This paper presents the structural testing of four full-scale reinforced concrete beam-column connections, extracted from reinforced concrete buildings that suffered minor damage from the Canterbury Earthquakes in New Zealand. Two connections are extracted from a moment frame comprising the secondary seismic-resisting system of a concrete building; two are extracted from moment frames of the primary seismic-resisting systems of a precast concrete building. The seismic performance of the connections is evaluated from the test results and compared to recommendations in ASCE 41 (2013) for the evaluation of existing buildings. Due to the size of the specimens, the tests were stopped when the actuator reached its maximum stroke, at interstory drifts between 2.5% and 3. The cast-in-place connections showed moderate damage after the tests, at ductility levels above 2.9, and their initial lateral stiffness was approximately 80% of the lateral stiffness of numerical models representing the undamaged state. The precast connections exhibited extensive damage along the construction joint between the precast beams and the cast-in-place beam-column joint, at ductility levels above 3.4. The plastic mechanism was governed by sliding shear of the precast beams, which caused severe stiffness deterioration at the end of the tests. The measured stiffness in this case was approximately half of the stiffness predicted by numerical models in which nonlinearity is considered in the form of flexural plastic hinges only. This unexpected behavior is attributed to the low quantity of reinforcing steel crossing the construction joint, and presumably earthquake damage.

Performance based seismic design (PBSD) has been widely used for tall buildings as a code alternative design method for concrete shear wall structures. However, most PBSD studies are done for buildings taller than 240’ (73 m). Very few studies have been done for buildings shorter than 240’ (73 m) because PBSD is not required for buildings under 240’ (73 m). It is unclear if and how the shear demand increases observed in typical PBSD analysis should be applied to buildings shorter than 240’ (73 m). This study includes two buildings in the Seattle area that are designed per current codes. The study compares the shear demands predicted by the elastic analysis method with the demands predicated by the nonlinear time history analysis used in PBSD method. The intent of this study is to examine the merits of the new Seattle requirement using a factor to amplify the shear demand for buildings designed at code level and for the building height in the range of 160’ (48.8 m) to 240’ (73 m). It also explores the proper factor to be used in ACI 318 to determine the shear wall capacity.

The PERFORM-3D software package is used commonly in engineering practice to conduct nonlinear dynamic analyses of reinforced concrete walled buildings to their seismic response. However, few studies have evaluated or improved on common modeling approaches for structural concrete walls. The research presented here was conducted to establish best practices for modeling the full nonlinear response of walls exhibiting common flexural failure modes. First, an experimental data set consisting of eight planar concrete walls was collected; these walls were spanned a range of length-to-thickness ratios, shear stress demands, axial load ratios, and longitudinal reinforcement configurations. For each wall specimen, a reference numerical model was created using typical modeling methods as proposed by Powell. Comparison of simulated and measured cyclic response histories show that typical modeling techniques result in relatively inaccurate simulation of cyclic response and very inaccurate simulation of drift capacity. To improve the model accuracy, experimental data were used to determine appropriate values for the steel and concrete material model cyclic response parameters. Experimental data and mathematical definitions for the concrete compressive energy were used to develop recommendations for defining concrete post-peak stress-strain response to achieve accurate, mesh-independent simulation of drift capacity. Finally, recommendations for the minimum number of elements were examined. Comparison of simulated and measured cyclic response histories show that the new modeling recommendation result in accurate, mesh independent simulation of cyclic response, including drift capacity. Future work will evaluate the proposed modeling approach for asymmetric and flanged walls.

The U.S. Nuclear Regulatory Commission (NRC) defines seismic Category 1 structures as the structures (buildings) that should be designed and built to withstand the maximum potential earthquake stresses for the particular region where a nuclear plant is sited. Seismic Category 1 structures have been designed for ground-shaking intensity associated with a safe-shutdown earthquake (SSE) – the intensity of the ground motion that will trigger the process of automatic shutdown of the reactor in operation. The SSE generates floor response spectra at different floor elevations in a building, and these spectra and their associated forces are used for the design of piping and piping anchors and equipment and equipment anchors at their floor locations. The NRC policy requires that the seismic Category 1 structures whose collapse could cause early or/and large release of radioactive materials into the atmosphere to be analyzed/designed for “no collapse” during the ground-shaking intensity of a review-level earthquake (RLE), which is 1.67 times that of an SSE. Most seismic Category 1 concrete structures, such as containment and shield buildings (curved cylindrical wall; see Figs. 1 and 2 in the next section) and containment internal structures (straight wall; see Fig. 1), use walls to resist earthquakes. This paper presents guidelines for the performance-based seismic design for these wall-typed structures that could meet the NRC policy. The method consists of (1) proportioning wall thickness based on shear stress of 6√fc’ (0.5√fc’ megapascals (MPa)) generated by SSE ground motions, (2) limiting vertical compressive stress in walls to less than 0.35 fc’, (3) providing minimum percentage of reinforcement of 1.0 percent to prevent steel reinforcing bar fracture, (4) subjecting the building design to nonlinear dynamic response analyses under RLE ground motions, (5) identifying any members and their connections in the building that have failed or collapsed during the RLE ground motions, (6) increasing reinforcement or wall thickness, or both, to provide additional strength or/and ductility for the failed or collapsed members and their connections, and (7) resubjecting the revised building design to the nonlinear dynamic response analyses as stated in step (4) until no collapse of the building and its members and their connections. This performance-based seismic design method is a direct, transparent, and scientific answer to whether these important seismic Category 1 structures meet the NRC’s policy that they will not collapse during the RLE ground motions. Examples of using the nonlinear dynamic response analyses are cited and described. Guidelines for the performance-based seismic design of seismic Category 1 concrete Structures are listed at the end of this paper.

A 160-foot (≈ 49 m) tall 12–story reinforced concrete special moment frame building is designed following ASCE 7-16 and ACI 318-14, and assessed using three Performance-Based Seismic Engineering (PBSE) standards and guidelines including ASCE/SEI 41, the Tall Buildings Initiative (TBI) guidelines for performance-based design of tall buildings, and the Los Angeles Tall Buildings Structural Design Council (LATBSDC) procedures. The assessments are performed at the combination of two performance and hazard levels including Collapse Prevention (CP) at the risk-targeted maximum considered earthquake (MCER) hazard level and Immediate Occupancy (IO) at a frequent ground motion level with 50 percent probability of exceedance in 30 years, i.e. serviceability performance level. Based on the recommendations of each of the three PBSE documents, nonlinear finite element models are implemented in OpenSees. Through nonlinear time-history response analyses, the finite element models are subjected to eleven ground motions that are selected following the ground motion selection recommendations in ASCE 7-16. Assessment results indicate that for the serviceability performance level, the code-compliant building meets the design requirements of the three PBSE documents for the inter-story drift ratio and inelastic deformation of the structural components. At the MCER hazard level, although the building essentially satisfies the design requirements for the peak inter-story drift ratios and inelastic deformation, the mean of the residual inter-story drift ratios as well as the envelope of the residual drift ratios do not meet the limits of the TBI and LATBSDC guidelines. The results indicate that the newly designed building meets the ASCE 41 acceptance criteria but does not meet the design requirements set in TBI and LATBSDC guidelines.