International Concrete Abstracts Portal

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.

A new law known as the "Urban Renewal Law" for risk mitigation was passed in May 2012 with the objective of reducing seismic risk associated with the existing building stock in Turkey. As stated in the law, new provisions are set forth to assess and to identify seismically vulnerable residential buildings as quickly as possible. The buildings that are classified as high risk are either demolished or strengthened. New buildings are constructed through the financing options provided by the government. In this study, first, the technical provisions of seismic risk assessment, based on linear elastic analysis, are briefly described with special emphasis on the deformation limits. Because of the inability of the linear elastic analysis to allow for redistribution, some flexibility is provided on how many vertical load bearing elements are allowed to exceed their performance limits. Afterwards, three case study buildings are analyzed by using the new provisions and ASCE/SEI 41-06 linear elastic procedure. Level and sources of conservatism in the two approaches are critically evaluated.

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.

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.