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Common Defects in Concrete Formwork Systems

08 Jan 2019, Posted by F.A. in Concrete Forms

Concrete formwork systems may face several deficiencies that can lead to structural weaknesses and disrupt work, or worse, injure workers.

This article will look at some of the common defect found in concrete formwork systems:

Formwork Defects Due To Imperfect Design And Construction Practice

Any lacking in formwork design or construction can cause a defect. The main causes include:

  • Inability to sustain the vertical rate of concrete placement
  • Failing to check whether the bolts and wedges in the formwork have been tightened properly
  • Not providing an allowance for the uplift of the concrete when using inclined formwork systems
  • The difference in load distribution between two or more members that are supposed to support common loads
  • Inaccurate calculation of weight stresses because of an oversimplified design
  • Failing to provide for the vibration effect on ties, struts, wedges, and braces
  • Not accounting for the wind load
  • Not providing a structural allowance for the stress generated by natural factors, such as temperature, prestressing, and moisture movements.

Formwork Defects In Foundation Level Of Formwork Systems

For concrete formworks to work properly, they require a firm and strengthened foundation. Common causes of foundational defects include:

  • Sole plates that are not leveled or placed eccentrically
  • Insufficient load distribution between the horizontal and vertical members – which leads to the crushing of the sole plate
  • Insufficient load carrying capacity of the ground or uneven hedding
  • Deteriorated sole plates – due to several factors such as poor weather conditions, erosion or wear & tear
  • Inadequate lateral restraint to bedding when standards are based on a sloping ground

Formwork Defects Caused By Defects In Horizontal Supports

Concrete formworks make use of both: horizontal and vertical supports to back the whole system. Defects in horizontal support can cause a defect in the whole concrete forming system. Some horizontal support defects include:

  • Untied standards at the point of loading
  • The supporting elements are lacking plumb
  • Screw connections lacking rigidity because of overextension or a general lack of bracing
  • Utilizing adjustable steel props with anything other than correct pins, such as nails, mild steel bolts or reinforcing bars
  • Coarsely cut folding wedges that are not properly secured or made out of poor material
  • Inadequate lateral and torsional bracing – such as between telescopic essences or between centers that carry heavy loads
  • Horizontal members that are centrally placed in position or not placed at the center of the fork head
  • Cantilevers lacking support – for instance, the struts that support the deep beam side on the outer side of the structure
  • Lacking bearing areas provided to vertical supports or underside and principle members – which may lead to crushing
  • Timber bolts connection not staggered properly – which may create a tendency to split out
  • Failing to provide braces when the fork heads are extended excessively
  • Omitting compression flange restraints entirely
  • Incorrect center placement – causing them to be far apart
  • Inadequate sizes of section
  • The quality of the material used is of poor quality, particularly when the formwork materials are being recycled
  • Incorrect installation of bracing
  • Loose bolted connections not tightened properly
  • Sections of members that are lapping for continuity are varying in depth

Formwork Defects Caused by Defects In Vertical Supports

Vertical supports are crucial components of a formwork structure that facilitate workers and concrete application. Defects in vertical support can cause a defect in the whole concrete forming system. Some vertical support defects include:

  • Inadequate bracing during erection of the formwork structure
  • Supports are not plumb enough
  • Standards are lacking lacing between the point of loading – particularly important when telescopic centers are being supported
  • Screw connections lacking rigidity due to over-extension or a general lack of bracing
  • Correct pins are substituted for adjustable steel props such as nails, mild steel bolts and reinforcing bars
  • Timber standards are more than a single piece with inadequate splice plates
  • Heads of standards are not firmly secured to the underside of horizontal support members
  • Omitting scaffold fork heads or supports without considering an allowance for such a condition
  • Distorted bearing plates
  • Props provisioned improperly from floor to floor
  • Discontinuous bracing
  • Centers placed too far apart
  • Sections placed inadequately
  • Fixings installed incorrectly
  • Questionable quality of material used, particularly when second-hand material is used as in the case of corroded scaffold tubes
  • The eccentricity of solid plates

Formwork defects can be a nuisance – for the contractor and for the site owner. While eliminating human error can be too hard a task, ensuring high quality formwork material is imperative to a timely construction project. At Forming America, we provide our clients with only the best. From small projects to large construction undertakings – we provide assistance from the initial planning stages of your project right up to the final steps.