Publications

A field experiment and numerical simulations were performed to investigate the progressive collapse potential of an existing steel frame building. Four first-story columns were physically removed from the building to understand the subsequent load redistribution within the building. Experimental data from the field tests were used to compare and verify the computational models and simulations. Due to the scarcity of data from full-scale tests, the experimental data produced during this research is a valuable addition to the state of knowledge on progressive collapse of buildings. The progressive collapse design guidelines typically recommend simplified analysis procedures involving instantaneous removal of specified critical columns in a building. This paper investigates the effectiveness of such commonly used progressive collapse evaluation and design methodologies through numerical simulation and experimental data.

This paper proposes a pipeline to automatically track and measure displacement and vibration of structural specimens during laboratory experiments. The latest Mask Regional Convolutional Neural Network (Mask R-CNN) can locate the targets and monitor their movement from videos recorded by a stationary camera. To improve precision and remove the noise, techniques such as Scale-invariant Feature Transform (SIFT) and various filters for signal processing are included. Experiments on three small-scale reinforced concrete beams and a shaking table test are utilized to verify the proposed method. Results show that the proposed deep learning method can achieve the goal to automatically and precisely measure the motion of tested structural members during laboratory experiments.

As part of an experimental program, a large number of in-service culverts were tested to investigate the influence of several parameters on field performance of culverts. These parameters included cover depth, load application, size, shape, and other properties of corrugated metal culverts. Response of 14 test culverts was simulated using a two-dimensional finite element program and a three-dimensional finite difference program. Deflections predicted from the two-dimensional analyses were larger than the deflections measured in the field. However, the experimental and calculated thrust forces were similar. Deflections and thrust forces predicted from the three-dimensional analysis were similar to the experimental results. The critical factors affecting the response of the culverts include cover depth, culvert size, metal thickness, and elastic modulus and other properties of backfill soil. The influence of these parameters on the culvert behavior is investigated through numerical simulations using the established modeling properties.

No abstract is provided for this article.

Predicting the shear strength of structural elements subjected to gravity loads and ground motions is an important component of seismic design. Among all primary structural components, the vital role of columns in load transfer and redistribution, structural stability, and collapse prevention has been well recognized through observations made in the aftermath of past earthquakes. Numerous analytical, numerical, and experimental studies have been conducted to assess the shear strength of RC columns in the past decades. However, there is still a large scatter (i.e., uncertainty) in the predictions of current empirical and numerical models relative to test data. In this paper, novel data-driven models are presented for predicting the maximum shear strength of rectangular and circular RC columns. To this end, two extensive experimental databases for both types of columns were used in the present study. The data were randomly partitioned into calibration and validation sets. The calibration data sets served as the basis for developing linear and nonlinear equations for predicting the ultimate shear capacity of rectangular and circular RC columns through regression analyses. The Monte Carlo method was employed by conducting 106, 107, and 108 realizations to exhaustively examine the optimal parameter space of the postulated equations. The calibrated predictive models were then validated using the validation data sets; and their performances were also compared to existing models. These validation and comparison studies revealed that a new linear model devised and calibrated in the present study achieved very high accuracy, even compared to various nonlinear models considered. It was, moreover, significantly superior to all prior models in predicting the column shear strengths. This linear model, which is based on physical parameters, can therefore be recommended for engineering practice.

Currently, there are only a few common methods that can be used to strengthen reinforced concrete columns. These methods, including steel jacketing, section enlargement by concrete jacketing, and fiber reinforced polymer (FRP) composite wraps, were are used to strengthen 15 column specimens. The ease of application, economy and efficiency of each method are discussed and compared. In this study, three exterior reinforced concrete beam-column joint specimens were tested under reverse cyclic loading. The damaged specimens were repaired by replacing the damaged concrete and then strengthened using FRP strips. The strength was restored and deformation capacities of the strengthened specimens were much larger than those of the original specimens.

No abstract is provided for this article.

Seismic probabilistic risk assessment (SPRA) requires a large number of simulations to evaluate the seismic vulnerability of structural and nonstructural components in nuclear power plants. The effect of structural modeling and analysis assumptions on dynamic analysis of 3D and simplified 2D stick models of auxiliary buildings and the attached nonstructural components is investigated. Dynamic characteristics and seismic performance of building models are also evaluated, as well as the computational accuracy of the models. The presented results provide a better understanding of the dynamic behavior and seismic performance of auxiliary buildings. The results also help to quantify the impact of uncertainties associated with modeling and analysis of simplified numerical models of structural and nonstructural components subjected to seismic shaking on the predicted seismic failure probabilities of these systems.

Modern society is demanding that the use of energy associated with construction and operation of structures be investigated during the planning and design phases. The engineering community has been striving to design more sustainable buildings in an attempt to reduce both raw material requirements and energy use during all phases of design. Structural engineers currently have very limited guidance on how to incorporate sustainability concepts in their designs. Innovative methods are needed to address the environmental impact, energy use, and other sustainability issues faced during planning and design of buildings. This paper investigates and discusses five sustainable structural design methodologies: Minimizing Material Use, Minimizing Material Production Energy, Minimizing Embodied Energy, Life-Cycle Analysis/Inventory/Assessment, and Maximizing Structural System Reuse. The goal of this paper is to describe and address issues associated with the proposed design methodologies to determine which, if any, can produce the most sustainable structural designs. It was determined that no single methodology can address all the issues surrounding sustainable structural design. Also, it was determined that combinations of two or more methodologies may increase the ability of design professionals to produce more sustainable designs.

In this paper, an existing beam-on-springs modeling methodology is examined for suitability in estimating vertical displacements and joint movement in jointed pipe culvert systems. Methods of determining the modulus of subgrade reaction, 𝑘𝑠, are used in beam-on-springs modeling and compared with results from laboratory tests on three buried culvert pipes. Pipes were buried in soil conforming to AASHTO specifications for buried structures and then loaded at the ground surface. Two of the methods provided reasonable estimates of 𝑘𝑠 for use with both rigid and flexible test pipes (with an average error of 25%). The first method relies on empirical parameters, whereas the second method relies on actual soil properties to estimate 𝑘𝑠. This makes the second model more appealing. However, the second model is somewhat less accurate than the first (10% average error compared with 25% average error). Movement at the culvert joint was estimated by beam-on-springs modeling with a moderate degree of accuracy (within 52% error when calculating the maximum movements) because of the complexities of the jointed culvert system being modeled. Accordingly, results from a beam-on-springs model should be used conservatively.

Seismic damage and vulnerability of five historical masonry structures surveyed after the 1999 Kocaeli and Duzce, Turkey earthquakes are discussed in this paper. The structures are located in two neighboring cities that have been struck by five very large (Ms ≥ 7.0) earthquakes during the 20th century alone. Older masonry mosques with arches and domes and their masonry minarets (slender towers) were among the most affected structures in this highly seismic region. While some of the religious and historical structures had virtually no damage, most structures suffered significant damage or collapsed. In the city of Bolu, for example, approximately 600-year-old Imaret, 500-year-old Kadi, 250-year-old Sarachane, and 100-year-old Yildirim Bayezid mosques suffered substantial structural damage after the 1999 earthquakes. Another historical mosque surveyed in Duzce partially collapsed. Most common factors contributing to deterioration of historical structures are also presented. Furthermore, a brief overview of issues associated with analysis and modeling of historical masonry structures is provided

Reinforced concrete columns with insufficient transverse reinforcement and non-seismic details are vulnerable to shear failure and loss of axial load carrying capacity in the event of an earthquake. In this study, the application of two macro models is examined using previously tested shear critical reinforced concrete columns subjected to lateral loads. One of the approaches simulates lateral load-deformation response by estimating deformation components due to flexure, reinforcement slip and shear individually and then combing them according to a set of rules specified for each category. The columns classified into categories based on comparison of their predicted shear and flexural strengths. The other approach, Axial-Shear-Flexural Interaction method, considers the interaction of axial deformations and concrete compression softening to couple shear and flexural mechanisms while satisfying compatibility and equilibrium conditions in average stress-average strain field. Capabilities of both models are evaluated in terms of predicting mode of failure, ultimate lateral loads and drifts, and post-peak responses. Based on the comparison of experimental and analytical results, conclusions are drawn to improve response estimation by either of the models. Implementation of suggested analytical procedure results in satisfactory response envelope curves which can be used for development of cyclic response models.

It is desirable that nonlinear dynamic analyses for structural fragility assessment are performed using unscaled ground motions. The widespread use of a simple dynamic analysis procedure known as Cloud Analysis, which uses unscaled records and linear regression, has been impeded by its alleged inaccuracies. This paper investigates fragility assessment based on Cloud Analysis by adopting, as the performance variable, a scalar demand to capacity ratio that is equal to unity at the onset of limit state. It is shown that the Cloud Analysis, performed based on a careful choice of records, leads to reasonable and efficient fragility estimates. There are 2 main rules to keep in mind for record selection: to make sure that a good portion of the records leads to a demand to capacity ratio greater than unity and that the dispersion in records' seismic intensity is considerable. An inevitable consequence of implementing these rules is that one often needs to deal with the so-called collapse cases. To formally consider the collapse cases, a 5-parameter fragility model is proposed that mixes the simple regression in the logarithmic scale with logistic regression. The joint distribution of fragility parameters can be obtained by adopting a Markov Chain Monte Carlo simulation scheme leading directly to the fragility and its confidence intervals. The resulting fragility curves compare reasonably with those obtained from the Incremental Dynamic Analysis and Multiple Stripe Analysis with (variable) conditional spectrum–compatible suites of records at different intensity levels for 3 older reinforced concrete frames with shear-, shear-flexure-, and flexure-dominant behavior.

The core damage frequency (CDF) of a representative nuclear power plant is estimated for design basis earthquake (DBE) and beyond DBE (BDBE) using state-of-the-art structural models within a dynamic probabilistic risk assessment (DPRA) framework. Randomness of seismic excitation and uncertainty of structural parameters are considered using a simulation-based approach. Finite element models are developed for the structure and a liquid container (hydro-accumulator), and fluid-structure interaction is considered with the arbitrary Lagrangian-Eulerian method. The CDF is evaluated through a time-dependent event tree. Also, correlation among multiple hydro-accumulators is investigated. The results show that operator action and independence of emergency diesel generators are crucial under BDE for damage control, while implementation time of mobile safety equipment is critical under BDBE in case of loss of offsite power following an earthquake. It was also found necessary to adopt a DPRA approach to determine the available time for action and core damage timing probabilistically.

Condensate storage tanks (CSTs) in nuclear power plants (NPPs) are classified as critical equipment capable of surviving strong shaking in a design basis earthquake to assure the ability to subsequently provide cooling water. Structural modeling and dynamic analysis of CSTs are complicated due to fluid-structure interaction (FSI) and coupling issues, which could have significant effects on seismic response. The capability of a number of approximate models to capture seismic response is investigated using dynamic analysis results from detailed finite element models. Modal analyses and time history analyses are carried out using both 2D and 3D models to predict the dynamic behavior of CSTs as a function of ground motion intensity. Although 2D simplified models can be used to quickly evaluate the dynamic response of CSTs when there is substantial margin to failure, a detailed 3D model is required when it is necessary to examine a limit state associated with the failure mode of the tank. The results show good agreement between the natural frequencies of convective modes determined from the 2D and 3D CST models. The difference between the frequencies of impulsive modes were found to be equal to or less than 25%.