Shoring Systems Explained: Types, Design & Installation

Why Shoring Is Needed

Shoring provides temporary structural support when the permanent load-carrying system is compromised, absent, or being replaced. Every structural element in a building is part of an unbroken load path from roof to foundation — gravity loads, wind loads, and live loads must travel along that path continuously. When any link in the chain is removed during construction, a temporary replacement must take its place.

The principal scenarios requiring shoring include: removing load-bearing walls during renovation; excavating adjacent to or beneath existing foundations; rebuilding deteriorated structural elements; constructing new floors beneath an existing building; and protecting neighboring structures during adjacent deep excavations. In every case, the shoring system must be engineered — not estimated — with specific verification that it can carry the loads imposed on it during the construction period.

Raking (Inclined) Shores

A raking shore is an inclined structural member — typically a steel wide-flange section or heavy timber — that braces a wall being supported at an angle from grade. The top of the raking shore bears against a wall plate (needles and packing) attached to the wall, and the foot bears against a sole plate embedded in the ground or a concrete deadman. The inclined geometry allows the shore to develop both vertical (gravity) and horizontal (out-of-plumb bracing) components of force resistance.

Raking shore angles are typically between 45° and 75° from horizontal — steeper angles reduce horizontal thrust but increase compression demand on the shore. Engineers calculate the required shore size, needle spacing, wall plate dimensions, and deadman bearing length based on the tributary wall load and the shore geometry.

Dead-Leg (Vertical) Shores

Dead-leg shores transmit floor loads vertically from above a work zone to the floor(s) below. They are the most common shoring type in NYC brownstone and loft renovation — when a structural floor beam is being replaced, dead legs above and re-shores below transfer the loads during the window in which the beam is absent. Dead-leg shores are proprietary steel props (Acrow or Aluma) or constructed timber posts, sized by the engineer based on tributary area and floor loads.

The key design consideration for dead legs is column buckling — slender props under compression can buckle at loads well below their material capacity. The engineer checks both the Euler buckling length and the cross-section capacity, and specifies bracing where required. In multi-story reshoring sequences, loads accumulate in the shores below the work zone, requiring careful sequential analysis.

Flying Shores

Flying shores are horizontal shoring systems that span between two parallel buildings — typically when the building between them is being demolished or rebuilt. The system transfers loads horizontally between the opposing facades, preventing the exposed walls from overturning or spreading once their internal structural support is removed. Flying shores are common in NYC terrace-style townhouse construction where buildings are constructed party-wall to party-wall.

A flying shore system consists of horizontal strapping timbers or steel sections bearing against wall plates on both buildings, with diagonal spur struts providing the inclined bracing components that carry the lateral loads. The design must address: wall plate bearing capacity, strut compression, and the reaction forces imposed on the adjacent buildings (which may be occupied during construction).

System Shoring & Acrow Props

System shoring refers to manufactured modular shoring frames, post shores, and telescoping Acrow props used for conventional formwork and slab support during concrete placement. These systems are proprietary — each manufacturer publishes load tables and assembly instructions — but they must still be engineered for the specific application. The engineer specifies: frame size and type; post height and load rating at that height; spacing grid; and bracing requirements for stability against lateral loads during placement.

Soldier Pile & Lagging Walls

A soldier pile wall is an excavation support system used to retain soil during open cuts. Steel wide-flange piles are driven or vibrated into the ground at regular spacing (typically 6–10 ft on center). As the excavation advances downward, horizontal timber lagging planks are inserted between the flanges of adjacent soldiers to retain the soil between piles. Tiebacks (soil anchors) or internal cross-struts may be used to brace the wall against earth and surcharge pressure.

Soldier pile walls are appropriate for competent soils with some cohesion. They are not suitable for high water table conditions (lagging gaps allow water inflow) or highly unstable soils. The structural design must assess: pile section modulus (bending capacity), embedment depth below excavation (passive resistance), lagging span capacity, and tiebacks (if used).

Sheet Pile Walls

Sheet pile walls consist of interlocking steel sections driven continuously into the ground to form a watertight retaining wall. Unlike soldier pile systems, sheet piles can be installed in water-bearing soils and high water table conditions. They are commonly used for bridge abutments, basement excavations in tight urban conditions, cofferdams around foundations, and permanent waterfront structures.

Load Calculations & Design Principles

All shoring design begins with load determination under ASCE 7-22 (gravity, wind, seismic, construction loads) and applicable material codes (AISC 360 for steel, NDS for timber, AASHTO/ACI as applicable). Key design checks include:

• Compression (axial) capacity: Both gross section and net section at connections; column buckling for slender elements
• Bending capacity: Beams and lagging under distributed soil pressure or concentrated floor loads
• Bearing: Wall plates, sole plates, and deadman must distribute reactions without overstressing the supporting element
• Stability: Lateral bracing of shoring system against racking, particularly during concrete pours when dynamic loading occurs
• Deformation: Pre-tensioning, camber, and pre-loading to control deflections that could damage adjacent structures

Installation, Monitoring & Removal

Safe shoring installation follows a specific sequence: survey neighboring structures and establish monitoring datum points → erect shoring in designed sequence → load monitoring at critical load stages → adjust as required → maintain during construction → remove only when the permanent system is confirmed at full capacity.

Monitoring during installation and construction is essential — particularly for excavation support walls where soil movement is progressive. Inclinometers track wall lateral movement; settlement pins monitor neighboring buildings; piezometers track groundwater levels. If movements approach trigger levels (typically 50% of allowable movement), work stops and the engineer is notified.