ASTM D198
Wood Testing Fixtures

 Standard Test Methods of Static Tests of Lumber in Structural Sizes - PDF

ASTM D198 provides standardized methods for performing various static mechanical tests on structural-sized lumber.
These tests determine the strength and stiffness properties of lumber under different loading conditions — including bending, compression, tension, and shear — and are critical for the evaluation of lumber intended for use in construction applications.

Purpose of ASTM D198

The goals of ASTM D198 are to:

• Measure fundamental mechanical properties like modulus of elasticity (MOE) and modulus of rupture (MOR) for full-sized lumber.

• Test lumber in a way that reflects real-world structural loading conditions.

• Provide reliable, standardized data for the grading, classification, and design of wood structures.

• Support lumber manufacturers, building code officials, and engineers in assessing material quality and performance.

Unlike small clear wood tests (e.g., ASTM D1989), ASTM D198 focuses on actual structural sizes like 2x4s, 2x6s, beams, and posts.

Equipment Required for ASTM D198 Testing

To perform ASTM D198 testing, the following equipment is typically required:

• Universal Testing Machine or Specialized Structural Testing Frame:
  Must be capable of applying large forces for static loading (often up to hundreds of kN or more).

• Hydraulic Actuators (for large specimens):
  Needed to apply controlled static loads in bending, compression, or tension.

• Load Cells:
  For precise measurement of applied force.

• Deflection and Strain Measuring Devices:

  • Extensometers

  • Linear Variable Differential Transformers (LVDTs)

  • Dial gauges

• Special Fixtures and Supports:

  • 3-point and 4-point bending fixtures

  • Compression platens for end loading

  • Tensile grips/clamps for pulling structural members without slipping or crushing

• Conditioning Chamber (optional but recommended):
  To prepare specimens at standard temperature (20°C) and humidity (65% RH) conditions.

Specimens

• Structural lumber sizes, such as 2x4, 2x6, 4x6, 6x6, etc.

• Specimens should be free of severe defects unless intentionally testing lower grades.

• Moisture content is measured and recorded, as wood strength is highly moisture-dependent.

General Test Procedures for ASTM D198

ASTM D198 includes several types of static mechanical tests:

1. Static Bending (Flexural Testing):

   • Load the lumber in simple beam configuration (either 3-point or 4-point loading).

   • Measure maximum load to failure and calculate:

     • Modulus of Elasticity (MOE)

     • Modulus of Rupture (MOR)

2. Compression Parallel to Grain:

   • Load specimen axially along the grain direction.

   • Measure compressive strength and stiffness.

3. Tension Parallel to Grain:

   • Pull specimen lengthwise to measure tensile strength and stiffness.

4. Shear Parallel to Grain:

   • Apply loads to test the material’s resistance to shear forces within the grain plane.

5. Compression Perpendicular to Grain:

   • Apply force perpendicular to the grain to evaluate bearing strength (important for connections and posts).

Each test specifies loading rates, support conditions, and specimen dimensions in detail.

Results and Reporting

A proper ASTM D198 report includes:

• Lumber species, grade, and dimensions.

• Moisture content and density at the time of testing.

• Load-deflection curves.

• Maximum load and corresponding stress values.

• Calculated material properties (MOE, MOR, compressive strength, tensile strength, shear strength).

• Description of failure modes (e.g., fiber buckling, splitting, crushing).

Related ASTM and Similar Testing Standards

Several other ASTM standards complement or are closely related to ASTM D198:

• ASTM D1989 – Test Methods for Static Tests of Lumber in Structural Sizes Using Small Clear Specimens:
  Focuses on small, defect-free wood specimens rather than full-sized members.

• ASTM D4761 – Standard Test Methods for Mechanical Properties of Lumber and Wood-Base Structural Material:
  A broader suite of mechanical property tests including fastener withdrawal and bearing tests.

• ASTM D1980 – Test Methods for Strength Properties of Adhesives in Plywood-Type Construction:
  Related to wood bonded structures.

• ASTM D2555 – Standard Test Methods for Establishing Clear Wood Strength Values:
  Statistical determination of clear wood strength properties (often used for design values).

• ASTM D2915 – Practice for Sampling and Data Analysis for Structural Wood:
  Provides statistical methods to analyze mechanical test data for lumber.

• ASTM D5456 – Specification for Evaluation of Structural Composite Lumber Products:
  Relevant for engineered wood products like LVL (Laminated Veneer Lumber) and PSL (Parallel Strand Lumber).

• ISO 3349 – Structural Timber — Determination of Modulus of Elasticity in Static Bending:
  The international equivalent of ASTM static bending tests for wood.

Applications of ASTM D198 Testing

Industries and fields that utilize ASTM D198 testing include:

• Residential and Commercial Building Construction

• Timber Bridges and Heavy Timber Construction

• Prefabricated Wood Components Manufacturing

• Structural Engineering and Code Compliance

By applying ASTM D198, engineers and manufacturers ensure that full-sized lumber components will perform reliably under the expected service loads in real-world structures.

Conclusion

ASTM D198 provides the foundation for evaluating the static mechanical properties of full-size lumber under realistic structural loading conditions.
It ensures consistency and reliability in lumber used for residential, commercial, and industrial construction.
When combined with standards like ASTM D4761 and ASTM D2555, ASTM D198 plays a critical role in modern wood design and quality control.