8-AMENDMENT2.pdf

AMERICAN LEGION POST 673

PENBID PROJECT # 251713

AMENDMENT NO. 2

Commercial Floor System Structural Engineering & Material Guidelines for a New Public Assembly (American Legion) Facility

Span Specification: 18 Feet | Live Load Mandate: 100 PSF

1. Structural Load Requirements

This building falls under the regulations of the International Building Code (IBC). Because these venues house assembly spaces (halls, dance floors, dining rooms, and bar areas), the structural configuration demands rigorous performance thresholds:

Live Load Mandate (IBC Table 1607.1): Assembly areas with movable seating, exhibition halls, or social floors require a minimum uniform live load of 100 pounds per square foot

(psf). Live load reductions are strictly prohibited for public assembly areas; framing must withstand 100 psf simultaneously across the full footprint.

Deflection Constraints: To control floor bounce and preserve rigid finished surfaces, structural members are engineered to strict deflection criteria, typically limited to L/360 under live load and L/240 under total load.

2. Approved Engineered Floor Systems (18-Foot Span)

The building is 36 feet wide with a wide flange beam in the center for an 18-foot span. To clear an

18-foot span reliably under commercial loads, three engineered systems are structurally viable for a new build. Profile depths should be intentionally maximized where possible; increasing depth inherently stiffens the floor, enabling wider joist spacing and reducing absolute structural weight.

One of three systems is required and listed as:

Floor System Type Recommended

Depth

Required

Spacing

Key Commercial Benefits

Engineered I-Joists

(e.g., TJI Series)

14" to 16" 12" to 16" o.c. Lightweight, uniform, cost-effective initial lumber package. Requires precise drilling for mechanical utilities.

Open-Web Floor Trusses

(Wood/Metal Web)

16" to 18" 16" o.c. Excellent for assembly buildings.

Open channels allow complex

HVAC, plumbing, and fire lines without drilling.

Laminated Veneer Lumber

(LVL Composite)

11-7/8" to 14" 12" o.c. Extreme density and load capacity.

Specified when a low-profile floor thickness is micro-managed.

3. Structural Subfloor Architecture

Material Grade & Spec: High-Density, Exposure-1 rated structural plywood or engineered

OSB panels (e.g., premium commercial subfloor sheets) are required.

Thickness Requirements: A minimum thickness of 23/32-inch (3/4-inch nominal) is required for spans framed up to 16 inches on center. If truss layouts utilize wider 19.2-inch or 24-inch spacing, subfloor thickness must expand to 7/8-inch or 1-1/8-inch premium panels.

Profiling & Joints: Panels must have matched Tongue-and-Groove (T&G) edge profiles to mechanically interlock adjacent sheets, neutralizing edge dipping and vertical deflection under concentrated pedestrian weight.

Fastening Schedules: Panels must be continuously adhered to the upper framing member chord using a heavy-duty structural polyurethane subfloor adhesive. Fasten using structural subfloor screws spaced tightly at 6 inches along outer perimeter panel lines and 12 inches across inner intermediate supports. Leave a strict 1/8-inch perimeter gap at all sheet boundaries to allow expansion..

4. Commercial Composite Finished Flooring System

SPC Structural Specifications:

Commercial Wear Layer: Specify a robust 20-mil to 28-mil commercial top wear layer to guarantee lifetime defense against scuffing, scraping, and high-volume pedestrian shear stresses.

Acoustic Absorption: Utilize planks built with integrated closed-cell acoustic backing (e.g., IXPE foam layers) to dampen footstep clicks and control echo inside wide open assembly areas.

Underlayment Mechanics:

Pre-Padded Floating Systems: If the chosen commercial SPC material contains a pre-attached underlayment pad, do not roll out an extra soft underlayment cushion. Excessive cushion layer flexibility induces severe articulation along click-lock tongue-and-groove joints, causing shearing under heavy localized dynamic crowd loads. Lay down only a 6-mil polyethylene sheet vapor barrier, overlapping boundaries by 8 inches, taped securely.

Bare-Back Systems: If installing pad-free composite sheets, implement a high-density

IXPE or commercial virgin rubber underlayment confined tightly between 1mm and 2mm.

Avoid soft, elastic residential padding layouts.

Expansion Mitigation & Curing: Any underlying gypsum concrete layer must be fully cured and tested for strict residual relative humidity metrics. Given the extensive room footprints of assembly spaces, standard code dictates distinct perimeter expansion gaps (10mm to

15mm) alongside physical expansion moldings across designated transition planes to intercept thermal buckling or floor lock.