Precast Slabs Research Articles

Residual flexural behaviour comparison between composite and monolithic beams after fire exposure

Fourteen T-shaped composite beams and seven T-shaped monolithic beams were tested after fire exposure. To investigate their distinct residual flexural behaviour, the beams, which had different load ratios and thicknesses of precast slabs, were exposed to specific fire exposure times (60, 90, and 120 min) in a fire furnace and loaded to failure after natural cooling. The results showed that the residual flexural capacity of the composite beams was generally lower than that of monolithic beams. The fire exposure time was found to dominantly influence the residual flexural capacity of the composite beams. Increasing the thickness of the precast slabs can slightly enhance the residual strength of the composite beams. However, the horizontal cracks at the interface between the precast and cast-in-place concrete slabs of the composite beams reduced the horizontal shear strength and further increased the horizontal slip along this interface. Accordingly, a finite element model of the composite beams was proposed. A three-dimensional spring element was introduced into the model to consider the effect of slip at the concrete–concrete interface. To predict the residual flexural capacity of the composite beams, based on the 500°C-isotherm method, three modified equations suitable for the Chinese, American, and European codes were proposed. In comparing the test values, the modified equation applicable to the European code is recommended for subsequent predictions.

Study on recyclable precast-slab-fabricated road based on arching effect theory

Precast slab parameters are important factors affecting the mechanical performance and service life of precast-slab-fabricated recyclable roads. To clarify the force mechanism of recyclable precast-slab-fabricated roads and provide a basis for selecting slab parameters, a field test of a recyclable road fabricated using a large-scale precast slab was conducted in this study. The horizontal and vertical stresses on the top and bottom surfaces of the precast slab are determined. The stress-time history curves show that the horizontal and vertical stresses have peak values corresponding to the time at which the axle acts directly on the precast slab. Based on the arching effect theory, the mechanical mechanism of a precast-slab-fabricated recyclable road was analyzed. Owing to the arching effect between the precast slabs, they were cooperatively stressed. Compared with precast slab bearing vehicle load independently, When the arch effect works, both the maximum horizontal stress and the vertical stress decrease. According to the field test results, the influence laws of the material, size, thickness, and shape of the precast slab on precast slab stress were obtained. In order to achieve maximum service life and road performance of recyclable Precast-Slab-Fabricated road, the characteristic parameters of the precast slab are suggested as follows. The grade of concrete used for the precast slab should be more than C30, the size of precast slab can be 2 m, large thickness of precast slab should be used(e.g.0.2 m), and square precast slab with width-length ratio of 1 should be adopted as far as possible.

Study on the Mechanical Performance of H-Shaped Steel-Concrete Laminated Plate Composite Beams under Negative Bending Moment

To make the construction of assembled steel-reinforced truss concrete laminated plate composite structure faster, safer, and more efficient, this paper proposes an H-shaped steel-reinforced truss concrete laminated plate composite structure with new angle connectors embedded in the precast bottom panel. Through experimental studies on the H-shaped steel-concrete laminated plate composite beams with precast bottom panels protruding from the bent-up bars, precast bottom panels with embedded new angle connectors and laminated whole cast slab, the similarities and differences of load-deflection, deflection distribution, interface slip, crack distribution and cross-section strain distribution of three groups of composite beams under negative bending moment were analyzed and compared. Using ABAQUS finite element software, we established a finite element model and found the numerical simulation results were in good agreement with the experimental results. Based on this, five groups of finite element models were established for parametric analysis to investigate the effect of concrete strength on the flexural load capacity and flexural stiffness of the steel-laminated plate composite beams with embedded angle connectors. The results of the study show that the combined performance of the H-shaped steel-concrete laminated plate composite beams with the new angle connection embedded in the precast bottom panel was better and the flexural stiffness was greater. The slippage of the H-shaped steel-concrete laminated plate composite beams with embedded new angle connectors in the precast bottom panel was less than the slippage of the precast bottom slab bent-up bars protruding and the laminated cast plate, with the maximum slippage being only 1/2 of the precast bottom panel bent-up bars protruding. In the composite structure of H-shaped steel-concrete composite slabs under negative bending moment, shear angle connectors can replace the bent-up bars protruding from the laminated bottom panel to achieve without extending the reinforcement of the laminated bottom panel.

Emission of fugitive dust from railway maintenance vehicles operating on gravel track

The railway is using gravel to mitigate impact and noise. Since these gravel tracks are deformed due to wear and weathering, they must be replaced at regular intervals. A large amount of fugitive dust(FD) is generated during the gravel replacement work, but research on the amount of generation has not been conducted. The characteristics of FD generated from railway maintenance vehicles (RMVs) operating on gravel tracks were investigated. FD concentrations were measured during the operation of three types of RMV machines: the multiple tie tamper (MTT), ballast regulator (RE), and ballast cleaner (BC). The concentrations of FD generated from MTT, RE, and BC use were 10.69, 16.58, and 17.55 mg/m 3 , respectively. Annual FD fluxes were calculated based on FD concentrations and emission speeds as well as annual RMV operating times. The EPA AP-42 provides a formula for calculating the FD generated by cars, but this formula is not applicable to railroad vehicles. In previous FD studies, FD flux was calculated using nearby wind speeds, but in this study, we took the speed of the force each RMVs applied during maintenance work as the emission speed. The results of this study can be used as baseline data in future studies of the environmental aspects of gravel track and precast concrete slab track use.

Experiments on flexural behavior of the prefabricated RAC and NWC composite slab

The development of prefabricated buildings is a long-term industrial policy in China. In the prefabricated frame structure, the slab is one of the critical components. However, two kinds of famous prefabricated slabs in China need the template system and sometimes need a particular fabrication site. The paper proposed a novel prefabricated concrete composite slab, which adopts the high-strength bolt as the shear connector. Compared with the traditional precast concrete composite slab, the novel prefabricated concrete composite slab does not need a template and temporary support. Compared with the conventional composite slab, it has analogous rigidity. Still, it does not require a fireproof coating. It has fast construction speed and a low comprehensive cost. The paper conducted 13 slab specimen bending tests on the novel composite used recycled aggregate concrete (RAC) and normal weight concrete (NWC) to reveal the slab's flexural behavior. The test data and analysis show that the three-inch-high profiled steel sheeting as a shear connection can have an excellent composite effect. The neutral axis of the whole section always locates within profiled steel sheeting. And the profiled steel sheeting has been participating in the load-bearing work of the composite slab. The composite slabs showed good bending bearing capacity and ductility. The RAC with a replacement ratio of 50% recycled aggregate has the same material performance and member performance. The composite slab proposed can meet most civil buildings' design requirements. The standard push test revealed that the bolt shear connectors' ultimate bearing capacity meets the Chinese design code with the floor's considerable slippage.

Comparative Analysis of The Cost of Conventional and Precast Concrete Slabs on High-Rise Building Projects


 Construction processes, particularly floor slab systems, can be executed using precast/precast methods as technology advances. Compared to traditional methods, which need more time and production expenses, precast/precast methods are more cost-effective for floor slab formwork, neater, and have a more consistent finish. This study is based on an eight-floor building project with 92 residential units on a 3,500 m2 plot of land and a 1,700 m2 building size. This investigation used two technologies: conventional precast slab and full slab precast. The purpose of this research is to compare the most cost-effective strategy for reducing production costs on floor slab work for the construction of the case study. Based on the calculation results, the full slab precast method is 14.31% or around Rp. 980,508,000 is more economical than the conventional method. For the conventional method, the total cost is Rp. 3,914,657,000 while for the precast method, the result is Rp. 2,934,149,000.

COMPARISON OF COST AND TIME OF FLOOR SLAB WORKS ON CONVENTIONAL AND BUBBLE DECK SLAB METHODS

Floor slab is one of the most important structure members in a building and one of the largest members consuming concrete. Conventional floor slab has been used for years and has disadvantages that can be improved with alternate methods. There is lot of alternative methods that have been used in the construction world such as precast slab, half precast, hollow core slab, and many more. One of the alternative methods is bubble deck slab. The spherical hollow reinforced concrete slab has been patented named Bubble Deck Slab is a method that removes concrete from the center part of a slab which doesn't do any structure functional, so it can reduce the dead load significantly. High-density polyethylene hollow sphere is used to replace the ineffective part of the slab, so it reduces the dead load and increases efficiency. With the HDPE ball substitution, there will be differences in cost and time compared to the conventional method. This research is taking the case research in Central Control Building of Power Plant Muara Tawar Project with quantitative method approach. The analysis is calculating the budget plan and scheduling with Microsoft Project. After the analysis, there is differences in cost and time between the methods. The bubble deck slab method has the advantages which have the cheaper cost of IDR. 142,128,506.44 or 14,442% and 1 day or 3,846% faster compared to the conventional. Even so, the conventional method is still the first choice because the very common methods in Indonesia and the ease of execution.

Analysis of the Mechanical Properties of a Bidirectional Laminated Slab with Shear Keys

The load-bearing capacity of a bidirectional laminated slab with shear keys arranged in a rectangular grid (BCSWSK) was investigated to determine its mechanical properties, using load tests on a fabricated laminated slab and finite element models. The shear force distribution across the shear keys was measured and analysed, and the effects of different parameters were identified. The interfaces between the cast bottom slab and the shear keys were strongly bonded, as was the interface between the precast bottom slab and the cast-in-place upper slab, despite it being a secondary concrete pouring. The shear force was distributed similarly along the X direction (columns) and the Y direction (rows) of the shear key arrangement. The shear forces along the Y direction were greater and reached a maximum value sooner, but the differences between columns were mostly less than 10%. A square cross-section is recommended for the shear keys. The number of rows, number of columns, and the cross-sectional area of the shear keys are the main factors influencing the mechanical properties of the composite slab, but as they individually increased, they reached a point at which further increase had little effect. Similarly, after a certain number of shear keys were used, the concrete grade cast in situ, the shear key concrete grade, and the friction coefficient between the precast bottom slab and the cast-in-place upper slab had little influence on the BCSWSK.

Flexural Performance of Prestressed Composite Recycled Aggregate Slabs with Steel Tube Trusses

A new type of prestressed composite recycled aggregate floor slab was developed and its flexural performance was studied. The composite floor comprises a top cast-in-place slab made of recycled coarse aggregate concrete and a bottom precast concrete slab with grouted steel tube trusses. The cracking load, ultimate load, deflection, steel tube strain, concrete strain and failure process are studied for different contents of recycled coarse aggregates. Results show that the mechanical performance of the prestressed composite recycled aggregate slab has two distinctive stages. And the load bearing capacity decreases with the increase in the amount of recycled coarse aggregates. When the composite slab fails, the prestressed steel wires in the tension zone yield and concrete in the compression zone is crushed. This failure characteristic reflects that the reinforcement ratio of the component is appropriate. The cracking moment and ultimate moment calculation formulas of the composite slab are established and could predict the cracking and failure points. In the formulas, the influence of the amount of recycled coarse aggregates on the flexural capacity is considered. By controlling the content of recycled aggregates, the composite slabs with steel tube trusses can be sued in practical applications.

Modelling of demountable steel-concrete composite connections: Validation of finite element model and parametric study

A three-dimensional finite element modelling and parametric analysis of a composite connection having prefabricated concrete slabs and preload bolted shear connectors are presented in this study. The load-slip relationship for this type of shear connection subjected to monotonically loading with the effect of different parameters including bolted shear connector size, bolt grade, hole size in precast concrete slab and steel beam top flange, concrete strength, and bolt preloading force is studied by means of ABAQUS software. A finite element model of the composite connection considering the non-linearities of the geometry, interfaces between the components, and materials is developed and verified against the results of the experimental study. An extensive parametric study is conducted, and the influences of different parameters on the structural behaviour of demountable steel-concrete composite shear connection are discussed in detail. In addition, a comparison of the estimated values obtained from design equations proposed by current standards, including EC4 and AISC for headed stud shear connectors, and the design recommendations provided in other studies for bolted shear connectors are conducted. According to the calculation result, the accuracy of different design methods is evaluated. Finally, a regression analysis of the data produced by the FE analysis has been employed to propose a new design equation to determine the ultimate strengths for the post-installed preload bolt shear connectors. It is concluded that the ultimate shear load capacity values predicted by EC4 and AISC provisions for composite connections having prefabricated concrete slabs and preload bolted shear connectors found to be relatively less accurate but conservative.

Flexural behaviour analysis of wet joint of precast bridge deck with UHPC functional gradient

To optimize the wet joint structure of a precast bridge deck and make effective use of ultrahigh-performance concrete (UHPC), five specimens of the prefabricated UHPC functional gradient wet joint plate (UFGWJP) and one normal concrete prefabricated wet joint plate were tested by four-point bending, and their failure modes, bearing capacity, deformation performance, and strain distribution were analysed. The results show that the failure mode of all joint plates was bending failure, and the initial cracking position was basically at the interface between the joint and the precast slab. The excellent mechanical properties of UHPC enhance the bonding performance between the joint and the precast plate interface and significantly improve the cracking load. With an increase in the thickness ratio of UHPC and the flexural toughness ratio of UHPC/normal concrete (NC), the bearing capacity and deformation performance of the joint plate gradually increase. Furthermore, the wet joint of a prefabricated bridge deck with a functional gradient can be designed and fabricated, and the structural optimization of the prefabricated bridge deck wet joints is proven successful by tests.

Rebar corrosion and ASR durability assessment of fly ash concrete mixes using high contents of fine recycled aggregates

This research assessed the potential alkali silica reaction (ASR) of fine recycled aggregates (FRA) derived from precast concrete slabs using petrographic examination and expansion tests, the effects of incorporating FRA on some chloride related transport properties and the corrosion risk of fly ash blended concretes. Mixes incorporating 20 % fly ash (FA) were produced using water-to-binder ratios of 0.45 and 0.50 and FRA replacements of 0 %, 20 %, 60 % and 100 % to test concrete’s mechanical performance, chloride penetrability and rebar corrosion risk using electrochemical techniques at different ages. FRA presented an ASR expansion 227 % higher than natural aggregates. Using high contents (>60 %) of FRA didn’t increase corrosion risk and a comparable risk to conventional concrete was observed when incorporating FA.

Structural reliability of hollow core slabs considering compressive membrane action

Compressive membrane action can considerably improve the load bearing capacity of concrete slabs and beams in case of excessive loaded due to an accidental event. Currently, only limited research has been focusing on compressive membrane action in prestressed concrete elements, or on concrete elements with large cavities, such as precast concrete hollow core slabs. Therefore, a novel real-scale test setup has been developed in order to assess this effect in precast hollow core slabs, and how it can enhance the load-carrying capacity in accidental events. In parallel with these tests, a numerical finite element model has been developed in order to perform a more detailed structural analysis of this phenomenon, and to study the influence of various input parameters. The details of this test setup are briefly explained, and some relevant experimental test results are provided. Considering the experimental findings and validated numerical model, this contribution aims to quantify the influence of compressive membrane action on the structural reliability of precast concrete hollow core slabs. To this end, probabilistic models for the most important material and geometric variables are gathered, and the structural reliability is assessed using Latin Hypercube sampling. Overall, the results indicate that considering the formation of compressive membrane action strongly influences the variability of the ultimate load-carrying capacity of precast concrete hollow core slabs.

Experimental Investigation of Hybrid Beams Utilizing Ultra-High Performance Concrete (UHPC) as Tension Reinforcement.

Ultra-high performance concrete (UHPC) is a new generation concrete with extremely high tensile and compressive strength, high durability, and ductility. UHPC offers tremendous opportunities for use in new thin and slender structural concrete elements and repair of existing concrete structures and has an excellent potential to replace conventional steel reinforcement in normal concrete (NC) members. This paper investigated the potential application of a hybrid NC-UHPC beam using a thin UHPC layer on the tension face to cater to tensile stresses, eliminating the need for passive steel reinforcement. Four-point flexural load tests were performed on 24 composite beams with a thin UHPC layer overlaid with NC. The parameters considered include the thickness of the UHPC layer, depth, and span of the beam. A linear behavior categorizes the flexural behavior of the hybrid NC-UHPC beam up to the ultimate load, after which the hybrid beam shows a non-brittle failure, and softening ensues associated with cracking, increased deflection, and loss of load resisting capacity. The unfinished top surface of the UHPC layer and the overlying NC developed a full composite action without any slip. It was found that a two-day self-curing of the UHPC layer was found to be essential for the development of a strong bond between the layers. The random dispersion and orientation of steel fibers in the UHPC can lead to a decreased tensile response for larger hybrid NC-UHPC beams. The experimental results validate the potential of hybrid NC-UHPC beams as an attractive, structurally feasible, and alternative sound form of construction in terms of their high flexural strength and corrosion-free service life. The proposed unreinforced hybrid system could be used in the construction of precast beams and slabs for residential as well as industrial buildings. Further research, including full-scale load testing of the hybrid beam, is needed prior to practical applications.

Flexural Behavior of Precast RC Deck Panels with Cast-in-Place UHPFRC Connection

Precast concrete bridge structures have been extensively used because of the mature construction techniques, fast construction, and their economy. Considerable practical applications, however, present certain disadvantages, such as cracking and water infiltration in their normal strength concrete (NSC, compressive strength 40 MPa) joints connecting prefabricated deck panels. Ultra-high performance fiber reinforced concrete (UHPFRC, compressive strength 143 MPa) has been proven highly effective in replacing the conventional cementitious grout materials in precast bridge structures. In the present study, three types of UHPFRC connections, rectangular, zigzag-shaped, and diamond-shaped, were experimentally evaluated on their flexural capacities, interface bonding performances, and failure modes through four-point bending tests (loading rate 0.1 kN/s). The results showed that all the UHPFRC connections exhibited apparently higher flexural capacities than an intact precast NSC member and had such strong UHPFRC-NSC interfacial bonding that the interfacial first-crack strengths were not less than the NSC member. Having the capability of modeling the UHPFRC connections and their interface properties, the developed finite element (FE) models of the precast slabs with UHPFRC connections produce numerical results in good agreement with the flexural tests. By means of the FE models, parametric investigations were carried out to make suggestions on optimizing the UHPFRC connection designs for practical use.

Flexural behavior of precast concrete hollow-core slabs with high-strength tendons

Precast concrete hollow core (PHC) slabs have been widely used in brick and concrete structures of rural buildings due to their economic and rapid construction in China. A new PHC slab with high-strength tendons and spliced slab made of the short slabs were proposed in this paper. To investigate the flexural behavior of the slabs, full-scale tests were conducted on three PHC slabs, including one long slab and two spliced slabs with side beams. In detail, the spliced slab was assembled by two short slabs through U-type bars, anchorage bars, and post-pouring concrete. The mechanical properties of specimens were evaluated including the failure modes, strain of concrete and bars, flexural capacity and deflection. The tests results shows that the flexural performance of the spliced slab is close to that of the long slab. Subsequently, finite element models were established and validated by the test data. Based on the validated models, an additional specimen made up of long slab and side beams, was studied to further verify the reliability of the spliced slab. And parametric analysis were carried out on the spliced slab to investigate the influence of prestress of tendons, diameter of tendons, concrete strength, etc. Moreover, the cracking and failure moment of the slabs were calculated by the formulas of GB50010 and ACI318, respectively. The calculated results were compared with the test and simulation results. The results proves that the prediction values calculated by the codes on the flexural capacity of the spliced slab is not conservative. Therefore, considering a reduction factor to correct the results calculated by the codes is necessary.

Effect of Stirrups on the Behavior of Semi-Precast Concrete Slabs

A semi-slab of precast concrete (or half-slab) is a structural system that consists of concrete at the bottom half of a slab and concrete cast in situ at the top. To avoid traditional formwork and minimize the bottom half of the slab, this section can function as formwork and reduce the thickness of precast slabs, which makes their transportation easy. The interface between precast and overtopping concrete is effective for the slab system's performance. To improve the half-slab floor system, it is needed to have a shear connector (stirrups). Therefore, to better understand the behavior of this slab system, six full-scale slab specimens (2×7.5 m) with different shapes of the stirrups and spacing between them were constructed for this study. One specimen was produced with no connections and served as a reference specimen, while the other employed stirrups to connect slab units. The tests found that the distribution and type of stirrups affect the structural performance of the semi-precast concrete slab. The maximum load capacity of slabs with rectangular or triangular connections was nearly more significant than reference slabs, reaching 136.11 and 86.11%, respectively. The maximum load increased by 81.4 % for rectangular connections and 54.9% for triangular connections when the distance between the connectors was reduced from 600 to 300 mm. Furthermore, stirrups in semi-precast slabs could improve the cracking behavior, stiffness, and ductility. Doi: 10.28991/CEJ-2022-08-08-09 Full Text: PDF

Numerical Analysis on the Structure Design of Precast Cement Concrete Pavement Slabs

The performance of cast-in-place cement concrete pavement can be greatly influenced by the surrounding environment and the quality of construction, and it requires longer curing time before opening to the traffic. The precast cement concrete pavement has the potential to address the disadvantages of using the cast-in-place cement concrete as the pavement surface material, and it also provides an alternative solution for the rapid repair of pavement damage. The current study aimed to assess the influences of geometry of full-scaled precast concrete slabs with various load transfer joint types. A numerical analysis was conducted using the finite element method to analyze the mechanical responses of the single and double slabs in accordance with the elastic thin-plate theory and the Specifications for Design of Highway Cement Concrete Pavement. Under the premise of determining the most unfavorable load position for different mechanical parameters, the mechanical response regularity under the critical loads was determined. The precast concrete pavement slab with dimensions 4 m long, 3 m wide and 0.28 m thick exhibited better mechanical responses when considering the maximum deflection and flexural stress as the evaluation index. The results indicated that the variation of joint forms has marginal influences on the maximum deflection and displacement transfer coefficient. When considering the maximum flexural stress and load transfer coefficient of the precast slabs, the circular tongue-and-groove joint form was recommended for application.

An experimental study of the mechanical behaviour of squat shear walls built with precast concrete two-way hollow slabs

This paper proposes an innovative precast shear wall system built with precast concrete two-way hollow slabs (PCHS shear walls). In the joints of the precast panels of the PCHS shear walls, noncontact lap splices of rebars with vertical and horizontal holes are used to connect adjacent precast panels. These panels contribute to an automated assembly and facilitate pouring concrete in-situ. The mechanical behaviour of PCHS shear walls and the connection performance of vertical joints are examined through pseudo-static loading testing on one cast-in-situ concrete shear wall and four PCHS shear walls. Moreover, the influences of different parameters, including axial compression ratio, aspect ratio and the magnitude of horizontal distribution reinforcements, were analysed. It was found that the "strong bending and weak shear" requirement was achieved for all specimens. For the PCHS shear walls, the typical prominent diagonal cracks and brittle failure were prevented by the shear slippage at vertical joints and vertical cracks. And the vertical joint enabled the PCHS shear walls to exhibit stable load-bearing capacity with extensive deformations. In addition, the displacement ductility coefficient of all PCHS shear walls was over 5.0, and their ultimate drifts were over 1/100. The bearing capacity was improved with the increase of the axial compression ratio or with the decrease of the aspect ratio, but the deformation capacity was weakened.

EFFECTIVE LATTICE PUNCHING SHEAR REINFORCEMENT WITH DIFFERENT ARRANGEMENT

Reinforced concrete flat slabs supported by columns may fail by punching shear in form of a cone-shaped concrete breakout. To avoid this failure and to increase the shear resistance of a flat slab, shear reinforcement in the slab adjacent to the support can be used. The special Filigran-Punching-Shear-Reinforcement consists of mechanically welded three-dimensional lattice reinforcement and is able to increase the shear resistance of a slab to more than double compared with a slab without any shear reinforcement. This Filigran-Punching-Shear-Reinforcement is used in monolithic slabs and in semi precast slabs as well. In prefabricated lattice girder slabs a parallel arrangement of the punching shear reinforcement is beneficial. In case of monolithic slabs an orthogonal arrangement is more efficient. Both arrangements were tested in full scale tests successfully. The evaluation of eight punching shear tests with slabs of 180 mm to 360 mm thickness led to a European Technical Assessment. The maximum punching shear resistance based on the tested failure loads is 2.1-times of the resistance of slabs without punching shear reinforcement according to Eurocode 2.