Structures Congress 2019: Bridges, Nonbuilding and Special Structures, and Nonstructural Components

Thin-walled steel tubular circular columns are an attractive choice for elevated highway bridge piers due to both their structural advantages, and ease and speed of construction. However, local buckling, global buckling, or a combination of both are considered a main reason for a significant loss of strength and ductility in these columns, or possibly a full collapse under severe earthquakes. This paper investigates the hysteretic behavior of circular thin-walled steel columns with uniform and graded thickness under constant axial and bidirectional cyclic lateral loading. The paper’s analysis is carried out using a finite-element model (FEM) which considers both material and geometric nonlinearity. The accuracy of the employed FEM is validated based on experimental results. Then, five different configurations of graded-thickness thin-walled columns with the size and volume of material equivalent to a uniform column are investigated. The graded-thickness columns are found to make significant improvements in ultimate strength, ductility, and post-buckling behavior as compared to their counterpart uniform column, emphasizing the sectional configuration in the graded-thickness columns.

External post-tensioning by means of high-strength steel cables can be used to effectively increase the ultimate capacity of steel-concrete composite beams. Most of the previous fatigue studies are based on the results of push-out tests, and the external post-tensioning, as a strengthening technique, cannot be applied to these types of tests. Therefore, this paper presents fatigue tests on two steel-concrete composite specimens to evaluate the effect of externally post-tensioned tendons on the fatigue behavior of composite beams. Fatigue tests are conducted to a million cycles under a four-point bending test. A numerical model is described to predict the fatigue response of the strengthened beam by considering the fatigue damage in the concrete flange. The accuracy of the developed numerical model is validated using the existing test data. The external post-tensioning significantly decreases strains in the shear connector, concrete flange, and steel beam at all stages of loading.

Finger plate expansion devices are frequently used to account for medium and large expansive or contractive movements and reasonable rotations of two bridge deck slabs. Under high traffic volume, these expansion devices have experienced some premature deterioration affecting the structural integrity and causing safety concerns for vehicles passing over the joint. Therefore, a group of experimental tests, in addition to 3-D elastic-plastic finite element models (FEMs), were conducted to study the structural behavior and modes of failure of finger plate expansion devices. The finite element model results have a good agreement with experimental measurements. In general, welding zones represented the sites of crack initiation in most cases of finger plate expansion devices. The present numerical results showed also that the site of the highest stress concentration was in the weld between the finger plate and the supporting beam top flange. Furthermore, other sites of stress concentrations were located at the vertical stiffener weld and the finger base curve.

Continuous bridge sensing and monitoring is an important component of smart infrastructure. Traditional bridge monitoring techniques require sensors to be installed on bridges, which is costly and time consuming. Also, a certain set of sensors have to be used to monitor a single bridge at a time. In order to resolve these issues, a novel bridge damage detection method focusing on monitoring a population of bridges simultaneously utilizing crowdsourcing data collected from smartphones on passing-by vehicles is developed. In this method, Mel-frequency cepstral coefficients (MFCCs) are first extracted on the acceleration data collected from smartphones in all the vehicles within a certain period. Principal component analysis (PCA) is used to transform the features so that they are linearly uncorrelated. The damage is then identified by comparing the distributions of these transformed features. The results from lab experiments show that the approach not only identifies the existence of the damage, but also provides useful information about severity.

Real-time fatigue health monitoring has the potential to serve as a valuable complement to structural health monitoring (SHM) for bridge inspections. SHM is an objective supplement to visual bridge inspections with a minimum interval between bridge inspections at 24 months. SHM can provide quantitative and objective data on a bridge’s fatigue condition for fracture-critical components, of which fatigue is a criterion. Current methods of continuous structural health monitoring for condition assessment are performed by collecting measured bridge response subjected to operational traffic from an array of sensors installed on fracture-critical members of a bridge. The measured responses are used to determine the remaining fatigue life of the bridge—the minimum time before repair. The large amount of data involved in this process complicates the design of a system that will automate the data collection process at a bridge, analyze that data, and display information about bridge health to researchers and engineers. Variations in bridge designs and condition assessment algorithms also necessitate that such a system be modular and adaptable to allow for expansion to additional structures. A new system has been developed that separates bridge SHM from the data storage and communication system. This architecture creates a reliable interface for sending data from one or more bridges to a cloud server where it can be processed using modular algorithms that can be adapted for different use cases. The cloud-based web service and data repository makes bridge structural health data available to researchers at all steps of the process. This system provides significant advantages over previous platforms for structural health monitoring and condition assessment, most notably in the areas of modularity, extensibility, and reliability.

Concrete cracking due to restrained drying shrinkage is a widespread problem that could happen to any structural element including bridge decks. One of the main causes of bridge deck cracking is the development of tensile stresses due to restrained drying shrinkage. Cracks allow harmful substances such as water and deicing salts to penetrate the deck and initiate corrosion. This research investigates the effects of using lightweight aggregate (LWA) on enhancing the performance of expansive Type-K cement. Four large-scale bridge decks of 2 m×3 m were built using four different types of concrete mixtures: (1) a mixture containing 100% Portland cement, (2) a mixture incorporating expansive Type-K cement, (3) a mixture containing internally cured fine lightweight aggregate (LWA), and (4) a combined mixture of Type-K cement and internally cured LWA. The combined mixture uses internal water from LWA to enhance the expansion of Type-K cement and produce compressive stress in the concrete; and eventually reduces the onset of cracking.

The unbalanced eccentric loads on the overhang portion of the deck slab during construction cause excessive rotation in the exterior girders and deflection of the overhang formwork. Hence, issues during the construction occur in addition to future deficiencies in the deck slab. This study investigates the effect of different lateral bracing system layouts on exterior girder rotation in skewed bridges during construction. Finite element models of bridges with different diaphragm layouts and screed machine orientations are developed to examine this phenomenon. The results showed that utilizing the diaphragms perpendicular to the girders leads to lower rotation values compared to using diaphragms parallel to the skew. It also concluded that placing the screed machine perpendicular to the girders can cause a high differential rotation between both exterior girders.

Many in-service steel bridges rely on the successful load transfer between critical members at connections. These connections often have high stress concentrations that make a way for crack propagation, resulting in a reduction in load capacity. Thus, detecting cracks in the connections on a steel girder bridge in a timely manner is of paramount importance. To date, visual inspection has been the principal method for detection of cracks. Recently, monitoring methods using in-house radio frequency identification (RFID)-based crack sensors or other patch-type sensors have been developed to complement visual inspection with quantitative damage information. However, their application in the field is costly. On the other hand, commercial ultra-high frequency (UHF) passive RFID tags offer similar properties at a more viable cost. This paper presents a development of a new crack sensor for metallic structures using commercial passive RFID technology. This sensor uses backscatter power as the main damage identification parameter. A new method for crack propagation testing was designed to evaluate the performance of any backscatter power-based crack sensor to monitor propagating cracks on a metallic surface using plate specimens designed for standard fracture toughness testing. Crack and fracture mode characteristics were determined with high precision using digital image correlation and high-resolution photography. The development and performance evaluation of this commercial RFID-based crack sensor contributes to the advancement of this technology for steel girder bridge monitoring.

A sensing skin has been employed to detect and monitor cracks in reinforced concrete specimens. This sensing skin is constituted of a flexible electronic termed soft elastomeric (SEC) capacitor, which detects a change in strain through changes in capacitance. The SEC is a low cost and robust sensing technology that has previously been studied for the monitoring of fatigue cracks in steel bridges. The sensor is highly elastic and as such offers a unique capability to detect and monitor the growth of cracks in structural elements. In this study, an array of surface-deployed SECs was used to detect and locate bending-induced cracks. To validate the proposed approach, an experimental campaign was conducted using reinforced concrete beams. Three-point bending tests were conducted on two small-scale reinforced concrete beams. Different configurations of SEC arrays were used on the two specimens to assess the capacity and limitation of the proposed approach. Results show that the sensing skin was capable of detecting and localizing cracks that formed in both specimens. Additionally, the sensor is shown to offer a good signal-to-noise ratio and thus could represent a cost-effective alternative to current sensing technologies for the monitoring of cracks in concrete structures.

This paper presents an experimental and analytical study on slender concrete columns reinforced with glass fiber-reinforced polymer (GFRP) bars. The experimental program included ten concrete columns with rectangular cross-section (203×305 mm) where nine of them were reinforced with #6 GFRP bars and one of them was reinforced with steel rebars. Three different reinforcement ratios of 4.70, 2.82, and 2.04 as well as four slenderness ratios of 17, 22, 40, and 60 were considered under two load eccentricities of 0.1 and 0.25 of width of the cross-section. The analytical model considered the material nonlinearity as well as the geometric nonlinearity. The model was verified against an independent experimental program. The model showed that as the load eccentricity and slenderness ratio increase, the load capacity decreases and as the reinforcement ratios increases, the load capacity slightly increases which shows effectiveness of GFRP bars in compression.

Accelerated bridge construction (ABC) offers advantages such as rapid construction, limited traffic disruption, cost savings for the formwork, more accuracy in construction due to prefabrication, better quality control, higher durability, reduced weight of the bridge structure, enhanced safety, and less environmental impacts. The research investigates analytical modeling of a precast bent with emulative monolithic connections. The column-to-footing connection is member socket, while the column-to-cap beam connection is grouted ducts. These connections intend to emulate the traditional formation of plastic hinges in monolithic bridge piers during an earthquake. The paper presents simplified analytical procedures based on moment-curvature analysis and displacement-based design that could be used by bridge practitioners and researcher to construct the backbone curve for the emulative monolithic bent. It further discusses Takeda-Thin hysteretic rule with appropriate parameters that can capture the cyclic response of the bent under quasi-static loading. Analytical results were compared against experimental data. It is shown that the simplified analytical procedure proposed in this research can predict the response of the bent adequately.

High cycle fatigue is a major cause of cracking in steel structures subjected to cyclic loading. It can result in substantial financial losses and structural failures compromising the safety of users. Uniaxial methods are in many cases insufficient for large in-service structures with complex geometry and connections subjected to multiaxial non-proportional loadings. A new method for fatigue life prediction for complex structures is presented using the critical plane method and the Kalman filter. The applicability of the methodology proposed is demonstrated and evaluated in a roller coaster support structure. Strain rosettes and accelerometers were installed on a support bracket near weld lines to measure responses. A substructure model is defined and used to estimate response prediction in the weld of the support bracket. The estimation of the input and the state estimation is performed using the augmented Kalman filter method, based on the response measurements and the substructured model. This new methodology is anticipated to be used for real-time fatigue prognosis of highway bridges.

With coupled dynamic impacts from coastal multi-hazards, such as hurricane induced wind and waves, slender coastal bridges could have complex dynamic responses and stress states in structural details, leading to fatigue damage accumulations. Simulation of the coupled vehicle-bridge-wind-wave (VBWW) system could be very complicated. Different loading scenarios especially associated with stochastic environmental loadings from wind and waves with potential correlations have even larger computational demands. Therefore, there is a significant need in modeling the coupled VBWW more effectively. High computational efforts are also needed to establish multi-scale coupled dynamics with sub-modeling techniques to capture the stress variations in the local details that might have short cracks initiated or propagated. To account for the uncertainties resulting from stochastic loads, machine learning (ML) algorithms have been applied in the probabilistic assessment of fatigue damage accumulation for bridges. Since the performance of different ML algorithms, such as the support vector machines (SVM) and Gaussian process (GP), strongly depends on the size and structure of the data, it is necessary to check their applications on the probabilistic fatigue damage assessment. In the present study, SVM and GP are implemented to quantify the fatigue damage of bridge details based on the established probabilistic fatigue damage assessment framework for coastal slender bridges. Firstly, the long-term field measurements are employed to build parametric probabilistic models of truck loads as well as correlated wind and wave loads. In addition to these input parameters, the multi-scale finite-element analysis (FEA) were carried out based on VBWW system to obtain the dynamic stress ranges and fatigue damage accumulation. With different training strategies, the fatigue life for critical local details can be obtained considering the life-cycle changes of coastal environmental conditions. The training and testing results show that GP algorithm outperforms SVM algorithm even though SVM exhibits reasonable capability of predicting the fatigue damage accumulation. Case studies for a coastal slender coastal bridge are provided.

Bridge overhang construction often introduces torsional moment acting on the exterior girder due to the unbalanced loads coming from fresh concrete, finishing equipment, and other construction live loads. Sometimes this torsional moment can create excessive rotation on the exterior girder in the transverse direction, leading to thin deck, reduced concrete cover, and potential maintenance problems in the service stage. Permanent and temporary diaphragms are widely used in wide flange steel girder bridges to resist these loads and subsequent transverse rotation of the exterior girders. However, those diaphragms are generally designed for resisting lateral wind loads, improving vertical loads distribution, and creating lateral stability during construction, which often results in insufficient bracing for reducing the exterior girder rotation. In this study, the effective diaphragm depth, which is determined based on the size of diaphragm and the type of girder to diaphragm connection, was introduced to determine the minimum diaphragm size in order to limit the distortion of the girder web during the bridge overhang construction. A parametric study was conducted to evaluate the significance of different bridge geometries using finite element analysis. The result shows that the diaphragm depth and spacing, as well as girder section, and overhang width, are the most important parameters that affect the exterior girder rotation. To evaluate the relationship among those parameters, around three thousand finite element models were built in SAP2000 using the bridge modeling computer program developed in this study. Finally, a simple method to determine the maximum diaphragm spacing to limit the exterior girder rotation was developed. This method uses the combination of primary curves and modification coefficients based on the girder section and overhang width.

Characterizing the effect of varying design parameters on the seismic performance of bridges can assist in optimum seismic design, especially for those in complex geotechnical conditions where scour and liquefaction hazards occur. This paper presents results of sensitivity analyses on the seismic performance of pile-group-supported bridges under combined effects of scour and liquefaction hazards. A fragility-based tornado diagram method is proposed for the sensitivity analyses. The studied parameters include the column height, diameter and axial compressive ratio, pile diameter and center-to-center distance, and relative densities of loose and dense sands. Special attentions are paid to the influence of scour depth on the sensitivity-ranking of the parameters. Main findings are that the pile diameter and center-to-center distance show increasing sensitivity with the increase of scour depth. These two parameters should be treated carefully in the seismic design of scoured bridges in liquefaction ground. On the contrary, relative densities of loose and dense sands that show significant influences for the scenario without scour turn to be the least sensitive parameters for scoured scenarios.

Concrete filled steel tubes (CFST) are composite structural elements which provide an economical alternative to traditional RC columns for their ease of construction and efficient structural properties. Recent research has resulted in practical and structurally robust CFST column connections for highway bridge construction in seismic regions. One such connection, referred to as the embedded ring (ER) connection, is a fully restrained, full-strength moment resisting connection which relies on an annular ring, welded to the end of the steel tube, and embedded in the cap beam or foundation. This paper is focused on the development of practical repair strategies for the ER CFST connection following seismic events. Several repair strategies which rely on plastic hinge relocation have been numerically investigated. In each strategy, the damaged region of the CFST is encased in a concrete pedestal, and different methods are used to transfer force from the CFST column into the pedestal. Namely, shear studs, steel rings, and simple weld beads have been investigated. Preliminary results indicate that all repair methodologies are effective shifting inelastic deformation away from the damaged region and restoring the stiffness and strength of the CFST column.

Structural integrity of steel bridges can be compromised when it is inadequately protected from the exposure environment due to corrosion. In U.S., approximately 15% of all bridges are structurally deficient due to corrosion. Application of protective coatings has been widely used for corrosion mitigation of structural steel and zinc-rich-primer three-coat (ZRP) systems are the widely used since the 1980s. However, coating failure of ZRP has been identified within 15 years of application, well short of typical bridge design service life. Maintenance of bridge coating is costly and as estimated, annually half a billion dollar is spent only for coating maintenance of steel bridges. For these reasons durable novel coating systems are of interest. The present study aims to investigate the corrosion durability of a nanoparticle enriched zinc rich primer (NPE-ZRP) coating for steel infrastructure application in aggressive marine environment. A conventional ZRP coating was evaluated as a reference to assess the influence of nano-particles. Zinc consumption was attributed from the bulk primer layer for NPE-ZRP whereas for ZRP coating zinc consumption continues along the coating/steel interface. Comparative testing with regular ZRP showed similar positive results to date but improved performance in coating adhesive strength.

Fatigue stresses in steel bridges can cause cracks to propagate and slowly weaken the structural stability of the bridge. Traditional rehabilitation techniques have proven to be disadvantageous and do little to stop the crack from growing. This research looks into using ultra high modulus carbon fiber reinforced polymer (UHM CFRP) plates to extend the fatigue life of cracked steel beams. All of the steel specimens had the same initial crack length which was manually created. The goal of the experiments was to compare how much the fatigue lives of the cracked steel beams were extended by the regular application of the CFRP plates, compared to the application of the prestressed CFRP plates. All of the beams were tested under the same fatigue loading control. Many factors went into comparing the performance of the different reinforcement configurations, such as the midspan deflection of the beam, the strain in the beam, and the fatigue life of the repaired beam. By using UHM-CFRP plates, the fatigue life of cracked steel beams can increase.

The Mersey Gateway Bridge was procured under a design, build, finance, and operate contract, one of the largest of its type in the U.K. Key aspects of the design and construction are described. The crossing is 2.25 km long and includes a 1 km long three-tower cable stayed bridge across the River Mersey estuary, together with approach viaducts to the north and south. Main spans are 294 m and 318 m, with approach viaduct spans at around 70 m each. The deck features a single central plane of cables and a continuous single cell concrete box girder 4.6 m deep with transverse post-tensioned ribs at around 6 m centers. Construction of the cable stayed bridge was based on the balanced cantilever principle and the approach viaducts were built using full span in situ casting on a self-propelled movable scaffold system (MSS).

Structural monitoring has been an important aspect of bridge construction for many years and has generally been considered a form of quality control. While ensuring compliance of material and design specifications is essential to quality construction, most monitoring programs have not been considered mission critical by the contractor; rather, it has been a necessary means to check boxes off a list. With advances in measurement technology coinciding with innovative construction methods, the role of structural monitoring has changed in recent years where measurements are an integral part of the erection process. For example, forces in hanger rods or cables during erection of complex suspended bridge structures is often part of the tensioning sequence along with geometric checks. These measurements can be made with permanent inline sensors or temporarily installed sensors which are critical to the completion of each stage of construction. This transition in monitoring goals has changed the nature of measurement importance, required system reliability, system quality control methods, and installation requirements. This paper will highlight several bridge projects where construction decisions and procedures were highly dependent on structural monitoring. The discussion will include the importance of the measurements along with the associated risks with measurement quality. When quality and safety of a finished structure is dependent on the quality of data in a litigious environment, quality assurance programs become critically important regarding validation, documentation, system reliability, and overall cost. This paper will include both technical and operational information for structure owners, designers, and contractors. The topic will be relevant to all professionals dealing with complex construction methods.

Wind loading is one of the critical parameters for the design of long-span bridges due to their inherent low stiffness and damping. The analysis of the dynamic behavior of long-span cable-stayed and suspension bridges under wind excitation is usually performed using wind tunnel testing. In the last two decades, computational fluid dynamics (CFD) has been gaining attention towards its general use in bridge design. From the late 1990s, the number of references in literature of numerical simulations of aerodynamic and aeroelastic problems in bridges has increased, and the accuracy in the simulations has enhanced due to improvements in modeling formulation, computer power, and software. The objective of this research is to utilize a commercial CFD software, ANSYS CFX, to study the response of two long-span bridges, namely a bluff-body and an aerodynamic shaped section, due to wind-induced instabilities, in particular, flutter. The first bridge is the bluff-body double-deck Bay Bridge in San Francisco and the second is the aerodynamic twin-deck Stonecutters Bridge in Hong Kong. Results are compared against wind tunnel test results.

Scoured pile-group foundations, as one of the most vulnerable parts of bridges, can suffer inelastic deformations under earthquakes. Other than capacity-protection strategy, one alternative solution is to treat the scoured pile-group foundations as potential energy-dissipation components with limited ductility. To this end, the seismic behavior of scoured pile foundations should be evaluated carefully. In this study, to reveal the impact of pile uplift on the seismic behavior of scoured pile-group-foundations, quasi-static cyclic loading tests were conducted on two 2×2 RC square-pile foundation specimens with and without significant pile-uplift potentials. The hysteretic behavior, cap rotations, and pile damages were recorded. Dissipated seismic energy were also discussed. Test results reveal that the specimen with significant pile-uplift, compared with its counterpart, has flag-shaped hysteretic loops, indicating a pile-uplift failure mode. The seismic energy was mainly dissipated by the pile-soil interface friction, suggesting the effect of pile-uplift should be considered carefully.

Accelerated bridge construction (ABC) employs prefabricated bridge elements moved to the bridge location and installed in place. Accordingly, ABC reduces many uncertainties associated with construction processes and performance during service life. It also improves the life cycle cost by reducing construction time and traffic interruptions, better control over schedule, and normally by the higher quality of elements resulting in better life-cycle performance. Nevertheless, prefabricated elements need to be made continuous using cast-in-place joints. ABC “closure joints” connecting deck elements to each other and to the bridge girders have greater exposure to degrading environmental effects, and often there is more focus on their evaluation. These joints, expected to become serviceable quickly can therefore be viewed as critical elements of the ABC bridges. Instances of defective (leaky) joints have been reported, and concerns have been raised about the long-term durability of the joints. The long-term deflections and environmental loading will only exacerbate this situation. These may overshadow the many advantages of ABC specifically as life-cycle performance and costs are concerned. Hence, health monitoring of ABC critical details, i.e., joints, becomes a priority for first assuring a life-cycle performance compatible with the prefabricated elements, and more importantly to address potential problems before damages become excessive. A variety of non-destructive testing (NDT) methods has been utilized in the past for structural health monitoring of bridges in general. However, a concerted attempt for evaluation of NDT techniques, comparison of capabilities, and selection of methods most applicable to ABC closure joints is lacking. As a part of the ABC-UTC program at the Florida International University, a research study is being undertaken to identify the defects associated with closure joints, to evaluate NDT methods for applicability to ABC closure joints, and finally to determine the most promising methods. This paper summarizes the results of this research study.

Roller coasters are unique structures and there is little information available on its structural analysis methods. The problem is in the type of loads it needs to withstand—the loads produced by a train with passengers moving along a rail path of a complex trajectory. The paper describes the design process of a steel roller coaster starting with its trajectory analysis and determination of train velocity and g-forces via kinematic calculation. The data obtained from kinematic analysis is then used to determine track loads and load time-functions for time-history analysis. Subsequently, two types of the analyses are performed: 1st—static analysis for the series of independent load cases, 2nd—dynamic time-history analysis. The results of dynamic and static analyses for several variants of track sections are compared in order to assess the impact of dynamic effects on the structure.

Performance-based design (PBD) has been proven to be a robust approach in the building industry that can help achieve a client’s desired target performance objectives during the design of structural systems, especially for areas prone to severe natural hazards. Implementation of PBD in the design of industrial structures is believed to be beneficial to industrial facility owners; and promotes sustainability and fit-for-purpose design. While PBD has been widely applied to design earthquake-resisting structural systems and has recently expanded to wind engineering, the concept has not been explored for the design of structures in petrochemical and other industrial facilities. Wey and Horton have adapted the PBD methodology from Seismic Rehabilitation and Retrofit of Existing Buildings and proposed to define the target performance levels of these types of structures based on various loading hazard levels. Still, many structures in petrochemical and other industrial facilities, in which the designs are governed by serviceability requirements, have been incorrectly designed at the code-required life safety load levels. This paper illustrates how PBD can be applied to those structures based on operational, maintenance, economic, environmental, and owner’s desired serviceability objectives using various examples. It impacts the structural engineering profession by providing clarity to the definition of performance level criteria for loading cases outside of the code required life safety levels for serviceability. Using these criteria, practitioners in this field can implement PBD to design structures more efficiently, save project costs, and use fewer natural resources.

Vehicle barriers play a crucial role in maintaining smooth traffic flow, perimeter protection, and passenger safety. The International Building Code and ASCE 7 provide guidelines to design such barrier systems in a parking structure. These provisions require the system to be designed to resist an equivalent static force of 27 kN. Such provisions based on an average force are too simplistic and may result in an inadequate design. This paper presents results of the numerical investigations of these recommendations. High-fidelity, physics-based, three-dimensional finite element simulations are performed in the study. Calibrated finite element models of passenger vehicles are used to simulate a crash into a vehicle barrier and impact forces are deduced. Additionally, life safety issues associated with stopping a moving vehicle is discussed using vehicle deceleration as the metric. The primary factors affecting the impact forces and deceleration are found to be the vehicle weight, its speed, and barrier rigidity.

Coupled structural systems are commonly found in either vertical (i.e., “stacked”) or horizontal (i.e., “adjacent”) configurations. Stacked industrial structures typically consist of elevated equipment supported by a primary nonbuilding structure. Adjacent industrial structures are often linked structurally by piping, electrical trays, struts, and mechanical equipment components. Regardless of the interaction between structures, they are often analyzed independently because it is the simplest and most cost effective method for completing the engineering and design. There are key factors which determine when a combined analysis of coupled industrial structures subjected to seismic loading is more appropriate to accurately capture the overall structural system behavior. The mass of the supported equipment and pipe is one of these factors since the added component mass can become the driver of the system’s natural frequencies and affect the overall seismic response. Another factor affecting the seismic response of coupled industrial structures is the relative natural frequencies of the interconnecting components. Currently, there is limited guidance within the codes and standards that specifies whether a combined analysis of coupled structures is necessary to accurately model the seismic behavior of the structural system. Parametric studies have been performed on analysis models of both stacked and adjacent coupled structures; the studies evaluate the effects of mass and natural frequency of the structures on the overall structural system response. A set of decoupling criteria or “triggers” for combined analysis are obtained by means of this study. The proposed triggers provide guidance to practicing engineers regarding the conditions in which a combined analysis of industrial structures is required in order to appropriately capture the behavior of coupled structural systems subjected to seismic loading.

Many nuclear facilities house reinforced concrete spent fuel pools that are used to process nuclear fuel prior to its long term storage. These water pools contain fuel storage racks that sit on the pool floor. During a seismic event, the unbraced fuel storage racks undergo interaction with the surrounding fluid which results in fluid pressures on the pool walls that must be accounted for in design. In addition, the racks may slide during a seismic event and may subsequently impact the pool walls. This paper presents the seismic fluid-structure interaction (FSI) effects of these submerged storage racks on pool wall fluid pressures and rack sliding distance through parametric studies which consider variations in friction coefficient, rack flexibility, and rack mass. The results of these studies are used to develop a simplified approach to calculate design wall pressures that is applicable for unbraced equipment within the impulsive fluid zone. Additionally, the effects of various factors on rack sliding distances were studied.

In steel lattice transmission line towers, an internal horizontal bracing diaphragm is required to redistribute shear forces along the structure and to provide enough rigidity. Horizontal bracing is used in various configurations in a square layout to provide a stiffer system to assist in reducing distortion caused by nonsymmetric loads and oblique wind loads. The spacing of bracing diaphragm is assigned according to general stiffness requirements to maintain tower geometry, while the brace configuration could vary in complexity and adequacy. The main objective of this study is to examine the effect of various horizontal bracing schemes currently used in the industry. Six different bracing schemes are studied on three different tower types. The tower models were analyzed under several load cases including gravity and environmental loads, oblique wind load, cable loads, and maintenance and construction loads. The analysis of the schemes is carried with reference to both the tower lateral deflection and internal forces development in horizontal braces. The results of the analysis present recommendations on the most efficient diaphragm bracing scheme.

The food industry utilizes large cookers for sterilization of food products in a variety of containers. Typically, these cookers are in the form of large, slender steel tanks that are partially filled with water and product. Depending on the application, these tanks can be installed in a horizontal or vertical configuration and are supported at discrete limited locations to provide for thermal expansion. The design challenges arise when designing for wind and seismic effects that include sloshing effects and wide temperature variations. In addition, with changing consumer demands for healthy food, cookers are retrofitted for new product lines that put demands on the original design that require modification and upgrades. Cookers can weight in excess of 1,000 kips (454 tonnes) and have temperatures in excess of 250°F (121°C). Several large industrial food cookers are presented in this article, and the analysis and design challenges associated with developing structural design and retrofit solutions to ensure safe operations of these giant cookers are discussed.

Tornado generated missile for the design of nuclear power plant (NPP) concrete structures requires special considerations. The requirements for missile impact according to Reg. Guide 1.76 are summarized. The barrier thickness has been determined using empirical formula used widely for this purpose. A non linear finite element analysis using the ANSYS program has been performed and results are compared. It is shown that the results of the analysis are very consistent with that obtained using formula.

Recent failures of high mast luminaire poles have showcased the vulnerability of these structures due to wind loading. High mast luminaire poles are long and slender structures with low damping and highly susceptible to the vibrations caused by wind. These vibrations add up to a large number of cycles during the structure life cycle and can result in fatigue failures. These structures have various components which include: base plate, anchor bolts, reinforced cut-out hand holes, weld details, and the hollow tubular pole supporting the luminaire. These components involve a number of design parameters which can affect the support structure’s fatigue failure susceptibility. This study focuses on the fatigue life of the base connection and the tube-to-hand-hole connection under wind loading. For this purpose, a model for the fatigue assessment is developed for the base connection and the tube-to-hand-hole connection. Fatigue analysis is carried out for these structures in the static load ranges to determine the hot spots for the respective static loads with complete stress reversal. Wind time histories are generated for different mean wind speeds and are used to analyze the fatigue performance in terms of stress cycles to failure and damage indices. The range of mean wind speeds that were simulated have a probability of occurrence for a given mean wind speed and direction. The results can provide a general framework to help designers and fabricators in better determining the impact of various design parameters on the fatigue life of high mast luminaire poles.

Steel silos are very common structures used to store granular bulk solids in various industries worldwide. These special non-building structures are subjected to unconventional loading conditions and may lead to failure if not designed properly. Sometimes, failure only involves distortion or deformation of silo components. In other cases, failure of a silo can be a disastrous structural collapse resulting in material loss and contamination, possible damage to the environment, and in extreme cases loss of life. In many cases, insurance claims and lawsuits follow, exacerbating the burden already carried by all the parties involved in the failure. Failures in steel silos often occur due to the following reasons: design errors, construction errors, improper usage, and/or lack of maintenance. In this paper, we will discuss steel silo failures due to design errors. Silo design requires specialized traits, which includes knowledge of stored material behavior and loads exerted on the silo walls. How these loads interact with the entire structural system is normally not well understood at the design stage. At the same time, there is not enough guidance available in the adopted building codes and standards for the design of steel silos, which often leads to inadequate designs. Engineers in charge of the design and construction of silos will benefit from this paper through a better understanding of the structural implications of silo design as well as the loads imposed by the stored material. Forensic engineers will be able to identify areas of distress in steel silos caused by different loading scenarios commonly observed in silo structures. This will help them to provide a more comprehensive evaluation while investigating the structural damage and/or failures in steel silo structures.

It is not uncommon to see in the news alarming headlines about silo failures in the USA and around the world. Sometimes the failure only involves distortion or deformation of the bin/silo which does not pose a safety or operational hazard. In other cases, failure involves complete collapse of the structure with accompanying loss of use and even loss of life. In many cases, lawsuits are inevitable lasting for several years after the incident, which exacerbates the burden already carried by all the parties involved in the failure. One of the main causes of bin and silo failures is due to inadequate design. Part of the problem lies in the lack of training in this subject at the undergraduate program level as well as guidance in the literature including standards and codes. Many engineers when faced with the need to analyze a container storing a bulk solid tend to assume theories that may be better known but inapplicable. For example, the wrong assumption that a flowing bulk material behaves like a flowing liquid is commonly made. For those familiar with bulk solids behavior, it is well understood that solid particles can transfer shear stresses between each other and between themselves and silo walls even if there is no relative motion between them. Fluids do not exhibit this behavior. The material-induced loads not only have to be in line with the bulk solids behavior but also with the design of the storage structure. Appropriate theories related to shell structures need to be utilized including their failure modes and critical structural details taking into consideration operation and properties of bulk solids. Engineers in charge of the structural design and construction of bins and silos as well as industrial facilities will benefit from this presentation as they will be able to better understand the implications of not having a comprehensive standard/code for the design of bulk solids storage structures. Committee members for the loading and structural design of special structures will be able to gather information and discuss how a new standard/code can be beneficial to many industries in the USA.

Tornadoes may be one of the most destructive natural disasters. They cause about 10 billion dollars in damage and kill 70 people on average annually in the United States. Effects of tornadoes on civil structures have been widely studied. However, the research on their dynamic impact has been lacking. In this study, non-stationary characteristics of tornadoes are investigated, and then their dynamic impact on a dome structure is determined. Computational fluid dynamics simulations are applied to characterize tornado-induced time-variant wind pressure on the dome surface, which is then mapped onto the finite element model of the dome structure. Next, transient time-history analyses are conducted to explore tornado-induced dynamic responses. Numerical results show that wind pressure becomes non-stationary and the induced dynamic responses are significant when the core radius of the tornado translates to the dome edge. More severe dynamic impact is observed when the tornado first approaches the dome structure.

Qatar was chosen to host the prestigious FIFA World Cup 2022, which had instilled Qatar to act swiftly in delivering FIFA-compliant stadiums and training fields. One of such stadium planned was Al Gharafa Stadium. Though this stadium isn’t entirely new, but upgrading the seating capacity from 25k to 40k, upgrading the pitch, and covering it partially for air conditioning without any additional support/load on the existing structure is unprecedented. The stadium had to be built ground up with new planning and challenges posed by, weaker ground, aged structure of quarter a century, larger span, FIFA compliance, and to air-condition. Air conditioning such a large stadium to 23°C with external temperature ranging 45–50°C, to achieve this cooling solution, larger roof structural system was conceptualized with unobstructed spectators’ view. The structural challenge was posed by the discontinuity of the span at the apex to have central opening to skylight. The design was achieved with single layer triangulated space structure inspired by a football, with peripheral support over piled strip foundation.

Modular construction for both facility and process skids has become popular due to the benefits of efficiency, speed, safety, quality, economy, and convenience. Modular design applications include process equipment, power delivery data center modules (PDC), pipe racks, and other equipment which can be assembled off-site. Modularization, while efficient, creates challenges for structural engineers, including, but not limited to: design of the support system for the modules, transportation of the modules, erection planning, and the variety of foundation systems and anchorage conditions to be addressed. In this paper, the systems of modularized structures will be discussed. As with buildings, we will consider moment frames, braced frames, shear wall systems, or non-building structures; depending upon the layout and nature of equipment. Tubes, channel, W shape, and angle are frequently used. The module size and weight may be dictated by transportation, lifting plan, or even the sizes of internal tanks when they exist. Not all modularized structures will be installed on a concrete mat foundation directly. For example, a PDC usually requires a crawl space for electrical conduits; a chemical or process module may require containment so as to collect water or chemicals due to accidental release. Therefore, concrete pedestals, tall columns, or more complicated elevated steel structures may be needed to support the modules. At the interface of the module and its foundation, the seismic shear forces may be significantly larger than that of conventional stick-built system because of the additional mass contained within the module due to its self-contained structure. For seismic resistance, the structural system should follow building codes and standards such as ASCE 7-16. For some configurations a combined system must be analyzed, i.e. the combined effects and behavior of the module and its supporting system must be analyzed together. This may pose a challenge as often the module is designed and completed by a vendor prior to the design of the supporting structure and/or foundation. For example, a cantilevered column support is not a foundation, but a supporting structure. As per ASCE 7 Section 15.3, a combined analysis may be required for non-building structures. The requirements ASCE 7 Section 15.3 are as follows: Type 1: the non-building structure is less than 25% of the combined structures. Type 2: the non-building structure is larger or equal to 25% of the combined structures, and where fundamental period, T, of non-building structure is less than 0.06 seconds. For both Type 1 and Type 2, the module (non-building) can be considered as a rigid element per Chapter 13 (Nonstructural Components). Type 3: the non-building structure is larger or equal to 25% of the combined structures, where the fundamental period, T of non-building structure is 0.06 seconds or greater. For Type 3, the non-building structure and supporting structure shall be analyzed combining the structural characteristics of both, and should be modeled together in a combined model. Some modules that have building-like lateral force resisting systems can be designed as building per Chapter 12 to avoid higher seismic loads required for non-buildings as per Chapter 15.

Original equipment manufacturers (OEM) that supply essential electrical and mechanical systems for critical building applications are often multinational equipment suppliers. This necessitates that OEM product development strategies consider earthquake demands from a global perspective. The goal is to develop a single product offer that simultaneously conforms with global seismic requirements. This paper outlines a systematic approach to mechanical and electrical equipment qualification that can be applied to satisfy the earthquake demands specified in country or region-specific building codes and seismic design standards. The process includes three steps: (1) global earthquake demands, (2) nonstructural product line capacity, and (3) seismic conformance validation. The focus in this paper is on electrical equipment applications.

In 2017, the ICC Evaluation Service, LLC adopted AC273—Acceptance Criteria for Handrails and Guards to establish criteria for the testing and assessment of proprietary handrails and guard systems pursuant to issuance of evaluation reports under the International Building Code and International Residential Code. However, real-world test situations under code-level loads demonstrated the inadequacy of the deflection limits as set forth in AC273. This article presents an analysis of AC273, a discussion of the deflection limits already existing within the code, the results of real-world testing using an on-site test rig and code-level loading (with photos and tabulated results), and proposed revisions to the acceptance criteria. The information presented is of use to engineers designing handrails and may help them avoid undesirable handrail performance and potential claims.

The floor acceleration response of special steel moment frames (SMF) subjected to earthquakes has been evaluated by multiple investigations. It has been demonstrated that peak floor accelerations and floor spectra, which are the most evaluated responses, are reduced when inelasticity is included in the mathematical model. However, the amount of detail required by the model to evaluate floor accelerations in nonstructural components has not been assessed. In this study four different models are used to compute the peak floor accelerations and the floor spectra of an 8-story special steel moment frame. The first model includes concentrated inelasticities and has been used to evaluate the collapse performance of SMFs, thus making it the most detailed model since the constitutive laws incorporate strength and stiffness deterioration. The second model also has concentrated inelasticities, but with a simple elasto-plastic behavior, therefore no degradation is included. The third model was created using fibers with displacement-based elements and a material that does not include any degradation. The last model to be analyzed does not include any inelasticity. All the mathematical models are analyzed to obtain the floor acceleration responses under design level ground motions. The results show that all the methods are accurate enough to be used to evaluate the accelerations in nonstructural components at design level earthquakes.

Seismic isolation of specific equipment, or specific floors of buildings, can be an effective protective measure for acceleration-sensitive equipment or equipment sets. However, satisfying performance requirements may be difficult due to severe horizontal absolute floor accelerations and large isolator displacements. In the present study, a novel variable stiffness isolator is proposed for seismic isolation of acceleration-sensitive equipment. It will be shown that the variable stiffness isolator can be designed to have positive stiffness at small and large displacements, and zero stiffness in between. This results in a variable restoring force that ensures stability of the system under service loading, limits excessive displacements under extreme seismic loading, and allows for zero stiffness isolation at the design level earthquake. The concept for the variable stiffness isolator will be presented along with a model for predicting its force-displacement characteristics. Then, the results of laboratory testing will be provided for validation of the variable stiffness concept. Finally, numerical simulation results will be presented to demonstrate the effectiveness of the variable stiffness isolator for seismic isolation of equipment.