Lesson Notes By Weeks and Term v5 - Grade 11
Working drawings, detailing and interpretation of building plans – Week 5 focus
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Working drawings, detailing and interpretation of building plans – Week 5 focus
Download the Lessonotes Mobile South Africa app for faster lesson access on Android and iPhone.
Subject: Civil Technology
Class: Grade 11
Term: Term 4
Week: 5
Theme: General lesson support
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Working drawings, detailing, and the interpretation of building plans are fundamental skills for anyone involved in the construction industry. In South Africa, with its dynamic housing needs and infrastructure development goals, the ability to accurately read and understand building plans is crucial. This knowledge allows you to participate effectively in building projects, ensuring accurate construction, efficient resource allocation, and adherence to safety standards and building regulations. This week focuses specifically on reinforcement detailing in concrete structures and understanding electrical layouts within building plans.
2.1 Reinforcement Detailing in Concrete Structures Reinforcement (rebar) is steel bars used to strengthen concrete structures. Concrete is strong in compression but weak in tension. Rebar provides the tensile strength necessary to resist bending and shear forces. Working drawings provide crucial information about the size, spacing, and location of rebar.
Types of Reinforcement: Main Reinforcement: Carries the primary tensile loads in beams and slabs. Usually larger diameter bars.
Shear Reinforcement (Stirrups/Links): Resists shear forces, especially near supports. Smaller diameter bars bent into U or closed shapes.
Distribution Reinforcement: Prevents cracking and distributes loads evenly. Smaller diameter bars placed perpendicular to main reinforcement.
Column Ties/Spirals: Confine the concrete core of a column, preventing buckling of the main reinforcement.
Reinforcement Symbols and Notations: `H` or `Y` typically indicates high-yield steel (e.g., Y12, Y16). `R` typically indicates mild steel (e.g., R10, R6). The number indicates the bar diameter in millimeters (e.g., Y12 means a high-yield steel bar with a 12mm diameter). Spacing is indicated as "spacing @ centre-to-centre distance" (e.g., Y12 @ 200 c/c). `T` represents top reinforcement. `B` represents bottom reinforcement.
Bar Bending Schedules: These schedules provide detailed information about the shape, dimensions, and quantity of each type of rebar required for a structure.
The schedule typically includes: Bar mark (identification number) Bar type and size Shape code Dimensions (A, B, C, etc., corresponding to the bar shape)
Quantity Total length Cover: The minimum distance between the surface of the concrete and the reinforcement. This protects the steel from corrosion and provides fire resistance. Cover requirements vary depending on the exposure conditions and the type of structural element (e.g., beams, slabs, columns).
Example 1: Interpreting Reinforcement Detailing for a Beam Consider a beam detail showing the following: Bottom reinforcement: 3Y20 Top reinforcement: 2Y16 Shear reinforcement: R10 @ 150 c/c Interpretation: 3Y20: Three high-yield steel bars with a diameter of 20mm placed as bottom reinforcement. 2Y16: Two high-yield steel bars with a diameter of 16mm placed as top reinforcement. R10 @ 150 c/c: Mild steel stirrups with a diameter of 10mm spaced at 150mm centre-to-centre.
Example 2: Calculating the Length of Rebar Needed for a Slab A slab has dimensions 5m x 4m. The reinforcement is Y12 @ 200 c/c in both directions. Assume a cover of 25mm on all sides.
Number of bars: Along the 5m side: (4000 mm / 200 mm) + 1 = 21 bars Along the 4m side: (5000 mm / 200 mm) + 1 = 26 bars Length of each bar: Along the 5m side: 5000 mm - (2 25 mm) = 4950 mm = 4.95 m Along the 4m side: 4000 mm - (2 25 mm) = 3950 mm = 3.95 m Total Length: Along the 5m side: 21 bars 4.95 m/bar = 103.95 m Along the 4m side: 26 bars 3.95 m/bar = 102.7 m Total Rebar length = 103.95m + 102.7m = 206.65m 2.2 Electrical Layout Plans Electrical layout plans show the location of electrical components within a building. They are essential for electricians to install wiring and fixtures correctly and safely.
Common Symbols: Light fixture: Typically a circle with lines radiating outwards. Different line styles indicate different types of fixtures (e.g., fluorescent, incandescent).
Switch: A line connected to a half-circle. Different types of switches are indicated with variations of this symbol (e.g., single-pole, double-pole).
Outlet (Plug point): A circle with a line or lines inside. The number of lines indicates the number of sockets.
Distribution Board (DB): A rectangle or square, often with a lightning bolt symbol.
Wiring: Represented by solid or dashed lines. Dashed lines often indicate wiring concealed within walls or ceilings.
Earth point: Typically a triangle with a line extending downwards.
Interpreting an Electrical Layout: Identify the location of the DB. This is the central point for all electrical circuits in the building. Trace the wiring from the DB to each outlet, switch, and light fixture. Note the type and number of outlets and switches in each room. Pay attention to any special requirements, such as dedicated circuits for appliances like stoves or geysers. Importance of SANS 10142 - Wiring of Premises. South African National Standard (SANS) 10142 is a critical safety standard that governs the wiring of premises. It addresses the types of cable to use, the earthing system, circuit breakers, and all aspects of electrical installation to ensure safety and compliance.
Example 3: Interpreting an Electrical Layout Plan A room shows the following: One light fixture controlled by a single-pole switch near the door. Two double outlets on opposite walls.
Interpretation: The electrician will install a light fixture in the room, connected to a single-pole switch near the entrance. This allows the light to be turned on and off from that location.