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.     

DEM Algorithm for Progressive Collapse Simulation of Single-Layer Reticulated Domes under Multi-Support Excitation

In this paper, the Member Discrete Element Method (MDEM) is modified and perfected for three aspects: the algorithm itself, loading and computational efficiency, and to accurately and quantitatively simulate the progressive collapse for large-span spatial steel structures. In addition, the corresponding computational programs are compiled. First, from the perspective of the method, a meshing principle for discrete element models is determined, a treatment for material nonlinearity and strain rate effect is proposed, and a damping model is established. Next, the Displacement Method is introduced to determine the multi-support excitation for the MDEM, and then motion equations of particles under multi-support excitation are derived. On this basis, the specific process of gravitational field loading is presented. Furthermore, parallel implementation strategies for the MDEM based on OpenMP are constructed. Finally, the collapse simulation of a 1/3.5-scaled single-layer reticulated dome shaking table test model under multi-support excitation is carried out. The comparison demonstrates that the ultimate load and failure mode as well as the complete collapse time of the numerical results are consistent with the experimentally measured responses, and the configuration variations from member buckling and local depression until collapse failure are fully captured. Moreover, the displacement time-history curves obtained using MDEM are almost identical to the experimental measurements, and there is a nuance only in the amplitude. It is verified that MDEM is capable of precisely addressing the collapse failure for large-span spatial steel structures. Additionally, the failure mechanism for structures of this type is naturally revealed.     

Capacity Design of Coupled RC Walls

Capacity design aims to ensure controlled ductile response of structures when subjected to earthquakes. This article investigates the performance of existing capacity design equations for reinforced concrete coupled walls and then proposes a new simplified capacity design method based on state-of-the-art knowledge. The new method is verified through a case study in which a set of 15 coupled walls are subject to nonlinear time-history analyses. The article includes examination of the maximum shear force in individual walls in relation to the total maximum shear force in the coupled wall system, and subsequently provides recommendations for design.     

Constant and Variable Amplitude Cyclic Behavior of Welded Steel Beam-to-Column Connections

This article presents a study on welded beam-to-column joints of moment-resisting steel frames. The main features of the joint specimens are summarised, in order to identify key parameters influencing the joint response as well as their low-cycle fatigue endurance. The cyclic behavior and the low-cycle fatigue strength of the connections were initially assessed by cyclic quasi-static testing, carried out at the Technical University of Milan. Analysis of the results has been carried out in order to verify the validity of a linear damage accumulation model combined with a low-cycle fatigue approach based on S-N lines concept. Moreover, a criterion to predict the type of failure and a procedure of appraising the fatigue endurance are presented and their validity proved by the results of variable amplitude tests.     

A Modified Capacity Spectrum Method with Direct Calculation of Seismic Intensity of Points on Capacity Curve

A direct methodology for solving the seismic intensity of each point on the capacity curve is proposed. By utilizing the procedure, a continuous curve between the structural response and the seismic intensity, the structural response function, can be easily generated. Unlike previous procedures that search for the performance point of a determined seismic intensity, the proposed methodology easily draws the full curve without iterations. The procedure is applicable to both a smooth design spectrum and an actual response spectrum. Examples indicate the methodology is accurate and fast, and convenient to be combined with existing procedures, such as Modal Pushover Analysis.     

Seismic Demand on Shear Panel Dampers Installed in Steel-Framed Bridge Pier Structures

This study is aimed at investigating the demand on shear panel dampers (SPDs) installed in steel structures under strong earthquake motions to serve as guidance for the recommended capacity of SPDs in seismic design. For this purpose, an extensive dynamic analysis is carried out on steel bridge pier structures with SPD devices. To describe the restoring force characteristics of SPDs, the analysis uses a newly developed combined hardening model based on experimental data. The seismic demands made on SPD devices are examined and then summarized to give recommended values for determining the necessary deformation capacity of SPDs.     

Numerical Investigation of Residual Strength and Energy Dissipation Capacities of Corroded Bridge Members Under Earthquake Loading

Recent damage examples of aged steel bridge infrastructures around the world are so alarming. They intensified the importance of careful evaluation of existing structures for the feasibility of current usage and to ensure public safety. Corrosion and fatigue cracking may be the two most important types of damages in aging structures. Furthermore, recent earthquakes demonstrated potential seismic vulnerability of some types of steel bridges. Corrosion and its effects can trigger the damages caused by earthquakes, and it will be vital to understand the behavior of existing steel bridges which are corroding for decades in future severe seismic events as well. This article comprises the results of nonlinear FEM analysis of many actual corroded plates with different corrosion conditions and proposes a simple and reliable methodology to estimate remaining seismic strength and energy dissipation capacities by measuring only the minimum thickness of a corroded surface, which can be used to make rational decisions about the maintenance management plan of steel infrastructures.     

Successive Earthquake-Tsunami Analysis to Develop Collapse Fragilities

Over the last half century, scientists and engineers have developed methods to better understand and mitigate the damage caused by tsunamis. According to U.S. Federal Emergency Management Agency (FEMA) P646, buildings in many regions, including the U.S. Pacific Northwest, will experience substantial ground shaking from an offshore earthquake that precedes a tsunami and then experience the tsunami forces themselves. Thus, both hazards should be considered in computing the damage and collapse risk to buildings. This article summarizes a basic approach to numerically consider the successive seismic and tsunami risk to buildings in near-field tsunami regions such as the U.S. Pacific Northwest.     

Increasing inequality in Chalcolithic Southeast Europe: the case of Durankulak

Economic measurement tools allow a quantification of social differences not only for modern societies, but also for prehistoric communities. The use of Gini indices and Lorenz curves for the much discussed Chalcolithic cemetery of Durankulak (Bulgaria) indicates an average increase in material items from 5000 cal BC onwards and a tendency of these items to be distributed somewhat more equally. Towards the end of the Chalcolithic sequence, however, strongly growing inequality was associated with lower average welfare. The steep increase in social inequality might be one of the main reasons for the collapse of Chalcolithic societies around 4100 cal BC in Durankulak, but also in other South East European regions.