Issue #9

1. Code & Standards Watch

2. Research Snapshot

Sufficient number of core samples and method to determine compressive strength of in-use and reclaimed concrete elements
Researchers examined current practice in in-situ sampling of concrete compressive strength in existing elements being considered for reuse, and their conclusions are somewhat troubling: they surmised that current methods often overestimate the compressive strength of existing elements by 1-10 MPa (about 150 - 1500 psi) due to smaller-than-appropriate sample sizes.

While this work is preliminary, it’s a strong step towards a more robust future standard.  This study suggests that a more appropriate sample size for coring of existing elements is 12-15, rather than the current 3-6 recommended in most jurisdictions in the US and EU.

Key Takeaways: Low sample sizes should always be suspect in structural design, which is something the industry has unfortunately become desensitized to by a prevailing “convenience and cost” challenge in testing large elements in the literature.  Watch for more development in this area, and expect costs associated with this sort of characterization to increase in the future.

3. Tools & Workflow

Mathcad Prime 12.0 Released

4. Case Study of the Week

The New York Coliseum Construction Collapse of 1955

Approximately 10,000 square feet of falsework and workers fell over twenty feet to the story below when a collapse occurred during the concrete pour of a large, main hall floor.  Dozens of workers were injured, luckily with no fatalities, and rescue efforts involved hundreds of emergency personnel.

Technology had evolved, and falsework design wasn’t rechecked.  The massive waffle slab pour demanded huge amounts of concrete over a large area, and motorized buggies became the technology of choice for placement.  Unfortunately, the dynamic loads of these heavy buggies and their large payloads of wet concrete were much higher than the falsework was designed for, especially laterally.

Key takeaways: Falsework design is one of the most overlooked aspects of concrete structure construction, with collapses still occurring today (a small bridge falsework collapse happened this past week in Oconomowoc, WI, dumping concrete into a river below).  Especially as construction technologies evolve, assumptions and designs must be rechecked to confirm they accurately reflect the true loads during construction, not just the historical assumptions.

5. Upcoming Free Live PDH

6. Quick Hits

👋 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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