Joseph R. Loferski

Technologies for Wood Preservation in Historic Preservation

Because of the abundant forests of the world, wood is one of the most common materials found in historic buildings. Wood is relatively easy to fabricate into beams, columns, and roof systems using simple hand tools. However, because of its biological origin, wood is one of the most complex constructions materials. It is produced by thousands of different species of trees, and each type of wood has unique properties. Wood has an affinity for moisture and this can lead to biological deterioration caused by insects and decay fungi. This chapter presents information on understanding and preventing the mechanisms of wood deterioration in historic buildings. The chapter includes a discussion of wood preservation and technology, including wood finishes and wood preservative treatments, diffusible preservatives, and naturally durable wood species. A brief discussion about the repair of deteriorated timbers in buildings is also included.

Strength of Sawn Lumber and Wood Composite Dowel Connections Loaded Perpendicular to Grain. I: NDS Design Equations

Connections are important design elements in timber engineering. Connections loaded perpendicular to grain for structural composite lumber (SCL) materials have received little attention. Connection strength can be determined as the minimum of the Technical Report 12 (TR-12) equations, a generalized form of the National Design Specification (NDS) connection equations, or a shear stress check for reduced beam section. This paper presents test results and compares the 5% offset yield and capacity of double-shear single bolt connections with steel side plates loaded perpendicular to grain to TR-12 equations for solid-sawn lumber and two SCL products. Testing considered three different span/depth ratios and three different loaded edge distances. Splitting failures were observed at the 4D loaded edge distance and mixed mode failures contained splitting at the 7D and 10D loaded edges. The allowable shear stress values dominated the connection at the 4D loaded edge distance and were conservative in some cases. Comparing the TR-12 equations to experimental connection strength, there was little difference for the span/depth ratios and main member materials. Different loaded edge distances demonstrated significant differences between the TR-12 equations and experimental values. The choice of displacement limit for the capacity dowel bearing strength was identified as an important factor in the TR-12 equations.

Strength of Sawn Lumber and Wood Composite Dowel Connections Loaded Perpendicular to Grain. II: Fracture Mechanics Equations

Splitting failure modes of perpendicular to grain bolted connections have received little attention when compared to splitting modes in parallel to grain connections. Previous research by the authors tested a series of single bolt, double shear perpendicular to grain connections of machine stress rated (MSR) lumber, laminated veneer lumber (LVL), and parallel strand lumber (PSL). Many of the experimental tests resulted in failure by splitting. Two fracture mechanics based models for connections proposed elsewhere were applied. Input parameters for the models were generated by testing matched sections to the connection strength samples. Input properties for the Van der Put model included shear modulus and Mode I fracture energy. Inputs for the Jensen model included shear modulus, modulus of elasticity, Mode I fracture energy, and tension perpendicular to grain strength. Mode I fracture energy of PSL was markedly greater than the energy associated with MSR Lumber and LVL. The Van der Put model overpredicted the experimental connection strength by at least 77%. The Jensen model was found to most accurately predict the connection strength over the entire range of configurations tested. Comparing the Van der Put and Jensen models to the previous work using the national design specification, the Jensen model performed the best in terms of accuracy. The tension perpendicular to grain strength and the method of fracture energy calculation may be important parameters for the capacity of perpendicular to grain loaded wood members.

Inspection of Metal Plate-Connected Wood Trusses in Residential Construction

AbstractThe engineered nature of metal plate–connected wood trusses may not be well understood by installers and other trade professionals, which can result in installation errors. Truss manufacturing, handling, and installation specifications are included in national design standards and truss misinstallation is therefore a code violation. Through use of the Delphi method, an expert-validated inspection methodology was developed by interviewing code officials, home inspectors, and truss manufacturers. The results included (1) identification of truss installation errors most likely to occur, (2) best practices for inspection methods, (3) determination of authoritative documentation, and (4) validation of the research methods. The inspection should begin at the top of the structure and move in a circular, systematic pattern downward through each level, and should concentrate on the identified high-risk aspects of truss installation. Installation problems include the following: broken or cut webs and chords...

Inspection of I-Joists in Residential Construction

AbstractI-joists may be used as floor joist and roof-rafter members in residential construction but require different installation practices compared with solid-sawn lumber because of I-joist geometry and design. The building codes in this paper contain clear specifications for the installation of sawn-lumber products. Because I-joists are proprietary and installation requirements vary by brand, manufacturer literature is incorporated by reference into the building codes discussed herein. The engineered and proprietary nature of I-joists may be unfamiliar to carpenters and other trade professionals, resulting in installation errors. I-joist installations that do not comply with manufacturer specifications are considered code violations. Through use of the Delphi method, an expert-validated inspection methodology was developed by interviewing code officials, home inspectors, and engineered-wood-product manufacturers. This paper summarizes the results, including best practices for inspection methods and I-j...

Development of a Methodology for the Visual Inspection of Engineered Wood Products and Metal Hangers in Residential Construction

This paper presents the development of a visual inspection methodology for engineered wood products that are commonly used in residential construction in the USA. Engineered wood products include wood composite structural elements such as I-joists, oriented strand board, and structural composite lumber products, and metal plate connected wood trusses. Due to the proprietary nature of wood composite engineered products, there are no uniform standards between different manufacturers for installation and use. If improper installation methods are used, engineered wood products may not be able to safely carry design loads. Improper use or modifications constitute prescriptive code violations. Construction errors that result from the unique installation requirements demonstrate the need for specific inspection methods to detect installation errors early in the construction process. The goal of this research is to develop an expert-validated visual inspection methodology, associated knowledge base, and software application for selected engineered wood products and hanger hardware for non-compliance at the pre-drywall stage of new residential construction. A modified Delphi method was used to solicit and refine inspection methods from subject matter experts. Based on these results, an inspection method and computer software application were developed. The method establishes a systematic expert-validated inspection procedure that identifies known high-risk areas for installation problems for engineered wood products. The software contains the instructions for implementing the inspection method, a reference library of authoritative installation guidelines and illustrations, the ability to document observed defects, and a vehicle to create a report. The experts validated the method and software application, and confirmed the usefulness for detecting construction errors.

Light Gauge Steel Reinforcement for Improperly Cut I-joists

One of the biggest problems with the use of wood composite I-joist products are issues related to improper installation. There are restrictions on the size of holes which can be placed in the web of the I-joist while the flange of the I-joists must remain uncut. However, these instructions are not always explicitly followed on the construction site. When errors are made, such as placing a toilet drain directly over an I-joist, the resulting solution is difficult and complex, requiring engineering expertise. Two new light gauge steel reinforcement devices have been developed to increase the bending capacity of I-joists which have been cut in the web and flange, respectively. These devices were tested to determine the bending strength and stiffness compared to uncut joists. The flange reinforcer had a maximum load 35.4% less than the uncut joist, the single web reinforcer had a maximum load 19.1% less than the uncut joist and the double web reinforcer had a maximum load greater than the uncut joists. Looking at the loads at the L/360 deflection limit, the flange reinforcer load was 10% less than the uncut joist, while both web reinforcers were greater than the uncut joist.