International Concrete Abstracts Portal

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.

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 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”.

Case studies on seismic assessment and rehabilitation of reinforced concrete buildings are discussed based on the projects in which Degenkolb Engineers has been involved in the past 5 years. Design, analysis and challenges are discussed to present applications of ASCE 31-03, Seismic Evaluation of Existing Buildings and ASCE 41-06, Seismic Rehabilitation of Existing Buildings.

There are many vulnerable reinforced concrete (RC) buildings located in earthquake-prone areas around the world. These buildings are characterized by the lack of seismic details and corresponding non-ductile behavior and significant potential of partial and global collapse. One of the current challenges of the earthquake engineering profession and research communities is the identification of such buildings and determination of effective and economical retrofit methods for response enhancement. Identification of these buildings is not a trivial task due to the various sources of non-ductile behavior and the large number of involved sources of uncertainty. Furthermore, accurate determination of collapse-prone buildings is important from an economical perspective. Unfortunately, there are not enough economical resources to retrofit all the non-ductile buildings that have the symptoms for collapse potential. In order to use the available monetary resources in an effective manner, these buildings should be accurately and reliably ranked to identify those that are most vulnerable to collapse. This paper intends to provide a contribution to the accurate determination of the most collapse vulnerable non-ductile RC buildings by discussing the methods from existing literature and exploring the research needs related to (a) gravity load failure modeling and (b) consideration of sources of uncertainty in an efficient manner.