Shimming on Concrete vs Steel Structures
While most pipeline shimming occurs on structural steel pipe racks, many pipe supports are mounted directly on concrete piers, foundations, or precast sleeper supports. Shimming on concrete surfaces presents unique challenges including uneven surfaces, anchor bolt alignment, and the decision between shimming and grouting.
When to Shim vs When to Grout
The choice between shimming and grouting at a concrete pipe support depends on the gap size, the loading requirements, and the project specification.
Shimming vs Grouting Decision Guide
- Gap under 25mm (1 inch): Steel shims are typically preferred. They are fast to install and easy to adjust.
- Gap 25mm to 50mm: Either shimming or grouting may be acceptable. Check the project specification.
- Gap over 50mm (2 inches): Grouting is usually required for proper load distribution. Shims alone may not provide adequate bearing.
- High vibration: Grouting provides better vibration dampening than steel shims on concrete.
- Temporary supports: Shims are preferred because they can be removed and adjusted during construction.
Base Plate Leveling with Shims
Pipe support base plates mounted on concrete foundations often require leveling shims to achieve a flat, true bearing surface. The concrete surface may have minor irregularities from forming, finishing, or curing that prevent the base plate from sitting flat.
Leveling Procedure
- Check the concrete surface: Use a straightedge and level to identify high and low spots on the concrete pier top
- Set leveling nuts: If the base plate is on anchor bolts, use leveling nuts below the base plate to set the initial elevation
- Insert shims: Place steel shims between the leveling nuts and the base plate, or between the concrete and base plate
- Check level: Verify the base plate is level in both directions using a precision level
- Torque anchor bolts: Once level, torque the anchor bolts to the specified value
- Grout if required: Pour non-shrink grout under the base plate if the project specification requires it
Precast Concrete Sleeper Supports
Precast concrete sleepers are commonly used for small-bore pipe supports in pipeline right-of-way applications. These precast blocks are set on prepared ground or on gravel pads, and the pipe rests on the flat top surface of the sleeper.
Shimming at precast sleepers typically involves placing steel shims between the pipe shoe and the top of the sleeper to achieve the correct pipe elevation. The shims must be wide enough to distribute the pipe load across the sleeper surface without exceeding the concrete bearing capacity.
Anchor Bolt Considerations
When shimming pipe supports that are anchored to concrete with bolts, the shim thickness affects the effective bolt grip length. Thick shim packs increase the distance between the concrete surface and the nut, which may require longer anchor bolts or threaded rod extensions.
Verify that sufficient thread engagement remains after shimming. Most specifications require a minimum of one bolt diameter of thread engagement above the nut.
Documenting Concrete Support Shims
ShimSheet tracks shim data at every support point regardless of whether the support is on steel or concrete. Recording the support type along with shim dimensions helps maintenance crews understand the installation context when they need to make future adjustments.
Track Shims on Any Support Type
Use ShimSheet to document shim dimensions at steel and concrete pipe supports. Generate reports that include complete installation details.
Try ShimSheet FreeFrequently Asked Questions
Can steel shims be used directly on concrete?
Yes, steel shims can be placed directly on concrete surfaces for pipe support leveling. For permanent installations, a thin layer of non-shrink grout may be placed under the shim to fill minor surface irregularities.
What is the maximum shim height on concrete supports?
Most project specifications limit shim pack height to 50mm to 100mm on concrete supports. Gaps exceeding this should be filled with non-shrink grout for proper load distribution.
Do I need to grout after shimming on concrete?
Grouting requirements depend on the project specification. Many specifications require grouting under base plates after final alignment is achieved, even when shims are used for initial leveling.