One-way Reinforced Concrete Slabs Research Articles

Effects of structural configuration on perforation/spalling damage and secondary fragment velocity of reinforced concrete slabs subjected to close-in explosion

Reinforced concrete (RC) slabs are vulnerable to localized damage from close-in TNT explosions, suffering perforation and extensive spalling damages that generate high-velocity secondary fragments posing severe risks to nearby facilities and personnel. Current numerical methods such as the Finite Element Method (FEM) face challenges in accurately predicting fragmentation due to mesh distortion caused by large deformations and discontinuities, underscoring the need for enhanced modelling techniques. As a result, although numerous studies have numerically investigated how structural configurations influence RC slab damage under blast loads, the issue of mesh distortion and element erosion in FEM has led to the inability in reliably predicting the associated threats from high-velocity fragments. This study numerically investigates the influences of structural configuration (e.g., concrete strength, reinforcement ratio and layout, dimensions of slabs, and concrete cover depth) on the perforation/spalling area and fragment ejecting velocity of one-way RC slabs subjected to close-in explosions through an ALE-FEM-SPH numerical model, which has been demonstrated effective and reliable in the authors’ previous studies. The results indicate that concrete strength and slab thickness most significantly affect both the damage and fragment characteristics, while the slab's width-to-height ratio, reinforcement ratio, and layout, have less influence, particularly on fragment velocity. Empirical equations derived from extensive numerical data are provided to help engineers and security personnel quickly evaluate the blast effects on RC slabs. The accuracy and robustness of the proposed formulae, which can be straightforwardly used to predict blast fragments of reinforced concrete slabs, have been statistically evaluated and the proposed formulae demonstrate satisfactory precision, with less than 20 % error in estimating damage area, maximum fragment velocity, and total kinetic energy of fragments.

3D non-linear finite element modeling of one-way RC slab strengthened with concrete overlay

Reinforced concrete (RC) slabs often require strengthening due to deterioration, increased loads, or design changes. Concrete overlay is a commonly used technique for strengthening, but predicting the behavior of overlays can be challenging. To address this challenge, this study presents a three-dimensional non-linear finite element model using Abaqus/CAE to analyze the structural performance of one-way reinforced concrete (RC) slabs strengthened with concrete overlays. The model considers three different bonding conditions at the interface: friction, epoxy, and shear connectors. The predictions of the model were compared to experimental results, and it was found that the model accurately captures the load–deflection response, cracking behavior, and interfacial slip in the strengthened slabs. Additionally, the model accurately predicts the new structural capacity of the strengthened slabs, showing good agreement with experimental data. These findings offer valuable insights into the effectiveness of concrete overlays as a traditional strengthening technique for RC slabs. Moreover, the developed finite element model provides a useful tool for optimizing the design of these overlays.

Experimental study on the flexural strengthening of one-way RC slabs with end-buckled and/or externally bonded CFRP sheets

Reinforced concrete (RC) slabs are widely strengthened in flexure by externally bonding (EB) carbon-fiber-reinforced polymer (CFRP) sheets, where debonding failure remains a critical issue. To solve the debonding problems, a self-locking device is initially proposed to enhance the anchorage at the end of FRP sheets for strengthening of RC slabs in this study. The effects on the debonding resistance and the improvement of the strengthening efficiency are experimentally investigated. Six one-way RC slabs strengthened with end-buckled and/or externally bonded CFRP sheets were prepared for the four-point bending tests. All strengthened specimens had higher ultimate loads than the reference specimen. While the slab strengthened by EB CFRP had a limited increase in ultimate load, the improvement was significant for the cases with hybrid anchored (HA) CFRP including both end-anchorage and external bonding, which was 46.2%. In this case, the interfacial stresses could be reduced and the end debonding can be avoided due to the increasingly tight anchoring effect, and the ultimate load can be increased even after partial debonding since the stress can continue to be transferred via mechanical anchorage. When the specimens were strengthened with HA CFRP, the surface treatment had a marginal influence on the strengthening effect. The strength of the slabs strengthened with HA CFRP decreased with the length of CFRP sheets, which is contrary to the trend of cases using EB CFRP. Finally, expressions were proposed to estimate the strain of the CFRP and load-carrying capacity of the strengthened members at the ultimate state, and the test results were within the range of the calculated results.

Flexural behaviour of RC one-way slabs reinforced using PAN based carbon textile grid

Textile reinforced mortar (TRM) is mainly used for strengthening of existing structural members whereas, on the other hand Textile reinforced concrete (TRC) is a technology implied in construction of new members for enhancing the structural behaviour. Application of TRM on the tension zone of the reinforced concrete (RC) slabs to improve the flexural capacity has been investigated by many researchers in the past. However, the effectiveness of textile fabrics, used as internal reinforcement in the RC slab (TRC technology) needs to be studied. The paper, therefore, presents the experimental research conducted on three one-way RC slabs specimens reinforced using textile grid. An innovative Polyacrylonitrile (PAN) based carbon textile grid was used as internal reinforcement in combination with the steel bars. Two textile-reinforced RC slabs having one and two layers of textile grid (SRC + 1T and SRC + 2T respectively) and one reference slab (SRC) was fabricated to investigate the flexural behaviour under a four-point loading system. The internal textile reinforcement layer(s) was confirmed to be effective, particularly in terms of improving the cracking load, ductility, deformability and toughness. The material ductility of SRC + 1T and SRC + 2T slabs were increased by 41% and 44% compared to SRC slab. Also, the deformability ratio was found to be greater than 4, indicating a ductile failure of textile-reinforced slabs. Further, based on the load-deflection relation, moment-curvature curves were derived. Moreover, these curves were also developed using Eurocode two prediction model. The experimental and the predicted moment-curvature curves showed good agreement.

Experimental and numerical investigation of one-way reinforced concrete slabs using various strengthening systems

This paper presents different effective strengthening techniques to enhance the flexural strength of one-way reinforced concrete (RC) slabs. To assess the effectiveness of utilizing the suggested strengthening techniques, an experimental and numerical study was conducted. The experimental program included seven one-way RC slabs with dimensions of (2000 mm × 1000 mm x 150 mm). The first specimen was considered a control slab without providing any strengthening technique, and the remaining six specimens were strengthened with various systems. Ultra-High Performance Fiber Concrete (UHPFC) was used to strengthen the second specimen (S1-UHPFC), where a layer of UHPFC with a thickness of 50 mm was placed in the tension side of the slab within the specified slab depth. The third specimen (S2-HSC) is the same as the second specimen, but it is strengthened with High-Strength Concrete (HSC). The fourth specimen (S3-R.B) was strengthened from the bottom of the slab by bonding steel skewer bars with square cross sections (12 mm × 12 mm) by near-surface mount (NSM) technique. The fifth specimen (S4-C.B) is the same as the fourth specimen (S3-R.B) but the square skewer bars have been replaced by circular ones with a diameter of 12 mm. The sixth specimen (S5-S.P) was strengthened from the bottom of the slab by bonding stainless steel strips with a width of 50 mm and a thickness of 1 mm. The last specimen (S6-A.P) is similar to the sixth specimen (S5-S.P), but the stainless steel strips were replaced with aluminum ones. The results show that the failure loads of specimens S3-R.B and S4-C.B are greater than the control specimens S0-C.S by about 62 % and 41 %, respectively. In addition to specimen strengthening, using stainless steel strips or aluminum strips was less effective than the previous strengthening methods. However, this type is distinguished by its resistance to corrosion. To verify the outcomes of the experimental tests, a finite-element model using ABAQUS program was performed. Finally, An excellent agreement between the experimental and numerical results was obtained.

Flexural behavior of concrete slabs strengthened with textile reinforced geopolymer mortar

This paper presents results from experimental and numerical studies on the flexural behavior of reinforced concrete (RC) one-way slabs strengthened with textile reinforced geopolymer mortar (TRGM). Eight one-way RC slabs, comprising of five TRGM strengthened slabs, two TRPM (textile reinforced polymer-modified cement mortar) strengthened slabs and one un-strengthened slab, were tested under static loading. The varied parameters in the experiments included the number of textile layers, spacing of the lateral textiles, presence of anchorage, and type of binder. Data from the tests is utilized to validate finite element models developed to simulate the flexural response of TRGM strengthened slabs. Then a set of parametric studies were conducted, to evaluate the effect of reinforcement ratio, slab thickness and the number of strengthening layers. Results from the tests and numerical studies clearly show that use of TRGM for strengthening delays the development and progression of cracks in slabs and enhances the post-cracking stiffness, as well as flexural capacity. In addition, the flexural capacity increases with increased number of strengthening layers, and decreased spacing of lateral textiles. Compared with TRPM strengthened slabs, TRGM strengthened slabs possess higher flexural capacity and better crack control. Finally, a calculation model for predicting the flexural capacity of TRGM strengthened slabs is proposed and the model predictions of flexural capacity is in good agreement with the results from tests and numerical simulations.

A Design Method to Induce Ductile Failure of Flexural Strengthened One-Way RC Slabs.

Strengthening existing reinforced concrete (RC) slabs using externally bonded materials is increasingly popular due to its adaptability and versatility. Nevertheless, ductility reduction of the rehabilitated flexural members with these materials can lead to brittle shear failure. Therefore, a new approach for strengthening is necessary. This paper presents a methodology to induce ductile failure of flexural strengthened one-way RC slabs. Ultimate failure loads can be considered to develop the proposed design methodology. Different failure modes corresponding to ultimate failure loads for RC slabs are addressed. Flexural and shear failure regions of RC slabs can be established by considering the failure modes. The end span of the concrete slab is shown for a case study, and numerical examples are solved to prove the essentiality of this methodology.

Probabilistic Moment Capacity Models of Reinforced Concrete Slab Members for Underground Box Culverts

This study was performed to evaluate the probabilistic characteristics of the flexural strength of reinforced concrete (RC) flexural members adopted for underground box culverts. These probabilistic models were developed to be adopted for the development of limit state load combination formats for underground RC box culverts. The probabilistic models of uncertainties inherent in the basic design variables were developed to evaluate flexural strength using field material test data as well as field survey data collected from various domestic construction sites of underground box culverts in Korea. The basic design variables include concrete strength, steel rebar strength, and section dimensions, such as slab thickness and rebar locations. Some design variables are assumed to have inherent construction error characteristics, which may be different from those inherent in the RC members for buildings and bridges. The bias models on flexural strength were evaluated based on the experimental results of four-point flexural tests on one-way RC slabs, which were fabricated following the general practice adopted in the local underground box culvert construction process. Based on the probabilistic models of basic design variables, as well as the bias models of flexural strength, Monte Carlo simulations were performed to examine the probabilistic characteristics of both ultimate flexural strength and yield moment strength of RC slab members. Some sensitivity analyses were performed to confirm the soundness of various probability models and the assumptions adopted in the development procedure. The proposed procedure may be applied to develop probabilistic resistance models for structural members, in which the construction error characteristics are assumed to be different from other practices.

Enhancing the Behavior of One-Way Reinforced Concrete Slabs by Using Laced Reinforcement

This paper studies experimentally the behavior of laced reinforced concrete one-way slabs under monotonic load. The experimental program included testing three simply supported one-way slabs of dimensions (1500 mm length, 600 mm width, and thickness 130mm. One of these slabs was the control specimen which was designed without lacing reinforcement steel and the other two specimens designed were with two variable lacing reinforcement ratio (0.27% and 0.52%). All specimens were cast with normal of 22 MPa compressive strength. Specimens were tested under two equal line loads applied at the third parts of the slab (monotonic load) gradually applying up to failure. The specimens showed an enhanced in ultimate load capacity up to 40% as a result of increasing the lacing steel ratio to 0.52 %. Also, decreasing in deflection at service and at ultimate load levels by 42% and %57 respectively. In addition, the results showed that specimen with lacing reinforcement are more ductility than specimen without lacing reinforcement so using of lacing steel reinforcement leads to significant improvements in ductility index which reached to about 49% with increasing the lacing steel ratio to (0.52%).

Flexural behaviour of one-way patched reinforced concrete (RC) slab under concentrated load

Repair of deteriorated reinforced concrete (RC) elements may be necessary to restore their strength and serviceability. In this research, unsaturated polyester resin (UPR)-mortar is used to repair one-way RC slabs. The performance of the patched RC slabs is investigated experimentally by comparing their behaviour under concentrated load with the corresponding normal slab. The obtained load–deflection relationship up to failure and the cracking failure mode are assessed to determine the efficacy of the UPR-mortar in restoring the strength and serviceability of the slabs. In addition, theoretical ultimate loads determined on the basis of the yield line theory are used to assess the effectiveness of UPR-mortar to restore the strength of the damaged RC slab. As long as a proper execution of repair is carried out, the results indicate a satisfactory performance of UPR-mortar to be used for repairing the damaged RC slabs.

Numerical Modelling of Reinforced Concrete Slabs under Blast Loads of Close-in Detonations Using the Lagrangian Approach

This paper includes an investigation for the deformations, including deflections and damage modes, which occur in reinforced concrete (RC) slabs when subjected to blast loads of explosions. The slab considered for the investigation is a one-way square RC slab with the dimensions of 1000 x 1000 x 40 mm, fixed supported at two opposite sides. It was subjected to close-in detonations of three different charge weights for a constant standoff distance. For the study, the slab was analysed using the numerical method by means of nonlinear finite element analysis. The slab was modelled as 3-D structural continuum using LS-DYNA software. For concrete modelling, two constitutive models were selected, namely the KCC and Winfrith concrete models. Blast loads were applied to the slab through the Lagrangian approach, and the blast command available in the software, namely LOAD_BLAST_ENHANCED, was selected for the application. The deflections and damage modes results obtained were compared to those from a previously published experiment. From the study, both the KCC and Winfrith concrete models effectively and satisfactorily estimated the actual slab maximum deflection. For damage modes, the KCC model appeared to be capable to capture satisfactorily the general damage mode including flexural cracks. However, the model could not capture the local shear mode at the middle of slab (spallation) because the Lagrangian approach does not simulate the interaction between the ambient air and the solid slab.

Numerical Simulation of One-Way Reinforced Concrete Slabs Subjected to Blast Loadings

The damage and failure of reinforced concrete (RC) slabs under blast loadings may cause significant hazards for frame systems even progressive collapse of whole structures. The numerical simulation of one-way RC slabs using the finite element explicit code LS-DYNA to estimate the dynamic response and failure mode of one-way RC slabs .Blast loadings are imposed on the top surface of slabs using a blast model based on conwep algorithm. Concrete was modeled using a concrete damage constitutive model considering strain rate effect, and reinforcement was modeled using a elastoplastic material type with kinematic hardening and strain rate effect. The numerical model is introduced in details and adopted to simulate the dynamic responses of RC slabs in reference test. The numerical model can match well with the test data, and thus the proposed numerical model can be considered as a valuable tool in assessing the deformation or failure mechanism and predicting the dynamic responses of one-way RC slabs subjected to blast loadings.

Case Study on the Restoration of Flexural Capacity of Continuous One-Way RC Slabs with Cutouts

Introducing openings in existing reinforced concrete (RC) slabs can severely weaken the slabs because of the cut out of the concrete and reinforcing steel. This paper reports field tests on the use of carbon fiber-reinforced polymer (CFRP) composite strengthening techniques to restore the flexural capacity of RC slabs after having openings cut out in the positive moment region. The uniqueness of this study is that the tests were performed on an existing multistory RC building that was scheduled for demolition. Five tests on five different slabs were conducted using three different strengthening techniques—namely, externally bonded (EB) CFRP plates, EB CFRP plates with CFRP anchors, and near-surface mounted (NSM) CFRP strips—to determine the most effective system for strengthening. Test results showed that the three strengthening techniques increased the load-carrying capacity of the slabs with openings, with the NSM technique being more effective than the EB technique. However, the use of CFRP anchors to mechanically anchor the EB plates prevented complete detachment, and hence enabled the restoration of the slab to its full flexural capacity.

Time-dependent reliability analysis of existing RC structures in a marine environment using hazard associated with airborne chlorides

In the design of reinforced concrete (RC) structures in a marine environment, it is important to consider the effects of this environment on structural long-term performance. In this paper, a time-dependent structural reliability analysis method taking the hazard associated with airborne chlorides into consideration is proposed. Also, a procedure to obtain the failure probabilities of RC structures in a marine environment updated by the Sequential Monte Carlo Simulation (SMCS) is indicated. In this procedure, the corrosion crack width and chloride concentration distribution by coring test are used as observational data. For illustrative purposes, time-dependent reliability analyses are presented for one-way RC slabs in a marine environment. Using SMCS, multiple random variables related to observation information can be updated simultaneously. This is realized by taking into consideration the joint probability density functions of the random variables. The effects of various marine environments, inspection results, and number of inspections on the updated estimates of an RC slab reliability are discussed in this paper.

Deflection Calculation of Frp-Strengthened Reinforced Concrete Flexural Members

SummaryExternally bonded fibre-reinforced polymer (FRP) composite plates can enhance the flexural strength, as well as stiffness to a limited degree, of reinforced concrete (RC) flexural members. Understanding the behaviour of these strengthened members at the serviceability and ultimate load ranges of response is of particular importance to engineers. The description of such behaviour is best described via plotting of the complete moment-curvature, as well as load-deflection responses from initial load to member failure. Based on the assumption of a tri-linear moment-curvature relationship, closed-form analytical solutions are presented in this paper for calculating the complete load-deflection response of FRP flexurally-strengthened one-way RC slabs and beams, which are simply-supported (three- and four-point bending), as well as cantilevered (free-end point load). The analytical predictions compare well with test results and the basis of a new “quad-linear” moment-curvature relationship is proposed that may better capture a so-called “pseudo-ductile” response occasionally observed in experiments. The influence of anchorage of the FRP strengthening for the prevention or delaying of debonding and a procedure for its inclusion in the analytical model is also discussed. Finally, the results of parametric studies are presented.

Robustness to Uncertainty: An Alternative Perspective in Realizing Uncertainty in Modeling Deflection of Reinforced Concrete Structures

This paper describes an alternative perspective in evaluating of computational models for predicting deflection of cracked reinforced concrete (RC) structures. The concept of robustness to uncertainty in modeling input parameters is introduced in addition to the classical perspective of modeling accuracy. A new method to quantify robustness to uncertainty is proposed and applied to the problem of modeling deflection of RC structures. Monte Carlo simulation is used for uncertainty propagation in serviceability calculations. The propagation of random uncertainties in deflection of a continuous one-way RC slab is examined. We introduce a method for the practical use of the proposed robustness metric by considering the reliability analysis. A cracked plane frame model to simulate deflection of the RC slab was adopted. We show that by considering a threshold of uncertainty in predicted deflection, the robustness to uncertainty in model inputs for different deflection prediction models can be evaluated. Our investigation proves that a tradeoff between model robustness and model accuracy exists in modeling deflection of RC structures.

Strengthening of one-way spanning RC slabs with cutouts using FRP composites

This paper reports the results of tests on fibre reinforced polymer (FRP) strengthened one-way spanning reinforced concrete (RC) slabs with central cutouts. Four wide slabs with cutouts were tested in addition to two narrow slabs without cutouts. Different positions of applied line loads for the slabs with cutouts resulted in different slab bending action and hence different FRP behaviour for the strengthened slabs. All FRP-strengthened slabs achieved a higher load-carrying capacity than their unstrengthened control counterparts. In addition, all strengthened slabs failed by debonding initiating at intermediate cracks (IC debonding) and in the case of the slabs with cutouts, the critical cracks were diagonal and originated from the corners of the cutout. The ability of the FRP to redistribute stresses around the cutout, the failure mechanisms, as well as pre- and post-debonding behaviour of the strengthened slabs was therefore assessed for different load application positions. Strains on the FRP, concrete and internal steel reinforcement, as well as deflections at different positions on the slab surfaces are also reported. An analytical model, which is based on the ultimate moment of resistance about critical crack lines, is also reported and it its predictions are found to correlate well with the experimental results. The analytical model is able to capture the different slab bending actions in addition to the debonding failure of the strengthened slabs.

In Situ Load Testing of Parking Garage Reinforced Concrete Slabs: Comparison between 24 h and Cyclic Load Testing

This paper reports on the results obtained on the applicability of the diagnostic cyclic load test method in comparison with the existing 24 h test procedure adopted in ACI-318. A parking garage, owned by St. Louis County, St. Louis, Missouri, scheduled for demolition during the summer of 2002 was used as a research test bed before demolition. This structure, a two-story steel and reinforced concrete (RC) frame with one-way RC slabs built in 1970's, was ideal, in terms of size and construction system, for performing comparative field experimentation on load testing. Investigation and validity of acceptance criteria of existing and proposed testing methods were performed. Two identical RC slabs were tested, according to both the standard procedure (ACI-318-02) and the proposed diagnostic load testing. In both instances, the applied total test load was such that the slab did not pass the load test. This allowed characterizing the critical test parameters that govern acceptability and draw conclusions on their values. After load testing, both slabs were loaded until partial collapse was reached. This allowed making observations on the margin of safety with respect to collapse, a determination that is not generally possible in a proof test. The analysis of the experimental data provides professionals with evidence on the validity of in situ assessment for the adequacy of structural members.

Strengthening of Openings in One-Way Reinforced-Concrete Slabs Using Carbon Fiber-Reinforced Polymer Systems

Six prototype one-way RC slabs with openings were strengthened with externally bonded carbon fiber-reinforced polymer (CFRP) systems and subjected to concentrated line loads. The results were compared to those of a solid slab without opening and a slab with an unstrengthened opening. The CFRP system proved to be effective in enhancing the load-carrying capacity and stiffness of RC slabs with an opening, provided that premature failure due to CFRP debonding is excluded. An analytical model based on the modified yield line method is presented, in which four failure modes comprising one orthogonal and three nonorthogonal yield line patterns were considered. The analytical model predicts the load carrying capacity of the strengthened slabs very well. The opening width has a more prominent effect on the load-carrying capacity than does the opening length.

Performance of One-Way Reinforced Concrete Slabs with Externally Bonded Fiber-Reinforced Polymer Strengthening

Research is given from experimental work conducted on full-scale 1-way reinforced concrete (RC) slabs. 26 slabs with and without an overhang at 1 extremity were tested under simply supported conditions. The geometry and loading configuration allowed for the study of positive and negative moment regions. The slabs were strengthened with unidirectional carbon fiber-reinforced polymer (CFRP) laminates installed by manual lay-up. Different failure mechanisms--namely, concrete shear and crushing, CFRP rupture, and CFRP peeling--were obtained by varying the CFRP laminate cross-sectional area and amount of internal steel reinforcement. Findings from an analytical model that simulates and interprets the experimental results are also provided. These findings confirm the notion that peeling of the CFRP laminate affects the system performance but can be predicted by monitoring interface shear stresses.