One-way Slabs Research Articles

Implication of Yield Lines Theory in Method Three of the ACI Code for Two-Way Reinforced Concrete Slabs

Reinforced concrete slabs are one of the most important and complicated elements of a building. For supported edges slabs, if the ratio of long span to short span is equal or less than two then the slab is considered as two-way slab otherwise is consider as one-way slab. Two-way reinforced concrete slabs are common in use in reinforced concrete buildings due to geometrically arrangement of columns suggested by architects who prefer a symmetric distribution of columns in their plans. Elastic theory is usually used for analysis of concrete slabs. However, for several reasons design methods based on elastic principles are limited in their function. Correspondingly, limit state analysis offers a powerful technique for considering such matter. The Yield Lines Theory, which is one of limit state analysis based on expected failure criteria of slabs. The assumed failure criteria is termed by a pattern of yield lines, along that the reinforcement has yielded and the location of which counts loads and boundary conditions. This paper deals with comparison of Method 3 for two-way slabs that was provided by the ACI Code and exact derivation of this method by the Yield Lines Theory. Total of nine cases of slabs that have been described by method three are studied and evaluated by plastic analysis assumptions of the yield lines theory. The results are summarized in terms of proposed formulae that derived according to the Yield Lines Ttheory, which could be used as an alternative method for design of two-way reinforced concrete slabs in the ACI Code.

Numerical and Theoretical Analysis of Slab Transverse-Moment Distributions in Twin-Girder Crossbeam Composite Bridges

AbstractIn twin-girder crossbeam composite (TGCBC) bridges, the concrete slab supported only by steel plate girders is typically regarded as a one-way slab, and its transverse bending moments are e...

Structural Behavior of Reinforced Concrete One-Way Slabs Cast with Self-Compacting Concrete Containing Recycled Concrete as Coarse Aggregate

This work deals with the effect of using Recycled Concrete Aggregate (RCA) as a partial replacement of coarse aggregate in Self-Compacting Concrete (SCC), on the structural behavior (flexure and shear) of reinforced concrete one-way slabs. To the authors’ knowledge, this study is one of limited studies concerning the behavior of recycled aggregate concrete one-way slabs subjected to line loading with significant replacement of conventional aggregates by recycled concrete aggregate (up to 75 %). Three replacement ratios were considered 25 %, 50 % and, 75 %. The mixes (with natural stone coarse aggregate, NCA) have an averaged compressive strength of (Fcu = 42 MPa) at the age of 28 days with a tolerance of (± 1.5 MPa). While, the mixes (with RCA) have an averaged compressive strength of (38.5, 36.5 and 34 MPa) for the three replacement ratios respectively, at the age of 28 days with a tolerance of (± 2 MPa). All the slabs were cast with length of (1600 mm), width of (600 mm), while the thickness was variable. For this purpose, sixteen reinforced concrete one-way slabs were cast and divided into five groups (G1 to G5). Different parameters that affect the behavior of one-way slabs were studied and include type of failure, replacement ratios of NCA by RCA, amount of main reinforcement, thickness and locations of line loadings along the span. Hardened concrete specimens results show that the compressive strength Fcu, tensile strength Ft, modulus of rupture Fr and modulus of elasticity E were decreased as the RCA replacement increased. The experimental results of slabs show that the ultimate capacity of slabs decreased as the RCA replacement increased, the deflection and strain increase as the RCA replacement increases and the crack width increases as the RCA replacement increases. From the results of ultimate capacity, cracking load and moment, deflections, crack width and pattern and concrete surface strains, it can be concluded that the recycled concrete aggregate can be used as a partial replacement of natural coarse aggregate to produce self-compacting concrete mixes. Also, the behavior of one way slabs cast with SCC containing RCA is acceptable.

Experimental Investigation on Out‐of‐Plane Flexural and Shear Performance of Half Steel‐Concrete Slabs

Half steel‐concrete slabs have been used in nuclear power plants and high‐rise buildings as floor and roof panels. In order to study the failure mechanism, fifteen one‐way Half‐SC slabs with different steel faceplate thicknesses, stud numbers, shear span ratios, and volume tie bar ratios were tested under three‐point or four‐point loading. Mid‐span deflections, strains of steel faceplate and concrete, and slippage between concrete and steel faceplate were measured. The result shows that Half‐SC slabs exhibited four types of failure mode: flexure, shear, balanced, and interface slippage failure. Flexural failure was initiated by the tensile yield of the steel plate and followed by concrete crushing, which was similar to reinforced concrete slabs. In shear failure, when the shear span ratio is greater than 1.5, the steel plate in the shear‐compression zone would achieve yield strength, and the ultimate failure is caused by the concrete crushing between the loading point and the support or by excessive plastic deformation of steel faceplate. This is significantly different from that of the reinforced concrete slabs. The increases in the volume tie bar ratio could postpone the occurrence of shear failure and even converted failure mode to flexural failure. The flexural strength was calculated. Based on a tie‐arch model, the calculation equation of shear strength was proposed. The calculated results agree well with the experimental data. Besides, these formulas were a good predictor of the transition between bending failure and shear failure with the shear span ratio.

Calculation methods of bridge deck for prestressed short rib T-beam bridges

Because of the low height of the prestressed short rib T-beam bridge and the poor torsion resistance of the main beam, the positive moment in the middle span of the bridge deck will increase correspondingly compared with the normal rib beam bridge. At present, there is little research on the calculation method of the bridge deck of the prestressed short rib T-beam bridge. In this paper, the space finite element method and the continuous one-way slab method are used to calculate the forces on the bridge deck, based on the space finite element method, a finite element elastic supported continuous beam method is proposed to calculate the forces on the bridge deck. By comparing the calculation results of the three methods with the test results, the reasonable calculation method of the bridge deck is studied. The results show that the spatial finite element analysis method can simulate the mechanical performance of the deck of the bridge of the prestressed short rib T-beam bridge well, the stress calculation results are consistent with the test results, and the calculation accuracy is high, which can be used in the actual engineering design; The finite element analysis method of elastic support continuous beam can also simulate the mechanical performance of the deck of the bridge of the prestressed short rib T-beam bridge. The concept of the method is clear, the calculation is convenient, and it is more suitable for the application of engineering design; The calculation results of the continuous one-way slab method are too large to be safe for design.

Optimum Endurance Time of Reinforced Concrete One Way Slab Subjected to Fire

In concrete structures, determining the fire endurance time is fundamental so as ensure that structural elements be able to withstand an aggressive fire for a reasonable time period. Slabs are the most susceptible to fire damage because of their large surface area and shallow depth. Analyzing their bearing capability after sustaining fire requires the knowledge of temperature distribution in the cross-sections, as well as thermal properties of concrete and embedded steel. In this paper, fire endurance a typical reinforced concrete one-way slab is investigated analytically by using ANSYS in terms of time to failure and physical changes associated with exposure to failure. A nonlinear finite element (NLFEA) model was developed and validated by the experimental data before predictions were extended to investigate the significance of concrete density, concrete mechanical properties, and bottom concrete layer cover on the fire endurance time.

Flexural Strength of Modified Reactive Powder Concrete One Way Slabs

Background: Over the last three decades, the interest in using advanced high-performance materials in the construction industry has been increasing worldwide. Recently, a very high strength cement-based composite with high ductility called Reactive Powder Concrete (RPC) has been developed. The RPC concept is based on the principle that a material with a minimum of defects such as micro-cracks and voids will be able to achieve greater load-carrying capacity and durability. Methods: In the present paper, an experimental program of sixteen reinforced concrete one-way slabs was conducted to investigate their behavior under flexural loading. Four of these slabs were with Normal Concrete (NC) and the others of Modified Reactive Powder Concrete (MRPC). All slabs were identical in the dimension of its length and width (1000×500) mm, respectively, and its thickness was varied as one of the variables used in the present work. Other parameters for a one-way slab are concrete type, steel fibers content and flexural steel reinforcement ratio (0.33 and 0.66)%. Results: The results showed that the MRPC slabs with steel fibers failed in a ductile manner and had ultimate load capacity more than that of non-fibrous MRPC with an improvement percentage that reaches up to (66) %. This percentage became (212) % in comparison with normal concrete slabs. Conclusions: Moreover, the results showed that slabs, for both concrete types, reinforced with lower steel ratio failed by tension mode, otherwise, the slabs of higher reinforcement steel ratio failed by combined tension-shear mode. However, an improvement was observed in the ultimate load capacity up to (53 and 98) % when the ratio of steel reinforcement and slab thickness increased, respectively.

Performance of Hollow Core Concrete Slab reinforced by embedded steel tubes

The aims of this paper are gaining additive knowledge about using steel tubes as reinforcement for hollow-core concrete slabs. For this purpose, this paper presents an investigation of how one-way concrete slabs would behave after embedding steel tubes within the cross section. Five concrete slabs were cast, these specimens differ from one another in the horizontal distance (spacing) between the two steel tubes placed within its cross section, steel tubes positioned in the center of the shorter lane of the specimen (width) which is 400 mm, the steel tubes spaced from each other with 4 different configurations, they were 0, 100, 200 and 300 mm. The ratio of the clear spacing between the two tubes and to the total width of the specimen is indicated (s/b) equal to (0, 0.25, 0.5 and 0.75). In addition to one solid slab cast and tested as a reference for the testing results. All five concrete slabs were loaded up to failure by submitting load at one point at the center of the slab. Only one variable was deemed to be considered and checked on this study which is the (s/b) ratio defined earlier. The results exhibit that, using steel tubes as reinforcement increase the first crack load by 12.75% compared to the reference slab, as well as increasing the ultimate load capacity by 59.02% compared to the reference slab. As for the mid-span deflection, the specimens with steel tubes embedded decreased the deflection values up to 47.37 %.

Reinforced recycled aggregate concrete slabs: Structural design based on Eurocode 2

This paper presents the design of simply supported one-way recycled aggregate concrete slabs in compliance with Eurocode 2 (EC2), to illustrate the design process of slabs with these materials. Calculations were based on various evidence-based assumptions from previous studies, namely the effect of incorporating RA on several properties of concrete. The design process followed conventional methods and the solutions were attained by altering the geometry of the slab’s cross-section to exhibit the same pre-determined service life, load bearing capacity and deflection limit in accordance with the ultimate limit state and serviceability limit state of EC2. Four variables were evaluated: increasing incorporation of recycled aggregates with different quality classes; two environmental exposure classes; choice of maintaining target strength class or accepting loss with increasing recycled aggregates; structural design in conservative vs. average conditions. The results showed that an increase to nominal cover and slab thickness was required with increasing replacement level, in order to maintain the same service life and mitigate deflection, the effect of which was most impacted using lower quality recycled aggregates. Between the two exposure classes, marginal relative changes were observed with the incorporation of recycled aggregates. Maintaining target strength was found to be a more practical approach and with less changes to the slabs’ cross-section dimensions. As expected, using the values corresponding to the fiftieth percentile, obtained in previous studies involving meta-analyses of data, resulted in less changes to the geometry of the slabs’ cross-section. Nevertheless, several cases in more conservative settings also required minimal alterations to limit maximum deflection within the EC2′s serviceability limit state.

Assessment of reinforced concrete slabs post-fire performance

An analytical study is presented of the post-fire structural performance of one-way RC solid slabs that have been cooled off from various scenarios of fire events. Three possible fire scenarios were considered for a mid-span section: Fire below or above the slab and a simultaneous fire above and below it. According to the fire scenario and duration, the profile along the slab cross-section's height of the temperatures, from which the slab has cooled off, is calculated. Then, existing models of the residual constitutive relations of the steel and of the concrete are applied in cross-sectional moment-curvature analyses. The results are presented and analyzed in terms of the residual moment-curvature curves and two non-dimensional ratios, which are indicative of the residual moment capacity and ductility. It is noted that the residual deformation capacity, indicated by the latter ductility ratio, has been rarely examined in studies that deal with the residual, post-fire performance of RC members. Findings of this study show that evaluation of the post-fire load bearing capacity may not be enough in order to assess its performance. They clearly indicate that the possibility of decrease of its ductility due to the exposure to fire needs to be assessed as well.

Structural Behavior of High Strength Laced Reinforced Concrete One Way Slab Exposed to Fire Flame

In this study, an experimental investigation had conducted for six high strength laced reinforced concrete one-way slabs to discover the behavior of laced structural members after being exposed to fire flame (high temperature). Self-compacted concrete (SCC) had used to achieve easy casting and high strength concrete. All the adopted specimens were identical in their compressive strength of ( , geometric layout 2000 750 150 mm and reinforcement specifics except those of lacing steel content, three ratios of laced steel reinforcement of (0.0021, 0.0040 and 0.0060) were adopted. Three specimens were fired with a steady state temperature of for two hours duration and then after the specimens were cooled suddenly by spraying water. The simply supported slabs were tested for flexure behavior with two line loads applied in the middle third of the slab (four-point bending test). The average residual percentage of cubic compression strength and splitting tensile strength were 57.5% and 50% respectively. The outcomes indicated that the residual bending strength of the burned slabs with laced ratios (0.0021, 0.004, 0.006) were (72.56, 70.54 and 70.82%) respectively. However; an increase in the deflection was gained to be (11.34, 14.67 and 17.22%) respectively with respect to non-burned specimens.

Improving the Flexural Capacity of Reinforced Concrete One-Way Slabs by Different Techniques

Improving the Flexural Capacity of Reinforced Concrete One-Way Slabs by Different Techniques

Cracking behaviour of green lightweight concrete one-way slabs using medium K Basaltic Andesitic pumice and Scoria

This paper investigates experimentally the cracking behaviour of green lightweight concrete one-way slabs where coarse aggregates comprised medium K basaltic andesitic pumice and scoria. Three points bending test was performed on 24 one-way slabs of both lightweight concrete with three compressive strengths and four reinforcement ratios, and 1 one-way slab of normal concrete as control. Responses consisted of crack width, mid-span reinforcement strain and mid-span deflection that were measured for observation purposes. To show the cracking behavior, their low tensile strengths were evaluated by representing their compressive strengths. Load versus crack width and reinforcement strain diagrams are simultaneously used to evaluate their cracking behaviors. Effects of reinforcement ratio, reinforcement stress, type of lightweight concrete and compressive strength to the maximum crack width are also investigated. Similarly, cracking patterns as well as failure modes are observed to show their appropriate performances. The results show that the reinforcement ratio and reinforcement stress are the main factors that affect significantly the cracking behavior and maximum crack width. However, the type of lightweight concrete and compressive strength affect them but less significantly. All one-way slabs exhibited a typical flexural crack, at the first time the reinforcement yields and then the concrete compressive zone crushes.

Blast responses of one-way sea-sand seawater concrete slabs reinforced with BFRP bars

Avoiding steel corrosion in seawater sea-sand concrete (SSC) members, basalt fiber reinforced plastic (BFRP) bars behaving as reinforcement have advantages in coastal civil engineering and protective structures. One-way BFRP-bar reinforced SSC slabs (BRSSs) were designed to investigate their mechanical responses under static loads and close-in explosions. The SSC blocks have comparable quasi-static compressive strength with plain concrete blocks. The BRSSs have comparable quasi-static flexural strength and identical failure mode with the BFRP bars reinforced plain-concrete slabs (BRPSs). Under close-in explosions, the BRSSs have comparable blast resistance and similar failure modes with the BRPSs. Together with the excellent anti-corrosion ability, the BRSS is an ideal selection for costal protective structures.

Structural behavior of reinforced concrete one-way slabs voided by polystyrene balls

In the last two decades, the use of voided (bubbled) slabs in constructions has been increased because of several advantages such as light self-weight, cost-saving, and accelerated construction schedules. However, the structural behavior of such slabs has not been adequately inspected, especially for one-way slabs. Therefore, this paper presented an experimental investigation to assess the effect of voids’ size on the structural behavior of one-way slabs. Four slabs were fabricated using self-compacting concrete. Three of them were bubbled slabs, containing 68 polystyrene balls with different sizes (60 mm, 70 mm, and 90 mm); these balls were regularly distributed inside the slabs. The fourth slab was conventional solid without balls and assigned as a control slab. The presence of balls led to reducing the self-weight of slabs, by about 6.4%–21.6%, compared with the solid slab. The slabs were subjected to the four-point loading up to collapse. The results stated that the use of balls with a size of 60 mm, which is equal to half thickness of slab, was the optimum where the reduction in the strength, compared to the control slab, was approximately nonexistent and the drops in stiffness, ductility, and toughness were relatively slight, smaller than 11.1%. For other sizes, the influence of balls became significant, especially for balls with a diameter of 90 mm where the reductions in strength, stiffness, ductility, and toughness reached, respectively, 21.3%, 23.7%, 67.0%, and 79%, in comparison with the control slab. Also, using 90 mm- diameter balls changed the failure mode from flexural to shear. Finally, the flexure and shear strengths of the slabs were determined per the ACI 318M-19 and EC2 codes. The predictions of the EC2 code were more accurate and less conservative than those of ACI 318M-19 code.

Performance of GFRP bar anchored PBO-FRCM composite on one-way RC slabs under flexure

The use of FRCM (Fabric Reinforced Cementitious Matrix) composites for reinforced concrete elements structural strengthening is gaining increased popularity. This causes the need to better understand the work of the material and to propose an effective way of using it. The mechanical behaviour of FRCM composites related to their ductility and tendency to debond or delaminate causes that its typical use, known from the older FRP (Fibre Reinforced Polymers) technology, is inefficient, that was the reason for the anchoring concept. This paper presents the results of the research based on three slab type elements, two of which were strengthened with one layer of PBO-FRCM composite with GFRP rebar anchorage of the composite mesh ends. The most important mechanical properties of the elements were measured and analysed.

Structural Effect of Using Steel Fiber Reinforcement on the Punching Shear of Self-Compacting Fiber Reinforced Concrete (SCFRC) Ribbed Slabs

—Ribbed slab is an ideal structure for architects and contractors. It has an attractive soffit appearance and also giving economical value when it is come in weight and material saving. Placing and finishing of concrete slab normally influence about 30% - 35% of overall cost of flooring system. Ribbed slab or also known as one-way joist slab system consist of regularly spaced concrete joist or ribs spanning in one direction, a reinforced concrete slab cast integrally with the ribs and beam span between the columns, perpendicular to the ribs. However the complexity of the structure itself has become an issue due to honeycomb and poor workmanship. To overcome this problem, the use of Self-Compacting Steel Fiber Reinforcement Concrete (SCFRC) could improve the workmanship quality and to minimize the occurrence of honeycomb in concrete. Steel fiber in concrete improved the resistance of reinforced structural members cracking, deflection and other serviceability condition. Thus, this alternative approach will be the main focus in this study.Punching shear strength in reinforced concrete slabs subjected to concentrated loads has received a lot of emphasis due to its importance in the structural system, this failure may take place due to in conservative design of slab overloading and deterioration of strength in concrete and reinforcement. The continuous improvement of the technology of SCFRC and the better knowledge on the mechanical behavior of this SCFRC ribbed slab are contributing to a larger field application of SCFRC. Determination of punching shear strength has received considerable attention by the engineering profession in recent years.

Experimental study on the flexural behavior of insulated concrete sandwich panels with wires as shear connectors

Composite structural elements can serve dual purposes of transferring the load and insulating the buildings. This paper presents and discusses the results of experimental study carried out to understand the flexural behavior of prototype precast insulated concrete sandwich panels using truss-shaped continuous shear connectors. Experimental study consisted of four prototype concrete sandwich panels tested under four-point bending simulating one-way slab action. Panel thickness and size of wire mesh used as reinforcement in concrete wythes are the major parameters considered. Test results indicate that the truss-shaped shear connectors are effective to achieve composite action of the panels until failure. Test results also indicate that the panel thickness affects the flexural load carrying capacity, and size of wire mesh affects the ductility. Experimental and analytical studies are required in this area towards developing guidelines for design of concrete sandwich panels for field applications.

Shear strength analysis of slabs without transverse reinforcement under concentrated loads according to ABNT NBR 6118:2014

Abstract Concentrated loads in slabs without transverse reinforcement, usual in highway bridges, result in the horizontal spreading of the shear force towards the supports, situation in which not all the slab width contributes in the shear strength. Based on this, the analytical models of shear strength and punching capacity in slabs may not be suitable to deal with this loading. Since this topic is not widely discussed in the national technical literature, the paper aims to present contributions to these analyses with a focus on the accuracy level of the shear strength analytical models recommended by ABNT NBR 6118:2014. Therefore, the models available in the Brazilian code were applied to an experimental database with 118 test results and the results obtained by the Brazilian and European codes were compared. The results demonstrated that, as presented in the Brazilian code, shear strength model in one-way slabs can lead to unsafe resistance predictions while the punching capacity model can lead to very conservative predictions. From the analysis, it is concluded that considering the reduction of the shear force, in the case of loads distributed in small areas close to the support in slabs, and the use of more suitable procedures to define the effective width, it is possible to improve the level of accuracy of relations between experimental and theoretical values, but this still leads to high percentages of unsafe predictions of resistance (> 40%).

Strengthening and repair of one-way and two-way self-compacted concrete slabs using near-surface-mounted carbon-fiber-reinforced polymers

The effectiveness of near-surface-mounted carbon-fiber-reinforced polymers on strengthening and repair of self-compacted concrete slabs was investigated experimentally and numerically. Twenty slabs were cast (10 one-way and 10 two-way) and tested under four-point load. Strengthening and repair effectiveness was investigated on slabs using near-surface-mounted carbon-fiber-reinforced polymer strips with straight and inclined orientation. Repair was performed on eight slabs using near-surface-mounted carbon-fiber-reinforced polymer strips with an orientation based on the best cost/capacity ratio, with two preloading levels: 35% and 50% of the ultimate load of the control slab. The results showed that using near-surface-mounted carbon-fiber-reinforced polymers increases the ultimate strength of one-way strengthened self-compacted concrete slabs (45%–163%) for both strip orientation, with the straight orientation performing better. Also, the cracking load and stiffness increased, while deflection decreased. The increase in ultimate strength for strengthened two-way slabs was 15% to 17%. The ultimate deflection and toughness of the two-way strengthened slabs increased 43% and 34%, respectively. Using near-surface-mounted carbon-fiber-reinforced polymers restored the load capacity of repaired one-way and two-way slabs but was more effective for one-way slabs. The repaired one-way slabs regained up to 223% of the control slabs’ ultimate strength, with a significant increase in stiffness (296%). The repaired two-way slabs regained up to 116% of the control slabs’ ultimate strength. The strength was higher in the case of the 50% preload compared to 35% preload. The finite element model shows somehow a reasonable capability of predicting the experimental behavior with a gap in terms of the stiffness and the maximum load.