Opposite Peak Ratio to Characterize Ground Motion Loading History for Performance-Based Design

Recent studies have revealed the impact of ground motion loading history on performance limit states of reinforced concrete (RC) bridge columns such as reinforcement bar-buckling and residual drift ratio. Conventional hazard characterizations such as peak ground acceleration, spectral acceleration, and spectral displacement only capture peak values of ground motion hazard and, therefore, fall short of providing the necessary information to account for these limit states. In this study, a parameter termed as the opposite peak ratio (Rop) is defined, explored, and shown to be useful in reproducing loading history characteristics of ground motions for displacement-based design. Several past ground motion records were analyzed to develop empirical models that can estimate Rop. These models provide the mean and confidence intervals of Rop as a function of earthquake magnitude, epicentral distance, structural period, hysteretic model, and displacement ductility. To motivate practitioners to make use of Rop, a design scenario and two case studies are discussed. In an RC bridge column design scenario, it is shown that having prior information about the expected Rop at the site could reduce the structural cost of the bridge. Next, case studies designed to investigate correlations between Rop and the performance limit states of RC bridge columns are discussed. By analyzing the results of nonlinear time-history analyses of numerical RC column models, it is established that Rop could potentially be a significant variable in generating fragility models for these limit-states.

Development of Performance Limit States for Concrete Bridge Piers with High Strength Concrete and High Strength Steel Reinforcement

Current design codes and guidelines do not permit reinforcing the plastic hinge region of bridge piers using high strength steel (HSS) rebars. This is due to the lack of adequate research on the seismic response of HSS reinforced bridge piers. The objective of this study is to develop analytical expressions for predicting the drift at the onset of different performance limit states for high strength concrete (HSC) bridge pier reinforced with HSS reinforcement. Utilizing damage data obtained from Incremental Dynamic Analysis of HSC circular bridge piers reinforced with HSS, this study developed drift ratio relationship accounting for the aspect ratio, concrete and steel material properties, axial load ratio, and reinforcement ratio, using validated finite element models. Analytical equations are developed for estimating the drift at the inception of rebar yielding, concrete spalling, and bar buckling using multivariate regression analysis. The proposed equations showed reasonable precision when corroborated against experimental results.

Fragility analysis of the self-centering prestressed concrete frame with web friction devices

A novel self-centering prestressed concrete (SCPC) beam-column connection with web friction devices has been recently proposed for moment-resisting concrete frames. This paper presents the fragility analysis results of a SC concrete frame and a conventional reinforce concrete (RC) frame at various performance levels. Three performance limit states (i.e., Immediate Occupancy, Life Safety and Collapse Prevention limit states) are defined based on the peak story drift ratio and two other performance limit states (i.e., Re-centering and Repairable limit states) are defined based on the residual story drift ratio. Statistical analyses of the seismic demands reveal that the SC frame reduces the softening and dispersion of the residual story drift behavior. Fragility curves indicate that the SC frame experiences much smaller residual deformations and shows considerable reduction in the median fragility and probability of exceedance for the residual drift-related performance levels, as compared with the conventional RC frame.

Impact of Damping Scaling Factors on Direct Displacement-Based Design

Damping scaling factors (DSFs) play an important role in direct displacement-based design (DDBD) as they provide a means to establish displacement response spectra for damping values beyond 5%. Response spectra for multiple damping values are needed for DDBD as the approach relies on equivalent linearization, expressed in the form of effective stiffness and equivalent viscous damping, to establish design forces for prescribed performance limit states. In the past, DSFs based on the Eurocode have been employed for DDBD; however, recent research has resulted in more robust DSF models. This paper examines the accuracy of the current DSF equation used in DDBD across the parameters that are important for structural design. A nonlinear regression analysis is performed based on the data obtained by the Rezaeian et al. (2014) model, and a base shear adjustment factor (SAF) is proposed for application to the DDBD base shear equation.