Practice Periodical on Structural Design and Construction

Structural health monitoring (SHM) is an important and practical procedure for ensuring the structural integrity and serviceability of civil engineering structures such as bridges, buildings, and dams. Model-driven or data-driven strategies for structural response prediction are now widely combined with advances in engineering for use in SHM applications. Engineers have recently demonstrated increasing interest in using machine learning (ML) and artificial intelligence (AI) to achieve a variety of benefits and possibilities, notably for predicting structural reactions. This study serves as a comprehensive overview of the use of ML applications for structural response prediction in the context of SHM for civil engineering structures, with a particular focus on ML, deep learning (DL), and meta-heuristic algorithms. Accordingly, this study summarizes existing knowledge, presents concepts in a simple way, highlights trends, provides methodological insights, and provides a valuable resource for researchers, stakeholders, and decision-makers to benefit from. It is observed that the use of ML, DL, and meta-heuristic algorithms to predict the response of civil engineering structures within an acceptable accuracy range can be employed for SHM, resulting in improved speed, efficiency, and accuracy compared to conventional approaches.

The construction industry has always been prone to uncertainties due to its dynamic nature, but the COVID-19 pandemic highlighted the need for a deeper understanding of its present challenges and their implications for the future of the industry. Despite numerous studies conducted on this topic, a comprehensive understanding of the factors stemming from COVID-19 that disrupted the industry is still lacking. This study aims to bridge that knowledge gap by identifying the challenges, categorizing them into four areas (cost overruns, schedule overruns, contractual implications, and health and safety issues), ranking them based on their frequency of occurrence in previous studies, and outlining management strategies to lessen their detrimental impacts on projects. A systematic literature review was conducted, and 284 publications were shortlisted for further review. The review revealed 26 challenges, of which shortage of labor, suspension or slowing of ongoing projects, force majeure confusion, and workplace safety concerns were among the most frequently cited, and offered strategies, such as workforce investment, supplier management, legal consultation, and transparent communication, for managing them. This research provides valuable insights for stakeholders and project managers in the construction sector that will help them comprehend and effectively manage the pandemic-induced challenges.

Based on construction project data provided by the Connecticut Department of Transportation (CTDOT), this investigation provides an overview of transportation project delivery impactors during the COVID-19 pandemic. Some 205 CTDOT projects are the basis of this comparison study. Of the total number of projects reviewed, 95 were completed before COVID-19 government health guidelines were issued, and 110 were under construction during COVID-19. The two data sets permitted a comparison of the pandemic’s effect against prepandemic work. The total value of the projects studied was approximately $2.2 billion over the two distinct periods—one before the emergence of the pandemic and the other during the pandemic. The preCOVID era saw $1 billion worth of work completed, while during the pandemic, an additional $1.2 billion worth of work was carried out. The study demonstrates the pandemic’s impact based on 13 factors: schedule, material supply, environmental, weather, extra work, site restrictions, noncompliance/rending notices, surrounding residents, coordination with utilities, design/redesign, quality control, contractor’s quality of work, and no major risks/issues. Material supply and schedule were the two major study factors demonstrating pandemic impact. Because of social distancing guidelines, many construction sites had to reduce their workforce, leading to site-wise labor shortages. The projects of the study were separated into eight different types: safety improvements, traffic signal, roadway, bridge rehabilitation, bridge replacement, highway signage, facility renovation, and train station rehabilitation. Out of these categories, train station rehabilitation projects faced the greatest disruption in their material supply chain compared to the other types of projects.

This investigative study explored the potential of a novel approach called the modular insulated concrete core—advanced and optimized panelized production system (MICADO) method within the realm of modular structures, focusing on its parametric development. By combining frame-supported modular systems with premanufactured panels for exterior walls, the MICADO approach allows for simultaneous installation, and has demonstrated promising prospects. This research investigated the challenges associated with assembling and connecting MICADO structures in the face of seismic and gravity loads. Through rigorous worst-case scenarios, critical load combinations were identified and analyzed. The outcomes of this research provide valuable insights into the design of joints in MICADO structures, ensuring their overall structural integrity and stability. These findings have the potential to benefit professionals in architecture, engineering, and construction, equipping them with effective techniques and best practices for creating resilient modular structures. Ultimately, this work seeks to enhance efficiency, sustainability, and safety within the domain of built environments.

Abstract

The current research adapts waste foundry sand (WFS) as a partial replacement to fine aggregate, which contributes to the principles of circular economy, providing economic and environmental advantages by rethinking waste as an essential resource of innovative and environmentally friendly building materials. This article mainly aims to showcase the research outcomes from the investigations carried out on the development of pavement quality slag-based conventional concretes (PQSC) and alkali-activated concrete (PQAC) using WFS as a partial substitution to conventional river sand (RS) aggregates. The mix design and the mechanical performances have been studied to comprehend the performance of WFS in concretes at various levels. Rigorous works were further carried out to fix the aggregate percentage of RS and WFS for the satisfactory mix design of the concrete mixtures. The mechanical strength parameters were studied along with volume-of-permeable-voids, density, and water absorption for durability assessments. The selected blends were sent to microstructural investigations involving scanning electron microscope (SEM), energy-dispersive X-ray analysis (EDAX), X-ray diffraction (XRD), and thermogravimetric analysis (TGA) studies. A successful attempt was also made to develop rigid pavement design models using both the IRC method and KENPAVE software, and a comparative scrutiny was carried out. The results demonstrate that the utilization of WFS can be achieved to a maximum of 15% to 20% without significantly reducing the performance of PQSC and PQAC mixtures for road applications after ensuring satisfactory mechanical performances. The research results will pave a path for effective utilization of WFS in construction industry and provide a sustainable solution to significant waste management problems in the casting industry.

Practical Applications

This research paper focuses on the fruitful utilization of industrial waste materials in the construction industry, specifically in the context of rigid pavements. Specifically, the study highlights the potential benefits of incorporating blast furnace slag and waste foundry sand (WFS), in achieving a more sustainable and circular construction economy. It compares the mechanical performances of slag-based AAC and conformist OPC concretes for pavement applications, finding that the former is superior. The study also explores the optimal percentage replacement of WFS in place of natural fine aggregates, noting that alkali-activated mixes can accommodate a higher percentage of replacement than OPC concretes. Rigid pavements, made of developed concrete, are a durable and sustainable alternative to flexible pavements. They are suitable for various highway infrastructure applications due to their load-bearing capacity, resistance to wear and tear, and ability to handle heavy vehicles and traffic volumes. They also offer improved aesthetics, walkability, reduced lifecycle costs, and sustainability through the use of industrial waste materials. Therefore to summarize, the adaptation of WFS incorporated, slag based alkali-activated concrete offers a better mechanical performance making it suitable for rigid pavement applications which in turn help in preserving the natural aggregates contributing to sustainability.

Concrete columns are the backbone of any major structure, and their strengthening, repair, and retrofit have always drawn special research attention. One of the techniques for strengthening and improving the ductility of concrete columns has been the application of carbon fiber–reinforced polymer (CFRP) materials. A total of 43 columns of different configurations were experimentally investigated to evaluate the uniaxial compressive behavior of composite columns. Experimental and international code–recommended load-carrying capacities, stress–strain relations, axial stiffness, ductility factor, and failure modes were examined in the study. When fully wrapped, the strength of both plain cement concrete and reinforced cement concrete columns improved by 21% each with reference to the unwrapped columns. In addition to providing the advantages of external confinement to the columns, full wrapping contributed to a strength increment of 21%, which compared well with the steel reinforcement contribution to a strength increment of 28% to 39%. The partial wrapping technique was found to be an economical alternative to the full wrapping technique, with strength enhancements of 6% to 12% in the case of both plain cement concrete and reinforced cement concrete partially wrapped columns. Two regression models for the load-carrying capacity for columns with and without wraps were developed with four key performance parameters: percentage steel reinforcement, percentage concrete, percentage carbon fiber–reinforced polymer wrap, and the weight of the specimen. The formulated models were validated and found to be robust and consistent with the results.

Floor openings and nonstructural full-height partitions are often ignored in both finite-element modeling of long-span office floors and calculations of vertical footfall-induced vibrations, despite quite a few research studies pointing out that nonstructural elements may affect floor response. The consideration of layouts of partitions on the stiffness of the floor was not present in most design guides such as those for vibration serviceability, which only recommend the increase of modal damping to account for partitions. The absence of such a consideration is due to the existence of uncertainties for modeling partitions. This study assessed the effects of openings (also referred to as “voids” in this paper) and partitions, by parametrically studying finite elements (FE) models of steel-concrete composite floors featuring three configurations: (1) unpartitioned floors without voids; (2) unpartitioned floors with voids; and (3) floors featuring partitions and voids. All floor models were parametrically generated, by changing the size of supporting steel beams and the deck depth. It is found that, in floors with partitions, walking-induced vibration levels can be as high as twice the levels of vertical vibration across unpartitioned floors. If structural modifications across the whole floor area are then introduced to control such vibrations, that can lead to up to 40% higher carbon footprint. However, it was also shown that alternative layouts of partitions can significantly reduce floor vibrations due to their stiffening effect in hotspot areas, requiring fewer structural modifications of steel beams and concrete deck sizes to meet vibration serviceability, thus reducing considerably the floor carbon footprint (20% less), structural mass (47% less steel and concrete), and floor cost (13% less).

This paper provides universal structural design criteria for heavy industrial projects. Structural design requirements for pipe racks, steel modules, modularized equipment skids, vertical and horizontal vessel supports, and vibrating equipment foundations are discussed. An overview of loading mechanisms of various systems is provided for operational, testing, and lifting conditions. Design recommendations are provided for permanent and removable structures. Several structural idealization concepts are also proposed to ensure accurate load transfer. The theoretical basis and the merits of various methods used in the practice are also discussed. Industrial design examples are provided including multilevel pipe rack and pump foundations. The paper overviews and pieces together the engineering requirements for critical structures that are encountered in heavy industry.

Geogrids, first developed in the late 20th century, revolutionized soil reinforcement using polymer materials in grid-like structures to enhance soil stability, reduce erosion, and strengthen infrastructure, marking a pivotal advancement in geotechnical engineering. However, geogrids typically find limited application in structural engineering, especially reinforced concrete (RC) columns. The present research explores the feasibility of geogrids in concrete columns, thus optimizing construction practices by exploring innovative reinforcement methods beyond conventional steel, aiming to bolster durability and performance in diverse structural scenarios. The traditional method of using steel stirrups to confine circular columns was substituted with a new approach; i.e., geogrids were introduced partially as confining material alongside steel stirrups. Furthermore, the research examines the performance of concrete columns confined partially with geogrid, both with and without the inclusion of steel fibers, in comparison to traditional columns reinforced with steel. Columns, 16 in number, with different steel stirrup spacing, concrete types, and geogrid configurations, were cast and put under axial load. Load-deflection curves were obtained, and parameters including ultimate load, maximum axial displacement, ductility, secant stiffness, and energy dissipation were assessed and compared. The findings indicated that incorporating geogrids with greater tensile strength alongside steel fibers could uphold a peak load value 10.16% higher than the control column, improved stiffness, and enhanced energy dissipation, indicating a promising approach for reinforcing columns in conjunction with steel fibers.

In railway tracks, additional stresses occur in rails due to interaction between the rail and the bridge superstructure, which is a phenomenon known as track–bridge interaction (TBI). The additional rail stresses (ARSs) develop primarily as a result of temperature effect, vertical bending of bridge superstructure, and braking/acceleration of trains traveling over the bridge. One of the major parameters affecting the TBI response is the behavior of interface elements simulating the coupling between the bridge superstructure and the rail. In TBI analysis this coupling is defined by the so-called longitudinal resistance-displacement curves (RDCs). The present study deals with the longitudinal aspect of TBI though a numerical investigation. The numerical modeling approach was verified with available analytical solutions and data obtained from bridge monitoring. The primary interest was to illustrate how sensitive the TBI response is to changes in RDCs with both separate and sequential analysis approaches, which has not been investigated thoroughly earlier. The parametric study was extended to investigate the effects of expansion length and substructure stiffness, in addition to RDC type. For simply supported precast girder bridges, RDCs that are experimentally proven specific to ballastless railway bridges can be used as an economic alternative to those specified by provisions.

Abstract

A column is a critical member in a reinforced concrete framed building. It transfers lateral shear during an earthquake, in the presence of gravity loads. Failure of short wall-type shear-critical columns in the soft and weak open ground story (OGS) of a building during an earthquake can trigger pancake-type collapse. To avoid these types of failures, the weak columns in the OGS can be strengthened locally, in addition to a global retrofit strategy applied to the entire structure. This research focuses on the seismic strengthening of such short columns using the concrete jacketing technique. The study presented in this paper demonstrates a methodology to model the shear behavior of short columns before and after jacketing. This pertains to the nonlinear static analysis of a building under lateral loads, such as a static pushover analysis. The development of shear hinge properties for as-built and jacketed short columns is presented in this paper. These were based on a proposed generalized truss analogy, which was validated based on the tests of column specimens conducted as part of this research. Pushover analyses of a building model without and with jacketed columns in the OGS were conducted. Selected results of the analyses are presented in this paper. The modeling of the shear hinge properties for the short columns in the OGS demonstrated the brittle behavior under lateral loads before jacketing and the improvement in ductility after jacketing. The proposed method can be used in professional practice for evaluating buildings with short columns strengthened by concrete jacketing. Since all the columns in a story cannot be jacketed due to economic and functional considerations, the effect of selective jacketing of the columns on the behavior of the building under lateral loads is illustrated.

Practical Applications

An existing reinforced concrete framed building can be retrofitted to mitigate the damage expected during a future earthquake. The effect of retrofit on the structure should be justified preferably by a nonlinear method of analysis such as pushover analysis. The primary input in such an analysis is the nonlinear behavior of each structural member under increasing lateral loads, modeled as the hinge property. The presented study discusses the pushover analyses of a building, before and after strengthening its short wall-type columns in the open ground story by concrete jacketing. A method to develop the shear hinge properties of as-built and jacketed short columns is explained in this paper. The method is based on extending the truss analogy for modeling the shear deformation of a short frame member after the diagonal cracking of concrete in the web. The procedure does not need any special purpose program for calculation and can be implemented using a spreadsheet. Also, a parametric study on optimum strengthening is presented, showing the effect of jacketing selected columns, as all the columns need not be intervened, to reduce the cost as well as the disruption to the users.

Ensuring the safety of construction sites is a pivotal aspect in the field of construction engineering and management. Frontline supervisors, acting as a central link between upper management, safety personnel, and field workers, play a vital role in this regard. Despite their significance, their role remains largely unexplored and underinvestigated. This study utilized a blend of survey methodology and literature review to assess the mediating impact of frontline supervisors on the behavior of field workers and to identify factors contributing to the enhancement of their overall contribution to site safety. According to the study findings, frontline supervisors play a significant role in mediating workers’ behavior. Consequently, the accountability of frontline supervisors emerges as vital for elevating construction site safety. Moreover, seven factors contributing to the safety performance and overall contribution of frontline supervisors were identified in the reviewed literature. The factors are safety management system, management commitment, safety training, experience, safety knowledge, safety attitude, and leadership skills. As a result, this research enriches the existing body of knowledge and provides practical insights for the industry, enhancing our understanding of the role of frontline supervisors and the necessary resources required to empower them. Industry professionals and practitioners can utilize this study’s findings to make decisions that positively impact safety conditions on their construction sites.

Structural systems are vulnerable to dynamic loading and need special protection while facing extreme conditions. This study proposes an integrated structural control and health monitoring (ISCHM) system to enhance the safety and performance of building structures subjected to seismic loading. The system encompasses a semiactive controller based on reinforcement learning (RL) as well as a real-time damage identification (RTDI) system for structural health monitoring. The controller uses Deep $Q$-Networks (DQNs) to operate a semiactive control device and suppress the dynamic vibrations. The DQN controller was integrated with the RTDI system proposed in the preliminary phase of the project. The damage information provided by the RTDI was used to train the DQN controller and optimize the control policy in different damage conditions. The performance of the ISCHM system was evaluated through the numerical example of a building structure with variable viscous dampers installed between adjacent floors. OpenAI Gym and Keras were used to create a custom environment, define the DQN agent, simulate the interaction between the agent and environment, and train the agent while exploring the environment. The smart structure equipped with the ISCHM system was subjected to earthquake loading and the performance was compared with conventional semiactive control alternatives including skyhook and Lyapunov controllers. The results show the effectiveness of the proposed ISCHM system especially in the presence of damage. The ISCHM system can enhance the episode score by up to 58%.

This study investigates the influence of steel fiber content (0%, 0.3%, 0.6%, 0.9%) on the axial compressive performance of ceramsite concrete. Four types of ceramsite concrete specimens were prepared and the cube compressive strength of each type of ceramsite concrete was tested. Four sets of uniaxial compression tests on prismatic specimens of ceramsite concrete were conducted. The failure process and characteristics of the specimens were analyzed, and the uniaxial compressive performance of each group of specimens was systematically studied. Additionally, the stress-strain curves equations were proposed. The research indicates that, after the addition of steel fibers, the strength and ductility of ceramsite concrete are significantly enhanced. The compressive strength of cubic specimens can increase by up to 42.6%, axial compressive strength can increase by up to 25.6%, and residual stress can increase by more than 300%. Ceramsite concrete with a steel fiber volume fraction of 0.9% demonstrates clear advantages. Its energy dissipation coefficient has increased by 17%, ductility coefficient has improved by 33%, toughness coefficient has enhanced by 68%, and stiffness degradation has noticeably become more gradual. The stress-strain curve model proposed in this study aligns well with the experimental results, accurately describing the stress-deformation characteristics of steel fiber ceramsite concrete under uniaxial compression. It demonstrates good applicability. The research findings of this study can provide a theoretical foundation for the structural analysis and design of such concrete, which is of significant importance for the utilization of ceramsite concrete as both a structural material and as a component in prefabricated lightweight wall panels.

In the pursuit of a sustainable energy future, this study employs multicriteria decision analysis (MCDA) to present a concise and comprehensive strategy for onshore wind project cost analysis, addressing the critical consideration of structural stability under survival wind loads. Navigating the challenges of the contemporary industrial economy, including escalating energy costs, supply uncertainties, and environmental concerns, the research explores turbine selection based on power factor considerations, economic evaluations, and a meticulous wind resource assessment using the robust Weibull distribution. Recognizing the economic advantages of proximity between power generation sources and load centers, the study introduces the groundbreaking E-115 model, a cost-effective wind turbine. Evaluation metrics, including the levelized cost of energy (LCOE), simple payback period (SPP), net present value (NPV) per kW, benefit-to-cost ratio (BCR), internal rate of return (IRR), and cost of turbine per kW, underscore the robust viability and economic advantages of the E-115 model. Beyond economic considerations, the research emphasizes structural stability for resilience under survival wind loads and highlights the potential of wind turbines to reduce greenhouse gas emissions by 97.26% compared to coal power plants. Positioned as a central force in steering nations toward responsible and eco-conscious development, wind energy emerges as a transformative and imperative component of the sustainable energy landscape. The study’s implications extend beyond numerical revelations, providing a foundation for future research and policy decisions, shaping the discourse around renewable energy, and offering insights that transcend mere statistics to chart a course toward a greener, more resilient future.

Over the past few decades, the concept of base isolation has gained prominence as a prospective methodology for safeguarding structures against severe seismic events and wind forces. Many international building codes have recognized its effectiveness and incorporated relevant sections. This paper aims to demonstrate the exceptional performance of Lead Rubber Bearing (LRB) isolation systems through an extensive parametric study. The study showcases a significant reduction in various response parameters and emphasizes the substantial energy dissipation capabilities of the LRB system. These compelling results underscore the urgent need to develop a novel design methodology for isolated buildings in alignment with Algerian seismic regulations, which currently lack provisions for this advanced technique. The research introduces an innovative approach for LRB isolators, employing the equivalent static method. This technique is characterized by its utilization of an iterative procedure for adjusting the isolator’s displacement in accordance with the mechanical and geometric attributes of the structure. To validate the proposed model, a comprehensive parametric study was conducted on a building designed in compliance with several international codes, including IBC 2000, Italian, Chinese, Japanese, Taiwanese, and Algerian codes. The results stemming from this innovative design methodology closely align with the requirements of these international codes, affirming its global applicability and relevance.

This paper presents a streamlined and simplified framework to select the optimal corrosion-resistant reinforcement type and subsequently calculate the corresponding life-cycle costs for concrete bridge decks. Additionally, a design-oriented methodology that accounts for the effect of high-strength reinforcement, most notably reduced ductility and its implications on structural safety decision-making, is also included as part of the framework. The researchers developed a design-friendly high-strength reinforcement factor that is predicated on the net tensile strain of the high-strength reinforcement relative to the corresponding value of an equivalently designed bridge deck using conventional reinforcement. The framework provides two approaches for estimating life-cycle costs; the first adopts a theoretical present-value calculation from previous researchers, and the second serves as a simplified approach that directly superimposes material and repair costs over the intended service life. Example life-cycle cost estimates are then shown for a series of corrosion-resistant bar types including epoxy-coated; galvanized; stainless steel; and high-strength low-carbon, chromium (A1035) bars. A case study focusing on the ductility of high-strength reinforcement then provides further recommendations for implementing such bars into the larger framework. Lastly, two example bridge deck scenarios are highlighted to demonstrate the implementation of the proposed framework. The framework is designed to facilitate straightforward optimal design solutions for department of transportation (DOT) officials, consulting engineers, and others, for bridge deck applications where enhanced corrosion resistance is necessitated and access to more theoretical life-cycle cost methodologies is limited.

Shear connectors play a crucial role in achieving composite behavior, and their utilization has expanded in recent decades owing to the efficiency of constructing composite structures. Headed stud (HS) connectors are commonly employed for their role in establishing composite action, with connector strength being pivotal to overall connection effectiveness. This research introduces a methodology to enhance the shear-carrying capacity (SCC) of HS shear connectors through the incorporation of a concrete gradation in the slab. The study focuses on investigating the impact of the concrete gradation on headed stud shear connectors by dividing the concrete slab into two zones: Zone 1 and Zone 2. Six experimental push-out tests were conducted to evaluate the effectiveness of the concrete gradation concept on the stud’s SCC. Subsequently, finite-element analysis (FEA) was performed using software to analyze the shear connector’s ductility and failure mode. The parametric study considered size, shape, and concrete grade as the parameters for Zone 1. The numerical study results aligned with the experimental findings. Comparisons between graded and standard slabs showcased that a higher concrete grade in Zone 1 yielded superior results compared with normal standard slabs. The parametric study identified that the model combining M50+M25, M50+M30, and M40+M25 concrete grades exhibited better results, with an average percentage increase of 12.29%, 10.37%, and 4.49%, respectively, in the SCC of HS shear connectors. Additionally, adopting a cylindrical configuration for Zone 1 demonstrated enhanced stress distribution and increased SCC compared with a square shape for Zone 1. The parametric study further revealed a positive correlation between an increase in the dimensions of Zone 1 and increase in the SCC of the headed stud shear connector. Finally, two equations were proposed for evaluating the shear-carrying capacity of the headed stud embedded in graded concrete slab based on the dimensions of the Zone 1 region of the graded slab.

Soil–structure interaction (SSI) is a well-established phenomenon with significant implications for the dynamic response of structures subjected to earthquake loads. This study aimed to find the optimum stiffness of a lead rubber bearing (LRB) isolator within a multi-degree-of-freedom (MDOF) structure using a genetic algorithm (GA) while accounting for SSI effects through analytical formulation and numerical simulation. The simplified linear cone model was utilized to model the SSI effect, with two degrees of freedom of the soil: sway and rocking. Analytically, the main contribution is the presentation of an equivalent frequency formula for both the structure and the isolation layer, allowing the presentation of these later with respect to dimensionless parameters. Numerically, the displacement of the base level was targeted as the response to be reduced through the GA optimization, which is a further contribution of this work. To achieve this, 28 earthquake records with two components each were used during the optimization procedure. These records were regarded as near-field excitations, and 14 of them had pulse-like characteristics while the other 14 did not. The obtained results showed a local optimum of isolator stiffness for each earthquake and soil type. Owing to the stochastic nature of earthquakes, a weighted averaging method was used to obtain the global optimum isolator stiffness for each soil type, which is a novelty in this work. Further investigation of the local and general optima in the time and frequency domains showed a significant reduction in response in terms of base-level displacement, root-mean square (RMS) of top-floor acceleration, and strain energy of the entire structure. These findings may represent added values for designers working on base isolation (BI) devices in various soil conditions.

It has been challenging to predict the peak spatial accelerations of tall buildings experiencing wind-induced motion. Frequency domain solution techniques using modal analysis are typically employed for wind tunnel studies, in which it is necessary to combine the modal responses statistically to estimate the peak spatial responses. An improved solution technique is presented that treats the determination of the peak accelerations as an optimization problem with a closed-form solution. The peak X, Y, and torsional accelerations are solved using matrix multiplication of the modal response covariance matrix and mode shapes. The peak resultant acceleration is determined by solving an eigenvalue problem. The proposed solution method accommodates correlation between modal responses, which existing methodologies have neglected. A case study is presented in which significant correlation exists between a building’s modal responses due to a strong across-wind loading exciting two modes simultaneously. A tuned mass damper (TMD) is incorporated into the building design to reduce wind-induced motions. The TMD transfers energy between structural modes of vibration and increases the correlation between modes considerably. Neglecting modal correlation effects results in a considerable overestimation of some spatial responses and a considerable underestimation of other spatial responses. While a bidirectional TMD decreased the modal responses by a similar amount, due to the strengthened modal correlation not all directions of motion were decreased as much as would be expected if the correlation was not present. It is therefore necessary that DVA systems designed for tall buildings properly account for modal correlation.

This paper aims to investigate the effects of using palm leaves ash, when it partially replaces the concrete cement content, to treat the effects of using seawater as a mixing water and curing water on concrete. The paper also explores the suitable replacement percentage of cement with palm ash to give the concrete more strength and suitable workability. A slump test was used to assess the fresh concrete’s workability, as well as concrete strength testing after 7, 28, and 60 days. It was found that 5% of the cement replacement with palm leaves ash in conjunction with the full replacement of the mixing of pure water with seawater achieves an 84.188% increase in the ultimate compressive strength after 28 days of curing in tap water compared with that gained by normal concrete with mixing in seawater. Also, a reasonable workability was obtained. In the case of curing with seawater for 28 days, the partial replacement of 2.5% of cement with palm leaves ash achieves a 70.75% increase in the compressive strength when compared to normal concrete with mixing in seawater.

Abstract

Numerous structural analysis techniques are employed to model the pavement structure, considering factors such as thickness of the pavement layer, mechanical properties, and loads. These techniques include the multilayered elastic theory, finite element method, and finite difference approach. Various computer programs are accessible for estimating pavement responses and conducting analyses using these techniques. The primary focus of this paper is the modeling of pavement structures, utilizing a range of computer programs, including KENLAYER, IITPAVE, and ANSYS. This study compares surface deflections measured at different sensors during a falling weight deflectometer (FWD) test. This study also aims to enhance the finite element model by utilizing static and dynamic analyses within the ANSYS computer program. According to the comparison study, all computer programs are more likely to accurately predict the deflection value, with a small percentage of root mean square error (RMSE) ranging from 0.138% to 3.29% for all models created by the computer programs and field measurement. Additionally, it was determined that dynamic analysis is the superior approach for modeling pavement in FWD testing, as it exhibits an RMSE variation of only 0.13% to 1.0%.

Practical Applications

The fundamental aim of modeling pavement structures is to ascertain the essential responses of the model, encompassing stress, strain, and deflection. The essential point is that the pavement model adequately depicts the behavior of the pavement in the field; it should not matter whether a pavement is represented using multilayered elastic program or a finite element (FE) program. Several researchers have focused predominantly on modeling FE for flexible pavement designs, with limited attention given to investigate FWD deflection values. Based on the observations, it can be concluded that ANSYS, utilizing the FE approach, emerges as the most efficient and adaptable computer program for simulating the FWD test and accurately calculating parameters such as deflection, tensile strain, and compressive strain. Thus, this study facilitates distinct target groups of pavement engineering in terms of a simple, robust model for predicting pavement structural performance using the ANSYS dynamic program that can be adopted during the maintenance phase of the pavement.

Semiactive vibration control devices have grown in popularity due to their ability to regulate devices while consuming little power. Magnetorheological (MR) fluids with regulated rheological properties are used in large-scale MR dampers (MRDs) in structures. Many researchers have improved MRDs in various ways depending on their application. This paper focuses on the experimental study of a designed, developed, and fabricated small-scale MRD to enhance the structure’s performance against seismic/cyclic excitations. The tests were performed in real time, with the input parameters being the excitation frequency, current input to the MRD, and damper piston displacement. The experiment was carried out by specifying three piston displacements (5, 10, and 15 mm) and subjecting them to varying excitation frequencies ranging from 0.1 to 1 Hz. The experimental study’s findings, which include force-displacement, energy dissipation, the relationship between excitation frequency and piston velocity, and total damping force, have been discussed, tabulated, and plotted for easy comprehension. The experimental tests were carried out to check the damper’s performance, which yielded satisfactory results without any damage. Various conclusions have been presented based on findings such as shear-thinning and shear-thickening phenomena during the test. Generally, the developed small-scale MRD exhibits good energy dissipation, an essential criterion for seismic resilience, and can be used as a semiactive vibration control device for building structures in seismicity regions.

Ductility and strength characteristics of hardened concrete can be enhanced by using optimum percentages of steel (ST) fibers and polypropylene (PP) fibers. It moreover helps to control multi-level cracking in reinforced concrete (RC) structures. However, such addition gradually diminishes the workability. Self-compacting concrete (SCC) is capable of flowing freely due to its own weight; it fills the form completely and consolidates without any vibrational device. Hence studies have been done to modify the properties of SCC with optimal content of such fibers to achieve greater workability. European federation of national associations representing for concrete (EFNARC) and ASTM standard guidelines have been utilized to conduct all the tests on the fiber-reinforced fresh and hardened SCC concrete. These steel and polypropylene fibers were varied in SCC from 0% to 1.5% by weight of concrete under varying mix proportions. Different tests including slump flow, V-funnel, L-box, and the U-box test were performed to achieve the fluidity and filling ability for fresh SCC. Furthermore, unit weight, spilt tensile strength, compressive stress, and flexural strength of the SCC were also evaluated. The 28-day compressive strength of the SCC-I and SCC-II mixes having a fiber content of 1.5% was found to be increased by 10% and 32% than those of controlled concrete mix. The 28-day flexural strength of the SCC-I and SCC-II mixes having a fiber content of 1.5% was found to be enhanced by 16.82% and 23.9%. Hence, all the fluidity, filling ability, and strength properties of SCC with steel and polypropylene fiber mixes are discussed in detail.

The fineness modulus (FM) denotes the average particle size of fine aggregates. The FM of the sand, and other constituent qualities, have a major effect on the strength and durability of geopolymer mortar. Finer particle size increases the surface area, influencing heat absorption and emission, impacting the mechanical strength of geopolymer concrete. Heat energy notably accelerates reaction kinetics, accelerate geopolymerization processes. The purpose of this study is to ascertain how the compressive strength (CS) of fly ash (FA) and Ground granulated blast-furnace slag ($S_{\mathrm{lag}}$) based geopolymer material (GPM) is affected by the fineness modulus (FM) of sand that has been heated to $100°\mathrm{C}\pm 5°\mathrm{C}$. To make the paste for the geopolymer material, natural river sands with FM of 1.85, 2.41, 2.79, and 3.32 were used. For the investigation, 36 samples of a $50\times 50\times 50{\mathrm{mm}}^3$ cube were hot cured at 50°C for 3 h to determine the CS of GPM paste after 3 h, 1 day, and 7 days. The study’s conclusions show that sand FM has a large effect on the flow rate (%) of GPM. In particular, a greater flow rate (%) of GPM paste was connected to a higher sand FM. Notably, the most pronounced improvements in CS growth rate (%) were seen in GPM paste made with heated sand that had FM values of 1.85 (fine sand) and 2.79 (medium sand). Furthermore, when heated sand was utilized, the FM had a substantial impact on the CS of GPM matrix. The mineral composition, including unreacted FA and $S_{\mathrm{lag}}$ components, underwent assessment using energy dispersive X-Ray analysis (EDX) and scanning electron microscopy (SEM). These analyses revealed that fine aggregates, with increased surface area content, contributed to higher concrete strength compared with those with a higher concentration of coarse aggregates. It follows that when attempting to create geopolymer material with strong early-strength qualities, fine sand, well graded sand ideal match to the ASTM upper and lower bound limits are the best options for fine aggregates.

Abstract

Many structures such as buildings, power plants, stacks, sea walls, bunkers, and tanks are built with reinforced concrete; and durability is a major concern. Corrosion of reinforcement is the most important process of deterioration. Reinforcement corrosion is prevented by maintaining appropriate quality of concrete mix, casting, and curing and by providing the requisite clear cover to reinforcement according to the postulated exposure. The provisions of several international codes were reviewed from these aspects. Many codes can be interpreted in favor of providing different clear covers on different faces of members in a reinforced concrete structure. The authors’ interpretation of the Australian and New Zealand codes revealed that these specifically allow the above. However, this practice might lead to severe durability-related concerns, particularly due to corrosion of reinforcement. Case studies conducted with postulated data from a few international codes revealed that internal corrosion cracks might occur earlier than external cracks in certain cases. Internal cracks can be hidden from view and consequently lead to higher damage to the structure prior to detection. For the simultaneous occurrence of corrosion cracks on the internal and external faces of a member, the internal surface chloride concentration would have to be between 18% and 73.2% of the external, with a median of 38%. These could hardly occur in practice—except for treated air facilities. If construction periods are long, this durability issue would be applicable even for treated air facilities. Higher differences in clear cover between internal and external faces, and higher external chloride exposure – both call for larger reduction of chloride exposure from external to internal. Unless the members are designed for corrosion as specified in some (Japanese) codes, the authors advocate the conservative option of using the same cover for all faces of concrete members to achieve a lower life cycle cost of the facility.

Practical Applications

Design codes across the world can be interpreted in favor of different clear covers (to reinforcement) on different faces of concrete members according to exposure conditions. Only the Australian and New Zealand codes specifically mention different clear covers for internal and external faces, by the authors’ interpretation. This article examines the durability of concrete members with different clear covers on internal and external faces, with case studies generated from a few international codes. The results indicate that in such cases, corrosion cracks might occur on internal surfaces much earlier than the external surfaces. For cracks to occur simultaneously on both surfaces, the internal surface chloride concentration must be as low as 18% of the external, which is difficult to ensure in practice. Early internal cracks could be hidden from view on account of equipment or false ceiling/panels—thereby causing more damage before detection. They would be difficult to detect, to evaluate, and to carry out structural repairs. Therefore, it could be expensive to maintain and could adversely affect the service life of the structure. This study would sensitize the clients, regulators, and engineers to these concerns. The authors suggest that the conservative approach of the same clear cover may be adopted on all faces, according to the worst exposure on any face, to ensure the durability of the concrete structures.

This study is focused on an evaluation of the correlation between the soil conditions and the seismic damage observed after the Vrancea March 4, 1977 intermediate-depth earthquake in Craiova, Romania. A significant number of existing studies in the literature have focused on the evaluation of damage for Bucharest, but the effects of the 1977 earthquake in Craiova have been very rarely discussed and presented. Craiova was the second city in Romania after Bucharest in terms of building damage and casualties as a result of the 1977 Vrancea seismic event, even though it is situated at a considerable distance (more than 250 km) from the epicenter. The 1977 event affected old low-rise masonry structures located in the central part of the city, as well as low-rise unreinforced masonry structures built after 1950. The soil conditions are evaluated based on a recently compiled collection of geological, geotechnical, and ground motion data from the study area. No correlation between the earthquake observed damage andthe number of standard penetration test (SPT) blows at a depth of 6 m or the soil layer at a depth of 3 m can be inferred from the available data. Moreover, the analyses show practically no influence of the terrain slope on the ground motion amplitudes for Craiova, which is situated on the left bank of Jiu River. The vulnerability characteristics of unreinforced masonry structures from Craiova and other cities are also evaluated in this study. The relative frequencies of unreinforced masonry structures having increased damage degrees is significantly larger for the Iasi and Craiova data sets. Finally, an estimation of the peak ground accelerations in four cities in Romania is evaluated based on the damage of unreinforced masonry structures.

This study aimed to conduct a finite element analysis-based seismic evaluation of an existing reinforced concrete (RC) building for a high seismic zone in northeast India. The building model was evaluated for demands using response spectrum analysis (RSA) per the latest Indian standards. Data on the condition of existing material strength, geometry, and initial design are collected on site. Here, a procedure has been introduced to evaluate the seismic demand and capacity of structural members, for prioritizing strengthening work. The focus of the study was on assessing the potential failure of columns, with an aim to evaluate a building’s susceptibility to failure and collapse. This evaluation procedure was applied to an existing low-rise RC building in northeastern India that was originally designed for gravity loads. The building had significant plan irregularities and stiffness irregularities. As anticipated, it was observed that the building did not withstand seismic design action, and all the columns failed, while the beams failed partially. For various load combinations, the demand–capacity ratio, particularly in terms of axial load and biaxial bending moments of the columns, emerged as a critical force-based factor in evaluating the building’s safety under combined forces. The obtained results were validated on site by visual inspection of structural longitudinal cracks under high combined (axial with biaxial moment) demand in columns. The case study identified the six most critical columns that might lead to building collapse and need immediate strengthening. This approach demonstrated its feasibility as a tool for assessing the seismic performance of existing low-rise RC buildings for prioritizing structural strengthening work.