TimberLogic Log Wall Performance Estimator (LWPE)

posted Dec 27, 2012, 2:22 PM by TimberLogic LLC   [ updated Dec 28, 2012, 4:19 AM ]

Demonstrate whether the performance of a log wall system meets or exceeds the requirements of ICC400.

The Log Wall Performance Estimator (LWPE) is a report that describes and analyzes a specific log building system (a specific log profile, wood species, and moisture content). It reports the performance of an individual log profile in a manner designed to assist outside engineers and code officials evaluate the building system, help refine product development, and provide designers with critical capacities to be considered during plan layout.

The first page of the LWPE report provides the properties of the log profile, while the next 9 pages report the capacity of the log wall as an assembly.

The resulting report shows the log profile with grading criteria and associated design stress values, establishes settling allowances, calculates the wall’s fire-resistance rating and thermal properties. The report also includes design capacities for the log in simple span conditions (e.g., headers, interior girders, etc.), and provides information relating to fastening options.

The LWPE provides design limitations for layout of a log structure in a form that can be used by designers during the creation of the plans. The report consists of

  • A log profile sheet with an illustration of the wall-log and data pertaining to the individual component (section properties, weight, visual grading criteria, design stress values, average wall thickness, thermal value, fire-resistance rating, and settling analysis).
  • An analysis of the structural capacity of a wall-log for both horizontal and vertical load paths, expanded to demonstrate allowable loading (plf) for 7 spans.
  • Tables presenting maximum allowable spans for wall-logs of three structural grades for 1-, 2-, and 3-course beams/headers supporting vertical loads. Additional information is provided for bolted headers.
  • A presentation of the estimated performance of the log wall as an assembly in response to horizontal loading.

Using the Log Wall Report

The first page of the report provides the properties of the log profile, while the next 9 pages report the capacity of the log wall assembly.

PAGE 1: Shows the log profile and physical properties relating to its species, strength, size, shape, and moisture content. The data on this page is generated to comply with ICC code requirements.

  • Building codes have long required that structural products be certified as to their strength. This assessment is made for wood products through stress grading.
  • In addition to the design stress values, the slope of grain and maximum allowable knot size are calculated in the report in accordance with applicable American Society for Testing & Materials (ASTM) standards. Certified graders on the your log production line use this criteria to visually inspect each log and assign a grade.
  • The education component here is to make sure that the designer specifies the grade for each log placed in the structure, the certified grader marks the log with an identifying mark, and the builder installs that grade of log in the particular position.
PAGES 2 TO 4: Provide designers with tables relating to the structural capacity of the log profile.
  • Sections 1.2 through 1.4 provide reference tables for the structural capcity of a single log, then relate that capacity to an applied load for a specific span length.
PAGE 3 contains tables that report the number maximum allowable header spans for the wall-log for different grades and different multiples of log used in a header.
  • Beginning on page 5, Section 1.5 combines the log properties from Section 1.1 (page 1) with the standard fastening schedule to define the maximum unsupported length of a sidewall (typically the eave wall, or one facing the wind). The fastening schedule may become slightly restricted due to high wind speeds.
  • Section 1.6 on page 6 explores the structural capacities of the log wall under horizontal loads. The primary focus of this section is to establish the required fastening schedule to match the maximum allowable wall span and to satisfy the load zones in shear walls.
  • Pilasters are analyzed (page 8) as a method for supporting the log wall. Also referred to as a stiffener post, pilasters are an alternative where interior shear walls are not available.
  • Generally speaking, shear walls that are at least as long as they are high will not require special fastening requirements. However, shorter wall segments or walls with openings can require twice as many fasteners to account for the shorter length of wall available to resist the shear loads.
PAGES 10 & ON...
The detailed analysis of the log wall system that is summarized on pages 1 through 9. These pages are provided as substantiation for design professionals who need to know how the summary data was generated. These pages should be included in copies of the Log Wall Performance Estimator that is provided to anyone involved with structural analysis and code enforcement.