Browsing by Author "Pozo Ocampo, Paul Sebastian"

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Level of detail required to model special steel moment frames to evaluate floor accelerations in nonstructural components
(American Society of Civil Engineers, 2019) Martinez Pesantez, Ivanna Lisseth
The floor acceleration response of special steel moment frames (SMF) subjected to earthquakes has been evaluated by multiple investigations. It has been demonstrated that peak floor accelerations and floor spectra, which are the most evaluated responses, are reduced when inelasticity is included in the mathematical model. However, the amount of detail required by the model to evaluate floor accelerations in nonstructural components has not been assessed. In this study four different models are used to compute the peak floor accelerations and the floor spectra of an 8-story special steel moment frame. The first model includes concentrated inelasticities and has been used to evaluate the collapse performance of SMFs, thus making it the most detailed model since the constitutive laws incorporate strength and stiffness deterioration. The second model also has concentrated inelasticities, but with a simple elasto-plastic behavior, therefore no degradation is included. The third model was created using fibers with displacement-based elements and a material that does not include any degradation. The last model to be analyzed does not include any inelasticity. All the mathematical models are analyzed to obtain the floor acceleration responses under design level ground motions. The results show that all the methods are accurate enough to be used to evaluate the accelerations in nonstructural components at design level earthquakes.
Objective Phenomenological Constitutive Law for Collapse Analyses in Distributed Plasticity Steel-Frame Models
(2021) Flores Solano, Francisco Xavier
Nonlinear static and dynamic analyses are increasingly being used to evaluate the seismic performance of structures. The level of detail that mathematical models should include depends on the required analysis. In a collapse performance evaluation of special steel moment frames, models must include material and element deterioration due to local geometrical instabilities that will allow triggering structural instability. However, capturing these effects in distributed plasticity models is challenging for two reasons: (1) the selection of a constitutive law that incorporates the geometrical phenomenon, and (2) the localization issues related to the material softening. This paper proposes a simple approach to implement phenomenological calibrated constitutive law that includes compression softening applied on a distributed plasticity model. Additionally, a regularization method is proposed to reduce mesh-sensitivity, ensuring an objective response. The constitutive law and the regularization method are tested under different modeling levels: material, element, and structure. Furthermore, the model is used to perform collapse analyses of 2-, 4-, 8-, 12-, and 20-story special steel moment frame buildings. The proposed model can incorporate critical features, such as flexure-axial force interaction, postpeak deterioration, and an objective global response regardless of the element discretization.
Seismic performance of steel moment frames considering the effects of column-base hysteretic behavior and gravity framing system
(2021) Pozo Ocampo, Paul Sebastian
This paper presents a parametric study conducted on five Steel Moment Frames (SMFs) varying in height (2-, 4-, 8-, 12-, and 20- story) to assess the interactive effect of the column base hysteretic behavior, continuous gravity columns and partially restrained gravity beam-column connections in their seismic performance. The frame response is examined through sophisticated Nonlinear Time History (NTH) and Nonlinear Static Pushover (NSP) analyses conducted as per FEMAp695 methodology. For each SMF, a range of base connection strengths (and their corresponding rotational stiffnesses) accompanied by different levels of gravity columns rigidity and gravity connection strengths are assigned, resulting in a total of 80 model simulations. Two collapse/failure limit states are formulated for the assessment 1) sidesway collapse defined as per FEMAp695; and 2) column-base connection failure, defined as base rotations exceeding a 0.05 rad threshold. Results from the simulations indicate that the gravity framing system profoundly affects the behavior of the SMFs analyzed by reducing their probability of collapse. In this manner, the seismic demands for the design of column-base connections can be reduced safely, incorporating their high deformation capacity as part of the energy dissipative mechanisms. Potential design implications are discussed, and limitations, as well as lines for future research, are outlined