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.

On September 7 and 19, 2017 two earthquakes of magnitudes 8.2 and 7.1, respectively, and their aftershocks occurred in Mexico in regions where more than 750 dams operate, from which around 154 were exposed. Most of the reservoirs were full at the time of the earthquakes, and therefore subject to unprecedented intense dynamic loads. A description of the earthquakes and an account of the affected dams is provided; some of the dams presented cracking in various parts, especially on the crests, due to large peak ground acceleration (PGA) values. Previous studies related to dam safety are briefly described, together with a comparison of current dam design criteria against dam design practices in Mexico at the time the dams were built. Safety revision protocols as well as design criteria and stability estimation procedures are also revised. Then, inspection actions are taken, and damages and seismic evaluation after the events are presented, as well as a discussion on seismic-induced dam crest settlement estimation. Finally, conclusions and recommendations regarding remedial actions are presented.

An innovative discontinuum-based micromodeling approach, the Applied Element Method, is used in this work to investigate explicitly potential failure mechanisms that might have contributed to the collapse of the Morandi Bridge in Genoa, Italy, which occurred on August 14, 2018. While, consistently with the findings presented in a previous contribution by the same authors, the initial trigger of the collapse mechanism was assumed as the release of one of the stays, this study investigates, through a sensitivity study, the impact that several parameters and epistemic uncertainties, including reduction of cables’ cross section (potentially induced by corrosion) and various possible configurations of both passive and active reinforcements in the main deck, have on the predicted failure mode. Then, to indicate the structural elements and details in which a potential presence of corrosion should be more carefully explored, the observed debris distribution is compared with its numerical counterparts.

During the operation of tunnels, structural performance could inevitably degrade due to stochastic and adverse factors. To reduce the randomness and uncertainty of the tunnel operation, this paper provides a novel global sensitivity analysis (GSA) approach for monitoring parameters. The Wuhan Yangtze River Tunnel was utilized as a case study to verify the applicability of the proposed approach. The particle swarm optimization–least-squares support vector machine (PSO-LSSVM) was used to establish the model relationship between the input and output parameters, and the variance-based extended Fourier amplitude sensitivity test (EFAST) algorithm was employed to investigate the parameters sensitivities. Results of this GSA quantified the parameter sensitivities, and the sensitive and insensitive parameters were distinguished. The sensitive parameters can be identified as major factors for structural health monitoring and proactive maintenance in tunnels. This study evaluated the variations of sensitivity index with various target functions, parameter ranges, and distributions. The variations of parameter sensitivities were observed under various conditions, which indicated that sensitive and insensitive parameters may be different under different conditions. The GSA in this research can aid in optimizing tunnel design, construction, and operating period safety management.

Granite is one of the most common stones used historically in Korean architecture. Given the abundance of high-quality granite, more than 90% of the pagoda structures in Korea–tiered towers with multiple eaves—were built using this stone. Recognition and understanding of the structural behavior of this material are crucial for preservation of these pagodas. Hence, material properties of granite such as compressive and tensile strength, and Young’s modulus were investigated by conducting tests from quarries having undergone comparable differentiation processes with stones having similar mineral composition. To enhance the mechanical behavior of the stone and efficiency, a proposal to reinforce the stone through use of titanium bars was suggested. Subsequently, a series of experiments were also performed to determine strength dependency. Several pullout tests using resin epoxy were made to determine bond behavior between the two. Here, granite specimens were reinforced at the center of a single titanium bar having varied lengths and diameters. Experimental results indicated that upon reaching effective development length, larger embedment length did not result in increased tensile strength.

Existing methodologies to calculate the minimum separation distance between adjacent buildings are based on the estimations of the peak relative horizontal displacement of adjacent structures that are characterized by unknown pounding probabilities. The present study proposes a probabilistic performance-based procedure for determining the critical separation distance (CSD) with a designed pounding probability for adjacent buildings under different structural properties and seismic hazard sites. In the proposed procedure, the pounding events are formulated as single-barrier, first-passage reliability problems using the performance-based seismic design theory. Using the random vibration theory, the nongeometric spectral characteristics of the relative displacement response of adjacent buildings are deduced, and the approximate analytical solutions of the seismic pounding fragility are obtained by employing analytical approximations. Based on the seismic pounding fragility of adjacent buildings, the calculation of the CSD is described as an inverse reliability problem, and the specific CSDs with a target probability of pounding during the design life of the given adjacent buildings are derived using a proposed piecewise fitting iterative search algorithm. The proposed procedure is applied to different linear elastic single-degree-of-freedom (SDOF) and multi-degree-of-freedom (MDOF) systems. The accuracy and efficiency of the proposed methodology for determining CSD are verified by referencing the importance of sampling using the elementary events (ISEE) method. Furthermore, different parametric analyses are conducted based on the proposed methodology and that consider the influences of different ratios of natural periods, the floor numbers of the adjacent buildings, and the different site hazard curves on the value of the CSD to verify that the procedure to determine the CSD of the adjacent buildings, as proposed in this paper, can obtain a uniform pounding probability for adjacent structures with different structural properties and seismic hazard sites.

Chloride-induced corrosion is the main cause of premature deterioration and failure of RC structures in corrosive environments. Therefore, modeling chloride permeation and investigating different methods for the repair and maintenance of RC structures exposed to corrosive marine environments are very important for optimizing the service life and life-cycle cost of these structures. This study introduces a prediction model for the chloride diffusion coefficient for portland cement (PC) RC under long-term exposure in the tidal zone of a marine site of southern Iran. A regression analysis ($R^2=0.9972$) best fit was performed to check the accuracy of the prediction model based on Fick’s second law of diffusion. Various thickness equivalents for surface coatings were simulated as repair methods for the maintenance of RC structures exposed to corrosive marine environments. A finite-element model is provided for analysis to assess the time-dependent capacity of corroded RC structures using nonlinear analysis and the impact of corrosion on inelastic buckling of reinforcements. This analysis investigated and compared the influence of a number of repair or rehabilitation methods on the performance of a corroded square RC column due to chloride-induced corrosion, including concrete surface coatings used on the external surface of concrete, and increasing concrete cover thickness repair after the initial cracking of concrete cover. Results indicated that, compared with the no-repair scenario, the corrosion percentage of longitudinal bars of PC concrete with water-to-cement ratios of 0.35, 0.40, and 0.50 decreased 58.8%, 64.9%, and 71.7%, respectively, by increasing the concrete cover thickness by 7-mm; 53.5%, 59.9%, and 64.3%, respectively, by using epoxy polyurethane (PU) surface coating repair; and 52.3%, 57.4% and 63.0%, respectively, by using aliphatic acrylic (AA) surface coating. The AA surface coating had better performance in reducing the corrosion level of reinforcement than did the PU surface coating, which had better performance than increasing the concrete cover thickness by 7 mm.

Heritage bridges, such as covered bridges, provide a connection to a past time and engineering methods, and form part of the architectural landscape. Accordingly, quality examples of heritage bridges should be maintained for future generations. To support the preservation of New Brunswick’s covered bridges, a novel prioritization framework was developed. The framework assesses both the network link importance and the social importance of each bridge. Four overarching strategies were then developed based on the social-link ratings. Based on the ranking of each bridge, one of the four strategies is used to inform the future management of each of the 54 covered bridges located on New Brunswick’s road network. The strategies include preservation of the existing bridge and movement of the traffic to a new bridge, preservation of the bridge and closure to traffic, decommissioning the existing bridge and replacement with a new bridge, and decommissioning of the existing bridge and removal of the highway link. How the strategy was developed and the components that form part of the assessment framework are described herein. The framework is currently being used to facilitate the transition of the exemplar covered bridges from active highway assets to lasting heritage sites.

Unbonded concrete overlay (UBCO) is a widely used rehabilitation technique for deteriorated pavements, which is accomplished by placing concrete overlay on top of existing pavement with a sandwiched bond breaker layer between them. This technique is commonly used in Ohio and is proven to be practical in extending the service life of aged concrete pavements. The structural capacity of UBCO over concrete pavement is significantly high due to its two layers of Portland cement concrete (PCC). The objective of this study is to assess the performance of several UBCO pavements in Ohio and to identify causes of early failures. A comprehensive forensic investigation was conducted following the National Cooperative Highway Research Program (NCHRP) guide, including nondestructive testing, destructive testing, lab testing, and computer analyses. It was found that the causes of failure are different for each UBCO project but that they share some commonality. Water damage and poor construction quality control were identified as two major factors in causing the failure of UBCOs. This paper summarizes the performance assessment of UBCO pavements in Ohio. The findings contribute to the understanding of failure modes of UBCO pavements as well as forensic practice.

A novel self-centering cable brace (SCCB) with friction devices was developed to improve the seismic performance of existing frame structures. To investigate the enhancing effect of the SCCB on reinforced concrete (RC) frame structures, seismic fragility evaluation of SCCB-enhanced RC frame structures was conducted based on the incremental dynamic analysis (IDA), through which probabilities of exceedance at various performance limit states are calculated. The proposed evaluation procedure was applied to a seismically deficient six-story RC frame, where buckling-restrained braces (BRBs) and SCCBs with similar damping properties were used and compared for strengthening effects. According to the IDA results, the seismic fragility curves of the two strengthening schemes were obtained. Compared with the BRB-enhanced frame, the SCCB-enhanced frame exhibits significantly better seismic capability under rare earthquakes. In addition, lower probability of exceedance is observed in the SCCB-enhanced frame under the repair available state, indicating that the SCCB-enhanced RC frame is more seismic resilient than the BRB-enhanced frame.

On January 3, 2017, adjoining states of Tripura and Bangladesh witnessed a moderate earthquake of a magnitude of 5.7 ($M_{wb}$) originating in the Dhalai district of Tripura with an intensity of IV to VI in Modified Mercalli intensity (MMI) scale. The earthquake caused damages in reinforced concrete (RC) building structures, old masonry buildings, nonengineered rammed earth/adobe houses, landslides, liquefaction, and ground cracks at different locations near the epicenter of Tripura. Two districts, Dhalai and Unakoti, situated in the northern part of Tripura were mostly affected due to this earthquake. However, it is noteworthy that low-cost houses, such as bamboo houses, bamboo reinforced rammed earth houses and brick masonry houses with frames made of precast reinforced cement concrete (RCC) pillars performed relatively better as compared to unreinforced/unstabilized rammed earth and brick masonry houses. Analysis of damages identify cases of initiation of lateral spreading near the riverbank, landslide due to inadequate slope and presence of unstabilized soil, shear cracks and joint failure at earthen walls, structural cracks in rammed earth and masonry buildings situated at hill slopes, and minor structural cracks in RCC buildings as predominant damage features. Suggestions on enhancement of seismic safety of different types of structures are also discussed keeping a view on the current construction practices at Tripura. This study will help to develop preparedness for the possible vulnerability issues learned from this earthquake and assist to identify the future direction of research for overcoming seismic hazard for this state.

A vast majority of existing substandard reinforced concrete (RC)-framed buildings are prone to seismic damage because of improper design and construction applications as well as poor material properties. In this study, field investigation and analytical research have been conducted for adjacent buildings, which were exposed to an earthquake with a magnitude of 5.0 occurred in Çiçekdağı/Kırşehir/Turkey on January 10, 2016. A building with a basement story was severely damaged following the earthquake and collapsed eight days after the main shock whereas the other building with no basement did not experience significant damage and survived. Except for the presence of the basement in the collapsed building, both buildings have the same structural system and material properties. To let in daylight, ribbon windows were constructed on the partial infill walls adjacent to some of the columns at the basement story level, which resulted in the short-column phenomenon in the collapsed building. Material tests were conducted on the concrete and reinforcing steel samples taken from the collapsed building to determine their mechanical properties. Then, analytical models of both buildings with masonry infill walls were generated based on the information obtained from the site observations, the blueprints of the buildings and the results of material tests. Nonlinear static pushover analyses were performed to obtain the capacity curves of the buildings. Analyses results showed that the formation of short-column damage, which was visually observed in the field, in the basement because of imposed excessive shear demand was found to be the main reason for the total collapse as well as the high axial load level of columns.

The goal of this investigation is to assess the performance of rural structures in natural hazard events in 2018. Digital reconnaissance was implemented to retrieve data on damage-inflicting events, where collected data included a general summary of the event, the severity of damage inflicted, and the types of structures affected. To better understand the benefits and shortcomings of digital reconnaissance, findings are compared with those of traditional, field reconnaissance for two hazard events. The 2018 digital reconnaissance database is analyzed to discern regional, structural, and event-type trends and the fragility of specific rural structural systems. The investigation identified that, in 2018, damaged rural structures substantially outnumbered damaged urban structures, and the vast majority of damaging events occurred in the South and Midwest regions of the United States. Structures typical of rural areas, particularly barns, grain bins/silos, and manufactured homes, proved especially vulnerable, with many of these structures suffering complete failure in events causing only minor damage to structures more typical of urban areas. However, a comparison with field reconnaissance indicated that quantities of damaged structures are likely underestimated through digital reconnaissance, particularly in rural areas.

The blast resistance of a typical reinforced concrete bridge pier column design was modeled with a nonlinear finite element approach that considers material damage, fracture, and separation. While varying concrete strength, amount of longitudinal reinforcing steel, and gravity load, the effect of applying an externally bonded steel fiber reinforced polymer (SFRP) wrapping was assessed. The presented approach uniquely quantifies column blast resistance in terms of charge weight. It was found that blast capacity was roughly linearly related to concrete strength and steel reinforcement ratio, the former of which is most influential. It was further found that a single layer of SFRP modestly increased blast resistance, while additional SFRP layers provided minimal benefit.

This article presents a proposal of a method for the restoration and rehabilitation of Liben Bridge, a historic concrete vaulted arch bridge structure from the early 20th century. The bridge is appreciated as a unique structure and a remarkable example of purist architecture with cubist elements. The uniqueness of its structure is the reason it should be preserved, as opposed to the demand to demolish and replace it with a new bridge. The proposed solution would allow the preservation of the historic concrete arch bridge structure in its entirety, at the same time ensuring the required loading capacity after its restoration. This method employs a steel truss bridge structure, embedded in the space created by the extraction of the bridge backfill, between the bridge deck and the vaulted arch structure. The proposed rehabilitation method can be applied in the restoration of other historic stone or concrete arch bridges.

Construction of underground box structures that underpass existing infrastructures or facilities at shallow depths is being widely conducted in urban areas in order to avoid the interference of existing structures without the rerouting of traffic. Consequently, it is crucial to ensure safety during and after construction by monitoring the ground settlement induced by underground box installations that can be influential for the existing various structures. This paper provides a method to assess the risk potential around underground box structures with artificial neural networks (ANN), taking into account input variables that can be monitored in the field. By introducing the numerical methods and ANN, the probability of failures considering the variability of design parameters such as ground conditions, structure sizes and shapes, traffic loads, and presence of existing structures could be assessed and utilized for the safe construction of underground box structures at shallow depths. Experimental programs were also performed to investigate the effect of the umbrella method, which contributes to the decrease of risk potential in a practice. A limited field test evaluation using ground-penetrating radar (GPR) along with a pneumatic dynamic cone penetrometer (PDCP) was found to be promising in the assessment of risk potential at shallow depths.

The lateral impact of barges is a vital load case for river-crossing bridges. In addition, flood-induced scour has been recognized as a leading cause of bridge failure. However, current bridge performance assessment often takes the original bridge configuration as the basis for analyzing such impact without considering the effects of scour depth. In this paper, high-resolution finite-element (FE) based modeling is conducted to investigate barge impact on the nonlinear response of a pile-supported bridge with variable scour depths. The significant findings are multifold. First, it is favorable to find that the peak impact force and the crush deformation in the bow of the barge generally do not change significantly as scour depth varies. However, it is cautious to note that the peak displacement at the pier and the local deformation in the piles significantly increases as scour depth increases. It is stated that these findings and the method in this paper can assist in the quantitative assessment of the performance of river-crossing bridges in service and may provide information for the development of the next-generation bridge design specifications regarding barge impact.

Fiber-reinforced polymer (FRP) composites are being increasingly used in the construction sector, especially in corrosion-prone applications. However, there is still a lack of knowledge about their long-term behavior under real service conditions. This paper presents a study about the in-service performance of FRP constructions, which involved the field inspection of 410 FRP constructions included in 31 water and sewage treatment plants in various locations in Portugal. The analysis of the data gathered in these inspections allowed (1) validating a classification system previously proposed by the authors for anomalies, causes, inspection methods, and rehabilitation techniques for FRP constructions; (2) determining the most common anomalies that occur during their service stage; and (3) their most probable causes; and (4) predicting the most suitable diagnosis and rehabilitation techniques for each anomaly. Moreover, this study provided a better understanding of the long-term in-service behavior of FRP constructions when exposed to different environmental conditions. The analysis of the data obtained in the field study allowed identifying the main parameters governing the in-service performance and durability of this type of construction. The results obtained show that nonmechanical anomalies are the most common. As expected, the durability performance is very different in indoor and outdoor constructions, the latter presenting much more frequent and severe anomalies. Ultraviolet (UV) radiation and chemicals are found to be the most aggressive exposure environments. The results obtained also show that visual inspection is the most effective diagnosis method for this type of construction and that surface cleaning and protection is the most commonly recommended rehabilitation technique.

Coordinating construction trades on historic building restorations requires additional collaboration and expertise to ensure the building’s functional goals are met while respecting the building’s history and aesthetic. Mechanical upgrades present a major challenge because they must be designed for and installed in a building that was not built to accommodate modern building systems while meeting modern building codes. Construction managers and engineers took unique approaches to mechanical systems when restoring the Wyoming Capitol Building to ensure the building is functional for the state and for the public while highlighting the building’s historic significance and grandeur.

This paper presents the results of an experimental investigation on the response of plain concrete (PC) and reinforced concrete (RC) slabs subjected to contact explosion effects of 500-g TNT. A finite element model was developed and validated with the experimental results. Parametric studies of the response of RC slabs to contact explosion effects were conducted using the validated numerical model. The influence of explosive mass, slab thickness, concrete strength, reinforcement ratio, and reinforcement spacing were investigated in the parametric studies. Concrete compressive strength was found to have little influence on the threshold breach charge mass when compared to the effects of reinforcement ratio. An empirical equation was proposed based on the numerical results for predicting the threshold breach charge mass that incorporates the effect of the reinforcement ratio.

Pounding damages are frequently encountered in concrete continuous girder bridges during strong earthquakes. In the evaluation of pounding responses, the simplified lumped mass model with the contact element are usually adopted. However, the pounding responses calculated based on the simplified model are often significantly different from the real results, because the simplified model fails to consider the details of pounding processes and ignores concrete damage. In addition, the seismic parameters (e.g., peak ground acceleration, peak ground velocity) affects the pounding responses greatly. To further enhance the aforementioned considerations, this study presents the longitudinal pounding analysis of an isolated continuous girder bridge subjected to the unidirectional ground motions based on a multiscale simulation scheme. The pounding between the bridge and side abutments was simulated with a contact algorithm, and the concrete damages were considered. Thirty-three nonpulse and thirty-three pulse-like real ground motions were selected as seismic excitations to investigate the effects of seismic properties on pounding responses. Two pounding patterns were recognized and found to be related to the V-shaped velocity segment of the seismic input. Correlation coefficient and semipartial correlation coefficient were used to analyze the relationship between the seismic parameters and corresponding pounding responses.

Live load tests were conducted on an in-service bridge containing decked Northeast Extreme Tee (NEXT-D) girders. The purpose of the tests was to evaluate transverse load distribution and to determine which (if any) of the AASHTO LRFD standard bridge sections should be considered when calculating moment distribution factors (DFM). The NEXT-D girders in the test bridge span 12.2 m (40 ft) and utilize ultrahigh performance concrete as the girder shear key fill. The live load tests consisted of crawling ($<5\mathrm{mph}$) loaded dump trucks at several critical transverse locations across the bridge while simultaneously measuring bending strain in the girders. From this data, experimental interior and exterior girder DFMs were calculated for both one and two lane loads. Based on comparison with the experimental DFMs, it is recommended that the AASHTO LRFD type-k standard bridge section be used when calculating design moment distribution factors for NEXT-D girders.

Determination of the depth of surface-opening (visible) cracks is of critical importance for evaluating the structural safety of concrete elements. Accurately determining the crack depth with traditional nondestructive testing methods, however, is challenging. This study developed a new method using ultrasonic shear-horizontal (SH) waves to detect the depth of surface-opening cracks in concrete. The method is based on the diffraction of ultrasonic SH waves at the bottom edge of a crack. An off-the-shelf ultrasonic imaging device was used with dry-point contact transducers having a set of transmitters and a set of receivers performing in a pitch-catch configuration. SH waves are superior to other waves in data interpretation because the SH waves have a higher signal-to-noise ratio as the only wave type generated by their transmitter and without mode conversion after diffraction. Thus, accurately identifying the travel time of diffracted SH waves in the time domain is very achievable. The crack depth can be calculated with the two-way travel time of SH waves, the spacing between the transducers, and the SH-wave speed. The method was validated with a-finite element model and experimental data from two case studies. Results indicated that this method can significantly improve the accuracy of determinations of the depth of surface-open cracks compared with the ultrasonic longitudinal wave method.

Various numerical models have been developed to appraise alkali-silica reaction (ASR) induced expansion and to predict its potential to generate further damage. A previous work proposed a finite element approach that does not oversimplify nor overcomplicate the reaction analysis, while still being capable of representing the anisotropic expansion and its macroscopic consequences. Slender structures have already been successfully simulated using this approach, although it has never been applied to assess massive structures. This paper presents the validation analyses and the simulations performed on an ASR-affected dam in Brazil to appraise the accuracy of the previously proposed approach for massive structures. The results suggest that the numerical model is quite promising for appraising ASR development over time, based on the damage observed both in the field and on test specimens. Moreover, phenomena not directly accounted for in the model (such as alkali release from aggregates and the absence of an important amount of leaching) were found to play an important role in ASR-affected massive structures.

The early-age cracking of bridge decks is a typical issue in the US that reduces service life. Internally cured (IC) concrete has been used in some states to reduce or eliminate the development of cracks in reinforced concrete decks. However, limited research has been conducted to evaluate the field performance of internally cured concrete bridge decks. This paper presents the field behavior of an IC concrete deck and an adjacent conventional concrete (CC) deck during their early age. Strain gauges and thermocouples were installed at several locations along the bridge length to measure the concrete and reinforcement strains and the temperature in both bridges. The results indicated that the majority of shrinkage occurred during the first week after the concrete placement. However, the deck with the IC concrete experienced less longitudinal and transverse strains when compared with the conventional concrete deck. The largest reduction in longitudinal and transverse strains of the IC concrete deck were 64% when compared to the CC concrete deck. The lower strains led to a reduction of early age cracks. Furthermore, it was noted that the rise of hydration temperature in the CC deck was higher than that of the IC concrete deck. However, the IC concrete deck remained warmer over time. Also, the contribution of reinforcement at the early age was investigated. It was observed that the reinforcement reduced the tensile strain in the concrete deck generated due to shrinkage. The largest reduction in longitudinal strain at the top and bottom of the IC concrete deck was 65% compared to the free shrinkage strain.

The seismic assessment of heritage buildings has great importance in terms of preservation and sustainability due to their priceless inheritance. In general, the material properties used in the construction of heritage buildings, static and dynamic effects, to which they are exposed, and the existing structural damages are uncertain. Additionally, heterogeneous walls are often assumed to be homogeneous and many assumptions are made for the boundary conditions to reduce the computational burden in numerical analyses. In order to handle these uncertainties, operational modal analysis (OMA) has been successfully applied to moderate historical constructions. In this study, the seismic behavior of a large-scale historical building, which is located in Istanbul/Turkey and known as the Davutpasa Barracks is discussed. At first, an initial numerical model was created and calibrated using the data provided by OMA and in-situ observations. Afterwards, the seismic analyses of the barracks were performed using the initial and the calibrated model. The stress distributions and the displacement time histories of the building were examined and the critical sections of the barracks were estimated. The results have shown that the existing damages arise from both the seismic effects and the ground settlements. Additionally, it was revealed that the corridor facade walls and the corners, where the two very long monoblock building sections engage, are sensitive to seismic excitations.

The tendency of architects and engineers to reduce construction costs by using high-strength, lightweight materials, and owners’ requirements for large open spaces, along with the new trend in the use of paperless or electronic offices, have resulted in office building floors with excessive vibrations due to walking. The evaluation and assessment of floor movements are important factors that require the attention of architects and engineers. In the past, standards and design guides have simply used the time domain response of the floor when subjected to human movements and suggested limits on the peak or Root Mean Square (RMS) of acceleration for vibration evaluation. Recent standards and design guides have recommended the use of frequency-weighted response (generally acceleration) of the floor to compute the vibration dose value (VDV) in order to assess the vibration serviceability of structures. Based on the results of a number of walking tests conducted on six different office building floors over a span of 6 years, this paper proposes a relationship between VDV and the maximum transient vibration value (MTVV), which is used to recommend acceptable VDV limits to evaluate office floor vibrations. The results of this study also showed a relatively consistent relationship between the VDV and peak frequency-weighted acceleration ($a_{w,p}$). In addition, a novel usage- (or performance-) based vibration evaluation method was introduced, which is a new approach for the assessment of existing office floors and design of new office floors. In this approach, the acceptable VDV limit for one floor walk is defined based on the expected number of daily walk events. An equivalent equation in terms of the acceptable $a_{w,p}$ limit [$(a_{w,p}{)}_a$] was introduced for use at the design stage. The appropriateness of the proposed limits was verified using the subjective assessment of the tested building floors, and was compared with the provisions of the current design guides. Comments regarding the definition of high frequency floors, based on the results of the conducted studies, were made.

After middle or corner column removal, multistory frames exhibit different anticollapse mechanisms, and one of the most important anticollapse mechanisms is Vierendeel action. Based on instantaneous column removal tests, a dynamic nonlinear analysis considering damage, damping, and strain rate was used to simulate Vierendeel action under column loss. Considering the combined contributions of bending, catenary, and Vierendeel action, two calculation models of progressive collapse resistance are proposed for middle and corner column removal and the models are verified by a two-dimensional (2D), four-span steel moment frame. To fully utilize the contribution of Vierendeel action, a new braced system is proposed on the basis of the vertically braced system; the braced system was set up on the prototype structure of the Ohio Union building. The results show that Vierendeel action reflects the redistribution of internal force by the columns; the new braced system can fully utilize Vierendeel action to improve the performance of progressive collapse resistance. Using the new braced system, the load transfer paths after columns removal are as follows: the loads in the failed span are transferred to horizontal braces and then to the foundation by vertical braces.

The ability to properly assess existing reinforced concrete (RC) structures provides an opportunity to prevent costly rehabilitations or replacements and aid in the optimization of future designs. Distributed fiber-optic sensing (DFOS) is a promising option in the assessment of these complex structures. Previous uses of this technology, however, have been limited to static measurements, prohibiting the assessment of structures exposed to dynamic loads. This research intends to assess the dynamic sensing capabilities of a DFOS system and, in turn, improve the current understanding of the dynamic behavior of an existing RC beam tested in situ through a case study. Based on the data provided by the dynamic distributed fiber-optic sensors (DDFOS), dynamic measurements of distributed strains, distributed deflections, and crack widths can all be provided. Further details regarding the use of the DDFOS system in assessment, including the determination of support conditions and dynamic response factors, are presented and discussed.

Concrete-face rockfill dams (CFRDs) are widely used in hydropower engineering. Deformation monitoring and safety operation of CFRDs is of great significance in ensuring the safety of human life and property in downstream areas. A new prediction model for the horizontal displacement of CFRDs, the statistically optimized back-propagation neural network model, was proposed by combining a statistical model and a back-propagation neural network (BPNN) model, which was applied to Deze Dam, Yunnan Province, Southwest China. First, the thermometer selection method is improved based on the correlation coefficients between the measured values of thermometers and the horizontal displacement. Further, combined with water level and time factors, three thermometers with large correlation coefficients were selected and applied to Deze Dam’s model training. On this basis, an improved statistical model for the horizontal displacement of CFRDs is proposed. Subsequently, prediction results of the improved statistical model are taken as an input vector of the traditional BPNN model. Then the statistically optimized BPNN model, a combination of the improved statistical model and BPNN model, is proposed to predict the horizontal displacement of CFRDs. Compared with the improved statistical model and the BPNN model, the statistically optimized BPNN model has a higher prediction accuracy and a strong nonlinear prediction capability, which can compensate for the errors of statistical models and overcome the defects of overfitting and local minima. In addition, the statistically optimized BPNN model proved to have a strong generalization capability by changing the training sample sizes.

Sustaining functionality of water distribution networks (WDNs) following hazardous events is essential to public health and safety. Developing efficient restoration plans for rapid recovery is needed because of several factors such as the ubiquitous nature of WDNs, severely deteriorated segments, increased level of urbanization, availability of various restoration methods, and possible uncertainties in time and cost estimates of such methods. This paper presents a multiobjective resilience-based optimization model that maximizes the resilience of WDNs while minimizing the total time and cost of the selected restoration plans. A real WDN was utilized to demonstrate the practicality of the proposed model. The problem was solved deterministically and stochastically to generate a prioritized list of segments to be restored along with a schedule of their restoration that accounts for available work crews. When compared with current planning practices, the output plan achieved 4% cost saving, 48% duration reduction, and 4% resilience improvement. The model is expected to help city managers establish optimal restoration plans, especially in cases of limited budget and workforce.

Large-diameter concrete-filled steel tube (CFST) arch bridge transverse braces adopt self-compacting concrete to avoid laitance and air void defects. However, several old CFST arch bridges in China use ordinary concrete, whose fluidity before initial setting produces cap gaps at the top of the transverse brace. Furthermore, harsh environments and concrete dry shrinkage enlarge the gaps, producing composite defects. Hence, using ultrasonic scanning, this study performs a scale-model experiment and finite-element analysis to determine the bearing capacity of a serviced CFST arch bridge transverse brace with cap gap and air void defects in the concrete core column under small eccentric axial compression. Parametric analyses were conducted to investigate the influence of the composite defects on the bearing capacity of the transverse brace. A new ultimate strength index of the brace with composite defects was proposed, including a simplified formula for estimating the effects of cap gap and air void defects on the ultimate strength of the CFST arch bridge transverse brace. Thus, this study can provide a strong foundation for the construction of reliable CFST arch bridges.

On September 21, 2018, two major tornadoes occurred in Ottawa, Canada. The most severe was an Enhanced Fujita (EF3) storm that happened in Dunrobin area. The second major storm took place in the Arlington Woods area and was an EF2 tornado. These severe events destroyed numerous buildings, and thus a field investigation was conducted to observe the damages in the structures. The survey included both low-rise commercial and residential buildings in the Dunrobin and Arlington Woods areas; in the first area many buildings experienced extensive damage and in many cases local collapse, whereas in the second area the damage was limited on garages and roofs. The paper presents a set of damage-assessment data with a focus on damage failure modes and functionality of the buildings during the inspection. Lessons learned from the damages are finally presented, with comparisons with evidence from past tornadoes in Ontario that induced damage to infrastructure. The damage to the buildings surveyed is characterized based on different levels and discussion is included regarding the way residential buildings should be built to assure resilience if they are affected by tornadoes. The field investigation based on the performance of the examined buildings suggests a need for new design and retrofit methods to strengthen buildings envelopes. The buildings should have adequate anchorage of the walls into the foundation and well-constructed connections of the roof to the walls.

In the onshore and offshore chemical industries, a gas explosion is a major accident in terms of damage scale and frequency. To prevent disastrous damages, the Task Committee on Design of Blast Resistant Buildings in Petrochemical Facilities of the ASCE suggested several empirical methods to determine gas explosion blast loads for the structural design of petrochemical facilities. However, the procedures for determining overpressure from gas explosion are not easy for practicing engineers to follow, due to the complexity of gas explosion mechanisms and numerous affecting factors. In addition, the blast loads are greatly influenced by the class or Mach number in the empirical methods, but high uncertainty exists in selecting a reasonable class or Mach number for preliminary design. In an effort to reduce the difficulty and ambiguity, this study provides a thorough review and comparative analysis of the empirical methods suggested by ASCE for determining overpressure from gas explosion. In addition, this paper presents a case study that demonstrates the determination of blast loads in accordance with the ASCE guidelines.

China is actively building urban utility tunnels and incorporating gas pipes into the tunnels. However, there is a certain risk of leakage and explosion when gas enters the tunnels. If the gas pipe leaks and causes an explosion, this will not only seriously damage the integrated tunnel structure and other pipelines, but also lead to a catastrophic impact on the surrounding buildings. It is therefore necessary to study the safety of urban utility tunnels under gas blast loadings. In the present work, based on a completed gas explosion model, we investigated the blast loading characteristics of a typical utility tunnel to achieve the shock wave propagation law and distributions of the explosion. We also analyzed the effects of gas concentration, pressure relief vent, and gas volume on the shock wave load. By dimensional theoretical analysis, we established a formula for calculating the overpressure peak and impulse for such utility tunnels. The research can therefore provide loading information for the safety assessment and further improve the antiexplosion safety performance of utility tunnels.

This work deals with the corrosion evaluation of steel rebars in an underground water-storage tank using visual inspection, half-cell potential, and electrochemical impedance spectroscopy (EIS). The studied case has a service life of 65 years. From the inside, red stains were observed on the roof of the tank, and some cracks, as well as spalling of the concrete’s cover, raised suspicion of corrosion damage. Twenty-seven points on the tank’s roof were selected to drill out cores for further investigation. Measurements of the chloride penetration in the roof showed that the bottom part of the roof that was exposed to greater humidity and chloride-laden vapor was at risk of heavy corrosion. EIS studies of the steel rebars at different depths confirmed that those located in the upper part of the roof still have appropriate resistance to corrosion, but the lower ones exhibited a high corrosion rate. As a result, a repair of at least 12 cm in depth of the bottom of the roof and the installation of a proper ventilation system inside the tank were recommended.

Manufactured homes historically have been some of the most vulnerable structures to earthquakes, tornadoes, and hurricanes. More than 20 million people reside in manufactured homes in the US, leaving many at considerable risk across the country. Approximately 10% of the nation’s manufactured home stock is in Florida, where they were subjected to 2 consecutive years of intense hurricanes, including 2017 Hurricane Irma and 2018 Hurricane Michael. This paper presents posthurricane imagery and damage assessment of 279 manufactured homes assessed after each of these hurricanes in Florida. Predicted and mapped peak and sustained wind speed data were coupled with public database information of manufactured homes and parks in order to identify site locations with particular ranges of wind speeds in the impacted areas. Damage observations at the component- and system-level were presented based on post-Michael reconnaissance imagery. It generally was observed that manufactured home performance was consistent with historical observations, including 20% of surveyed homes classified as completely destroyed. These findings are intended to highlight the physical vulnerabilities of manufactured housing and to provide impetus for further research and updated standards for safer, affordable housing.