Jennifer E. Tanner

Seismic Testing of Autoclaved Aerated Concrete Shearwalls: A Comprehensive Review

Autoclaved aerated concrete (AAC) is a lightweight cementitious material that has recently been introduced into the United States construction market. This article reports on the first phase of a comprehensive research program that 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 the program addressed extensive testing on AAC shearwalls, which are the fundamental lateral force-resisting elements of AAC structural systems. The 19 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, the authors developed reliable procedures and corresponding provisions for the design behavior of AAC shearwalls as governed by flexure, shear, and other limit states. Flexural cracking was observed in two directions in 15 shearwall specimens, with a resulting limiting value of tensile bond strength between leveling bed mortar and AAC of 50 psi based on a lower 20% fractile. Flexure-shear cracking was observed in seven shearwall specimens, and web-shear cracking was observed in 13 shearwalls.

Development of Seismic Force Reduction and Displacement Amplification Factors for Autoclaved Aerated Concrete Structures

This paper addresses the development and application of a rational procedure to select the seismic force reduction factor (R) and the displacement amplification factor ( Cd ) for the design of autoclaved aerated concrete (AAC) structures. The values of R and Cd are proposed based on a combination of laboratory test results and numerical simulation. The test results are obtained from 14 AAC shear-wall specimens tested under simulated gravity and quasi-static reversed cyclic lateral loads. Analytical responses are predicted using nonlinear analysis models whose hysteretic characteristics are based on the experimentally observed responses. Using an iterative procedure, typical AAC structures are designed using successively larger trial values of the factor, R, until the structures response (either ductility or drift) exceeds the experimentally determined capacity. A lower fractile of those critical values, modified for probable structural overstrength, is taken as a reasonable value of 3 for R. Using an analogous procedure, a reasonable value of Cd is determined as 3. These values will undoubtedly be refined based on field experience, just as they have been for other structural systems.

Seismic Performance of Engineered Masonry Buildings in the 2010 Maule Earthquake

Engineered masonry, namely reinforced and confined masonry, has been widely used for housing construction in Chile over the last few decades. Most one- and two-story single-family masonry dwellings did not experience any damage due to the 27 February 2010 Maule earthquake, with the exception of a few dwellings of pre-1970 vintage, which suffered moderate damage. A similar statement can be made for three- and four-story confined masonry buildings: a large majority of buildings remained undamaged. However, several reinforced and partially confined three- and four-story masonry buildings suffered extensive damage, and two three-story partially confined buildings collapsed. The key damage patterns and the causes of damage are discussed in the paper. The extent of damage observed in the field was correlated with calculated vulnerability indices, and relevant recommendations were made related to the design and construction practices.

Applicability of the Accelerated Mortar Bar Test for Alkali-Silica Reactivity of Recycled Concrete Aggregates

Using recycled concrete aggregate (RCA) as a replacement for natural aggregate in new concrete is a promising way to increase the overall sustainability of new concrete. This has been hindered, however, by a general perception that RCA is a sub-standard material because of the lack of technical guidance, specifically related to long-term durability, on incorporating RCA into new concrete. The goal of this research was to determine whether current testing methods (namely, ASTM C1260) for assessing natural aggregate susceptibility to alkali-silica reactivity could be used to assess the potential reactivity of concrete incorporating RCA. Seven different RCA sources were investigated. It was determined that ASTM C1260 was effective in detecting reactivity, but expansion varied based on RCA processing. Depending on the aggregate type and the extent of processing, up to a 100 % increase in expansion was observed. Replicate testing was performed at four university laboratories to evaluate the repeatability and consistency of results. The authors recommend modifications to the mixing and aggregate preparation procedures when testing the reactivity of RCA using ASTM C1260.

Development of Accelerated Aging Test Methodology and Specimen for Bonded CFRP Systems

Determining long-term behavior of bonded CFRP systems requires developing an accelerated aging test method for CFRP applications. This paper examines the development of test methodology and specimen for both flexure and direct tension behavior of bonded CFRP materials using a specimen submerged in a water bath subject to elevated temperature. Test results of three commercial CFRP systems are presented. A discussion of accelerated aging is included in the developmental effort.

Guide for Using Autoclaved Aerated Concrete Panels: I - Structural Design

The paper provides an overview of ACI 523.5R, a guide for using autoclaved aerated concrete (AAC) panels. The guides design provisions are non-mandatory and are a synthesis of design recommendations from the Autoclaved Aerated Concrete Products Association and previously conducted research. The design equations discussed include flexural, axial compression, shear, bearing, bond and development of reinforcement and special seidmic design.

Technical Justification for Proposed Design Provisions for AAC Structures: Introduction and Shear Wall Tests

The paper presents the first part of of consistent technical basis for the design of autoclaved aerated concrete (AAC) structures. The basis includes an overview of an overall strategy for development of design provisions in the context of the U.S. code framework, and the development and testing of shear wall specimens.

Technical Justification for Proposed Design Provisions for AAC Structures: Assemblage Test and Development of R and Cd Factors

A general procedure for selecting values for the seismic force reduction factor (R) and the corresponding displacement amplification factor (C) for use in the seismic design of different structural systems is presented. The proposed procedure is based on comparing the predicted ductility and drift demands in autoclaved aerated concrete (AAC) structures as functions of the ductility reduction factor with the ductility and drift capacities of AAC shear walls as observed in quasi static testing under reverse cyclic loads. Seismic performance of AAC shear wall structures was evaluated using nonlinear analyses with hysteretic load displacement behavior based on test results .The paper presents the second part of a consistent technical basis for the design of AAC structures.

ASR Potential and Mitigation Measures for Wyoming Aggregates

AbstractDiscovered in the 1940s, alkali-silica reaction (ASR) causes undesired expansions in concrete. If unmitigated, ASR may cause premature deterioration. Since its discovery, researchers have s...

DESIGN AND SEISMIC TESTING OF TWO-STORY, FULL-SCALE AUTOCLAVED AERATED CONCRETE ASSEMBLAGE SPECIMEN

Autoclaved aerated concrete (AAC) or cellular concrete, is an innovative new construction material that is currently fabricated in large panels or modular blocks. This article reports on an AAC assemblage specimen that was constructed and tested as the culmination of a research study of AAC structural systems. The objectives of the two-story assemblage specimen were to verify that a system of squat AAC shearwalls designed to fail in a flexure-dominated mode would indeed fail in flexure; to verify proposed design provisions for AAC shearwalls and floor diaphragms; to verify proposed analytical models for such elements and systems; and to verify proposed seismic design procedures for AAC structural systems. The authors discuss background information, specimen design, testing procedure and instrumentation, global results, and individual observed behavioral modes. The authors conclude that the assemblage test met those objectives. The shearwalls conformed to predictive models, with stable hysteretic loops up to drift ratios exceeding 0.3%, and displacement ductilities ranging from 2.5 to 6. The tests confirm that the design objective of flexure-dominated failures can be achieved even with relatively squat walls.