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Renovation of Wood Trusses

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Instructor Information: Alexander Newman, P.E., F.ASCE

This webinar was co-sponsored by ASCE's Structural Engineering Institute and ASCE Continuing Education

Course Length: 1.5 Hours

Purpose and Background

Wood trusses, common in existing buildings with long clear spans, are often found to be deteriorated or in need of strengthening. The webinar explores typical truss problems and methods of their remediation. The main focus of the presentation is on the multiplemember heavy trusses (because of difficulty of their replacement), but renovation of lightweight metal-plate-connected trusses is examined as well.

Truss deterioration can result from a variety of causes, including lack of maintenance, roof leaks, wood decay, insect infestation, and defects in the original construction. Trusses may need strengthening when the original design used lower structural loading than the present service dictates, or was based on overly optimistic allowable stresses. Sometimes strengthening is required because of a failure caused by defective design or construction, natural disasters, or even by careless renovations.

Starting with an overview of the common truss types, the instructor proceeds to an examination of their common problems and then to repair and strengthening methods. Among the methods discussed are member replacement and augmentation, epoxy repair, stitching, clamping, and post-tensioning. The problems of bowstring trusses, one of the most troublesome types of wood structures, receive special attention. The participants examine a real-life case study, where both repair and strengthening of a building with multiple-member trusses were needed.

Learning Outcomes/Benefits

- Become familiar with common problems of wood trusses 
- Learn about various methods of truss strengthening and repair
- Understand how natural and man-made wood defects affect structural behavior of wood trusses 
- Discover why bowstring trusses frequently require attention and what can be done about their retrofit 
- Learn what caused changes in the allowable lumber stresses over the years and how these changes contribute to problems of timber trusses 
- Examine a case study, where both repair and strengthening of multiple-member trusses were needed

Intended Audience

Structural and civil engineers, architects, facility managers, and building officials seeking to broaden their knowledge of the issues involved in renovation of wood trusses will benefit from this webinar. The discussion is easy to follow, and the many technical issues involved will not overwhelm those who are not engineers.

Webinar Outline

- Introduction: Types of wood trusses, references
- Why renovate wood trusses? 
- Wood defects and methods of their repair 
- Repair and strengthening of heavy trusses
  – Typical problems
  – Evaluation
  – Methods and techniques
  – A case study
  – Renovation of bowstring trusses 
- Repair and strengthening of light trusses
- Conclusion, Q&A