Structures Congress 2023

Published research on the response of civil engineering structures subjected to underwater explosions (UNDEX) is relatively scant when compared to response for air blast. This paper presents preliminary assessment of the response of reinforced columns subjected to underwater explosions. The physical phenomena of underwater explosion and its effects are discussed. This is followed by a short summary on publicly available small-scale experiments conducted on reinforced concrete columns subjected to UNDEX and used as benchmark in this study. Peak blast pressures measured from the experimental tests are compared with those obtained from legacy empirical equations with proper magnification factors. The concrete damage plasticity (CDP) model used for analyzing structural response of the columns in a finite element program and its calibration are discussed.

As modern society faces unprecedented challenges related to climate stability and conflict, the need to design more sustainable and resilient buildings is undeniable. Several studies show that building with precast concrete components can result in significant advantages with respect to sustainability. However, the fact that such structures exhibit clear lines of weakness at the joints between elements can make them more vulnerable to progressive collapse. Although this can be overcome by adequate detailing of connections, there exist several uncertain factors which may affect the interaction between different precast elements and the global behaviour of such structural systems. This means that experimental testing is usually required for safe development of adequate solutions. Despite this fact, there have been very few studies on the robustness of precast concrete structures when compared to research on cast-in-place and steel structures. As such, this work presents the results of an ambitious experimental campaign involving the sudden removal of 3 different columns from a specifically built 15 m × 12 m two-storey precast concrete building incorporating simple and practical solutions to enhance robustness.

Protective design methods for blast, shock, and impact loading, such as from a blast event, are not addressed in typical design codes, but may be requested by project owners or end users. A risk assessment provides a basis of understanding from which users and stakeholders can make informed decisions to direct protective design for a project. Risk assessments include identifying asset values and threats, determining vulnerabilities, quantifying the impact of a loss event, and suggesting risk mitigation measures. For Department of Defense (DoD) facilities, this process is required and follows the procedures set forth in the UFC 4-020-01 DoD Security Engineering Facilities Planning Manual resulting in a level of protection (LOP) and a design basis threat (DBT) for the project facility. When explosive threats are identified for a project, the LOP dictates the performance-based criteria based on allowable damage in the event of the DBT incident. This paper highlights two case studies where the building designs deviated from the risk assessment results. In one case the users and stakeholders employed the risk reduction method to reduce potential damages and asset loss by decreasing the allowable damage for a modified DBT. In the other case, the users and stakeholders chose to accept the risks associated with designing the facility to a lower level of protection than determined from the risk assessment. Though government agencies have their own methods for producing risk assessments, the private sector may rely on protective design specialists to assist in determining risks and the appropriate protective design criteria for a project. This paper aims to generalize the procedure set in UFC 4-020-01 to be adaptable to a variety of projects based on understanding user goals and risk tolerances.

Threat, vulnerability, and risk assessment (TVRA) is a primary pillar in any security program. The TVRA lays the foundation for several steps to a comprehensive security program that might cover technology investment, network security, drone detection/monitoring, active shooter planning, emergency preparedness, mutual aid agreements, and business continuity. The goal of the TVRA is to utilize limited security resources to maximize risk reduction and provide no-cost or low-cost options first before going directly into capital investment. This article will discuss the development of a customized TVRA mythology for a typical intermodal transit center. The process will include development of site-specific hazards, acceptable performance criteria for each hazard, vulnerability assessment, consequence assessment, and finally risk assessment. Mitigation strategies are customized for specific hazard that produce consequences not satisfying the performance criteria. The TVRA is followed by a cost/benefit analysis to select the most cost-effective mitigation strategy. Workshop sessions, that involve end-users and other stakeholders, are a crucial step in the development of a successful TVRA.

In the wake of recent calamitous events at home and abroad, private and public facility owners and operators are increasingly interested in protective design measures that are not prescribed by typical building codes. At the same time, global understanding is increasing of the impacts of climate change, and the related need to integrate sustainable strategies into facility design. The primary goal of protective design is to protect human life, property, and operations by developing specific measures that reduce risk exposure and vulnerabilities while improving resiliency and recovery following an undesirable event. Sustainable design prioritizes resiliency as well, along with environmental, health and wellness, social equity, and economic vitality considerations, to create sustainable environments for current and future generations. This article will discuss the synergies and conflicts between protective design and sustainability, highlighting where they contradict each other and where they might converge towards a shared successful outcome. A typical, conventional USA Federal facility and site will be used as a model to highlight the discussion points in this article. The assessment will start at the site perimeter (the first line of defense), the site design around the facility, the facility enclosures and facade, and finally the facility design.

Blast hardened buildings typically employ higher quantities of standard building materials than their conventionally designed counterparts to meet protective design requirements. Regarding the recent push for net-zero structures, it is important to explore the use of low-carbon materials in building design and other measures to mitigate embodied carbon in structures while maintaining a hardened blast envelope. A case study of a local, reinforced concrete building project with no existing protective design or sustainability requirements was redesigned to determine if it is possible to offset the additional embodied carbon from blast design for a more sustainable outcome. After blast hardening was applied to the building and the additional embodied carbon quantified, the standard concrete mix was converted to a low-carbon mix with the same strength, and it was found that the total embodied carbon in the project was reduced below that of the original, unhardened building.

The use of glazed facades is a common feature in buildings. With evolving environmental factors caused by climate change, building and energy code requirements, and security priorities from clients and occupants, the expectations for building glass have risen in the global market. However, meeting these expectations can be challenging for designers as designing to security standards requires the use of more, while sustainability targets often benefit from the use of less. As such, special consideration must be given to the design of glazing systems to balance the sustainability and security goals of a project. Glass design affects sustainability outcomes like embodied carbon and energy performance. Industry standard blast-resistant glazing is comprised of laminated, heat tempered layers. The glass panes may be thickened from the baseline design, and even more so if forced entry and ballistic threats are an area of concern. The additional material used in security glazing and the extra energy required to manufacture heat tempered glass all work against reaching sustainability goals. Synergies between security and sustainability goals in glazing design are not immediately apparent. With the seemingly conflicting priorities between sustainable and secure glazing, designing glazing to meet both goals can be challenging. The intent of this paper is to provide guidance and support for designers by identifying possible linkages or contradictions between glazing security and sustainability performance. System comparisons will be drawn using industry standard security and sustainability performance metrics such as fragment flight distance, embodied carbon, and thermal performance to quantify the impact that different glazing layups have towards achieving sustainability and security goals.

The threat of a vehicle as a weapon attack continues to be a security risk for unprotected spaces. As a result of this, increasingly more spaces have incorporated hostile vehicle mitigation (HVM) into their security designs. Many times, the use of HVM measures is mandated by company policies or governmental regulations. Clients are seeking to understand the carbon costs of the HVM mitigations proposed and want the most sustainable security design, while also meeting their applicable safety requirements. This paper aims to analyze the carbon costs associated with two different types of HVM measures: bollards and walls. The carbon costs of each method will be quantified via established material quantity carbon calculations. This information will then be combined with relevant product data such as the foundation depth, crash impact energy rating, and system footprint. This paper displays the relationship between carbon cost estimates and HVM barrier features, as well as insights that will help in the recommendations and design of HVM measures with lower carbon costs.

In this paper, an analytical model is proposed, where the nonlinear material behaviors of steel and concrete are adopted. The proposed model is carried out by the computer software MATLAB to run the iterations to satisfy the equilibrium of the internal forces in the post-tensioned composite sections. Test data for full-scaled steel-concrete continuous composite beams are used to calibrate the proposed model. The influences of the post-tensioning and steel beam grade on the post-tensioned continuous composite beam behavior are investigated. The steel rebar strain is reduced by 84% at the cracked moment and starts to yield when the moment on the strengthened beam is 9.3% higher than that moment on the unstrengthened beam. The initial compressive strain created by the external post-tensioning helps to relieve part of the tensile strain in the concrete flange and then improves the cracking resistance of the concrete. Higher stiffness is obtained in the case of carbon steel relative to the stainless steel case. Moreover, the yielding moment is reduced by 16.3% when using stainless steel. However, the ultimate deformation is improved by 53% relative to the carbon steel grade.

Damage to bridges during natural hazards can cause major difficulties in post-event emergency activities. In addition, the deterioration of bridges over their lifespan significantly impacts the life-cycle performance of bridges. This study intends to evaluate the overall life-cycle resilience performance and post-hazard loss analysis of isolated bridges equipped with different isolation systems, including lead rubber bearings and friction pendulum bearings. For the lifetime resilience and vulnerability assessment of a curved base-isolated bridge, bridge deterioration resulting from rebar corrosion and suites of ground motions representing possible seismic hazards at the bridge site are considered. The comparative resilience assessment and loss analysis results represent the base-isolation technique's comparative adequacy, resiliency, and cost-effectiveness. Statistical analysis is conducted to identify the parameters affecting base-isolated bridges' resiliency and life-cycle cost. The results demonstrate that the resilience, loss, and cost analysis results are highly sensitive to the type of isolation bearings.

The proliferation of element level condition data recorded by state departments of transportation on bridges makes it pertinent to consider a more efficient use of these data for an improved bridge and asset management. This paper unravels how individual elements can predict the overall condition of the bridge since the direct relationship between component rating and element health index does not follow a regular pattern. For this study, element data from 20,250 bridges across five different states in the Mid-Atlantic United States were collected from the Federal Highway Administration web portals. The health indices of the bridge elements were computed using four different weight distribution ratios based on the four condition states: good, fair, poor, and severe. The efficiency of each weight distribution method was tested by running an artificial neural network (ANN) and logistic regression model with the health index of the elements as the feature variable and the overall bridge condition as the target variable. The results show that the dataset with 1:0.40:0.25:0 weight distribution ratio gave the highest prediction accuracy of 87% and also for the f1-score. The weight of the bridge elements were also determined from this ANN model.

Conventional methods in bridge inspection are labor extensive and highly subjective. This study introduces a novel approach with the use of real-time machine learning and the mixed reality platform to assist the inspector in localizing and quantifying concrete’s surface defects. Two separate deep learning models were selected for real-time detection and segmentation of the defects. These models were chosen from several available deep learning models based on their accuracy, inference speed, and memory size. For defect localization, Yolov5s showed the most promising results compared to several other CNN architectures including EfficientDet-d0. For the defect quantification model, 12 different architectures were trained and compared. UNet with EfficientNet-b0 backbone was found to be the best performing model in terms of inference speed and accuracy. The selected models were then quantized and deployed in a mixed reality platform and image tracking libraries were configured in the platform environment. An accurate distance estimation was accomplished using spatial meshing. Lastly, a methodology for condition assessment of concrete defects using the mixed reality system is discussed. The proposed approach eliminates the subjectivity of human inspection and reduces labor time. It also guarantees human-verified results and eliminates the need for post-processing.

This paper presents the results of a numerical study conducted to assess the effects of site-specific arrays of simulated ground motions from large magnitude earthquakes on the response of distributed infrastructure. Focus is laid on specific ground-motion features that are known to largely affect the response of long-period structures, including pseudo-spectral acceleration (PSA), peak ground velocity and displacement (PGV and PGD), fling step, and impulsive characteristics. The study is conducted on a detailed numerical model representative of the West San Francisco-Oakland Bay Bridge developed in the OpenSees environment and a suite of fifteen realizations of an M_w7 Hayward Fault strike-slip earthquake generated in SW4. The realizations differ from each other for the rupture model and depth of the fault plane. A core component of the study is the rigorous evaluation of the simulated ground motions based on the use of ground motion models (GMMs). The main objective is to verify the realistic character of the motions for their utilization in the risk assessments of distributed infrastructure, yet recognizing that the physics-based models are herein utilized to simulate events for which the GMMs are not well constrained. Therefore, insight into the interpretation of such comparisons is also provided. Results show a close agreement between the simulated motions and several GMMs, across multiple intensity measures. Finally, the preliminary results of nonlinear dynamic simulations carried out on the bridge model are discussed. Emphasis is laid on the influence of both between-events (multiple realizations at one location) and within-event (one realization at multiple locations) ground-motion variability on the structure response statistics.

Condition of bridge infrastructure is critical to the operation of transportation networks. Out of more than 617,000 bridges across the US about 7.5% are considered to have structurally “poor” condition. The objective of this study is to develop a data-driven approach to evaluate conditions of small and medium span bridges and propose new prediction models based on the existing Federal Highway Administration bridge inspection data. Using Maryland’s more than 5,000 bridges, Structure Inventory and Appraisal (SI&A) and National Oceanic and Atmospheric Administration data from 2010 to 2021 were employed, and inconsistent or missing data were identified, cleaned, and processed. The processed data was used to carry out a preliminary analysis to identify the most influential variables on deteriorating a bridge. Several machine learning models were examined to find the most suitable prediction model with the highest accuracy for bridge deterioration. This can help decision-makers to accurately predict bridge condition and effectively allocate funds for bridge management.

Ledges in shiplap hinge joints are pivotal elements of the overall structural system because they support other spans with in-span hinges to form a multi-frame bridge system. While this design allows for sufficient longitudinal expansion and contraction caused by various loads, relatively high tensile and shear stresses are concentrated in this shallower region that can lead to bridge collapse if not properly designed and constructed. This study focuses on evaluating the ultimate strength capacity of a bridge ledge designed in 1969 and comparing the results to design estimates using the empirical method. The ultimate capacity is determined from a physics-based finite element model created in ABAQUS. The finite element model is used to estimate the existing capacity and predict the failure mechanism for a bridge located in the Midwest (USA). Results also reveal different failure mechanisms determined from the two methods: (1) punching shear when using the empirical method and (2) shear friction as the governing failure mechanism determined by the finite element model. Moreover, the estimation results show that the shear friction capacity and the nominal interface shear computed using the empirical method were overestimated by approximately one and a half times more than the capacity determined from the finite element model.

Although post-tensioning elements bring efficiency by increasing the capacity and allowing more elegant spans for bridges, recent findings and observation have raised the need for health monitoring of post-tensioned (PT) bridges with a focus on PT tendons. One of the methods for verifying the health and safety or detecting potential damages for bridges in general is the application of non-destructive evaluation (NDE) methods. Dealing with nondestructive inspection results and updating structural model is the first stage of activities in order to assess the current condition of the bridge. The accuracy of nondestructive tests is always a concern because of the need for interpretations and special skills. Updating structural model based on inspection results is necessary, however the accuracy of nondestructive inspection results should be accounted for when making decisions for further action. This paper recommends a procedure for investigation on stochastic parameters of condition rating diagnosis in post-tensioning elements prior to structural model updating. In another word, the probability distribution for the accuracy (stochastic parameters) of the NDE method is needed to be able to obtain a distribution (stochastic parameters) for the structural condition of the bridge to be used in its model updating within a risk-based reliability framework. To demonstrate the procedure, an actual segmental post-tensioned bridge is used for which the inspection results for PT tendons are available. For this case, after spot inspection, impact testing was identified as the NDE method of choice through the procedure of selection of inspection method. Hands-on and nondestructive tests were performed on several external tendons to verify the accuracy of the method and to determine the stochastic parameters for condition assessment. True condition rating, overrated false condition rating, and underrated false condition rating have been defined and introduced as stochastic parameters of the condition rating. It was shown that the results from impact testing as NDE method and dissection as hands-on inspection are correlated, as such, the level of accuracy for the method was determined to be acceptable to continue the inspection in a large scale.

This study presents the use of a fiber model for the seismic design of ductile elements for several bridges on the California High Speed Rail (CAHSR) project. The application of a fiber model to represent plastic deformation was not traditionally used in the bridge design practice because of the large computational effort required. However, the fiber model can be used as a design tool to describe inelastic behavior more realistically than the conventional plastic hinge method. Specifically, the fiber model can capture loading and unloading of the different parts of the cross section with higher accuracy than the concentrated plastic hinge method. With the fiber model, non-linear evaluation of cracking and spalling of concrete can be directly observed for reinforced concrete structures without requiring an assumed composite behavior curve. For complex structures, such as bridges carrying track on the CAHSR project, non-linear time history analysis for several seismic records is required. A three-dimensional dynamic fiber model has been developed for several locations on the project to consider flexural hinging as well as a pushover model. Fiber nodes were included at the base of single column elements, and at top and bottom of columns for multi-column rigid bents. A comparison between the traditional plastic hinge method and fiber model is presented, noting that this higher-level analysis is still within the acceptable range for industry design.

Bridge deck construction often uses overhang brackets to support the deck overhang formwork, the self-weight of the fresh concrete, and the loads from the heavy construction equipment. These loads can introduce significant torsional moments on the exterior girders and sometimes lead to the excessive rotation of the bridge girders, which may induce many safety and maintenance issues. To prevent these issues and limit the exterior girder rotation, detailed finite element analysis is usually recommended for the torsional analysis during the bridge deck overhang construction, which can be tedious and difficult in some cases. This study developed a deep neural network model to predict the maximum exterior girder rotation during deck construction. More than 10,000 finite element models were developed using SAP2000 to obtain sufficient data for the deep neural network model. The deep neural network model was validated using field bridge monitoring and finite element analysis data. The results indicate that the deep neural network is an effective and efficient method to predict exterior girder rotation during bridge deck construction.

A partial collapse at the Government Center Garage in downtown Boston involved three concrete beams and a construction vehicle impacting the ground directly over a portion of the Massachusetts Bay Transportation Authority’s (MBTA’s) Green Line in the Haymarket Tunnel. Collapses are complicated, often tragic, events, and the Haymarket Tunnel is a complex structure. With service ceased, the MBTA needed to promptly understand the implications of the collapse on their infrastructure. Our team responded quickly and creatively with a pragmatic approach, leveraging field observations, analyses of varying complexity, and proof testing to give the MBTA confidence that it was safe to resume Green Line train service.

While inspection methods and codification of damages have been in use for a long time for conventional steel and reinforced concrete bridges, standardized and unified methodology or guide for inspection and damage detection of concrete elements reinforced or strengthened with FRP does not exist. Despite many advantages provided by Fiber reinforced polymers (FRP), there have been issues and concerns associated with its use. This included some unique problems for each system in addition to possible damages and defects that include debonding, delamination, and aging from UV exposure. Lack of clear guidelines and effective methods for condition assessment of FRP reinforced/strengthened concrete (FRP-RSC) elements has noticeably dampened the proliferation of its use. Bridge owners are not comfortable with products whose condition cannot be effectively assessed and proper maintenance implemented. This study provides a unified inspection methodology tailored and enhanced specifically for FRP-RSC elements. Accordingly, this study first introduces damages and anomalies attributed to FRP-RSC bridge elements, and then investigates the application of state-of-the-art nondestructive testing (NDT) for their detection. The results of this study are expected to provide the inspection community with more clarity in the application of NDT to FRP reinforced/strengthened concrete elements. Availability of such means and methods will have exponential effects in increasing the use of FRP in civil structures.

Mass timber structures have been gaining ground in recent years due to several factors including aesthetics, scheduling, and sustainability. However, there is limited guidance on how key design decisions, such as mass timber structural types and bay sizes, affect a project’s ability to meet sustainability targets, particularly at the early design stage when many decisions are made. To develop a dataset that would help inform early decisions, a parametric modeling approach was developed to study five mass timber and hybrid mass timber structural floor systems. This paper discusses the methods used in the model, as well as a model verification process using code and solution verification. The model consists of both a Grasshopper model interfaced with Rhino and a spreadsheet-based model, which are used to evaluate the multi-disciplinary nature of the design space. This modeling process is part of a larger research effort to develop early-stage design guidance for practitioners.

The built environment generates approximately 40% of the annual global carbon emissions. To achieve the Paris Agreement target towards net-zero emissions, timely and sufficient plans for emissions reduction in the sector need to be made. One of the optimal strategies to realize sustainable structures is to select decarbonisation alternatives that will present a holistic view of environmental impacts. This research effort examined how decarbonisation alternatives are prioritised to achieve carbon neutrality in building projects. Based on extensive semi-structured interviews with experts, this research identified energy, emissions, economy, and exergy (4Es) as the four critical variables considered when making decarbonisation decisions. These 4Es were then assigned to different evaluation criteria, resulting in a total of 27 evaluation criteria. These findings will assist built environment professionals to prioritise decarbonisation alternatives across the entire project lifecycle. It will also provide policymakers with new insights for assessing potential impacts based on these four variables.

This paper addresses the structural challenges related to the concourse renovation work for New York Penn Station Long Island Rail Road (LIRR) Train Hall. This renovation has introduced an inspirational destination and offered increased width and height for the 33rd Street concourse located below 33rd Street between 8th and 7th Ave in Manhattan. This paper focuses on the challenges associated with the LIRR concourse Head-Knockers removal. Head-Knockers refers to seven deep box girders which spanned across the LIRR concourse corridor and limited the corridor headroom. In order to eliminate the overhead obstructions and open up the corridor, the removal of these girders and the interior columns was needed. This created significant changes in the load paths of the supporting system. The complexity of this work was amplified by the fact that these girders supported some of the columns adjacent to Madison Square Garden (MSG). In absence of complete existing construction documents, major field investigations were performed to generate a building information model (BIM) to understand the existing structural system. New load paths consisting of built-up transfer girders and columns were erected. These girders were supported on the new columns and cantilevered out to carry existing columns adjacent to MSG. The stiffness and strength of theses girders were designed to minimize the movement of the existing building and support their base reactions. Different loading schemes and sequences of loading were examined to ensure that the uplift on the back spans remained balanced. Each loading stage represented a different stage of demolition and construction. Connections of the new girders to the existing steel were complicated due to accessibility issues created by the presence of multiple layers of framing erected at different phases over the years. The design of these connections relied on threading new plates between existing framing to reach the unsupported members rather than framing to these members or disconnecting them. Preloading was performed to ensure the smooth transition of loading from existing to new load supporting systems and minimize the existing construction movement caused by the deflections of the new girders. Loads used in preloading were determined based on existing loading conditions and new girder stiffnesses. The self-weights of these girders were leveraged to reduce the jacking loads. Preloading of the new plate girders was controlled using a calibrated jacking system. Optical monitoring was also implemented to observe the responses of MSG and Penn Station structures during construction.

The Keith Drive Office building, a 10-story, exposed tall wood structure located in Vancouver, Canada, will serve as landmark building in central Vancouver. The 43-m-tall structure is comprised of nine floors of mass timber gravity and lateral construction over a concrete podium and four levels of below-grade concrete parking. The 2-h fire rated exposed gravity structure consists of cross laminated timber (CLT) floor panels supported on dropped perimeter glulam beams and flush interior steel beams. The seismic force resisting system (SRFS) consists of perimeter timber braced frames and interior balloon framed CLT shearwalls. Tectonus resilient slip friction joint (RSFJ) devices specified at each brace, and both ends of each shear wall, allowing energy dissipation without damage to the structural system. To support the SFRS design, Non-linear time history analysis (NLTHA) was completed as part of a larger peer review. Iterative NLTHA was used to optimize the RSFJ design for the 2% in 50-year design earthquake. NLTHA was also implemented at 130% and 150% of the design UHS to review the collapse risk for an earthquake exceeding the design earthquake.

The use of reinforcement and prestress for strengthening mass timber glulam beams is not new and has been previously used to increase the beams' capacity, stiffness, and ductility. Different reinforcing and prestressing techniques using cables, curved tendons, slotted steel bars, strips, plates, and fiber-reinforced polymer (FRP) bars, strips, and sheets were previously studied by gluing and anchoring with timber. However, the complexity associated with the reinforcing/prestressing technique such as anchoring devices, mechanical jacking system, geometric limitations, prestress loss, and slotting preparation makes the conventional strengthening technique challenging. Shape memory alloys (SMAs) have been studied extensively for prestressing steel and concrete members, but using SMAs for prestressing glulam beams was not given any attention so far which can be an emerging trend in strengthening mass timber. Therefore, in this study, an innovative localized prestressing technique for mass timber using SMA was studied through numerical analyses, which was compared with the conventional FRP strengthening. The new prestressing technique showed promising results with a significant improvement in the beam bending stiffness.

The application of precast concrete members has been on the rise due to their advantages including rapid construction, quality assurance, and higher safety. These elements must be connected onsite to realize fully their advantage. Current connection systems for prefabricated elements have shortcomings, including susceptibility to corrosion, complexity of their application, and inspection of the finished product. Also, for the case of unforeseen connection necessitated by the site condition, they may be unable to develop the required strength. This study introduces two novel methods for splicing precast concrete members that are simple, corrosion-resistant, and can be applied rapidly. The new methods utilize near surface mounted fiber reinforced polymer (NSM FRP) and FRP sheet/jacket splice systems for connecting the precast elements. The capacity of the proposed splices to develop the required strengths in compression, tension, and bending was investigated according to several design specifications. The results of this study show that the proposed systems satisfy design requirements. This study is expected to enhance durability of precast structures and hence expand their use in future construction.

This study provides an overview of the ongoing Post + Panel research program on point-supported cross-laminated timber (CLT) floors. Recent studies on rolling shear and punching shear have found that the capacity of CLT in shear may be higher than those specified in the standards. However, while there is a compelling case for higher point supported strengths, most tests have been completed outside of North America, and limited tests have been completed on point supported CLT panels. The work presented herein addresses this critical research need and consists of CLT rolling shear testing, CLT punching shear testing, and full-scale point-supported CLT floor testing. Rolling shear values are based on both short- and long-term testing including testing using both bend and inclined tests. Rolling shear strength amplification factors and typical stress distributions around columns are presented from previous research in various column configurations. The rolling shear strength was determined for CLT with lamellas of different species, grades, and aspect ratios. The results show that the mean rolling shear strength of CLT was between 0.9 and 1.8 MPa.

This paper presents an experimental investigation to evaluate the connection performance of self-tapping wood screws for use in steel-timber composite construction. Monotonic pushout tests were conducted on cross-laminated timber (CLT) made from Southern Yellow Pine species that was fastened to a hot-rolled wide flange steel section using three different brands of self-tapping wood screws available in the US construction market. The ultimate load and relative slip of the connection was measured to make design recommendations for using self-tapping screws in steel-timber composite floor systems. Additional testing parameters included: fastener length, fastener spacing to investigate group effect, panel layup orientation to investigate loading screws in different wood grain orientations, and edge distance to investigate potential panel side failure modes. Experimental results revealed that screw geometry at the steel-timber interface is critical for developing a plastic hinge to reach higher connection strengths and deformation capacities. Results are compared with design yield mode equations and to previous studies, and a simplified calculation method for predicting the ultimate connection strength of mechanical fasteners used in steel-timber construction is proposed.

Steel-timber composite floor systems pose an advantageous alternative to traditional systems for steel frame structures due to their improved environmental benefits, ease of construction, and decreased unit weight. However, there lacks guidance as to what levels of composite action can be achieved within the system based on the type and spacing of fasteners used to connect the timber deck to the steel element. A higher degree of composite action between the timber and steel increases the beam strength and stiffness, which is expected to result in an optimized and economical structural design. To highlight the impact of composite action on the flexural behavior of steel-timber composite floor members, a numerical parametric study is conducted in this study. The numerical model is a section fiber model that accounts for partial composite action to predict the flexural behavior. The model used to conduct the parametric study was validated against an experimental database compiled from available literature on steel-timber composite beam tests, with comparisons focusing on sectional stress and strain, interfacial slip, end rotation, and mid-span deflection. Finally, the section model was used to conduct a numerical parametric study investigating the influence of critical design parameters on the flexural performance of steel-timber composite systems. The experimental database was also used for evaluating the applicability of existing strength and stiffness design equations for similar composite systems.

Interest in automating visual inspections of critical infrastructure has rapidly risen in recent years. Many studies have been published in the last decade focusing on machine-learning-based computer models for automated defect detection in imagery. Research on ground, aerial, and marine robotic systems with sensing capabilities and autonomous navigation for structural inspections has also gained heightened traction. However, existing systems rarely go beyond assisted image capture and data collection systems, and there is a significant gap toward fully integrated systems that can mimic human inspectors. In order to create autonomous systems that can deliver human-level actionable inspection output, there is a need for an improved understanding of how human inspectors perform different tasks. This preliminary study focuses on developing a data collection platform for sensing, data extraction, and human inspector behavior analysis. To that end, we develop a platform based on mixed reality (MR) while leveraging eye-tracking technology to sense and measure the visual performance of inspectors during virtual inspections. Incorporating eye tracking with MR visualizations enabled the study of the potential of MR in enabling and facilitating this analysis. Furthermore, a comparison of different modalities of reality capture including two-dimensional on-screen imagery, spherical 360 imagery, and three-dimensional models based on photogrammetry was also presented. The platform created in this study will be helpful in future studies on integrating human inspection patterns into robotic platforms, and the promising results obtained in this study will pave the way for creating automation systems that will help realize next-generation smart cities.

The building and construction industry is one of the major drivers of global energy use and emissions. With climate change mitigation being a forefront topic of concern, the building and construction industry has a responsibility to alleviate its environmental impact. Therefore, there is a need for more sustainable structural systems that explicitly consider environmental impact. This study performs comparative life cycle analyses on the superstructures of functionally equivalent steel-timber composite and steel-concrete composite office buildings at 7-story and 18-story heights. The environmental impacts associated with both structural systems are quantified, creating equivalent comparisons of sustainable merit of each structure and the materials within. The scope of the assessment was cradle-to-gate and included end-of-life impacts. Results indicate steel framing mass and environmental impacts are comparable between systems of the same height. As a result, environmental benefits attributed to STC structures stem primarily from floor assemblages. Overall, the steel-timber composite systems had less severe environmental impacts than the steel-concrete systems, averaging 46% lower global warming potential and 27% lower energy demand.

Dimensional control surveys are used to facilitate the correct design, fabrication, and installation to ensure that pre-assembled units fit together prior to setting at their final locations. Validating the dimensional geometry can facilitate effective fabrication, construction, and installations. Minimizing site rework for resolving fit-up issues ensures successful project executions by avoiding additional project costs and schedule delay. Digital scanned survey activities using electronic laser and infrared total stations provide accurate, high quality dimensional data. For small and medium-sized pre-assembled unit projects, structural engineers often find noticeable deviations as compared to project’s specified tolerances, resulting in additional time spent on examining whether fit-up issues at those locations will truly require design modifications. This paper addresses some of the common concerns by structural engineers in order for them to more adequately interpret the collected dimensional control survey data. The paper also provides pre-assembled unit design suggestions, including connection designs that facilitate fit-up. These design considerations, when working with the dimensional control surveyors, can enhance interface compatibility at pre-installation and reduce the chances of potential fitting problems. A better understanding of the required survey checks will help structural engineers determine which out-of-tolerance data must be reviewed, and thus finding solutions in a timely manner, to mitigate costly delays and rework during the installation phase.

At a chemical facility in Channelview, Texas, a 35-year old ground supported pressurized carbon steel tank was at its end of life and was due for a replacement in-kind. Tank is 24 in. in diameter and 22 in. tall. It is supported on a 4 in. thick octagon mat foundation which is still in good shape and will be supporting the new tank for a myriad of reasons. Twenty-eight 2 in. dia. J-bolts were used to tie the original tank to the foundation, these original anchors were badly corroded and could not be reused for anchoring the new tank. It was decided to cut the existing anchors and use the same number of new post-installed adhesive anchors on the same bolt circle diameter, staggering the location of original anchors. In calculating the required depth for post installed anchors, bond-failure/concrete-breakout was occurring no matter the depth. A rather novel adhesive implementation and installation was devised. Use of a set of smaller size rods post-installed around each anchor bolt transferred the load and mitigated the bond failure/concrete breakout. In this paper we discuss the problem and elaborate on the solution in detail.

Cable brace assemblies used for seismic protection of sprinkler systems consist of a hanger and two high-strength “aircraft” cables. These cables follow a defined manufacturing process, and their minimum breaking strength is defined by ASTM A1023. In 36 shake table tests with 12 different test setups, however, it is demonstrated that the seismic performance of cable brace assemblies does not only depend on the cable properties, but also on the hanger and the quality of the installation. Unrestricted pipe movement due to cable slack can lead to impact loads on the cables which may exceed their design strength. This does not get addressed by ASCE 19 and ASCE 7. The impact loads are particularly critical if the pipe can swing upwards and gain potential energy which is then released in a high shock load on the stiff and brittle cables when the pipe drops. Both numerical simulations and shake table tests showed that impact loads increase with larger cable slack and larger allowable pipe upswing.

There is a compelling need to standardize electrical equipment certification practices for essential building applications. Today, the only “standard’s vehicle” to provide guidance on electrical equipment certification is loosely outlined in ICC-ES AC156 nonstructural test protocol. The ICC-ES AC156 test protocol was intentionally developed to be highly generic in construct to cover all types of nonstructural components, including architectural, electrical, and mechanical components. It was written not to focus on product-specific criteria for answering the question of “what to test” but to address the important question of “how to test,” which was not explicitly defined in model building code seismic provisions. At the time of AC156 development, defining “how to test” was the primary motivation. This paper focuses on answering the former question of “what to test” when certifying highly variable electrical nonstructural components. Type testing equipment certification is the rationalization process to select appropriate test unit candidates from within the pre-engineered design options controlling equipment enclosures and the subcomponent functional units that provide equipment functionality. The goal of this paper is to outline a new “standard’s vehicle” to provide product-specific criteria for certification of electrical equipment including: (1) selection criteria for identifying appropriate test unit configurations, (2) performance criteria for validating equipment functionality pre- and post-seismic testing, and (3) rating criteria for quantifying seismic withstand resilience across multiple test unit configurations. The National Electrical Manufacturers Association (NEMA) is developing product-specific certification criteria to assure the right test candidates are selected and tested in order to bring needed objective transparency to seismic certification of electrical equipment. The development of ICC-ES AC156 was a necessary first step. The development of complimentary industry standards to close the loop on “what to test” will increase the resilience of electrical equipment to resist earthquake demands.

Federal and state departments of transportation, the US Army Corps of Engineers, electric utility companies, and other decision-makers need accurate and timely information about the condition of infrastructure to prioritize investment decisions. Currently, there are no broadly applicable automated tools to provide timely information about structural health. Artificial intelligence (AI) provides a forward-looking perspective to conceptualize and implement a data-driven and physics-informed structural health monitoring (SHM) strategy to overcome some of the challenges in traditional approaches. In September 2020, the National Science Foundation funded a project to demonstrate the proof-of-concept of an AI-driven SHM platform. The project team interacted with potential end-users and decision-makers to identify important aspects to consider in an AI-driven SHM platform. This paper summarizes the feedback received from the stakeholders and presents the project's preliminary results that serve as proof of concept.

Technological advancements have facilitated the application of digital image correlation (DIC) in condition assessment, structural evaluation, and even structural health monitoring (SHM). Specifically, the advantages of using vision-based measurement approaches include but are not limited to high accuracy for non-contact, non-destructive measurements over long distances (e.g., 50 m). The accuracy and robust measurements obtained when taking video-based measurements are leading engineers to use them for faster deployment than mounted sensor arrays. In this study, the structural performance of a corroded corrugated metal pipe (CMP) culvert rehabilitated with a spray applied pipe liner (SAPL) is monitored by using a commercial DIC system and video-based post-processing capabilities to characterize in situ behavior. The culvert is subjected to different static and dynamic loads resulting in deformations captured by video-based measurements before and after the CMP has been lined with a spray applied pipe liner (SAPL) to evaluate its effect during load testing. Despite poor lighting conditions and circumstantial limitations such as the forbiddance of mounting hanging targets, the DIC system captured the deformations of the culvert when subjected to a set of controlled load tests. The lining improved the structural performance of the culvert by increasing its ring stiffness, and the semi-beam behavior of the culvert under the loads. The recorded data also validated the structural behavior observed in the finite element (FE) model of the culvert before and after it was lined.