A High-Performance Quadrilateral Flat Shell Element for Seismic Collapse Simulation of Tall Buildings and Its Implementation in OpenSees

Shear walls are important lateral force-resistant components of tall buildings. Hence, a reliable numerical model that can accurately represent the mechanical characteristics and large deformations of shear walls is critical for realistic collapse simulation of tall buildings. Based on the theory of generalized conforming element, a high-performance quadrilateral flat shell element, NLDKGQ, accounting for the large deformation using the updated Lagrangian formulation, is proposed herein and implemented in OpenSees. The reliability of NLDKGQ is validated using classical benchmark problems and reinforced concrete specimens. In addition, its capability in simulating the collapse of a tall building is also demonstrated.     

Assessment of Effects of Reductions of Lateral Stiffness along Height on Buildings Modeled as Elastic Cantilever Shear Beams

A simplified model useful for assessing economic losses due to moderate seismicity events in urban areas has been developed by studying the behavior of buildings before yielding their structural system, allowing for nonuniform stiffness along their height. In particular, buildings are modeled as cantilever shear beams with uniform mass and parabolic reduction of lateral stiffness. This particular stiffness distribution is relevant, as it could be expected to occur in buildings where earthquake action is a critical structural design criterion. The equation of motion governing the dynamic behavior of the proposed model is solved analytically, finding mode shapes in terms of first and second zero-order Legendre functions. The solution is verified by comparing it with results obtained from fine mesh finite element models. The effect of reducing the lateral stiffness is then studied in the first five modes of vibration. Results include modal periods, mode shapes, modal participation factors, and derivatives of mode shapes. In general, it is found that effects of reduction of lateral stiffness in mode shapes are moderate when the lateral stiffness in the free end is smaller than about seventy percent of the lateral stiffness at the fixed end, but become significant for larger reductions. Effects are particularly important for the derivative of the mode shapes, which could play a significant role in estimating interstory drift demands in buildings. Model usefulness is showcased by analyzing a test case where both acceleration and drift demands are assessed by considering uniform beams and beams with parabolic stiffness variation, finding notable improvements by considering the latter.     

Earthquake Resilience of Reinforced Concrete Structural Walls with Replaceable “Fuses”

The concept of providing a fuse in a structural system has been both developed and investigated over the past few years (e.g., the use of replaceable links in eccentrically braced frames or the use of replaceable links in the new San Francisco-Oakland Bay Bridge). This paper presents a new coupling beam with a creative fuse installed in the mid-span of a steel-concrete composite beam via an end plate and high-strength bolts. First, a practical design methodology of a replaceable coupling beam is presented. Next, the seismic behavior of the proposed fuse is tested and evaluated, and two structural wall specimens with or without a fuse are designed and fabricated according to the proposed design methods. The two specimens possess similar shear capacities under large-scale cyclic loading, and the walls of the two specimens show similar failure modes; however, the new walls exhibit slightly lower levels of damage than the conventional walls. In particular, the inelastic deformation and damage of replaceable coupling beams are mainly concentrated in the fuse, whereas the non-yield segment and the beam-wall pier interfaces remain nearly intact and produce only slight damage, which is beneficial regarding the replacement of the fuse in post-earthquake events.     

Immersive Visualization and Curation of Archaeological Heritage Data: Çatalhöyük and the Dig@IT App

Advanced data capture techniques, cost-effective data processing, and visualization technologies provide viable solutions for the documentation of archaeological heritage and material culture. Work at the UNESCO World Heritage site of Çatalhöyük has demonstrated that new digital approaches for capturing, processing, analyzing, and curating stratigraphic data in 3D are now feasible. Real-time visualization engines allow us to simulate the stratigraphy of a site, the three-dimensional surfaces of ancient buildings, as well as the ever-changing morphology of cultural landscapes. Nonetheless, more work needs to be done to address methodological questions such as follows: can three-dimensional models and stratigraphic relationships, based on 3D surfaces and volumes, be used to perform archaeological interpretation? How can a 3D virtual scenario become the interface to cultural data and metadata stored in external online databases? How can we foster a sense of presence and user embodiment in the simulation of ancient cities and archaeological sites? This article aims to provide viable solutions to the methodological challenge of designing a comprehensive digital archaeological workflow from the data acquisition and interpretation in the field to a three-dimensional digital data curation based on interactive visualization, searchable 3D data, and virtual environments. This work describes the results we achieved developing the application Dig@IT, a multi-platform, scalable virtual reality tool able to foster archaeological data analysis, interpretation, and curation in a realistic and highly interactive virtual environment.     

A Cost-Based Ripley’s <Emphasis Type="Italic">K</Emphasis> Function to Assess Social Strategies in Settlement Patterning

Most quantitative approaches to distributional analysis in archaeology assume a homogeneous study surface that is amenable to easy generalisations. This framework has been widely used to describe settlement processes, disregarding the spatial heterogeneity inherent to geographic reality. In other words, researchers have often assumed that the correlation between the elements of a spatial distribution is a function of the Euclidean distance (i.e. straight line distance) between them. Other archaeological studies have tested alternative measures to Euclidean distances, such as cost-based ones, both to describe optimal routes and to assess spatial autocorrelation in a point pattern. Nevertheless, until now there has been no suitable model to introduce these measures into spatial statistical equations. In order to overcome this obstacle, we approach the implementation problem inversely by embedding the spatial pattern under study into a Euclidean frame of reference based on its cost-distance pairwise matrix. This paper describes the application of this methodology on one of the main tools used by archaeologists to assess settlement patterns: Ripley’s K function. We present two case studies, covering both macroscale and mesoscale, with significant variations in the results depending on the use of the Euclidean or cost-based approach. Data, functions and results have been R-packaged for the sake of reproducibility and reusability, allowing other researchers to build upon our methods.     

Time-Averaging Slows Down Rates of Change in the Archaeological Record

Measuring the pace of cultural change, and understanding its determinants is a fundamental goal of anthropological research. The archaeological record is the main source of information about the pace of cultural change, but it is an imperfect one, as taphonomic loss and mixing distort rate measurements. Here, I focus on the impact of time-averaging on rate measurements. Time-averaging arises when archaeological materials associated with activities and events that took place at different points in time are mixed into the same unit, whether because of depositional processes, disturbance factors, or because archaeologists lump together archaeological contexts when creating analytical units. I use analytical models to show how time-averaging can slow down the observed rates of change under two general modes of cultural change: random drift and directional change. I test this prediction using empirical rates of change from the archaeological record of North America. I show that empirical rates of change are indeed inversely correlated with the duration of time-averaging and provide a range estimate for this correlation.