How To Setting Out A Building Works | Culvert | Location Of Bridge Pier | Construction Survey #settingout

 

Setting Out Works

In This Article, We Explained About How To Setting Out A Building, Culvert And Location Of Bridge Pier With A Simple Procedure And Diagram 

 

SETTING OUT A BUILDING

A building is set out in order to clearly define the outline of excavation and the centre lines of the walls so that construction can be carried out exactly according to plan. The centre-line method of setting out is generally preferred and adopted.

Procedure

1. From the plan, the centre lines of the walls are calculated. Then the centre lines of the rooms are set out by setting perpendiculars in the ratio 3: 4: 5. Suppose the corner points are A, B, C, D, E, F, and G which are marked by pegs with nails on top.

Fig. 1 Centre-line Method

2. The setting of the corner points is checked according to diagonals AC, BD, CF and EG.

3. During excavation, the centre points A, B, C,… may be removed. Therefore, the centre lines are extended and the centre points are marked about 2 m away from the outer edge of the excavation. Thus, the points A1, A2, B1, B2,… are marked outside the trench. The centre lines are shown clearly by stretching thread or rope. The centre points fixed 2 in away from the excavation are marked with stout pegs.

4. From the plan, the width of excavation is found out and set out around the centre line. The excavation width is also marked by thread with pegs at appropriate positions.

5. The excavation width is then marked by lime or by making a furrow with a spade.

6. If the plan is much too complicated and follows a zig-zag pattern, the centre pegs are kept at suitable positions according to site conditions.

 

SETTING OUT A CULVERT

The abutments and wing walls of a culvert are set out by coordinates from the centre of the culvert, which is taken as the origin.

From the plan, the coordinates of different points on the abutments and wing walls are calculated as tabulated as follows:

Point	Coordinate		Remark
	x	y
P1	x1	y1	Data calculated for left half of culvert
P2	x2	y2
P3	x3	y3
P4	x4	y4

 

As the culvert is symmetrical about both the axes, the necessary data for the right half are similar to those for the left half. Again, the data for both sides of the X₁X line are similar ( Fig. 2 ).

 

 

 

 

Procedure

Fig. 2 Setting Out a Culvert

1. The axes (centre line) X X₁ and Y Y₁ are set out, with O is the origin.

 

2. Along the line OX₁, points 1, 2, 3 and 4 are marked at distances x₁, x₂, x₃ and x₄  from origin.

 

3. Now Along OY, points 1′, 2′, 3′ and 4′ are marked at distances y₁, y₂, y₃, and y₄ from O.

 

4. Now two tapes are taken with their zero ends together and held at P₁ by the overseer in such a way that when two assistants hold them fully stretched at 1 and 1′, the readings are exactly equal to y₁ and x₁ (i.e. P₁1 = y1 and P₁1′ = x₁). Then the point P₁ is marked with a stout peg.

 

5. Similarly, the other pegs are fixed at P₂, P₃ and P₄. The pegs for the right half are fixed according to the data available from the table prepared for the left half. The culvert is symmetrical about the centre line X X₁. So, the other half can be easily set up.

 

 

LOCATION OF BRIDGE PIER

The procedure for locating a bridge pier is as follows:

 

Procedure

 

1. The centre line AB of the bridge is ranged by setting a theodolite at A and two stout pegs are fixed at T₁ T₂ on the line AB ( Fig. 3 ).

Fig. 3 Locating a Bridge Pier

2. The effective length of the bridge (S₁S₂) is determined by triangulation or by the stadia method.

 

3. The number of spans and the width of each are theoretically ascertained and plotted in a plan.

 

4. A baseline AC is taken perpendicular to the centre line AB. The distance AC is accurately measured by invar tape.

 

5. On the plan points S₁ and S₂ represent the centres of abutments and points P₁ and P₂ the centres of piers.

 

6. The distance AS₁ is measured accurately by invar tape.

 

7. From the effective width of the bridge, the widths of spans S₁P₁, P₁ P₂ and P₂ S₂ are ascertained.

 

8. Then the angles θ₁, θ₂, θ₃ and θ₄ are calculated as follows.

and so on.

 

9. Another theodolite is set up at C and the angles θ₁, θ₂, … are set out in the usual manner.

 

10. The line of sight of the theodolite at A and that of the theodolite at C will intersect at points S₁, P₁, P₂, and S₂. These points are marked in position accurately.

 

11. In order to ensure extreme accuracy, the centre lines of the piers are checked by setting a theodolite on a baseline taken on the other bank of the river.

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