Masonry-Steel Interaction — Embedded Anchors, Lintels, Veneer Ties

Design of steel elements embedded in or connected to masonry construction — anchor bolts, lintels, shelf angles, and veneer ties. This guide covers TMS 402/602, AISC 360, and ASCE 7-22 provisions.

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Overview of Masonry-Steel Interaction

PRELIMINARY — NOT FOR CONSTRUCTION. All results are for educational and reference use only. Must be independently verified by a licensed Professional Engineer (PE) or Structural Engineer (SE) before use in any project.

Steel elements play several critical roles in masonry construction: they anchor masonry walls to structural frames, support masonry over openings, connect veneers to backing walls, and provide seismic reinforcement. The interface between steel and masonry involves different material properties, different deformation characteristics, and potential corrosion concerns that must be addressed in design.

Masonry is strong in compression but weak in tension, with modulus of elasticity E ≈ 900-2,000 ksi (depending on unit type and mortar strength) compared to steel at 29,000 ksi. This 15-30× stiffness difference means that steel elements embedded in or connected to masonry must be detailed to accommodate differential movement without overstressing the masonry.

Anchor Bolts in Masonry

Anchor bolts are used to connect steel elements (base plates, bearing plates, embed plates) to masonry walls, piers, and foundations. Per TMS 402 Chapter 4:

Anchor Types

Cast-in-place headed anchors — The most common type for new construction. A headed bolt or threaded rod is cast into fresh mortar during masonry construction. The head provides mechanical anchorage through bearing on the mortar. Advantages: highest capacity, proven performance, lowest cost. Disadvantages: must be placed during construction, requires coordination between trades.

Adhesive anchors — Threaded rods bonded into drilled holes using epoxy or grout adhesives. Advantages: ideal for retrofit and post-installed applications, can be placed anywhere after construction. Disadvantages: sensitive to installation quality, reduced capacity in wet/drilled conditions, limited to certain temperature ranges.

Mechanical expansion anchors — Wedge anchors that expand against the masonry substrate. Per TMS 402, these are limited to non-critical applications and must not be used in tension for seismic-force-resisting systems.

Anchor Design Strength (TMS 402 Section 4.2)

The nominal tensile strength of a headed anchor in masonry is the minimum of:

Steel strength: Ba,n = Ase × fy, where Ase is the effective cross-sectional area and fy is the anchor yield strength.

Masonry breakout strength: Ba,n = 4 × √(fm') × Abr, where fm' is the masonry compressive strength and Abr is the projected area of the breakout cone. The breakout cone extends at a 45-degree angle from the anchor head to the masonry surface. For multiple anchors, overlapping breakout cones reduce the effective breakout area.

Pull-through strength: Ba,n = 1.5 × √(fm') × d × hef, where d is the anchor diameter and hef is the effective embedment depth.

Minimum embedment: The anchor embedment depth hef must be at least 4 × d (for cast-in-place) and at least 2 inches. For most applications, hef = 6-12 inches is typical.

Edge Distance and Spacing

Per TMS 402, minimum center-to-center anchor spacing: 4 × d. Minimum edge distance: 1.5 inches for anchors parallel to the load direction, 3 inches for anchors perpendicular to the load direction. Reduced spacing and edge distances require capacity reduction factors.

Steel Lintel Design

Steel lintels support masonry over openings (windows, doors, arches) and transfer the masonry load to the adjacent wall. Lintels can be: (1) hot-rolled shapes (angles, channels, W-shapes) — the most common for wide openings, (2) cold-formed shapes (L-header angles) — for smaller openings (up to 6 ft / 1.8 m), or (3) built-up sections — for large openings or heavy loads.

Load Determination

The lintel must support:

Masonry dead load: For a masonry wall, the load above the lintel depends on arching action. If the height of masonry above the lintel is sufficient (H ≥ L/2 where L is the lintel span), a triangle of masonry is assumed to load the lintel. The triangular load height = L/2, and the maximum load at the apex = γ × H, where γ is the masonry unit weight (typically 120-140 pcf for clay brick, 100-130 pcf for CMU). If H < L/2, the full masonry height above the lintel loads the lintel as a uniform load.

Floor/roof loads: If the wall is load-bearing, the lintel must also support the tributary floor or roof loads. These loads are applied at the bearing points (beam seats) which are typically at the lintel ends.

Lintel self-weight: The lintel section weight per foot.

Design Checks

Per TMS 402 Section 5.2:

Bending: Mu = w × L²/8 (simply supported). φMn = φ × Fy × Zx (compact section). Minimum bearing length: 4 inches (100 mm) at each end.

Shear: Vu = w × L/2. φVn = φ × 0.6 × Fy × Aw × Cv (AISC G2).

Deflection: Δ ≤ L/600 for unreinforced masonry above, L/400 for reinforced masonry. The L/600 limit prevents cracking in the masonry above the lintel — this is the tightest deflection limit commonly used for steel members (compared to L/360 for floor beams).

End reaction: The bearing stress at the lintel support: fb = R/(bb × Lb) ≤ 0.25 × fm', where bb is the bearing width, Lb is the bearing length, and fm' is the masonry compressive strength.

Design Example — Steel Lintel

Consider a window opening 8 ft wide in an 8-inch CMU wall (fm' = 1,500 psi, unit weight = 125 pcf). Masonry height above lintel: 4 ft.

Step 1: Load calculation. H = 4 ft, L/2 = 4 ft. H = L/2, so triangular distribution governs. Maximum load at apex: w_max = 125 pcf × (4 ft/8 ft × 4 ft + 4 ft/8 ft × 4 ft) spread over lintel length... Actually: The triangular load height = L/2 = 4 ft. Load per foot at apex = γ × (L/2) × twall = 125 × 4 × (8/12) = 333 plf. Equivalent uniform load: w_eq = (2/3) × w_max = (2/3) × 333 = 222 plf.

Step 2: Add self-weight. Try L6×4×5/16: weight = 9.6 plf. Total w = 222 + 9.6 = 232 plf.

Step 3: Moment and shear. M = 232 × 8²/8 = 1,856 ft-lb = 22,272 in-lb. V = 232 × 8/2 = 928 lbs.

Step 4: Section check. For L6×4×5/16: Zx = 7.12 in³ (strong axis), Sx = 5.55 in³. φMn = 0.9 × 36 × 7.12 = 230.7 kip-in = 19,225 ft-lb. OK (DCR = 0.10). Deflection: Ix = 19.9 in⁴. Δ = (2/3) × (5 × w_eq × L⁴) / (384 × E × I) ... deflection is minimal. L6×4×5/16 is adequate.

Shelf Angles

Shelf angles support masonry veneer at floor lines, transferring the veneer weight to the building structure. Per TMS 402 Section 6.2:

Design requirements:

Masonry Veneer Ties

Veneer ties connect masonry veneer to the structural backing (steel frame, concrete, or masonry wall). Per TMS 402 Section 6.1:

Types of ties:

Spacing and placement:

Differential Movement

The most common cause of masonry distress at steel interfaces is differential movement. Steel frames move vertically due to: (1) elastic shortening under load (typically 0.03-0.10 inches per story), (2) thermal expansion — steel expands 6.5 × 10⁻⁶/°F compared to masonry at 3-4 × 10⁻⁶/°F, and (3) creep under sustained load.

Masonry undergoes: (1) initial shrinkage/expansion — clay brick expands slightly, CMU shrinks, (2) moisture movement, and (3) thermal movement.

The differential movement between steel and masonry requires: (1) horizontal joints (soft joints) at each floor line, (2) slotted connections at shelf angles to allow vertical adjustment, and (3) compressible filler between steel columns and adjacent masonry.

Corrosion Protection

Embedded steel in masonry requires corrosion protection. Per TMS 402:

Frequently Asked Questions

What types of anchors are used in masonry? Three primary anchor types: (1) Cast-in-place headed anchors — embedded in fresh mortar, best for new construction, provide highest capacity. (2) Adhesive anchors — bonded into drilled holes with epoxy or grout, good for retrofit. (3) Mechanical expansion anchors — wedging action, limited to non-critical applications. Per TMS 402 Chapter 4, anchor design must account for masonry prism strength, edge distance, and spacing effects.

How are masonry lintels designed? Steel lintels over openings in masonry walls must support: (1) dead load from masonry above (triangle of masonry or full height if bonded), (2) floor/roof live loads if the wall is loadbearing, (3) deflection limit of L/600 to prevent masonry cracking above the lintel. Per TMS 402 Section 5.2, the lintel bearing length must be at least 4 inches (100 mm) at each end. Lintel depth is typically L/12 to L/20 of the span.

What are shelf angles and how are they designed? Shelf angles support masonry veneer at floor lines. Per TMS 402 Section 6.2, shelf angles must be designed for the full weight of masonry above, limited to one story height (typically 10-12 ft). They must allow vertical deflection without transferring load through shims. AISC Design Guide 15 recommends a minimum angle size of L6×4×3/8 with stiffeners at 4-6 ft spacing. Corrosion protection requires galvanizing or stainless steel in exterior applications.

How are movement joints designed between steel and masonry? Movement joints accommodate differential vertical movement between steel frames and masonry infill walls. Per TMS 402 Section 6.3: (1) horizontal soft joints at each floor line using compressible filler (min 1/2 inch thickness), (2) slotted connections at shelf angles with 3/4-inch diameter bolts in 1-inch vertical slots to allow 1/4-inch vertical adjustment, (3) sealant at column-to-masonry interfaces (1/2-inch wide minimum), and (4) bond breakers between steel columns and masonry. The joint width should accommodate the computed differential movement plus 50% for safety — typically 1/2 to 1 inch per floor for steel-framed buildings up to 10 stories.

What corrosion protection is required for embedded steel in masonry? Per TMS 402, steel embedded in exterior masonry walls requires: (1) minimum G90 hot-dip galvanizing for shelf angles and lintels (3.0 oz/ft² zinc coating), (2) stainless steel (Type 304 or 316) for veneer ties, anchors, and joint reinforcement in severe exposure, (3) epoxy coating on reinforcing bars in masonry in Seismic Design Categories D, E, and F, and (4) bituminous coating on steel embedded in below-grade masonry. Contact between dissimilar metals (galvanized steel and stainless steel, or carbon steel and galvanized steel) should be separated by an isolation layer (neoprene pad or plastic shim) to prevent galvanic corrosion.

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Disclaimer (educational use only)

This page is provided for general technical information and educational use only. It does not constitute professional engineering advice. All results must be independently verified by a licensed Professional Engineer.