Lesson Notes By Weeks and Term v5 - Grade 10

Lesson Video

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Performance objectives

• Define setting out and its importance.
• Describe different methods of setting out.
• Explain the purpose and function of foundations.
• Identify three types of shallow foundations.
• Calculate dimensions for a simple strip foundation.

Lesson summary

This week, we delve into the critical first steps in any construction project: setting out and foundations. Setting out is the process of accurately transferring the building design from the architectural plans onto the actual construction site. It's like creating a precise map for the builders to follow. Without accurate setting out, walls won't be straight, rooms won't be the right size, and the entire structure could be compromised. Foundations are the load-bearing elements that transfer the weight of the building to the ground. Understanding foundations is critical for building safety and stability.

Lesson notes

Setting Out: Ensuring Accuracy from the Start Setting out is the process of transferring the building plan onto the ground, marking the exact location of walls, columns, and other structural elements. It’s the foundation (pun intended!) for all subsequent construction work. Accurate setting out is crucial for several reasons: Accuracy: Ensures that the building dimensions match the design plans, preventing costly errors and rework.

Cost-effectiveness: Minimises material wastage and reduces the need for corrections, saving time and money.

Structural Integrity: Proper alignment of structural elements is essential for the building's stability and safety.

Compliance: Ensures that the building complies with building regulations and property boundaries.

Methods of Setting Out: Pegs and Strings (Traditional Method): This is the most basic method, suitable for small, simple structures. Pegs are driven into the ground at strategic points, and strings are stretched between them to define the building's outlines. A builder's square is used to ensure right angles.

Pros: Simple, inexpensive, requires minimal equipment.

Cons: Less accurate, time-consuming for larger projects, susceptible to errors due to string sag and peg movement.

Theodolite: A precision instrument used to measure horizontal and vertical angles. It allows for accurate setting out of complex shapes and large structures. The theodolite is set up at a known point, and angles are measured to locate other points according to the plan.

Pros: High accuracy, suitable for complex shapes and large sites.

Cons: Requires skilled operators, relatively expensive equipment.

Total Station: An electronic instrument that combines a theodolite with an electronic distance meter (EDM). It can measure angles and distances simultaneously, providing precise coordinates for setting out points. Data can often be downloaded and used directly in CAD software.

Pros: Very high accuracy, fast and efficient, integrates with CAD software.

Cons: Most expensive option, requires skilled operators and specialised software.

GPS (Global Positioning System): Increasingly used, particularly on large sites. Allows for accurate setting out using satellite technology.

Pros: Can be used on very large sites, relatively accurate.

Cons: Signal can be blocked by buildings or trees, needs good satellite coverage, relatively expensive. Setting Out Process (Using Pegs and Strings - A Simple Example): Let's say you're setting out a simple rectangular building foundation with dimensions 6m x 4m.

Establish a Baseline: Choose a straight line on the site as a reference. Mark this line with two pegs (A and B).

Set Out the First Corner: Drive a third peg (C) at one end of the 6m side, ensuring the angle between the baseline AB and the side AC is 90 degrees using a builder's square or the 3-4-5 method (explained below). Measure 6m along AC and place the peg.

Set Out the Opposite Side: Measure 4m from peg A along the baseline AB to peg

D. Create the Rectangle: From pegs C and D, measure 4m and 6m respectively, and where these measurements intersect, place peg

E. This creates the fourth corner of the rectangle.

Check Accuracy: Measure the diagonals (AE and CD). They should be equal. If not, adjust the pegs until the diagonals are equal and the sides are at right angles. Use a string to define the perimeter.

The 3-4-5 Method for Right Angles: A simple and reliable way to create a right angle is using the 3-4-5 method. Measure 3 meters along one line (AC). Measure 4 meters along another line (AB). The distance between the end points of these lines (BC) should be exactly 5 meters if the angle between AC and AB is 90 degrees. This method is based on the Pythagorean theorem (a² + b² = c²). 3² + 4² = 5².

Foundations: The Unsung Heroes Foundations are structural elements that transfer the weight of a building (and its occupants and contents) to the underlying soil or rock. The type of foundation required depends on several factors: Soil Type: Different soils have different bearing capacities (the amount of load they can support). Sandy soils generally have higher bearing capacities than clay soils.

Building Load: Heavier buildings require stronger foundations.

Site Conditions: The presence of groundwater, sloping ground, or unstable soil can influence the choice of foundation.

Building Regulations: Local building codes specify minimum foundation requirements. Types of Shallow Foundations (Common in South Africa): Shallow foundations are typically used when the soil near the surface is strong enough to support the building's load. They are relatively inexpensive and easy to construct.

Strip Foundations: A continuous concrete strip that supports a load-bearing wall. Commonly used for houses and small buildings on stable soil. The width of the strip depends on the load and the soil bearing capacity.

When to Use: Suitable for light to medium loads on relatively firm soil.