L01 · Foundation · 2–3 hours
Self-weight and load take-off
Calculate element self-weights for a load schedule, by element and in total, with every unit shown.
Tool: Draft · Lesson: Drafted awaiting review · Example: Drafted awaiting review · Workbook: Built awaiting check · Assessment: Drafted awaiting approval
Outstanding before release: Engineering checker to confirm the supporting unit-weight source (CDC A3 does not appear to tabulate concrete unit weight; SS EN 1991-1-1 Annex A is the likely supporting source) and sign off v0.1.0.
Sources
| Role | Source | Note |
|---|---|---|
| Contextual | LTA CDC A3 Chapter 3 ACTIONS | Chapter 3 Actions — permanent actions context (mapping awaiting checker verification) |
| Supporting | SS EN 1991-1-1 Annex A (densities of construction materials) — to be confirmed by checker | Unit weight source; licensed copy required (mapping awaiting checker verification) |
"Primary" marks the governing clause for this exercise; "contextual" marks related clauses; "supporting" marks the design-method or data source outside the CDC. A CDC chapter mapping does not mean the CDC contains the equation used.
Prerequisites: F01 Design basis and calculation register · Topics: Loads and actions, Reinforced concrete
Lesson
Lesson draft v0.1 — awaiting trainer and technical review.
Load take-offs are one of the first tasks given to a junior engineer. You take dimensions from drawings, compute each element's self-weight, and pass a clean schedule to the engineer designing the supporting members. The task is simple; the expectation is that every number is traceable to a drawing, a unit weight source, and a unit.
Learning outcomes
- Compute volume, self-weight and self-weight per metre for rectangular elements.
- Present results as a load schedule with consistent SI units.
- State the source of each unit weight and mark training assumptions clearly.
- Recognise when a simple prism model is not adequate.
Model, assumptions and limitations
Each element is idealised as a solid rectangular prism: width b, depth h, length L, all in metres, with number off n.
Volume V = n·b·h·L (m³). Self-weight W = γ·V (kN), where γ is the unit weight in kN/m³.
For beams and walls it is often more useful to give the weight per metre along the length: g = γ·b·h (kN/m).
These are characteristic (unfactored) permanent actions. Partial factors are applied later in the combination stage — never in the take-off — so the same number is not factored twice.
Unit weight: the CDC A3 text reviewed so far does not tabulate a concrete unit weight. Offices commonly take it from SS EN 1991-1-1 Annex A or the project design basis. The checker will confirm the governing source for this module; until then the worked example labels 25 kN/m³ as assumed for training.
Worked example — rectangular beam (assumed for training)
- b = 0.30 m, h = 0.60 m, L = 5.00 m, n = 1
- γ = 25 kN/m³ (assumed for training)
| Step | Substitution | Result |
|---|---|---|
| Cross-section area | A = b·h = 0.30 × 0.60 | 0.18 m² |
| Volume | V = A·L = 0.18 × 5.00 | 0.90 m³ |
| Self-weight | W = γ·V = 25 × 0.90 | 22.50 kN |
| Per metre | g = γ·A = 25 × 0.18 | 4.50 kN/m |
This is a self-weight exercise only, not a beam design.
Common mistakes
- Mixing millimetres and metres (0.3 m entered as 300 gives a weight 10⁹ times too large).
- Applying a load factor in the take-off and again in the combination.
- Forgetting the number off for repeated elements.
- Quoting a unit weight with no source.
Interpretation questions
- Which element dominates the total? Would a 10% error in its dimensions matter?
- What information would you request if a drawing shows a haunch or an opening?
Technical English task
Write a short transmittal note (3–4 sentences) sending your load schedule to the designing engineer, stating the unit weight source and any assumptions.
Burmese explanation: awaiting reviewed translation.
Calculator
Purpose: Self-weight (permanent action) take-off for prismatic rectangular elements, by element and in total, for use in a load schedule.
Model: Each element is a solid rectangular prism b × h × L of uniform unit weight γ. Number off n. Volume V = n·b·h·L; self-weight W = γ·V; self-weight per metre along L: g = γ·b·h.
Units: SI only: lengths in m, unit weight in kN/m³, forces in kN, line loads in kN/m. Ranges: b, h, L: > 0 and ≤ 100 m. γ: 5 to 100 kN/m³ (outside → outside supported scope). n: integer 1 to 1000. Up to 10 elements.
Equations: V_i = n_i · b_i · h_i · L_i ; W_i = γ_i · V_i ; g_i = γ_i · b_i · h_i (per member, per metre of L) ; ΣV = Σ V_i ; ΣW = Σ W_i
Not covered: Openings, voids, haunches, tapers and non-rectangular sections; Finishes, services and imposed loads; Partial factors and load combinations; Member design or any resistance check
Version 0.1.0 Draft
Not available for use. Not yet released for use. Status: Draft. Engineering checker to confirm the supporting unit-weight source (CDC A3 does not appear to tabulate concrete unit weight; SS EN 1991-1-1 Annex A is the likely supporting source) and sign off v0.1.0.
Excel workbook
The workbook is available with the calculator once this version is released.
Exercises
L01-EX1 — Pile cap and ground beams take-off
Drafted — awaiting approval of the brief, rubric and pass mark before submissions open.