Lecture 1

Design to plan or to make drawings which is not yet structured . Reinforced in the oxford dictionary means make it stronger so reinforced concrete with

steel bars. Water is another governing elements so it plays an important role in the concerted

mixing. We cant simply put a specific proportion and say that concrete is made because it is

made in the field on vise versa of steel which is made in factories. Even if make concrete you have to cure it. It depends on target straits Common type of structures residential school… Analysis is following a method. Same formula but everyone has a design philosophy Clear cover from the end of the bar to the end of section Effective cover from the end to the section to the diameter of bar So coming to this particular point…….. Increase stiffness and decrease the deflection Chaotic situations Detailing how to provide the reinforcement :

1. Lapping depends on diameter of bar is aspect of detailing2. Tie bar and spacing

Even if it casted well but curing is the most important thing for reaching the appropriate strength.

Test and cast in the field Characteristic strength: 150 mm meter cube, two test at casting field tests for bending and compression. Keep the cube between to steel plate and start compressing until it cracks We can adjust it INSTRON testing mission whatever available in the engineering laboratory Guideline, specific rules we should follow, (codes)… every section and chapter

has specific purpose. One can argue why shall we……. Code is a guideline we should follow for different cases and formula are given

empirical. How much load we shall consider. Certain type of load and what type of building

what for it is made.. whether it is a residential ,,,whether it is ….. Unit weight of building material and stored materials. Seismic load are considered separately. The stuff is being constructed what is the wind condition over years on the

basis of that we have to find out.

It is having an impact One important aspect we should consider Dead and live Load is the one for which we have to design the structure. Primary combinations I am giving this one a broad idea Reasonable assumption Assume that we wouldn’t provide an economic design Properties of concrete a.m.neivle, ultimate state design reinforced concrete

Varghese.p.c

Lecture 2

You should know the limit you are going to use. A proportion as it shown We will to the one that it is called workability It means concrete it can flow , mix, any shape, if add less water then it would

be dry and what will happen then it will break, get the proper shape. Workability a concrete can be readily compacted is said to be workable. The amount of useful internal work necessary to produce full compaction. ASTM definition of workability ; the propriety determining the effort required

to manipulate a freshly mixed quantity of concrete with minimum loss of homogeneity.

As well as you see the other own to help to write down. Whenever you see… That so far the concrete depends on, otherwise concrete will become weak. Consistency is the relative mobility or ability of freshly mixed concrete or

mortar to flow, this is measured by slump, in direct way to measure the workability. It used extensively in site.

Slump test; a figure would show many things…the mould for the slump test is a frustum of a cone, 300 mm high. It is placed on a smooth surface with the smaller opening at the top and filled with concrete in three layers.so what it exactly means. More slump more workable.

That is an important criteria Nominal mix..simply use this one cast it and simply design. Whatever available you have to cast it. On the basis of that ,one can design . I have already told these things so I wont repeat. Strength and serviceability should be holding hand by hand Concrete should maintain its required strength and serviceability during the

expected service life. Concrete is said to be durable if it withstands the process of deterioration to

which it can be expected to be exposed. Concrete would be deteriorate over time we cant help it we can just accept it.

Compressive strength; And we can find therefore the corresponding strain When we test the concrete cube what we find out, we can measure the stess

and the strain,in other word we can find out the deflection and the applied load (how much it is compressed ),gereraly it is 1.5 by 1.5,,, on the basis of that we will come up with the stess strain curve,,,,it is something that go like this, this one only you can get it from a test there’s no other way.

Modulus of elasticity, design calculation. Tensile strength, it is observed from experimental studies that the tensile

strength of concrete is higly variable and ranges from approximetaly 8 to 10 per cent of the compressive. we shall assume that concrete wont take any tensile,,,other interesting things,

If you look from this sight (section), since we are not going this far, How it interacts,,,biaxial strength,,,generally we can get it like this ,,,let us

state let us give a schematic description ,,, what we shall state here,,,since cocncrete is very weak in tension, we shall get very low components here,,but the other side we can go like this, and this particular one this compression side will be more,, failure theories ,,,,

If it goes beyond this then the it fails Obviously we are getting an idea Creep; observation; it is important because it is time dependent both axial and

bending deformations and reinforced concrete members increase with time. We can consider that age that is say in month ,, what happens here,,if we cast

for a day,,,it will,,, It will keep on deforming under a constant load. That deflection we getting this much.. We will get the elastic recovery but it will not come down to 0 that will be

called non- recoverable deformation.that will getting due to creep. Creep is divided into two parts; An initial deformation that occurs with the application of a load A time dependent deformation, termed creep that continuous at a decreasing

rate for a period of years. Please note that,,,, This is the one Is creep the other one is shrinkage. Shrinkage; aas the moisture evaporates, the cocncete volume shrinks, the

shortening per unit length associated with the reduction in volume due to moisture loss is termed the shrinkage strain or simply shrinkage.

Almost we have finished this material part ,,,then we shall consider for steel. If it is done properly it will really stand the load even over its expected life

whatever way it is designed. What way we should apply to come up with size of the section. Finally you have to produce one drawing. When detailing is wrong it might mislead to catastrophic failure. The way it Is oriented or configured not necessarily should take all the loads.

The top will be the tension that means we shall provide reinforcement on the top.

Lecture 3

That we have seen in the last class We will come again in brief The basic concept of modular ratio I can explain this thing Since it is homogeneous which means section permissible stresses at top and

down are the same. Bending moment is the governing force If it is not possible due to other reason we can go for more. Dominating one is bending Most of the cases you will find this scheme in beams except for cantilever

beam. Tension is being developed at the top. Neutral axis . Stress will maximum at the edges or the outer side at the top and bottom. Each material have its own permissible limit The material will yield This is the simple and handy equation so we can find out in more clear way. I am assuming b depending on practical dimension. Loads due to external load and self-weight We provide some regular number multiple of 25 mm It will be registered by those two bars only with no taking load under the

neutral axis. Assumptions

Both steel and concrete act together.steel is embedded in concrete and there’s no slipping

Perfectly elastic at all stages of loadings. Factor of safety about 3 with respect to cube strength concrete Steel 1.8 with respect to yield strength. It deals only with elastic behavior of the member Generally even if we provide the reinforcement at the bottom we also provide

reinforcement at the top though it is not required but we need it to hold stirrups that one will resist shear .

Two different support conditions Concrete does not have definite modulus of elasticity Therefore It is worth considering Design for strength and serviceability

If sections are designed by ultimate strength requirements alone, the cracking and deflection at the service loads may be excessive.

It is another conflict That means the crack may appear and crack opening the user or residence of

the building feels discomfort or panic It is necessary to keep crack widths and deflection within reasonable limiting

values. Not only the strength as well as the serviceability condition. Limit state method due to collapse and serviceability Correspond to each of the states in which the structure becomes unfit. The one we have already told But the things that we have,, Limit state is considered due to collapse/failure point of view and other for

serviceability Characteristic strength the maximum one we shall assume the strength that

one can safely assume for materials are called their….. These are two parts we have to consider in our design Don’t under estimate that is dangerous Don’t over estimate but not economic particularly for regular manner of

building,,, you can imagine it is 10 m!

Lecture 4

Working stress method Different steps of construction I don’t know either can you see It will take the wall load from a tie We start from the bottom but when we design we start from the other way We should have the limit We have this one though we don’t use it The limiting values We shall mainly consider these two Permissible stresses otherwise we cant design Permissible stresses in compression have two parts bending and direct You are pressing the column like this then you have a direct compression And also in bond You are free how far you want Ft is the total tension on the member minus pretention in sted, if any Ac is area of concrete excluding any finishing mat. Nad reinforcing steel To be more specific ,,,,

Lecture 6

Limit state of collapse flexure Every method has new assumptions There also we make certain kind of assumptions Assumptions Plane sections normal to the axis remain plane after bending The maximum strain in concrete at the outermost compression fibre is taken as

0.0035 The tensile strength of the concrete is ignored The stress block may assume to be rectangle ,trapezoid parabola or any other

shape which results in prediction of strength in sustaible agreement with the result of test

In a good agreement The stresses in the reinforcement are derived from representative stress strain

curve for the type of steel used We never take the ultimate limit for design calculation For design purpose, the partial safety factor ,,,, The maximum strain in the tension reinforcement in the section at failure shall

not be less than Most of the cases we use,,, The maximum strain allowed in concrete plane …0.00035 One more thing I would like to point out It will go up and slowly it will go down Steel bar with definite yield point Mild steel ,high yield reinforcement Singly reinforced section: Let us draw a cross section of the beam You’ll never go beyond this value The moment carrying capacity that is the target Lever arm is Z And the moment capacity nothing but the value,,,, The stress block is the compressive part of the stress curve The depth of neutral axis of a given beam we shall take it from the equilibrium

of forces We shall reach the yield stress in bars We are giving a special name Let us check limiting values of…. I am getting this one from the strain diagram Expression of resisting moment for a balance section in terms of steel stress fy

and p Balanced sections : Sections in which the tension steel reaches yield strain

simultaneously as the concrete reaches the failure strain in bending are called balanced sections.

The applied load we shall stop when measuring the strain until it reach ….

Under reinforced sections: Sections in which the tension steel reaches yield strain at loads lower than the load at which the concrete reaches the failure strain in bending are called balanced sections.

We shall measure the strain when it achieve 0.00035 and then stop there,and maybe steel didt reach that value.

Over reinforced sections: Sections in which the failure strain in concrete is reached earlier than the yield strain of steel is reached are called over,,,,

Form the strain we get the corresponding stress Is preferable (under) … That also we can find out,,,,,this or this whatever you say

Mosley handout book

Reinforcement is designed to carry these tensile forces Which are transferred by bond between the interfaces of the two materials. If the bond is not adequate, the reinforcing bars will hust slip within the concrete and

there will not be a composite action. The concrete will be well compacted around the bars We assume in analytical design the perfect bond so the strain of reinforcement is

identical to the strain of the adjacent concrete This is normally known as “compatibility of the strain” across the cross section of the

member Concrete is a very variable material, having a wide range of strengths and stress-strain

curves. Cocncrete generally increases its strength with age. This characterisitic is illustrated by

the graph which shows how the increase is rapid at first becoming more gradual later. The precise relationship will depend upon the type of cement used Elastic modulus of steel Es= 200 Kn/mm2 Gpa Reduction in volume called shrinkage The expected life or the intended use Inconsistency and contradiction Concrete is about placing ,compaction and curing 1.6x10-6 = one point six times ten to the minus six In the same set of calculation = the same units used Passion ratio is the lateral strain by the longitudinal strain Having applied this load I have to be able to determine very small changes in resistance Cube mould are the container that concrete casting will be attended A beam continuous over several spans, is to be designed for the largest sagging bending

moment it will have sustain any action that has the effect of increasing the bending

moment will be considered unfavorable whilst any action that reduces the bending m0mnet will be consider to be favorable.

Beam failure modes

The cracks opens up at the tension side at the beam as expected and all of the sudden the concrete in the top surface of the beam fails explosively

Remember that the top side of a beam is under compression < because we are heavily load the lower part of the beam which allows a large amount of a load to be carried , the same large amount in compression needs to carried by the concrete near the top this called a concrete crush before the reinforcement start to yield , for the structural engineer it is a bad way for a beam to fail because concrete crushing is a brittle sudden and you don’t get a gradual fail in an under reinforced beam .

The curve simply stops which is implies a sudden failure Cracks means that the steel in a beam is taking up the tension that is developing in the

lower part of the section The crackes opens up as the steel taking the tension Which allows the beam deflect greatly and eventually the beam fails (gradual vs brittle )