Journal of Performance of Constructed Facilities

Forum papers are thought-provoking opinion pieces or essays founded in fact, sometimes containing speculation, on a civil engineering topic of general interest and relevance to the readership of the journal. The views expressed in this Forum article do not necessarily reflect the views of ASCE or the Editorial Board of the journal.

This article presents an experimental and numerical study on the structural safety of an old buried water reservoir built in the second half of the nineteenth century. The main goal of the study was to assess the feasibility of changing the reservoir roof from a garden with limited access to an outdoor exhibition or concert area, with an increase in service loads. The reservoir comprises a set of cylindrical vaults, built with rubble masonry and lime mortar, supported by a set of stone masonry arches and columns. Because no original design elements exist, the following methodology was followed: (1) a structural survey was first carried out for geometrical and material identification and for assessment of anomalies; (2) core samples were extracted from the vaulted roof to characterize the material properties of the rubble masonry and lime mortar; (3) a three-dimensional (3D) nonlinear finite element (FE) model of the structure was developed and used for structural safety verification; and (4) an in-situ static load test was carried out, in which the roof was subjected to a uniformly distributed load for assessment of its structural response and to validate the results from the numerical model. Overall, this study showed that the vaulted roof of the water reservoir has sufficient load capacity for its future use. Moreover, this work illustrates the application of a comprehensive methodology to assess the structural safety of a historical and very particular type of construction.

Image processing-based health assessment of underwater concrete structures is a challenging task. The complex underwater environmental disturbances and serious image degradation significantly affect the accuracy of crack detection. To reduce the impact of these factors, an underwater concrete crack detection algorithm based on fractal theory [fractal underwater crack detection algorithm (F-UCD)] is proposed in this study. Meanwhile, a four-level structural assessment criterion is established to assist in underwater crack measurement and structural health assessment. To validate the optimal distance of the algorithm, four distances of $0.6\mathrm{m}$, $1\mathrm{m}$, $1.4\mathrm{m}$, and $1.8\mathrm{m}$ are set. The results show that the F-UCD algorithm can effectively detect cracks in underwater concrete members within $0.6\mathrm{m}$. The structural assessment standards based on fractal theory can be used to assist managers in determining the health condition of structures.

This paper investigates the evolution of damage in a reinforced concrete flat slab that is impacted by a flat slab that is falling from above due to failure of its connections with its supporting columns, thus starting a progressive collapse scenario. The momentum transmitted to the impacted slab develops severe damage at the column-slab connection zone of the impacted slab and causes complete failure of the connection within a very short duration. This paper aims at investigating the processes occurring during this short duration from the instant of contact between the impacting slabs until a complete failure of the impacted slab-column connections is reached, thus gaining insight into the evolution of the damage. Understanding these processes will enhance the understanding of the governing mechanisms and contribute to improve the design of these connections and lead to derive physically based engineering models. Using a powerful numerical simulation, a structural model for the present investigation had been established and the entire failure event is analyzed. The damage increase in the concrete within the slab is carefully followed, showing a radial spread of a full-damage zone outward from the column circumference that exceeds several column widths within less than 20 ms, during which a complete failure of the connection occurs. During this time, the rebars in the connection zone undergo plastic deformation and failure, and the reinforcement contribution to the shear resistance of the connection decreases rapidly. The paper investigates the growth of damage with time and examines the rate of processes in the different reinforcement types. It examines the effect of the ductility of the steel rebars and investigates the dependence of concrete damage on the effectiveness of the shear reinforcement. This study provides a deep new insight on the complex short-duration mechanisms involved in this impact event.

With the rapid deterioration of infrastructure, accurate predictions of bridge deck performance is critical in bridge management systems (BMS). The US Federal Highway Administration (FHWA) has developed the National Bridge Inventory (NBI) database, which has accumulated a vast repository of bridge performance data in the US. Although alternative methods have been used for harvesting such data, the use of machine learning (ML) has been explored to a lesser degree due to its modeling complexity. Objective of this study was to develop and assess alternative sequential models by employing long short-term memory (LSTM) and convolutional neural networks (CNN). The advantage of such modeling alternatives in relation to past ML studies is that consider (1) fixed or variable number of sequences of observations combined with (2) continuous or flexible sequences, producing better condition rating predictions. The results indicated that the models exceeded accuracy prediction from the mid 80% in past studies to levels of 95% for Maryland bridges, and all the way to 97% when Massachusetts data were added. Such results indicate that the proposed models are able to better capture the complex relationships between bridge-related features and condition rating. Transferability of the proposed approach was confirmed with the successful model response when data from the second state were used. It is expected that improved predictions of condition rating will promote more effective maintenance and rehabilitation strategies in BMS.

A structural health assessment of the tunnel lining is carried out to investigate and mitigate the cause of defects in the tunnel lining to ensure user safety. Many factors affect the tunnel’s integrity, causing a wide range of defects. Identifying the possible cause and its relation with the degree of associated defect is essential for tunnel stability. In conjunction with defects of tunnel failure, liner cracks were found to be most critical because they could trigger other defects to form and jeopardize tunnel stability. Thus, this research acquires visual inspection followed by comprehensive mapping and quantification of liner cracks to enhance our understanding of the effect of varying overburden on the intensity of liner cracks. The numerical analysis was further performed to analyze the influence of varying topography (overburden) on the crack intensity of the liner using the stress ratio, $K$ as a parameter in terms of the state of stress using induced stress (IS) and stress concentration factor (SCF) as a performance evaluation criterion. The work demonstrates that the shift in magnitude and position of liner cracks on the different portions of the tunnel liner implies the effect of a regionally external factor (varying overburden depth) on tunnel degradation. For advances in tunnel assessment based on the regional diversity of cracks along the longitudinal profile of the tunnel, the tunnel should be divided into zones based on the overburden to identify the varying intensity of the liner crack. This study shows the variable crack density of 575 m to 628 m, 650 m to 700 m, and 704 m to 724 m for shallow, intermediate, and deep zone, respectively. The findings of this study can provide scientific guidance to tunnel inspectors and engineers regarding the tunnel liner health assessment and identifying the subsequent method of repair.

Earthquakes can cause extensive damage to buildings, with lengthy impacts in terms of community recovery. As a result, there is a growing interest in design approaches and standards for buildings that ensure postearthquake functional recovery. This paper qualitatively explores barriers and opportunities for achieving functional recovery in the retrofit of existing buildings. The study employs a set of focus groups engaging 21 participants who are experienced in the seismic retrofit of reinforced concrete buildings in the US. Qualitative analysis methods were used to analyze the collected data and to identify the key themes. The thematic analysis revealed three groups of owners and buildings: (1) those for which functional recovery-based retrofit may be achievable, including owners with long ownership time horizons, high-value contents or operations, and buildings whose functions cannot easily be relocated; (2) those for which retrofit for functional recovery is likely not needed nor practical, including buildings whose functions can be distributed to provide geographic redundancy or replaced with remote operations or a different building; and (3) buildings for which life safety retrofits, sustainability upgrades, or other renovations may improve functional recovery even if not explicitly targeted. The study also revealed significant barriers related to retrofit costs, insufficient or inadequate tools and guidelines for retrofit implementation, difficulty in communication of benefits, and a contradiction between community-scale goals and building-scale decisions. Opportunities identified to address these barriers include strategies to improve access to capital and funding, measure and communicate economic and other benefits, and develop tools and guidelines. This study is the first to rigorously explore the feasibility of achieving functional recovery for existing buildings, which make up a major part of the US building stock and are, therefore, significant impediments to postearthquake community recovery. The study suggests actions that can facilitate moving towards functional recovery objectives.

Abstract

The Dnipro hydroelectric power plant (HPP) is the oldest hydroelectric power station in Ukraine built almost 100 years ago. The HPP dam was heavily damaged during World War II. Long-term operation of the dam requires the monitoring of spatial movements and its deformation processes. The purpose of the research is to develop a spatial displacement monitoring model of the global navigation satellite system (GNSS) dams at the Dnipro HPP. The study is based on the data received both from an automated monitoring system and changes in ambient temperature from 2017 to 2020. The input data are presented by time series of changes in GNSS coordinates. They are based on the results of around-the-clock measurements obtained at the points of the Dnipro HPP dam during 2017–2020. The information also includes the results of measuring the average daily air temperature at the Dnipro HPP. A specially developed software product analyzed the time series of GNSS measurements to determine seasonal spatial displacements. It also revealed their connection with seasonal changes in air temperature. As a result we managed to find the decisive influence of ambient temperature on the seasonal spatial displacements of dams, though significant changes in the reservoir water level were absent. The crest of the dam shifted toward the reservoir and rose in the first 6 months. In the second half year, the horizontal displacements were directed toward the lower reaches, and vertical subsidence took place. The velocity distribution of spatial displacements along the dam’s crest was uneven in time. The magnitude of extreme displacements and the epoch of their representation depended on the dam’s design and technical parameters. They were different for each dam. The study helped to develop an average statistical model that revealed the dependence of the spatial displacements at the Dnipro HPP dam crest on the average integrated air temperature. The conducted research allows us to establish and predict the values of seasonal spatial deformations of the Dnipro HPP dam, as well as disclose the effect of air temperature. Deviations from the temperature deformation model might be considered as possible changes at certain points of the dam during either its operational period or technical defects obtained during its construction. Such deformations can cause cracks in the dam’s body and thus impact its stability. The pattern of the connection between the change of temperature and the displacements of GNSS points was revealed as a result of the study. This can be used for research on processing and analysis of monitoring data of other engineering constructions.

Practical Applications

The paper presents the method of computation an average statistical model demonstrating the dependence of the dam spatial displacements on the average integrated air temperature. This method can become an addition to automated GNSS monitoring systems installed on hydroelectric dams. This makes it possible to identify problem areas in the structure deformation field that may be invisible from the outside. However, they can manifest as stresses, deformations and subsidence of reinforced concrete structures, the appearance of cracks, and water seepage. Timely detection of these anomalies enables to clarify the safety state of the concrete dam. The proposed technique can be integrated into automated GNSS monitoring systems of other large engineering structures (high-rise buildings, bridges, pipelines). This is especially relevant for engineering structures that are operated under the influence of seismic activity or located in areas of military operations where natural or human-made earth’s surface vibrations lead to the internal irreversible structure deformations. According to the forecasts, global warming and climate change can lead to an increase in the intensity and frequency of extreme weather conditions (hurricanes, floods, temperature changes). Therefore, we emphasize the importance of the automated GNSS monitoring of large engineering structures. Furthermore, modeling the influence of these factors on their deformation fields is absolutely relevant.

This paper presents fragility functions for clay brick unreinforced masonry (URM) buildings that were developed using the data of damage and earthquake intensity by the September 24, 2019, Mirpur, Azad Jammu and Kashmir earthquake. These data were collected through reconnaissance surveys in the affected region. The intensity of the earthquake ranged from V to VII on the Modified Mercalli Intensity scale in the surveyed areas. The damage to clay brick piers of bridges was caused by compression or shear-compression forces applied by the vertical seismic forces. Most of the damaged URM buildings showed in-plane wall cracking with very few cases of out-of-plane wall failure. The damage in these buildings was influenced by both the ground motion’s horizontal component and ground motion amplification due to site conditions. The damage types to the URM buildings in the surveyed areas were classified into five damage grades and these data were employed to propose fragility curves for clay brick URM buildings.

Modernist architecture buildings have been socially undervalued as part of the heritage of architecture. Fortunately, in recent times, some movements have emerged, such as the International Committee for Documentation and Conservation of Buildings, Sites, and Neighborhoods of the Modern Movement (DoCoMoMo). The Auditorium of the Labor University of Cheste is an example of Spanish brutalism, which, due to its low appreciation, has fallen into disuse and is currently immersed in an accelerated pathological process. In this research work, supported by the Jean Paul Getty Trust, the structural system of the building and its pathological state are studied in depth, with the aim of rehabilitating the structure and putting it back into use. For this, a detailed documentation of the location and type of damage was carried out, and interventions are proposed in each case. Nondestructive testing and techniques (NDT), such as infrared thermography (IRT) and laser scanning, were used to carry out this research. This work aims to help revalue these emblematic buildings of the 20th century, opening the way to an appreciation and reuse of this heritage.

Ground-penetrating radar (GPR) is a mainstream tool to detect defects behind tunnel linings, but the difficulty in interpreting GPR signals limits its application. This paper proposes an intelligent way to differentiate the defects behind tunnel linings by means of a model test and feature parameter analysis, to achieve an efficient and accurate analysis of GPR signals. The model test reveals the differences between defect and non-defect GPR data in amplitude, signal entropy, standard deviation, and other feature parameters. The amplitude of the defect data was on average six times as large as that of non-defect data, and the signal entropy was about 1.2 times larger. The two feature parameters lay the basis for defect detection by GPR. On this basis, a GPR-based automatic identification method was proposed, and the program was compiled on MATLAB. The program achieved a defect recognition rate as high as 96% through a field test at a rapid speed. The program is highly accurate and feasible for detecting defects behind tunnel linings with the aid of GPR.

Although overpressure burst of pipeline with pressure-protection systems occurs infrequently in case of blockage, it endangers personnel safety and causes serious economic loss when it happens. Therefore, assessing the dynamic probabilistic risk of overpressure burst of pipeline with pressure-protection systems in case of blockage is necessary to prevent accidents. This study proposes a method based on a dynamic Bayesian network (DBN) for assessing the dynamic probabilistic risk of overpressure burst of pipeline with pressure-protection systems in case of blockage. First, a fault tree (FT) model of pipeline overpressure burst is constructed. The constructed FT model is then mapped into the DBN model to solve the uncertainty of the model. Second, the leaky Noisy-OR gate is used to define the uncertain logical relationships of relevant nodes in the DBN model. The effect of common cause failures on a pipeline’s redundant pressure-protection system is analyzed using the multiple error shock model. Finally, a natural gas export pipeline is presented as an example to demonstrate the proposed method. Results show that the method can effectively assess the dynamic probabilistic risk of overpressure burst of pipeline with pressure-protection systems in case of blockage.

Abstract

A gravity dam monolith bounded by the transverse contraction joints on both sides is usually recognized as an independent element in various dynamic analyses. However, in most cases a gravity dam monolith is actually subdivided by longitudinal joints for mass concrete construction requirements. Previous studies of gravity dams subjected to underwater explosion (UNDEX) shock loadings have not dealt with the longitudinal-joint issue in much detail. In this work, a numerical simulation of the dynamic response of an old gravity dam without good longitudinal-joint connection integrity in an UNDEX event is performed. The coupled acoustic-structural analysis procedure with ABAQUS/Explicit is employed. The reliability of the procedure is validated by numerical simulations of two UNDEX impact tests in the literature. Nine calculation cases are considered to compare different responses of the dam with different connection states between monolith sections and underwater detonation depths. The results of this numerical investigation show that the longitudinal joints play an important role in the UNDEX response of the dam. The longitudinal joints greatly weaken the flexural rigidity of the dam and make the dam damaged in a piecemeal manner. This study adds to the rapidly expanding field of the UNDEX resistance performance evaluation of gravity dams by accounting more for the longitudinal-joint issue.

Practical Applications

The antiterrorism situation worldwide is experiencing constant changes, making the world continually face multiple unstable factors. Dams are easy attack targets for their enormous social and economic values. Among various dam types, gravity dams are commonly recognized to have the best blast resistance performance owing to their monumental body sizes. A gravity dam is routinely divided into several monoliths by transverse joints. Each monolith is then subdivided by longitudinal joints for mass concrete construction requirements. After the completion of a dam monolith, the longitudinal joints should be grouted to ensure the integrity of the monolith. For some dams serving several decades, their longitudinal-joint connection integrity might deteriorate. Such structural integrity losses should lead to blast resistance performance degradation. With this in mind, the authors carried out a series of numerical simulations of an old gravity dam when it is experiencing underwater explosion (UNDEX) shock loadings. Nine cases are considered concerning different longitudinal-joint connection states and UNDEX scenarios. This work clarifies the mechanism that the longitudinal-joint connection failure deteriorates the UNDEX resistance performance of the dam. Great efforts on reinforcing old dams through enhancing their longitudinal-joint connection integrity are thus needed to ensure their adequate blast resistance performance.

This paper evaluated the progressive collapse robustness of steel intermediate moment-resisting frames (MRFs) under different fire-induced column failure scenarios. For this purpose, 3-, 7-, and 12-story intermediate MRFs were modeled numerically and analyzed under different gravity and fire loads. The effects of the seismic design requirements, number of stories, gravity load ratio (utilization ratio), and redundancy and position of the heated column were discussed. Because the investigations included models with different number of stories and different seismic to gravity load ratios, the results can be applied for a wide range of IMFs. The results show that none of the studied frames in the high seismic zone with a low gravity loads ratio experienced progressive collapse under any of the considered fire scenarios. However, by increasing the ratio of gravity loads in frames, the vulnerability to progressive collapse was increased. This suggests that in areas with a lower risk of environmental lateral loads, where MRFs generally are designed for gravity loads and smaller lateral forces, the progressive collapse robustness of MRFs under fire-induced column failure should be given serious consideration. In addition, the results show that the possibility of progressive collapse under the fire-induced column failure scenarios in the first story of low-rise frames is more than that in the first story of high-rise frames, and generally low-rise frames are more vulnerable to progressive collapse than high-rise frames. Furthermore, the possibility of progressive collapse under fire scenarios in the upper stories is more than that in the lower stories, especially for the top story. In this study, a new combined failure mechanism for global collapse of MRFs was identified.

A glued-in rod, which combines timber, a metal rod, and structural adhesive, is a type of connection whose fire performance is complicated to define since the rod depends on the adhesive’s thermomechanical properties. The objective of this study was to characterize the fire performance of adhesives used in glued-in rods. A total of five structural adhesives were tested: three epoxies and two polyurethanes. The tests performed consisted of applying an axial load to the glued-in rods after heating the connection to a target temperature. Load-slip curves were generated for each sample to determine their behavior at different temperatures. The results show that a reduction of up to 70% can occur in the initial stiffness of the glued-in rod when the temperature at the bond line exceeds the glass transition temperature of the adhesive determined by a dynamic mechanical analysis. This research helps to determine the guidelines for the fire design of glued-in rods and related testing and ultimately leading to a design method for providing fire-resistance to connections made of glued-in rods.