amount of reinforcement in terms of a minimum net tensile strain of = 0.005

Frther the ACI code defines a tension controlled member as one with a net tensile strain greater than or equal to 0.005. The coresponding strength reduction factor is Ø = 0.9. For compression controlled members as having a net tensile strain of less than 0.002. The strength reduction factor for compression controlled members is 0.65. A value of 0.70 may be used if members are spirally reinforced and ACI code allows a linear interpolation of Ø based on as shown.

0.005 => Ø = 0.9

0.002 ==> Ø = 0.65

Graph of Net tensile strain

Minimum reinforcement ratio (ρmin)

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If the external moment applied on the beam is very small and the dimensions of sections are specified (as is sometimes required architecturally) and are large than needed to resist the external ultimate moment, the calculations may show that very small or no steel reinforcement is required. In this case the maximum tensile stress due to bending moment may be equal to or less than the modulus of rupture of concrete.

If no rinforcement is provided, sudden failure will be expected when the first crack occurs, thus giving no warning. ACI code specifies a minimum steel area.

Design procedure for double reinforced beams

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Step # 1:

Find the strength Mu of a singly reinforced beam /section using the already established 'b' and 'd' i.e. the dimensions of the section and with > ρ = ρ_max (OR) ρ for = 0.005 to ensure that Ø = 0.90

M_u = Ø A_s f_y (d - a/2)

a = A_s f_y / 0.85 f_c' b

If M_u required > M_d of simply reinforced beam . Proceed with doubly reinforced beam design.

Step # 2:

Find excess moment i.e

M_u1 = M_u - M_u2

and determine the resulting compression steel area A_s1 = A_s and rentaively assume that f_s = f_y, then

A_s' = M_u1 /Ø f_y (d - d' )

Step# 3:

Find the total tensile stel area i.e

A_s = A_s' + A_s2

Step # 4:

Check whether the compression steel is yielding or not and use the corresponding stress in the steel for calculating the forces and moments. If compression steel is less than f_y, then the compression steel area is to be revised ==> A_s' f_s' < A_s' f_y ==> increase As rev.

The revised compression steel area acting at f_s must provide the same force as the trial steel area that was assumed to act at f_y.

So

C = T1

A'_{s rev} f '_s= A_{s trial} f_y

A'_{s rev} = A_{s trial} f_y / f_s'

Tensile steel area need not to be revised because it acts at f_y, as assumed.

Step # 5:

Check for satisfactory minimum and maximum reinforcement ratios

Step # 6:

Select appropriate bar size and draw the sketches.

what is civil engineering estimate?

estimate
An estimate of the cost of a construction job is the probable cost of that job as computed from plans and specifications.

For a good estimate the, actual cost of the proposed work after completion should not differ by more then 5 to 10 % from its approximate cost estimate, provided there are no unusual, unforeseen circumstances.

What is ESTIMATION?

Estimation is the scientific way of working out the approximate cost of an engineering project before execution of the work.

It is totally different from calculation of the exact cost after completion of the project.
Estimation requires a thorough Knowledge of the construction procedures and cost of materials & labour in addition to the skill , experience, foresight and good judgment.

Purpose of Estimating:

To give a reasonably accurate idea of the cost 
An estimate is necessary to give the owner a reasonably accurate idea of the cost to help him decide whether the work can be undertaken as proposed or needs to be curtailed or abandoned, depending upon the availability of funds and prospective direct and indirect benefits. For government works proper sanction has to be obtained for allocating the required amount. Works are often let out on a lump sum basis, in which case the Estimator must be in a position to know exactly how much expenditure he is going to incur on them
1. Estimating Materials 
From the estimate of a work it is possible to determine what materials and in what quantities will be required for the work so that the arrangements to procure them can be made.
2. Estimating Labor
The number and kind of workers of different categories who will have to be employed to complete the work in the specified time can be found out from the estimate.
3. Estimating Plant
An estimate will help in determining amount and kind of equipment needed to complete the 

work.
4. Estimating Time
The estimate of a work and the past experience enable one to estimate quite closely the length of time required to complete an item of work or the work as a whole.
Whereas the importance of knowing the probable cost needs no emphasis, estimating materials, labor, plant and time is immensely useful in planning and execution of any work.

Types of Construction Estimates:

There are several kinds of estimating techniques; these can be grouped into two main categories

1. Approximate estimates
2. Detailed estimates

1. Approximate Estimates
An approximate estimate is an approximate or rough estimate prepared to obtain an approximate cost in a short time. For certain purposes the use of such methods is justified.

2. Detailed Estimate
A detailed estimate of the cost of a project is prepared by determining the quantities and costs of every thing that a contractor is required to provide and do for the satisfactory completion of the work. It is the best and most reliable form of estimate. A detailed estimate may be prepared in the following two ways

(a). Unit quantity method
(b). Total quantity method.

(a) Unit Quantity Method
In the unit quantity method, the work is divided into as many operations or items as are required. A unit of measurement is decided. The total quantity of work under each item is taken out in the proper unit of measurement. The total cost per unit quantity of each item is analyzed and worked out. Then the total cost for the item is found by multiplying the cost per unit quantity by the number of units. For example, while estimating the cost of a building work, the quantity of brickwork in the building would be measured in cubic meters. The total cost (which includes cost of materials. labor, plant, overheads and profit) per cubic meter of brickwork would be found and then this unit cost multiplied by the number of cubic meters of brickwork in the building would give the estimated cost of brickwork.
This method has the advantage that the unit costs on various jobs can be readily compared and that the total estimate can easily be corrected for variations in quantities.

(b) Total Quantity Method
In the total quantity method, an item of work is divided into the following five subdivisions:
(I) Materials
(II) Labor
(III) Plant
(IV) Overheads
(V) Profit.

The total quantities of each kind or class of material or labor are found and multiplied by their individual unit cost. Similarly, the cost of plant, overhead expenses and profit are determined.

Qualifications of an Estimator

A good estimator should possess the following quantifications:
1. A thorough understanding of architectural drawings.
2. A sound knowledge of building materials, construction methods and customs prevailing in the trade.
3. A fund of information collected or gained through experience in construction work, relating to materials required, hourly output of workers and plant, overhead expenses and costs of all kinds.
4. An understanding of a good method of preparing an estimate.
5. A systematic and orderly mind.
6. Ability to do careful and accurate calculations.
7.Ability to collect, classify and evaluate data that would be useful in estimating.

Good instruction or careful and thorough study of a standard book will help a beginner to become a good estimator. He must, however, try to develop all the above mentioned qualities while obtaining practical experience.

what is survey in civil engineering??

civil engineering survey
The planning and design of all Civil Engineering projects such as construction of highways, bridges, tunnels, dams etc are based upon surveying measurements. Moreover, during execution, project of any magnitude is constructed along the lines and points established by surveying.
Why is land surveying important?
Surveying is important and most of us depend on it so as to ensure order in the physical world around us. Surveyors play an integral role in land development, from the planning and design of land subdivisions through to the final construction of roads, utilities and landscaping.
What is an engineering survey?
The American Society of Civil Engineers (ASCE) defines engineering surveyingas those activities involved in the planning and execution of surveys for the. location, design, construction, operation, and maintenance of civil and other engineered projects
What is surveying and leveling?

Levelling (or Leveling) is a branch of surveying, the object of which is: i) to find the elevations of given points with respect to a given or assumed datum, and ii) to establish points at a given or assumed datum. ... It is, therefore, perpendicular to the plumb line through the point.
What is a surveyor in construction?
Construction surveying or building surveying (otherwise known as "staking", "stake-out", "lay-out" or "setting-out") is to stake out reference points and markers that will guide the construction of new structures such as roads or buildings.
What is a building surveyor?
A. Building surveyors and building inspectors are responsible for making sure thatbuildings are safe, energy efficient and livable. They interact with other professionals such as engineers, architects and builders to ensure that buildingsare designed and constructed to comply with building regulations

what is civil engineering drawing?

civil engineering drawing

A civil drawing, or site drawing, is a type of technical drawing that shows information about grading, landscaping, or other site details. These drawings are intended to give a clear picture of all things in a construction site to a civil engineer.

Civil drafters prepare drawings and topographical and relief maps used in major construction or civil engineering projects, such as highways, bridges, pipelines, flood control projects, and water and sewage systems.

What are the structural drawings?

A structural drawing, a type of Engineering drawing, is a plan or set of plans for how a building or other structure will be built. Structural drawings are generally prepared by registered professional structural engineers, and informed by architectural drawings.

What is a drawing in construction?

Construction drawings are sometimes referred to as working drawings. They are used by all involved in a project to work on the actual building of the design. Thesedrawings provide all the information, both graphic and written, about the project. ... Standard drawing symbols are used to cross reference information.

What is an architectural drawing?

An architectural drawing or architect's drawing is a technical drawing of a building (or building project) that falls within the definition of architecture.

What is a section in drawing?

A section view is a view used on a drawing to show an area or hidden part of an object by cutting away or removing some of that object. The cut line is called a “cutting plane”, and can be done in several ways.

What is an elevation view?

Plan and elevation. When architects design buildings, they have to do 2D drawings to show what the building will look like from each side. These drawings are called plans and elevations. The view from the top is called the plan. The views from the front and sides are called the elevations.

What is a plan view in technical drawing?

Plans are a set of drawings or two-dimensional diagrams used to describe a place or object, or to communicate building or fabrication instructions. Usually plans are drawn or printed on paper, but they can take the form of a digital file.

INTRODUCATION (PART1)

1. 1. Introduction to Civil Engineering
2. 2. What is Engineering The word engineer originates from the Latin term ingenerare, meaning to invent, to create or to regulate It is the professional art of applying scientific principles to every day things to help make life easier
3. 
   
4. 3. Engineer vs. Scientist • Deviations between engineers and scientists arise through the differences in the ways both apply their educations in mathematical and natural sciences to their work Scientists Engineers Use their education to acquire new knowledge Use their education to develop usable devices, structures and processes Seek to know Aim to do
5. 4. What is a Civil Engineer? • One who improves the quality of life through the production of infrastructure – Buildings, bridges and other structures – Highways – Dams and levees – Water treatment plants, waste disposal • This infrastructure must be safe, functional, elegant and economically sound
6. 5. Why We Need Civil Engineers • Make sure our human habitat is livable • Make sure we use resources wisely – Sustainable development • Help maintain our competitiveness in the global economy – Increase productivity
7. 6.  Construction Engineering  Structural Engineering  Geotechnical Engineering  Transportation Engineering  Environmental Engineering  Water Resources Engineering Specialization in Civil Engineering
8. 7. Structural Engineering Design of new structures Upgrading existing structures Intelligent use of new technologies and materials to control structural behavior Structures include buildings, bridges, offshore platforms, transmission towers, and other specialized facilities
9. 8. Dubai Towers Dubai, United Arab Emirates
10. 9. Burg al Arab Dubai, United Arab Emirates A self proclaimed 7-star hotel
11. 10. Nebraska State Capital Lincoln, Nebraska
12. 11. Construction Engineering Concepts and designs become reality Management skills project cost estimating and scheduling financial planning, labor coordination and supervision
13. 12. Eiffel Tower Paris, France
14. 13. Dubai’s expansion from 1991 to 2005
15. 14. Geotechnical Engineering • Geotechnical Engineering is concerned with engineering behavior of earth materials • Geotechnical engineers: • Investigate existing subsurface conditions (tunnels excavations, pipelines) • Determine physical and chemical properties relevant to project considered • Assess risks posed by site conditions • Design earthworks and structural foundations • Monitor earthwork and foundation construction
16. 15. The World Islands A modern marvel of geotechnical engineering!
17. 16. The World Islands Fun Facts •Located 2.5 miles off the coast of Dubai, United Arab Emirates •The 300 islands are composed of 321 million cubic meters of sand and 31 million tons of rock •The land used to create the islands largely consists of sand dredged from Dubai’s shallow coastal waters •Overall development costs are estimated at $14 billion USD •Cost for full ownership of one of the undeveloped islands ranges between $10 million and $45 million USD
18. 17. Transportation Engineering Planning, Design, Operation and Maintenance of safe and efficient transportation systems Incorporating new technologies to improve system performance Intelligent Transportation Systems
19. 18. Environmental Engineering Protect & improve environmental quality  natural systems  engineered systems Protect human health & well-being  provide safe drinking water  waste water treatment systems  hazardous waste site clean-ups
20. 19. Environmental engineers turn disease into delicacy!
21. 20. 1956 1936 2010
22. 21. BP Oil Spill Cleanup
23. 22. Water Resources Engineering Physical control of water public water supply flood control irrigation, navigation etc. Computer modeling of water flow Performance requirements for lock and dam structures
24. 23. Hoover Dam Clark County Nevada Mohave County, Arizona
25. 24. Panama Canal Isthmus of Panama
26. 25. • Lesson: – Goals the same, techniques change One last example …
27. 26. Pretty Amazing! A WATER BRIDGE .. OVER A RIVER!!!
28. 27. Activity – Penny Boats • Construct your boat using only one piece of the heavy duty aluminum foil provided. • Predict how many pennies your boat will hold: _______________ • Slowly add pennies to your boat. Once water enters the boat, or if any part of the boat touches the bottom of the container, your turn is over. • The last penny added will not count in the total amount held.
29. 28.civil engineering design is a very important ...part...