Hollow Slab Research Articles

A FBG pull-wire vertical displacement sensor for health monitoring of medium-small span bridges

With the increase of service life, a growing number of medium-small span bridges have suffered degradation and even serious damage, and the vertical displacement is one of the significant parameters for their safety condition and performance evaluation. In terms of medium-small span bridges, to solve the difficulty for long term vertical displacement measuring and the demand for low-cost monitoring, this paper proposes a fiber Bragg grating (FBG) pull-wire vertical displacement sensor, which owns advantages of low cost, high accuracy and convenient installation. Firstly, the calibration and temperature correction of the sensor were carried out. Secondly, the influences of the fixed angle and sag effect of the sensor on measuring results were investigated. Finally, the sensor was installed in an in-service hollow slab bridge and the static and dynamic load experiments were carried out. Results show that the linearity of the proposed sensor is 0.998, the sensitivity is 7.87 pm/mm, the hysteresis error is 1.54 %, the temperature correction coefficient is 18.08 pm/°C, the relative combined uncertainties are within 4 %; the fixed angle of this sensor is recommended to choose in the range of 15°-30° in order to obtain higher measuring accuracy; when θ = 15° and the radius of the external wire is 0.3 mm, the limit of the external wire length can be set to 19.5 m to avoid the influence of the wire sag effect on measuring results; the sensor is feasible in vertical displacement measurement of in-service medium-small span bridge, and the relative measuring errors in both static and dynamic load experiments are less than 5 %.

Experimental Study on the Bending Resistance of Hollow Slab Beams Strengthened with Prestressed Steel Strand Polyurethane Cement Composite

In order to explore the toughening performance and failure mechanism of hollow slab beams strengthened with prestressed steel strand polyurethane cement composite, three test beams (L1–L3) were strengthened and one test beam (L0) was used as a comparison. The influence of different tensile stresses of steel strand and fiber additions on the flexural bearing capacity of the hollow slab beams, was studied. The cracking characteristics, load deflection relationship, ductility and strain of each test beam were compared and analyzed. The test results showed that the toughened material was well bonded to the hollow slab beam and the steel strand, which effectively inhibited the development of cracks in the test beams. The flexural bearing capacity of the strengthened test beams was significantly improved. The use of prestressed steel strand polyurethane cement composite material effectively improved the flexural bearing capacity of the test beams, and this reinforcement process can be further extended to engineering applications.

The flexural behavior of Hollow core concrete slabs with different shape

Hollow slabs are slabs of reinforced concrete in which voids allow the concrete to be reduced in size. This type of slab results in reduced raw materials Consumption and increased insulating properties to achieve sustainability goals. This paper reported an experimental research program focused on the study of the bending behaviour of the elements of hollow slabs of normal-strength concrete. Three models of the one-way concrete slab were cast, It had dimensions of 1020 mm length, 420 mm width, and 100 mm thickness. The first model did not contain holes (solid) and the second model contained five circler opening holes with a 50 mm diameter, while the third model contained five square opening holes with 44 mm dimension, where the area of the second and third model were the same despite the difference in the shape of the opening. The results showed that the bearing capacity of the circular hollow core slab is higher by 12% compared to the square hollow core slab according to the type of voids and both of holes made the hollow core slab with a decrease in load capacity of 11% to 25% when compared to the solid slab. The solid slab has lower deflection value compared to the two hollow slabs whose weight is reduced by 23% compared to the solid slab.

An experimental study of thermal performance of 3D printed concrete slabs

• Thermal performance of 3D concrete printed solid and hollow slabs were experimentally evaluated. • Due to interlayer air gaps, the solid printed slab showed more thermal resistance in direction of heat flow. • 3D printed solid slab has shown better thermal performance than hollow slabs. • The void-to-footprint ratio and insulation materials affects the final result. This work presents the most important advances in 3D printing, specifically the thermal performance of 3D printed concrete slabs with potential use as walls elements. One of the principal factors restricting widespread adoption of 3D printed concrete is the lack of thermal insulation, which needs an immediate attention. It is with this backdrop that this paper conducts a preliminary investigation on the thermal performance of 3D printed slabs containing two different cavity patterns with and without insulation material. The 3D printed solid slab has shown slight reduction in inside surface temperature (1℃) than casted slab owing to the cold joints between the printed layers. Compared to solid printed slab, 3D printed hollow slab with two and three identical cavities have shown 6℃ and 4 °C higher inside surface temperature respectively. However, with added insulation, the inside temperature of printed hollow slabs was found to be similar to the solid slab due to increased insulation capacity. The delayed heat transfer resulted in higher outside surface temperature for the 3D printed hollow insulated slabs.

Dismantling and Removal of PC Continuous Hollow Slab Bridge

Dismantling and Removal of PC Continuous Hollow Slab Bridge

Research on Flexural Bearing Capacity of Reinforced Hollow Slab Beams Based on Polyurethane Composite Material Positive and Negative Pouring Method

In order to explore the construction technology of prestressed steel strand–polyurethane cement composites for strengthening hollow slab beams, two reinforced test beams (L1, L2) and one unreinforced test beam (L0) were subjected to flexural static load tests. The deflection, ductility, stiffness, strain, and bearing capacity of each test beam were used to summarize the influence of different reinforcement techniques on the flexural performance of hollow slab beams. Research shows the prestressed steel strand–polyurethane composite material was well-bonded to the hollow slab beam, which effectively inhibits the development of concrete cracks and delays the damage process of hollow slab beams, that the reinforcement effect of the test beam L1 under the reverse pouring process was remarkable, and the bending performance of the test beam L2 under the forward pouring process of the simulated real bridge was good, which was much better than that of the unreinforced beam L0. The use of tensile prestressed steel strands and forward casting of polyurethane–cement composite materials effectively improved the flexural bearing capacity of the test beams, and this reinforcement process can be further extended to engineering applications.

Stress Analysis of Hollow Slab Bridge Deck Pavement

Abstract The asphalt-concrete pavement is an essential component of the bridge deck. Its stress characteristics are different from the general pavement structure. This research employs finite element technology (ANSYS) to model a three-span bridge and pavement layer in order to ascertain the stress distribution and provide a deeper knowledge of the mechanical properties of the pavement layer on concrete bridge decks. The effects of varying the thickness and stiffness of the deck pavement on the stress distribution in its different layers were investigated. Stress absorption is increased as the stiffness of the deck layers increases, and with increases in pavement thickness, stress on pavement layers decreases. The response of deck pavement under moving load, both under full bonding and sliding conditions, was simulated to determine stress distribution. By comparing the response under the full bonding and sliding conditions, it was found that stress induced on layers during sliding is high as compared to the full bonding condition; pavement layers will be prone to failure if sliding occurs between layers.

Study on the Structural Performance of UHPC Pavement and Hinge Joint Reinforcement for Hollow Slab Girder Bridges

To address the problem of structural performance degradation caused by hinged joints and pavement damage, we utilized actual engineering to conduct a construction study on the overall replacement of pavement and hinge joint reinforcement in ultra-high-performance concrete (UHPC) hollow slab girder bridges. A replacement and reinforcement design was developed and reconstruction was undertaken. By using UHPC and reinforcement bars, the adjacent slab girders were designed to work together under specific construction process guarantees for the characteristics of UHPC. The corresponding interface treatment and a combination of planting bars and steel mesh were necessary. According to the strain and deflection monitoring results, the overall performance of the bridge after pavement and hinge joint reinforcement was verified. The strain amplitude of the reinforcement was approximately 10 με, and that of the concrete was approximately 5 με. The deflection difference of the adjacent girder was similar, which proved that the hinge joints connect girders and transfer force effectively. All the results clearly demonstrated the positive overall effect of the UHPC replacement method. The conclusions could provide a reference for the reinforcement and reconstruction of similar projects.

Equivalent Solution Method for the Analytical Transverse Modal Shape of Hollow Slab Bridges

Hollow slab bridges are the most widely used form of small- and medium-span bridges. The existing research on the dynamic characteristics of hollow slab bridges is mostly based on numerical models, but there is a lack of theoretical analyses of their dynamic characteristics. In this paper, the relationship between the dynamic characteristic parameters and structural parameters of a hollow slab bridge is explored theoretically. Firstly, the solid model of a hollow slab bridge was established, and a modal analysis was carried out on it as a reference. Then, an orthotropic plate was used as an equivalent dynamic analysis model, and the analytical form of the transverse modal shape was deduced based on Kirchhoff thin plate theory. Furthermore, one hinge joint was considered as being equivalent to the elastic support boundary, and the local structure and the equivalent elastic support boundary were used to reflect the transverse modal shape of the original structure. The analysis shows that the influence of hinge joints on the transverse modal shape is mainly reflected in the transmission of bending deformation. Through comparison and verification, the results show that the analytical expression of the transverse modal shape can well describe the low-order transverse modal shape of a hollow slab bridge.

Experimental study on residual bearing capacity of full-size fire-damaged prestressed concrete girders

With the increasing development of three-dimensional transportation network, the probability of bridge fire accidents is increasing year by year, which leads to reduced bearing capacity of the bridge exposed to fire. Existing bridge detection and evaluation methods are not suitable for bearing capacity evaluations of fire-damaged bridge, since material degradation or localized damage of structural members caused by elevated temperature are not considered. This paper took actual fire-damaged bridge as a case study to analyze the influence of fire on residual bearing capacity as well as bending test on two 20 m span hollow slab girders with different degrees of damage. The prestress loss, failure mode, load–displacement curve, and residual bearing capacity were tested. A method integrated the FDS (Fire Dynamics Simulator) and the FEA (Finite Element Analysis) was proposed to calculate the actual process of bridge fire and mechanical property of fire-damaged girders. The dimensional temperature fields around the bridge and internal temperature field in a concrete hollow slab girder during the fire were obtained. Based on the research results of mechanical properties of concrete and prestressed tendon under elevated temperature, the mechanical numerical model considering internal temperature field was established; The failure mode and residual bearing capacity of fire-damaged girders were simulated. The results show that the post-fire residual bearing capacity mainly depends on the maximum temperature of prestressed tendons. The higher the temperature of prestressed tendons is, the lower the residual bearing capacity is. In the case bridge, compared to the girders at ambient temperature, bearing capacity of the two test girders decreased by 17.6 % and 15.1 %, respectively. The method proposed in this paper can be used to evaluate the post-fire bearing capacity of fire-damaged concrete girder bridges.

Simulation of structure and power generation for Self-Compacting concrete hollow slab solar pavement with micro photovoltaic array

To explore new solar pavements, a self-compacting concrete hollow slab solar pavement based on a micro photovoltaic array was proposed. The hollow slab solar pavement is composed of three layers: a surface transparent protection slab, a middle micro photovoltaic array, and a bottom concrete base slab. Using ANSYS software and PVsyst software, through the 3D finite element numerical simulation and power generation simulation of the pavement structure, based on orthogonal experimental design and single-factor sensitivity analysis, the structure size of the hollow slab and the layout mode of the micro photovoltaic array were optimized. Then, the optimal hollow slab model was determined. The results show that the optimal size of the hollow slab is 1000 × 1000 × 250 mm; the tilt, azimuth, pitch and edge distance of the solar cells in the best layout mode of the micro photovoltaic array are 18°, 0°, 45 mm and 65 mm, respectively; the power generation capacity in the first year is 140.697 kWh. The life cycle economic analysis indicates that the increased cost can be recovered through the power generation income after 10.2 years, and 1 km of two-way four-lane pavement could reduce by 2.15 × 107 kg of CO2 emissions, with good economic, social, and environmental benefits.

Temperature distribution simulation and thermal properties investigation of hollow slab beam based on meteorological data

Natural environment has a great impact on the performance of bridge structures, such as the ambient temperature, solar radiation, climate extremes and so on. Due to the lack of regional pertinence in the provisions of the existing specifications on the temperature load standard, and the lack of verification of its adaptability of hollow slab beam bridge in the reconstruction and expansion project, it is necessary to study the temperature load of the beam based on the temperature data of the area where the bridge site is located. Based on the measured meteorological data, the cross-section temperature distribution characteristics of the hollow slab beam and the temperature load effect were investigated. The vertical temperature load model of the short and medium-span hollow slab beam was proposed according to the simplified temperature curve. Firstly, based on the annual measured meteorological data, the plane model was established to analyze the temperature distribution characteristics of the hollow slab beam. Secondly, according to the temperature field distribution of the beam cross-section, the solid model of 16 m hollow slab beam was established to analyze the distribution of the temperature load effect. Finally, based on the preliminarily proposed temperature curve, vertical temperature load models were proposed by introducing the theory of extreme value extrapolation. The studies have shown that the temperature of the hollow slab beam is approximately horizontal distributed, and temperature extreme value appear at the location of the beam web. The roof and floor of the hollow slab beam are compressed and the webs are tensioned in the positive temperature difference state, the stress condition is opposite under the negative temperature difference state. The positive and negative temperature load models can meet the extrapolation requirements of the bridge design reference period. This study innovatively proposed a temperature load model based on the temperature curve corresponding to the most unfavorable effect of the beam. The extrapolation idea in the derivation of vehicle load model is introduced as well. And a temperature load model suitable for the extension of hollow slab bridges in Guangdong is established in this study.

Damage modes and residual deflections of multi-beam hollow slab bridge under car explosions

The purpose of this study is to investigate the damage modes and residual deflection of multi-beam hollow slab bridges under car explosions. To comprehensively estimate the blast response, the failure process of the bridge with different beam numbers are cautiously simulated and compared. With the experimentally validation of the constitutive laws and the fluid–structure interaction parameters, the impact analysis software Autodyn is adopted to capture the damage mechanisms and the vibration histories. After cautious numerical simulations, local punching shear failure and global flexural failure dominate the damage modes of multi-beam hollow slab bridges. Due to the oversized impact energies and the insufficient structural resistance, overall collapse is observed in bridge with 4 or 6 beams in middle and acentric explosions. For bridge with 8 or 10 beams, the formed plastic hinges imply the large residual deflection and possible overall collapse during middle explosions. Owing to the easier energy dissipation and the smaller impact areas, limited flexural damage are discovered in bridge with 8 or 10 beams under acentric explosions. Due to the limited flexural damage and the small residual deflection of the distant beams, these beams can maintain great bearing capacity and can be repaired after explosions.

A hybrid method for damage detection and condition assessment of hinge joints in hollow slab bridges using physical models and vision-based measurements

The simply supported slab bridge is a typical perfricated reinforced concrete bridge. Under the influence of increasing vehicle loads and natural environmental erosion, the hinge joints between slabs suffer from damage that cannot be easily evaluated, which brings negative effects on the load carrying capacity of bridges. In the present study, a hybrid method for damage detection and condition assessment of hinge joints in hollow slab bridges using physical models and vision-based measurements was proposed. The stiffness reduction of hinge joints is taken as the damage degree and condition level of the inspected hinge joints. An analytical model of a simplified spring-mass system was firstly built to demonstrate the applicability of using the relative displacement ratio as the damage index of hinge joints. The relationship between the relative displacement ratio and the stiffness reduction of hinge joints was then studied thoroughly through a parametric study on finite element models considering different damage levels of hinge joints. Thresholds of the relative displacement ratio were defined to classify the damage states of hinge joints. The damage index of target hinge joints can be calculated from the actual data provided by using computer vision-based multi-camera and multi-point displacement measurements. Lastly, the application of a real-life bridge under normal traffic was demonstrated to verify the feasibility of the quantitative evaluation of the service status of joints in hinged-slab bridges. It indicated that the proposed method could evaluate the damage degree of joints quantitatively, effectively and economically.

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.

Analysis of The Most Affecting Factors in The Selection of Conventional and Precast Concrete Floor Slabs on Time Performance

One of the efforts to achieve the goals of construction project in terms of cost, quality and time is to replace conventional methods with more modern ones, namely by applying precast concrete. Precast concrete products, especially for buildings, are quite varied, one of them is Hollow Core Slab (HCS). Supported by previous research which explains that precast concrete floor slabs can save processing time compared to conventional floor slabs. Therefore, it is necessary to identify factors and variables that affecting the selection of conventional and precast
 floor plates on time performance and how the influence of the X variable (Factors) on the Y variable (Time performance).The results showed that the most affecting factors in the selection of conventional floor slabs on time performance were manpower factor with variable number of workers (41.3%), location factor with variable distance of batching plant to project site (19.8%), and also technical factors with shop drawing revision variable (by 41.8%). As for, the most affecting factors in the selection of precast concrete floor slabs on time performance include manpower factors with worker’s expertise variable (29.7%), and technical factors with shop drawing revision variable (by 38.4%).

Time Domain Damage Identification Approach of the Newly Hollow Floor Structure with TRMD

A tuned rolling mass damper system (TRMD) is newly combined with structural hollow slabs to act as an ensemble passive damping device to mitigate structural responses. The main advantage of this controlled configuration lies in its capacity to maintain architectural integrity. To investigate damage identification of this controlled structure with TRMD, a time domain identification approach with sensitivity-based model updating is studied in this paper. The simplified model and motion equation of a controlled structure with TRMD are derived considering the interaction force between the main structure and the damper. Furthermore, the dynamic response and dynamic response derivatives with respect to elemental variations in the controlled structure are analyzed to identify damage by minimizing the response difference between the intact state and the damaged state in the sensitivity-based updating procedure. A numerical example for a six-story frame structure with a TRMD on the top is employed to verify that not only the structural dynamic responses are controlled effectively by the rolling ball damper subjected to the earthquake excitation, but also damage location and extent can be identified accurately by the proposed method even with measurement noise considered. The shaking table test of a single-story frame equipped with TRMD is additionally carried out to validate the accuracy of the proposed structural damage identification method in the laboratory.

Flexural performance of assembly integral floor structure voided with steel mesh boxes

Enhancing the ease of construction of fillers and large-span floors and their overall mechanical performance is critical for prefabricated hollow slabs in modular building structures. Therefore, we propose a novel assembly integral two-way hollow floor structure (8.4 × 8.4 m) consisting of permanent fillers (BDF ribbed steel mesh box) and three precast one-way hollow-core slabs with I-shaped flexural sections to address the above problem. This report evaluates the overarching flexural mechanism of a large-span full-scale model of the proposed system under uniform vertical loads. The experiment supports that the structure possesses a high bi-directional vertical bearing capacity and achieves the purpose of turning three one-way precast slabs into a two-way integral floor. The deflection value of the cast-in-site concrete frame beam, as the junction between the precast and cast-in-situ sections, is 88% below the damage limit value in GB/T 50152–2012. The strain of the bottom rebars in the ribbed girder of the precast hollow slab is identical to in the hidden girder. The strain profile in the mid-span of the frame beam reveals a noticeable membrane effect, strengthening the bending resistance of the system. Additionally, the original structure was modeled using ABAQUS to study the damage mechanism further. The analysis of the plastic development history and stress-strain distribution of the specimen reveals that upgrading the concrete strength has a slight improvement on the stiffness but could lessen its damage. While rationalizing the steel configuration is a more cost-effective option. Based on the pseudo-plate method and simulation results, the deflection and internal force equations were also recommended for preliminary design.

Comparative analysis of flexural performance of old full-scale hollow slab beams reinforced with fiber composites

To address the problems of inadequate load carrying capacity, deformation and deflection of the main beams of in-service reinforced concrete (RC) bridges, the flexural performance of old full-scale hollow slab beams was investigated based on four-point bending tests in the field, and a qualitative and quantitative comparison was made between innovative solutions (TRC, TRECC) and conventional solutions (prestressed CFRP plates). The results show that the three fibre composite reinforcements increase the load carrying capacity of the hollow slab beams by 9.09% to 21.2% and the stiffiness by 0.4% to 46%, and that the deflection is effectively controlled and limits the development of cracks, while the ductility is reduced. The prestressed CFRP plates are more beneficial in delaying the stiffness degradation under service loads, and the deflection values of their reinforced beams are smaller; while TRECC shows better performance in controlling the crack width. On this basis, the effect of the axial stiffness of the reinforcement on the overall performance and local stress distribution of the beam was evaluated by load calculation and numerical simulations, and showed good agreement between the experimental and theoretical results. The effect of external reinforcement on the beam depends more on the axial stiffness than on the nature of the reinforcement material, and the effect of external reinforcement on the tensile side of the beam is mainly concentrated on the plastic phase.

Multifractal analytical method and experimental study on crack evolution of dismantled RC hollow-slab beam

Reinforced concrete is the earliest and most commonly used bridge construction material and there are a large number of RC bridges in service all over the world. Due to a long-time operation and external load, most concrete bridges suffer from various degrees of damage. The most common method used in the maintenance of these bridges is visual inspection, which is highly subjective, lacks quantitative means and provides little information about the mechanical properties of the structure. Therefore, this paper conducts a set of failure experiment of the reinforced concrete hollow slab beams based on multifractal theory, and then proposes a convenient damage detection method for reinforced concrete beam bridges based on crack distribution images. Firstly, this paper introduces the basis of multifractal theory and an example of its application to the cracking characteristics of concrete beam members. Then a set of failure experiment on demolished members of in-service reinforced concrete hollow slab bridges was conducted, and two high-precision industrial cameras were used to record the full process of crack development on the surface of the beams. Then the multifractal theory was used to quantitatively characterize the crack distribution characteristics of the beams during the load process. The function relationship between the fractal dimension and the bending moment and the main mechanical properties (mid-span deflection, maximum crack width) of the test beam was analyzed and the damage index based on fractal dimension is calculated. The results show that the multifractal theory performs appropriate in describing the crack distribution of the beam, the points on the multifractal spectrum continuously move to larger values as the bending moment increases, and the generalized fractal dimension values have similar conclusions. The functional correlation between main mechanical properties and the fractal dimension is strong. Based on the experiment results, the damage classification criteria for reinforced concrete bridges are proposed referred to the IAEA guidelines. Three damage classes and corresponding the range of values of fractal dimension (FD) and the damage index (DI) are given. These findings provide a useful tool for exploring the cracking performance and rapid detection of reinforced concrete bridges.