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  • 1. DESIGN ENGINEERS BENEFIT FROM WOODREHABILITATE INVESTIGATE SCIENCE AND TECHNOLOGY KNOWLEDGE Milan Vatovec www.sgh.com Introduction  Objective to show importance of understanding wood as a material in engineering projects and applications  Real projects used as case-study examples: – Evaluation of wood biodeterioration – Structural assessment, in-situ stress grading – Dimensional stability (moisture movement) investigations – Analysis, design, repair and rehabilitation of wood structures. © 2007 Simpson Gumpertz & Heger Inc. Proprietary and Confidential 1
  • 2. Wood Science, Technology and Engineering Applying knowledge pertaining to physical, mechanical, and chemical properties of wood and wood products, as well as historic and current construction practices, to engineering applications. Organic material: behavior is influenced by physical and mechanical properties, the natural growth characteristics, and effects of biological and other deterioration agents. Because of its complexity, its material composition, orthotropic nature, and variable response to environmental conditions, optimal use of wood often benefits from special knowledge requiring integration of material science, structural analysis and design, and construction practices. Rare amongst most structural engineers © 2007 Simpson Gumpertz & Heger Inc. Proprietary and Confidential Biodeterioration of Wood - General  Microbiological agents: fungi (rot), insects, bacteria, marine borers.  Risk of attack varies depending on application (end use) and on present conditions.  Special conditions needed for fungal deterioration: temperature, oxygen, right amount of moisture, food source.  Often, insect, fungal, or marine-borer attack can be hidden (is not visible from the outside of the member), and the structural integrity can already be lost - can result in sudden, catastrophic failures.  Incipient decay is a significant factor – Material properties can be significantly affected without change in appearance © 2007 Simpson Gumpertz & Heger Inc. Proprietary and Confidential 2
  • 3. Fungal Decay © 2007 Simpson Gumpertz & Heger Inc. Proprietary and ConfidentialDamage Is Often Buried or Hidden © 2007 Simpson Gumpertz & Heger Inc. Proprietary and Confidential 3
  • 4. Could Also Be Hard to Reach © 2007 Simpson Gumpertz & Heger Inc. Proprietary and ConfidentialIt Could Also Be Visible and Causation Known © 2007 Simpson Gumpertz & Heger Inc. Proprietary and Confidential 4
  • 5. Insect Attack © 2011Simpson Gumpertz & Heger Inc. Proprietary and ConfidentialMarine Borers © 2007 Simpson Gumpertz & Heger Inc. Proprietary and Confidential 5
  • 6. Deterioration of Architectural Members Damage could be economically staggering even if not structurally significant Problems frequently due to poor waterproofing design or construction detailing Contractor or designer at risk of being blamed for a deficient product that resulted in a multi-million dispute over decay damages (e.g. window and framing problems with condominium structures) Engineer must not only be able to recognize and correct the damage, but also to evaluate the cause, extent, and the ensuing cost to repair the damage – understanding wood as a material is essential. © 2007 Simpson Gumpertz & Heger Inc. Proprietary and ConfidentialRotting of Wood Members Due to Exposure to Water © 2007 Simpson Gumpertz & Heger Inc. Proprietary and Confidential 6
  • 7. Understanding the Type and Extent of Damage © 2007 Simpson Gumpertz & Heger Inc. Proprietary and ConfidentialRemedial Solutions Need to Consider theUnderlying Cause of Problem © 2007 Simpson Gumpertz & Heger Inc. Proprietary and Confidential 7
  • 8. Wood Biodeterioration - Takeaways  Usually caused by water infiltration through isolated leaks, condensation, systemic breaches, etc.  Important to understand the exposure, risks, causation, extent, and degree of problem before offering design, detailing, or remedial solutions.  Water path is not always obvious: wood-educated inspector must be able to recognize all signs of distress, should understand current and historic methods of construction, and be able to recognize potential locations and conditions for attack.  Understanding biodeterioration mechanisms helps prevent wood loss in service, allows effective evaluation and remediation, and enables prediction of remaining useful life: crucial for wood applications. © 2007 Simpson Gumpertz & Heger Inc. Proprietary and Confidential Natural Growth Characteristics of Wood Reclamation, renovation, and redevelopment of old timber buildings is resulting in the need for evaluation and reuse of old wood and timber structural members. Drawings are seldom available – engineer must assess the condition and evaluate wood members for the new role (e.g. higher loads due to change of use). Conventionally educated engineers lack understanding of particularities associated with wood species, natural growth characteristics, their effect on member strength, etc. © 2007 Simpson Gumpertz & Heger Inc. Proprietary and Confidential 8
  • 9. Splits, Shakes, Slope of Grain © 2007 Simpson Gumpertz & Heger Inc. Proprietary and ConfidentialKnots, Reaction Wood © 2007 Simpson Gumpertz & Heger Inc. Proprietary and Confidential 9
  • 10. In-Situ Stress Grading  Ability to accurately assess the existing member strength can be a powerful tool, often resulting in significant savings due to less required retrofit.  ASTM D 245 – Standard Practice for Establishing Structural Grades and Related Allowable Properties for Visually Graded Lumber  Knot size, species, wood defects and their location, slope of grain, moisture content are considered to arrive at allowable strength for individual members – typically higher than based on conventional grading.  Extremely useful in certain situations (small areas seeing large loads, condition assessments, use of reclaimed timber, etc.) © 2007 Simpson Gumpertz & Heger Inc. Proprietary and Confidential In Situ Wood Stress Grading (ASTM D 245)No. N e, C am ode D ensions (in.) im Classification MC R / in. ings SlpName, Code No. of G rn Knots onN Classification arrowFace Dimensions (in.) MC EdgeKnots onw Knots on NarrowM Edge Knots onW Face Shakes Shakes Checks Rings / in. Slp of Grn ideFace Face Knots on wide Face Middle Knots on Wide Face C iddle ide hecks Splits Splits Width Depth Width Depth Length(in.) (D , B S P T, S ) IM & , & R (%) 1in: S Length (in.) Location ize (DIM, B&S, P&T, SR) (%) Size 1 in: Size Location Location S Size ize Location Size Location Location (in.) (in.) (in.)(in.) (in.) (in.) 1 par 6 12 96 B&S 11 8 12 2 1.75 3 1 1.5 2 2 par 6 12 96 B&S 11 7 15 1.5 1 2 1 1.5 11 par 6 12 96 B&S 11 8 3 12par 6 2 12 96 B&S 11 1.75 6 15 2 3 0.5 2.5 1 1 1.51.5 1.5 2 4 par 6 12 96 B&S 11 8 9 0.5 2 1 1 1.5 2 5 par 6 12 96 B&S 11 9 14 0.25 1.75 3 1 1.5 2 6 par 6 12 96 B&S 11 11 12 1 1.25 2 1 1.5 1 7 par 6 12 96 B&S 11 12 11 1 1.75 2.5 1 1.5 1.5 8 par 6 12 96 B&S 11 8 15 2 2 1 1 1.5 2 9 par 6 12 96 B&S 11 7 9 1 1 3 1 1.5 2 10 par 6 12 96 B&S 11 8 12 1.5 1.5 2 1 1.5 2 11 par 6 12 96 B&S 11 9 8 2 0.5 2.5 1 1.5 2 12 par 6 12 96 B&S 11 8 18 3 0.25 3 1 1.5 1 13 par 6 12 96 B&S 11 8 19 2 1.75 1 1 1.5 1.5 14 par 6 12 96 B&S 11 6 12 1 1.75 3 1 1.5 2 15 par 6 12 96 B&S 11 8 8 2 0.5 2 1 1.5 2 16 par 6 12 96 B&S 11 9 10 1 1.25 2.5 1 1.5 2 17 par 6 12 96 B&S 11 9 12 1 1.75 3 1 1.5 1 18 par 6 12 96 B&S 11 8 12 2 1.75 1 1 1.5 1.5 19 par 6 12 96 B&S 11 8 11 1 0.75 2.5 1 1.5 2 20 par 6 12 96 B&S 11 8 12 0.5 1.75 3 1 1.5 2 ALLOWABLE PROPERTIES No. Species Fb Fcpar No. FcperpFb Species Fcpar Fv Fcperp Fv Ft Ft E E (psi) (psi) (psi) (psi) (psi) (1000 psi) (psi) (psi) 1 SYP(psi) 1678 1172 (psi) 602 116 (psi) 1126 1566 (1000 psi) 2 SYP 1849 1295 602 129 1241 1566 1 SYP 1678 1172 3 SYP 602 1678 1234 116 602 129 1126 1126 1566 1566 4 SYP 1289 1018 602 116 865 1409 5 SYP 1800 1172 602 116 1208 1566 6 SYP 1678 1265 602 129 1126 1566 7 SYP 1484 1141 602 129 996 1566 8 SYP 1678 1295 602 116 1126 1566 9 SYP 1289 1018 602 116 865 1409 10 SYP 1678 1265 602 116 1126 1566 11 SYP 1289 1018 602 116 865 1409 12 SYP 1289 1172 602 129 865 1409 13 SYP 1678 1295 602 129 1126 1566 14 SYP 1678 1172 602 116 1126 1566 15 SYP 1289 1018 602 116 865 1409 16 SYP 1484 1141 602 116 996 1566 17 SYP 1678 1172 602 129 1126 1566 18 SYP 1678 1265 602 129 1126 1566 © 2007 Simpson Gumpertz & Heger Inc. Proprietary and Confidential 19 SYP 1484 1141 602 116 996 1566 20 SYP 1678 1172 602 116 1126 1566 10
  • 11. Hygroscopic Nature of Wood Wood, when under FSP, undergoes dimensional changes in service due to fluctuations in temperature and humidity of the environment. Wood floor and finish performance very sensitive to system design intricacies and installation procedures Environmental control during installation and in service critical. Compatibility between materials and components is key © 2007 Simpson Gumpertz & Heger Inc. Proprietary and ConfidentialFloors Buckle, Delaminate, Move © 2007 Simpson Gumpertz & Heger Inc. Proprietary and Confidential 11
  • 12. Compatibility, Restraint, Movement © 2007 Simpson Gumpertz & Heger Inc. Proprietary and Confidential Hygroscopic Nature of Wood - Takeaways Designer (or the installer) must be aware of the sensitivity to moisture fluctuations and should anticipate wood movement in service – cause of a lot of investigations involving responsibility allocation. Problems with wood flooring and woodworking finishes most common troubleshooting projects, often caused by incompatible materials. Development of new systems: lack of behavioral and compatibility consideration in design can be disastrous. Shrinkage or swelling can cause structural distress as well Special engineering techniques: dimensional back- calculations, FEM, etc. Wood-behavior knowledge and familiarity with standard design and construction practices are essential. © 2007 Simpson Gumpertz & Heger Inc. Proprietary and Confidential 12
  • 13. Design of New Wood Structures, Repair and Rehabilitation of Existing Wood Structures  Wood design offered maybe as a one-semester course at many accredited engineering schools in the US – covers codes, analysis and design methodology  Little emphasis placed on the orthotropic nature of the wood, detailing, old construction practices, analysis of existing structures, heavy timber structures and connections, etc.  Literature is available, but few use it  Several examples discussed here: © 2007 Simpson Gumpertz & Heger Inc. Proprietary and Confidential Design of New Wood and Timber Structures Design of new, large residential homes: many new McMansions require complex engineering – detailing important Can we really neglect seismic forces? © 2007 Simpson Gumpertz & Heger Inc. Proprietary and Confidential 13
  • 14. Design of New Wood and Timber Structures Wood structures often exposed to view and may require unorthodox structural solutions – understanding of available options important. © 2007 Simpson Gumpertz & Heger Inc. Proprietary and Confidential Troubleshooting Engineer must be able to recognize weak points in the existing timber structures (notched members, tension members, serious natural defects, unorthodox connections) both as a designer and as an investigator, even though failure may not be imminent. © 2007 Simpson Gumpertz & Heger Inc. Proprietary and Confidential 14
  • 15. Troubleshooting Imminent failures must be recognized and remediated. © 2007 Simpson Gumpertz & Heger Inc. Proprietary and Confidential Repair and Rehabilitation Important to understand the existing structure to be able to determine the underlying cause of problem and arrive at an adequate and cost-effective repair solution © 2007 Simpson Gumpertz & Heger Inc. Proprietary and Confidential 15
  • 16. Repair and Rehabilitation  “Repairs” sometimes require repairs;  Shoring may be needed until permanent repairs are done © 2007 Simpson Gumpertz & Heger Inc. Proprietary and Confidential Repair and Rehabilitation Strengthening of existing structures: count on load sharing, consider creep, jack load into new elements, understand the interaction between the structure and the strengthening elements – must understand wood © 2007 Simpson Gumpertz & Heger Inc. Proprietary and Confidential 16
  • 17. Conclusions In-service wood performance problems can have significant public safety, loss of utilization, and economic consequences. Specific wood-material and wood-engineering knowledge allows engineers to extend the useful service life of wood structures and systems: – Biodeterioration mechanisms – Moisture-driven compatibility of displacement issues – Microscopic wood species and problem identification – In-situ grading – Special construction and detailing knowledge, etc. This special skill will be more significant and needed in the future, with technological advancements allowing utilization of engineered-wood products and multi-material systems in a wide range of previously unattainable applications. © 2007 Simpson Gumpertz & Heger Inc. Proprietary and Confidential QUESTIONS? © 2007 Simpson Gumpertz & Heger Inc. Proprietary and Confidential 17