Safety Of Building Structures Research Articles

Hyperbranched organic-inorganic co-modification improves the strength, dimensional stability, and thermal stability of poplar wood

High-strength, dimensionally-stable, moisture-absorbing, and heat-insulating materials are critical for ensuring the safety of building structures and human comfort. As a natural moisture-adjusting and heat-insulating material, wood is widely used in buildings, but its low strength and flammability pose safety hazards. This paper reports a simple method to construct an organic-inorganic hyperbranched structure in poplar wood (W Si-Al-EP ). The bending and compressive strength of W Si-Al-EP reached 103.50 MPa and 80.41 MPa, respectively. This composite wood material exhibited high strength and stable performance, and it also improved the shortcomings of traditional inorganic-modified materials such as unstable sizes and the loss of modifiers. Moreover, the material did not burn in a long-term high-temperature flame, indicating its heat and combustion resistance, and showing that it can be used in wooden building structures. • A method for preparing organic-inorganic hyperbranched structure in wood (W Al-Si-EP ). • W Al-Si-EP has high strength and good dimensional stability. • W Al-Si-EP has strong thermal stability and flame resistance.

Relaxation of stress in elements of reinforced concrete structures

The calculation and prediction of the long-term safety of building structures is associated with the dynamics of the stress state of their composite elements and leads to relaxation problems for assessing the redistribution of stresses between the components that make up the structural element. In this study, reinforced concrete elements and the redistribution of stress from concrete to reinforcement are considered. To solve the corresponding relaxation problem an approach based on the concept of the strength structure of materials is proposed, which considers them as a union of their fractions (layers, fibers) with statistically distributed strengths. The loss of the ability of force resistance caused by loading by part of the fractions of the element entails a redistribution of stresses to its entire fractions. As a result of this, a nonlinear dependence of deformations on the design stresses arises, calculated under the assumption of equal strength of all fractions. For a material isotropic in strength, the relaxation problem is reduced to solving a linear integral equation conjugated with its linear rheological equation. The linear integral equation relatively structural stresses is reduced. After solving it, the desired stress is determined as the root of the algebraic equation connecting the structural and design stresses. The proposed approach significantly simplifies the obtaining of necessary for the long-term safety prediction of structures stress estimates in the components of structural elements.

Numerical Verification on Optimal Sensor Placements for Building Structure Before and After the Stiffness Decrease

Japan and Taiwan are located in an area where earthquakes and typhoons occur very frequently. To ensure the safety of building structures, it is necessary to proceed with structural health identification before and after a disaster. This study proposes the optimal placement of sensors to reduce the number of sensors installed in the mid/high-story building for monitoring and inspection purposes, while simultaneously enhancing the accuracy of the determination of modal frequencies for the building structure. To achieve this goal, the first step is to obtain the reference modal frequencies of the structure. That is to install reference sensors on the structure for recording actual time-histories, then to obtain simulated time-histories using the cubic spline interpolation method. After the actual and simulated time-histories are collected from each structure floor, the Frequency Domain Decomposition (FDD) method is used to enhance the accuracy of reference modal frequencies, and then the Stochastic Subspace Identification (SSI) method is utilized to plot out the stabilization diagram. Several reference modal frequencies shown in the stabilization diagram will be determined. Finally, the Optimal Sensor Placement (OSP) locations for placing acceleration sensors can be obtained using a genetic algorithm. Structural models with different story numbers will then be simulated to obtain OSP locations. The condition of stiffness decrease will also be discussed. A comparison is made before and after stiffness decrease to discover the modal frequencies of the structures under the case of both optimal placement and original placement, ultimately to verify the feasibility of the methods proposed in this study.

Building structures of thermal power plants: analysis of fire resistance limits

Introduction. The author analyzes real-life fire resistance limits of metal structures for one building of a thermal power plant. Experimental and computational methods were applied to identify the fire resistance limits of building structures. The temperature setting of the research, conducted to solve the problem, was the same as that of a real fire.Research goal and objectives. The purpose of the analysis is to identify the fire resistance limits of structures comprising the building of a thermal power plant using the method of heat-mass exchange analysis that takes account of conditions of a real fire. The following objectives are to be attained in compliance with the pre-set goal:to analyze the principal provisions of technical norms and regulations in terms of the fire safety of building structures of thermal power plants;to justify the principal provisions for the method of heat-mass exchange analysis, taking into account real-life fire conditions;to justify the need to improve the real-life fire resistance limits by fire-proofing agents with account taken of the most dangerous scenario of the real fire development.Methods of research. The heat-transfer equation is analyzed to identify the distribution of temperatures inside a building structure for a one-dimensional case. The field-based method of analysis is applied to solve this problem. This method is generally applied to premises having complex geometric configuration, if one geometric dimension exceeds the others.Results and their discussion. The authors have analyzed the most dangerous fire scenario characterized by the most dangerous impact on metal structures, such as the furnace oil fire spill in a boiler room.The authors also address the most dangerous fire propagation scenario in terms of the heating of bearing metal structures: the combustion of furnace oil spills in a boiler room. The computations have proven that in case of the selected fire development scenario maximal temperatures of bearing metal structures are much lower than the critical temperature of 500 °С fifteen minutes after the onset of fire.Conclusions. Having analyzed the fire resistance computations of thermal power plant structures, including their metal constructions, the have found that in case of emergency, resistance to the most dangerous manifestations of fire exceeds the required R15 value. No fireproofing of bearing metal structures in the boiler room is needed.

Short-term operational safety of original European road bridges

Short-term operational safety of original European road bridges Looking at the basic requirements for building structures in Regulation (EU) No 305/2011 of the European Parliament and of the Council, Professor Janusz Rymsza explores the operational safety of structures. He elaborates the need to ensure durability, or the adequate safety of the structure over its assumed service life, and looks at the possibility of demolishing structures and the inadequate operational safety of building structures due to their lack of durability. This article analyses the cost and effectiveness of the safety of bridges, and the requirements for building structures, diving into what has changed in bridge construction over the past 30 years.

CALCULATION METHODS OF MONOLITHIC REINFORCEDCONCRETE STRUCTURES WITH POST-TENSION REINFORCING ROPES

In Ukraine, the use of "post-tensioning" technology, which consists in the use of monolithic structures with pre-tensioned ropes, is growing. Domestic construction practice uses the term "prestressed reinforced concrete structures with tension of cable reinforcement on concrete." Post-tensioning technology is a modern approach to construction that allows you to create monolithic structures with great strength and stability. Its main advantage is the use of pre-tensioned ropes, whichprovide additional structural strength.In this article, the main methods of calculating such monolithic reinforced concrete structures are presented and the experience of using this technology in the construction of public buildings in Ukraine is presented.The use of prestressed reinforced concrete structures with the tension of cable reinforcement on concrete has numerous advantages. They are more durable, resistant to deformations and able to support large loads. Such structures are used in the construction of bridges, overpasses, high-rise buildings and other industrial and civil structures.Ukraine is increasingly adopting modern and efficient construction methods, which is confirmed by the increased use of this technology. This helps to improve the quality and reliability of building structures, and also ensures optimal use of materials and resources.In general, the article aims to promote the popularization, study and development of monolithic structures with pre-tensioning of cable reinforcement on concrete, as well as the creation of an appropriate regulatory and legal environment for their design and construction. This will help improve the quality and safety of building structures and ensurefurther progress in the construction industry of Ukraine.

Seismic performance assessment of conventional construction concrete moment-resisting frame buildings in Canada using the FEMA P695 methodology

National Building Code of Canada (NBC) specifies 45 Seismic Force Resisting Systems to ensure the safety of building structures. Conventional construction concrete moment-resisting frame (CC-CMF) is one of these systems whose seismic response has not been systematically studied in Canada. This paper is an attempt to study the seismic performance of this system using the FEMA P695 methodology. In this regard, different archetype configurations were developed and analyzed through nonlinear static and dynamic analyses. Performance assessment results show that the CSA and NBC requirements for CC-CMF system represent the lower bound of values for seismic force modification factors, and conservatively meet life safety objectives presented in the NBC. Furthermore, different scenarios were considered for identifying ductility-related seismic force modification factor from pushover curves. The effect of height and gravity load levels on seismic force modification factors and collapse margin ratios are also presented by comparing archetypes having different configurations.

Acoustic emission characteristics and damage law for prefabricated single‐crack sandstone under uniaxial compression

The cracks of rock seriously threaten the safety of building structures and underground space. Uniaxial compression tests were carried out on prefabricated single-crack sandstone samples with different angles and lengths. The results show that the existence of a prefabricated single-crack has a certain influence on the mechanical properties and acoustic emission response characteristics of sandstone samples. A function formula of the effect of uniaxial compression stress on the angle and length of prefabricated crack is established. It is found that there is an obvious moment of acoustic emission energy mutation in the three deformation and failure stages before sandstone failure. The change of angle and length of crack has a great influence on the stress value corresponding to the energy mutation at the stable development stage of the micro-crack. Meanwhile, the acoustic emission waveform characteristic parameters of sandstone samples under various fracture conditions are analyzed. Thus, the crack propagation mode of the sample with small angle can be judged. The damage variables based on real-time acoustic emission energy were defined, and the damage constitutive model of rock material with a single fracture under uniaxial compression was established based on real-time acoustic emission energy. The results show that the new model and method can not only reasonably explain the damage mechanism of prefabricated rock with a single fracture under uniaxial compression but also accurately simulate the full stress-strain process of rock with a single fracture at different angles and lengths, which has good rationality and feasibility.

'Building back better' is neoliberal post-disaster reconstruction.

'Building back better' (BBB) has become one of the most common expressions in disaster risk reduction. Disasters offer an opportunity to encourage improvements not only in the structural safety of buildings and infrastructure, but also in addressing structural inequalities and injustice. Consequently, they are an opportunity to make things 'better'. However, in the context of neoliberalism, the definition of 'better' does not always mean 'good for all'. We argue here that BBB allows for widely varied definitions of what is and what is not a risk, who is and is not responsible, and what forms of action are to be taken in response to these dangers. This serves as a designation for capacity to make 'better', but not actively change, social and political systems that initially create risk. Disasters and its terminology, therefore, are not ideologically neutral and should thus be deliberately unpacked and critically evaluated rather than accepted unquestioned.

Structural Vibration Analysis of Historical Drum Tower Structure Caused by Underground Train Running

The vibration induced by underground metro operation could have significant impacts on the safety of building structures. In this study, the dynamic response of the Nanjing Drum Tower affected by the metro line four operation was investigated by a three-dimensional FEM coupling train-track-tunnel-foundation-soil-basement–Drum Tower model performed on a 64 CPU parallel computing cluster platform. The results show that the vertical vibration caused by the subway operation has a more serious impact on the historical structure of the Drum Tower than the horizontal vibration. The vertical vibration attenuates rapidly from the basement bottom to the top of the tower. The horizontal vibration amplifies along the height of the historical building. The truss roof significantly weakens the vibration. As the speed of the train increases, the amplitude of horizontal and vertical vibration increases gradually from the bottom to the roof of the Drum Tower despite a relatively smaller increase for the horizontal vibration. As for the double-track operation case, the vertical vibration amplitude is much greater than that for the single-track operation, and no significant difference is observed in the horizontal direction. The amplitudes of horizontal vibration velocity for the basement and Drum Tower are 0.131 and 0.060 mm/s, respectively.

Structural health monitoring of building rock based on stress drop and acoustic‐electric energy release

The process of building rock failure is often accompanied by stress drop and energy release, which seriously threaten the safety of building structures. To reveal the law of energy release and transformation in the process of rock stress drop and establish a rock structural health monitoring index based on stress drop energy, the relationship between the stress drop and acoustic-electrical (acoustic emission and electromagnetic radiation) energy of the shale and limestone failure process is studied in this paper. The results show that, in the early stage of rock loading, there is almost no stress drop dissipated energy, and the change in acoustic-electric signals is not obvious. In contrast, in the later stage of deformation and failure of rock, the generation process of stress drop is accompanied by significant stress drop dissipated energy and acoustic-electric energy release. With the increase in stress drop dissipated energy, the released acoustic-electric energy gradually increases, and there is a good linear positive correlation. The release mechanism of the acoustic-electric energy in the process of stress drop is mainly related to the crack propagation effect. The more significant the stress drop is, the faster the crack unstable propagation, the more intense the charging and discharging processes are on the crack faces, and the more acoustic-electrical energy is released. Finally, a new indicator of rock structure health monitoring based on stress drop energy is established by a statistical method, and the health status of the rock mass structure is divided into weak, medium and strong danger, thus reflecting the stress distribution state and structural stability of rock.

A damage assessment method for masonry structures subjected to long duration blast loading

With frequent blast accidents of hundreds of tons equivalent explosion, increasing attention has been paid to the damage assessment and anti-explosion safety of building structures. Some evaluation methods give procedures to obtain the pressure-impulse diagrams on the structural components. However, to the best knowledge of authors, how to evaluate the damage degree of building structures as a whole still remains open. In this paper, a weighted component damage method is proposed to evaluate the damage of structures subjected to long duration blast loading. The method, as its name suggests, is to define a damage degree of the whole structure by adding the damage degrees of all components in a weighted manner. The weight of a component, which represents its contribution to the anti-explosion safety, is defined by a strain energy based method. In order to verify the effectiveness of the proposed method, a high-resolution numerical simulation has been performed on a two-story masonry structure subjected to blast loading with a positive phase duration of 100 ms using a self-developed parallel finite element program for shock wave structure destruction simulation. A support rotation criterion based on the flexural deformation model of components is adopted to determine the damage degree of load-bearing components such as brick walls, columns and floors. The damage degree of the whole structure is then obtained using the proposed weighted component damage method. Upon the overpressure-damage curve is obtained, interpolations was carried out to obtain the threshold values of the overpressure corresponding to the six predefined damage levels. The numerical predicted overpressure values were compared with those from literature data. It was shown that the relative error of the overpressure is between −16.9% and 26.2%, and the effectiveness of the proposed method was verified. The proposed assessment approach can be used to obtain the pressure-impulse diagrams of masonry structures and provide effective measures in protecting structures against blast loads.

Corrosion failure analysis of low alloy steel and carbon steel rebar in tropical marine atmospheric environment: Outdoor exposure and indoor test

Carbon steel rebar seriously corrodes in severe tropical marine atmospheric environment, threatening the safety of building structures. Hence, it is of great significance to design and manufacture low-alloy steel rebar which can be used in tropical marine atmospheric environment. In the paper, both of the self-designed low alloy (LA-1) steel rebar and carbon steel (HRB400E) rebar has been exposed in Sriracha for two years. The corrosion rate of LA-1 steel rebar is only half of that of carbon steel rebar after two years. However, it is difficult to study the root cause of low alloy steel rebars’ enhanced corrosion resistance by alloy elements due to the presence of a large amount of CaCO3 in the rust layer. Therefore, the mechanism of improving the protective effect of alloy elements on rust layer is further studied by dry/wet cycling corrosion tests to simulate a tropical marine atmosphere environment. The formation of dense product film on LA-1 steel surface is mainly because of the addition of Cr and Mo elements, leading to the corrosion rate of LA-1 steel rebar far less than that of HRB400E steel rebar. The protective film formed by molybdate in alkaline environment hinders the further corrosion of steel rebars. Cr(OH)3 formed by hydrolysis of Cr in low alloy steel rebars inhibits the growth of FeOOH in rust, resulting in the generation of smaller size of FeOOH particles. The experiment proves that the newly designed LA-1 steel rebar can be well applied in tropical marine atmospheric environment.

Applying Interactive Teaching Experience and Technology Action Puzzles in Disaster Prevention Education

This study incorporated technology action puzzle and obstacle challenge activities in the course design. Using the 921 Earthquake in Taiwan as the theme, this study integrated the content of various subjects and course modules and applied information technology to present the humanistic care elements. The subjects of this study were Grade 9 students of a public middle school in central Taiwan. After the interactive operation introduction and theme film viewing, the students were divided into groups to participate in the technology action puzzle and obstacle challenge activities. Students’ learning performance using smart technological tools and overall course feedback were evaluated from the aspects of building structure safety knowledge, disaster prevention and mitigation, integrated interdisciplinary thinking, and problem-solving abilities through the course planning and quasi-experimental design. The results show that (1) in terms of the learning achievement scale, the pre-test and post-test of paired samples reached statistical significance; (2) in terms of the learning response scale, the mean of the Likert five-point scale reached above 4.0; (3) the results of mediating regression analysis show that, compared with the traditional classroom teaching mode, the interactive teaching experience and technology action puzzle have a mediating effect on learning performance and overall course feedback.

Analysis and assessment of the risk of accidents of a structure as a system by the method of "Fault Tree Analysis" on the example of a nuclear power facility under seismic impact

The article discusses a method for analyzing the risk assessment of failures of the structure as a system by developing a "Fault Tree Analysis". Formulas were proposed for the numerical estimation of the probability of system failure, taking into account the stochastic dependence of the failures of its elements. On the example of a nuclear power facility, a "wet" stand-alone storage facility for spent nuclear fuel, an analysis of possible scenarios of a facility failure was carried out, a "Fault Tree Analysis" was developed and calculated under seismic impact. It has been determined that the risk of structure as a
 system under seismic impact is determined by the risk of falling process
 equipment and building structures on the overlap of storage compartments or
 stored nuclear fuel. To increase the safety of building structures under
 seismic impact, it is necessary to pay special attention to the design features
 of the frame part and the interface between the monolithic storage compartment
 and the frame part, as the most vulnerable link.

Comparison of seismic reduction schemes for frame structures under frequent earthquakes

In recent years, viscous energy dissipation wall is widely used in China. In the case of a 5-story frame structure, the combination of viscous damping wall (VDW), buckling restrained brace (BRB) and (VDW + BRB) is used for seismic design. Under frequent earthquakes, (VDW + BRB) scheme has the best damping effect, which can effectively reduce the response of superstructure and greatly improve the seismic safety of building structures.

Evaluation of risk and safety in building structures under construction

Many of the structural defects in the past have happened during the project development process. While a structural engineer must build a safe, economic and functional structure, the durability of the partially constructed structure cannot be ignored at various construction levels. During the building, structural health is a major problem for the industry of construction. Collapses of temporary structures or unfinished permanent structures pose a hazard to safety. Predictive risk analysis methods have been applied over the past decade to evaluate the efficiency of the current existing structural building framework. Identification of risks is aimed at recognizing possible risks that can result in accidents. It describes the types of hazards and random parameters connected with the individual risks and subsequent incidents. The quantifying risk values identified with building structures built according to uniform rules are widely distributed. This study provided importance to a conversation about risk and safety in building structures under construction, to build buildings without damage and destroying, also steps of safety in building structures. The outcome of the project depends on the specifics of the prescription. Building structure safety may lead to big problems if subjected to those loads such as earthquakes and storms. A lot of structural problems happen during construction. Most failures were related to a malfunction in the formwork. This study describes how building systems can carry risks to buildings, as well as resisting the impact of loads that could cause trouble.

Построение концептуальной конфайнмент-модели базы знаний технической диагностики зданий и сооружений

Своевременная техническая диагностика конструкций зданий и сооружений является важным условием обеспе­чения их безопасности. Объективность и достоверность информации, предоставляемой экспертами о техническом состоянии строительного объекта, в большой степени зависят от опыта эксперта, то есть от человеческого фактора.
 Внедрение интеллектуальных технологий в экспертную деятельность инженера-строителя мотивировано необходи­мостью передачи знаний опытных экспертов специалистам разной квалификации для расширения и укрепления их профессиональных возможностей. Логика рассуждений человека-эксперта в интеллектуальной системе должна легко поддаваться машинной обработке. Для этого её необходимо структурировать в виде концептуальной схемы системы знаний.
 Представлен эффективный метод конфайнмент-моделирования на примере создания концептуальной структуры базы знаний (БЗ) технической диагностики конструкций зданий и сооружений, который позволяет унифицировать процесс разработки онтологических баз знаний, помогает от­сеивать неважные факторы и сосредоточиться на тех, которые действительно влияют на результат. Разработанная структура является основой для реализации следующего этапа - по­строения интегрированной базы знаний интеллектуальной системы диагностики технического состояния строительных объектов разных конструктивных форм и назначения, вы­полненных из разных материалов, которая должна также включать: методы цифровой обработки результатов лазерного сканирования повреждений конструкций; методы оценки ри­сков и определения остаточного ресурса конструкций зданий и сооружений с использованием теории нечётких множеств и нечёткой логики; оценку экономического эффекта от ме­роприятий по обеспечению конструкционной безопасности.

Planar tomography and numerical analysis for damage characterization of impact loaded RC plates

AbstractThe damage analysis of reinforced concrete (RC) is of high interest for reasons of effective maintenance and structural safety of buildings. The damage structures of RC plates loaded by an impact were investigated, applying X‐ray planar tomography and finite element method (FEM). Planar tomography allows getting three‐dimensional information of the RC elements and the damage including crack, spalling, and scabbing. The FEM model validated on the tomography data justifies the application for further predictions of the damage description. In this study, we investigated concrete plates of three different thickness subjected to impacts at different low‐ and medium‐velocity, whereby the used impactor had a flat tip, which resulted in small penetrations on the front side and scabbing on the rear side. In order to quantify the damage, the damage volume and its distribution through the plate were computed and the correlations between degree of damage and impact velocity were found out.

Data-based Distributed Fault Diagnosis for Adaptive Structures using Convolutional Neural Networks

Adaptive structures are able to react to environmental impacts and have become a promising approach in civil engineering to improve the load-bearing behavior of buildings. Since reliability and safety of building structures are major concerns, the detection and isolation of faults are essential. In this work, the data-based distributed fault diagnosis of sensor and actuator faults in an adaptive high-rise truss structure is investigated and compared to a centralized approach. The decomposition of the different subsystems is given by the hardware layout of the different sensor systems and actuators. The mechanical structure is modeled and extended by dynamic sensor and actuator models containing different faults. Based on the simulation model, different fault scenarios are generated and used for training a convolutional neural network with dropout regularization. It is shown that the distributed approach needs less training data and yields better classification results than the centralized approach due to a significant reduction of the complexity and dimensionality.