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24-Bld-A3 Construction Engineering · Undated paper

Question 4 of 7: Wall-Form Components and the Formwork Design Process

Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)

Notes on this paper

National Examinations — 07-Bld-A3, May 2019 — Construction Engineering. Closed book; candidates may use one of the two approved calculators (Casio or Sharp). The paper prints seven questions of equal value (20 marks each) and states that any five questions constitute a complete paper, only the first five appearing in the answer book being marked. Candidates are urged to record any interpretive assumptions with their answers. All seven questions are worked below, because the set is intended as a study resource rather than as a single exam sitting.

Reference texts: Hendrickson, C. & Au, T., Project Management for Construction (2nd ed., Carnegie Mellon) — precedence networks with SS/FS lags, cash-flow financing, contract types; Halpin, D.W. & Senior, B.A., Construction Management (4th ed., Wiley) — CPM/LOB scheduling, formwork & equipment production, bonding and cash flow; Canadian Construction Documents Committee, CCDC 2 — Stipulated Price Contract (2020) — contract clauses, addenda, change orders, holdback; Canadian Foundation Engineering Manual (CFEM) & WorkSafeBC Occupational Health and Safety Regulation, Part 20 — excavation support and shoring.

Question 4: Wall-Form Components and the Formwork Design Process (20 marks)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

Check: the printed figure is an isometric line drawing; the four callouts are read as (a) a through-tie/wedge-clamp assembly, (b) the outer waler (wale), (c) the inner waler paired with (b), and (d) a diagonal kicker brace — the standard four elements of a braced wall-form panel. If the paper intends a different assignment of the same four elements, the functional description below still identifies every labelled part correctly.
aa — tie bb — waler cc — waler dd — kicker brace
Fig. Q4-1 — schematic wall-form panel: studs, a pair of double walers, a through-tie, and a diagonal kicker brace.

The four labelled components. (a) Tie — a steel rod (or proprietary snap-tie) passing through both wall-form panels and the fresh concrete between them; it carries the lateral fluid pressure of the concrete in direct tension, holding the two faces at the design wall thickness. (b) & (c) Walers (wales) — horizontal double members (timber or steel) clamped against the outside of the studs; they gather the pressure delivered by the sheathing/studs and transfer it to the discrete tie points, so ties can be spaced widely instead of needing one at every stud. (d) Diagonal (kicker) brace — an angled member anchored to a stable base (a stake, a slab, or the previous lift) that holds the panel plumb and resists lateral loads — wind, an eccentric pour, or a workers' platform — that are not balanced by the opposing panel the way concrete pressure is.

The formwork design process. (1) Establish the design lateral pressure of the fresh concrete, which depends on the placement (pour) rate, concrete temperature, unit weight, slump and whether a retarder is used — a fast pour or cold concrete stays fluid (and therefore keeps exerting near-hydrostatic pressure) over a taller lift than a hot, slow pour does. (2) Select the sheathing (plywood or steel-faced panel) thickness so its bending stress and deflection stay within limits at the chosen stud spacing. (3) Size and space the studs so they in turn stay within allowable bending/deflection between walers. (4) Size and space the walers and the ties so both the waler bending capacity and the tie's rated tension capacity are not exceeded at the design pressure. (5) Design the bracing for wind and incidental lateral load, and confirm the base connection (kicker to slab, or stakes) can take the resulting overturning force. (6) Confirm a safe stripping time from the concrete's strength-gain curve before removing formwork or re-shoring, and check the assembly for reuse economy over the project's total number of pours.