Top Slab Research Articles

Modeling of in-plane floor flexibility in existing reinforced concrete buildings

The paper addresses the problem of determining the mechanical characteristics of an orthotropic slab that best represents the in-plane behavior of a complex reinforced concrete (RC) floor system. To represent the structural behavior of the real RC floor, a reference model composed of solid finite elements is developed. The mechanical parameters of the equivalent orthotropic slab are determined by different homogenization techniques. In particular, two numerical algorithms and an analytical procedure to derive the elastic parameters of the equivalent slab representing the in-plane behavior of a single floor cell are proposed. Then, to determine which homogenization technique best predicts the structural behavior, representative one-story and six-story structures are modeled using both the equivalent slabs obtained using the three proposed techniques and the reference floor model. A discussion of the suitability of modeling floor in-plane flexibility taking account of only the top RC slab, for the considered case studies, is also provided.

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.

Seismic Retrofit Case Study of Shear-Critical RC Moment Frame T-Beams Strengthened with Full-Wrap FRP Anchored Strips in a High-Rise Building in Los Angeles

This paper discusses the iteration of a seismic retrofit solution for shear-deficient end regions of 19 reinforced concrete (RC) moment-resisting frame (MRF) T-beams located in a 12-story RC MRF building in downtown Los Angeles, California. Local strengthening with externally bonded (EB) fiber-reinforced polymer (FRP) fabric was chosen as the preferred retrofit strategy due to its cost-effectiveness and proven performance. The FRP-shear-strengthening scheme for the deficient end-hinging regions of the MRF beams was designed and evaluated through large-scale cyclic testing of three replica specimens. The specimens were constructed at 4/5 scale and cantilever T-beam configurations with lengths of 3.40 m or 3.17 m. The cross-sectional geometry was 0.98 × 0.61 m with a top slab of 1.59 m in width and 0.12 m in thickness. Applied to these specimens were three different retrofit configurations, tested sequentially, namely: (a) unanchored continuous U-wrap; (b) anchored continuous U-wrap with conventional FRP-embedded anchors at the ends; and (c) fully closed external FRP hoops made of discrete FRP U-wrap strips and FRP through-anchors that penetrate the top slab and connect both ends of the FRP strips, combined with intermediate crack-control joints. The strengthening concept with FRP hoops precluded the premature debonding and anchor pullout issues of the two more conventional retrofit solutions and, despite a more challenging and labor-intensive installation, was selected for the in-situ implementation. The proposed hooplike EB-FRP shear-strengthening scheme enabled the deficient MRF beams to overcome a 30% shear overstress at the end-yielding region and to develop high-end rotations (e.g., 0.034 rad [3.4% drift] at peak and 0.038 rad [3.8% drift]) at strength loss for a beam that, otherwise, would have prematurely failed in shear. These values are about 30% larger than the ASCE 41 prescriptive value for the Life Safety (LS) performance objective. Energy dissipation achieved with the fully closed scheme was 108% higher than that of the unanchored FRP U-wrap and 45% higher than that of the FRP U-wrap with traditional embedded anchors. The intermediate saw-cut grooves successfully attracted crack formation between the strips and away from the FRP reinforcement, which contributed to not having any discernable debonding of the strips up to 3% drift. This paper presents the experimental evaluation of the three large-scale laboratory specimens that were used as the design basis for the final retrofit solution.

Experimental and numerical studies on prestressed concrete box girders strengthened with PVA-ECC and external prestressing

To improve the shear capacity and repair shear cracks in prestressed concrete box girders, a novel strengthening method utilizing Polyvinyl Alcohol-Engineered Cementitious Composite (PVA-ECC) was proposed and studied. The integrated method consisted of section enlargement with PVA-ECC and decentralized prestressing using prestressed steel strands, which were embedded in the PVA-ECC after being prestressed and bonded. Field investigations were conducted to study and evaluate the effectiveness of this method under random traffic loads using health monitoring systems. Additionally, based on engineering practices, three finite element models (unreinforced box girder, box girder with strengthened side web only, and box girder with strengthened entire web) representing different construction sequences were established to investigate changes in shear behavior before and after strengthening. Finite element analyses were conducted under various loading conditions, and the results showed that the stress response of the webs decreased by approximately 30–40 % after strengthening. Additionally, the deflection of the top slab decreased by approximately 25–35 %. The results from monitoring data and finite element analyses demonstrated that the proposed strengthening method effectively enhanced the shear performance of the box girder webs. This research can provide a reference for strengthening and evaluating existing prestressed concrete box girders.

Capacity reinstatement of reinforced concrete one-way ribbed slabs with rib-cutting shear zone openings: Hybrid fiber reinforced polymer/steel technique

This study examined the use of two configurations for capacity restoration of reinforced concrete (RC) one-way ribbed slabs containing openings in shear zones. Four specimens of half-scale comprised three ribs in addition to a top RC slab. The test plan included a control specimen without openings, one with two rib-cutting shear openings, one strengthened using a blend of carbon FRP (CFRP) composites and steel plates, and another retrofitted with a combination of glass FRP (GFRP) composites and steel plates. The two strengthening schemes were found successful at fully restoring the ultimate load of the specimens. The ultimate load of specimen strengthened using the hybrid CFRP/steel system exceeded the control slab without openings by 52%. However, in the other specimen where a mix of steel plates and GFRP sheets was used, the load capacity was only 5% less than the control specimen without openings. While the dissipated energy and stiffness were reinstated and improved for the hybrid CFRP/steel system, they were partially restored for the GFRP/steel system. Additionally, a prediction approach was developed to estimate the maximum load of the slabs. The developed approach considered potential shear and flexural modes of failure, providing close predictions of the ultimate load.

Research on the method of identifying vertical earth pressure of hinged prefabricated culvert box culvert on the top slab

In China, several expressways have been designed as prefabricated box culverts with hinge connections, which have different structural features from the prefabricated culverts in other countries. The difference would contribute to the culvert–soil interaction of prefabricated box culverts, which could affect the earth pressure on the culvert. Based on the field test and numerical simulation method, a hinged prefabricated box culvert (HPBC) with a span of 4 m and a rise of 4 m was investigated, which was applied to the Xi-Yu expressway in China. The objective of this research was to investigate the vertical earth pressure on the top slab of the HPBC culvert at different backfill heights through the field tests. The FLAC3D software was employed to conduct further analysis of the effects of backfill height, backfill modulus, and foundation modulus on the vertical earth pressure on the top slab of HPBC. The differences between the HPBC and monolithic box culvert (MBC) were also examined. Furthermore, a revised method for calculating the vertical earth pressure on the top slab was put proposed and compared with the AASHTO method for calculating earth pressure on the top of culverts and the values taken from the Chinese culvert design code. The proposed method is capable of improving the accuracy of the earth pressure approach, making it more representative of actual conditions. Subsequently, the sensitivity analysis of backfill height, backfill modulus and foundation modulus to the vertical earth pressure concentration coefficient of the top slab was carried out by using the principle of orthogonal array analysis and the modified calculation method proposed in this paper. The findings of this study offer valuable insights into the determination of culvert top earth pressure of HPBC.

Effect of live loads on top slab of cast-in-place reinforced concrete box culverts

Reinforced concrete box culverts (RCBCs) designed according to old codes, using lighter truck weights (e.g., H15), may require posting when rated for current design and permit vehicles. When load ratings are calculated based on current AASHTO Specifications, they can be negatively affected by the conservative live-load attenuation through soil fill. This study evaluates the positive bending strains induced by live-load distribution through soil fill when load rating cast-in-place (CIP) RCBCs. Eighteen (18) single and multicell RCBCs in Kentucky were load tested and the effects of truck live loads analyzed. Fill heights, HF, varied from 0 m (0 ft) to 3.57 m (11.7 ft), clear cell spans, S, from 3.05 m (10.0 ft) to 6.71 m (22.0 ft), and culvert spans from 6.71 m (22.0 ft) to 18.59 m (61.0 ft). Field data were collected using strain gauges attached to the interior surfaces of culverts. Irrespective of how many cells the RCBCs had, strain variations with fill height in the top slabs were similar. At fill heights greater than 3.05 m (10.0 ft), maximum strains in the top slabs measured less than 10 microstrain, a value at which live-load effects are considered negligible. Combining live-load strains measured on the Kentucky culverts with ones from field tests in Missouri and Louisiana, a live-load tensile strain envelope is proposed to load rate the top slabs of RCBCs for positive bending when cell spans are less than 4.6 m (15.0 ft).

Numerical modeling of seismic performance of shallow steel tunnel

Advanced numerical models can be used to complement experimental results and further elucidate their findings. This is particularly true when certain scaled model “adjustments” are incorporated in the testing scheme to reduce the testing cost or schedule. This study conducts comprehensive finite element modeling to simulate large-scale shaking table tests conducted by Kim et al. (2023) [1] to evaluate the seismic performance of steel tunnels. The numerical model was calibrated by comparing its predictions with the experimental observations in the initial tests. The calibrated model was then validated by comparing its predictions with the results obtained from other test models and subjected to different input ground motions. The validated model was employed to comprehensively investigate the effects of the testing scheme parameters including the input motion time scaling, tunnel burial depth, and soil relative density. It was found that reducing the time scale factor during the tests led to decreased seismic responses. It was also found that the presence of overburden soil on top of the tunnel resulted in higher seismic bending moment values, and that higher overburden height increased both lateral and vertical soil pressures on the tunnel side walls and top slab. In addition, lateral soil distortion and tunnel deformations were found to be directly correlated with the overburden soil height. Furthermore, in the absence of overburden soil, there was a significant amplification in horizontal soil acceleration. The results demonstrated that lower-density sand bed experienced greater acceleration amplification and larger displacement, and the tunnel experienced larger lateral soil pressure and higher racking. Additionally, the results revealed that subjecting the same soil bed to several shaking tests affected its stiffness, and hence affected the test observations in the subsequent tests. This should be considered when planning shaking table tests. Finally, the strain values and racking ratios obtained from the numerical simulations and the shaking tests were in agreement with the values obtained from the FHWA procedure.

Flexural cracking behaviour and crack width calculation of steel-plate-reinforced ribbed UHPFRC deck panels

Ribbed ultra-high performance fiber reinforced concrete (UHPFRC) deck panels have been designed and implemented in buildings and bridges due to being increasingly slender, lightweight and tough. To further improve the crack resistance, this paper studies a neotype ribbed UHPFRC deck panel using steel plates and headed studs to reinforce the ribs. Bending tests were conducted to reveal the various crack and strain developments at different specimen parts with an aim to selecting the interesting primary-crack position and spacing. Then, theoretical calculation equations were proposed and verified on the differential strain, crack spacing and crack width for the interesting primary crack. The test results showed that the maximum crack width was invariably located at the rib instead of the top slab, and the primary-crack spacing varied from 52.1 mm to 151.2 mm after the cracks penetrated the whole rib into the top slab. The theoretical study showed that the tensile property of UHPFRC can be taken account by a two-line model, the shrinkage strain of UHPFRC as 556.5 με herein should be amended in the equation of the differential strain between reinforcement and UHPFRC. Besides, the crack spacing before and after the cracks penetrated the whole rib can be predicted by the standard AFNOR: 2016 and the headed-stud spacing, respectively. Finally, the theoretical crack-width calculation method was verified to have a satisfactory accuracy by comparing the calculated and test results with a percentage error within 4.0 %.

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.

Study and Analysis of Steel, RCC, and Composite Structure Comparison

In India, plain concrete is a common building material, especially for medium- and low-rise buildings. Even while steel is still widely used in high-rise structures and composite construction is less frequent, it's possible that composite construction could prove more beneficial in these projects. Reinforced concrete is often used in construction projects. Steel beams are put into concrete to make reinforced concrete, an efficient composite material. The distinguishing feature of composite construction is the secure joining and bending of two load-bearing structural elements into a single piece. When compared to RCC most steel frames, composite constructions are considered to be some of the least expensive and transient building materials. The main component of a composite construction is an I-section column embedded or encased in building materials, or a tube of steel filled with steel and concrete. Composed of cold steel plates plus mortar, Part I consists of a beam plus a plate for the deck. The beams are connected to the top slab using fire-resistant and robust shear connections. Keywords— Steel Concrete Composite Building, RCC building, Seismic Analysis etc.

Experimental and theoretical investigation of shear lag effect in twin box‐shaped composite girders of long‐span cable‐stayed bridges

AbstractSteel‐concrete composite box girders offer notable advantages such as high stiffness, excellent torsional performance, and light self‐weight, making them prevalent in large‐span bridges, particularly in cable‐stayed configurations. However, a persistent challenge arises from the shear lag effect in the concrete slab within the flanges induced by shearing interactions between the webs and flanges. Limited attention has been devoted to investigating the experimental and theoretical aspects of shear lag in long‐span cable‐stayed bridges with twin box‐shaped composite girders. This research addresses this gap by designing a segmental scale twin box‐shaped composite model specimen to simulate the cable spacing of the main girder in a cable‐stayed bridge, specifically targeting the shear‐lag effect. The study successfully captures the non‐uniform distribution of cross‐sectional strain in the top concrete slab. Subsequently, analytical strain solutions for the composite girder under mid‐span concentrated load and axial load are derived using the energy variation method. The theoretical model's applicability is then calibrated against experimental results. The investigation extends to the in‐situ testing of the Chibi Yangtze River Bridge, the world's largest steel‐concrete composite girder cable‐stayed bridge, boasting a main span of up to 720 m. An established finite element (FE) analysis model for the Chibi Yangtze River Bridge simulates the transverse stress distribution under typical construction conditions of CC6. Comparative analyses between the simulated results, calculated values from elementary beam theory, and the theoretical model against field‐measured values reveal that the FE model provides a more accurate estimation of the shear lag effect in the concrete slab. Notably, the FE model effectively reflects the bridge's characteristics and serves as a baseline for subsequent studies. This comprehensive investigation contributes significantly to the understanding and analysis of shear lag phenomena in twin box composite girders of cable‐stayed bridges. The integration of experimental, analytical, and construction site validations establishes robust tools for engineering design and the construction of safe and serviceable cable‐stayed bridges. The research augments knowledge regarding shear lag behavior and underscores the necessity to appropriately consider its effects in bridge analysis and design.

Fatigue performance of stud connectors in joints between top slabs and steel girders with corrugated webs subjected to transverse bending moments

Steel-concrete composite box girders with corrugated steel webs (CSWs) are broadly used in bridge engineering, in which the joints between top RC slabs and steel girders with CSWs are usually subjected to transverse bending moments caused by off-center vehicle loads. Stud connectors arranged in the joints usually bear repeated pull-out forces in this case and are prone to fatigue failure. Therefore, two reduced scale joints between top slabs and weathering steel girders with CSWs were designed and tested, on which variable amplitude fatigue loads were applied to investigate the fatigue performance of studs incorporated in the joints. The two joints presented similar fatigue behavior, i.e., cracks of not more than 0.26 mm in width appeared on the surface of the top slab during the fatigue loading, and the separation of the top RC slabs and the top girder flanges was observed; meanwhile, minute cracks developed along the welds connecting the CSW with the bottom girder flange, and the stiffness of the joints gradually decreased due to the accumulation of fatigue damage. The two joints underwent 2,650,000 and 2,103,600 load cycles respectively before fatigue failure occurred. After partially demolishing the RC slabs, several welded head studs in the joints were observed fractured at the roots and detached from the top girder flange. Whereafter, finite element (FE) models referring to the test joints were developed and analyzed, and the effect of the wave height (WH) of the CSW and the transverse row spacing (TRS) of studs on the distribution of pull-out forces among studs was investigated. It showed that the pull-out force bore by each stud in the joint was distributed unevenly even in the same row. Then, a modification factor α was introduced to revise the pull-out forces of studs calculated in the theoretical method. An equation to determine the factor was fitted, considering the effect of the WH of the CSW and the TRS of studs. Finally, the detail category for studs bearing pull-out forces in the joints was discussed based on the experimental results and the collected test data, and it was preliminarily recommended studs subjected to pull-out forces can be classified into detail category 45 specified by Eurocode 3 in fatigue design.

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

AbstractTo 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.

Web‐shear capacities of composite hollow‐core slabs with core‐filling and topping concretes

AbstractThis paper presents an experimental shear test performed to investigate the web‐shear capacity of composite hollow‐core slabs (HCS) with cast‐in‐place (CIP) concrete. Five HCS specimens are fabricated, and the presence of a topping slab and number of cores strengthened by core‐filling concrete are set as key test variables. The shear force–displacement responses of the specimens, patterns of cracks occurring in the HCS and filled cores, strain behavior of stirrups, and composite action between the HCS and CIP concrete are measured and analyzed comprehensively. In addition, the web‐shear capacity of the composite HCS with CIP concrete is calculated based on elasticity theory and the transformed area method, in which the residual stress ratio factor is introduced to reflect the shear contribution of the core‐filling concrete after its shear cracking. Moreover, a practical equation is proposed to allow structural engineers to easily perform the shear‐strengthening design of HCS via the core‐filling method. The detailed model and the simplified equation accurately evaluate the web‐shear capacities of the HCS specimens.

Flexural behavior of two-layer reinforced concrete slab with hollow cores

Flexural behavior of a concrete slab system with an optimal weight-to-strength ratio comprising layered and hollow-core slab structures was investigated using two-layered slabs with hollow cores (LS/HCS). Six slabs with dimensions of 180, 450, and 1600 mm were tested experimentally and numerically using ANSYS software. Each layered slab comprises a 90-mm-thick lightweight concrete bottom layer and a 90-mm-thick high-strength concrete top layer. Three parameters were studied: core diameter (58, 86, and 110 mm), reinforcement ratio (0.37%, 0.53%, 0.95%), and treatment type (bonding agent, nails). Treatment types were analyzed via push-out testing; both nails and agents connected the slabs with sufficient bond strength. A control slab with 86-mm core diameter, shear-span-to-effective-depth ratio of 4, reinforcement ratio of 0.53%, and agent material was used. Concrete, steel bars, and loading support plates were modeled using SOLID65, LINK180, and SOLID185 elements, respectively. Analytical results were validated experimentally. A parametric study analyzed other parameters affecting LS/HCS behavior, including compressive strength, opening numbers, core shape, applied loading type, added top steel reinforcement, slab type, and slab height. Core diameter reduction, increased reinforcement ratios, and using nails enhanced the failure load. The LS/HCS gives an optimum weight-to-strength ratio with a 33.672% reduction compared with solid slabs.

An Analytical Seismic Response for Rigid Underground Rectangular Tunnel Subjected to Incident P Waves

A diffraction model based on the diffraction theory of elastic waves for the dynamic response of underground rectangular tunnel subjected to incident P waves is established. The rectangular structure is assumed to be a movable rigid body embedded in a homogenous, isotropic, and linear elastic medium. One particular advantage of the model is that the effects of vital factors such as the rigid scattering, radiation scattering, as well as the two‐dimensional scattering effect, and the wedge diffraction during movement are fully considered. The numerical method is verified by comparing with experimental data and other solutions in the literature. In addition, a parametric analysis of the effects of the incident angle, surrounding rock medium, and aspect ratio on the tunnel is also presented. The results show that with the increase of the incident angle, different parts of the tunnel exhibit obvious nonuniform distribution characteristics, and the bending moment of the sidewall is greater than that of the top slab. When the impedance ratio exceeds 0.26, the influence of surrounding rock characteristics on the dynamics of structure is more obvious; with the increase of the aspect ratio, the peak values of axial force at the top slab increases, whereas it decreases at the sidewall.

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