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Concrete formwork systems suffer from several deficiencies such as defects due to imperfect design and construction practice, defects in foundation level of formwork systems, defects in vertical support of formwork systems and defects in horizontal support of formwork systems. These common defects are discussed below.Contents:
Common Defects in Concrete Formwork Systems
1. Formwork Defects due to Imperfect Design and Construction Practice
- Too much tolerances in construction
- Inability to control vertical rate of concrete placement
- Inability to check the tightness of bolts and wedges before loading formwork systems
- Insufficient allowance for uplift of concrete under inclined formwork systems
- Different load distribution between two or more member that supposed to support common loads
- Incorrect computation of stresses because of over simplification of design assumptions
- Lack of required provision for the vibration effect on ties, struts, braces, and wedges
- Failure to properly account for wind loads
- Insufficient allowance for the influence of stresses generated by temperature, prestressing, and moisture movements
2. Defects in Foundation Level of Formwork Systems
- Sole plates are not leveled
- Crushing of sole plate because of insufficient distribution of loads form horizontal and vertical members
- Poor load carrying capacity of the ground under sole plate
- Deterioration of load carrying capacity of the ground for instance washing out ground
- Deterioration of sole plates with time because of several factors for example weather condition
3. Defects in Vertical Support of Formwork Systems
- Lack of ties between standards at point of loading
- Supports are out of plumb
- Insufficient bracing to scaffold
- Bearing plates at the top and bottom of props are distorted
- Insufficient lateral ties, vertical and plan bracing
- Lack of rigidity of screw connection because of lack of bracing or over extension
- Utilizing adjustable steel props with nails, mild steel bolts and reinforcing bars instead of correct pins
Fig.: Formwork for Beams and Slabs with Vertical Supports
4. Defects in Horizontal Support of Formwork Systems
- Horizontal members are not centrally placed in forkheads
- Lack of staggering in timber bolted connection which may lead to split out of the timber bolted connection
- Insufficient lateral and tensional bracing
- Inadequate support to prevent overturning of deep principal elements since forkheads are frequently omitted
- Insufficient support to cantilevers
- Inadequate bearing area to vertical supports and underside of main members lead to crushing
- Folding wedges cut to too coarse a taper, not properly cleated, cut from wet material
