Structural designers use parametric equations to convert results of simple beam models to detailed hot spot stress distributions. Knowledge of hot spot stresses improves fatigue performance predictions. This paper extends the use of the parametric equation approach to joints with extra stiffening such as doubler plates. Doubler plates are commonly used on tubular structural joints against actual or anticipated punching shear failure. Reinforced tubular T, Y, K, X, and DT joints with and without doubler plates are considered. Results without doubler plates are compared against past studies and also the recommended design formulas used in international codes. Finally, a sensitivity analysis is performed describing the effect of joint geometry variations on the stress concentration factor values.
Composite girders consisting of concrete deck on built-up girders are frequently used in bridge construction for their economic advantages. The use of composite girders results in a very economical design. Additional savings can be obtained in design and material costs for some members by automating design approaches based on optimization techniques. This paper describes the use of EXCEL Solver to find the minimum weight for a composite trapezoidal box cross section for a two lane bridge. Design aid tables were generated for structural steel Grades 250, 345, 485, and 690MPa , and different spans varying from 3.0–100m . The search for the minimum cross section used in this research satisfies the 17th Edition of the American Association of State Highway and Transportation Officials Specifications—Load Factor Design method.
The objective of this study was to determine the effect of misplaced hold-downs on the monotonic and cyclic behavior of wood shear walls. Three shear wall configurations were considered: (1) walls with hold-downs at the ends; (2) walls with one misplaced hold-down to the first interior stud; and (3) walls with misplaced hold-downs plus additional nailing applied to the stud attached to misplaced hold-downs. Results showed that misplaced hold-downs cause reductions in strength and absorbed energy. Specimens with misplaced hold-downs achieved strength values 42% lower under monotonic loading and 35% lower under cyclic loading when compared to the specimens with hold-downs at the ends. Specimens with misplaced hold-downs plus additional nailing reached an average strength that was 21% lower under monotonic loading and 19% lower under cyclic loading when compared to the specimens with hold-downs at the ends. Denser nail spacing applied to the stud with misplaced hold-downs significantly increased the amount of energy absorbed by the shear walls. The monotonic and cyclic test results showed that misplaced hold-downs have detrimental effects on the structural performance of wood shear walls. Application of denser nail spacing can help such walls regain strength.
Repair mortars are needed for replacing mortar in damaged or severely weathered masonry mortar joints (repointing), for reconstruction of deteriorated masonry, and for renewal of rendering. The main components in a mortar mix are sand, binder and water. Additional materials may be added to modify the properties or appearance of the mortar. The intention of this article is to raise awareness of issues involved in the choice of mortars for the repair of mortar joints in traditional masonry (usually with thicker walls and weaker mortars than modern construction) by providing a brief overview of mortar binders, performance requirements, and mortar mix types. Work is ongoing to assess performance requirements and how to achieve them. Il faut des mortiers de réparation pour remplacer le mortier des joints de maçonnerie endommagés ou sérieusement abîmés par les intempéries (le rejointoiement), pour reconstruire les ouvrages de maçonnerie détériorés ou renouveler l'enduit. Les principaux éléments constituants d'un mortier sont le sable, le liant et l'eau. On peut ajouter certains matériaux et modifier les propriétés ou l'aspect du mortier. Le présent article est destiné à sensibiliser le lecteur aux questions en cause dans le choix d'un mortier pour la réparation des joints d'un ouvrage de maçonnerie traditionnel (dans lequel les murs sont habituellement plus épais et le mortier, plus faible que dans une construction moderne) en donnant un bref aperçu des liants, des exigences de performance et des types de mortier. On effectue présentement des travaux en vue d'évaluer les exigences de performance et la façon de les satisfaire. PRAC
In this research, a comparative study was conducted on the amount of required reinforcement using American Concrete Institute (ACI) and British Standards Institution (BSI) building codes. The comparison included design cases of rectangular beam sections subjected to combined loads of bending, shear and torsion, and punching shear at slab-column connections. In addition, the study included comparison of the differences in the amount of reinforcement required owing to different codes' factors of safety for design loads. It was found that the BS code requires less reinforcement than the ACI code does for the same value of design load. However, when the load safety factors are included in calculating the design loads, the values of the resulting design loads become different for each code, and in this case, the ACI was found to require less reinforcement than the BS. The punching shear strength of flat slab-column connections calculated using the ACI code was found to be more than that calculated using the BS code for the same geometry, material, and loading conditions. The minimum area of flexural reinforcement required by ACI was found to be greater than by BS, while the opposite was found for the minimum area of shear reinforcement. In case both codes unify the load safety factors while keeping the other design equations as they are now, the BS code will have preference over the ACI code owing to lower reinforcement requirements, which leads to cheaper construction while maintaining safety. The study showed that both codes are good choices for design in Oman. Because SI units are becoming more and more enforced internationally, material that is available in Oman is conversant more toward SI units; to unify the knowledge of design among municipality and site engineers, it is recommended to use the BS code as a first choice until a national code is established.
Forum papers are thought-provoking opinion pieces or essays founded in fact, sometimes containing speculation, on a civil engineering topic of general interest and relevance to the readership of the journal. The views expressed in this Forum article do not necessarily reflect the views of ASCE or the Editorial Board of the journal.
Movable bridges were built for centuries with wood, iron, and steel. The earliest drawbridges of short span were followed by swing bridges. In the United States, swing bridges were originally built across canals such as the Erie and the Chesapeake and Ohio (C & O) with wood and iron. Starting around the Civil War, longer span swing bridges were built across the major rivers of the country. This paper, largely a pictorial history, traces the development of the swing bridge between 1797 and 1907. After 1907 few bascule swing bridges were built, and vertical lift bridges generally replaced them.
Early in the morning of March 3, 2020, a storm system producing multiple tornadoes passed through middle Tennessee. One of the tornadoes—touching down in Cookeville and Putnam County—was classified as an EF4 with winds of approximately 282 km/h (175 mph). Damage observations after the tornado in Cookeville suggest that modifications to certain common construction practices might significantly enhance resistance to extreme wind forces. This paper provides recommendations for improving strength and resiliency within residential structures, particularly in four critical areas: (1) stiffness and strength of gable trusses, (2) wall-to-floor connections, (3) sill plate anchorage, and (4) shear and tensile capacity at interior foundation piers. Though improvements to construction practices are unlikely to eliminate damage to residential structures, such measures may well mitigate damage and extend the time between onset of the extreme forces and final damage or collapse.
Technological innovation. Lifelong learning. Two forces - continual and interwoven - that not only define the workplace in the 21st century, but also demand that workers in every discipline exhibit a commitment to lifelong learning as a fundamental necessity and ingredient for success. For construction companies, the use of computer estimating programs, building information modeling, the Internet, advanced communications devices, and platforms such as Facebook and Twitter has provided more flexibility and connectivity and a need for continued learning.
Applying advanced technologies and efficient project management techniques helped United States (US) contractors build a strong track record in international construction. Engineering News-Record (ENR) data from the early 1980s to 2008 show that US contractors led the international construction arena during that period. However, starting in 2009, Chinese construction firms took a lead in the international construction market, with increasing volume and revenue. In addition, companies from newly industrialized countries (NICs), mainly South Korea and Turkey, also increased their volumes and revenues. This study analyzes the changing trends in international construction from the beginning of the 21st century. The study also analyzes the factors that helped contractors from NICs to advance in international construction. Study findings indicate that having advanced technological capabilities and project management skills does not provide the same distinctive competitive advantage to US contractors in the 21st century’s international construction industry. US contractors need to form strategic alliances with other international companies that are successfully operating in the Middle East and Asia. Financial support from government can significantly improve US companies’ competitiveness. To improve the capabilities in delivering full-cycle services, US construction companies can acquire facilities management companies. In addition, use of emerging delivery methods and contract strategies, such as build-operate-transfer (BOT), design-build-finance-maintain-operate (DBFMO), and public–private partnerships (PPP), can improve the competitiveness of US contractors in international markets. Other strategies for US construction companies include seeking international mergers and acquisitions (M&As) to improve their performance.
This paper presents a rehabilitation project concerning the settlement of a 35-year-old building. The foundation system of the northwest wing of the building consists of strip footings and slab on grade. Differential settlement results in significant cracking of the masonry partition walls located on the footing, and hence rehabilitation of the footing is required to stabilize the foundation system. Geotechnical and structural investigations are conducted, including site borings and analytical modeling on the basis of one-dimensional consolidation theory that is incorporated into a finite-element analysis. The predictive model exhibits that the differential settlement does not cause noticeable distress for the primary structural members, whereas the continued settlement affects use of the building. Site implementation is performed with the push-pile method to terminate the continuous settlement of the foundation.
The acceptance of utilizing three-dimensional (3D) modeling programs for planning purposes in the heavy civil construction industry is on the rise. The ability to play out all possible construction process scenarios in a virtual world rather than in reality and to remove conflicts prior to the start of the work is a priceless construction planning tool. This paper explains the successful use of a 3D modeling program to plan and execute a critical lift on the Moses Wheeler Bridge project located in Connecticut. The critical lift examined here consisted of four drop-in girders. Specifically, 3D modeling was used to examine the placement of these four girders by two cranes positioned on each side of the river channel. During the planning stage, a virtual construction site was created in a commercial 3D modeling program utilizing contract plans and actual as-built survey data. Over a period of 3 days, four girder lines were erected safely and ahead of the planned project schedule. Besides the schedule gains, the project benefited from decreases in engineering costs and possible construction quality-related issues that might arise during a traditional analysis.
The increasing use of the design-build project delivery method has resulted in it now being one of the most popular nontraditional methods for delivering road, bridge, mass transit, and rail projects in the United States. However, although the use of design-build is widespread, there remains a substantial lack of information about how to effectively plan and implement design management procedures for design-build transportation projects. In particular, transportation agencies lack information about how to shape appropriate design management roles for various contractual parties and to manage design activities for design-build megaprojects. To fill this gap, this paper presents a case study of the SR 99 Bored Tunnel project in Seattle, Washington. It provides detailed information on how the owner, the Washington State DOT (WSDOT), incorporated design management procedures into its requirements and how the design-builder, Seattle Tunnel Partners, implemented them within its project management processes.
A cantilevered sign support structure failed, which was attributed to fatigue fracture of the anchor bolts. The failed structure was designed before the publication of the AASHTO fatigue provisions. The structure was replaced with a similar arrangement but designed using the AASHTO fatigue provisions. It was equipped with a double-nut-moment joint to concrete foundation using a 31.75-mm (1.25-in.) thick, 889-mm (35-in.) diameter base plate and eight galvanized 38.1-mm (1.5-in.) diameter bent anchor bolts. Significant clearance discrepancies between the base plate and the foundation for each of the anchor bolts existed because of topographical limitations. Experimental evaluation on the fatigue behavior attributable to natural wind was conducted on the anchor bolt attachments for validation of the AASHTO fatigue provisions. The results of the study indicated an irregular distribution of stress ranges between anchor bolts, with a portion having stress ranges greater than the values calculated using the AASHTO standards as well as the constant-amplitude fatigue limit of the anchor bolt connection detail.
Postinstalled anchors are frequently installed with unpredictable abandoned drilled holes (ADHs) at the job site. While ADHs may have a reducing impact on the original ultimate tensile strength (Nu) of the anchor per the design code, this effect was not adequately investigated. In this study, 60 wedge anchors in three diameters (d) and two (deep and shallow) effective embedment depths (hef) per d were tested in tension in five repeats. Half of the tests (30) served as the reference scenario for the other half (30) that included one ADH drilled at 2×d offset from the anchor. The ADH scenario resulted in (4.5-21%) reduction in Nu, regardless of the failure modes, and the percent reductions decreased as d and/or hef increased. Based on the results, an area method was proposed to predict the reduced Nu in the ADH scenario. This method can be used to predict reduced Nu when ADH conditions occur in the field and calculate the increased d and/or hef to minimize the reducing effect if the application allows.
Rotationally molded polyethylene water storage tanks have been produced since the 1950s when the technology became available for this manufacturing process. For circular tanks manufactured in this way, the traditional method of design has been based on hand calculations considering internal hydrostatic pressure from the stored liquid as the primary applied load. This study presents the results of the optimal structural design of 16 circular polyethylene water tanks of various sizes. Based on the results derived, optimal design recommendations for these tank structures are provided when both hydrostatic pressure and wind loads are applied.
A comparison is made between the three conventional methods used for accelerated bridge construction (ABC) of railroad bridges in Iran: single-piece deck installation by heavy cranes, multisegment deck installation by cranes, and single-piece deck installation by the so-called roll-in or sliding method. Both the safety of the construction and the serviceability of the railway line during the construction process are the main factors influencing the appropriate alternatives. Four railroad bridge construction case studies are demonstrated and compared here. Based on the individual situations, it is shown that the use of the roll-in method, in comparison with installation by crane, can reduce the installation costs significantly, eliminate the fatigue-prone details of the steel connectors, and eliminate the time for concrete casting in conventional multisegment deck installations.
Forum papers are thought-provoking opinion pieces or essays founded in fact, sometimes containing speculation, on a civil engineering topic of general interest and relevance to the readership of the journal. The views expressed in this Forum article do not necessarily reflect the views of ASCE or the Editorial Board of the journal.
An analysis-based vehicular-access door design protocol for pre-engineering metal buildings is introduced. Existing access door curtain and jamb design approaches are viable for rigid door jambs. However, it was shown with experiments that wind-lock forces decrease and door out-of-plane deflection increases when the door jamb and framing are more flexible (e.g., in the case of typical cold-formed steel-framing details in which a C-section jamb is discretely braced by wall girts). A beam strip model based on an Euler-Bernoulli elastica solution is implemented in a freely available wind-analysis computer program that considers jamb and framing flexibility. This tool is integrated with an access door design protocol that provides designers both door serviceability and jamb strength limit-state checks that are explained with step-by-step videos and spreadsheets. Maximum and minimum values for the wind-lock spacing, wind-lock gap, and door curtain moment of inertia are provided for various door spans to accommodate situations in which the door jamb and framing design must be completed before the door type is selected.
Interactions between project personnel, passing motorists, and mobile equipment in a restricted area make work zones risky for construction workers. In addition, the pressure on workers to maintain a high level of production can often lead to increased exposure to hazards. An analysis of reports on occupational fatalities in work zones in the United States indicated that the most common accident involving mobile equipment was workers being struck by backing dump trucks. This paper evaluates strategies for reducing accidents involving mobile equipment using different systems of backing cameras on dump trucks. An ordered probit model with random effects was developed to evaluate the factors that influence the identification of a worker (represented by a mannequin) in the path of a backing dump truck. Results of the analysis of this model indicate that the position of the mannequin, similarity in colors of the safety vest used and that of some construction equipment, and the presence of glare in images reduced the likelihood of identifying the mannequin at a safe distance from the truck. This paper concludes with recommendations for implementing strategies to reduce the occurrence of accidents involving backing dump trucks.
Built-up beams and columns comprised of dimension lumber fastened with nails, bolts or lag screws, are common in construction. Current design practice for stability checks is to use the lower-tail modulus of elasticity (E min) value tabulated for dimension lumber; however, this ignores the averaging effect on Emin that occurs when the mechanically fastened laminations are constrained to deflect in unison. In this paper, we propose a method for checking stability of these assemblies that is based on established statistical theory. A factor (Cs) is proposed to adjust E min value used in column and beam stability calculations to account for the reduced variability of E when the laminations are constrained to deflect together. Using Cs to account for the reduction of Emin variability produces more efficient designs with respect to stability. Two examples are provided and each results in larger design capacities compared to current design methods for built-up beams and columns.
The structural design of a three-story building in Palmela, near Lisbon, Portugal, is analyzed. Because of architectural constraints, the main facade of the first floor was designed in a setback of the second floor, which created a 13.0 m (42.6 ft) span between supports. To comply with deflection requirements a Vierendeel girder was projected between the second and third floor slabs. Taking advantage of the reduced size of the structure and therefore low computation demand, two nonlinear analyses were conducted. To account for the effect of creep in the construction phase, a physically nonlinear analysis was performed. Furthermore, the second-order effect on the vertical elements was accounted for through a geometrically nonlinear analysis. The nonlinear analyses allowed for a more slender and cost-efficient design when compared with values obtained from the traditional abacus to account for viscoelasticity.
An office floor with a typical grid size of 10.8 × 8 m in a multistory building was considered for design with flat-slab, flat-plate, and beam-slab systems. In all cases, both RC and post-tensioned systems were used for the comparison of structural performance and cost together with safety. The slab systems were designed using three different codes of practice: Indian Standard (IS), British Standard (BS), and American Concrete Institute (ACI) standards. From the cost analysis, it is observed that the post-tensioned flat-slab system provides better cost reduction of approximately 16.5 and 20% in the case of IS and BS standards, respectively. In the case of ACI standards, the RC and post-tensioned flat-slab systems yield 17.7 and 12.5% cost reduction, respectively. From the study, it was concluded that the post-tensioned flat-slab system using ACI standards is considered to be durable because the tensile stress is restricted and designed as an uncracked section, whereas the IS and BS allow 0.2-mm crack width.
Determining the most efficient and economical way to build a new or replacement bridge is not as straightforward a process as it once was. The total cost of a bridge project is not limited to the amount spent on concrete, steel, and labor. Construction activities disrupt the typical flow of traffic around the project and results in additional costs to the public in the form of longer wait times, additional mileage traveled to get around the work zone, or business lost attributable to customers avoiding the construction. The risk of injury to workers because of traffic interactions or construction activities increase with each hour spent at the construction site. Finding a way to shorten the time spent on the jobsite is beneficial to the contractor, the owner, and the traveling public. Prefabricating certain bridge elements reduces the time spent at the construction site and reduces the effects on the road users and the surrounding community. For example, steel beams with composite concrete decks reduce the construction time over cast-in-place concrete superstructures. In some instances, entire structures have been fabricated off-site under strict environmental and quality controls and then shipped to the site and erected in a matter of days instead of months. The total cost of using prefabricated bridge elements (PBE) depends greatly on the scale of the prefabrication. The more that prefabrication is used, the lower the costs. Even under limited use, however, prefabrication is usually comparable to traditional construction techniques. However, when durability and user costs are taken into account, the overall cost may be significantly less than traditional piece-by-piece construction. To improve the competitiveness of prefabricated composite bridges, a European research and development project, ELEM RFSR-CT-2008-00039, was started in 2008. The overall objective of the project is to make prefabricated bridges more competitive through development of new cost-effective, time-efficient, and sustainable bridge structures. The project has started with a knowledge extension, in the form of the workshop on "Composite Bridges with Prefabricated Deck Elements." This workshop was held in Stockholm, Sweden, in March 2009 to share the knowledge and experience gained by agencies around the globe. During the workshop, experiences from Europe and the United States were presented in an effort to promote the use of accelerated bridge construction (ABC) and prefabricated bridge elements.
The future success of the construction industry relies heavily on students and emerging professionals obtaining the requisite and desired skills necessary for a career in the field. The path to obtaining a career in the heavy civil sector of the construction industry in particular is not well documented. A number of challenges in obtaining the skills, experience, and career path in the heavy civil sector are presented and discussed from the perspectives of educators, the industry, and students. Primarily, the relationship between the educational and industry sectors is explored, and suggestions for improvement are developed. For students and emerging professionals, information is presented to assist in determining their desired career path and creating a path toward achievement of their career goals. The critical points are for students to determine which route is most interesting and to gain preliminary experience in the field. Lastly, recommendations are extracted to enable better relationships between industry and educational professionals that foster collaboration and continuing education in the heavy civil sector.
In recent years, by the development of nanoscience and technology, new ideas have emerged for enhancing the performance of cement composites. In this regard, the nano modified mixes, particularly those with nano-silica, have found a special position. However, there are challenges in using nano-silica in the cement mixes such as high price and workability problems. Thus, these materials must be consumed at certain levels to reach goal characteristics. In addition, there are complications in the properties and interactions of materials, which make it difficult to find a simple model for the prediction of concrete properties. In the present study, it has been tried to predict the compressive strength of cement composites, utilizing artificial intelligent approaches, including an adaptive neuro-fuzzy inference system (ANFIS), artificial neural network (ANN) technique and linear and non-linear regression analyzes. ANFIS and ANN are highly reliable methods for predicting the various properties of concrete, thus these methods have been used extensively in the concrete researches. However, similar studies were not found on using these methods for prediction of compressive strength of cement mixtures with nano silica. This study has utilized these methods to provide a comparison between the ANFIS and ANN models in predicting the strength of cementitious mixes and show the capability of the models of ANFIS and ANN compared to the traditional regression methods. For this purpose, the mix proportions and the quantity and size of nano-silica have been considered as input parameters and compressive strength of mortars as output parameters. The results indicate that the ANN and ANFIS outperformed the regression analyses. Based on the obtained results, ANN had higher accuracy in predicting the compressive strength.
Timber substructure bridges supported by three, four, or five piles were commonly used in Alabama in the past for secondary and county highway bridges. Because of the large number of such bridges in the state, the Alabama DOT recently developed a screening tool to assist its engineers in assessing the adequacy of bridge pile bents for extreme flood and scour events. The evaluation procedure employed in the screening tool is presented in this paper through the following sequence: (1) preliminary or general checks; (2) possible kick-out or plunging failure; (3) bent pile buckling failure; (4) transverse pushover failure from combined vertical gravity and lateral floodwater loadings; and (5) bent upstream pile beam-column failure from combined vertical gravity and lateral debris raft loadings. This paper discusses the theoretical background for the equations used to evaluate each failure mode in the timber screening tool, in addition to describing the flow of the screening process.
The standards and policies set forth by the Occupational Safety and Health Administration (OSHA) for the construction industry are for the most part directed at the constructor. As the traditional employer of the construction workers, the constructor is given the primary responsibility for their safety. As a result, other parties to the construction project, such as the design professional, are typically unfamiliar with the safety standards. Given the trend to hold design professionals responsible to some extent for safety and the expanded role of professional engineers in the construction phase an understanding of the OSHA safety standards is worthwhile for design professionals. This paper summarizes the aspects of OSHA and the safety standards that are of significance to professional engineers. Provided are a general description of the OSHA standards for construction, a synopsis of OSHA's Multi-Employer Policy, and an outline of the safety standards that involve professional engineers. With background knowledge of their prescribed involvement in safety, professional engineers may more effectively assist constructors in providing a safe worksite and, ultimately, reduce construction site injuries and fatalities.
This paper describes an investigation into the use of advanced manufacturing techniques for the creation of a new class of
intermeshed steel connections that rely on neither welding nor bolting. The project detailed herein lays the groundwork to transform
the steel building construction industry by advancing the underlying science and engineering precepts for intermeshed connections created from precise, volumetric cutting. The proposed system enhances the integration between design, fabrication, and installation. Fully auto�mated, precise, volumetric cutting of open steel sections poses challenges regarding the load-transfer mechanisms and failure modes for intermeshed connections. Implementation of the intermeshed connection would cause a discontinuity in the beam; therefore, the effects of such a configuration on the behavior of the steel frame are investigated in the current paper. Load resistance and design of these connections are also explored with physical tests and finite element modeling to investigate the mechanics of intermeshed connections, including stress and strain concentrations, fracture and failure modes, and connection geometry optimization.
With the increased interest in applying integrated forms of project delivery to complex and uncertain construction projects, the building industry has been experiencing an increased demand for integrated project delivery (IPD). With the trend, many empirical studies have examined the collaborative characteristics of IPD and reported that participants must make the necessary transition for its contractual, technological, and cultural requirements. However, little study has been done to investigate relevant education, training, or professional experience that can support the transition. In response, this study used an online survey that was designed to investigate the level and type of education, training, and professional experience of project members and their corresponding level of background knowledge for each IPD requirement. The key survey findings include (1) project members have the highest level of background knowledge on the cultural requirements of IPD, but the lowest level on the technological requirements; (2) the group with more design-build experience has more background knowledge; (3) the group that received an IPD kick-off training has more background knowledge; and (4) having a lean construction class can prepare students for the IPD environment. It is expected that the survey findings will advance the education, training, and levels of background knowledge of IPD participants, which will enhance their IPD experience accordingly.
One of the challenges faced by young academics is to perform industry research in a way that university requirements for academic tenure are fulfilled. This paper provides ideas for assistant professors in the construction disciplines for integrating industry into their research programs. The paper provides insight on connecting with industry, administrative issues to consider in industry research, traits of industry research, and advantages and challenges of industry research. In addition, the paper looks at specific industry research examples and describes the outcomes of this involvement. The final component of the study provides industry's perspective of academic research.
Project control operations in construction are mostly executed via direct observations and the manual monitoring of progress and performance of construction tasks on the job site. Project engineers move physically within job-site areas to ensure activities are executed as planned. Such physical displacements are error-prone and ineffective in cost and time, particularly in larger construction zones. It is critical to explore new methods and technologies to effectively assist performance control operations by rapidly capturing data from materials and equipment on the job site. Motivated by the ubiquitous use of unmanned aerial vehicles (UAVs) in construction projects and the maturity of computer-vision-based machine-learning (ML) techniques, this research investigates the challenges of object detection - the process of predicting classes of objects (specified construction materials and equipment) - in real time. The study addresses the challenges of data collection and predictions for remote monitoring in project control activities. It uses these two proven and robust technologies by exploring factors that impact the use of UAV aerial images to design and implement object detectors through an analytical conceptualization and a showcase demonstration. The approach sheds light on the applications of deep-learning techniques to access and rapidly identify and classify resources in real-time. It paves the way to shift from costly and time-consuming job-site walkthroughs that are coupled with manual data processing and input to more automated, streamlined operations. The research found that the critical factor to develop object detectors with acceptable levels of accuracy is collecting aerial images with for adequate scales with high frequencies from different positions of the same construction areas.
In this paper, the effects of air tightness tests on steel box structures with rectangular or circular cross sections typical of port cranes (legs, arms, and crosspieces) are analyzed. Legs and arms are generally made with elements with profiles having a square or rectangular cross section, while the diagonal struts are made with profiles having circular cross sections. To verify the air tightness of these elements, a necessary requirement to protect them from corrosion if they are not protected with other protection techniques, air tightness tests are performed. These tests, in the framework of durability tests, must be carried out while maintaining the structure elasticity well below the yield limit of the material. The tests must therefore be carefully designed regarding the choice of the air pressure to be injected into the box structures to verify their tightness and the way the air is put into the structures. As shown in the present work by means of an experimental investigation supported by numerical analyses, the choice of the test pressure depends on the shape of the element to be tested and in particular on the shape of the cross section of the profile. To this end, by means of laboratory tests on small-scale models and numerical simulations in the nonlinear field, the actual induced stress state of the internal pressure on the watertight box structures is shown, indicating the values of the pressures, which produce local yields or ruptures.