One-way Slabs Research Articles

Predicting reinforced concrete response to blast loads

Computer software was developed for inelastic analysis of structural members subjected to blast-induced shock waves. The software can predict the dynamic response of structural elements, provided the load–deformation characteristics are defined. The software has built-in capabilities to generate the load–deformation characteristics of common structural and non-structural members. Currently this capability includes reinforced concrete columns, one-way walls, beams, and one-way slabs. The input consists of member geometry, boundary conditions, dynamic material properties, explosive threat parameters, and desired performance levels. The results are presented in graphical format in terms of structural load–deformation characteristics, single degree of freedom displacement – time histories and iso-displacement pressure–impulse diagrams. The program was verified extensively using experimental data generated from simulated explosive loading of reinforced concrete members at the University of Ottawa shock tube testing facility. The shock tube has been shown to generate a wide range of pressure–impulse combinations, accurately simulating free-field detonation of high explosives of various mass and standoff distances.

The structural behaviour of HCWA ferrocement–reinforced concrete composite slabs

This study was performed with the aim to assess the structural behaviour of ferrocement–reinforced concrete composite slab system with high calcium wood ash (HCWA) high strength mortar used as the compression zone. The proposed slab system consisted of conventional reinforced concrete slab topped with a layer of high strength ferrocement composite containing various contents of HCWA by total weight of binder. A total of six numbers of one-way composite slab prototypes were subjected to four point flexural load test to ultimate failure. The main parameters of the study include serviceability moment, ultimate moment capacity, flexural stiffness in serviceability and post cracked conditions, crack width development, crack spacing and failure mode. Results of the investigation indicate a significant enhancement in the first crack load and ultimate failure load of the composite slab system with the use of HCWA in the mortar layer at cement replacement level of 2% to 8% by binder weight. In addition, the inclusion of HCWA at various replacement levels also contributed to a reduction in the magnitude of average crack width at a given flexural load.

Influence of steel fibers and fiber-reinforced polymers on the impact resistance of one-way concrete slabs

In this study, to estimate the impact resistance of steel fiber-reinforced concrete slabs strengthened with fiber-reinforced polymer sheets, a series of 50 × 100 × 350 mm3 sized slabs with 0.5%–1.5% (by volume) of steel fibers and two types of fiber-reinforced polymer sheets were impact-tested using drop-weight impact test machine. From the test results, the maximum impact load, dissipated energy and the number of drops before failure were all increased, whereas the maximum deflection and support rotation were reduced by strengthening the steel fiber-reinforced concrete slabs with externally bonded fiber-reinforced polymer sheets in the tensile zone. It was noticed that the impact resistance of the steel fiber-reinforced concrete slabs was substantially improved by externally strengthening the fiber-reinforced polymer sheets. In addition, the dynamic response of the steel fiber-reinforced concrete slabs strengthened with fiber-reinforced polymer sheets under a low-velocity impact load was analyzed using explicit code LS-DYNA with strain rate-dependent material models and debonding failure analysis. These numerical analyses were verified by comparing with the experimental results.

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.

Non-Linear Behavior of Unbonded Post-Tensioned one-way Concrete Slab Panel

In this research, a nonlinear finite element model developed to investigate the behavior and ultimate load capacity of unbonded post-tensioned one-way concrete slab panel. The numerical treatment adopted by finite element ANSYS software has been carried out on two different one-way concrete slabs chosen from previous available experimental study in order to evaluate their results. Mode of failure and the loaddeflection relationship are presented for two cases. A parametric study was conducted to study the effects on the global structural behavior due to the effect of concrete compressive strength, effect of effective prestressing stress, effect of prestressing (post-tensioning) technique, types of loading, effect of tendon profile, effect of tendon bonding, effect of span to depth ratio of concrete slabs.

Design limits for RC slabs strengthened with hybrid FRP–HPC retrofit system

A polymeric hybrid composite system made of high-performance concrete (HPC) and an innovative carbon/epoxy reinforced polymer (CFRP) unidirectional laminates was proposed as a retrofit system to enhance flexural strength and ductility of reinforced concrete (RC) slabs. The effectiveness of the proposed system was confirmed through experimental evaluation of three full-scale one-way slabs having two continuous spans. In this study, the results of the loading tests for the hybrid high-performance retrofit system are presented and discussed. Design limits to derive a flexural failure of a continuous RC slab strengthened with the hybrid retrofit system are extracted. Using the proposed design limits, the procedure of a flexural failure design for a continuous RC slab strengthened with the hybrid retrofit system is demonstrated with numerical examples for two types of the retrofit systems with respect to overlay strength. The flexural failure design limits can be extended for flexural and shear strengthening design with externally bonded FRP to ensure flexure failure for a continuous flexural members.

Comparative Study for Punching of FRP-Reinforced Concrete Slabs

The noncorrosive fiber-reinforced polymer (FRP) composite bars are an excellent alternative reinforcement. In this paper, a review of the available punching load equations of two-way FRP-reinforced slabs and shear strength equations of one-way FRP-reinforced slabs is provided. All the models were verified against results for test specimens from the literature. The equivalent steel ratio model of Theodorakopoulos and Swamy produced the best estimates for the punching load while the model of Deitz, Harik, and Gesund yielded the best predictions of shear capacity. One of the punching strength models was modified in the current research and it gave excellent results. Using this modified model, it is proved that the increase in the reinforcement ratio is accompanied by an increase in the punching strength.

Shear in One-Way Slabs under Concentrated Load Close to Support

One-way slabs under concentrated loads are generally designed for shear by checking the beam shear resistance and the punching shear resistance over an effective width. Only a small number of test data regarding the shear resistance of one-way slabs subjected to concentrated loads is currently available. To be able to better evaluate the shear resistance of one-way slabs, a series of experiments was carried out on continuous one-way slabs (5 m x 2.5 m x 0.3 m [16.4 ft x 8.2 ft x 11.8 in.]) subjected to concentrated loads close to the supports, in which the load position, transverse reinforcement ratio, and concrete strength were varied. The test results are compared with code provisions and a method developed by Regan. The results show a different behavior in shear for slabs under concentrated loads than for beams.

Innovative Applications of Textile-Based Composites in Strengthening and Seismic Retrofitting as Well as in the Prefabrication of New Structures

The authors review investigations which have provided fundamental knowledge on the use of a new generation of composite materials, namely textile-reinforced mortar (TRM) and textile-reinforced concrete (TRC), as strengthening and seismic retrofitting materials of existing concrete and masonry structures, as well as in the prefabrication of new reinforced concrete (RC) structural elements. In the first part of the paper, TRM are investigated as a means to provide confinement in concrete, to increase the deformation capacity of old-type RC columns subjected to simulated seismic loading, to increase the shear and flexural resistance of RC members and to increase the out-of-plane or in-plane strength of unreinforced masonry walls. In all cases, the effectiveness of TRM systems is quantified through comparison with equivalent fiber-reinforced polymer (FRP) ones. It is concluded that TRM jacketing is an extremely promising new technique, which is expected to enjoy the attention of the research community and to be employed in numerous applications in the near future. In the second part, the paper gives a brief overview of the application of TRC in the field of advanced prefabricated systems, with a focus on stay-in-place (or permanent) formwork elements in hybrid construction projects. Along these lines, the paper provides experimental results on the behavior of TRC/RC composite beams and one-way slabs under flexure. The results indicate that the use of prefabricated TRC stay-in-place formwork elements is a promising solution for achieving reduction of the construction time, minimization of labor cost and defect-free finishing of external surfaces.

Determination of load transfer in reinforced concrete solid slabs by finite element computer analysis

According to the ACI building code, the concrete slab can be divided into two types depending on the ratio of the long side to the short side. Regarding the results of the ratio, the concrete slab can be divided as one-way and two-way slabs. The main objective of this paper is to study the stress or moments distribution in solid slab panel in its two directions and compare with ACI code assumption that the load is transferred mainly in short direction and most of the load is transferred in one direction only if the ratio of the longer span to the shorter span is greater than one. This will be discussed by analyzing one panel of solid slab using the computer software SAP2000. Two types of panels will be used; the first one a panel that is supported simply on its four sides and the second panel is supported only by four pin supports and beams. This paper shows that the gravity load on the slab is transferred to long and short direction. This means that one-way concrete solid slab doesn't exist and all concrete solid slabs work as a two-way concrete slab.

Flexural Behavior at Service and Ultimate Limit State of One-Way Concrete Slabs Reinforced with Corrosion-Resistant Reinforcing Bars

The paper presents the results of an experimental investigation of the structural performance and susceptibility to deformation of a concrete bridge deck with corrosion-resistant reinforcing (CRR) bars (i.e., bars that exhibit better corrosion resistance than traditional black steel when embedded in concrete). Flexural tests of one-way slabs were conducted to simulate negative transverse flexure over a bridge girder as assumed in the commonly used strip design method. Grade 60 (uncoated), epoxy-coated reinforcing Grade 60, Enduramet 32 stainless steel, 2304 stainless steel, MMFX2, and glass fiber–reinforced polymer bars were studied. The experimental program was designed to evaluate how flexural performance at service and ultimate limit states are affected by a one-to-one replacement of Grade 60 with CRR bars, a reduction of concrete top clear cover, and a reduction in rebar quantities in the top mat of the bridge deck. Moment–curvature predictions from Response 2000, a computer-based sectional analysis program, were consistent with the test results. This consistency demonstrated the viability of Response 2000 for use with high-strength and nonmetallic rebar without a defined yield plateau. The susceptibility of the specimens of concrete slab strips to deformation was defined with ultimate- to service-level ratios of midspan deflection and curvature. The susceptibility to deformation of the specimens of MMFX2 and Enduramet 32 stainless steel (one-to-one replacement) was consistent with the Grade 60 controls; this consistent response demonstrated that bridge deck slabs with high-strength rebar without a defined yield plateau still can provide sufficient ductility at an ultimate limit state. A reduction in rebar quantity and cover provided acceptable levels of ductility for the specimens of 2304 stainless steel and MMFX2-reinforced slabs.

Behavior of One-Way Concrete Slabs Reinforced with GFRP Bars

The replacement of conventional steel reinforcement with fiber-reinforced polymer (FRP) bars was investigated previously to overcome the problem of steel reinforcement corrosion and structural deterioration in concrete structures exposed to aggressive environments. However, the lower modulus of elasticity of FRP materials and their non-yielding characteristic results in large deflection and wide cracks in FRP-reinforced concrete members. Hence, there is a need for a suitable design philosophy and for methods that can provide a reliable estimate of such behavior.This paper evaluates the behavior of simply supported concrete slabs reinforced with bars of glass fiber-reinforced plastic (GFRP) and subjected to four-point monotonic loading. The slabs had sizes of 4000 × 1000 × 150 mm and 4000 × 1000 × 200 mm with different reinforcement ratios. This research investigated the flexural and shear limit states of the slabs, including pre-cracking behavior, cracking pattern and width, deflections, ultimate capacities and strains, and failure modes. The information presented is valuable for future field application and development of design guidelines for FRP-reinforced concrete structures.

등가플레이트 요소를 이용한 일방향 중공슬래브의 동적해석에 관한 연구

Considering that the weight of a hollow slab system is not increased with an incremental increase in its thickness, and that the flexural stiffness of a hollow slab is not significantly lower than that of a general slab, there has been a growing need for hollow slab system, because long span structures are in great demand. In a long span structure, the problem of vibration of floor slabs frequently occurs, and the dynamic characteristics of a hollow slab system are quite different from the conventional floor system. It is required to investigate the safety and the serviceability of hollow slab. Therefore, there exists a necessity for accurate vibration analysis. Hollow slab should be modeled by refined mesh for accurate vibration analysis. For the efficiency of the Eigenvalue Analysis, an equivalent plate slab model when can relatively precisely represent the dynamic behavior of a one-way hollow slab system is used. In conclusion, equivalent plate models relatively precisely presented the dynamic characteristics of one-way hollows.

A generic model for investigation of arching action in reinforced concrete members

A generic nonlinear compound frame model is developed and applied for investigation of arching action in reinforced concrete beams. This model takes account of geometrical and material nonlinearities including cracking and crushing of the concrete and yielding of reinforcing steel. Further, a non-local model is adopted to resolve the numerical sensitivity associated with compressive softening of concrete. The effect of support stiffness is incorporated into the formulation by a set of nodal rotational and translational springs that, respectively, represent the flexural and axial stiffness of the supports. The developed model is verified by available experimental data and advanced continuum-based FE models and it is shown that the generic model can predict the ultimate loading capacity and load–displacement response of reinforced concrete beams and one-way slabs with reasonable accuracy. Lastly, a parametric study is undertaken and effects of end supports stiffness and concrete compressive strength on development of arching action is investigated.

Vulnerability analysis of RC buildings with wide beams located in moderate seismicity regions

A significant number of short-to-mid height RC buildings with wide beams have been constructed in areas of moderate seismicity of Spain, mainly for housing and administrative use. The buildings have a framed structure with one-way slabs; the wide beams constitute the distinctive characteristic, their depth being equal to that of the rest of the slab, thus providing a flat lower surface, convenient for construction and the layout of facilities. Seismic behavior in the direction of the wide beams appears to be deficient because of: (i) low lateral strength, mainly because of the small effective depth of the beams, (ii) inherent low ductility of the wide beams, generated by high amount of reinforcement, (iii) the big strut compressive forces developed inside the column-beam connections due to the low height of the beams, and (iv) the fact that the wide beams are wider than the columns, meaning that the contribution of the outer zones to the resistance of the beam-column joints is unreliable because there is no torsion reinforcement. In the orthogonal direction, the behavior is worse since the only members of the slabs that contribute to the lateral resistance are the joists and the façade beams. Moreover, these buildings were designed with codes that did not include ductility requirements and required only a low lateral resistance; indeed, in many cases, seismic action was not considered at all. Consequently, the seismic capacity of these structures is not reliable. The objective of this research is to assess numerically this capability, whereas further research will aim to propose retrofit strategies. The research approach consists of: (i) selecting a number of 3-story and 6-story buildings that represent the vast majority of the existing ones and (ii) evaluating their vulnerability through three types of analyses, namely: code-type, push-over and nonlinear dynamic analysis. Given the low lateral resistance of the main frames, the cooperation of the masonry infill walls is accounted for; for each representative building, three wall densities are considered. The results of the analyses show that the buildings in question exhibit inadequate seismic behavior in most of the examined situations. In general, the relative performance is less deficient for Target Drift CP (Collapse Prevention) than for IO (Immediate Occupancy). Since these buildings are selected to be representative of the vast majority of buildings with wide beams that were constructed in Spain without accounting for any seismic consideration, our conclusions can be extrapolated to a broader scenario.

Geometry and restraint effects on the bending behaviour of the glass fibre reinforced polymer sandwich slabs under point load

The behaviour of structural glass fibre reinforced polymer (GFRP) composite sandwich slab was investigated under static point load. In this paper, the effects of dimensions aspect ratio, skin fibre orientations, overall thickness, boundary restraints, and boundary conditions on the static behaviour of the GFRP slab were presented. It was found that the ultimate load of the fibre composite sandwich slab is reducing with increasing panel dimension aspect ratio. The experimental results also showed that the fibre orientation of the skin has an effect on the failure mode and stiffness of the slab. As expected, the flexural stiffness of 18mm thick slab is higher than the 15mm thick slab. Finally, the restraint conditions did not affect much on the failure load and stiffness of the one-way and two-way slab systems.

보 및 1방향 슬래브의 균열제어

The KCI Building Code (2003 and 2007) provisions to control flexural cracking in beams and one-way slabs are discussed for related researches and the development of the provisions. Based on the basic ideas over the development of current provisions, possible problems with cracking control are identified and discussed for the remedies to fix the problems. Simple and clear equations to control flexural cracking in beams and one-way slabs are presented. The presented equations would avoid any conflicts with other provisions for the spacing of reinforcement.

One-Way Slabs Subjected to a Combination of Loads Failing in Shear

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Theoretical Model for Limit Load-carrying Capacity of One-way Concrete Slabs at Large Displacements

Theoretical Model for Limit Load-carrying Capacity of One-way Concrete Slabs at Large Displacements

FRP-UHPC 복합 보강기법으로 보강된 RC 슬라브의 휨 파괴를 위한 설계 조건

This study proposes flexural failure design criteria of continuous slabs enhanced by a hybrid system of fiber reinforced polymer (FRP) and ultra high performance concrete (UHPC). The proposed hybrid retrofit system is designed to be placed at the top surface of the slabs for flexural strengthening of the sections in both positive and negative moment zones. The enhancing mechanisms of the proposed system for both positive and negative moment regions are presented. The neutral axis of the enhanced sections in positive moment zone at flexural failure is enforced to be in UHPC overlay for preventing the compression in FRP. From this condition, a relationship between design parameters of FRP and UHPC is established. Although the capacity of the proposed retrofit system to enhance flexural strength and ductility is confirmed through experiments of one-way RC slabs having two continuous spans, the retrofitted slabs failed in shear. To prevent this shear failure, a design criteria of flexural failure is proposed.