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Civil Engineering ConstructionChapter 4

Introduction to Formwork

Dr Mohamad Syazli Fathi

Department of Civil EngineeringUTM RAZAK School of Engineering & Advanced Technology

UTM International Campus

July 15, 2012

DDA 2132 Timber/Formwork Design

Introduction to Formwork

DDA2132 - Timber/Formwork Design

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Temporary Structures (TS)

• Definition– Any means or methods which provide

temporary support (TS), access, enhancement, or otherwise facilitate the construction of permanent structures.

• Necessity


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– TS form the interface of design and construction. Most permanent structures simply could not be built without TS.

Temporary Structures (continued)

• Impact on Schedule, Cost, and Quality– Losses in time and money will occur if the TS are not

planned and coordinated with the same degree of thoroughness as the permanent structures.

• Safety


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– Failure of TS have been responsible for hundreds of deaths on construction sites. Safety should be the overriding priority of contractors and designers responsible for implementing TS.

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Categorizing Temporary Structures

• Several common types of work which• Several common types of work which occur on construction sites are:– Formwork– Falsework– Rigging


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– Scaffolding– Excavation support– Miscellaneous (site specific)

Responsibility

• The norm in construction industry is to place the responsibility for TS solely on the general contractor. However, architects and engineers must at least have formulated their own method of construction.


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• Coordinating the design of permanent structure with the TS that will be required can lead to more efficient and cost effective construction.

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Design Consideration

• Safetyi l h fi i i f OS A– Designers must place the first priority on safety. OSHA

codes, as well as other codes in the industry, provide stringent performance specifications (how the system should work) regarding TS.

• Cost– TS can be the most expensive part of some construction

j t D i i t ff ti l ti t TS


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projects. Designing cost-effective solutions to TS problems could easily be the competitive advantage of a contractor over others. The designer must have a thorough knowledge of all the options which will sufficiently solve the TS problem.

Design Consideration (continued)

• Unique Design Challenges– TS are subject to unique loading conditions which do not

apply to a permanent structure (fluctuating or dynamic loads, impact loads, loads which change position).

– Working within spatial constraints- Cramped sites require the most efficient TS so that workers still have room to maneuver safely.


– Uncertainty of soil conditions- It is always possible that an unforeseen condition could arise during an excavation. Designers must include an appropriate factor of safety in their calculations or they may consider contingency plans for changing soil conditions.

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Concrete Formwork (FW)

• Forms are TS that provide containment for the freshForms are TS that provide containment for the fresh concrete and support it until it can support itself.

• Forms must be designed to support loads of the fresh concrete, equipment, workers, impact of various kinds, or sometimes wind without collapse or excessive deflection.


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• The cost of FW is between 40% to 60% of the cost of concrete structure. Design of a good forming system could both expedite a project as well as reduce costs.

Formwork Requirements - 1

• Safety – FW must be:• Safety FW must be:– Strong ( to carry the full load and side pressure

from freshly placed concrete, together with construction traffic and equipment).

– Sound (made of good quality, durable materials).


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• Quality – FW must be:A ( i hi ifi d l f f– Accurate (within specified tolerances for form dimension)

– Rigid (adequately braced and tied to prevent movement, bulging, or sagging during construction).

– Tight Jointed (to prevent cement paste leakage which disfigures the surface of concrete)


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disfigures the surface of concrete).– Properly Finished (to provide a concrete surface of

good appearance).


• Economy – FW must be:• Economy FW must be:– Simple (simple to erect and dismantle)– Easily handled (the sizes of units should not be

too heavy to handle)– Standardized (ease of assembly and possibility

of reuse)


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)

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Causes of Failures

• Improper stripping and shore removal• Improper stripping and shore removal• Inadequate bracing• Vibration• Unstable soil under mudsill, shoring not plumb• Inadequate control of concrete placement.


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• Lack of attention to FW details• When FW is not at fault


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Planning for Formwork

• The contractor should plan FW at the time ofThe contractor should plan FW at the time of making bid considering the following factors:– Placing schedule and stripping time requirements– Capacity of equipment available to handle form sections and

materials– Capacity of mixing and placing equipment– Construction joints

Re se of forms as affected b stripping time


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– Reuse of forms as affected by stripping time– Relative merits of job-built, shop-built and ready-made forms.– Weather (protection requirements and stripping time)

• Compare alternative methods to determine the most efficient plan.

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Key area of Cost Reduction - 1

• Planning for maximum reuse• Planning for maximum reuse– A form designed for max reuse is stronger and more expensive, but

it can save on the total form cost.

• Economical form construction– Shop-built (greatest efficiency in working conditions and in the

purchase and use of materials and tools)– Shop area on the site (form sections too large or transportation cost


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Shop area on the site (form sections too large or transportation cost too high)

– Job-built (for small jobs, or where forms must be fitted to terrain)

Key areas of Cost Reduction - 2

– Buying prefabricated forms(large number of reuses)R i f b f (b fl ibili i l i– Renting prefab forms(better flexibility in regulating volume of work)

• Setting and stripping– Repetition of the same functions to increase the crew

efficiency as the job progresses

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– Use of metal clamp or special wedge pin connections that are secure, yet easy to assemble and dismantle

– Add extra features that make handling, erection, and stripping easier (handles, lifting eyes)

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Other costs affected by FW - 1

• Cranes and Hoists• Cranes and Hoists– Size of form sections should be limited to the capacity of the

largest crane planned for the job.– Stair towers may be completed early in the schedule to be used for

moving men and materials.– Leave one bay open to permit mobile crane and concrete truck

movement.


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• Bar Setting– Form design can permit the rebar to be pre assembled before

installation (more favorable condition)

Other Costs affected by FW - 2

• Concrete Placement• Concrete Placement– High lifts in wall construction make placing and vibration difficult.– Placing rate is limited by form design.

• Other Trades– The plan should permit other trades to perform their work


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efficiently and minimize interruptions in placing.

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