Composite Slabs Research Articles

Flexural Response of GFRP–UHPC Composite Slabs under a Hogging Moment

Flexural Response of GFRP–UHPC Composite Slabs under a Hogging Moment

Tensile membrane action of RC slabs and steel-concrete composite slabs at elevated temperatures

Slabs can take full advantage of tensile membrane action (TMA) in fire conditions to improve the ultimate bearing capacity. This paper proposed a novel analytical method to determine the ultimate bearing capacity of both reinforced concrete slabs and composite slabs at elevated temperatures, considering the influence of TMA. In this analytical model, a well-defined equation for the elliptical boundary of the TMA region is reasonably determined, and the enhancement of TMA is derived from a series of force and moment equilibria. The analytical method shows a good agreement with the test results. The analytical analysis reveals that while increasing temperature has little effect on the geometry of the membrane action region, it significantly influences the enhancement of ultimate load due to the temperature-induced stress redistribution in the slab. In addition, the membrane action predicted by the analytical method aligns well with that predicted by the numerical method. The development of TMA progresses from the boundary of ellipse to centre, according to the stress distribution predicted by numerical analysis. Finally, with the aid of test results and numerical results, span/10 and span/8 are suggested as the failure criteria for reinforced concrete slabs and steel-concrete composite slabs in fire conditions, respectively.

Flexural behavior of open-web composite slab with I-shaped steel bottom chord and vertical flat webs

Traditional composite floor truss systems with top and bottom chords and web trusses have encountered difficulties in system erection, installation, and the passage of utilities. In order to address these challenges, this study introduces a novel open-web composite floor system that only consists of a bottom chord and vertically placed flat web elements. These vertical web members are essentially short I-shaped steel elements and are connected to the I-shaped steel beam bottom chord and concrete slab through steel top plates and shear connectors, forming an innovative composite floor system. This paper presents the results of static loading tests conducted on two specimens with distinct web members, evaluating deformation, cracking characteristics, ultimate bearing capacity, failure mode, and stress and strain distributions. The findings indicate that the new composite floor system offers good flexural performance. Furthermore, finite element models of the composite floor system have been developed to analyze the influence of the web element’s geometry on the composite slab’s ultimate bearing capacity. This study also develops a theoretical calculation method for determining the internal force, elastic deflection, and ultimate bearing capacity of the composite floor system. The theoretical calculation results regarding the failure mode and ultimate load capacity align closely with the experimental values, and the deformation calculation formula can be used to estimate the deformation curve shape and elastic deflection of the floor system.

Flexural behavior of composite ribbed slabs employing cold-formed steel lipped channels

By means of a series of full-scale laboratory tests, this research studied the flexural behavior of a composite ribbed slab employing cold-formed steel profiles as formwork before and after concrete casting. An experimental program was devised and separated in two sets of tests. The first set consisted of the execution of four-point bending tests on eight specimens to represent the system during construction, featuring three specimen types; isolated profile, profile with plastic spacers along the channel and a full assembly including the profile, the plastic spacers and a rebar truss. Displacement and strain as a function of load were measured and the data was used to analyze the influence of the different components on the flexural strength and stiffness of the system. On the second set of tests, three ribbed composite slab specimens featuring steel profiles were subjected to four-point bending. Displacement was registered along with strain on the concrete layer. A formulation to determine the flexural strength of the slabs based on Eurocode is presented and compared to experimental observations. The first phase indicates significant increases of flexural strength and stiffness by coupling a truss to the profile and varying the height of the former, namely a maximum increase of 708% in stiffness and 357% in strength. Isolated profiles and profiles with plastic spacers all failed by distortional buckling, while the full assembly specimens failed by instability of the top chord on the trusses. Second phase results show that the analytical prediction is adequate to determine the flexural strength of the prototype slabs, with approximately 95% accuracy for this sample size. All slab specimens failed by plastic hinge formation within the pure moment span. Furthermore, strain measurements on the concrete indicate that the formulae chosen to determine the effective width of the concrete “tee” section is also adequate.

Geometry optimization of steel formwork for steel–concrete composite slabs

The use of steel formwork incorporated into composite steel–concrete slabs stands out for contributing to sustainable development in civil construction. However, this construction system still has limited usage in Brazil, which may be due to the restricted availability of formwork geometries in the national market. As such, this study aims to determine the optimal steel geometry that results in the lowest steel consumption during manufacture of the composite slabs, taking into consideration the initial construction phase, in which the formwork is under the highest load demand. The Direct Strength Method (DSM) and the traditional Effective Width Method (EWM) are applied for designing the steel formwork during the construction phase, where the cold-formed steel profile resists the applied forces independently. For DSM, the critical buckling moments are determined using the elastic stability analysis program CUFSM, via Finite Strip Methods. The solution of the optimization problem was implemented in MATLAB® using Particle Swarm Optimization and considering two design variables: the thickness and the bend angle of the formwork web. In addition, the reliability of the proposed formulation was evaluated in the implementation phase of DSM and EWM. Numerical analyses are carried out on four different steel geometries currently available in the Brazilian market. The main results showed that the developed computational program was successful in finding optimal solutions for said geometries, as the optimization reduced steel consumption by an average of 21.6%. Thickness had a greater effect on the steel savings, and this variable decreases in the optimal solution, while the height and bend angle increase.

Stiffness Warming Potential: An Innovative Parameter for Structural and Environmental Assessment of Timber–Concrete Composite Members

Timber hybridization with concrete is a rising widespread strategy to obtain members with a structural performance comparable to traditional ones—e.g., RC members—but characterized by a greater sustainability potential thanks to the presence of timber-based materials; this solution is of great interest due to its low embodied carbon content, which supports the decarbonization goals set, especially for the building sector. Such systems enhance the concrete and timber favorable properties and ameliorate their detrimental characteristics, both from the structural and environmental perspectives. In general, since these two aspects are generally considered separately, a new parameter is proposed to simultaneously combine a structural performance indicator with a warming potential one. Focusing on composite slabs in bending, the stiffness warming potential (λ) is introduced, which combines the evaluation of effective bending stiffness (according to Eurocode 5 γ-method) with the Global Warming Potential—GWP (on the basis of data from Athena Impact Estimator for Building software and data from an Environmental Product Declaration of a timber panel). The method provides a multi-criteria analysis concerning the slab design accounting for vibration, deflection, and acoustic criteria when optimizing the member span. On the other hand, GWP is assessed according to cradle-to-cradle Life Cycle Assessment analysis, where two scenarios with different sustainability levels are encompassed. Results firstly confirm the viability of the novel methodology, with a different outlook on timber–concrete hybrid members, stressing the importance of maintaining thinness of the concrete layer and clearly bringing out the importance of correct re-use and/or a timber recycling management to guarantee effective reductions in terms of CO2 emissions.

Carbon emission calculation of prefabricated concrete composite slabs during the production and construction stages

Prefabricated buildings provide favorable technical support to achieve the "carbon peak and carbon neutral" target in the building field. The accurate and reliable quantification of building carbon emissions is an important basis to achieve the dual carbon target. However, research on the carbon emissions of prefabricated buildings is limited, and few studies have been conducted on the calculation of carbon emissions from prefabricated components. Based on the process inventory analysis method, the carbon emission calculation model for prefabricated components in the production and construction stages was established. The prefabricated concrete composite slabs and cast-in-place floor slabs of two typical residential buildings were selected for the case study, and a comparative study was conducted on their carbon emissions during the production and construction stages. The results indicated that the carbon emissions per unit area (net floor area) of prefabricated concrete composite slabs (43.31 kgCO2e/m2 and 43.01 kgCO2e/m2, respectively) were lower than those of cast-in-place floor slabs (46.32 kgCO2e/m2 and 46.09 kgCO2e/m2, respectively) in the production and construction stages. The carbon emissions in the production and construction stages of prefabricated concrete composite slabs accounted for about 97.45 % and 2.55 %, while those of cast-in-place slabs accounted for about 91.21 % and 8.79 %, respectively. The carbon emissions at the building material production stage mainly originated from rebar and cement. When the change rate of building materials consumption and materials carbon emission factors was the same, the change rate of carbon emissions per unit area was ranked as rebar > cement. Furthermore, the cases showed that the prefabrication rate of case B was higher than that of case A, but the carbon emissions per unit area of case B were lower than those of case A. This study provides a scientific calculation method for the carbon emissions of prefabricated components, as well as enriches the data for studying building carbon emissions.

Pseudo-Static Tests on Top Joints of Hybrid Precast Utility Tunnel

This paper introduces a new type of hybrid precast MUT, consisting of precast composite top slab and double-skin sidewalls with reserved rebar. The seismic behavior of the top joints was examined through pseudo-static tests. Four full-scale specimens, including both exterior and interior precast joints, in addition to two corresponding cast-in-place (CIP) joints, were fabricated and subjected to reversed cyclic loading. The results showed that both the precast and CIP joints exhibited flexure failure, characterized by the formation of a plastic hinge at the end of the sidewall. The hysteresis curves of both precast and CIP joints exhibited comparable shapes and quantities of hysteresis loops. The load-carrying capacities for exterior precast joints and corresponding CIP joints were 141.25 kN and 143.5 kN, exhibiting a difference of less than 1.6%. The load-carrying capacities for interior precast and corresponding CIP joints were 60.5 kN and 62.75 kN, displaying a variance of less than 3.6%. The precast specimens demonstrated comparable levels of ductility, energy dissipation, and structural integrity as the CIP specimens. These findings provide validation for designing and analyzing the hybrid precast utility tunnel using identical principles and models as applied CIP structures.

The permeability, mechanical and snow melting performance of graphene composite conductive-pervious concrete

Snow on the roads poses a serious threat to the safety of vehicles, and the traffic system will be paralyzed under harsh conditions. In this study, composite conductive concrete with straight pervious channels were prepared by using carbon fiber, steel fiber and reduced graphene oxide (RGO) as conductive materials to remove snow from roads as soon as possible. The effects of RGO on the workability, mechanical properties and electrical conductivity of composite conductive concrete were studied, and the influence of pervious channels on snow melting efficiency and energy consumption of composite conductive concrete snow melting slabs were analyzed. Results showed that the permeability coefficient of composite conductive concrete with pervious channels reached 6.28 mm/s, meeting the requirements of pavement pervious concrete. For the RGO content of 0.09 % cement mass, the mechanical properties and conductivity of the composite conductive concrete were improved because of the filling effect of nano-RGO on the matrix, while it exerted adverse effects when RGO contents were over 0.09 %. The pervious channels weakened the mechanical and conductive properties of composite conductive concrete. However, compared with the composite conductive concrete without straight pervious channels, the snow melting time and energy consumption were reduced by more than 10 % and 15 %, respectively.

Optimizing ultra-high performance cementitious functionally graded composite slab towards bullet impact resistance

This study develops functionally graded composite slab (FGCS) by a one-time grouting approach based on the design concepts of ultra-high performance fibre reinforced concrete (UHPFRC) and two-stage concrete (TSC). The anti-penetration performance of the FGCS targets is investigated against 7.62 mm in-service bullets with shooting velocity of 843 m/s. The results show that while the TSC target presents superior bullet penetration resistance, it concurrently poses a significant threat of widespread cracking damage. Upon weighing the factors of bullet penetration and risk of cracking, the FGCS emerges as a more viable candidate for protective structures. The FGCS target is cast through a one-time grouting method, and there is no interface delamination under the projectile impact. The optimized FGCS exhibits enhanced in-service bullet impact resistance and a reduced safety thickness of 80 mm compared to the normal UHPFRC.

A new method of interlayer shear performance evaluation for permeable composite pavement (PCP) in laboratory

Permeable composite pavement (PCP) has been increasingly applied for road design and construction. However, interlayer shear resistance is still a challenge for the road performance improvement of PCP. This paper presents a new method of interlayer shear performance evaluation for PCP with a self-made molding device and shear clamp. PCP test slabs are made in two ways, the porous asphalt mixture + impermeable and + permeable concrete layer, named PAIC and PAPC, respectively. The interlayer shear test of PCP slab specimens is conducted under different bonding material types, dosage, temperature, and interlayer contact interface morphology. The results indicate that: (1) The type and amount of bonding materials influence the interlayer shear performance of PCP slabs. The stronger the bonding property of the interlayer material, the greater the interlayer shear strength (ISS) of the PCP. There is the best amount of the same material as the interlayer bonding material. The optimum dosage of styrene-butadiene-styrene (SBS), matrix, and spraying cationic emulsified (PCR short in Chinese) asphalt on the PAIC board is 0.8, 0.6, and 0.4 L/m2, respectively. However, the optimal amount for each bonding of the PAPC slab is 0.6 L/m2. (2) The temperature has a great influence on the ISS of the permeable composite slab due to asphalt being a temperature-sensitive material. For the two slabs, the ISS decreases with the increase in temperature, and even the ISS at 5 °C is 10 times that at 50 °C. (3) The interface morphology of interlayer contact affects the performance of ISS. For PAPC, the contact interface between the two materials is rougher, and the high friction between layers leads to the larger ISS. PAPC's ISS is at least twice that of PAIC. (4) A new method of interlayer shear performance evaluation for the optimization design and application of PCP has been proposed in the final. The method includes material design, specimen making, testing, and quick evaluation. This method has the potential to contribute to the development of PCP tests in the laboratory.

Design, implementation and performance prediction of profiled steel sheet-mixed aggregate recycled concrete hollow composite slab

Profiled steel sheet-mixed aggregate recycled concrete composite slabs are widely studied and applied in engineering applications by virtue of their good durability and recyclability. As an alternative to concrete composite slabs, concrete hollow composite slabs that can reduce their self-weight are also attracting people’s attention. However, the internal holes will increase the risk of collapse and shear failure of the concrete composite slabs. In order to reduce the risk and ensure the flexural performance of the concrete hollow composite slabs, this paper designs the recycled concrete hollow composite slabs with PVC pipes. A full-scale experiment is carried out on five open-mouth profiled steel sheet-mixed aggregate recycled concrete hollow composite slab specimens, to explore the influence of whether the bottom of the plate is reinforced, the thickness of the concrete surface layer and the hollow size on the working performance of the composite slabs. In order to predict the mechanical performance of the proposed hollow composite slabs, a prediction model based on artificial neural network (ANN) consisting of several sub-ANN modules is established. Moreover, according to the priority of the factors affecting the mechanical performance of composite slabs, a decision tree is designed to select appropriate testing sub-ANN module and thus improve the testing accuracy. Predicted results and experimental results are given to validate the feasibility and effectiveness of the developed ANN-based prediction framework for the mechanical performance prediction of composite slabs.

Retracted: Impact Sound Insulation Performance Testing of Nano-Inorganic Composite Floor Slabs for Green Buildings.

[This retracts the article DOI: 10.1155/2022/5642361.].

Flexural Behavior of Ferrocement Composite Slab

Abstract: This project presents a Flexural behaviour of composite ferrocement slabs to investigate the effect of impact and ultimate flexural load on ferrocement slabs of size 600mmx400mmx15mm (thickness) reinforced with PVC coated steel weld mesh, and compare the results with slabs made of GI-coated steel weld mesh. PVC-coated weld mesh is used as non-corrosive reinforcement in ferrocement slab. The ferrocement slab was cast using Ordinary Portland Cement, locally available river sand and portable water with cement mortar ratio of 1:3 and water cement ratio of 0.5. The aim of this study is to observe the influence of PVC coated weld mesh ferrocement slab using ferrocement in enhancement of the mechanical properties of slabs subjected to impact and flexural load. The flexural load, maximum deflection, crack- pattern and crack-width of ferrocement slabs reinforced with PVC and GI coated weld mesh were analysed. Finally, the analytical results were compared with experimental results to predict the effectiveness of ferrocement techniques in structural applications.

Higher-order trigonometric series-based analytical solution to free transverse vibration of suspended laminated composite slabs

Suspended floors can be designed as effective pendulum seismic isolators for high-rise buildings. However, research studies on the free vibration of suspended laminated composite slabs are relatively limited. This paper presents a comprehensive analytical solution to the free vibration problem of suspended laminated composite slabs. The equations of elasticity are used to establish the equation of motion. The critical factors influencing free vibration are explicitly considered, including the material anisotropy, number of layers, elastic properties, rotatory inertia, and transverse shear of plates. The higher-order trigonometric series are utilized to solve the dynamic equations. The developed analytical solution is a complete and realistic form of the existing analytical solutions in literature and has the capability of converging fast. The proposed analytical solution does not have a dependency on the shape function as well as separate-of-variable forms unlike the Finite Element Method (FEM). Moreover, the FEM requires an in-depth mesh convergence analysis, particularly for higher-magnitude natural frequencies, which is not the case for the proposed analytical solution for any infinite range of eigenfrequencies. The proposed solution procedure is first verified by the simplified problems available in the literature. For more complex problems, the finite element analysis results obtained from Abaqus are employed to validate the analytical solution. The comparison demonstrates that the proposed analytical solution is accurate and reliable for a wide range of case-study examples. It is found that the natural frequencies of suspended laminated composite slabs are significantly influenced by the crucial factors under investigation.

An integrated section model to enable simulating composite slabs in fire simply as modelling a flat slab

Modelling slabs is vitally necessary when simulating building structures in fire. The composite action between slabs and beams and tensile membrane action after fire induced deflections significantly reshape the load redistribution mechanisms and failure patterns. Modelling slabs particularly composite slabs of ribbed sections as a common choice of modern steel structures is a challenging task. Currently, those existing modelling approaches, such as beam & shell model and strip models, require elements for ribbed and flat parts separately, which produces much complexity and ideally it can be solved using a suitable section model to appropriately represent the behaviour. This paper begins with formulating the theoretical base of state determination in the integrated composite section, which enables correct deformation distribution to ribbed and flat subsections. While being compatible to typical modelling infrastructure for slabs, the integrated section model has demonstrated excellent capability in comparison to the strip models and fire tests. Even using a coarse mesh scheme (e.g. 8 × 6 elements), the prediction error of mid-span deflection remains low (around 10%). The appealing benefit is further shown in modelling Cardington Corner fire test, which significantly reduces the efforts of determining geometric details, the number of nodes & elements, and the computation time cost.

Synergistic sono-adsorption and adsorption-enhanced sonochemical degradation of dyes in water by additive manufactured PVDF-based materials

The present study proposes the first mechanistic model accounting for the most meaningful physico-chemical phenomena taking place in liquid phase adsorption processes under ultrasound. Initially, this study was aimed at developing an easy-to-make and easy-to-recover piezocatalyst for the degradation of RhB in water by combining the high piezocatalytical performance of BaTiO3 with a compatible piezoelectric support such as PVDF, manufactured by a customised additive manufacturing – direct ink writing system with in-situ poling. However, initial results showed that the resulting PVDF-BaTiO3 composite slabs performed worse than BaTiO3 piezocatalysts on their own, and that poling did not have any effect on their performance (82% RhB removal after 2 h when using either poled or unpoled PVDF-BaTiO3 composite slabs compared to 92% RhB removal after 2 h in presence of BaTiO3 piezocatalysts). Further investigation with pure PVDF materials demonstrated that, instead of piezocatalysis, synergistic ultrasound-assisted adsorption and sonochemical degradation were taking place, enabling the removal of >95% of the dye within 40 min of ultrasound treatment in the presence of 4 g L–1 of additive manufactured PVDF slabs. The results of this study and their evaluation with the mechanistic model proposed for liquid phase adsorption under ultrasound suggest that the adsorption of RhB on additive manufactured PVDF slabs was enhanced by the structure, higher specific surface ratio and higher volume of mesopores achieved through the 3D-printing process, as well as the minimisation of film resistance to mass transport due to ultrasound. Moreover, adsorption on additive manufactured PVDF enhanced the sonochemical degradation of the dye due to its high concentration in the adsorbed phase. This study demonstrates that adsorption processes, especially in the presence of PVDF materials, may be significantly more important in piezocatalysis than what has been reported to date, to the point that the synergistic combination of sono-adsorption and sonochemical degradation in presence of additive-manufactured PVDF slabs may be enough to achieve high removal rates of dyes in water.

Materials, Structure, and construction of a low-shrinkage UHPC overlay on concrete bridge deck

As ultra-high performance concrete (UHPC) has superior mechanical and durability properties, it is a promising solution to apply a thin layer of UHPC on top of normal concrete bridge decks to extend the service life and enhance the structure integrity. However, the large autogenous shrinkage characteristics of UHPC is still an issue, and there is a lack of research focus on the structural design and stress analysis of the concrete bridge deck and UHPC overlay system. Thus, this study first designs and evaluates a new low-shrinkage UHPC mixture internally cured with a high-strength, high-abrasion resistant, and porous aggregate (calcined bauxite, CB), and the optical mixture design is validated by testing the fresh, mechanical, autogenous shrinkage, abrasion, and impact properties of the UHPCs. Second, the outdoor UHPC overlay-NC composite slab experiments and the numerical modeling are carried out to analyze the shrinkage performance of the UHPC, debonding potential of the overlay layer, stress and strains development in the system. Then, the significant influencing factors and the key measures to assure the UHPC-NC interface bonding properties are obtained, including proposing a grouped L-shape steel rebar arrangement for strengthening the interface. Finally, the applicability of the new low-shrinkage UHPC mixture as overlay materials on a real concrete bridge deck is demonstrated. Based on these, the engineering design scheme and the construction recommendations of an environmentally-cured low-shrinkage UHPC overlay on concrete bridge deck is given. The utilization of UHPC overlay on concrete bridge decks offers a novel paving system that substantially enhances strength, abrasion resistance, and durability.

Damage modes and mechanism of steel-concrete composite bridge slabs under contact explosion

The steel-concrete (SC) composite bridge slab is widely used in long-span bridges. With the increasing threat of explosive attacks on bridges, understanding the blast-resistant performance of composite bridge slabs is important. In this paper, SC composite slabs with different types of interfaces between concrete slab and steel plate, and different steel plate thickness, were tested under contact explosion. The damage modes and dynamic responses were carefully observed and measured. Refined FE models were developed to investigate the damage mechanism by analyzing and comparing the detailed damage process of slabs and characteristics of stress wave propagation. The results revealed that the damage modes of SC composite slabs varied significantly depending on the type of interface. For slabs with stud connectors, the compressive stress wave propagated within the composite slab in a spherical pattern and finally induced a circular concrete crater and steel plate deformation. Increasing the thickness of steel plate significantly reduced steel plate deformation. For slab with PBL connectors, the stress wave in the concrete was attenuated when it propagated across the PBL ribs, while the stress of concrete between the ribs nearest to the explosion was much large than that outside the ribs. Stress reflection on the top of PBL ribs increased the damage degree of concrete, potentially leading to induced cracks along the ribs. The overall response of composite slabs could be divided into the combined phase and separated phase. The PBL ribs could better restrain the interface detachment compared to studs.

Resilient performance of steel connections with low yield point fuses considering the effect of RC floor slab

The beam-column connection of a steel frame equipped with replaceable low yield point steel cover plates (SF-LYCP) was proposed to address the significant repair challenge and financial losses caused by beam-column connection brittle failure after an earthquake. According to an experimental study, the SF-LYCP exhibited outstanding bearing capacity, ductility, energy dissipation, and post-earthquake rapid recovery performance. To explore the effect of the reinforced concrete (RC) floor slab on the mechanical behavior of SF-LYCP in a natural working environment, the finite element method of steel beam-column connection with low yield point (LYP) steel cover plates considering the effect of the RC floor slab (SF-LYCP-RCslab) was developed and analyzed by ABAQUS. The results demonstrated that the proposed finite method was able to accurately predict the behavior of SF-LYCP-RCslab. The load capacity, initial stiffness, and energy dissipation capacity of the SF-LYCP-RCslab were increased in comparison to the SF-LYCP. The LYP cover plates in the SF-LYCP-RCslab still played the desirable role of structural fuses. However, the concrete of the RC floor slab had severe damage and prevented the quick replacement of repairable LYP cover plates. Based on these findings, four improved strategies for the SF-LYCP-RCslab were proposed to reduce concrete damage and increase the replacement convenience of damaged elements. Comprehensively considering the bearing capacity, ductility, energy dissipation, structural fuse function, concrete damage, and post-earthquake rapid recovery performance, the improved strategy, which adopted a profiled steel–concrete composite floor slab with a gap, was recommended in steel frame beam-column connection design.