Bottom Slab Research Articles

Correlation analysis of long-span cable-stayed bridge strain response with environmental and operational variations based on feature selection

The structural response of large-span bridges is significantly influenced by environmental and operational conditions. This study employs a data-driven approach, which utilizes various techniques such as multiple linear regression, best subset regression, stepwise regression, Lasso regression, Ridge regression, and ElasticNet regression to analyze in detail the effects of environmental variables (temperature variables including temperature principal components, lateral temperature gradients, and vertical temperature gradients), and traffic loading on bridge strain response. Based on the analysis of 21 months of health monitoring data from a newly constructed cable-stayed bridge, Lasso regression is shown to perform best in predicting strains on the bridge deck and bottom slab. Furthermore, sensitivity analysis identifies several key influencing factors and quantifies their relative contributions to the strain. Although the 10-min average of the strain due to traffic loading has a minimal impact, the root mean square of the strain shows a significant correlation with the cumulative gross vehicle weight during busy traffic periods. The methodology proposed in this study helps to understand the strain response patterns of large-span bridges from a data perspective, and provides an effective approach to establishing a strain baseline model that eliminates environmental and operational variations.

Shear Capacity Prediction of Extremely-Loaded Box Culvert on Elastic Soil Using Artificial Neural Network

A box culvert, buried at shallow depths beneath roadways, may experience deflections caused by the dynamic impact of traffic loading and the vertical pressure exerted by the soil fill. A computational model commonly employed used to various engineering issues, including those in geotechnical applications, is the beam-on-elastic-foundation model. In this context, the Moment Distribution Method (MDM) must be applied to account for the elastic foundation. To achieve this, the internal forces acting on the ends of both exterior and interior walls are transferred to the beam-like bottom slab of the culvert, which rests on an elastic soil bed. Subsequently, the secondary internal forces are determined by refining the structural parameters, taking into account the characteristics of the elastic soil bed. This study presents the development and application of an Artificial Neural Network (ANN) model to predict the shear capacity of box culverts on elastic soil under traffic loading conditions. The proposed model is trained and validated using a comprehensive database of beam on elastic foundation solutions. The input parameters include the geometrical and mechanical properties of the culvert and the soil, as well as the loading conditions. The results of the ANN model show R2 values of 0.9633 and 0.9581 for the training and testing sets, respectively, indicating the model's excellent accuracy. These findings suggest that the ANN model can reliably predict the shear capacity of culverts.

Assessment of the Crack Level in Silo Foundations Due to Settlement

A silo is a structure used to store bulk materials (bulk materials). Silos are generally used in agriculture as storage for grains and animal feed. The foundation silo must be designed to withstand the forces generated and accommodate the movements transmitted to the structure and foundation by the seismic ground motion design. The dynamic properties of the soil, the anticipated ground motion, the design basis for the strength and energy dissipation capacity of the structure, and the dynamic characteristics of the soil should be included in determining the foundation design criteria. In PT X, SILO structure serves as a place for livestock feed production, with the hope that it can last for a relatively long time. The condition of the existing SILO structure is currently some cracks in several parts of the piles and the bottom slab. The results of the visual inspection in the field regarding the condition and level of cracking in the silo foundation were compiled into a matrix inspection table using four categories: category 1 indicates no repairs needed, category 2 marked in green, represents an acceptable cracking condition with minor repairs, category 3 marked in yellow indicates moderate cracking that requires attention, and category 4 marked in red signifies major cracking or unacceptable conditions that require structural repairs. The results of the field inspection indicate that approximately 57% of the concrete slab foundation of the silo requires needs attention or repair. The condition of the plate/slab structure has some cracks measuring 0.3mm - 0.5mm, but injection and patching have been carried out. As for the condition of the silo foundation, about 30% requires needs attention and repair as well.

Shaking table tests on transverse seismic performance of a new type of combined prefabricated utility tunnel

Due to the limitation of hoisting weight in the construction site, standard segments of prefabricated utility tunnels usually have only one or two cabins, making it difficult to carry out the multi-cabin prefabricated utility tunnel construction. To solve this problem, two rows of prefabricated utility tunnels are often combined side by side with foam board filled in between them in engineering practice, forming a new type of combined prefabricated utility tunnel. However, there is currently no study on the influence of the interaction between two rows of prefabricated utility tunnels on the seismic performance of combined tunnels. This paper conducted shaking table test of the new type of combined prefabricated utility tunnel under transverse excitation. For the purpose of comparison, shaking table test of single prefabricated utility tunnel was also conducted. To simplify the model making, the combined tunnel was combined by two rows of single-cabin tunnels. Standard segments of utility tunnels were made by microconcrete and assembled longitudinally by bolting. The soil acceleration, utility tunnel strain, and relative displacement between two cabins of the combined tunnel were measured during the tests. Numerical simulation of the test cases was conducted. The numerical results matched the test results well. The research results show that the seismic performance of the combined tunnel is superior to that of single tunnel, because the interaction between two cabins of the combined tunnel reduces the relative deformation between the top and bottom slabs of each cabin. The relative displacement between two cabins of the combined tunnel is much smaller than the initial spacing between the two cabins, and there will be no violent collision between two cabins of the combined tunnel. This study may be of a reference for seismic design of the new type of combined prefabricated utility tunnel.

Mechanical Response and Anti-Reflective Crack Design in New Asphalt Overlays on Existing Asphalt Overlaying Composite Portland Cement Pavement

A detection and evaluation system containing a two-level index of structural integrity and bearing capacity was constructed based on ground-penetrating radar (GPR) and a falling weight deflector (FWD). This system was constructed to solve problems with the detection, evaluation, and structural and material design of asphalt rehabilitation for the prevention and control of asphalt reflection cracks in asphalt overlaying composite Portland cement pavement. Based on the detected data from the GPR and FWD, the reasonable and recommended thickness range of the stress-absorbing layer was determined by the finite element method, and the optimization design of an anti-reflective crack structure is proposed. Furthermore, a material design and engineering application of the stress-absorbing layer was carried out. The results show that an additional 10 cm layer of repaved asphalt can reduce temperature stress by 64.1%, reduce fatigue stress by 29.3% at the cement slab bottom, and extend the service life by 23.1 years. The reasonable thickness of the stress-absorbing layer ranges from 1.6 cm to 2.0 cm, and the recommended structural combination design is a 4 cm SMA-13 upper layer, a 4 cm AC-16 lower layer, and a 2 cm stress-absorbing layer overlaying existing asphalt overlay. The impact toughness of the designed stress-absorbing layer is 1.05 times and 1.44 times that of the other stress-absorbing layer and the AC-16 asphalt mixture, respectively, which have been successfully used for more than 5 years. The recommended design rehabilitation has good engineering application. The uniformity of the stress-absorbing layer can reach 63%, and an anti-reflective crack effect is expected. The results of this study provide design methodology and experience for composite pavement repaving.

Experimental and numerical investigation on flexural behavior of non-prestressed concrete precast bottom slab with a section steel and two ribs

Experimental and numerical investigation on flexural behavior of non-prestressed concrete precast bottom slab with a section steel and two ribs

Research on Temperature Distribution and Gradient Prediction of U-Shaped Girder Bridge under Solar Radiation Effect

With the development of bridge engineering, U-shaped girder bridges have been applied in numerous bridge designs due to their structural characteristics. However, the U-shaped girder bridge is sensitive to solar radiation effects, leading to uneven temperature distributions that can affect the service performance of the structure. Thus, this study proposes an analysis method for the temperature distribution of U-shaped girder bridges and develops a prediction model to estimate temperature gradients. First, an improved ASHRAE clear sky model is proposed to calculate the structural shadow areas under sunlight, which provides a basis for the numerical simulation of U-shaped girder bridges under solar radiation effect. Then, a three-dimensional finite element model of the U-shaped girder bridge is established, and its correctness is verified by comparing with the actual temperature data. The temperature distribution of the U-shaped girder bridge under solar radiation is simulated using the verified model to obtain the maximum temperature difference and temperature variation characteristics. Finally, a prediction model for the temperature gradient is developed using nonlinear fitting approaches, and its accuracy is confirmed through comparison with actual data. The results indicate that the temperature distribution of the U-shaped girder bridge has minor changes along the longitudinal direction, while there are significant changes in the transverse distribution; the temperature distribution exhibits nonlinear changes in the height direction of the two side webs and the lateral direction of the bottom slab, with the maximum temperature difference reaching 17 °C; the fitting effect of the prediction model is very good, the correlation coefficients of the fitting curve and the actual data are all greater than 88%, providing a basis for the analysis of the temperature effects on U-shaped girder bridges and its application in design specifications.

Shear resistance test analysis and calculation method of shear capacity of UHPC-NC beam without web reinforcement

In order to study the failure phenomenon and shear resistance performance of UHPC-NC beams without web reinforcement, shear resistance tests were carried out on 15 UHPC-NC beams without web reinforcement. The variation parameters were shear span ratio, web thickness, steel fiber content, and compressive stress level. The load-deflection curve, failure phenomenon and crack development of the test beam are analyzed. The test results show that the joint between the top plate and the bottom plate of UHPC-NC I-beam without web reinforcement is the weakest, and the cracked web is easy to be “cut off” at the joint; The “banding crack area” of web is closely related to the shear span ratio, and the width of ribbon area increases with the increase of shear span ratio. The shear capacity of UHPC-NC I-beam without web reinforcement decreases with the increase of shear-span ratio. The shear capacity increases with the increase of web thickness and compressive stress level. The shear capacity has little relationship with steel fiber content, and the initial stiffness of the structure can be improved by applying prestress. Finally, considering the influence of the top slab compression-shear zone and the bottom slab tension-shear zone on the shear capacity of UHPC-NC prestressed composite beams without web reinforcement, the corresponding calculation method of shear capacity is given based on the modified compression field theory and the idea of sub-item superposition, and the applicability of the calculation method is verified by the test results.

Comprehensive Study on Design and Construction Methodology of Precast Box-Type Minor Bridge

Abstract: Bridges are crucial elements in modern transportation infrastructure, facilitating connectivity across different points on roads. In areas with challenging topography and site conditions, such as rivers or streams, it becomes essential to construct structures that allow for the unobstructed flow of water. These structures, commonly known as bridges and culverts, are vital for maintaining natural water flow. The flow rate through these water bodies is a key consideration in the design of bridges, culverts, and other drainage structures. This study focuses on the design of precast box type minor bridge, exploring alternative design modules that incorporate fixed and hinged end condition for both top and bottom slabs of single and double box cells. The objective is to determine the optimal design configuration for box Type Minor Bridge components, balancing considerations of functionality, efficiency, and cost-effectiveness.

Observed Characterization of Multi‑level Retaining Structure for Deep Excavation of Subway Station

Traditional support structures cannot meet the complex conditions of different excavation depths and areas in underground transportation hubs. On the basis of fully considering the spatial position relationship of foundation pit groups, this article proposes a multilevel retaining system that meets the requirements of multilevel foundation pit excavation. The evolution law of the support structure during the excavation process of the inner pit was explored using on-site monitoring and numerical simulation methods. The results indicate that the excavation of the inner pit reduces the passive earth pressure, and the deformation of the outer support structure can be effectively suppressed by setting a retaining structure or a bottom slab in the bench zone. The excavation of the inner pit causes significant vertical deformation of the support structure adjacent to the foundation pit, while the impact on the structure far away from the foundation pit is relatively small. According to the contact force chain and soil pressure between the two rows of support structure, the soil in this area is divided into a “relaxation zone” and a “compression zone.” The evolution mechanism of earth pressure in the case of mutual-effect failure between two rows of piles is revealed. This paper addresses the deformation properties of multilevel support structures as well as the mechanism of earth pressure evolution between structures.

Investigation of Concrete Damage on a Prefabricated Steel Spring Floating Slab Track by Finite Element Modelling

To investigate the concrete damage of prefabricated steel spring floating slab tracks (SSFST), a three-slab prefabricated SSFST system was established using the ABAQUS finite element software. Full trainload conditions and fatigue load conditions of a train passage were successively applied to the system. Plastic damage and fatigue damage of the floating slab were simulated based on concrete damage plasticity theory and model code, respectively. For comparison, a simulation of the fatigue experiment was conducted. Parametric analyses of the concrete strength and isolator stiffness were also performed. The results show that the maximum positive and negative bending moments of the floating slab throughout the loading stage are close in value. The positive bending moment causes stress concentration on the top slab surface which leads to plastic damage and low-cycle fatigue damage, while the negative bending moment causes middle-level elastic tensile stress on the bottom slab surface which leads to high-cycle fatigue damage. Under experimental conditions, damage on the bottom surface is much more severe, while the upper part is undamaged. Improving the concrete strength can reduce both kinds of damage, while increasing the isolator stiffness can only mitigate the high-cycle fatigue damage. Accordingly, recommendations are provided for improving fatigue experiments and structural design of prefabricated floating slabs.This study can inform the design and maintenance of the prefabricated SSFST system, ultimately enhancing their safety and longevity.

Ispitivanje poprečne unutarnje sile sandučastog nosača primjenom principa varijacije energije

This study investigated the transverse internal force of a box girder with a trapezoidal cross-section under eccentric loading. The effects of the box girder distortion and frame shear difference on the transverse internal force were considered. An energy variation method based on the minimum potential energy principle was adopted for transverse internal force analysis of the frames. The variable shear difference of the top slab was considered an unknown quantity, and a fourth-order governing differential equation was established. The transverse bending moment of the frame was obtained by solving for the shear difference. Two examples were used to verify the proposed method and analyse the differences between the transverse internal force results calculated using different methods. The effect of the distribution of the box-girder distorted transverse bending moment on each slab was investigated for various stiffness ratios. The results showed that the transverse internal force of the box girder calculated using the proposed method agreed well with the finite element results, with a maximum error of less than 9.68 %. When the stiffness ratio of the box girder increased, the distribution of the distorted transverse bending moment on the top slab increased, whereas that on the bottom slab decreased.

Optimal arrangement of AE sensors for prestressed hollow slabs based on AE propagation characteristics

Acoustic emission (AE) health monitoring is crucial for effective data collection, rational monitoring of results, and economical engineering applications in prestressed hollow slabs. To achieve an optimal sensor arrangement, experiments were performed to measure AE attenuation with different propagation paths in both the longitudinal and transverse directions of a full-scale prestressed hollow slab. Then, the AE amplitude and AE energy are chosen as evaluation indexes to investigate the hybrid arrangement of AE sensors under multiple damage conditions. The results indicate that when the AE signal propagates along the longitudinal direction of the prestressed hollow slabs with the same propagation distance, the attenuation in the steel strand is smaller. Additionally, the attenuation in the concrete directly under the bottom strand is smaller than that in the concrete between the bottom strands. The attenuation of AE propagation is smaller in the complete hinge than in the defective hinge. In terms of transverse propagation, the attenuation of AE signals is less in the bottom slab concrete than in the bottom slab steel strands. At the longitudinal 1/3 section of the prestressed hollow slab, the amplitude attenuation rate shows a turning point, and the variation in the attenuation rate of the AE signal is relatively small. For greater efficiency, it is recommended to position the sensors in the middle part of the hollow slab hinge joint and the bottom slab cross section, as well as on the concrete surface directly under the bottom slab strand.

Study on precursor information and disaster mechanism of sudden change of seepage in mining rock mass

Abstract Changes in the stress field and seepage field of mining unloading are one of the important causes of deformation and destabilization of the rock body of the bottom slab. With the increase of mining intensity and depth, the disaster of water influx on the bottom plate under the dual action of mining unloading and pressurized water has become one of the main problems restricting the efficient and safe mining of coal. Based on the research background of confined water inrush from Ordovician limestone floor in North China Coalfield, the numerical analysis revealed that mining unloading concentrates stresses, increases deformation, and increases the plastic zone and permeability range. Based on laboratory acoustic emission and mechanical tests, it is found that the peak of acoustic emission ringing number can be one of the precursor information of limestone seepage mutation. This study reveals the evolution law of rock body deformation and permeability under the unloading path, and the research obtains the unloading seepage and water gushing disaster mechanism of the subgrade rock body.

Radial force analysis of long span bridge with trapezoidally corrugated steel webs

The study numerically and theoretically investigates the radial force effect of long span prestressed concrete (PC) box girders with trapezoidally corrugated steel webs (TCSWs). It reveals that under the influence of radial forces, the curved prestressing tendons in the bottom slab in long span box girder bridges with TCSWs exhibited higher levels of stress and deflection compared to conventional concrete box girder bridges due to the accordion effect of the TCSWs. Furthermore, this study simplifies the radial forces as concentrated forces of PC box girder with TCSWs. Based on this simplification, a formula is derived to accurately calculate the magnitude of these radial forces. Through parameter analysis of the power exponent in the equation defining the curve profile of the bottom slab, it was observed that lower power exponents result in more significant radial force effects. Finally, to eliminate the radial force effect, the study innovatively proposed an optimized structural scheme by adopting horizontal bottom slab at midspan and arranging horizontal diaphragms uniformly across the entire longitudinal span of the bridge. A contrastive study suggested that the horizontal arrangement of internal prestressing tendons in the bottom slab at midspan could effectively eliminate the negative impact of the radial force effects and greatly improve the overall bearing capacity of the box girders with TCSWs.

Cyclic Loading Test Conducted on the Bottom Joints of a Hybrid Precast Utility Tunnel Composed of Double-Skin Sidewalls and a Precast Bottom Slab

Four full-scale specimens were constructed, including two hybrid precast specimens with a haunch (height: 150 mm, PUT-H) and without a haunch (PUT). Additionally, two cast-in-place (CIP) comparative specimens (referred to as RUT-H and RUT) were included, all of which underwent reversed cyclic loading. The results showed that the four specimens suffered flexural damage at the ends of the sidewall and displayed similar hysteresis loops shapes. The bearing capacity of the PUT specimen was 2.7% higher than that of the RUT, while the bearing capacity of the PUT-H specimen was 8.5% lower than that of the RUT-H. Additionally, the displacement ductility values of the precast specimens PUT and PUT-H were 2.98 and 2.46, respectively, which are 11.3% and 3.53% lower than those of the corresponding CIP specimens. The haunch increases the local stiffness of the component, exerting a notable influence on the bearing capacity and displacement ductility of the specimens, increasing the bearing capacity by 20% and decreasing the ductility by 21%. Moreover, an assessment conducted using the criteria outlined in ACI 374.1-05 indicated that the four specimens exhibit excellent seismic performance.

Effect of main reinforcement on box girder flexural and shear behavior

The primary goal of the current study is to determine, in a lab setting, how the main longitudinal reinforcement ratio affects the behavior and load capacity of single-cell box girders made of reinforced concrete. Three specimens were cast and tested, each with a length of 1600 mm, top and bottom slab has a uniform thickness of 50 mm, an upper flange width of 430 mm, a bottom flange width of 300 mm, and a height of 230 mm. The three box girders are reinforced by having three distinct ACI 318–19 reinforcing ratios: the minimum, the maximum, and average of them, i.e., the reinforcing ratios were 0.0033, 0.0184, and 0.00591, respectively. All three specimens were subjected to 2-concentrated forces. For the tested box girders, the cracking load, crack pattern, failure load, deflection, average strain values on the concrete surface, strain values in steel bars, and failure mode were recorded and discussed. Experimental work has proven that increasing the ratio of the main steel reinforcement from minimum to maximum, passing through the average between them, i.e. 79-425%, leads to higher load capacity by about 66.67-99% and midspan deflection decrease by about 28-36%. It was also concluded that steel reinforcement yield occurred at both minimum and average main reinforcement resulting in flexural failure. While at the maximum of the main reinforcement, yield did not urge but rather a failure occurred in another place which is the shear, whose stirrups suffered from yield this time

Rebar detection: Comparison of stepped frequency continuous wave and pulsed GPR

Reinforced concrete structures are widely used in civil engineering owing to their versatility, strength, and durability. One of the most recommended methods for rebar mapping is Ground-Penetrating Radar (GPR) because of its non-destructive and non-invasive character. In concrete mapping, GPR is mainly used for locating subsurface objects (rebars, tendons, ducts), measuring concrete cover, mapping mesh configuration (spacing), and detecting bottom of slab. To achieve these, concrete scanning GPR practitioners often need very high-resolution images. This work presents a comparison in rebar mapping between two GPR systems with different modulation techniques: Stepped frequency continuous wave (SFCW) and pulsed radar. The SFCW system used has a frequency range of 400-6000 MHz, while the pulsed system used a ground-coupled central frequency antenna of 2.3 GHz. Measurements were conducted on laboratory specimens, with rebar diameters ranging from 8 to 32 mm. Three different specimens were used, with one for calibration and other two to analyze both the horizontal and vertical resolutions of the frequency antennas.

Fire Resistance of Prestressed Multispan Steel Truss Composite Slab

Prestressed steel truss composite slab is composed of a precast prestressed bottom slab, a steel truss, and a postcast concrete layer. In order to investigate the fire resistance performance of prestressed multispan steel truss composite (STPC) slabs under the coupled effect of high temperature and load, four specimens of such composite slab containing two spans with various postcast concrete layer thicknesses were fabricated. Fire experiments were conducted following the ISO 834 standard temperature–time curve. Two of the specimens underwent two-span fire experiments, while the other two underwent single-span fire experiments. During the experiment, the bottom of the multispan STPC slabs exhibited serious bursting under fire and the precast concrete layer at the bursting locations fell off. The experiment result showed that the degree of bursting was much higher than that of nonprestressed composite slabs and single-span slabs. Although bond failure was observed at the composite interface where horizontal cracks developed, the STPC slabs still performed well in terms of load bearing, which could be attributed to the contribution of the steel truss. Under the coupled action of high temperature and load, concrete cracks were prone to occurring at the cut-off position of the top reinforcement near the supports; therefore, the anchorage length of these reinforcing bars should be appropriately extended. The damage to the STPC slab specimens after fire was found to be more serious for those with a less-think postcast concrete layer. In the single-span fire experiments, the structural performance of the unfired span was not prominently affected. Due to the bursting of the precast layer, the thickness of the STPC slabs was reduced, resulting in decreases in the thermal insulation and the fire resistance limit. The fire resistance limits of the STPC slabs with 60 mm and 80 mm postcast concrete layers were 90 min and 130 min, respectively. When a high fire resistance limit of the STPC slabs is required in a design, it is recommended that the thickness of the postcast concrete layer be no less than 60 mm.

Analytical theory of composite beams with CSWs using the state space method

Based on the zig-zag theoretical model of corrugated steel web beam (CSW), the governing equations in the form of state equations are derived and their analytical solutions are obtained for different loads, variable cross-sections and boundary conditions. Through numerical examples, it is verified that the bending moment, deflection and stresses predicted by the present analytical method have a good agreement with the results of the three-dimensional finite element model. The applicability of the present method for non-prismatic continuous beams with CSWs under different loads is also demonstrated. Meanwhile, it is found that the quasi-plane assumption is still valid in non-prismatic continuous beams with CSWs. Through quantitative analysis of the flexural stresses in the top and bottom slabs, it is confirmed that the zig-zag theory in this study can well reflect the accordion effect of CSWs. Because of the inclined bottom slabs in the non-prismatic beams with CSWs, the Resal effect on the shear stresses in the CSWs and bottom slabs, which is caused by the vertical component of the axial force in the bottom slab, is discussed. A refined shear formulation is developed for more accurate shear stresses in the CSWs and bottom slabs, which provides fundamental theoretical support for the strength prediction of the non-prismatic beam with CSWs.