Development of Probabilistic Framework for Performance-Based Seismic Assessment of Structures Considering Residual Deformations

Recently, the importance of considering residual (permanent) deformations in the performance assessment of structures has been recognized. Advanced structural systems with re-centering properties as those based on unbonded post-tensioning tendons are capable of controlling or completely eliminating residual deformations. However, for more traditional systems, which count for the vast majority of buildings, residual deformations are currently considered an unavoidable result of structural inelastic response under severe seismic shaking.

In this article, a probabilistic framework for a performance-based seismic assessment of structures considering residual deformations is proposed. The development of a probabilistic formulation of a combined three-dimensional performance matrix, where maximum and residual deformations are combined to define the performance level corresponding to various damage states for a given seismic intensity levels, is first presented. Combined fragility curves expressing the probability of exceedence of performance levels defined by pairs of maximum-residual deformations are then derived using bivariate probability distributions. The significance of evaluating and accounting for residual deformations within a Performance-based Earthquake Engineering (PBEE) approach is further confirmed via numerical examples on the response of Single Degree of Freedom (SDOF) systems, with different hysteretic behavior, under a selected suite of earthquake records. Joined fragility curves corresponding to various performance levels, defined as a combination of maximum and residual response parameters, are derived while investigating the effects of hysteretic systems and strength ratios. It is observed that stiffness degrading Takeda systems result in lower residual deformations than elasto-plastic systems and show lower probability of exceeding a jointed maximum-residual performance level. For a chosen performance level, Takeda systems with higher strength ratios show better performance, particularly with lower intensity of excitations.     

Wavelet-Based Damage Detection in Reinforced Concrete Structures Subjected to Seismic Excitations

The feasibility of using output-only model-free wavelet-based techniques for damage detection in reinforced concrete structures subjected to seismic loads is explored through the analysis of the results of a full scale shake table test of a reinforced concrete bridge column recently performed at the NEES Large High Performance Outdoor Shake Table. The evaluated approaches are based solely in the analysis of the acceleration time histories recorded in the structure. The viability of using numerical models to validate this type of damage detection methodologies is also evaluated. Wavelet analyses were capable of identifying the rebar fracture episodes and partially identified the frequency shifts in the structure as the inelastic demand increased. It was also found that, depending on the methodology employed, the use of numerical models to validate damage detection techniques can oversimplify the actual problem and/or induce spurious irregularities.     

Seismic Displacement Demands on Skewed Bridge Decks Supported on Elastomeric Bearings

The unseating of decks is one of the most prevalent failure modes of bridges after earthquake events, as observed in the 2010 Chile Earthquake. Damaged bridges in Chile often had skew angles and were supported on elastomeric bearings. Similar bridge construction practices with decks supported on elastomeric bearings are also common in the central and eastern U.S. (CEUS). The seismic displacement demands on skewed bridges are more complicated than those on bridges without skew angles due to the coupling of translational modes with the rotational mode of vibration. The study presented in this article seeks to understand the seismic response of skewed bridge decks supported on elastomeric bearings. The scope of the study is limited to one- and two-span bridges, which constitute a large portion of bridge inventory in the CEUS. The vibration modes of skewed bridge decks are derived in closed form and the modes are compared when the gaps between the bridge deck and the abutment are open and when one of the gaps is closed due to seismic excitation. Nonlinear response history analyses are carried out to understand the effects of vertical ground motion, skew angles, aspect ratios, and different ground motion types on the seismic displacement demand in these cases. Amplification factors that approximate the increase in the displacement demand due to the skew angle are proposed.     

A Comparative Study on Ground Motion Attenuation in the 2012 Varzaghan-Ahar Doublet Event,Northwest of Iran

Predictive capabilities of the four updated NGA ground-motion models (NGA-WEST2) are evaluated in this study for acceleration response spectra using observed ground motions for August 11, 2012 Varzaghan-Ahar events in Iran. The predicted results were compared with those of regional attenuation equations and NGA08 models as well. The results of analyses revealed that the models of NGA-WEST2 improve prediction performance of NGA08 models for the two studied moderate events. All of models underestimate the recorded spectra of the second event for regionally significant period of 0.2 s at source distances below 50 km. For this distance range, almost all of the models underestimate the recorded spectra for periods larger than 1 s.     

On the Earthquake-Source Numerical Implementation in the Seismic Wave Equation

We present a detailed approach to implement a moment-tensor point source to compute displacements, particle velocities and accelerations using direct grid methods. Here, the wave modeling algorithm is based on pseudospectral methods to compute the partial derivatives. A comparison to the analytical solution in the 3D acoustic case verifies the discrete implementation of the source in the mesh. Then, the more general 3D elastic case is illustrated and simulations, with and without free surface, are performed that can be used as a reference solution for other grid methods.     

Modeling and Control of the CSCEC Multi-Function Testing System

In order to promote the research and development on evaluating the seismic performance of structures, China State Construction Engineering Corporation (CSCEC) planned to construct a large-scale loading testing facility, the Multi-Function Testing System (MFTS). This facility can perform full-scale, real-time, 6-degree-of-freedom static and dynamic testing of rubber bearings and many types of structural components including long columns, shear walls and cross shape joints. The basic performances of the MFTS are a clearance of 9.1 m × 6.6 m × 10 m for specimen installation, maximum x-directional displacement 1500 mm, maximum y-directional velocity 1570 mm/s and maximum z-directional compressive load 108 MN. The system configuration and performance specifications of the MFTS are presented in this paper. The inverse kinematics model and the nonlinear model of the hydraulic servosystem of the MFTS are built. A modified feedback forward kinematics algorithm is developed for real-time control of the MFTS. Internal force characteristics of the loading system are analyzed. The internal force control method based on real-time solution of basis of internal force space is proposed for the system with large motion ranges. The motion controller combining position control loop and internal force control loop is developed. To meet the requirement of simultaneously imposing vertical compressive load and horizontal displacement, a mixed load and displacement controller is designed, where a direct force control loop is used to improve the response speed of the force control and reduce spatial dynamic coupling effects. Finally, a dynamic bearing testing is performed. The test results demonstrate that the system using the proposed controller has good abilities on position tracking, force balance, and load following.     

Geotechnical Reconnaissance of the 2016 ML6.6 Meinong Earthquake in Taiwan

On February 6, 2015, a local magnitude (M_L) 6.6 earthquake struck southern Taiwan, devastating the Tainan area. A field investigation was conducted by a survey team from the National Center for Research on Earthquake Engineering immediately after the earthquake. This paper summarizes the observed geotechnical damage features caused by the earthquake, including liquefaction, slope sliding, levee failure, and dam performance. Several liquefaction sites were observed despite the intensity of ground shaking being moderate (peak ground acceleration, ~0.2 g). Most of these sites were originally old ponds that were backfilled during different periods in the last three to eight decades. Two significant types of damage to the levee of the Tseng-wen River were observed. At the Jianshan site, a typical type of levee damage was observed, in which the level crest subsided and the side slope developed several cracks. At the Rixin site, a flow-type of failure caused tremendous loss of levee (~400 m in total) at three adjacent locations. The levee embankments had “flowed” up to 60 m into the river.     

Aseismic Assessment of the Qiantang River Levee

Liquefaction potential is evaluated using both in-situ and laboratory testing methods. Liquefaction and dynamic stability for the levee are determined using Biot’s dynamic consolidation equation which is used to analyze the increase and dissipation of pore water pressure as well as liquefaction and dynamic stability in the levee during a magnitude 7 earthquake. By inverse analysis, the acceleration at the bedrock is obtained from the acceleration data monitored previously at free surface and is inputted as the seismic loading. Results presented in this paper can provide improved stability assessment for levees experiencing seismic events of this magnitude.     

A distinguished scientific field? Pursuing resources and building institutions for engineering research in Sweden, 1890–1945

The perennial issue of the relations between science and technology and society is a backdrop to this study of material, symbolic and economic foundations of engineering science in Sweden. It analyzes three cases of institutional reform from the first half of the twentieth century that were essential to the formation of engineering research as a distinct and respected scientific field. Taking the intersection of institutional and linguistic analysis as a starting point, two intertwined processes are followed: the drawing of boundaries by different actors that delineated the new kind of research, and the struggle over resources for the institutions that could enable this research. The institutional reforms are placed in context, relating arguments by the proponents of engineering research to the politicians and university academics who were in control of various resources. It is suggested that an institutionalist perspective enunciated in terms of form and content is a productive interpretive possibility.     

安岳石窟经目塔5.12汶川大地震后抢救性修缮——兼论三维激光扫描、计算机模拟技术在文物保护中的运用

"5.12汶川特大地震"对安岳石窟所属的孔雀洞经目塔产生了较大的影响和破坏。本次勘察修缮设计目标是修复经目塔震后的直接残损,对其结构进行必要的加固,减缓风化对塔体的影响,由于破坏的突然性及抢救工作的迫切性要求,从勘察到设计仅仅1个多月时间,勘察设计方在工作之初便决定引入三维激光扫描技术,并在评估及设计过程使用计算机模拟复原技术,力求准确翔实的得出经目塔震后的评估结论,及为震落构件找到准确的原有位置。作为最终修缮设计的依据。并通过结构计算,最终确定经目塔的修缮方案。本次勘察设计过程中引入的三维激光扫描技术及计算机模拟技术在石质文物勘察设计中均具有突破性进展,为今后石质文物的科技保护进行了切实有效的探索。