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