International Concrete Abstracts Portal

Editors: Kenneth J. Elwood, Jeff Dragovich and Insung Kim

This CD provides eleven papers summarizing new developments in the assessment and retrofit of concrete buildings, with a particular focus on the collapse prevention performance level. Many of the papers report on efforts by task groups of ACI 369, Committee for Seismic Repair and Rehabilitation. Several papers in this CD summarize research efforts related to the ACI 369 proposals under development, including modeling parameters and acceptance criteria for existing and jacketed columns, slender walls, and slab-column connections. Other papers report on retrofit case studies, a new assessment procedure for concrete buildings in Turkey, and practical numerical models for existing beam-column joints, in filled frames, and collapse simulation.

Note: The individual papers are also available. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP-297

A database of 490 pseudo-static tests of reinforced concrete columns subjected to load reversals was used to evaluate nonlinear modeling parameters that define the lateral force versus lateral deformation envelope relation of columns under seismic excitations. Based on the modeling parameters, criteria that identify acceptable deformation levels at various performance objectives are proposed. The effects of bi-directional loading and number-of-cycles of the displacement history on the drift ratio at axial failure are discussed, and recommendations are given to account for such effects. Modeling parameters and acceptance criteria are provided in a format that is consistent with provisions of the ASCE 41-06 Standard entitled “Seismic Rehabilitation of Existing Structures”.

The results of laboratory testing and earthquake reconnaissance studies of reinforced concrete frames indicate that beam‐column joint deformation can determine total frame deformation and that for older buildings joint failure can result in frames losing lateral and gravity load carrying capacity. Given the impact of joints on frame response, numerical models used to evaluate the earthquake performance of reinforced concrete frames must include nonlinear joint models. This paper reviews previously proposed models for simulating joint response with the objective of identifying models that provide i) accurate simulation of response to earthquake loading, ii) simple implementation in nonlinear analysis software, iii) numerical robustness, iv) computational efficiency, and v) objective calibration procedures. Ultimately, no set of models was identified that met all of these requirements for the range of geometric and design parameters found in reinforced concrete buildings in the United States. With the objective of extending current modeling capabilities for interior joints, an experimental data set was assembled. The data set was used to evaluate existing envelope response models and used to calibrate cyclic response parameters for use with the preferred existing model. A new response model for interior beam‐column joints is presented that meets the above requirements for the range of geometric and design parameters found in reinforced concrete buildings in the United States.

A database comprised of 59 reinforced concrete columns subjected to strong ground shaking using earthquake simulators (or shaking tables) is compiled. This paper will focus on insights provided by the database related to the concrete column provisions in ASCE/SEI 41. In particular, the Shaking Table Test Column Database is used to evaluate the accuracy of column effective stiffness models, column classification criteria, and the level of conservatism provided by the plastic rotation capacities specified in ASCE/SEI 41. It is found that the Standard generally overestimates the column effective stiffness, while providing a mean value estimate of the column shear strength regardless of tie spacing. The modeling parameters specified in the standard provide conservative estimate of the column drift capacities and are consistent with the targeted probability of failure. Refinements of the shear strength model and the criteria for column classifications are suggested. This study also compares the measured response of columns subjected to quasi-static cyclic loads and shaking table tests.

ASCE/SEI 41-06 provides guidelines for evaluating the seismic adequacy of existing buildings. For nonlinear dynamic analysis of a building, ASCE 41 provides modeling parameters to define the backbone curve for the response of structural components. Seismic adequacy is then determined by comparing simulated response to predetermined acceptance criteria. In the reinforced concrete (RC) community, there is interest in evaluating the modeling parameters and acceptance criteria for RC components, and if deemed necessary, developing updated values that reflect the current state of understanding of the seismic performance of RC components. For some structural components (e.g. columns), large databases of experimental data can be used to develop empirical acceptance criteria that reflect the behavior of the component. In the case of slender structural walls, relatively limited tests have been conducted such that sufficient variation in critical design and loading characteristics including shape, aspect ratio (elevation and cross-sectional), confinement, and axial load are not represented by experimental data to justify use of an experimental database to develop acceptance criteria. Evaluation of this limited set of experimental data indicates current ASCE 41 modeling parameters and acceptance criteria for flexure-controlled walls is inappropriate, generally resulting in overprediction of wall deformation capacity at high axial load ratios and underprediction at low axial load ratios and low shear demands. Although suitable for evaluation of criteria, the data set is not sufficiently varied such that revised provisions can be developed. To overcome the lack of sufficient experimental data, a parameter study was conducted to provide data to support development of updated acceptance criteria. The parameter study was conducted using a modeling approach validated to provide accurate simulation of flexural failures in slender reinforced concrete walls. Simulation results were used to develop preliminary recommendations for revised modeling parameters for slender RC walls. An evaluation of these simulation results and preliminary recommendations for revised flexure-controlled RC wall modeling parameters are presented in this paper.