Construction Technology 3 & 4 Unit 1 2009_10 Pt2

8/2/2019 Construction Technology 3 & 4 Unit 1 2009_10 Pt2

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Construction Technology 5

D39TF

Module Introduction


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Advanced structural frames- key issues

Eight interdependent areas need to be addressed:-

1. Which material is to be used to construct the frame.

2. What type of frame is to be adopted.

3. What type of floor system will be used in the frame.4. How is the frame organised- what goes where.

5. How is stability to be provided to the frame.

6. What components are needed within the frame.

7. Any special considerations that require extra attention.8. How are the components to be assembled?


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Decision 3: Type of upper floor construction

In the case of in situ concrete, the choice of floor structure is aninherent part of the choice of frame and cannot be varied. We willlook at in situ concrete choices momentarily.

But, in the case of steel, we have some further choices to make.

In particular, this would relate to Simple Cage Frames, ProppedCantilevers, Cantilevers and Parallel Beam frames in Steel.

In these cases we can use:-

Non- composite floor construction, OR

Composite floor construction.


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O/A

DEPTH

D

D

TYPICAL CELLULAR BEAM

1.08 D to 1.5 D DIAMETER =D

1.25D

1.75to

VARIES WITHSPACING


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One-way slabs with band beams

Advantages: medium range spans; simple; large and small

holes can be accommodated; fast; amenable to simpledistribution of horizontal services.

Ribbed slabs

Advantages: medium to long spans; lightweight; holes intopping easily accommodated; profile may be expressed

architecturally, or used for heat transfer in passive cooling.

Ribbed slabs with band beams

Advantages; medium to long spans; lightweight; holes intopping easily accommodated; large holes can beaccommodated.

Two-way solid slabs

Advantage: economical for longer spans and high loads.

Waffle slabs

Advantages: medium to long spans; lightweight; profilesmay be expressed architecturally, or used for heattransfer.


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Frame type choice

Can be made based on engineering, construction, or economicfactors.

Examples:- A steel parallel beam frame may be selected for engineering efficiency.

A SlimFlor Steel frame may be selected for economic reasons to keepthe floor to ceiling height minimised and so to reduce the cost of thebuilding or to get an additional storey in the building within certain

height restrictions.

A flat slab or plate floor approach in insitu concrete may be selectedfor construction reasons to simplify formwork and falseworkprocesses and allow the use of flying forms and table forms etc.


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Decision 4: HOW IS THE FRAME TO BE ORGANISED Once decisions on:-

Frame material,

Frame type, and Upper floor construction method

have been taken, (and can be justified!!), we can proceedwith the organisation of the frame.


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Frame Organisation In organising the frame, we are concerned with:-

The placement of Columns

Working out the span of the Main Beams

Determining the span of the Floor Slabs

Achieving efficiency and regularity througout the whole building as faras practically possible.


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Placing Columns This is done in plan form and begins with deciding where columns are

to be located.

The general arrangement plans are critical in this.

The aim is to locate columns efficiently, ensuring that load transferpaths are short and direct.

That columns, as far as practically possible, run directly from roof levelto foundations without horizontal deviation. This could involve makingalterations to the floor plans.

That columns are placed at appropriate centres- ie. not too close

together and not too far apart.


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Organising Beam spans

What spans should be aimed for:

As a very general guide, the optimum span for beams incommercial buildings, is 7.5m.

This is not always achievable, or desirable. So, as a roughguide, you should be aiming for main beams with spansbetween 5.0m and 10.0m.

Clearly, the main beams span between columns, so this is

really a part of the column arrangement process.

The span of beams can be varied in different parts of abuilding.


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The Structural Grid

Positioning the columns


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The Structural Grid

Positioning the main beams(This depends on the choice of frame-For the sake of this illustration we will assume a

steel cage frame, but note that the positions can be

different for concrete frames and for different frametypes).


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The Structural Grid

Starting to identify and codify the frame

components.

C1 C1 C1 C1 C1 C1

C2 C2 C2 C2 C2 C2

C3 C3 C3 C3 C3 C3

B1 B1 B1 B1 B1

B1 B1 B1 B1 B1

B1 B1 B1 B1 B1

B1

B1

B1

B1

B1

B1

B2

B2

B2

B2

B2

B2


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The Structural Grid

Next, we can superimpose the gridlines over theframe- these are used to dimension the spans of the

beams and the spacing of columns and also as a

quick reference tool to locate specific columns

C1 C1 C1 C1 C1 C1

C2 C2 C2 C2 C2 C2

C3 C3 C3 C3 C3 C3

B1 B1 B1 B1 B1

B1 B1 B1 B1 B1

B1 B1 B1 B1 B1

B1

B1

B1

B1

B1

B1

B2

B2

B2

B2

B2

B2

A B C D E F

1

2

3

6.000 6.000 6.000 6.000 6.000

6.000

9.000


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Secondary Beams

Depending on the frame/ floor type selection,

secondary beams may also be required.

These span between main beams and serve the

purpose of shortening the span of floorstructures, thereby reducing the necessarythickness of floor slabs. Alternatively, they may

be required to provide lateral restraint to theprimary beams to prevent them from buckling.


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The Structural Grid

Continuing with Steel frames in mind, we now needto add secondary beams, which provide lateralrestraint to the main beams and reduce the size of

floor spans

C1 C1 C1 C1 C1 C1

C2 C2 C2 C2 C2 C2

C3 C3 C3 C3 C3 C3

B1 B1 B1 B1 B1

B1 B1 B1 B1 B1

B1 B1 B1 B1 B1

B1

B1

B1

B1

B1

B1

B2

B2

B2

B2

B2

B2

A B C D E F

1

2

3

6.000 6.000 6.000 6.000 6.000

6.000

9.000

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3


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The Structural Grid

Now we need to indicate the direction of the floorspans

C1 C1 C1 C1 C1 C1

C2 C2 C2 C2 C2 C2

C3 C3 C3 C3 C3 C3

B1 B1 B1 B1 B1

B1 B1 B1 B1 B1

B1 B1 B1 B1 B1

B1

B1

B1

B1

B1

B1

B2

B2

B2

B2

B2

B2

A B C D E F

1

2

3

6.000 6.000 6.000 6.000 6.000

6.000

9.000

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3


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Decision 5: PROVIDING STABILITY TO THE FRAME

Frames can be inherently unstable, depending on material andframe choice.

Lateral stability needs to be provided in almost all cases.

Stability can be provided using:- Solid Cores (around services, stairs and lifts)

Shear Walls

Diagonal Cross Bracing


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The Structural Grid

Considering the stability of the frame, we need to

indicate the position of braced bays- assuming that

this steel frame will use diagonal cross bracing-again, there are other ways of bracing a frame asmentioned earlier.

C1 C1 C1 C1 C1 C1

C2 C2 C2 C2 C2 C2

C3 C3 C3 C3 C3 C3

B1 B1 B1 B1 B1

B1 B1 B1 B1 B1

B1 B1 B1 B1 B1

B1

B1

B1

B1

B1

B1

B2

B2

B2

B2

B2

B2

A B C D E F

1

2

3

6.000 6.000 6.000 6.000 6.000

6.000

9.000

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3

B3


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Process 6: Identifying the main framecomponents

Columns, beams and floors that span different distances,carry different loads or have different purposes need to beidentified.

Engineering decision?

Sizing the identified components??

Scheduling


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C2

B1

B1

B

1

B1

C2

C1C1

B3

B303

30 T12-03-150

The Structural GridReinforcement within bays is indicated

by the notation coloured red in thisslide- ordinarily this would not beshown in colour.

The codification 30 T12-03-150 is a standardway of referring to reinforcing bars. Broken downthe code means

30 is the number of bars to be placed between thearrow heads.

T is the type of steel: T = high yield steel;

R = mild steel

12 is the diameter of the steel bar.

03 is the bar mark: this is the code given to thisspecific bar within this project. The classificationbegins at 01 for all projects and works through towhatever number is required for all of the differentbar types required in the project.

150 is the spacing in mm between the centre lines ofthe bars.


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Decision 7: SPECIAL CONSIDERATIONS

It is rare that any building project would be quite asstraightforward as the example shown. Few commercial

buildings are simple rectangular boxes.

This means that there will normally be one or more featureswithin a specific building that will require special attention.

Such areas could include:-

Circular or curved building floor plans. Large cantilevered sections in a building. Changes in the layout of floor plans between the upper and lower

storeys in a building. Poor ground conditions.


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Creating curved edges to floor slabs...

How this is accomplished depends entirely on the choiceof frame and upper floor system.

If working in insitu concrete, the curved edge can beformed either in a beam and slab floor or in a plate floorapproach by adopting an appropriate formwork system.

If working in steel more attention is required. Precast concrete planks cannotbe easily cut to shape, however, the use of specials is an option. In the caseof composite floors, steel decks can be cut. Attention needs to be paid in thearea of the Deck Stop and again in the area of supporting beams. Some

degree of cantilevering is likely to provide the most efficient solution.

Curved beams will behave differently to straight beams because of theeccentricity in their loading. However, their use in this situation is reasonable.AngleRing is a company specialising in the production of curved structuralsteelwork......


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Cantilevers The basic structural behaviour of beams,

columns and floor slabs has not been fullyaddressed in this lecture.....

HOWEVER, you MUST be familiar with thebasic bending behaviour of simply supportedand continuously spanning (or contiguousbeams).....this is described in the Unit notes sobe sure to read them.

Many buildings feature some form ofcantilever in their layout for a variety ofdifferent reasons.


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Cantilevers- principles

Its absolutely obvious that all structure, no matter where it is,must be held still or remain stationary.....if it doesnt we are introuble!!

Beams, floors and columns must be static- this is a condition

that needs to be designed in!!

All structural forces in beams have to be resisted by equal andopposite forces.......


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Considering cantilevers...

Reaction (veritcal)

Rv

Force

F


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Reaction

Force

The result of justhaving a verticalreaction


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Reaction RV

Force

To keep the beam still, we need two morehorizontal reactions...

R H1 and R H2

R H1 is a pushing force (compressive)

R H2 is a pulling force (tensile)

Reaction R H2

Reaction R H1


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Considering Cantilevers In practice there are a number of ways RH1 and RH2 can be

accomplished.


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Transfer structuresFor situations when the floor plans at lowerlevels are substantially different from the floorplans at upper levels.

This can happen in hotels or in office blocksthat have different occupancy uses in thelower floors or in situations where the building

will overhang a pavement or road.

It can also occur where there are existingfoundations on the site which are sufficiently

strong to support the new building but whichare not ideally located in relation to thefootprint of the new building.


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Transfer structures usually involve 1 or 2 storey deep beams. Solid beams

would be useless and completely uneconomic for such purposes so the beamsare usually trussed in the form of:-

Girders, or

Vierendeel Girders.


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Issue 8: Assembly

Details that show how all of the individual

components identified in the frame layout areto be put together, must be produced.

This is the last stage.

Construction Technology 3 & 4 Unit 1 2009_10 Pt2

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Transcript of Construction Technology 3 & 4 Unit 1 2009_10 Pt2