Search Results (36)

Acoustic emission (AE) technology has been extensively applied in the damage assessment of steel strands; however, it remains inadequate in identifying and quantifying the number of strand fractures, which limits the accuracy and reliability of prestressed structure monitoring. In this study, a test platform based on practical engineering was built. The AE monitoring method using a waveguide rod was applied to identify signals from different numbers of strand fractures, and their acoustic characteristics were analyzed using Fourier transform and multi-bandwidth wavelet transform. The propagation attenuation behavior of the AE signals in the waveguide rod was then analyzed, and the optimal parameters for field monitoring as well as the maximum number of plates suitable for series beam plates were determined. The results show that AE signals decrease exponentially with an increasing propagation distance, and attenuation models for various AE parameters were established. As the number of strand fractures increases, the amplitude of the dominant frequency increases significantly, and the energy distribution shifts towards higher-frequency bands. This finding introduces a novel approach for quantifying fractures in steel strands, enhancing the effectiveness of AE technology in monitoring and laying a foundation for the development of related technologies. 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

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

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

To investigate the shear performance of 16 m span prestressed hollow core slabs, shear tests were conducted on three pre-tensioned prestressed hollow core slabs with the same shear-to-span ratio. A systematic analysis was performed on the failure modes, crack development patterns, load–deflection relationships, and load–strain relationships of the prestressed hollow slabs. The test results indicate that all specimens experienced shear-compression failure under the same shear-to-span ratio (2.71). The main diagonal shear cracks were distributed within a range of 1.35 m to 1.95 m from the beam ends, with crack angles approximately between 45° and 55°. Finite element software ABAQUS was used for detailed numerical simulation of the tests. By comparing the failure modes and load–displacement curves, the reliability and applicability of the finite element model were verified. 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

This work presents a study of a ventilated hollow core slab system (VHCS) that obviates the need to completely replace the slab of an existing residential building. It is assimilated to a heat exchanger to allow its effectiveness to be studied as a function of the area and airflow rate. The balance between the energy consumed by the fan and the heat evacuated by the system is also studied through the use of the thermo-hydraulic performance factor (THPF), for which a series of cases were simulated by CFD following a methodology in which a configuration is achieved by means of the sequential analysis of cases in which both the thermal effectiveness and the THPF are maximized. The configuration chosen in this study was found to benefit from high airflow rates since, although this implies an increase in fan energy consumption, the increase in heat removed is proportionally greater. It has also been found that the design of the airflow distribution through the slab is of high importance as it affects both the heat exchanged with the slab and the pressure losses. An applicability map has been developed as a function of the temperature of the space below and the air temperature at the inlet of the ventilated roof. The heat flux per unit area that the studied envelope is able to evacuate is about 20 W/m² K. 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

Void slabs offer a promising solution for sustainable construction due to their reduced weight and potential for recycled materials. However, their inherent hollowness can compromise shear capacity compared to solid slabs. This study investigates the effectiveness of shear reinforcement in mitigating this vulnerability. Experimental testing with a four-point support loading confirmed shear failure in all specimens and revealed a significant reserve of shear strength exceeding predictions from ACI 318-14 by at least 1.436. This suggests the potential for more efficient designs that utilize less shear reinforcement while maintaining structural integrity. An inverse relationship between porosity and shear strength was observed, highlighting the importance of considering void content during design. Among established design codes (ACI 318-14, UBC 2, and CEB-FIP 1990), CEB-FIP 1990 provided the most accurate prediction of shear capacity for these reinforced hollow slabs. These findings offer valuable insights for optimizing the shear design of voided slabs. The observed strength reserve suggests the potential for reduced shear reinforcement while maintaining safety. Additionally, the influence of porosity and the code comparison provide crucial considerations for future design practices. This research paves the way for developing efficient and safe voided slab applications, promoting sustainability in the construction industry. Full article

Hollow structures reduce weight without compromising load-bearing capacity and are widely used. The new Glass-Fiber-Reinforced Polymer high-strength thin-walled inner mold simplifies internal cavity construction and boosts structural performance. This study first investigates the influence of a GFRP high-strength thin-walled circular tube on the cross-sectional load-carrying capacity of hollow slabs. Then, a formula for the bending load-carrying capacity of the section under the action of the tube is derived. The results indicate that when the height of the concrete compression zone meets certain conditions, GFRP high-strength thin-walled circular tubes can improve the ultimate load-carrying capacity of the hollow floor slabs. In order to achieve a more economical design, the bending moment modification of a GFRP high-strength thin-walled circular tube of a continuous slab was studied. Research has found that the bending moment modulation limit for a continuous slab is 35.65% when it is subjected to a load of $P_u=24 \mathrm{k}\mathrm{N}$. Experimental analysis has shown that the results are generally consistent with the calculations. In practical engineering, the application of a GFRP high-strength thin-walled circular tube of continuous slabs has limitations. Therefore, this study investigated a GFRP high-strength thin-walled honeycomb core slab and found that its ultimate load-bearing capacity is greater compared to waffle slabs. In addition, the stress performance of the GFRP high-strength thin-walled honeycomb core internal mold is superior, making it more promising for practical applications. Full article

The main goal of this work is to combine the usage of the numerical homogenization technique for determining the effective properties of representative volume elements with artificial neural networks. The effective properties are defined according to the classical laminate theory. The purpose is to create and train a rapid surrogate model for the quick calculation of the mechanical properties of hollow concrete slabs. First, the homogenization algorithm was implemented, which determines membrane, bending and transverse shearing properties of a given parametrized hollow-core precast slab reinforced with steel bars. The algorithm uses the finite element mesh but does not require a formal solution of the finite element method problem. Second, the learning and training artificial intelligence framework was created and fed with a dataset obtained by optimal Latin hypercube sampling. In the study, a multilayer perceptron type of artificial neural network was used. This allows for obtaining rapid calculations of the effective properties of a particular hollow-core precast slab by using a surrogate model. In the paper, it has been proven that such a model, obtained via complex numerical calculations, gives a very accurate estimation of the properties and can be used in many practical tasks, such as optimization problems or computer-aided design decisions. Above all, the efficient setup of the artificial neural network has been sought and presented. Full article

The paper concerns the numerical modelling of a new slim-floor system with innovative steel–concrete composite beams called “hybrid beams”. Hybrid beams consist of a high-strength TT inverted cross-section steel profile and a concrete core made of high-performance concrete and are jointed with prestressed hollow core slabs by infill concrete and tie reinforcement. Such systems are gaining popularity since they allow the integration of the main structural members within the ceiling depth, shorten the execution time, and reduce the use of concrete and steel. A three-dimensional finite element model is proposed with all parts of the system taken into account and detailed geometry reproduction. Advanced constitutive models are adopted for steel and concrete. Special attention is paid to the proper characterisation of interfaces. The new approach to calibration of damaged elastic traction–separation constitutive model for cohesive elements is applied to concrete-to-concrete contact zones. The model is validated with outcomes of experimental field tests and analytical calculations. A satisfactory agreement between different assessment methods is obtained. The model can be used in the development phase of a new construction system, for instance, to plan further experimental campaigns or to calibrate simplified design formulas. Full article

A new type of assembled integral multi-ribbed composite floor system with novel wet joint and steel sleeve connections, which exhibits satisfactory strength and stiffness, was proposed in the previous study. To further study the flexural performances of the joints, six groups of specimens, including two cast in situ concrete slabs and four composite slabs sized 4700 mm × 1200 mm × 300 mm and 2450 mm × 1200 mm × 300 mm, were investigated under four-point flexural tests. Four main influence factors were experimentally studied, i.e., casting methods, joint amounts, shear span lengths, and steel sleeve layout directions, on the failure modes, crack distributions, and deflection–load carrying capacity relationship. Test results indicated that the proposed composite slab system could provide the ultimate bearing capacity lower by 7% than that of the cast in situ concrete slabs, largely exceeding the code-predicted strength. No strain difference between the steel sleeve connections and steel rebars indicated good wet joint connection behavior. More hollow-core sections and long shear spans increased the potential of interfacial splitting cracks, leading to a shorter elastic stage and lower elastic stiffness. A finite element model was further parametrically conducted to explore the structural performances. Finite element results also indicate that the precast concrete slab had a more significant influence on the failure loads than the influences of concrete compressive strength and lap-splice steel rebar strength. These findings indicate that the proposed composite slab systems possess a satisfactory performance in the ultimate bearing capacity and deformability. Thus, such an assembled integral multi-ribbed composite floor system can be widely applied in construction. Full article

This study aimed to evaluate the flexural behavior characteristics of prestressed concrete hollow-core slabs (HCSs) through bending experiments. Six specimens were used as variables, both with and without reinforced concrete, in the HCS. A four-point load was applied in the form of a simple support beam to assess the flexural behavior and ultimate strength of HCS. The results demonstrate that, compared to non-reinforced specimens, the reinforced HCS exhibited higher maximum loads and better ductility performance. The experimental outcomes demonstrate that HCS showed an average of 10% higher capacity than the maximum load of the concrete structure standards (KDS 14 20 20, ACI 318-19, and PCI handbook), with or without reinforced concrete, leading to relatively safe predictions. This study’s experimental findings are anticipated to aid in evaluating structural safety in a relatively secure way. The findings indicate that the HCS structural system is excellent at sustaining the weight of a structure and ensuring its safety. Additionally, this investigation is anticipated to furnish practical guidance for optimizing the use of HCS systems in structural design and construction. Full article