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H=Hyatt Regency Dallas; U=Union Station

Loading Protocols for Seismic Performance Evaluation of Structural Components, Part 1 of 2

Monday, October 24, 2022  1:30 PM - 3:30 PM, H-Reunion B

The evolution of the seismic design provisions in response to the lessons learned from previous earthquake events has led to the development of new design methodologies such as performance-based design (PBD). A key component of PBD is to lay out the engineering demand parameters identifying the initiation of different damage states (e.g., yielding, spalling, bar fracture, etc.). In this regard, reliable knowledge of structural members’ strength and deformation capacities is required, and it is often obtained through quasi-static cyclic testing programs. The selecting of an appropriate loading protocol is crucial in these programs to achieve.
Learning Objectives:
(1) Summarize existing research and standards on deformation limits and acceptance criteria for different performance levels of reinforced concrete elements and connections;
(2) Compare performance of different structural components tested under different types of quasi-static cyclic loading;
(3) Discuss relationship between quasi-static loading protocols and seismic response and collapse behavior of reinforced concrete columns;
(4) Analyze behavior of dampers using experimental data from real-time hybrid simulations to develop new models using machine learning techniques.

This session has been AIA/ICC approved for 2 CEU/PDH credits.

Guide for Testing Reinforced Concrete Structural Elements under Slowly Applied Simulated Seismic Loads

Presented By: Murat Saatcioglu
Affiliation: University of Ottawa
Description: ACI Committee 374 formed a Task Group to develop a testing guideline for structural elements under slowly applied simulated seismic loads with the aim of generating test data for performance-based seismic design of reinforced concrete structural elements. The Task Group was created in recognition of the change in seismic design practices worldwide toward performance-based design of buildings. This approach aims at producing buildings capable of developing predictable performance levels to achieve predefined performance objectives when subjected to earthquake ground motions. The performance objectives are met by ensuring the structure and its components achieve target performance levels associated with different states of damage for specified seismic hazards. Performance levels (capacity) that can be developed by structural components and the ground motion intensity (demand) for which the building is designed form the fundamental framework of performance-based seismic design of buildings. The guideline provides an overview of structural performance levels prior to describing recommended testing procedure. Details of test specimens, test setup and boundary conditions, as well as the required instrumentation are described for different types of structural elements. The requirements for standard material testing are discussed with appropriate references to relevant ASTM specifications. An important aspect of testing under slowly applied lateral load reversals includes the selection of loading protocol for unidirectional and bidirectional load reversals. The significance of number of cycles and the levels of incrementally increasing deformation reversals are presented. The document makes references to existing research and standards on deformation limits and acceptance criteria for different performance levels. Structural components are treated separately depending on the predominance of response as flexure or shear in combination with axial forces.

Protocols for Backbone Curves in ASCE 41 Performance-Based Engineering

Presented By: Bruce Maison
Affiliation: Structural Engineer
Description: Performance-based engineering, in which a structure is proportioned to meet certain predictable performance requirements, requires knowledge of component (e.g., concrete beam-to-column connection) inelastic behavior during earthquakes. A so-called backbone curve is the customary way of describing component behaviors over a range of deformations. The ASCE 41 standard, Seismic Evaluation and Retrofit of Existing Buildings, sets component modeling and acceptance criteria based on backbone curves. It is generally recognized that buildings designed to the modern codes (e.g., ASCE 7) are often rejected by ASCE 41. One reason is that ASCE 41 criteria are overly-conservative by underestimating actual component ductility. ASCE 41 criteria are mostly based on component quasi-static lab tests using “standard” loading protocols consisting of fully reversed cyclic loading with progressively increasing displacement amplitudes. Such standard protocols are often more demanding than actual earthquake building response typically characterized by a ratcheting behavior resulting with a mostly one-sided cyclic pattern. This article summarizes the evidence for the above and explains the development of protocols representative of actual earthquake loadings. The case is made that future component lab tests should use protocols representative of earthquake response in addition to standard protocols. Conventional practice of relying exclusively on standard protocols for development of backbone curves for performance-based engineering should be consigned to the past.

Incremental Dynamic Analysis–Based Procedure for the Development of Loading Protocols

Presented By: Jhordy Rodriguez
Affiliation: University of British Columbia
Description: Seismic assessment is of critical importance for structures in regions where earthquakes are prevalent. Such assessment in terms of determining the inelastic capacity of structures is often performed in laboratories of universities, government, and industry through quasi-static cyclic testing programs. In these programs, selecting an appropriate loading protocol is crucial for achieving an accurate assessment of inelastic capacity. Appropriate loading protocols need to be representative of the seismic demands to which a structural component may be subjected during seismic events. A standard loading protocol available in the literature may not necessarily yield a meaningful response. For the quasi-static cyclic test program, a loading protocol should be developed specifically for the site, structural component, or system. In this study, an incremental dynamic analysis–based approach is introduced to develop component-specific quasi-static cyclic loading protocols, which is illustrated for a single-column-reinforced concrete bridge bent in Vancouver, British Columbia. Here, different target displacement ductility demand levels, that is, 2, 4, and 8, and different sources of earthquakes, that is, crustal, intraplate, and subduction earthquakes, were considered. The number of inelastic cycles and cumulative ductility damage were the primary target demand parameters in the loading protocol development. Conventional loading protocols were found unrealistically more damaging than those proposed for crustal and intraplate earthquakes. The proposed loading protocols for subduction earthquakes were consistent with those developed by other researchers for the same but employed the classical constant ductility design approach to achieve the target displacement ductility levels.

Machine Learning Models for Seismic Performance Evaluation of Fluid Viscous Dampers

Presented By: Monique Head
Affiliation: University of Delaware
Description: Fluid viscous dampers (FVDs) are supplemental damping devices that dissipate energy and protect movement of structures during extreme events like earthquakes, windstorms, and associated hazards. FVDs can also reduce the cost of the structure to allow for smaller structural elements and less complicated foundation designs to improve dynamic performance. However, the damping (viscous) force is highly time-dependent, and the damping behavior varies as a function of loading, which makes FVDs challenging to model numerically. This study focuses on characterizing the material behavior of fluid viscous dampers using experimental data from real-time hybrid simulations (RTHS) to develop new analytical models of the FVDs using machine learning techniques. The machine learning model of the FVD is expected to adapt to the frequency content of the record in the time domain to predict the instantaneous damper coefficients representing the FVD response to a particular loading protocol. The results will be validated against RTHS data to examine the predicted performance compared to the measured FVD response when subjected to seismic demands.

Evaluating the Effects of Loading Protocol on the Collapse Behavior of Reinforced Concrete Columns Using Continuum Finite Element Analyses

Presented By: Seyed Sasan Khedmatgozar Dolati
Affiliation: University of Texas San Antonio
Description: Columns are considered critical elements concerning the stability of buildings during earthquakes. Experience shows that the collapse of reinforced concrete buildings in major earthquakes is typically associated with loss of gravity-load carrying capacity of vertical members such as columns. Moreover, tests have indicated that lateral cycling on concrete columns imparts cumulative damage. However, most experiments on concrete columns have used fully reversed cyclic loading protocols, while earthquake ground motions tend to impart lateral histories that are typically skewed to a loading direction. Continuum finite element models were calibrated to experimental tests for over thirty columns subjected to varying lateral loading protocols. Selected columns sustained flexural-shear, shear, and flexural modes of lateral strength degradation. Columns were selected to cover a range of shear stresses, axial loads, transverse reinforcement spacings and ratios, and longitudinal reinforcement ratios. All tested columns sustained axial collapse. The software ATENA was used for the nonlinear analyses. Calibrated column models were then subjected to a series of loading protocols, including monotonic pushover, and non-symmetric ratchetting protocols. The effects of the lateral loading protocols on damage progression, strength, and deformation capacities are discussed for these columns.

Effects of Loading Protocols on the Seismic Behavior of Identical RC Columns, Slab-Beam-Column Connections, and Coupling Beams

Presented By: Shih-Ho (Simon) Chao
Affiliation: The University of Texas At Arlington
Description: Several studies have explored the effects of loading protocol on the behavior of RC structural components. However, in only a limited number of previous investigations identical specimens were tested under distinctly different loading protocols. Also, in nearly all the previous experiments, RC specimens were subjected to fully reversed symmetric cyclic lateral displacements. However, in an actual earthquake, small loading reversals are often followed by large unsymmetric displacement excursions which can lead to major plastic deformations in one direction. Therefore, it is necessary to investigate the effect of unsymmetric cyclic loading protocols representative of that which RC structural components will experience during earthquakes. This presentation summarizes the effects of loading protocols on the seismic behavior of three series of different RC structural components detailed for seismic resistance: columns, slab-beam-column connections, and coupling beams. In the first series, five identical full-scale ACI 318 compliant columns were subjected to a constant axial load and various loading schemes including three different uniaxial fully reversed symmetric cyclic, near collapse unsymmetric cyclic, and monotonic loading protocols. The loading protocols were designed to attain drift ratios close to 10% such that the specimens would lose most of their lateral loading capacity and exhibit significant loss of flexural strength. The second series includes two identical full-scale ACI 318 compliant slab-beam-column sub-assemblages subjected to either fully reversed symmetric cyclic or near collapse unsymmetric cyclic loading protocol. The third series includes two identical large-scale coupling beams subjected to either fully reversed symmetric cyclic or near collapse unsymmetric cyclic loading protocol.

Upper Level Sponsors

Ash Grove
Controls Group
Euclid Chemical
Master Builders
ACI Northeast Texas Chapter

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