Simulation of Structural Collapse - 4252005

Project goals and objectives

Model the initiation and progression of collapse in RC framed structures

Role of this project in supporting PEER's mission (vision)

Allowing realistic prediction of potential collapse limit state and identifying the mode and extent of system collapse. For existing structures, such modeling will enable sound assessment of life- safety hazard and estimation of expected losses to life in the event of an earthquake. For new and retrofitted construction, collapse-capable simulations will lead to proper design of new RC framed structures against the undesired limit state of collapse

Methodology employed

• - Identification of generic systems representative of old non-ductile construction, and retrofitted construction.
• - Implementation, validation, and calibration of novel material models enhanced to capture the degrading behavior of components at extreme events (lap-splice failure, bar buckling, concrete crushing, loss of lateral confinement) and predict component collapse.
• - Implementing a numerically robust shear-axial interaction model, calibrated to results from ongoing experimental programs. This includes the development of a post-failure deterioration rule, accounting for the asymmetry in the behavior of shear-damaged columns, and criteria to trigger the removal of failed columns.
• - Implementation of a robust element elimination technique(s).

Brief Description of previous year's achievements, with emphasis on accomplishments during last year (Year 8)

• - This project is a continuation of a year 8 project. The following accomplished tasks derive from those previously identified:
• - Development of an analytical model for the full cyclic response of uniaxial concrete fibers under the effect of passive lateral confining stresses and hysteretic strength degradation (Figure 5).
• - Development of an analytical model for the distribution of confining stresses within the cross-section of a concrete member confined by transverse steel or external FRP wraps (Figure ).
• - Combining the confined uniaxial material and confinement distribution models into a fiber-discretized cross-section model capable of tracking the deformation and failure in the confining medium through enforcing compatibility between its circumferential strains and the lateral strains in concrete.
• - OpenSees implementation (Figure ) of the developed models into a computational tool for analyzing the axial-bending response of fiber-discretized confined concrete sections.
• - Experimental verification of the newly developed models by numerically simulating the experimentally-observed response of laterally-loaded RC columns. These included an experimental program (conducted with the participation of the PI) on monotonically- loaded columns using conventional and FRP confined columns (Figure , Figure ), in addition to experiments on cyclically-loaded columns using FRP confinement obtained from the literature (Figure 10).
• - Adaptation and verification of a confining stress-dependant analytical model for lap- splice failure; for implementation and use within the framework of the confined fiber section tool.

Enhancement of an analytical model for longitudinal reinforcement buckling, for implementation within the framework of the confined fiber section computational tool. The model relies on assessing the stiffness of the confining medium to accurately compute the critical buckling stress and length of individual reinforcing bars.

Other similar work being conducted within and outside PEER and how this project differs

RC Frame Validation Tests—5252002 (PI: Moehle)
This project is of direct relevance to the proposed research. We are closely collaborating with the researchers of this project and are making use of pervious study documented in the following PhD dissertation. The main difference is that the focus in our project is on implementation and numerical robustness, besides to experimental validation. K.J. Elwood, "Shake Table Tests and Analytical Studies on the Gravity Load Collapse of Reinforced Concrete Frames," Ph.D. Dissertation, Department of Civil and Env. Eng., Univ. of Cal., Berkeley, 2002.

Database and Acceptance Criteria for Column Tests—5282002 (PI: Eberhard)
This project aims at developing and calibrating tools and models for assessing and predicting the seismic performance of ductile and non-ductile RC columns. Its experimental findings will be used in validating the component failure models.

Shear-Flexural-Axial Interaction Models —4082004 (PI: Filippou) and Advanced Models for Cyclic Degradation of RC Members Including Low-Cycle Fatigue —4062004 (PI: Kunnath)
We intend to interact with the researchers of these two projects to make full use of their development in relevant areas to our objectives.

Dynamic Gravity Load Collapse Experiments of Low-Confinement RC Columns – National Science Council, Taiwan NSC92-2811-E-002-023 (PI: Wu)
This project is an ongoing research program to establish experimental data on the system interaction due to shear-axial collapse of columns. A direct use of the specimen and findings from this program will be used for validation of the shear-axial interaction model and the element removal algorithm. Documentation and information on this project is available online at: http://myweb.caece.net/yuansen/publications/aese2005/T087.PDF

Describe any instances where you are aware that your results have been used in industry

Expected milestones & deliverables

Implemented classes and algorithms into OpenSees that enable the simulation of progressive
collapse in RC framed structures.
Manual to use newly-developed capabilities.
Illustrative verification examples.