RC Slabs Research Articles

Evaluation of the flexural stiffness of a lattice girder composite slab at the construction stage according to the lattice girder shape

Lattice girder composite slabs (LGCS) for use in construction stages are structures in which part of the lattice girder is embedded in precast concrete panels with a thickness of less than 100 mm. they serve as a permanent formwork supporting the casting loads of on-site concrete while constituting a portion of the RC slab. In this study, analytical research was conducted to evaluate the flexural stiffness of LGCS effectively and simply considering a range of variables. Based on the results, an Euler-Bernoulli beam-theory-based equivalent sectional analysis method is proposed. To achieve this, the study extracted the second moments of area (Iexp) from the experimental results of previous researchers and compared them with the second moments of area (Ibeam) calculated using the Euler-Bernoulli beam-theory-based sectional analysis, analyzing how the ratio (Ibeam/Iexp) varies according to the design parameters. Variable analyses over a wide range were conducted by expanding the types and ranges of variables, and the effects of different variables and ranges were analyzed by comparing the second moments of area based on an FE analysis of LGCS (IFEM) with those based on a beam analysis (Ibeam). Furthermore, to apply the equivalent sectional analysis method to LGCS, equivalent second-moment-of-area formulas were proposed through the equivalent neutral axis and equivalent arm length for each sectional element.

Experimental study on seismic behavior of a novel RC slab- SC wall joint based on UHPC and rebar – steel plate lap splices

Steel plate concrete shear walls (SC walls) have been widely used in practical projects because of great mechanical properties. For the application in nuclear power plant containment, the joint of specially shaped reinforced concrete slab and SC walls is difficult to design and construct. By using ultra-high performance concrete (UHPC), a new type of joint with the non-contact lapping method is proposed in this paper, which has advantages of simple construction, superior performance, suitable cost, and wide application range. Five RC-UHPC slab-shear wall joints were designed and tested under reciprocating load to study the effects of structures of lapping steel plate, shear-resisting methods, and interfacial reinforcing methods on the mechanical properties of the joints. The test results showed that the joints adopting the new structures were damaged for the flexural failure of the concrete area, with no damage to the joint zone, while the other specimens failed in the shear failure of the joint zone. It can be demonstrated that the ribs formed by bars and studs on the lapping steel plates are effective measures for non-contact force transferring, and interfacial reinforcing bars can improve the strength of the interface between concrete and UHPC. The force transferring efficiency of the new joints was close to or more than 90%, which indicates that the proposed joint structures can effectively realize the non-contact lapping force transferring. The design formulas and suggestions are proposed based on the analysis of the mechanism of new structures.

Behavior of steel-plate concrete wall-reinforced concrete slab joint with UHPC-strengthened lap-splice connection

The comprehensive integration of modular technology is the crucial pathway for advancing the upgraded Hua-long Pressurized Reactor (HPR1000). However, previous studies are limited and numerous challenges remain concerning the modular curved steel-plate concrete (SC) wall-reinforced concrete (RC) slab joint. This paper focuses on the behavior and design of the SC wall-RC slab joint through large-scale tests and numerical simulation. Two UHPC-strengthened non-contact lap splice (NS) connections, including versions with normal and headed rebars, were proposed to ensure effective load transfer and modular construction performance. The test results indicated that the four joint specimens subjected to cyclic loading did not experience lap splice failure but instead suffered interface shear failure and shear failure of the RC slab under shear-span ratios of 1.5 and 3.0, respectively. The excellent load transfer performance demonstrated by these two NS connections validates them as effective methods for this joint, with lap lengths of 21d for normal rebar and 13d for headed rebar deemed adequate. Besides, the developed three-dimensional FE model with non-linear spring element accurately simulated the test failure modes and F-Δ curves. The parametric study results recommended that the volumetric steel ratio of tie-bar should not be lower than 1.03 %. The tension of longitudinal rebars for normal and headed rebars can be fully transferred within 80 % of the designed lap length. Furthermore, a complete design method was established based on the load-transfer model, encompassing interfacial shear, lap length calculation and tie-bar configuration, and is applicable to SC-to-RC connections or joints.

Bayesian Inference and Condition Assessment Based on the Deflection of Aging Reinforced Concrete Hollow Slab Bridges

This paper presents a Bayesian inference framework for updating the structural rigidity ratio of aging hollow slab RC bridges using deflection measurements. The framework models the structural rigidity ratio as a stochastic field along the hollow RC slabs, using the Karhunen–Loeve (KL) transform to capture spatial correlation and variation. Bayesian inference is then applied using deflection data from static loading tests, supported by a finite element model (FEM) and a Kriging surrogate model to enhance computational efficiency. The posterior distribution of the structural rigidity ratio is derived using a Markov chain Monte Carlo (MCMC) sampler. The proposed method was tested on an RC bridge with hollow slabs, using deflection measurements taken before and after reinforcement. The Bayesian updates indicated increased structural rigidity ratios after reinforcement, validating the effectiveness of the reinforcement. The deflection predictions from the updated models closely matched the measurements, with the 95% confidence bounds encompassing most of the data. This demonstrates the method’s validity and robustness in capturing the structural improvements post-reinforcement.

Experimental and numerical study on behavior of demountable T-shaped bolt shear connectors in sustainable composite beams

This paper proposed a new type of demountable T-bolt shear connector to improve the disassembly efficiency of composite beams and realize the sustainable of the structure components. The shear behavior of nine groups of push-out specimens was experimentally investigated through monotonic loading push-out tests. The finite element analysis (FEA) models were validated against the test results, specifically in terms of the load-slip responses and failure modes of the T-bolt shear connectors in these push-out specimens. The obtained results show that all the specimens have no obvious deformation and cracks in the steel beam and RC slab. The separation between the slab and the steel beam is no more than 1 mm, indicating that the anti-lifting ability is excellent. Moreover, parametric analysis demonstrates that increasing the bolt pretension of the T-shaped shear connector and the friction coefficient between the bridge gasket and the steel beam significantly enhances the initial stiffness and ultimate strength of the shear connectors. However, the shear behavior is relatively insensitive to variations in the channel thickness and bolt grade. Based on regression analysis, a load-slip mechanical model has been proposed. This model accurately describes the mechanical properties of this type of shear connector, providing a theoretical foundation for the application of demountable composite beams.

Experimental studies on fully demountable P-DBSCs shear connectors in sustainable reinforced concrete beam-slab

To improve the increasingly serious environmental pollution and waste of resources in the construction of traditional buildings, a novel type of shear connector P-DBSCs (Demountable Bolted Shear Connectors with connection Plate) was designed. The shear performance of P-DBSCs in RC beam and slabs were comprehensively evaluated by seven push-out tests and secondary loading. The failure mode, load-slip curve, ultimate shear capacity and ductility of the specimens were carefully discussed. As illustrated by the experimental results, the failure mode of the 7 push-out specimens is bolt fracture with no obvious crack in the beam and slabs, and the demount-ability is excellent after failure. The ultimate slip of all specimens is greater than 6 mm, which meets the requirements of Eurocode 4. The ultimate strength of P-DBSCs shear connectors increased with the increase of steel box thickness and bolt diameter, it decreased with the increase of channel spacing. The ductility of P-DBSCs shear connectors increased with the reducing of channel spacing and bolt diameter. Additionally, the shear performance of P-DBSCs is insensitive to the strength of concrete of slabs. After the first loading, the ultimate shear resistance; ultimate displacement and initial stiffness of the push-out specimen decrease slightly in secondary loading, but the influence code of each parameter remain constant. Finally, a comparison of ultimate strength between the calculated value and the experimental results showed that the theoretical values given by the Eurocode 3, Eurocode 4 and code AISC360–16 were higher than the experimental values, which indicated that the calculations overestimated the shear capacity of connection. Based on this, two formulae were proposed to predict the friction-type shear capacity and pressure-type shear capacity of P-DBSCs and the efficacy of the proposed design formula was proved by the comparison with the test results, which provides a research basis for such shear connectors.

Flexural Improvement of RC Slabs by FRP or Steel Using Different Strengthening Systems and Novel Anchoring Techniques

An experimental study on reinforced concrete one-way slabs strengthened by various methods and materials is introduced in this paper. Innovative anchorage procedures are presented and evaluated to prevent the strengthening elements with FRP system from de-bonding at the initial stages. Externally bonded embedded in concrete cover (EBECC) strengthening technology was proposed to save the fiber strips from being subjected to heat, degradation, and sabotage. Nine RC one-way slabs, including a control slab and eight strengthened slabs, were cast. One RC slab was strengthened using externally bonded embedded in concrete cover (EBECC), whereas the other tested RC slabs were strengthened using either externally bonded (EB) or near-surface mounted (NSM) procedures. The following test variables are used in this study: the proposed anchors, the area of steel, the kind of material utilized in NSM rods (carbon fiber reinforced polymer (CFRP), glass fiber reinforced polymer (GFRP), and steel), and the strengthening scheme. The ultimate and initial cracking loads, load–deformation response, cracking patterns, and failure behavior were recorded and discussed. Additionally, a comparison of the stiffness, ductility, and energy absorption of the examined slabs was reported. The strengthened slabs by various techniques showed a boost in flexural strength that varied from 67 to 107% compared to the control slab. In addition, RC slabs strengthened by NSM-CFRP bars showed a maximum flexural capacity when compared with slabs strengthened by GFRP and steel bars. Also, the results supported the superiority of a novel end anchorage. The ABAQUS program was employed to conduct a finite element analysis (FEA) employing 3-D geometries to compare and assess the numerical performance of the identical slabs under similar test settings. The results showed good agreement between the experimental and numerical findings.

The effectiveness of metaheuristic algorithms modified with Fitness Distance Balance (FDB) method on RC slab bridge superstructure optimization

The effectiveness of metaheuristic algorithms modified with Fitness Distance Balance (FDB) method on RC slab bridge superstructure optimization

Investigating the Behaviour and Strength of Unbonded Pre-tensioned RC Slabs Subject to Flexural Loads

Unbonded pre-tensioned systems, in which tendons are greased and wrapped in plastic sheathing, have several benefits in comparison to bonded systems. However, analytical evaluation of their capacity is taxing due to the iterative compatibility conditions necessary to determine the system’s behavior using the empirical equations available in the literature. To investigate the behaviour and strength of unbonded pre-tensioned RC slabs subject to flexural loads, four simply-supported post-tensioned slabs with unbonded tendons were tested in flexure. Experimental failure loads and tendon strains were compared to the ACI 318-19 provisions. While the provisions for unbonded specimens were found to be accurate, the strain in the unbonded tendons exceeded the yield stress in all specimens, suggesting that ACI 318-19’s stress limitations on unbonded post-tensioned concrete are unwarranted. The unbonded system also showed better crack control at the failure stage when non-prestressing steel reinforcement is used when compared to system with no non-prestressing steel.

An experimental and numerical study on two-way RC slabs with openings strengthened by ferrocement technique

This study investigates the impact of creating a central square opening on reinforced concrete slabs and assesses the strengthening process using ferrocement layers. The investigated key parameters were the opening sizes, type, number, and extension length (outside the opening sides) of steel mesh layers used to strengthen the tested slabs. The experimental program included the preparation and testing of twelve two-way reinforced concrete slabs with identical dimensions, thickness, and reinforcement, but were different with respect to opening sizes and strengthening schemes. Four slabs acted as control specimens without strengthening; one was solid; the other three had different opening sizes; and the other eight slabs were strengthened using a ferrocement layer of 2 cm thickness applied on the bottom of the slab around the openings with various reinforcement schemes which included the number, type, and extension length (outside the opening) of steel mesh. All slabs were supported along the four sides with a clear span of 1 m in both directions and tested under four-point loading. The test results demonstrate that creating an opening in the slab decreases the ultimate load by 21.5 %, 31.9 %, and 40.7 % for opening dimensions (15, 25, and 35 cm), respectively. Using the ferrocement strengthening method helps to increase slabs’ flexural load-carrying capacities and reduce crack propagation from opening corners. The study found that strengthening specimens with opening sizes of 15, 25, and 35 cm increased their flexural load-carrying capacities by 26 %, 33 %, and 34 %, respectively. The expanded steel mesh type also resulted in a higher ultimate load by 6–7 % than the welded mesh type. When the length of the strengthening ferrocement layers was doubled, the ultimate load went up by 6–7 %. Increasing steel mesh layer numbers from 1 to 4 increased the ultimate load by 25 % to 40 % compared to the corresponding un-strengthened slab with an opening. The maximum load of a slab with an opening was achieved by applying a 2 cm thickness of ferrocement layer reinforced with expanded metal mesh, with extension lengths equal to the opening's length. The study utilizes commercial software ABAQUS for finite element analysis (FEA) to validate the experimental results, resulting in a great agreement between the analysis and the experimental findings.

Performance of NSM GFRP Retrofitted Postfire RC Slabs Under Monotonic and Cyclic Loadings

Performance of NSM GFRP Retrofitted Postfire RC Slabs Under Monotonic and Cyclic Loadings

An innovative formulation for predicting the punching shear behavior in two-way reinforced concrete slabs

Punching shear failure represents one of the most critical and perilous challenges that slabs may encounter under load-bearing conditions. Numerous studies have delved into the mechanics of punching shear and the methods for assessing the strength of slabs against punching shear failures. However, owing to the inherent complexity of the punching shear phenomenon, a universally applicable relationship has remained elusive. This article introduces a mathematical framework for analyzing the punching shear strength of two-way reinforced concrete slabs. The framework leverages a dataset of 218 laboratory test results compiled from various literature sources. To achieve the objective, the authors preprocessed the database, optimized the computational architecture, established the computational structure, and extracted mathematical relationships from the resulting system, respectively. The punching shear values generated by the computational model presented in this article were also compared with those determined using existing relationships. The framework surpasses existing methods by achieving a demonstrably lower error rate in predicting punching shear strength. This translates into a significant advantage for engineers, enabling them to design two-way reinforced concrete slabs with greater confidence and accuracy. Furthermore, it can be a valuable tool for assessing the viability of strengthening strategies for existing slabs or guiding rehabilitation efforts to ensure structural integrity. By facilitating these applications, the proposed framework holds immense promise for enhancing the safety, reliability, and lifespan of two-way RC slabs.

Performance of an EBR CFRP-strengthened RC slab using 24-h and cyclic load tests: a real case study

Performance of an EBR CFRP-strengthened RC slab using 24-h and cyclic load tests: a real case study

Low-velocity impact behavior of two-way SFRC slabs strengthened with steel plate

Structural systems and structural elements can often suffer severe damage or even completely collapse under the effect of sudden dynamic impact loading, which is a different type of loading that is not considered during their design. Research on how structures behave under impact loading and how they can be strengthened to perform better against this type of loading has increased to avoid such undesirable severe damage. Within the scope of this study, it is aimed to improve the behavior and increase the performance of two-way steel fiber-reinforced concrete (SFRC) slabs, one of the leading structural elements that can be affected by impact loading, using steel fiber concrete (SFC) and placing steel plates on the surface of the RC slab. Within the scope of the study, the effects of placing FRC as layers in different positions within the slab and placing the steel plate on different surfaces of the slabs were examined. Impact loading was applied using a drop weight test setup designed by the authors, and the acceleration–time, displacement–time, and impact loading–time behaviors of the RC slabs were measured and interpreted. The use of fiber concrete in RC slabs and strengthened with steel plates increased the maximum acceleration values by an average of 3% and 113%, respectively. The use of fiber concrete in RC slabs reduced the maximum displacement and residual displacement values by an average of 2% and 25%, respectively. Placing steel plates on the slabs reduced the maximum displacement and residual displacement values by an average of 270% and 199%, respectively. In addition, the energy absorption capacities of RC slabs were calculated, and how they were affected by experimental variables was examined. Numerical analyses of the RC slabs tested in the study were also conducted using ABAQUS finite element software, and the results obtained were compared with the experimental ones.

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.

Examining ACI Development Length and Strength Provisions for RC Slabs Strengthened with NSM GFRP

This study aims to investigate the strengthening effect of GFRP bars on the capacity of RC slabs when subject to flexure loading. The objective is to show the effect of debonding failure on the capacity of the GFRP strengthened slabs relative to the different variables used. The variables used are the different bonding lengths, diameters, and numbers of GFRP bars in strengthening RC slabs. The work presents the details of the adopted experimental investigation and the results of the flexural tests performed on twelve slabs with the different variables. These results are adopted to validate the currently available design provisions of the ACI code of practice for using NSM GFRP to strengthen RC slabs.

Modeling the initiation and propagation of complex networks of cracks in reinforced concrete plates

The present paper proposes a new finite element formulation for the analysis of RC slabs, accounting for concrete cracking and reinforcement yielding. The proposed formulation, developed within the framework of Lumped Damage Mechanics, considers that all inelastic effects are localized in lines and relates all numerical parameters to the mechanical properties of the slab. The proposed variational approach is presented as a Nash noncooperative equilibrium point. It is verified, numerically, that the proposed FE leads to mesh-independent results. Numerical simulations of some experimental tests are also presented. The results in terms of collapse mechanism, cracking network, and force-deflection curves showed that the model has significant accuracy, even for non-symmetric free clamped and simple supported boundary conditions. It is also shown, through the confrontation with experimental results, that the model correctly characterizes the initiation and development of complex networks of cracks.

Experimental and numerical study of G-HPC slabs rapidly repaired by G-HPC canvas and G-UHPC under contact detonations

The rapid repair of engineering structures damaged due to explosions can enhance the structural impact resistance after an explosion, thereby reducing the potential for casualties and property losses. A novel concrete canvas was firstly proposed based on G-HPC (geopolymer-based high performance concrete), UHMWPEWF（ultra-high molecular weight polyethylene woven fabric), and 3D BFG (basalt fiber grid) to rapidly repair engineering structures and render their blast resistance. A sequence of contact blast tests was systematically conducted to verify the feasibility of the proposed G-HPC canvas. A normal reinforced concrete slab and a steel-wire mesh (SWM) reinforced G-HPC slab were initially damaged by the contact blast loading, afterwards, the damaged concrete slabs were rapidly repaired by G-UHPC (geopolymer-based ultra-high-performance concrete) and the novel G-HPC canvas. The rapidly repaired concrete slabs were subsequently tested by contact blast loading. A precise 3D finite element model was then developed and calibrated based on the experimental results. Eventually, numerical simulations were performed to better understand the contribution of main parameters including repair materials filling the internal slab, steel-wire mesh, G-HPC canvas location and its thickness towards the improvement of the rapidly repaired slabs against the contact blast loading. The experimental and numerical results indicated that the SWM reinforced G-HPC slab has superior blast-resistance compared with the RC slab and the proposed method to rapidly repair the damaged slabs was feasible. The G-HPC canvas should be placed properly since the location of the G-HPC canvas is related to whether fragments are produced on the rear surface of the damaged slab. Increasing the G-HPC canvas thickness and the layers of SWM could significantly reduce the damage area of the repaired slab.

Repairing of One-Way Solid Slab Exposed to Thermal Shock Using CFRP: Experimental and Analytical Study

This research was conducted to investigate, experimentally, theoretically, and numerically, the use of CFRP materials for repairing a reinforced concrete one-way solid slab exposed to thermal shock. Nine slabs, measuring 1800 mm in length, 500 mm in width, and 100 mm in depth, were cast. Seven of these slabs underwent thermal shock at a temperature of 600 °C, rapidly cooled by immersion in water for 15 min. Three primary parameters were examined: the type of CFRP (rope, strip, and sheet), spacing (100 and 200 mm), and the number of sheet layers (one and two). The experimental results revealed a significant decrease of approximately 45.4% in the compressive strength of the concrete after exposure to thermal shock. The thermally shocked RC slab showed a reduction in ultimate capacity by 15.4% and 38.5% in stiffness compared to the control slab. The results underscored the efficacy of CFRP materials, with all repair configurations exhibiting a substantial increase in maximum load capacity and stiffness. Capacity enhancement ranged from 23.7% to 53.4%, while stiffness improvement ranged from 27.6% to 57.1%. Notably, all repair configurations effectively minimized the maximum deflection. This reduction in deflection ranged from 5.2% to 26% compared to the control slab. Numerical results demonstrated strong concurrence with experimental results for both capacity and deflection. The enhancement in capacity ranged from 0.7% to 10.4%, while deflection decreased within a range from 0.95% to 14.16% compared to experimental results.

A Study on the Effects of Punch-to-Span Ratio and Longitudinal Reinforcement Eigenvalues on the Bearing Capacity of RC Slab–Column Connections

The region of the RC slab–column connection is subject to complex forces and is susceptible to localized damage, leading to progressive collapse incidents, which has raised considerable concern among the engineering community. At present, the research on slab–column connections exhibits several shortcomings, including a limited number of specimens, incomplete consideration of various factors, and unclear boundaries in defining failure modes. A comprehensive consideration of the punch–span ratio (a/h0) and longitudinal reinforcement eigenvalues (ρƒy/ƒc) is lacking, and the calculation formula for load bearing is not subdivided based on distinct failure modes. In this study, finite element software is utilized to construct 42 models of slab–column connections. The variables considered encompass three factors: the punch–span ratio, the longitudinal reinforcement ratio, and concrete strength. The examination and evaluation encompass the analysis of the load–displacement curve, reinforcement stress change curve, section crack distribution pattern, and stress contour map obtained through model loading. The primary parameters defining the boundaries of the three failure modes in the slab–column connection are the punch–span ratio and longitudinal reinforcement eigenvalues. Utilizing the punch–span ratio and longitudinal reinforcement eigenvalues as key parameters, a punching and flexural failure model for slab–column connections without abdominal bars is formulated. The calculation formula for bearing capacity, encompassing flexural, flexural and punching, and punching shear failure, is derived. A comparison between the revised formula and the standard formulas from major countries indicates that the revised formula is more comprehensive, providing a more accurate and secure prediction within the scope of this study.