21.2 Bearing, Embedded, and Precast Connections
Key Takeaways
- A bearing plate must distribute compression while satisfying plate bending, contact, supporting-material bearing, edge, splitting, and the downstream load path.
- Embed plates transfer tension, shear, and moment through plate bending, welds, headed studs or reinforcing bars, concrete anchorage modes, and surrounding-member reinforcement.
- Corbels and short brackets require a compatible strut-and-tie or code model, anchored primary tie, bearing, shear-transfer, and local confinement checks.
- Headed studs can serve different composite or anchorage roles; their steel strength does not replace concrete breakout, pryout, edge, spacing, or group checks.
- Precast seats, pads, ties, and connections must accommodate tolerances, rotation, movement, erection stability, and positive force transfer at every construction stage.
- A connector that passes in isolation can still fail through local plate deformation, concrete breakout, inadequate reinforcement development, or the supporting member.
Embedded and bearing connections introduce concentrated force into concrete or a precast member. Their visible steel is rarely the whole connection. For July 2026, use the April 2024 PE Civil: Structural specification, ACI 318-14, PCI Design Handbook 7th edition, and the AISC Steel Construction Manual 15th edition. Do not import April 2027 standards.
Bearing Plates: Follow the Pressure
A bearing plate spreads a column, beam, girder, or precast reaction over a larger area. Begin with force and moment at the contact surface. Check whether full contact is possible, then evaluate maximum pressure rather than only P/A. The plate must also span between the loaded footprint and supporting reaction, so plate bending and yielding can govern. Grout, concrete, masonry, a bearing pad, or soil below the plate needs its own compatible bearing limit and adequate dimensions.
Compression must continue through the supporting member. Near an edge, concentrated bearing can split or spall concrete. Deep within a member, bursting or transverse tension may require reinforcement. A base plate with moment can lift off on one side, forcing compression into a smaller region and tension into anchors. Concrete contact cannot carry tension merely because an elastic formula reports negative pressure.
Worked Eccentric Bearing Plate
A rigid 12 in-wide by 18 in-long bearing plate carries factored compression P_u = 240 kips and factored moment M_u = 30 kip-ft about the axis parallel to its 12 in width. Assume linear pressure and full contact for the trial calculation. Find extreme pressures.
Contact area:
A = (12)(18) = 216 in^2
Contact section modulus for pressure varying along the 18 in length:
S = BL^2/6 = (12)(18^2)/6 = 648 in^3
Convert moment:
M_u = 30(12) = 360 kip-in
Average pressure:
P_u/A = 240/216 = 1.111 ksi
Bending component:
M_u/S = 360/648 = 0.556 ksi
Extreme pressures:
q_max = 1.111 + 0.556 = 1.667 ksi
q_min = 1.111 - 0.556 = 0.555 ksi
Both are compressive, so full contact is plausible for the stated idealization. The eccentricity e = M/P = 360/240 = 1.5 in is below the kern limit L/6 = 3.0 in, confirming the sign check. If the problem supplies compatible concrete design bearing stress 1.80 ksi, the stated contact-pressure check passes because 1.667 < 1.80 ksi. Plate flexure, grout, local reinforcement, edges, anchors, and the receiving member still require checks.
Embed Plates and Headed Studs
An embed assembly can include a face plate, headed studs, deformed-bar anchors, welds, stiffeners, and reinforcing bars tied into the member. Resolve applied force into tension, shear, and moment at the plate. Plate flexure can make anchor demand nonuniform; prying can amplify tension. Welds must develop force between attachment and plate, while studs or bars transfer it from plate into concrete.
For headed anchors, possible modes include anchor steel failure, concrete tension breakout, pullout, side-face blowout where applicable, shear breakout, and pryout. Group effects, close edges, spacing, member thickness, cracked-concrete condition, and supplementary reinforcement affect resistance. A high-strength stud does not make a thin edge region stronger. Reinforcement intended to bypass breakout must be positioned, anchored, and detailed to receive the force.
Headed studs used for steel-concrete composite beam action transfer longitudinal interface shear under AISC provisions. Studs welded to an embed plate can instead act as concrete anchors under ACI. Similar hardware does not make the design models interchangeable; identify the force-transfer role.
Corbels and Short Brackets
A corbel carries a concentrated reaction over a short shear span. Ordinary slender-beam behavior may not represent its disturbed stress field. Use the ACI 318-14 corbel or permitted strut-and-tie model required by the problem. The load flows through a concrete compression strut and anchored steel tie, with bearing, interface shear, confinement, and local nodal zones.
The primary tie must develop beyond the loaded region, and horizontal force from creep, shrinkage, restraint, braking, or bearing friction may accompany vertical reaction. Welding or anchoring the supported member to the corbel changes that horizontal path. Check the column or wall receiving the corbel force; a corbel that passes locally can overload the parent member.
Precast Seats, Pads, and Ties
A precast beam seat needs adequate bearing length after erection tolerances, movement, rotation, and edge clearances are considered. Bearing pads distribute stress and permit intended rotation or movement, but they can bulge, slip, or create edge pressure. Do not use nominal seat length when the problem calls for net length after tolerances. Local ledges, dapped ends, hanger reinforcement, and splitting zones can govern.
Positive ties and connections establish diaphragm, robustness, uplift, or lateral transfer. Gravity bearing alone cannot resist tension. During erection, temporary braces and anchors stabilize panels before roof or floor diaphragms exist. Welded embeds, bolts, dowels, grouted sleeves, and closure pours develop their final roles only after the specified installation, cure, and inspection sequence.
Connection Audit
- Resolve force and moment at the interface.
- Check contact, plate or seat deformation, and local bearing.
- Trace force through welds, studs, bars, pads, ties, and anchors.
- Check steel and concrete modes, edges, group effects, and reinforcement development.
- Evaluate erection tolerances, temporary stability, movement, and final continuity.
- Continue the path through the supporting member and foundation.
The governing result is the weakest compatible link, not the catalog strength of the most visible connector.
A 12 in by 18 in plate carries 240 kips and a 30 kip-ft moment about the axis parallel to its 12 in width. Under the stated linear full-contact model, what is maximum pressure?
A headed stud's steel design strength exceeds its assigned tension demand. What additional conclusion is required?
Why is nominal precast seat length not always the available design bearing length?