Search Results (52)

In order to reduce the self-weight of steel sheet–concrete composite slabs and fully apply the superior performance of the composite slabs, this paper proposes a kind of open-profiled steel sheet–hollow concrete composite floor slab. Flexural behavior tests are conducted to five pieces of composite floor slabs with different parameters, and numerical simulation methods were applied to perform finite element analysis on the composite slabs with different hollow rates, reinforcement ratios, and steel sheet thicknesses. At the same time, the calculation methods were discussed for the flexural bearing capacities under different anchorage conditions. The results indicate that, when the profiled steel sheet is in a low anchorage degree, end debonding is one of the important failure modes for the composite floor slabs, and the flexural bearing capacity of the composite floor slabs is significantly reduced. The reinforcement arrangement in the tensile zone has a significant impact on the bearing capacity, deflection, and ductility coefficient of the composite floor slabs. When the reinforcement ratio increases from 0% to 0.6%, the ultimate bearing capacity is increased by 182.5%, and the ductility coefficient is increased by 246.0%. The ultimate deflection of specimens with a reinforcement ratio of 0.6% is 22.4 times of that of the specimens without reinforcement arrangement. When the hollow rate is less than 20%, the influence of the concrete hollow radius on the flexural bearing capacity, ductility coefficient, and maximum crack width is relatively small. As the thickness of the steel sheet increases, the increasing range in ultimate bearing capacity gradually decreases, the deflection gradually decreases, and the ductility coefficient gradually increases; increasing the thickness of composite floor slabs can help reduce deformation. The theoretical calculation values obtained by applying the flexural bearing capacity calculation method proposed in the paper match with the test results, and the method has a certain reference value for the engineering practice. Full article

Following World War II, the swift economic growth in construction and the soaring demand in urban regions led to the excessive extraction of natural resources like fossil fuels, minerals, forests and land. To tackle significant global challenges, including the consumption of natural resources, air pollution and climate change, radical changes have been suggested over the past decades. As part of this strategic initiative, prioritizing sustainability in construction has emerged as a crucial focus in the design of all projects. In order to identify the most environmentally sustainable reinforced concrete (RC) slab system, this research investigates the carbon emissions associated with various slab systems, including solid, voided slabs and precast floor systems. The results demonstrate that beam and slab floor and solid slabs have the highest embodied carbon due to the significant use of concrete and related materials, whereas voided slabs and two-way joist floors exhibit lower carbon emissions. The results indicate that the two-way joist system is the most environmentally advantageous option. For precast floor systems, post-tensioned concrete and hollow-core slabs demonstrate the lowest embodied carbon levels. This research provides practical recommendations for architects and engineers aimed at enhancing sustainable design methodologies. It emphasizes the importance of incorporating low-carbon materials as well as pioneering flooring technologies in upcoming construction initiatives to support the achievement of global sustainability objectives. Full article

The article presents the experimental and computational investigations on carbon-reinforced concrete (CRC) slabs with hollow-core cross-sections. Designed for use in building construction, they combine the benefits of lightweight construction, resource efficiency, and precise prefabrication. Three geometrically identical elements were manufactured and tested until failure in four-point bending tests. The slabs demonstrated a high load capacity of around 50 kNm, together with high ductility due to a deformation of more than 80 mm before failure. The load-deflection curves recorded could be reproduced very well with the analytical-physical calculation model created for both the non-cracked and cracked slab states. The strengths and stiffnesses of the materials used for input were derived from small-scale, accompanying material tests. As a result, the calculation model was ultimately used to design the carbon-reinforced ceilings of the CRC technology demonstration house CUBE, which was finished in 2022 in Dresden, East Germany. Full article

To reduce the maintenance requirements during the service life of highway bridges and enhance the cracking resistance of concrete slabs in the hogging moment zone of continuous composite girders, this paper proposes an innovative girder-to-pier joint for composite bridges with integral piers. Compared to the existing ones, this new joint has structural differences. The middle part of the embedded web is hollowed out to facilitate the construction, and the upper and bottom flanges of the steel girder within this joint are widened. Moreover, cast-in-place ultra-high-performance concrete (UHPC) is applied instead of normal concrete (NC) only on the top surface of the pier. A full-scale test was carried out for this new joint to evaluate the load–displacement relationship, load–strain relationship, crack initiation, and crack propagation. Compared with the numerical simulation results of the reference engineering, the test results demonstrated that the proposed joint exhibited excellent flexural performance and cracking resistance. This paper also proposes a calculation method for the elastic flexural capacity of the girder-to-pier joint incorporating the tensile strength of UHPC, and the calculated result was in good agreement with the experimental result. Full article

Ultra-high-performance fiber-reinforced concrete (UHPFRC) has the characteristics of high strength, toughness, and excellent crack resistance. In order to fully utilize the high-strength properties of UHPFRC and reduce the structural weight and construction cost, solid slabs can be fabricated into hollow-core slabs or composite sandwich slabs. In order to further analyze the mechanical properties and mechanism of action of UHPFRC hollow-core slabs, one solid slab and two hollow-core slabs with the same geometric dimensions, reinforcement, and steel fiber volume content are designed in this paper, and their stress performance under a static load was investigated using a four-point bending test. The research results show that the UHPFRC hollow-core slab is anisotropic, and the bending stiffness of the section with parallel, distributed tubes is slightly smaller than that of the solid slab. The addition of steel fibers can greatly limit the development of cracks on a slab surface, so the elastic limit of a UHPFRC hollow slab is higher than that of a conventional concrete hollow slab. The whole bending process is roughly divided into the elastic stage, the elastic–plastic stage, and the plastic stage; the crack development process on the bottom of the slab can be classified into the cracking stage, the stable crack development stage, and the rapid propagation stage. In the elastic stage, the cross-sectional deformation of the UHPFRC hollow-core slab in the bending process still satisfies the assumption of a flat section. A row of parallel, round tubes on the neutral axis has a little effect on the cracking load, bearing capacity, and deformation capacity of the UHPFRC slab. By conducting the comparative analysis of the hollow rate and bearing capacity, when the hollow rate reaches 13.57%, the comprehensive weight of the solid slab is reduced by 13.16%, the cracking moment is slightly reduced, and the ultimate load is only reduced by 8.78%. Under the premise of meeting the bearing capacity, the hollow rate of the UHPFRC hollow-core slab can be appropriately increased to save money and energy. Full article

A static performance experimental study was conducted on six simply supported reinforced concrete truss hollow composite slabs to analyze their flexural rigidity. The study investigated the effects of the slab thickness, the dimensions of the hollow thin-walled boxes, and the composite interfaces on the flexural rigidity of the hollow composite slabs. The flexural rigidity was calculated using methods from American standards, Chinese standards, and the relevant literature, and the results were compared with the experimental data. Based on the experimental findings, a method for calculating the flexural rigidity of hollow composite slabs using a reduced moment of inertia equation was proposed, and the calculated results showed good agreement with the experimental results. The research indicates that the composite interface and the size of the hollow thin-walled boxes have minimal influence on the flexural performance of hollow composite slabs, while the slab thickness significantly impacts their flexural performance. By employing the effective moment of inertia method and substructure calculation theory, a calculation method for the flexural rigidity of hollow composite slabs was established, demonstrating high accuracy. Full article

This study aims to investigate the bending load-bearing capacity of precast hollow composite slabs composed of ultra-high-performance concrete (UHPC) and Normal Concrete (NC). Through finite element numerical analysis and verification, this study analyzes various key factors influencing the performance of the composite slab, including the wall thickness of the square steel tube, the diameter of transverse reinforcing bars, the thickness of the precast bottom slab, and the strength grade of the concrete. The results indicate that the use of UHPC significantly enhances the bending performance of the composite slab. As the wall thickness of the square steel tube and the strength of UHPC increase, both the yield load and ultimate load capacity of the composite slab show considerable improvement. By conducting an in-depth analysis, this study identifies different stages of the composite slab during the loading process, including the cracking stage, yielding stage, and ultimate stage, thereby providing important foundations for optimizing structural design. Furthermore, a set of bending load-bearing capacity calculation formulas applicable to UHPC-NC precast hollow composite slabs is proposed, offering practical tools and theoretical support for engineering design and analysis. The innovation of this study lies not only in providing a profound understanding of the application of composite materials in architectural design but also in offering feasible solutions to the energy efficiency and safety challenges faced by the construction industry in the future. This research demonstrates the tremendous potential of ultra-high-performance concrete and its combinations in modern architecture, contributing to the sustainable development of construction technology. Full article

Prefabricated staircases are crucial components in modern architectural structures, but traditional concrete staircases are too heavy for efficient prefabrication, transportation, and construction. Therefore, this paper proposes a novel lightweight hollow slab prefabricated staircase (referred to as the KXB staircase). The staircase achieves hollow designs for steps and the baseplate by incorporating hollow tubes in the steps and adding polyethylene foam boards in the baseplate. Additionally, a standard prefabricated slab staircase (referred to as the CG staircase) was subjected to static loading tests to analyze failure characteristics, load-deflection curves, and strain distribution. A finite element model was created using ABAQUS (2020) and validated for accuracy through a comparison with experimental results. The results indicate that the novel lightweight hollow-slab prefabricated staircase surpasses conventional slab staircases in load capacity, deflection, and crack control. Furthermore, it achieves a 16% reduction in weight, a 28.6% improvement in load capacity, and a maximum error of 9.9% between the model and experimental results. The novel lightweight prefabricated staircase satisfies engineering requirements, minimizes transportation and hoisting costs, and demonstrates strong application potential. Full article

Prestressed, precast composite panels are a type of building component that combines prestressing technology with composite materials; but, for most of them, it is difficult to balance structural stress performance and assembly efficiency. This paper proposes a series of novel bidirectional, prestressed, prefabricated, composite slabs, aiming to enhance their bidirectional force characteristics and assembly efficiency. By implanting a kind of specially designed concrete movable core rib with the same geometry as the cavity in the hollow-core slab at medium spacing, the transverse stressing performance of the structure is enhanced without affecting the unidirectional structural performance. Then, in the pre-set transverse apertures, several pieces of unidirectional, prestressed, precast hollow-core slabs that are implanted in the core mold are connected in series with high-strength strands and prestressed; finally, we obtain a bidirectional, prestressed, prefabricated composite slab. Two types of slabs (i.e., 3.3 m × 4.5 m and 4.5 m × 4.5 m) are selected and their mechanical behavior is investigated experimentally and by the finite element method, and the results are in good agreement. The proposed bidirectional, prestressed, precast composite slab not only has better overall bearing performance but also improves the structural stiffness and assembly rate, which can greatly improve the economic benefits and is of great significance for the popularization and application of assembled concrete structures. Full article

This study aims to evaluate the potential of machine learning algorithms (Random Forest and Support Vector Machine) in predicting the open porosity of a general-use industrial mortar applied to different substrates based on the characteristics of both the mortar and substrates. This study’s novelty lies in predicting the mortar’s porosity considering the substrate’s influence on which this mortar is applied. For this purpose, an experimental database comprising 1592 datapoints of industrial mortar applied to five different substrates (hollowed ceramic brick, solid ceramic brick, concrete block, concrete slab, and lightweight concrete block) was generated using an experimental program. The samples were characterized by bulk density, open porosity, capillary water absorption coefficient, drying index, and compressive strength. This database was then used to train and test the machine learning algorithms to predict the open porosity of the mortar. The results indicate that it is possible to predict the open porosity of mortar with good prediction accuracy, and that both Random Forest (RF) and Support Vector Machine (SVM) algorithms (RF = 0.880; SVM = 0.896) are suitable for this task. Regarding the main characteristics that influence the open porosity of the mortar, the bulk density and open porosity of the substrate are significant factors. Furthermore, this study employs a straightforward methodology with a machine learning no-code platform, enhancing the replicability of its findings for future research and practical implementations. Full article

This paper presents a Bayesian inference framework for updating the structural rigidity ratio of aging hollow slab RC bridges using deflection measurements. The framework models the structural rigidity ratio as a stochastic field along the hollow RC slabs, using the Karhunen–Loeve (KL) transform to capture spatial correlation and variation. Bayesian inference is then applied using deflection data from static loading tests, supported by a finite element model (FEM) and a Kriging surrogate model to enhance computational efficiency. The posterior distribution of the structural rigidity ratio is derived using a Markov chain Monte Carlo (MCMC) sampler. The proposed method was tested on an RC bridge with hollow slabs, using deflection measurements taken before and after reinforcement. The Bayesian updates indicated increased structural rigidity ratios after reinforcement, validating the effectiveness of the reinforcement. The deflection predictions from the updated models closely matched the measurements, with the 95% confidence bounds encompassing most of the data. This demonstrates the method’s validity and robustness in capturing the structural improvements post-reinforcement. Full article

At Cracow University of Technology, attempts were made to develop national truck scale platforms with a capacity of 60 tons, made from prestressed concrete. For this work, we designed slabs partially prestressed with unbonded tendons featuring a cross-section of 1.00 × 0.28 m and a span of 5.94 m. To reduce the weight of the slabs, four channels made from commonly used ø110 × 2.2 mm PVC pipes were used. In this way, we created post-tensioned hollow-core slabs. Due to the unpredictable behavior of slabs operating in a cracked state under a repetitive load, two slabs were subjected to cyclic loads amounting to 1,000,000 cycles with different load values. This paper presents the basic design principles and design details of the slabs, as well as the methodology and results of the research conducted. Lastly, we provide appropriate conclusions directed at further optimizing the slabs. Full article

Functionally Graded Concrete (FGC) allows for a significant reduction in the mass of concrete components while maintaining their structural and functional requirements and improving recycling capacity. This is achieved by inserting spherical mineral hollow bodies into the structure where no material is required. Within the scope of this work, the behavior of FGC slabs exposed to fire is investigated both experimentally and numerically and compared to a corresponding solid cross-section. Therefore, FGC specimens are placed in a test furnace and subjected to fire exposure for 90 min. The temperature distribution, bending load-bearing capacity, and spalling behavior are investigated. The results of the numerical simulation of the solid cross-section are in good agreement with the values provided in the building code. However, for the FGC cross-section, differences in temperature at characteristic measurement points between the experimental and numerical results are observed, presumably due to convection. The experimental results suggest that the bending load-bearing capacity of the investigated FGC cross-section could be potentially greater than that of a corresponding solid cross-section. Furthermore, as expected through analytical analysis, the fire tests confirm that no spalling of the FGC specimens occurred. Full article

Mortar that is typically employed for interior or exterior coatings can be characterised using laboratory-prepared specimens according to specific test standards; however, its performance undergoes changes following application on substrates. When selecting mortar, it is vital to anticipate its in-service behaviour after its application on substrates to make the most informed choice. Most of the research work carried out to date analyses the characteristics of mortar in laboratory specimens. Some studies analyse these characteristics after its application to support, but very few exist that compare both behaviours. With this objective in mind, this research determined the properties of mortar when cured within laboratory moulds and assessed the behaviour of the same mortar after application on diverse substrate types. This study specifically evaluated the behaviour of a pre-dosed hydraulic lime mortar when applied on concrete blocks, lightweight concrete blocks, concrete slabs, hollow ceramic bricks, and solid ceramic bricks. Later, this behaviour was compared to the same type of mortar hardened in laboratory moulds and the same type of mortar applied on substrates and subjected to accelerated ageing. Moreover, data from previous experimental work were used to compare the behaviour of the pre-dosed hydraulic lime mortar with that of pre-dosed cement mortar when applied on similar substrates. The research drew upon a comprehensive characterisation of the physical and mechanical parameters of mortar, revealing that the performance of these types of mortar undergoes significant changes after application on substrates under in-service conditions, mainly when applied on more porous substrates. It was concluded that the application of mortar to substrates increased bulk density, decreased open porosity, enhanced compressive strength, and resulted in faster capillary absorption. For mortars subjected to accelerated ageing, a notable reduction in water vapour permeability was observed, which was attributed to changes in the pore profile. Full article

In this study, four-point load tests were conducted to evaluate the shear performance of factory-produced precast prestressed concrete hollow core slabs (HCS) assembled on-site. The test specimens were fabricated using compression molding and comprised six samples, with variables being the presence or absence of topping concrete and the shear reinforcement. According to the experimental variables, experiments were conducted using simple support beams to evaluate the shear performance and ultimate strength of HCSs. The results showed that HCSs, regardless of whether they included topping concrete or not, exhibited average values of shear strength more than 10% higher than the factored shear strength specified by concrete structure standards, confirming that these materials satisfy existing design standards. According to current standards, the overall reinforcement length should be increased to meet the minimum shear rebar placement requirements. However, the nominal shear strength of PS concrete hollow slabs exceeded the hollow design, with the ratio of experimental results ranging from 1.26 to 1.87 on average, satisfying the required performance. Full article