By combining the advantages of conventional reinforced concrete construction with unbonded post-tensioning, a hybrid is created that provides the opportunity to significantly and cost-effectively improve the seismic performance of structural wall systems. The implementation of this hybrid wall system is illustrated using a recently completed seismic retrofit of an existing six-story non-ductile concrete building in Berkeley, CA. Various restrictions during the retrofit led to the use of shotcrete to construct the walls, micropile foundations, and carbon fiber collector elements.

Post-tensioning was understood as early as 1860, but it was about 100 years before the first successful projects were built in the U.S. The subsequent 50 years saw rapid growth in the number of post-tensioned buildings and maturity in its construction and design technology. The performance and economical advantages of post-tensioned buildings have been recognized, and many other regions of the world are now embracing this U.S. spearheaded technology. This article reviews some of the critical milestones that have made post-tensioning the choice for many residential and commercial buildings.

Fly ash has become an integral and important part of good, durable concrete mixtures. The methods used to design and develop these mixtures, however, have evolved over a long period of time. Because fly ash has different properties than cement, it should be utilized as a mineral admixture rather than as cement, and therefore should never be used as a cement replacement.