8.2 Shoring, Reshoring & Formwork Removal Safety and Timing
Key Takeaways
Shoring supports formwork, concrete and construction loads. Reshores are installed snug after the original supports for a bay are removed and the member carries its own weight.
Under OSHA 29 CFR 1926.703, tiered single-post shores have specific design, inspection, vertical alignment, splice and bracing requirements.
Check shoring sill capacity, firm bearing and the loads on the supporting ground or structure against the approved layout.
Use the approved sequence and strength criterion before load-bearing form or shore removal. When unmodified ACI 301-20 Section 2.3.2.4 applies, its default is at least the specified compressive strength.
Use field-cured cylinders or the specified alternative for the applicable in-place strength determination and maintain required curing after stripping.
Shoring, Reshoring & Formwork Removal Safety and Timing
Before removal, identify where the loads will go when forms or supports are taken out. ACI 318-19 Section 26.11.2.1 requires the contractor to develop a removal and reshoring procedure and schedule, calculate loads transferred to the structure, and demonstrate sufficient strength for the actual loading and remaining formwork without impairing serviceability. The construction sequence can change which slabs, beams and supports carry the load.
1. Identify what each support does
| Support | Field distinction |
|---|---|
| Shore | Carries formwork, concrete and construction loads before the supported system can carry them safely. |
| Reshore | Fits snugly under a member after the original forms and shores have been removed from a full bay and the member has deflected under its weight and loads already applied. |
| Backshore | Fits snugly beneath the member as the original forms and shores are removed in a small area, without allowing the whole bay to deflect under its weight. |
| Drop-head shore | Lets specified forming components be removed without removing vertical support. Verify whether and when the approved procedure changes its function. |
ACI 347.2R-17 explains how these support arrangements affect load distribution. In a planned reshoring sequence, install the reshores snugly without lifting the member or imposing an unintended preload. Verify the specified layout and sequence before moving any support. Under OSHA 29 CFR 1926.703(b)(10), provide reshoring as original forms and shores are removed whenever the concrete otherwise would have to support more than its capacity.
2. Check bearing, alignment and bracing
Compare the support type, elevation, spacing, base, head and bracing to the engineered layout. OSHA 29 CFR 1926.703(b) addresses inspection of shoring equipment before erection and of erected shoring immediately before, during and immediately after placement. It requires sound, rigid sills capable of supporting the intended maximum load and firm contact at bearing points. An eccentric load is permitted at a shore head only if the member is designed for it.
Where single-post shores are stacked in tiers, Section 1926.703(b)(8) requires design by a qualified designer and inspection of the erected shoring by an engineer qualified in structural design. The posts must align vertically, their splices must prevent misalignment, and bracing at the splice and diagonally in each tier must act in two perpendicular directions. Across separate floors, use the designed multistory load distribution and approved support locations. Check whether a reaction lands on the intended support or loads a slab at an unplanned location. Report soft bearing, missing bracing or other deviations while they are accessible.
3. Verify the removal conditions
Check the actual load-carrying function of the component to be removed. Under ACI 301-20 Sections 2.3.2.1–.3, the timing for removing vertical or sloped face forms considers damage or sag and the required finish and continued protection. Section 2.3.2.4 retains structural formwork and shoring until the in-place strength is at least unless the project specifies otherwise. Section 2.3.2.5 allows facing and horizontal facing supports to be removed earlier where the approved system permits doing so while the vertical supports remain. Verify the additional project and stressing-record conditions for post-tensioned work under Section 2.3.2.6.
Under Section 2.3.4.1, where the criterion is a specified in-place strength, the default uses ASTM C31/C31M field-cured cylinders tested under ASTM C39/C39M. The specimens represent the relevant placement and are cured under conditions representative of the member. Section 2.3.4.2 lists specified alternatives, including C873/C873M cast-in-place cylinders for slabs 5 to 12 inches deep, C803/C803M penetration resistance, C900 pullout and C1074 maturity. A maturity estimate uses a strength relationship for the concrete mixture and the member’s measured temperature history. Apply the specified method and approvals, including those in ACI 318-19 Section 26.11.2.1(e). Model IBC Table 1705.3 item 13 assigns periodic verification of in-situ strength before shore and form removal from beams and structural slabs.
For example, a project requires 3,500 psi in place and continued reshoring at designated bays. The report for the correct bay and test method gives 3,300 psi. It is 200 psi short. Record that the strength criterion is unmet and notify the contractor. A higher result for a different placement or a standard-cured acceptance result does not verify the required strength for this bay. After an acceptable result, the contractor still follows the approved removal sequence and reshoring layout. Verify the required curing and protection continue if forms are removed before the specified curing period ends.
OSHA Section 1926.703(e) separately assigns the employer the sufficient-strength determination before removal of the covered forms and shores. It provides for following stipulated conditions or using an appropriate ASTM test that demonstrates adequate strength for the load. The inspector records the applicable evidence and discrepancies without taking over the employer’s decision or the temporary works design.
A structural slab must reach 3,500 psi in place before shore removal under its approved procedure. The specified field-cured test reports 3,300 psi for that bay. What should the inspector record?
The criterion is met because the difference is within a default 500 psi allowance.
The criterion is met if a different bay has a standard-cured cylinder result above 3,500 psi.
The result can be replaced by a calendar-day estimate without project approval.
The criterion is unmet by 200 psi. Notify the contractor and verify later evidence for that bay.
In the approved reshoring sequence, the original forms and shores for a full bay have been removed and the member is carrying its own weight. How are the reshores fitted?
Snugly beneath the member without lifting it or introducing unintended preload
By jacking the member up until the reshores take its entire weight
With a gap at each head to prevent contact during upper placement
Without regard to the approved support locations
Which requirement applies under OSHA 29 CFR 1926.703(b)(8) where single-post shores are stacked one on top of another?
The posts may be staggered at every splice if the deck is level.
The posts must be vertically aligned and spliced to prevent misalignment.
Splice bracing is needed only in one direction.
The posts must be adjusted to raise the form after concrete placement.
Sections you finish are checked off in the contents.