With slower summer code progress, fewer software updates, and generally less going on, we’re on a temporary, monthly basis until school gets started again.

Capacity models for timber under compression perpendicular to grain with screw reinforcement

Compression perpendicular to the grain in wood design is often considered a “serviceability” problem, as crushing at supports tends to lead to excessive movements and settlement, not brittle fracture of the system.  In the US, we handle this condition with allowable bearing stress checks per NDS Section 3.10 and simply design to keep the stresses low.  However, European practice is pushing for a method to reinforce highly-loaded bearing joints to achieve better performance by running wood screws into the transversely-loaded member, serving as tiny props or columns within the wood matrix.

This newer approach, which has shown strong success in laboratories around the world, is in the midst of code adoption.  Eurocode drafts for prEN 1995-1-1 introduce a complex capacity model with two distinct failure modes, and this study evaluates that model, finding it largely unsatisfactory.  The second failure mode, internal screw-tip failure, almost never occurred across a dataset of nearly 60 specimens that were selected to try to show the full range of behavior.  The complex model fit observed behavior poorly (R² of 0.27) vs a much simpler model that performed better (R² of 0.76).

Key Takeaway:  

Screw reinforcement of wood members subjected to compression perpendicular to the grain is proving extremely useful for high-load applications, but code equations are still catching up with real behaviour around the globe.  Take care in implementing these early proposed equations.

ETABS v23.3.1 Released

An overview of failures in large-span timber structures

This rapid-fire survey of wood building failures examines 18 failures across Europe in quick succession, root-causing each, and drawing some overarching conclusions about recurring themes that all potential timber designers should keep in mind.  Around the time of its publication, there was an emerging wariness of wood as “too variable” a raw material for safe design, which the author readily admits is a targeted myth to dispel.

The author’s analysis found that 0/18 failures actually traced back to the raw wood material itself.  Instead, fully 50% of the failures stemmed directly from poor structural design or lack of engineering analysis for mechanical loading.  Large notches and cutouts in critical locations prevailed in these failures, often exacerbated by the other leading cause: manufacturing defects.  33% of cases had issues in fabrication, such as poor finger-joint alignment, inadequate clamping pressure, or incorrectly mixed/applied glue.  Failure to consider service environment in design also was a recurring cause of failure, with some older adhesives pressed into service outside their working conditions.

Key Takeaway:

While wood itself isn’t inherently “too variable” for safe design, it IS notably more susceptible to brittle failure brought on by poor design, specifically notching leading to stress risers and tension perpendicular to the grain.  QA/QC is critical in wood, as with any other material.

Developments in Power-Actuated Technology

Designing HVAC and BAS for Serviceability in K-12 Schools

Corrosion and the Behavior of Materials Used to Protect Against it

Common Damage and Repair Strategies in Existing Steel Buildings

Moisture Control and Durability in Hybrid Light-Frame Panelized Roof Systems

Design for the Unexpected: Integrated Resilience Strategies for High-Performance Buildings

Technology of Mechanical Anchors

Engineering Ethics: The Collapse of the Willow Island Cooling Tower

Design Considerations for Wedge Anchors

👋 From the Editor

I’m Eric, the engineer behind the StructEd Bulletin.  I dig through stacks of journal articles and software patch notes to find useful information for practicing engineers and keep an eye on the scattered code updates & errata for you. I’m just getting started, so if you find this useful, the best way to support the newsletter is to share it with a colleague or post it on LinkedIn. It helps more than you’d think!

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