y2 Rpg Analysis

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CHAPTER I

ANALYSIS AND DESIGN OF STRUCTURAL MEMBERS


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Students should clearly understand the four architectural considerations

Students should be able to state the structural systems of a building

Students should be able to state the load types applied on a building( their source,calculation and application) and the path they follow.

Students must be able to analysis the different load deflection analysis of structures


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Deciding which structural system to use is one of the most prominent choices

the architect will have to make. Factors affecting the choice:


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LOAD TAYPESIntroduction

The successful design of any structure requires a satisfactory answer to the following

questions:1. Is the structure strong enough?

2. Is the structure stiff enough?

before attempting to answer these questions, two further questions must be

answered.These are:

1. What is the structure?2. What are the loads?

ThereforeThe role of structural design is to choose structures which will transfer theloads satisfactorily.


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A structures main function is to transfer loads, but before considering the form of a

structure we should to answer the question what are the loads? It is easy to classify loads by their sources, so they divided into natural, useful and

accidental loads.

A. Natural Loads

the first source ofnatural loads is the gravity load

The second source of natural loads is the wind load

Although the pattern of wind flow around buildings is complex (very!) the resultingloads predominately at right angles to the surfaces of the building.

As far as buildings and their supporting structures are concerned gravity and wind

loads are two types ofnatural loads they always have to resist.

There are other natural loads that the structure may have to resist.These are

earth or water pressure,

earthquakes,

temperature,

and ground movement.


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B. USEFUL LOADS

These loads happen because the building and hence the structure have been

constructed for a useful purpose.

E.g. the plank bridge, it has been constructed for people to cross the stream.

It is often practical for the useful load to be the maximum load that is likely to occur.

E.g. for a bridge we can consider the bridge full of peoples, or full of elephants so,unlike natural loads, there is a choice for useful loads

the majority of useful loads act vertically, sometimes they act horizontally. E.g. if the building uses to store sand, grain or water and these will cause useful earth or

water pressure loads both directions( vertically and horizontally)


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C. Accidental loads

These are dynamic loads, they happenwhen something is collided with thestructure or explosion in side the

structure

It is impossible for an individual to

decide which accidents, and henceaccidental loads, are unavoidable and

which arent and any society is neverclear.


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The major function of a structure is to transfer loads and the main sources of theseloads have now been identified

As the building must carry any combination it is usual to consider a range ofcombinations called load cases.

The only load case that will always be present is the natural gravity load.

almost endless variety of load combinations may act. For example: Load case 1 Natural gravity load + Useful gravity load on all floors

Load case 2 Natural gravity load + Wind load in a particular direction

Load case 3 Natural gravity load + Useful gravity load on some floors + Natural temperature load etc..

In other words only the worst load case is of interest

For buildings it is usual to consider:1. Natural gravity load + Maximum useful gravity load

2. Natural gravity load + Wind load in direction 1

3. Natural gravity load + Wind load at right angles to direction 1

It is unusual to have to consider loads due to earth or water pressure, ground

movement, temperature or accident depending on our site condition.


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To a every action there is always an equal and opposite reaction.

The reaction to the persons weight is in the structure, and the structure transfers this

reaction to the banks

Because ofNewtons law the numerical sum of the loads and the reactions must be

equal.

When loads are acting horizontally a reaction is required for equilibrium

Not only are there vertical and horizontal reactions there are also moment reactions!

A moment is a force times a distance.

Mostly the idea of moment reaction occurs at the support of a cantilever

Many structures require more than one type of reaction

E.g. wind blowing on a sign board, The support must provide vertical reaction to resist the weight of the sign

The support must provide horizontal reaction to resist the wind load to the sign

The support must provide moment reaction to resist the wind moment.

Every time there are loads on structures there must be reactions(vertical, horizontal,and moment ) and these reactions must balance the loads.This is:- Sum of vertical loads = sum of vertical reactions

Sum of horizontal loads = sum of horizontal reactions

Moments due to loads = moments due to reactions

These three statements must be true for all structures .


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This is basically a sequence of loads andreactions between structural elements

The important point here is oneelements reaction to the next elements

load.

As an e.g. see the picture (the beam ontwo walls)


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Lets see also a more complicatedsituation of two beams, supported by

walls, all sitting on a large spanningbeam First what are the loads?These are natural, the

self weight of the beams and walls, and

useful, the loads applied to the beams.

For the lowest beam:

The sum of the reactions =

p1+p2+p3+p4+p5+p6+p7+p8 but here how dothe loads get the reactions?

First consider the upper beam

Loads to the upper walls = p1+p6

Reactions to the lower walls = load from the

upper load + load from the middle beam + self

weight of the lower wall = ( p1 + p6 + p3) + ( p2

+ p7) + p4

R1 + R2 = p1 + p2 + p3 + p4 + p5 + p6 + p7 + p8

So the load path joins the load from itspoint of application to the final supportpoint.


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Not only do vertical loads need loadpathsbut so do horizontal loads.

These loads are usually caused

by wind

E.g. let see how does the sign board

resist wind load?

The wind load first blowing on theactual sign vertical stiffeners(vertically

spanningbeams) then goes to the top

and bottom rails vertical posts.


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So far loads, reactions and load pathshave been identified for structure. But

How does the structure transfer theload to the reaction?And,

What happens to the structure when ittransfers loads?

The structure transfers loads by force

that are in the structure and these

forces cause stresses in the structuralmaterial.

The structure also deforms under theeffect of the loads(this is called strain),and the size of the deformation

depends on the stiffness of the

structure


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Columns and Beams

The column transfers the end load to

the reactionb

y a system ofcompression we say the column is in

compression.

The column transfers the end load tothe reaction by a system of stretchingwe say the column is in tension.

The beams are transferring the loads tothe supports by a combination ofbending moments and shear forces.

The size of the bending moment variesfrom point to point .This is easily

expressedby bending moment

diagram. Bending moments do not resist the

vertical effects of loads on beams, these

are resisted by shear forces.

Likebending moments, shear forces

vary along a beam , so shear force

diagram can be drawn.


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The conceptual meaning of sets ofbending moment and shear force

diagrams is central to theunderstanding of structural behavior


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Frames


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Frames


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slabs


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slabs


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Frames and slabs


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Frames and slabs


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Frames and slabs


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Frames and slabs


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Frames and slabs


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Frames and slabs


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Frames and slabs


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Frames and slabs


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