GATE Architecture & Planning (AR) — Preparation Course

LESSON 2.3 — Formwork, Scaffolding and Temporary Structures

A. Standard Map

Topic	Governing Source	Exam Focus
Formwork types	NBC 2016 Part 7; BIS SP:46; GATE-2010; ch05-part03	Method identification by description; application context
Formwork pressure	IS:14687:1999 — Guidelines for Falsework [VERIFY: exact clause]	Simplified pressure formula; pressure factors
Scaffolding types	NBC 2016 Part 7; standard construction practice	Type identification — independent, putlog, suspended
Shoring	NBC 2016 Part 7; standard practice	Type identification — raking, flying, dead
Underpinning	NBC 2016 Part 7; IS guidelines	Pit method vs needle beam method; when underpinning is required

B. Mechanism in Words

Formwork:
1. Concrete is cast as a liquid; it needs a temporary mould to hold it while it gains strength.
2. Formwork (shuttering) provides this mould — its geometry determines the structural member shape.
3. Concrete exerts hydrostatic pressure on the formwork when freshly placed; deeper pours and faster placement rates produce higher lateral pressures.
4. Once concrete hardens sufficiently, formwork is stripped (struck) and reused for the next pour.

Scaffolding:
1. Workers, materials, and tools need access to heights during construction and maintenance.
2. Scaffolding provides a temporary elevated platform — a system of poles, ledgers, and working boards.
3. Type selection depends on whether the scaffold can lean against the building (putlog), must stand free (independent), or must hang from the structure above (suspended).

Shoring and Underpinning:
1. Shoring provides temporary support to buildings, walls, or trenches that have become unstable due to excavation, damage, or adjacent construction.
2. Underpinning transfers the load of an existing foundation to a new, deeper level — used when excavating adjacent to an existing building or when soil conditions require deeper founding.

C. Core Concept Explanations

C1. Formwork Types — Comparative Summary

Type	Mechanism	Best Application	Key Performance Data
Conventional Timber Formwork	Sawn timber planks, plywood, and framing assembled on site	One-off or low-repetition elements; irregular shapes	Low initial cost; labour-intensive; up to ~5–10 reuses
Steel Formwork	Pre-fabricated steel panels with connecting hardware	High repetition; columns, walls, beams; demanding finish	Up to 50+ reuses; heavy; excellent surface finish
Aluminium Formwork (MIVAN)	Lightweight prefabricated aluminium panels	Mass housing with repetitive floor plans; large-scale residential	250+ reuses; fast assembly; walls and slabs cast monolithically
Tunnel Form	Inverted-U tunnel-shaped form casts walls and slab simultaneously	Hotels, apartments, barracks — any repetitive cellular structure	1 floor per day cycle; extremely fast; requires crane
Slip Form	Form slides continuously upward as concrete is placed	Chimneys, silos, towers, elevator shafts, core walls of high-rise	150–300 mm/hour slip rate; 24-hour continuous operation
Climbing Form	Form is raised floor by floor by jacks or cranes; not continuous	Columns, piers, high-rise external walls	~1–3 day cycle per floor; better concrete quality than slip form
Table Form (Flying Form)	Slab form + supporting structure moved as one unit by crane	Repetitive slab construction; medium-rise frames	Eliminates re-erection of slab centering for each floor

Source: ch05-part03; NBC 2016 Part 7; GATE-2010 (tunnel form + slip form tested directly).

Exam Anchor — GATE-2010:
– Tunnel Form → 1 floor per day; walls + slabs cast together in one pour
– Slip Form → 150–300 mm/hour; continuous vertical motion; 24-hour operation
– MIVAN (Aluminium) → 250+ repetitions; precision finish; mass housing

C2. Formwork Pressure

Fresh concrete behaves like a fluid until it starts to set. The lateral pressure on vertical formwork depends on the rate of pour, temperature (which governs setting rate), concrete unit weight, and pour depth.

Simplified formula (for examination):

P_max = γ × H

Symbol	Meaning	Typical Value
P_max	Maximum lateral pressure on formwork (kPa or kN/m²)	Calculated
γ	Unit weight of fresh concrete	24 kN/m³ (standard)
H	Depth of pour above the point being considered (m)	Given in problem

Worked example: A column of 3.0 m height is cast in one continuous pour. Find maximum lateral pressure at the base.
– P_max = 24 × 3.0 = 72 kN/m²

Source: IS:14687:1999 — Guidelines for Falsework. [VERIFY: exact clause reference; the simplified formula P = γH is widely used in exam context.]

Exam Note: The full IS:14687 treatment also considers pour rate and concrete temperature — faster pour rate = less time for concrete to stiffen = higher effective pressure. For GATE/UPSC questions, the simplified P = γH formula is the expected answer unless the problem specifies pour rate adjustments.

Factors that INCREASE formwork pressure:
– Faster rate of placing concrete (less time to stiffen)
– Lower concrete temperature (slower setting → higher fluid head)
– Use of admixtures (retarders increase setting time → higher pressure)
– Higher pour height (greater head pressure)

C3. Scaffolding Types

Type	Support Mechanism	Key Characteristic	Application
Independent Scaffolding	Self-standing; two rows of vertical standards (uprights); completely independent of the building	Can be used where the building face cannot support scaffold	New construction; tall buildings; facade work
Putlog Scaffolding (Single-pole Scaffolding)	One row of standards; horizontal putlog members lean on and are supported by the building wall (one end in the wall, one end on the ledger)	Less material than independent; relies on building for partial support	New brickwork construction — putlog ends are left in the wall during construction
Suspended Scaffolding	Working platform hung by ropes, chains, or wire from projecting brackets or roof level supports	Can access any height without floor-level standards	High-rise maintenance; painting; cladding work post-construction
Cantilever Scaffolding	Brackets cantilevered from the building; standards rest on these brackets; no ground-level support	Used where ground cannot support standards (active traffic, existing structure)	Bridge maintenance; over footpaths
Trestle Scaffolding	Tripod or folding frame supports the working platform	Low-level interior work; lightweight	Interior plastering, painting; up to ~5 m height

Exam Anchor: Putlog scaffolding is the most economical for NEW masonry construction because the putlogs rest in the joints of the fresh brickwork — no wall brackets needed. Independent scaffolding is used where the wall cannot provide support. Suspended scaffolding is used after construction for maintenance.

C4. Shoring — Types and Applications

Shoring provides temporary support to prevent collapse of walls, structures, or trenches during construction, alteration, or adjacent excavation.

Type	Mechanism	Application
Raking (inclined) shore	Inclined struts transmit wall load to ground at an angle; a raking strut runs from base plate on ground to wall plate on the building	Supporting a wall that is bulging outward, cracking, or in danger of overturning; most common type
Flying (horizontal) shore	Horizontal shore transfers load between two parallel walls; shore connects opposite walls across a space	Supporting a wall whose adjacent building has been demolished; cross-party wall support during alterations
Dead (vertical) shore	Vertical props carry the load of floors or walls directly downward; requires needles through the wall to transfer loads	Supporting floors and walls above an opening being created (new door, window, or underpinning operation)

Exam Anchor:
– Raking shore → bulging/overturning wall → inclined to ground
– Flying shore → opposite walls → horizontal connection
– Dead shore → vertical → supports floors above an opening

C5. Underpinning — Methods

Underpinning is the process of strengthening or deepening an existing foundation, either because the existing foundation is inadequate or because adjacent excavation threatens it.

When underpinning is required:
– New deeper basement excavation adjacent to an existing shallow-founded building
– Change of use requiring higher loads than the existing foundation can carry
– Original foundation resting on unsuitable soil that has deteriorated
– Subsidence of existing foundation

Method	Procedure	Application
Pit (Mass Concrete) Method	Foundation exposed in short sequential pits (≤ 1.2 m wide); each pit concreted before adjacent pit is opened; sequence avoids simultaneous exposure	Traditional underpinning; most common; suitable for strip and pad footings with modest loads
Needle Beam Method	Steel needles (H-section beams) threaded horizontally through the wall above the foundation; wall load transferred via needles to temporary supports while new foundation is constructed below	Heavy walls or columns where pit method would require too many pits or is structurally insufficient
Pile Underpinning	Piles installed adjacent to or through the existing foundation; load transferred to piles via beams or brackets	Where the founding stratum is very deep; large loads; or access prevents traditional excavation
Resin/Grout Injection	Expansive resin or cement grout injected under pressure to densify and strengthen weak soil	Settlement correction; loose granular soils; non-invasive; sometimes called “mudjacking”

Exam Anchor: The pit method is the most widely used underpinning method in Indian practice. The needle beam method is used for heavy structures where the pit method alone cannot safely transfer the load. Pits are always opened in a 1-2-3 sequence — alternating pits so no two adjacent pits are open simultaneously.

C6. Centering vs Formwork

Term	Refers To
Formwork (shuttering)	The mould that gives shape to vertical or inclined concrete faces — columns, walls, beams (sides)
Centering	The temporary support structure under arches, vaults, and the SOFFIT of slabs and beams — it carries the weight of wet concrete

Trap: “Formwork” and “centering” are sometimes used interchangeably in informal usage. In technical terminology, centering specifically refers to the temporary support under arches and beam/slab soffits. GATE questions use both terms — recognise the distinction.

D. Design/Parameter Table

Parameter	Value	Unit	Source
Tunnel form cycle rate	1 floor	per day	GATE-2010; ch05-part03
Slip form rate	150–300	mm/hour	GATE-2010; ch05-part03
Aluminium (MIVAN) reuse cycles	250+	cycles	Industry standard
Steel formwork reuse cycles	50+	cycles	Industry standard
Timber formwork reuse cycles	5–10	cycles	General practice
Formwork lateral pressure (simplified)	P = γ × H	kN/m²	IS:14687:1999
Fresh concrete unit weight (γ)	24	kN/m³	IS:875 Part 1
Pit method — max individual pit width	~1200	mm	Standard practice
Dead shore — requires needle at height	Through wall above opening	—	Standard practice
Raking shore — direction	Inclined to ground	—	Standard practice
Flying shore — direction	Horizontal	—	Standard practice

E. Common Confusions

Confusion	Correct Distinction
Slip form vs climbing form	Slip form moves CONTINUOUSLY upward at a constant rate (24-hour operation). Climbing form is raised floor by floor (DISCONTINUOUS) — the form is stripped, raised, and re-fixed.
Tunnel form vs table form	Tunnel form casts WALLS AND SLAB TOGETHER in one inverted-U section. Table form handles the SLAB ONLY (the soffit centering + supporting frame moves as one unit).
Formwork vs centering	Formwork = mould for the sides/faces of members. Centering = temporary support under arches and beam/slab soffits.
Putlog vs independent scaffold	Putlog relies on the building wall for partial support (one end of horizontal member in the wall joint). Independent scaffold has TWO rows of standards and is completely self-supporting.
Raking shore vs dead shore	Raking shore = inclined; prevents a wall from OVERTURNING OR BULGING. Dead shore = vertical; supports the load of FLOORS AND WALLS ABOVE during alterations.
Pit underpinning — sequence	Pits are NOT all opened at once. They are opened in a 1-2-3 alternating sequence so no two adjacent pits are simultaneously open.

F. Exam Traps

Trap	Incorrect Assumption	Correct Answer
T13	“Slip form achieves 1 floor per day”	1 floor per day = TUNNEL FORM. Slip form achieves 150–300 mm/hour — used for towers, silos, chimneys, not floor-by-floor residential.
T14	“Tunnel form is used for chimneys and silos”	Slip form is used for chimneys, silos, and tower shafts. Tunnel form is for repetitive cellular building types (hotels, apartments).
T15	“Independent scaffolding leans against the building”	PUTLOG scaffolding leans against the building. Independent scaffolding is self-supporting — two rows of standards, no reliance on building wall.
T16	“Formwork pressure increases with slower pour rate”	Slower pour → more time for concrete to stiffen before full height is reached → LOWER effective pressure. Faster pour → higher pressure.
T17	“Centering and formwork are the same thing”	They are related but distinct. Centering = support under ARCHES and SOFFITS (horizontal). Formwork = mould for VERTICAL or inclined faces. All centering is formwork but not all formwork is centering.
T18	“All pits can be opened simultaneously in underpinning”	Pits are opened in a 1-2-3 alternating sequence — adjacent pits must not be open simultaneously; the completed pit provides support before adjacent pit is opened.

G. Answer-Writing Cues

For formwork type selection:

“[Formwork type] is selected because [application characteristic]. [Type] achieves [performance metric] and is best suited for [building type] due to [structural/economic reason].”

For scaffolding type identification:

“Putlog scaffolding is used for new masonry construction — the horizontal putlog member rests in the wall joint, reducing material requirement compared to independent scaffolding which is entirely self-supporting. For post-construction maintenance at height, suspended scaffolding is specified as no ground-level standards are required.”

For shoring selection:

“Raking shores are provided to a bulging or overturning wall — the inclined struts transmit wall load to a ground base plate. Flying shores are horizontal members connecting two parallel walls across a space — used when one side building has been demolished. Dead shores carry vertical loads of floors above an opening during construction — they require needles inserted horizontally through the wall to transfer the floor load.”

H. PYQ Linkage Note

Topic	Exam Appearance	Pattern
Tunnel form vs slip form	GATE-2010 (directly tested)	MCQ: identify formwork type from application description; “1 floor per day” → tunnel form
MIVAN (aluminium) formwork	GATE, UPSC-CPWD	MCQ: identify aluminium formwork by feature (mass housing, 250+ reuses)
Formwork pressure formula	GATE, UPSC-CPWD, state PSC	NAT: given height and γ, calculate P; MCQ on factors increasing pressure
Scaffolding types	UPSC-CPWD, state PSC	MCQ: identify type from description; putlog vs independent distinction
Shoring types	GATE, UPSC-CPWD	MCQ: match shoring type to situation (bulging wall, demolished adjacent building, new opening)
Underpinning methods	UPSC-CPWD	MCQ: identify method from description; pit method sequence

I. Mini-Check — Lesson 2.3 (5 Questions)

Q1 (MCQ): A construction site involves casting walls and floor slabs simultaneously in a single continuous pour using a formwork system that resembles an inverted U-shape tunnel. The system achieves approximately one completed floor per day. This describes:
(A) Slip form (B) Climbing form (C) Tunnel form (D) Table form

A1: (C) Tunnel form. Key identifiers: walls AND slab cast TOGETHER in one pour; inverted U-shape; 1 floor per day. Slip form moves continuously upward for towers/silos; climbing form is raised floor by floor (discontinuous); table form handles slab soffit only.

Q2 (NAT): A 4.5 m high concrete shear wall is cast in one continuous pour. Using the simplified formwork pressure formula P = γH and γ = 24 kN/m³, calculate the maximum lateral pressure at the base of the formwork.

A2:
– P_max = γ × H = 24 × 4.5 = 108 kN/m²

Q3 (MCQ): A contractor needs to access the facade of a building for window replacement work after construction is complete. No ground-level scaffold support is feasible due to active street traffic below. Which scaffolding type should be specified?
(A) Putlog scaffolding (B) Independent scaffolding (C) Cantilever scaffolding (D) Suspended scaffolding

A3: (D) Suspended scaffolding. For post-construction access at height with no ground-level support possible, suspended scaffolding is hung from brackets or roof-level anchors. Putlog (A) requires wall joint support for new construction; independent (B) requires ground-level standards; cantilever (C) requires fixed wall brackets.

Q4 (MCQ): An adjacent building has been demolished, leaving a party wall with no lateral support on one side. Which type of shoring is most appropriate to support this exposed wall?
(A) Raking shore (B) Dead shore (C) Flying shore (D) Needle beam shoring

A4: (C) Flying shore. A flying shore is a horizontal member connecting TWO PARALLEL walls — specifically designed to support a wall that has lost its adjacent building support across the gap. Raking (A) prevents overturning by inclined struts to ground; dead (B) supports loads vertically above openings.

Q5 (MSQ): Which of the following factors INCREASE the lateral pressure on concrete formwork? Select all that apply.
(A) Faster rate of placing concrete
(B) Higher ambient temperature
(C) Use of retarding admixtures in the concrete mix
(D) Greater pour height
(E) Slower rate of placing concrete

A5: (A), (C), and (D).
– Faster rate (A) ✓ — less time for concrete to stiffen; higher effective fluid head
– Higher temperature (B) ✗ — accelerates setting, REDUCES effective pressure
– Retarders (C) ✓ — slow setting time; concrete remains fluid longer; higher pressure
– Greater pour height (D) ✓ — P = γH; directly increases pressure
– Slower rate (E) ✗ — more time to stiffen; LOWER effective pressure