Edén Bojórquez

Evaluation of Structural Reliability of Steel Frames: Interstory Drift versus Plastic Hysteretic Energy

The structural reliability in terms of maximum interstory drift—and, alternatively, in terms of plastic hysteretic energy—is evaluated for six regular moment-resisting steel frames designed according to the Mexico City Building Code, and located in the Lake Zone of that city. While the maximum interstory drift was used because of its relevance within the format of current seismic design codes, the plastic hysteretic energy was considered due to its importance for the performance of structures when subjected to severe cumulative plastic deformation demands. The demand hazard curves of the frames in terms of drift and energy are compared to provide a general idea of the reliability levels associated to the models, and to provide insights into which response parameter dominates their dynamic behavior and structural performance. In some cases, large differences are observed in the reliabilities computed by measure of the two different response parameters under consideration.

Evaluating A New Proxy For Spectral Shape To Be Used As An Intensity Measure

The possibility to use a new vector‐valued ground motion intensity measure (IM) is analyzed; it is based on the spectral acceleration at first mode (Sa) and a parameter proxy for the spectral shape, namely Np. The potential of the vector 〈Sa,Np〉 is explored by efficiency comparison with other IMs. It will be illustrated how the form of the vector 〈Sa,Np may represent an improvement in predicting the seismic response in terms of ductility, dissipated hysteretic energy and Park and Ang damage index for nonlinear single degree of freedom (SDOF) structures subjected to ordinary, narrow‐band and near‐source pulse‐like records.

Force reduction factors for steel buildings with welded and post-tensioned connections

The seismic responses of steel buildings with perimeter moment resisting frames (MRF) with welded connections (WC) are estimated and compared to those of similar buildings with semi-rigid post-tensioned connections (PC). The responses are estimated in terms of ductility reduction factors (Rµ,), ductility demands (µG) and force reduction factors (R). Two steel model buildings, which were modeled as complex-3D-MDOF systems, were used in the study. Results indicate that the reduction magnitude of global response parameters is larger than that of local response parameters, contradicting the same reduction implicitly assumed in the static equivalent lateral force procedure, implying that non-conservative design may result. The value of 8 for R, suggested in many codes for ductile steel MRF, and the value of 1 suggested in the well known Newmark and Hall procedure for the ratio of R to µG, cannot be justified. The reason for this is that SDOF systems were used to model actual structures, where higher mode effects, energy dissipation and structural overstrength weren’t explicitly considered. The codes should be more transparent regarding the magnitude and the components involved in the force reduction factors. The seismic performance of steel buildings with PC may be superior to that of the buildings with WC, since their force reduction factors are larger and their ductility demands smaller, implying that PC buildings could be designed for smaller lateral seismic forces. The conclusions of this paper are for the particular structural systems and models considered. Much more research is needed to reach more general conclusions.

Ductility reduction factors for steel buildings considering different structural representations

The global ductility parameter

Prediction of Inelastic Response Spectra Using Artificial Neural Networks

(\mu _{G})

Seismic Response of 3D Steel Buildings considering the Effect of PR Connections and Gravity Frames

(μG), commonly used to represent the capacity of a structure to dissipate energy, and its effects, considered through the ductility reduction factor

Reliability-based Strength Amplification Factors for Structures with Asymmetric Yielding

(R_{\upmu })