Presentation Description:
What is the state of the practice in the design of void forms for expansive soils? Currently, structural engineers have not established a rational design method while the manufacturers have unilaterally developed all void form products on the market solely based on the empirical approach. No systematic testing nor comprehensive analysis for performance verification on these products has ever been conducted. Consequently, the field performance and safety factors of these installed void forms vary widely and are inconsistent.
Furthermore, the sufficient degree of degradation of the so-called popular void forms made of corrugated carton materials has never been fully verified. At the same time, the so-called non-degradable void forms made of plastic or expanded steel materials marketed by manufacturers specifically for inclement weather conditions create significant potential uplifting forces due to soil swelling. The effects of these uplifting forces have not been fully explored, including the cracking of invisible bottom slab surfaces due to the reversed bending moment distribution in the structural floor system and the altered load paths at the critical structural connections.
Under this manufacturer-initiated product development and manufacturer-controlled market conditions, structural engineers have been left to merely choose and specify one of the void forms available on the market without verifying the vital structural claims advanced by the manufacturers. The structural engineer of record should require manufacturers submit their full development test data for independent verification before approving the product.
This presentation critically reviews the current state of the practice for the design of void forms and proposes a rational design method in the format of ASD (Allowable Strength Design), based on the void form degradation curve and early-age concrete strength development. It also proposes the minimum requirements on void form material properties and void form degradation test data to be submitted by the manufacturers for independent verification.
It is time for structural engineers to establish rational design methodology different from the unverified empirical approach advanced by the manufacturers.
About the Presenter:
My active engineering practice started in January 1970 in Manhattan, New York City, designing high-rise reinforced concrete structures after receiving a Ph.D. in Structural Engineering from UT-Austin. For about 50 years, my practice has covered 6 states (NY, OH, TX, CO, GA, and KY) and the Republic of Korea. I retired in 2018 after working on the Korean Bullet Train Project ($6.5 billion, French TGV system, 217mph/350 km/h maximum design speed, 248-mile Seoul/Busan route) and, in 2023 I returned to the practice primarily to continue my research in the area of void forms for expansive soils.
For 13 years, taught two graduate-level courses (Advanced Reinforced Concrete Design and Highway Bridge Design) as Adjunct Lecturer of Civil Engineering at UT-Arlington.
Served two terms of Chairmanship of ACI Design Handbook Committee, one term of ACI Technical Activities Committee, and five ACI technical committees. Received ACI Delmar L. Bloem Distinguished Service Award in 1993 and 50-year ACI Membership Citation in 2013 from the American Concrete Institute (ACI).
Ran two Cowtown marathons in Fort Worth; climbed Three Sisters volcanic mountains (10,363 feet high) in Bend, Oregon; Hopped over 7 Hawaiian major islands, and drove Fiat (bought in Milan, Italy) over 3,000 miles through 6 European countries (Italy, Switzerland, France, Spain, Portugal, and Monaco).
