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.

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

Probability of collapse is currently used to set targets for system performance and response measures of new buildings. This study compares the probability of collapse for new, retrofitted and existing concrete buildings. Retrofitting plays an important role in reducing seismic risk from older concrete buildings. In order to decide on the most appropriate and economical retrofit strategy for an existing structure, it is necessary to assess the risk of collapse of each rehabilitation measure. At present, it is frequently assumed that retrofitting a non-ductile concrete building will enhance the seismic performance such that it can reach the same performance level as a ductile building designed based on current seismic codes. However, based on the evaluation of the concrete frames presented in this paper, typical retrofit schemes (such as: adding an additional lateral force restraint system; increasing ductility of existing concrete columns; and weakening the existing beams) cannot achieve the same performance as modern code-conforming structures. The study finds that retrofitting schemes where the columns or beams are modified such that the frame satisfies the collapse prevention level of ASCE 41-13 have the least beneficial effect regarding seismic collapse safety; and conversely, adding a shear wall will significantly improve the seismic performance in terms of the probability of collapse.

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 assessment of the seismic vulnerability and collapse potential of masonry‐infilled RC frame buildings presents a significant challenge because of the complicated failure mechanisms they could exhibit and the number of factors that could affect their behavior. In general, there are two types of analysis methods that can be used to simulate the inelastic behavior of infilled frames. One is to use simplified frame models in which infill walls are represented by equivalent diagonal struts, and the other is to use refined finite element models that can capture the failure behavior of RC frames and infill walls in a detailed manner. However, both types of models have limitations in simulating structural response through collapse. While refined finite element models are not computationally efficient, simplified models are less accurate because of their inability to represent some failure mechanisms that could occur in an infilled frame. In this paper, possible failure mechanisms and causes of collapse of masonry‐infilled RC structures are discussed, and both simplified and refined finite element analysis methods that can be used to simulate the inelastic response of these structures and assess their vulnerability to collapse are presented with numerical examples. Additional research and development work needed to improve collapse simulations is discussed.