Top Slab Research Articles

Experimental study of a geosynthetic-reinforced soil bridge abutment

The article presents an experimental study of a geosynthetic-reinforced soil (GRS) bridge abutment (BA). The BAs are seated on a saturated soft foundation layer and support a 16 m long concrete bridge. Laboratory tests were conducted on the foundation soil, geogrid, and fill material. The BA is constructed from 14 geogrids and has a total height of 4.2 m. The strain values in the geogrids were measured and recorded during the construction of the abutments and after installation of the bridge structure. The test results show that more than 50% of the total strain in the geogrids was developed during the construction of the BAs, mostly embedded in the ground. The remainder of the measured strain was a consequence of installing the prefabricated bridge girders, back fill placement, concreting the top slab, and placing the asphalt concrete. The strain distribution along the geogrids shows that the maximum strain was recorded below the sill, and was 50% higher than at the center of the BA. Based on an analysis of the construction costs, it can be concluded that conventional reinforced concrete abutments could cost up to five times the amount of optimally designed GRS-BAs.

Behavior of Cantilever Composite Girder Bridges with CSWs under Eccentric Loading

A study on the torsion and distortion properties of the cantilever single-box three-cell composite girder bridge with corrugated steel webs (CSWs) is carried out based on experimental testing and finite element model analysis. Firstly, the mechanical characteristics such as the deformation, longitudinal warping normal stress were investigated based on a double cantilever girder model test. Secondly, the influence of parameters such as girder height, box width and corrugated steel web thickness on the warping stress of cantilever composite girder with CSWs under eccentric load were analyzed based on the finite element model. Finally, the eccentric load effect of the composite bridge with CSWs at the maximum cantilever construction stage under different load combinations was analyzed based on a finite element model of the real bridge. The results show that the longitudinal warping strain of the CSWs is significantly smaller than that of the top and bottom concrete slabs under eccentric loading due to the accordion effect. The maximum warping normal stress occurs at the corners of the bottom concrete slab. The additional shear stress of the steel webs distributes uniformly along the girder height, and the additional stress of the web on the loading side is clearly greater than that at the middle. The finite element parameter analysis results show that the height and width have a significant influence on the warping stress of single box three-cell composite girder with CSWs, and the thickness of CSWs has almost no effect. In practical engineering, the warping stress of the bottom slab accounts for approximately 20% of the bending stress when the self-weight is considered. Therefore, it is not trivial to consider the influence of the warping normal stress of a concrete slab and the additional shear stress of the CSWs in the design and calculation of this type of bridge.

A complete numerical model for low temperature composite form-stable phase change material slab based on dynamically simplified temperature transforming method

ABSTRACT Phase change material (PCM) that is used in the roof top slab can minimize the heat infiltration into the living space from the building envelope and increase the indoor thermal comfort level. The major disadvantage of PCM is leakage at liquid state. Expanded graphite (EG) is used here as supporting material for PCM to prevent the leakage and maintains the form stability. The composite PCMs are prepared by adding the EG with various mass ratios, i.e. 3%, 6%, and 9%. The thermal properties of all composite PCMs are determined by DSC and thermal conductivity analyzer. The optimum PCM composition was found at 9% of EG. In this study, the shape-stabilized PCM-integrated roof top was analyzed by simplified temperature transforming (TT) numerical model. The main advantage of this model is that it is used to combine the equivalent enthalpy and heat capacity. The numerical results are validated with experimental values and show the lower mean absolute percentage error (MAPE), i.e. 6.91%. This indicates that present model is well suitable to predict the thermal performance of composite PCM incorporated roof top. The effect of various parameters like thickness of the PCM slab, wind velocity, percentage of EG mass ratio, and location of PCM are investigated by simplified TT model. The results showed that the maximum inner surface temperature reach up to 53°C for BG model (concrete and gypsum) by distributing constant heat flux, i.e. 1,000 W/m2 for 180 min. At this same condition, the inner surface temperature of other PCM models PBG (PCM, concrete, gypsum) and BPG (concreate, PCM, Gypsum) reaches to 50°C and 41°C, respectively. PBG model exhibits excellent thermal performance compared to BPG model. The thermal performance of PCM slab is also investigated by varying the thickness of the PCM layer and found that time lag is raised with the thickness of the PCM slab.

Cost Aanalysis and Comparison of Rectangular and Trapezoidal Box Girder Section

The present study aims at design, analysis and parametric comparison of two different cross section of box girder deck system. Objectives of this study are to compare the stresses at important location like top slab and bottom slab using analysis tool MIDAS-2016. And design and estimates different sizes of rectangular and trapezoidal box girder section using hand calculation. Keywords: Box Girder, Rectangular box girder, Trapezoidal box girder and MIDAS-2016

ANALYSIS OF THE SHEAR LAG EFFECT IN WIDTH-VARIANT GIRDERS OF CABLE-STAYED BRIDGES

The research is based on a composite large-span double-tower single plane cable stayed bridge with the span of (54 m+108 m+340 m+108 m+54 m) in Zhejiang Ningbo Zhoushan port, the main girder of which faces the problem of a complex main girder with a large aspect ratio and remarkable shear lag effect. To study the shear lag effect of the cable-stayed bridge and the influence of the width-variant girder on the shear lag effect, we studied the main mechanical behavior and stress distribution of the main girder by combining the mixed finite element method and field measurement, and obtained the stress and shear lag coefficient distribution of the top and bottom slab in the finished state. The results show that the shear lag effect in the top and bottom slabs of the single-box triple-room cable stayed bridge is significant. With the increase of the width of the main girder in the widening section, the shear lag coefficient of the top slab decreases continuously. For the steel floor, the change of the number of U-ribs of the floor caused by the change of the width of the main beam leads to an uneven stress distribution of the bottom slab. Therefore, the arrangement of the longitudinal ribs of the floor can be optimized according to the distribution curve of the shear lag coefficient. The results are significant and provide useful reference for the design and construction of this kind of bridges.

Numerical Study on the Mechanical Properties of the Novel Wide Box Girders Stiffened by Transverse Ribs

The dimensioning of the cross section is a critical step in designing wide box girder bridges with long cantilevers. The typical box girder cross section may not be the most economical and reasonable choice for wide box girder bridges considering the stress conditions and construction costs. Arranging transverse stiffened ribs underneath the top slab is an effective way to widen the bridge deck. In this study, the influence of the transverse stiffened ribs on the mechanical performance of the ribbed top slab is investigated by finite element (FE) modelling. The results show that the transverse mechanical properties of the box girders with ribbed slabs are significantly different from those of the traditional box girders with solid slabs. The ribbed slabs can provide additional transverse capacities over those of the traditional solid slabs. Furthermore, the transverse tensile stress in the root section of the ribbed cantilever slab is found to fluctuate periodically along its length, and a considerable stress concentration is observed in the transverse ribs. The key design parameters of the transverse ribs (depth, width and spacing) influencing the tensile stress amplitude at the cantilever root section are determined through FE parametric analysis.

Influence of monolithic plate manufacturing technology on physical and mechanical characteristics of the coating

During operation in an open atmosphere, bridge structures are exposed to extreme natural and climatic conditions, chemicals and constantly changing temporary and dynamic loads. Bridge structures built in the 60s and 80s of the last century have approached a critical situation and require major repairs. Goal. The most vulnerable elements of the bridge structure are the upper part of the concrete span structures (slab) and waterproofing, so there was a question of strengthening the slabs and replacing the waterproofing layer. Metodology. When forecasting the durability of bridge structures, it is necessary to take into account the influence of temperature and humidity and climatic factors together with force factors. Result. The real necessity of mounting a monolithic reinforced concrete slab for strengthening a top slab of girder structures and putting a new waterproofing layer on it is shown. Originality. The technology of spraying a waterproofing layer that allows to waterproof a surface of any complexity evenly and reliably is offered. Practical value. Overhead monolithic slab enhances the bearing capacity of the power elements of the bridges and can be increased by 1.5–2 times.

Experimental study on lateral behavior of post-tensioned precast beam-column joints

In this study, experiments were carried out to evaluate the seismic performance of a hybrid prestressed precast concrete (HPPC) system devised to ensure the integrity of precast concrete (PC) beam-column joints by introducing the post-tensioning method. A total of four full-scale HPPC beam-column joints were fabricated, and the presence of a topping slab, a post-tensioned length, and a type of tendon were set as the main variables. The quasi-static cyclic loading tests were performed to analyze the load-story drift ratio response, failure mode, ductility, residual deformation, and energy dissipation capacity of each specimen. The seismic performance of the specimen was then quantitatively evaluated based on the acceptance criteria of the ACI 374 report. The shear strength estimation model for the HPPC beam-column joints was also proposed and the proposed model was verified in detail using the test results.

Structural performance of a medium-span RC three-sided culvert based on field measurements and numerical analyses

The structural performance and soil–structure interaction mechanism of a 7.3 m span, reinforced concrete (RC), three-sided culvert (TSC) with flat top slab are investigated through field monitoring and numerical analyses. The culvert was instrumented with six pressure cells and 14 strain gauges. Data were collected during and after construction. Two-dimensional finite element models were validated against the field measurements. The validated numerical models were then employed to evaluate the effects of the foundation soil condition (yielding or non-yielding) on the applied earth pressures along the culvert profile and the induced straining actions at the base of the culvert’s sidewall. Moreover, the structural performance of TSCs at the ultimate loading condition has been evaluated from the numerical model. The results indicate that for TSC supported on yielding foundation soil, significant bending moment develops at the sidewall base and that the assumption of hinged connection at the base is only realistic for the case of TSCs supported on rock (non-yielding foundation). In addition, the precast unit width was found to have minimal influence on the failure mechanism and the ductility of the precast unit. Finally, failure may occur at a lower backfill height for the non-yielding foundation case relative to the yielding foundation case.

Progressive collapse of RC flat slab substructures with unbonded posttensioning strands after the loss of an exterior column

Reinforced Concrete (RC) flat slab structures are mainly composed of load-bearing columns and RC slabs, which are vulnerable to collapse once one or several local load-bearing columns fail due to accidental loads such as terrorist bomb attack or vehicle collision. To investigate the progressive collapse performance of flat slab structures after the loss of an exterior column, static collapse tests were conducted on three 1 × 2 bay RC flat slab substructures. Effect of prestress and layout of the unbonded posttensioning strands (UPSs) on the progressive collapse of flat slab structures was discussed. Experimental results showed that punching shear failure (PSF) foremost occurred at the slab-column connection (SCC) of the failed exterior column during collapse, and then successively occurred at the SCCs close to the corner column and the exterior column adjacent to the failed column. Primary cracks on the top slab surfaces around the failed exterior column generally presented arc-shaped distribution; while primary cracks on the bottom slab surfaces radially propagated from the failed exterior column. Comparing with the flat slab substructure without UPSs in the slabs, the load-bearing capacity of the substructures with UPSs in the slabs significantly improved. Flexural action was the fundamental collapse resistance mechanism in the initial collapse stage, and tensile membrane action gradually formed during collapse. The flexural action, the tensile membrane action, as well as the post-punching behaviors of the slabs resisted the collapse load together before the final collapse occurred. Most of the load applied on the failed exterior column mainly transmitted along the shorter slab bay under the exterior-column-removal scenario. Arranging posttensioning strands in the slabs contributed to reducing vertical deformation of the slabs. The UPSs in the column strip passing through the failed column played a more important role in resisting collapse load than those arranged in the middle strip. The residual flat slab substructures still possessed satisfactory load-carrying capacity even if PSF occurred in one or several SCCs.

Numerical Analysis of Two I-shaped GFRP Composite Bridge with Corrugated Webs

With the advantage of high strength, lightness, and good environmental resistance, glass fiber reinforced polymer (GFRP) pultruded profile is regarded as an innovative way that has been used in infrastructure over the last few decades. However, some disadvantages also limited its widespread application in practice, including relatively low elastic and shear modulus and high deformability due to buckling failure. To overcome these disadvantages, some composite structure systems are proposed, such as GFRP-concrete composite structure system. This paper presents an innovative GFRP-concrete composite bridge prototype system, which mainly includes two I-shaped GFRP girders with corrugated webs combined with a thin steel fiber reinforced self-compacting concrete (SFRCC) deck. This composite bridge system is proved to improve structure shear stability and bending stiffness. Three-dimensional finite element (FEA) models are created to simulate the flexural behavior of two-I-shaped-girder composite bridge with straight webs, and the model result is validated with experimental data. Furthermore, the revised FE model that uses corrugated webs instead of straight webs is created, and the static and dynamic behaviors are investigated, including shearing stability properties, bending vibration frequency due to bending and torsion, mid-span vertical deflection, and lateral displacement due to wind load. Further research efforts on the influence of parameters dimension variation in corrugated webs girder composite system are needed. A total of four variable parameters are selected to test, which are GFRP corrugated web width, thickness, height, and SFRCC top slab thickness, respectively. All these conclusions will provide some design recommendations and guideline of a GFRP-concrete corrugated webs composite bridge in further study.

Cover Picture: Steel Construction 1/2021

AbstractThe building of the San Giorgio bridge in Genoa re‐establishes the connection between autoroutes A10 and A7 after the tragic event of the Morandi bridge collapse of 14 August 2018.The bridge deck layout required the use of a torsionally rigid section. This was achieved, in particular, with two longitudinal beams spaced 7.00 m apart, a curved, calendared soffit and a top slab made of composite concrete.The new bridge was opened on 3 August 2020, finally revealing the idea of the architect, Renzo Piano: A big, white vessel moored in the valley, a bridge that enters a dialogue with the sea, with the wind, with light, a structure that encourages builders to continue building bridges as links between territories and symbols of union. (Sarcina, G. et al., pp. 14–21)

Field Monitoring and Numerical Analysis of Large-Span Three-Sided Reinforced Concrete Culvert

This paper investigates the structural behavior and soil–structure interaction mechanism of a three-sided culvert (TSC) at service and ultimate load levels. Field measurements were used to verify a two-dimensional (2D) finite-element model (FEM) and evaluate the backfill height at which the TSC would fail. In addition, experimental data available in the literature of an arched TSC segment loaded to failure was adopted to verify a three-dimensional (3D) FEM for the analysis at the ultimate limit state (ULS). The results demonstrated that the Canadian Highway Bridge Design Code overestimates the earth pressures on the top slab. It was also found that the connection at the sidewall base does not behave as a perfect hinge. Finally, the nonlinearity of the reinforced concrete (RC) was evaluated throughout the loading spectrum and it was concluded that simplifying the behavior of RC using a linear-elastic model is only adequate at the service load levels.

Seismic response of utility tunnels subjected to different earthquake excitations

The influence of ground motions on the seismic response of utility tunnels was investigated. A series of small-scale shaking table model tests were carried out under uniform excitation in the transverse direction. Different peak accelerations of EL-Centro and Taft earthquake waves were applied. The acceleration responses, earth pressure, seismic strain, bending moment and structure deformations were measured and discussed. The results showed that the types of earthquake waves had significant influences on the soil-structure acceleration responses. However, the amplitude of the soil acceleration along the depth showed consistent variation regardless of the types of earthquake waves and tunnels. The horizontal soil pressure near the top and bottom slabs showed obviously larger values than those at other depths. In general, the strain response in the outer surface was more significant than that on the inner surface, and the peak strain in the end section of the model was larger than that in the middle section. Moreover, the bending moment at the corner points was much larger than that at middle point, and the bending moment was greatly affected by both input accelerations and seismic wave types. The opposite direction of shear deformation on the top and bottom slabs presented a rotation trend of the model structure.

Finite element analysis of temporary pre-stress system of precast segmental box girder bridge

The precast segmental bridge has the advantages of fast construction speed, good economic performance, and small impact on the surrounding environment. In order to study the role of the temporary pre-stressing system in the cantilever assembly process of the precast segment box girder bridge, ABAQUS was used to simulate the assembly process of the standard section of a viaduct. Studying the compressive stress and relative sliding of the joint section under the action of the self-weight and temporary pre-stress, the reasonable number and spatial arrangement of the tension pedestal are determined. The research results show that too few roof pedestals will cause the large area decompression state and too much will cause the construction period to be longer. When the roof symmetrical pedestal is located on the inner side of the web, it will obviously increase the area of the zero-compression stress at the end of the top slab. When the distance between the pedestal and the center of the web is 0.12L, the full section meets the minimum consolidation pressure requirement of the glued joint. The reasonable number of tension pedestals and their spatial arrangement will provide specific guidance and reference to assembling construction of actual precast segment box girder in the future.

Seismic performance and effective isolation of a large multilayered underground subway station

In this paper, the seismic performance of a reinforced concrete (RC)-framed underground subway station structure which has three stories and three spans was analyzed firstly under strong earthquakes. It was found that the central columns in the top and the bottom stories were the weakest seismic components in this type of underground structure. Thus, lead-core rubber bearings (LRBs) were installed at the central column-tops of the structure, and the seismic performance of the underground station structure with LRBs was also studied. The results show that LRBs can reduce the seismic damage to the central columns and interior slabs and the lateral deformation of the central columns effectively. While the installation of LRBs will also change the internal force transfer characteristics and energy distribution of the large underground structure and increase the seismic damage to the top and bottom slabs and side walls to some extent. In particular, when LRBs were only set on the central column-tops in the top and bottom stories, which have the most unfavorable seismic performance in the underground structure, the seismic damage to the central columns without LRBs was significantly exacerbated. The isolation method of installing LRBs at the top of the central columns in each story was clearly superior and could ensure that the underground station structure would not collapse due to serious damage of the columns under strong earthquakes.

Performance of Rc Skew Box Culvert: Application of The Finite Element Modelling And Artificial Intelligence

Box culvert structures are widely used nowadays in infrastructures such as roads or bridges worldwide. The skewness in the box culvert bridges is usually inevitable to achieve the desirable design of their layout. Based on the limited knowledge in proposing a simple mathematical model to predict the load-carrying capacity of these skew structures, more studies are regarded essential in this direction. The work presented is dealing with the modeling of the skewed reinforced concrete (RC) box culverts using a valid finite element modeling in ANSYS-11. In addition, artificial neural network (ANN) was adopted to formulate a mathematical model for the response of these bridges depending on the outputs of parametric study of the present finite element simulation. Specific nonlinear relationships have been employed in the numerical analysis to model the behavior of both concrete and embedded steel bars. A database of the performance of RC skew culverts, established from the outputs of over 285 finite element models, was utilized for the development of ANN-based models. The skew angle of the culvert, the span of its top slab, thickness of the slab and concrete compressive strength have been used as input variables to predict the behavior of the culvert via the developed ANN. Simple equations were derived depending on the results of this network to compute the failure load and maximum deflection of the top slab of the skew culvert. The proposed models showed superior efficiency over existing tedious analytical or numerical solution with consideration of combined effect of simplicity and accuracy in the output prediction. Moreover, the comparison of the finite element outcomes with those of previous experimental work confirms the validity of the used constitutive relationships in the analysis of single-cell concrete culverts.

Experimental analysis of the shear strength of composite concrete beams without web reinforcement

Composite concrete members without web reinforcement are often used in precast construction. The contribution of the cast-in-place concrete topping slab to vertical shear strength has been traditionally disregarded. However, significant cost savings can result from designing and assessing these structures if this contribution is considered. This paper presents the experimental study of a series of 21 monolithic and composite (precast beam and cast-in-place slab) specimens without web reinforcement, and with rectangular and T-shaped cross-sections, failing in shear. The vertical shear strength was analysed by the following test variables: cross-section shape, the existence of an interface between different aged concretes, strengths of the two concretes and the differential shrinkage effect. From these experimental tests, it was concluded that the slab contributed to shear strength, the use of high-strength concrete slightly increased specimens’ shear strength and the differential shrinkage did not reduce shear strength. Specimens’ failure modes were analysed based on their shear transfer mechanisms, noticing that the arching action in the slab was considerable after critical shear crack formation. The vertical shear strength experimental results were well predicted by the codes’ formulations (Eurocode 2, Model Code 2010 and ACI 318-19) when composite beam depth was taken for the calculations instead of beam depth. Codes significantly underestimated the horizontal shear strengths of the composite specimens.

Theoretical prediction of the punching shear strength of concrete flat slabs under in-plane tensile forces

RC slabs can be subjected simultaneously to transverse loads and in-plane tensile forces, as it happens in top slabs of continuous box girder bridges decks, in the regions of negative moments, or in flat slabs subjected to horizontal loads, produced by wind or earth pressure. Tensile forces can reduce the shear punching capacity of slabs. However, few studies have been carried out to quantify this effect. With this purpose, a mechanical model has been developed to capture the influence of in-plane tensile forces on the punching shear strength and verified with punching tests under different in-plane tensile load levels. The model, presented in this paper, consists of an extension of the Punching shear Compression Chord Capacity Model to account for the effects of tensile forces on the resisting actions. A linear reduction of the punching shear strength as a function of the external load applied has been obtained for moderate tensile forces, whereas high level of tensile forces may produce premature yielding of the reinforcement and further reduction of the punching shear strength. The proposed model accurately captures the available test results, including the effects of the premature yielding of reinforcement when the tensile force produces concrete cracking. In addition, predictions of punching-shear-tensile tests available in the literature were made with different theoretical models included in design codes, which yielded in general conservative results and showed high scatter.

Dynamic response of cut and cover tunnel section under blast loading

In the present study, three-dimensional nonlinear finite element analysis is used to investigate the dynamic response of cut and cover tunnel subjected to blast loading. The analyses are performed using a dynamic explicit analysis tool in ABAQUS. The blast load is modeled using the CONWEP blast function available in ABAQUS. The reinforced concrete section is modeled using three-dimensional solid elements and stress–strain response of concrete is simulated using a concrete damaged plasticity model. The reinforcements are modeled using three-dimensional truss elements, and material properties are simulated using a metal plasticity model with isotropic-linear-elasticity. The parametric studies have been performed to evaluate the performance of key structural elements of cut and cover facilities, i.e., top slab and walls considering (1) different cover thickness (buried depth-d) of tunnel to height of tunnel ratio (d/H) (2) explosive charge weight. The mitigation measure using steel polypropylene hybrid fiber-reinforced concrete (HFRC) was also explored to improve the performance of the sections studied. It is observed from results that the displacement of tunnel increases with an increase in charge weight and decreases with an increase in d/H ratio. It can be observed from damage assessment that tension accumulation is the governing factor for the damage of reinforced concrete sections of the cut and cover tunnels and the extent of damage is observed to be reduced by increasing d/H ratio, i.e., increasing burial depth. The intermediate wall of the cut and cover section is the most critical element to avoid the progressive collapse of the structure. It is observed that the use of HFRC in the tunnel as an alternative to conventional concrete improves the blast-resistant capacity of the tunnel.