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This paper summarizes the initial phases of the technical justification for proposed design provisions for AAC structures in the US. It is divided into two parts. The first part gives general background information, and presents an overall design strategy. Autoclaved aerated concrete (AAC), a lightweight cementitious material originally developed in Europe more than 70 years ago and now widely used around the world, has recently been introduced into the US construction market. AAC elements can contain conventional reinforcement in grouted cores, either alone or with factory-installed reinforcement. To facilitate the use of AAC in the US market, an integrated seismic-qualification program has been carried out, involving general seismic design provisions, specific element design provisions, and material specifications. The second part describes the design and testing of a suite of 14 AAC shear wall specimens, with aspect ratios from 0.6 to 3, under in-plane reversed cyclic loads at the University of Texas at Austin. The results of these tests have been used to develop predictive models and reliable design equations for AAC shear walls, the primary lateral force-resisting element of AAC structural systems.

A general overview of the approach to the design of autoclaved aerated concrete (AAC) structural walls and floor/roof panels is presented. Variations in design approach from concrete and masonry, and design equations specific to AAC are discussed and provided. Design examples illustrate the proposed approach.

This paper summarizes the final phases of the technical justification for proposed design provisions for AAC structures in the US. It is divided into two parts. The first part describes the design and testing of a two-story, full-scale AAC shear wall specimen that was designed and tested at The University of Texas at Austin, under reversed quasi-static loads representative of those experienced in a strong earthquake. The specimen withstood repeated reversed cycles to story drifts of about 0.3%, and displacement ductility ratios of about 3. The specimen conformed with the two main objectives. Those objectives were: 1) to show that the behavioral models developed for the shear walls also govern in a building; and 2) to demonstrate that a squat wall can exhibit failure governed by flexure. The second part describes the development of R and Cd factors for seismic design of AAC structures. The seismic force-reduction factor (R) specified in seismic design codes is intended to account for energy dissipation through inelastic deformation (ductility) and structural over-strength. The factor (R) is based on observation of the performance of different structural systems in previous strong earthquakes, on technical justification, and on tradition. For structures of autoclaved aerated concrete (AAC), the force-reduction factor (R) and the corresponding displacement-amplification factor (Cd) must be based on laboratory test results and numerical simulation of the response of AAC structures subjected to earthquake ground motions. The proposed factors must then be verified against the observed response of AAC structures in strong earthquakes. The objectives of this paper are: (1) to present a general procedure for selecting values of the factors (R) and (Cd) for use in the seismic design of structures; and (2) using that procedure, to propose preliminary values of the factors (R) and (Cd) for the seismic design of AAC shear-wall structures. The general procedure is based on comparing the predicted ductility and drift demands in AAC structures, as functions of the factors (R) and (Cd), with the ductility and drift capacities of AAC shear walls, as observed in quasi-static testing under reversed cyclic loads. Nonlinear numerical simulations are carried out using hysteretic load-displacement behavior based on test results, and using suites of natural and synthetic ground motions from different seismically active regions of the United States.

Three classes of specialty cementitious materials were evaluated for their potential benefits in sound absorption including a Foamed Cellular Concrete (FCC) with density ranging from 400 – 700 kg/m3, Enhanced Porosity Concrete (EPC) incorporating 20-25% open porosity, and a Cellulose Cement Composite (CCC) with density 1400 – 1700 kg/m3. Cylindrical specimens of these materials were tested for acoustic absorption in an impedance tube. The FCC specimens showed absorption coefficients ranging from 0.20 to 0.30, the higher value for lower density specimens. The closed disconnected pore network of FCC hinders sound propagation, thereby resulting in a reduced absorption, even though the porosity is relatively high. The most beneficial acoustic absorption was observed for EPC mixtures. When gap-graded with proper aggregate sizes, these no-fines EPC mixtures dissipate sound energy inside the material through frictional losses. The cellulose fiber cement composites use cellulose fibers at high volume fractions (~7.5%), which are believed to provide continuous channels inside the material where the sound energy can be attenuated. By engineering the pore structure (by careful aggregate grading as in EPC, or incorporating porous inclusions like morphologically altered cellulose fibers) cementitious materials that have the potential for significant acoustic absorption could be developed.

The use of lightweight concrete has many advantages over conventional concrete. The reduced self-weight of lightweight concrete will reduce gravity load and seismic inertial mass. The lightweight concrete reported here has compressive strengths from 8 to 50 MPa with dry densities from 800 to 1400 kg/m3, which is strong enough for any load-bearing and non-load-bearing applications. The compressive strength to flexural strength ratio increases as the compressive strength of the concrete increases. The introduction of a small amount of fiber does not affect the flexural strength and drying shrinkage of the concrete, but improves the ductility and handling properties of the product very significantly. The lightweight concrete has a higher moisture loss during drying, but a lower shrinkage than the normal weight concrete due to the buffer effect of the moisture in the lightweight aggregate. Properly designed fiber-reinforced ultra lightweight concrete can be easily cut, sawed and nailed like wood.