8.2 Masonry & Structural Steel Construction
Key Takeaways
- Concrete Masonry Units (CMU) have nominal dimensions of 8"x8"x16" but actual dimensions of 7-5/8"x7-5/8"x15-5/8" to accommodate standard 3/8-inch mortar bed and head joints.
- ASTM C270 specifies four primary mortar types under the 'MaSoN wOrK' acronym: Type M (2,500 psi, high compressive/below-grade), Type S (1,800 psi, high flexural bond/seismic), Type N (750 psi, general exterior above-grade), and Type O (350 psi, non-loadbearing interior/tuckpointing).
- Masonry grout requires a high slump of 8 to 11 inches to ensure fluid consolidation around dense rebar cages inside porous CMU cells without bridging or voids, achieving a minimum compressive strength of 2,000 psi per ASTM C476.
- Structural steel framing relies on ASTM A992 high-strength low-alloy steel (Fy = 50 ksi) for wide-flange beams and ASTM A36 (Fy = 36 ksi) for carbon steel shapes, joined by ASTM F3125 Grade A325 or A490 structural bolts.
- OSHA 29 CFR 1926 Subpart R mandates that all structural steel columns be secured with a minimum of four anchor bolts, and prohibits two structural beams from sharing a single set of column connection holes without clipped angles or seat lugs to prevent collapse during erection.
Last updated: August 2026
8.2 Masonry & Structural Steel Construction
Commercial structures, industrial facilities, and heavy residential buildings in West Virginia frequently rely on engineered masonry and structural steel framing systems. Contractors must master the material properties, ASTM standards, testing methods, connection classifications, and OSHA erection safety standards (29 CFR 1926 Subpart R) governing structural masonry and steel assemblies.
1. Concrete Masonry Units (CMU): Nominal Dimensions & Geometry
Concrete masonry construction utilizes precast Portland cement blocks manufactured in standardized modular sizes (ASTM C90).
+-----------------------------------------------------------------------------+
| STANDARD CONCRETE MASONRY UNIT (CMU) |
| |
| |<---------------- 15-5/8" Actual --------------->| |
| | (16" Nominal with 3/8" Mortar Joint) | |
| +--+-------------------------------------------------+--+ |
| | | [Cell / Core] [Cell / Core] | | ^ |
| | | +---------------------+ +-----------------+ | | | |
| | | | | | | | | 7-5/8" |
| | | | Vertical Rebar & | | Grout Placement | | | Actual |
| | | | Grout Core | | Core | | | (8" Nom)|
| | | | | | | | | | |
| | | +---------------------+ +-----------------+ | | v |
| +--+-------------------------------------------------+--+ |
| |<-- 1-1/4" Face Shell -->| |<-- Web (1") -->| |
| |
| Nominal CMU Size: 8" Wide x 8" High x 16" Long |
| Actual Block Size: 7-5/8" Wide x 7-5/8" High x 15-5/8" Long |
| Standard Mortar Bed & Head Joint: 3/8" (0.375 Inches) |
+-----------------------------------------------------------------------------+
- Nominal vs. Actual Dimensions: Concrete masonry operates on a 4-inch modular grid. A standard nominal $8" \times 8" \times 16"$ CMU has actual physical dimensions of $7\text{-}5/8" \times 7\text{-}5/8" \times 15\text{-}5/8"$ (194 mm $\times$ 194 mm $\times$ 397 mm). The $3/8$-inch difference accounts exactly for the thickness of standard horizontal bed joints and vertical head joints.
- Hollow vs. Solid CMU Units (ASTM C90):
- Hollow Units: Net cross-sectional area is less than 75% of the gross cross-sectional area (typically 50%–70% solid). The hollow cores (cells) receive vertical reinforcing steel and grout.
- Solid Units: Net cross-sectional area is 75% or greater of gross cross-sectional area. Used for high-load bearing piers, elevator shafts, and fire walls.
2. Mortar Types (ASTM C270) & Grout Specifications (ASTM C476)
Mortar bonds masonry units together, seals joints against air and water penetration, and accommodates minor thermal movement. Mortar is specified by ASTM C270 under either the Proportion Specification (measured by parts of Portland cement, hydrated lime, and sand) or the Property Specification (tested by laboratory compressive strength).
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| ASTM C270 MORTAR TYPES — "MaSoN wOrK" |
| |
| MORTAR TYPE COMPRESSIVE STRENGTH (28-DAY) PRIMARY TRADE APPLICATION |
| ----------------------------------------------------------------------- |
| Type M 2,500 psi Below grade, retaining |
| (High Strength) walls, heavy axial loads |
| |
| Type S 1,800 psi Exterior load-bearing, |
| (High Flexural) high wind, seismic zones |
| |
| Type N 750 psi Above grade exterior, |
| (General Use) veneer, chimneys |
| |
| Type O 350 psi Non-loadbearing interior, |
| (Low Strength) historic tuckpointing |
| |
| Type K 75 psi Historic preservation only|
+-----------------------------------------------------------------------------+
[!TIP] The "MaSoN wOrK" Memory Rule: Take every second letter of the phrase MaSoN wOrK to remember the mortar types in decreasing order of compressive strength: M (2,500 psi) $\rightarrow$ S (1,800 psi) $\rightarrow$ N (750 psi) $\rightarrow$ O (350 psi) $\rightarrow$ K (75 psi).
Detailed Mortar Characteristics:
- Type M (2,500 psi): High compressive strength, but low workability and low flexural bond flexibility. Specified for unreinforced below-grade foundation walls, earth-retaining walls, manholes, and heavily loaded columns.
- Type S (1,800 psi): Highest flexural tensile bond strength ($> 200\text{ psi}$). Recommended for structures subjected to high lateral forces, including seismic zones, hurricane-force wind zones, exterior cavity wall veneers, and retaining walls.
- Type N (750 psi): Medium strength, high workability, and superior freeze-thaw resistance. Standard for general above-grade exterior walls, interior loadbearing walls, parapets, and chimneys.
- Type O (350 psi): High lime content, low compressive strength, excellent plasticity. Strictly limited to non-loadbearing interior partitions, historic restoration, and repointing (tuckpointing) soft historic brick.
Grout for Masonry (ASTM C476):
Unlike mortar (which holds blocks apart), grout fills the internal cavities (cells) of CMU to bond rebar to the masonry and create a solid monolithic composite structure.
- Compressive Strength: Minimum 2,000 psi at 28 days (ASTM C476).
- High Slump Requirement: Grout must have a high slump of 8 to 11 inches (measured with an ASTM C143 slump cone).
- Engineering Rationale: Dry CMU blocks rapidly absorb moisture upon contact. High water content provides the necessary fluidity to flow freely through narrow block cores and around dense rebar cages without forming voids or honeycombing.
- Fine Grout vs. Coarse Grout: Fine grout uses sand aggregate (for grout spaces $< 2$ inches); coarse grout incorporates pea gravel ($\le 3/8$-inch aggregate for grout spaces $\ge 2$ inches).
3. Structural Reinforcement, Bond Beams & Cavity Wall Drainage
Reinforced masonry incorporates deformed steel rebar, horizontal joint reinforcement, and engineered cavity wall drainage assemblies.
+-----------------------------------------------------------------------------+
| REINFORCED CMU CAVITY WALL CROSS-SECTION |
| |
| [Exterior Brick Veneer] [1"-2" Cavity] [Structural CMU Backup Wall] |
| | | | |
| | +----------------+ | |
| | | Fluid-Applied WRB/Air Barrier | |
| | | Rigid Insulation Board (XPS) | |
| | | | |
| | | +==============================+ | |
| | | | U-Block Bond Beam (Horiz Rebar) | |
| | | +==============================+ | |
| | | | |
| | | [Vertical Rebar in Grouted Cell] | |
| | | [Horiz Joint Wire @ 16" o.c.] | |
| | | | |
| +---------+ | +------------------------------+ | |
| | Weep | <---+---| Stainless Through-Wall Flashing | |
| | Hole | | | with 5/16" Drip Edge & Term Bar | |
| +---------+ | +------------------------------+ | |
| ======================================================================= |
| [Reinforced Concrete Foundation Wall / Footing] |
+-----------------------------------------------------------------------------+
Core Reinforcement Components:
- Bond Beams: Continuous horizontal U-shaped CMU blocks containing horizontal deformed rebar (typically 1 or 2 #5 or #6 bars) embedded in coarse grout. Positioned at floor levels, roof lines, sill levels, and above wall openings to tie the building perimeter together, distribute floor diaphragm loads, and resist out-of-plane wind pressures.
- Horizontal Joint Reinforcement: Welded wire assemblies ($9\text{-gauge}$ or $3/16\text{-inch}$ wire in ladder or truss configurations) embedded in mortar bed joints at 16 inches o.c. vertically to control shrinkage cracking.
- Cavity Wall Weep Holes & Drainage:
- Air Space: Minimum 1-inch to 2-inch clean, unobstructed drainage cavity between veneer and structural backup wall.
- Weep Holes: Located in the head joints immediately above all through-wall flashings. Spaced maximum 24 inches o.c. for open head joints (or 33 inches o.c. for plastic/wick weep tubes).
- Through-Wall Flashing: Impermeable membrane (stainless steel, copper, or rubberized asphalt) extending across the cavity, turned up at least 8 inches onto the backup wall, anchored with a termination bar, and extending 5/16 inch past the exterior brick face with a downward drip edge.
4. Structural Steel Framing: Shapes & Metallurgy
Structural steel framing provides high strength-to-weight ratios for multi-story commercial buildings, industrial warehouses, and long-span trusses.
+-----------------------------------------------------------------------------+
| STRUCTURAL STEEL SHAPES |
| |
| [WIDE FLANGE: W-SHAPE] [CHANNEL: C-SHAPE] [HOLLOW STRUCT: HSS] |
| +-------+ +-----+ +-------+ |
| |Flange | | | | | |
| +---+---+ +--+--+ | | |
| | | | | |
| | Web | Web | | |
| | | | | |
| +---+---+ +--+--+ | | |
| |Flange | | | +-------+ |
| +-------+ +-----+ (Tube / Pipe) |
| |
| Designation: W14x90 Designation: C10x30 Designation: |
| (14" Depth, 90 lbs/ft) (10" Depth, 30 lbs/ft) HSS 8x8x1/2 |
+-----------------------------------------------------------------------------+
Steel Material Specifications & Alloys:
- ASTM A36: Standard carbon structural steel with minimum yield strength $F_y = \mathbf{36\text{ ksi}}$ (36,000 psi) and tensile strength $F_u = 58\text{--}80\text{ ksi}$. Standard for angles, channels, structural plates, and base plates.
- ASTM A992: High-strength low-alloy structural steel with minimum yield strength $F_y = \mathbf{50\text{ ksi}}$ (50,000 psi), tensile strength $F_u = 65\text{ ksi}$, and a maximum yield-to-tensile ratio of $0.85$ (essential for seismic energy dissipation). The universal standard for all modern wide-flange (W-shape) beams and columns.
- ASTM A500 (Grades B & C): Cold-formed welded and seamless carbon steel structural tubing for Hollow Structural Sections (HSS) ($F_y = 46\text{--}50\text{ ksi}$). Used for columns, trusses, and bracing.
5. Structural Steel Connections: Bolting & Welding
Steel connections are engineered to transfer axial, shear, and moment forces between structural members.
+-----------------------------------------------------------------------------+
| STRUCTURAL STEEL BOLTED CONNECTIONS |
| |
| [SNUG-TIGHT] [PRETENSIONED] [SLIP-CRITICAL] |
| - Plates in solid - High initial tension - High clamping force |
| bearing contact. in bolt. produces friction |
| - Spud wrench or - Prevents nut - Zero slip allowed |
| few impact impacts. loosening under between faying faces. |
| - Static shear loads. vibration. - Dynamic/seismic loads.|
+-----------------------------------------------------------------------------+
High-Strength Structural Bolts (ASTM F3125):
- Grade A325: Heat-treated medium-carbon steel (tensile strength $120\text{ ksi}$). Standard for general construction.
- Grade A490: Quenched and tempered alloy steel (tensile strength $150\text{ ksi}$). Specified for severe heavy-load and seismic connections.
- Tightening Verification Methods:
- Turn-of-Nut Method: Bolts are brought to snug-tight, then rotated a specified additional fraction of a turn ($1/3$ to $2/3$ turn depending on bolt length and diameter).
- Direct Tension Indicators (DTI): Specially manufactured hardened washers with raised protrusions that compress under tension. A feeler gauge measures gap closure to verify tension.
- Tension Control (TC) Bolts: Feature a splined end engaged by a specialized electric shear wrench. The spline shears off cleanly when precise pretension is achieved.
Structural Welding (AWS D1.1 Structural Welding Code):
- Processes: SMAW (Shielded Metal Arc Welding / "Stick"), GMAW (Gas Metal Arc Welding / "MIG"), and FCAW (Flux-Cored Arc Welding - standard for field structural erection).
- Fillet Welds: Triangular cross-section welds joining two overlapping or perpendicular steel surfaces (specified by leg size in sixteenths of an inch).
- Groove Welds: Complete Joint Penetration (CJP) or Partial Joint Penetration (PJP) welds deposited between beveled plate edges, capable of developing the full tensile strength of the connected members.
- Inspection: Non-Destructive Testing (NDT) conducted by certified technicians includes Visual Inspection (VT), Magnetic Particle (MT), Ultrasonic Testing (UT), and Radiographic Testing (RT).
6. Open-Web Steel Joists, Metal Decking & OSHA Subpart R Safety
+-----------------------------------------------------------------------------+
| STEEL JOIST INSTITUTE (SJI) MATRIX |
| |
| SERIES DEPTH RANGE SPAN RANGE PRIMARY USAGE |
| ----------------------------------------------------------------------- |
| K-Series 8" to 30" Up to 60 Feet Standard floors & |
| (Standard) flat roofs |
| |
| LH-Series 18" to 48" Up to 96 Feet Commercial long- |
| (Longspan) span roofs |
| |
| DLH-Series 52" to 72" Up to 144 Feet Industrial deep |
| (Deep Longspan) clear spans |
+-----------------------------------------------------------------------------+
- Metal Decking & Composite Slabs: Corrugated galvanized sheet steel ($22\text{ to }16\text{ gauge}$) fastened to steel joists using puddle welds (arc spot welds with weld washers) or powder-actuated fasteners. When used in composite floor systems, headed shear studs (Nelson studs) are welded through the metal deck to the top beam flange to mechanically lock the cured concrete slab to the steel beam.
OSHA Steel Erection Safety Mandates (29 CFR 1926 Subpart R):
- Four-Bolt Column Anchor Mandate (29 CFR 1926.755): All structural steel columns must be anchored by a minimum of four (4) anchor bolts / rods to provide base stability and prevent column tip-over before structural framing is tied in.
- Double Connections (29 CFR 1926.756): When two structural steel members share common connection holes on opposite sides of a column web or girder, the connection must be engineered with a clipped end angle or an extra permanent seat lug so that one member remains structurally supported while the connecting member is pinned and bolted.
- Fall Protection Trigger Elevations in Steel Erection (29 CFR 1926.760):
- General Steel Workers (Bolters, Welders, Detailers): Protected by personal fall arrest systems (PFAS) at 15 feet (4.6 m) above a lower level.
- Connectors: Must wear PFAS and be provided fall protection equipment at heights between 15 and 30 feet (or 2 stories), but are not legally mandated to tie off until exceeding 30 feet or two stories.
- Controlled Decking Zones (CDZ): Permitted for initial metal deck installation between 15 and 30 feet.
Test Your Knowledge
Under OSHA Steel Erection Standard 29 CFR 1926.756, what safety feature is mandatory when two structural steel members share common connection holes on opposite sides of a column web or beam?
A
B
C
D
Test Your Knowledge
According to ASTM C270, which mortar type provides the highest flexural bond tensile strength and is recommended for exterior load-bearing masonry walls subject to high lateral wind or seismic forces?
A
B
C
D
Test Your Knowledge
Why does ASTM C476 mandate that masonry grout placed inside Concrete Masonry Unit (CMU) cells have a high slump of 8 to 11 inches, compared to standard structural concrete which typically has a 3 to 5 inch slump?
A
B
C
D