Openings In Slabs Research Articles

Behavior of repaired heat-damaged self-compacted concrete slabs with openings using NSM-CFRP strips

PurposeIn this experimental investigation, the behavior of strengthened/repaired heat-damaged one-way self-compacted concrete (SCC) slabs with opening utilizing near-surface-mounted-carbon fiber reinforced polymers (NSM-CFRP) strips was explored.Design/methodology/approachCFRP strip configurations, number of strips and inclination were all investigated in this study. For three hours, slabs were exposed to temperatures of 23°C and 500°C. Four-point load was applied to control slabs, enhanced slabs and repaired slabs.FindingsThe results indicate that exposing the slabs to high temperatures reduces their load capability. The number of strips and angle of inclination around the slab opening have a considerable impact on the performance of the strengthened and/or repaired slabs, according to the experimental results. The load capacity, toughness and ductility index of a strengthened and/or repaired slab with opening increase as the number of CFRP strips increases by 143.8–150.5%, 137.3–149.9% and 122.3–124.5%, respectively. The use of NSM strips around the opening with zero inclination showed higher load compared to the NSM strips around the opening with other angles.Originality/valueIt is frequently important to construct openings in the slabs for ventilation, electrical supply, and other purposes. Making openings in slabs might affect the structure’s performance since the concrete and reinforcing would be cut off. SCC is a new type of concrete mixture that can fill in all the voids in the formwork with its own weight without the help of external vibration. As a result, it is necessary to reinforce the slab under flexure and increase the flexural strength of the SCC slab. Therefore, this work investigates the effect of using NSM-CFRP strip on the behavior of one way SCC slabs that have been heat-damaged.

Shaking table tests on inclined collapse mechanism of RC frame structures subjected to earthquakes

Inclined collapse of structures under strong earthquakes threatens the adjacent infrastructures. The collapse mode and collapse direction should be considered with caution to curb the secondary disaster in the urban area. However, current studies on the inclined collapse mechanism are predominantly limited to the qualitative and intuitive understanding. To fill this gap, this study presents an insight into the inclined collapse mechanism of the reinforced concrete (RC) frame structures with two typical features subjected to earthquakes, i.e., the structures with slab opening on one side of the first floor and the structures with disparate axial compression ratios of the first story columns on the opposite sides. First, shaking table tests were performed on two 1/10-scale three-story RC frame structure models undergoing inclined collapse. Then the multi-scale finite element models were established, validated against the test results and used for parametric studies. In the parametric studies, two coefficients were considered to describe the typical features of the RC frame structures, i.e., the strong column-weak beam ratio η and differential rate of the axial compression ratios λ. The test and numerical results found that the inclined collapse mechanism was attributed to the different distributions and discrepant resistance deterioration of the plastic hinges among the first story columns of the RC frame structures with the two features. This causes the inconsistent damage levels among the first story columns, the dominant direction of the lateral displacement, and the inclined collapse of the structures. Finally, the collapse mode and collapse direction can be controlled by appropriately adjusting the two coefficients η and λ for the structures with the typical features concerned in this study.

Numerical analysis on flat slabs with openings and SHEAR reinforcement

AbstractThe present study aims to parameterize the numerical models of flat slabs based on five experimental prototypes developed previously. The analyzed slabs had dimensions of 1800 mm × 1800 mm and a thickness of 130 mm. Two slabs did not have openings, and three slabs had stud‐type shear reinforcement. Subsequently, five new slab models were selected with position variations and several openings, with a fixed diameter of 75 mm and without shear reinforcement. After calibration of the models, the following results were obtained: the numerical rupture load approached at least 90% of the experimental rupture load, and the rupture modes and cracking patterns were similar to those observed in the experimental models. When it is impossible to move the column openings vertically, it is more beneficial to position them at the corners of the column rather than close to the same face of the column. Thus, it was possible to numerically analyze the effects of the position and number of openings in flat slabs.

Studying the Effects of Opening Size and Location on Punching Shear Resistance of Flat Slabs Using ANSYS V.19

To validate the accuracy of ANSYS V.19, an experimental model based on a previous study was used to determine the typical values of crack pattern, ultimate load, and deflection. The model was a flat slab with an internal column with dimensions of 1000 × 1000 × 100 mm³. Four groups used a slab with an edge column in parametric research. The first group studied the opening size relative to the column face. The second group of specimens studied opening sizes close to column corners. The third group consisted of four specimens: two had openings in front of the column face and two in front of the column corner to study how opening distance affected flat slab behaviour. The fourth group examined the optimum opening arrangement in slabs with two openings around the column. The findings showed that flat slab openings at the column corner had higher ultimate load capacity than those at the column face; however, increasing opening dimensions beyond the column dimension decreases punching shear capacity. If the column needs two openings, place them on opposite faces or near the corners; this minimizes ultimate load reduction.

Evaluation of punching strength of RC flat slabs with openings with different positions, size, and number: Experimental, analytical, and superposition approaches

In this study, three-stage research was carried out to investigate the adverse effects of openings in flat slabs. In the first stage of the study, full-scaled reinforced concrete two-way slabs were produced and exposed to a punching load. One of the test specimens was the reference test element produced without openings. For the other test specimens, the number of openings, the location of the opening, and the size of the opening were chosen as variables. The punching strength, initial stiffness, and energy dissipation capacity of the slabs were calculated with the load-displacement data recorded during the experiment. In the second stage of the study, the punching capacities of the test specimens were calculated by means of the punching capacity estimation equations presented in international regulations and compared with the experimental data. In the last stage of the study, the superposition principle, which is among the general principles of mechanics and has not been used before in the literature, was utilized. Considering the opening conditions presented in this study and the literature, it was investigated whether the new opening condition that will arise can be predicted with experimental data via the superposition principle.

Influence of openings on the punching shear behaviour of concrete slabs supported on special-shaped columns

Punching shear of special-shaped columns supporting reinforced concrete two-way slabs has been addressed in design codes since the late 1970s. While these provisions have existed for over 40 years their basis is unclear as previous studies related to the punching shear behaviour of irregular column geometries, such as L, T, and cruciform shapes, are limited. In this paper, the punching shear behaviour of L, T and cruciform slab-column connections, with or without slab openings near the connection, under concentric vertical loading is studied using a three-dimensional nonlinear finite element model (FEM) implemented in Abaqus/Explicit. The nonlinear FEM, based on the concrete damaged plasticity model, is used to study the influence of both the opening size and location on the punching shear behaviour of special-shaped (irregular) slab-column connections of various sizes. Based on the FEA results, the ideal location for openings around special-shaped slab-column connections (SS-SCCs) is between the column flanges. This location minimizes their negative influence on concentric punching capacity and is also beneficial architecturally. Finally, the accuracy of the ACI 318–19 punching shear provisions is evaluated. Based on the FEA results modifications to the existing provisions are necessary, particularly to account for the location of openings around special-shaped slab-column connections.

Numerical Studies on Composite Deck Slab With Floor Openings

Openings in slabs are provided mainly for service works. According to the purpose of the services, the size of the openings was classified as small, medium, and large. The provision of openings in a composite slab was not addressed in design codes like EC-4 and IS 11384. Normally the Longitudinal shear interaction is the influencing factor in determining the capacity and elastic rigidity of a composite slab which may be affected by the presence of openings. In the market, there are various forms of embossment/indentation available to enhance the interlocking at the interface of the Cold Form Steel decking sheet and the topping concrete thereby an increased longitudinal shear resistance can be achieved at the interface. In this numerical study, Among the various type of embossments, combined types of embossments (rectangular and chevron) are considered then the m and k values are determined with the help of the Penalty Friction interaction approach and the same was verified with the known experimental values for a solid slab. In addition, Finite Element [FE] models with various sizes of floor openings were created under the guidelines of SCI publication P300 and SDI Technical Guidance on Deck Damage and Penetrations. The effects of those openings located in the high shear region and no shear region are studied. The simulated load-deflection responses of various FE floor opening models were compared.

Numerical Analysis of Two Way Slab With Openings

Slabs are the concrete elements used as significant components in building. It is common to have openings in slabs for various operational reasons like electrical, mechanical and plumbing services as a result decreases their capacity to carry loads. Along with this, insufficient data is available for slabs having openings at centre and at eccentric positions to resist applied loads. Moreover, many difficulties were faced analytically while modelling the complex behaviour of RCC slabs in nonlinear zone. Therefore, they require special attention in both analysis and design. This research gives more attention on studying structural behaviour of two-way slab having openings at centre and at eccentric positions along with solid slab. To study this type of behaviour seven different models of square slabs having different shapes of openings like square, rectangular and circular at centre and eccentrically has been generated in ANSYS, which is a FEM based software. All specimens were subjected to load, which was increased from zero to failure load. The effects of opening shape on crack formation were also analysed.

Cyclic behavior of metallic damper connected reinforced concrete beam-column joint with an opening in slab

The study proposes a solution of constructing the inevitable rectangular opening in the reinforced concrete (RC) slab upon the metallic damper for the RC beam-column frame to alleviate the adverse effect of the slab for the system compared to the designed bare frame joint. To systematically understand the cyclic behavior of the system, a quasi-static test is conducted on two half-scale specimens, and a parametric study is carried out to explore the effects of the rectangular opening of the RC slab along with the top and bottom flanges of the damper on the hysteretic responses of the system. Test results show that the positive and negative bearing capacities of the system are asymmetric because the centroid shifts upward from the middle of the metallic damper and RC beam. Although the intervention of opening in RC slab for the dog-bone damper connected RC joint is hard to mitigate the additional stiffness and bearing capacity from the slab to the system, such application could restrain the out-of-plane instability of the dog-bone damper by about 21.74% and improve both loading capacity degradation and energy dissipation degradation of the system. Furthermore, numerical results confirm that the distance of opening from the RC slab significantly decreases the depth of the neutral axis of the RC beam with the slab so that the bearing capacity and initial stiffness of the system improve by about 26.47% and 27.88%, respectively, as the distance of the opening to the damper reduced from 0 mm to 60 mm. Moreover, benefitting from the significant influence on the depth of the neutral axis, the bottom flange of the dog-bone damper, especially the flange width and weakened depth of the damper, has a significant improvement on the hysteretic responses of the system.

Experimental behavior based on effective slab width acting as a flange with supporting steel beams in composite floors with openings

An experimental study with many variables was carried out to investigate the effective width of simply supported composite beams (T&L sec. beams) with & without slab opening. Three full-scale composite slab models with six different carrier simply supported composite beams (three with T-sec. & three with L-sec.) with constant slab rectangularity was tested. Each model loaded by uniform load (in the elastic zone) then loaded by means of two-concentrated load system acting at equal distances from supports till failure. One of them without slab opening and the others with two symmetric slab openings and constant opening horizontal position. All standard tests were performed and all instructions and precautions were followed as perfect as the laboratory instruments permitted. All experimental steps were executed in a manner such that meeting practical conditions as exactly as could. In this research, the tested model features, materials properties and measurement instrumentations are described in brief. The maximum load carrying capacity; crack patterns, generated strains and deflections at different positions were experimentally investigated. For the sake of analysis generalization and error minimization, all results were analyzed by means of dimensionless relations. The results were recorded and analyzed guided by their mechanical behavior. Interesting gained results, conclusions and recommendations are introduced.

Experimental and numerical investigation on strengthening of RC flat slabs with central opening

Slab openings occur quite often in practice to provide a convenient path for utility ducts. However, introducing an opening into a reinforced concrete flat slab causes local cracking in the vicinity of the opening leading to a reduction in stiffness and capacity of the slab. In this paper, different methods of strengthening flat slabs with central openings are investigated experimentally and numerically. The experimental program consists of six slab specimens with dimensions of (1100 × 1100 × 100) mm with cut out openings of (300 ×300) mm. Two slabs were considered as reference specimens and tested without strengthening; one of them had no opening, and the second had a central opening. The remaining four slabs had openings and were strengthened with different techniques. These include adding Near Surface-Mounted (NSM) steel bars, steel strips with anchor bolts, carbon fiber laminates (CFL), and an overlay of engineered cementitious composite (ECC) material reinforced with welded wire mesh. The results show that using different strengthening techniques leads to an increase in load-carrying capacity for all the strengthened slabs. The reinforced ECC overlay strengthening method achieved the largest increase in the capacity by 31% compared to the reference slab with central opening. The finite-element analysis is carried out to validate the experimental results. Good agreement between the finite-element analysis and the experimental results is obtained confirming many of the findings of this study.

Collapse testing of steel-concrete composite floor systems under an exterior-column-removal scenario

To evaluate the influence of openings in floor slabs on the collapse performance of steel-concrete composite floor (SCCF) systems, 2 one-third scale 1 × 2 bay SCCF substructures were fabricated and tested under static load up to final collapse in an exterior-column-removal scenario. The experimental results indicated that arch-shaped and radial cracks emerged on the top and bottom surfaces of the floor slab, respectively, for the SCCF substructure without openings in the floor slabs. Meanwhile, local buckling of the steel girders at the beam ends successively occurred during the loading procedure. As for the SCCF system with openings in the floor slabs, the crack distribution appeared more irregular, and torsion of the spandrel beam became prominent because of the discontinuity of the floor slab. The ultimate collapse resistance and the corresponding displacement of the failed column for the substructure with openings in the floor slabs were about 0.85 and 0.55 times as large as those of the substructure without openings. Owing to the existence of the openings, the tensile membrane action in the floor slab was weakened prominently, which further decreased the collapse resistance capacity of the SCCF system. After the removal of the exterior column, load was redistributed among the columns around the failed column and much more load was assigned to the adjacent exterior column. The flexural action and catenary action of the composite beams, as well as the tensile membrane action of the floor slabs worked together to resist collapse load at the large deformation stage.

Retrofitting of reinforced concrete flat slabs with cut-out edge opening

In existing buildings, it is common to create openings in slabs due to service supplies. In this case, the mechanical properties of slabs remarkably reduce, and strengthening must be applied. Therefore, this investigation proposed four methods to retrieve the lost mechanical characteristics of slabs owing to openings. Six reinforced concrete slabs were prepared with similar dimensions, 1300 × 1300 × 120 mm. One of them was reference without opening, whereas the others contained a square edge opening of 350 mm side. For slabs with openings, one specimen was the control left without strengthening, and the remaining four were strengthened utilizing various methods, which were Carbon Fiber Reinforced Polymer (CFRP), steel plates, steel bars, and near-surface mounted Engineered Cementations Composite (ECC) with steel mesh. The slabs were exposed to uniformly distributed load up to failure. The experimental tests showed that the opening reduced the mechanical properties of slabs remarkably, and the proposed strengthening methods, except for ECC, managed to restore a significant amount of these losses.

Screens surrounding openings in floor slabs of public buildings

Introduction. Screens often surround openings in the floor slabs of atrium buildings to prevent the spread of fire hazards to higher floors and to improve the efficiency of smoke ventilation systems. In this article, the co-authors assess the expediency of installing screens around openings in the floor slabs and identify the best screen height values. In this article, the co-authors perform a quantitative analysis of the ability of screens to prevent the propagation of hazardous fire factors, to identify general regularities typical for a multi-level space, and to develop recommendations for the installation of screens inside public buildings. The co-authors suggest that screen height should be a solution to the following tradeoff problem: the use of screens reduces acceptable evacuation time for the floor that has screens installed and rises the evacuation time for higher floors.Rational screen height selection algorithm. The co-authors propose the following algorithm for the two-stage selection of the rational screen height. At the first stage, the evacuation problem is resolved. As a result, evacuation completion time is determined for emergency exits. Further, acceptable evacuation time and the time needed to block emergency floor exits are identified for a particular type of a fire alarm system.At the second stage, the dynamics of hazardous fire factors in building rooms is assessed for various screen heights. As a result, the rational height of screens is established for the evacuation time to remain positive.Conclusions. Screen height values cannot be determined in advance. Each case requires an individual approach that entails the resolution of evacuation problems and the tracking of the dynamics of hazardous fire factors in buildings that have multi-height spaces. These ideas are in line with the concept of flexible regulation of fire protection systems designated for construction facilities.

Numerical investigation of the effect of beam slab openings in RC structures on seismic behavior

Earthquake negatively affects the behavior of reinforced concrete frame systems that have slab discontinuities. As a result of differences in diaphragm behavior according to slab void ratio and position, lateral loads cannot be distributed to vertical bearing elements in proportion to their rigidity. In this study, the topic of differences in the behavior of reinforced concrete frame system under lateral load if void ratio and position of the slab change have been examined numerically. For this purpose, five single-story three-dimensional carrier frame models with different void ratios and positions were created in the ANSYS program analyzing according to the finite element method. As a result of the study, an increase in slab void ratio of reinforced concrete frame type carrier systems resulted in displacement in more significant amounts. Along with 25% being a safe void ratio in terms of rigid diaphragm behavior when the void ratio is 50%, whether the void is symmetrical or not becomes extremely important in terms of behavior.

Experimental study of the effects of slab openings on seismic behaviour of buildings

Experimentation by producing three-dimensional samples for understanding the seismic behaviour of a structure takes a significant amount of time and these experiments may be highly complicated. Based on literature, the seismic behaviour of structures with slab openings usually was represented by analytical assessments instead of three-dimensional experimental studies. Moreover, the limiting values of slab openings vary greatly between earthquake regulations. This variability has made it important for experimental studies. For this purpose, a total of 5 reinforced concrete carrier system models, with different slab opening ratios, were produced at 1/2 scale. As a result of the study, it was observed that in cases where there were 25% or more openings in the slab, rigid diaphragm behaviour decreased in the structure. It was recommended that for analyses of these types of building systems that the finite element method, based on the assumption of an elastic diaphragm rather than the assumption of a rigid diaphragm, be used.

Nonlinear finite element analysis of punching shear strength of reinforced concrete slabs supported on L-shaped columns

Most current concrete design codes include provisions for punching shear of reinforced concrete slabs supported on columns with L, T, and cruciform shapes. Reference studies verifying the accuracy of these code provisions are typically not provided. Empirical data of punching failures of slabs supported on columns with L, T, and cruciform shapes are limited due to the cost and time required to test specimens with slab thicknesses and column sizes commonly used in practice. In this paper, the punching shear behaviour of five interior L-shaped slab-column connections, one without a slab opening and four with slab openings, subjected to static concentric loading are analyzed using a plasticity-based nonlinear finite element model (FEM) in ABAQUS. The FEM is similar to models previously calibrated at the University of Waterloo and are calibrated considering nine slabs that are tested to study the impact of column rectangularity on the punching shear behaviour of reinforced concrete slabs. The finite element analysis results indicate that shear stresses primarily concentrate around the ends of the L, and that current code predictions from ACI 318-19 and Eurocode 2 may be unconservative due to the assumed critical perimeters around L-shaped columns.

Experimental study of steel-concrete composite beams with slab opening

This study investigates experimentally the effect of openings in the concrete slab of the composite beams. Composite beams consisted of concrete slab connected with steel I-beams by steel headed stud connectors is used in the study with eleven specimens. The test specimens are designed to test and failed in flexure. The test specimens are classified depending on the variable parameters into the following groups: control sample; opening ratio; ratio the short to the long dimension of opening; thickness of the concrete slab; grade of compressive strength; strengthen of opening by steel plate. The results of the study indicate that the general trend in the ultimate load is to increase with increasing thickness of the concrete slab and increasing the compressive strength of concrete. While the ultimate load decreased when increasing the opening ratio because decreasing the effective width of the concrete slab and the cracks develop when the opening was near to the applied loads. Also, the distribution of shear connectors in place of opening on both sides and present the diagonal reinforcing rebars about the opening minimize from the significant decrease for the ultimate load.

Analytical Study on the Behaviour of Composite Space Truss Structures with Openings in a Concrete Slab

A space truss structural system is a three-dimensional arrangement of linear elements in a pyramid pattern forming a Double Layer Grid (DLG) system. Space trusses are an elegant and economical means of covering larger areas such as roof systems, in a wide variety of applications such as a stadium, aircraft-hanger, assembly hall, etc. The major problem encountered in using the space truss as a roofing system is the sudden failure of the whole structure due to critical buckling of the top chord member. Earlier research has shown that the optimal solution to overcome such a failure is by providing a small thickness of concrete slab over the space truss, so that the space truss with concrete slab (Composite Space Truss) will act as a floor system for the multi-storey building. For better ventilation and lighting in the building, the need for openings in the composite space truss is unavoidable; however, providing an opening in the concrete slab will reduce the load carrying capacity of the structure. The analysis of a composite space truss of size 30m x 30m with all possible locations of openings for four different support conditions was carried out using ANSYS in order to study the load - deflection behaviour. Further, the ductility factor and energy absorption capacity of the composite space truss with different locations of slab openings were compared.

Behaviour of Strengthened Flat Slab with Opening at Edge Column under Punching Shear Strength

Flat slab system is widely used because of its architectural flexibility Punching is one of the major and critical problems in flat slab especially for the edge column. There are many traditional ways to increase the punching shear strength of concrete slabs like increasing the slab thickness or column dimensions which is against the architectural desire Using FRP strengthening for the flat slabs against punching shear can be considered as a new application. Sometimes an opening is needed to be punched through existing slabs to install cables, elevators and ventilation systems, etc. This causes weakening due to the cutting of concrete and reinforcing steel and also increases the punching problems especially if the opening beside the edge columns. This research is aimed to evaluate the effects of strengthening with Glass Fiber Reinforced Polymer (GFRP) on the punching shear behaviour of flat slab with an opening varying in location with respect to the edge column. Bearing capacity, deflection, ductility, energy absorption and stiffness obtained from the tested slabs are compared to the control specimen, which was without opening and strengthening. It is observed that, the punching shear capacities of the strengthened specimens significantly increased compared to control specimen. Creating openings in flat slab beside the edge column should be approached with great caution and avoided if possible because of its bad effects. In case of openings are of extreme necessity, it is recommended to be created in the front of the edge column not in the side.