Seismic Testing of Autoclaved Aerated Concrete Shearwalls: A Comprehensive Review

ACI Structural Journal, May/Jun 2005 by Tanner, Jennifer E, Varela, Jorge L, Klingner, Richard E, Brightman, Matthew J, Cancino, Ulises

A comprehensive research program has recently been carried out to propose design provisions for autoclaved aerated concrete (AAC) and to develop the technical basis for those provisions. The first phase of that research program addressed extensive testing on AAC shearwalls, which are the fundamental lateral force-resisting elements of AAC structural systems. The shearwall specimens were made of a variety of AAC elements, including masonry-type units and reinforced panels, laid either horizontally or vertically. The aspect ratio of the specimens (ratio of height to base length) varied from 0.6 to 3, and each specimen was designed to fail in either shear or flexure. Based on the test results obtained at The University of Texas at Austin and elsewhere, reliable procedures and corresponding provisions were developed for the design behavior of AAC shearwalls consisting of masonry-type units or horizontally oriented reinforced panels as governed by flexure, shear, and other limit states. In this context, "reliable" connotes low coefficients of variation (generally below 15%) and values close to or exceeding 1.0 for the ratios of observed capacity to the capacity predicted using equations based on the tested strength.

Keywords: autoclave; shearwall; test.

(ProQuest Information and Learning: ... denotes formulae omitted.)

INTRODUCTION

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 U.S. construction market. Because AAC is a new material in the U.S., technical information is required to produce proposed design provisions for AAC structural systems. Although significant material exists on material and thermal properties of AAC produced in Europe, little information exists on the performance of AAC shearwalls subject to in-plane loads. The Autoclaved Aerated Concrete CEB Manual of Design and Technology (CEB 1978) and the CEB-FIB Model Code (CEB 1990) are silent on the design of AAC shearwalls. Bave (1980) mentions the conclusions of two independent investigations on aerated concrete panels oriented in a vertical direction. Full-scale tests of an AAC specimen consisting of a reinforced concrete frame with AAC infill blocks was completed in 1997 at the Building Research Institute NISI in Sofia, Bulgaria (Dimitrov and Guglev 1997). A suite of specimens consisting of AAC horizontal panels and blocks subject to lateral in-plane and axial loads was tested in 1998 at Hebel AG in Germany.*

A research program at The University of Texas at Austin was developed to test the results of an additional 19 AAC shearwall specimens. The specimens were made of a variety of AAC elements, including masonry-type units and reinforced panels, laid either horizontally or vertically. AAC masonry units are typically 8 × 8 × 24 in. (200 × 200 × 610 mm) and AAC panels are 8 in. × 24 in. × 20 ft (200 mm × 610 mm × 6.1 m), although the thickness is variable. The aspect ratio of the specimens (ratio of height to base length) varied from 0.6 to 3. These tests complement the results of the Hebel AG tests conducted on a single aspect ratio. The geometry and axial load of each specimen are presented in Table 1 (Varela 2003; Tanner 2003). Using coordinated research at The University of Texas at Austin and Hebel AG, integrated design provisions, commentary, and "super-commentary" (extensive technical justification) have been developed for AAC elements. This paper discusses the behavior of AAC shearwalls consisting of masonry (including field reinforcement) or factory-reinforced AAC panels (Klingner et al. 2003).

RESEARCH SIGNIFICANCE

A suite of 19 shearwall specimens and a full scale assemblage specimen constructed of AAC were recently tested to fill gaps in experimental data and provide predictive equations for the general behavior of AAC shearwalls. This paper presents the experimental program and a synthesis of results obtained from the suite of shearwall specimens tested at The University of Texas at Austin. The proposed equations resulting from the synthesis are under review by ACI Committee 523A.

TEST SETUP AND PROCEDURES

The AAC shearwall specimens tested at The University of Texas at Austin were constructed on a concrete foundation post-tensioned to the strong floor at the Ferguson Structural Engineering Laboratory. Each shearwall was constructed on a leveling bed of ASTM C 270 Type S masonry mortar placed on the concrete foundation. A very stiff longitudinally post-tensioned loading beam was placed on top of the specimen. Reversed cyclic lateral load was applied to each specimen using either a single hydraulic ram or dual hydraulic rams mounted to a strong wall at the Ferguson Structural Engineering Laboratory, and supplied through a manually controlled hydraulic pump. The test setup and notation to describe shearwalls is shown in Fig. 1 and 2 (Varela 2003; Tanner 2003; Brightman 2000).

At The University of Texas at Austin, axial load was applied through hydraulic rams, post-tensioned rods, or a combination of the two. Net axial force was maintained approximately constant under reversed cyclic loading by using a mechanical "load maintainer" and by ensuring that some post-tensioning force remained in the external rods. A complete description of the test setup and results is presented in Brightman (2000), Tanner (2003), and Varela (2003). The test setup for the Hebel AG walls was similar except that the axial load did not remain constant throughout the test (Tanner 2003).