Openings In Slabs Research Articles

The Effects of Temporary Tower Cranes on the Construction Process and Seismic Behavior of Reinforced Concrete Buildings

When space is limited on project site to install a tower crane for the construction of high and mid-rise buildings, project managers have to deal with the challenge of assembling such crane somewhere in the middle of the building, leaving an opening in the floor slabs. Nevertheless, there is limited evidence about the effects of this type of temporary structure on the seismic behavior of buildings. The study analyzes the effect of having temporary openings in slabs of reinforced concrete buildings, when tower cranes need to be mounted inside a building. A structural intervention on the buildings' slabs was simulated to resemble the temporary openings required to install a tower crane. Results indicated that seismic deformations were almost the same with and without the slab opening, which enables the installation of tower cranes through the slabs of reinforced concrete buildings, without affecting serviceability levels and seismic behavior of buildings.

Sensor location in concrete slabs with various layout of opening using modified ‘FEMS-COMAC’ approach

Two-way concrete slabs are widely used around the world for the construction of many types of infrastructures and common buildings. The optimal sensor placement (OSP) in slabs with various opening positions is the most important issue in structural health monitoring (SHM) to increase reliability. In this study, a novel approach of OSP was evaluated to obtain the number and placement of sensors using examination of the closed loop performance. The nonlinear finite element (NFE) was used to discretize the mechanism behavior of slab. Multi-Objective Optimization based on the coordinate modal assurance criterion (COMAC) and cost considerations was considered in the optimization processes. All of the analysis, discretization and optimization process was designed and developed as a novel approach in Matlab by the author under the name ‘FEMS-COMAC’ (FEM analysis of slab with COMAC). The points in the finite element method (FEM) mesh were classified as line by line information along the slab. The OSP in each line was optimized according to the objective function. The slabs with various width, thickness, aspect ratio and opening position were selected as case studies. The results of the OSP using the COMAC algorithm around the slab openings were compared with the novel ‘FEMS-COMAC’ method. The statistical analysis according Mann-Whitney criteria shows that there were significant differences between them in some of the case studies (mean P-value=0.54).

Strengthening of Prestressed Concrete Hollow-Core Slab Openings Using Near-Surface-Mounted Carbonfiber- Reinforced Polymer Reinforcement

Strengthening of Prestressed Concrete Hollow-Core Slab Openings Using Near-Surface-Mounted Carbonfiber- Reinforced Polymer Reinforcement

Nonlinear Behavior of Building with Varying Percentages of Slab Opening

The work describes about irregular plan geometric forms that are more in metro cities. Irregularities are not avoidable in construction of buildings. In present scenario many buildings have irregular configurations both in elevation and plan. Now a day’s openings in the floors are common for many reasons like stair cases, lighting architectural etc. The present study focuses on the behavior of 10 storey reinforced concrete buildings under seismic zone-v, the plan dimensions is taken as 28 m x 28 m. The plan irregularities such as openings in slab with varying percentages is taken in this study. Study is done on various plan configuration buildings and the action of structural diaphragm on its performance during earthquake is studied. Pushover analysis is performed by using ETABS software, for present work five models are studied 1) building without opening in slab 2) plan irregular building with 10% opening in slab 3) plan irregular building with 20% opening in slab 4) plan irregular building with 30% opening in slab 5) plan irregular building with 40% opening in slab. Output from software consisting of Pushover curve and hinge formation results of all five models which are presented. Plan irregularity find better structural system solution such as in 20% opening shows better base shear.

Torsional effect of relation between mass and stiffness center locations and diaphragm characteristics in RC structures

Structures exposed to the most destructive effects against seismic forces are constructions where irregularities are present. In this study, torsional irregularities were investigated by creating different slab openings on 5 three-dimensional reinforced concrete floor diaphragms. Except for slab openings, the configurations of the slabs were the same. The aim of this study was to investigate the effect of torsion on the relationship between the mass and rigidity of the center position and diaphragm behavior in reinforced concrete bearing systems. During the experiments, measurements were taken from points at the top of the carrier system columns by means of total station and the displacement changes at these points after each cycle were determined. Thus, structural geometry changes, torsion direction, and angles were drawn separately in the plan for all diaphragm models. In symmetric buildings where the mass center and the stiffness center overlap, torsion is not expected when there is no asymmetricity induced during nonelastic behavior and where there is no wave-passage or coherency effect of the soil. However, in cases where the diaphragm behavior is not rigid, different results can be obtained. As a result, even if the mass and stiffness centers overlap in the structures, the results of this study show that torsional irregularity can be seen in cases where horizontal rigidity is not enough.

Numerical Analysis of RC Slab with opening strengthened with CFRP Laminates

Openings in reinforced concrete (RC) structural floor slabs are sometimes necessary created as a result of variations in architectural function or structural upgrades, amongst other reasons. Architecture reasons for making openings may include change-of-usage, or improvement of air circulation, and lighting. Openings in structural slabs may reduce their strength and stiffness or may transform the original failure mode of the slab to different failure patterns. In the past decades, externally bonded fiber reinforced polymer (FRP) sheets have become popular to strengthen or rehabilitate RC structures for traditional force actions such as flexural, shear, or torsion. Strengthening and rehabilitation of beams, floor slabs, and columns may be necessary for seismic or non-seismic applications. This paper reports the results of numerical study to evaluate the effectiveness of strengthening of two-way RC floor slabs with openings, using carbon FRP (CFRP) composite sheets. Ten numerical models were created, consisting of a reference model with the slab having opening but not strengthened, and nine models with an opening and CFRP laminates applied to the tension side of the slab. The strengthening laminates varied in thickness and width. The results indicate that CFRP laminates can significantly enhance both the flexural capacity and overall stiffness of the floor slab containing openings. Increasing the thickness of CFRP laminates decreases the deflection of mid span. Load-deflection curves were generated, and ultimate load, and ductility index were discussed.

Experimental Study on a Prefabricated Lightweight Concrete-Filled Steel Tubular Framework Composite Slab Structure Subjected to Reversed Cyclic Loading

A building structure comprising a prefabricated lightweight concrete-filled steel tubular (CFST) framework composite slab structure is proposed. Five full-scale specimens (i.e., one empty framework and four-walled frameworks) were tested under reversed cyclic loading to study their earthquake-resistance performance. Of the four wall specimens, three were walled using composite slabs, one had no openings, one had a window opening, and one had a door opening. One was walled with a concealed steel-truss slab. A comparative study on the strength, stiffness, ductility, hysteresis characteristics, and dissipated energy of the specimens was performed. The working mechanism of the framework and slab was then analyzed. The results show that, if reasonably assembled and connected, the framework and slab work in a well-coordinated manner. The walled framework had greater lateral load-bearing capacity, better energy-dissipation, greater stiffness reduction, and better deformability than an empty framework. The area and type of slab opening had a significant impact on structural performance because a door or window opening contributed to a smaller lateral load-bearing capacity and initial secant stiffness of the structure. However, this had no clear impact on the accumulative dissipated energy of the structure.

Deformations of R.C.Circular Slabs in Fire Condition

Reinforced concrete slabs are elements in direct contact with superimposed loads, having high surface area and small thickness. Such a condition makes slabs highly vulnerable to fire conditions. Fire results in exaggerated deformations in reinforced concrete slabs, as a result of material deterioration and thermal induced stresses. The main objective of this paper is to deeply investigate how circular R.C. slabs, of different configurations, behave in fire condition. That objective has been achieved through finite element modelling. Thermal-structural finite element models have been prepared, using "Ansys". Finite element models used solid elements to model both thermal and structural slab behaviour. Structural loads had been applied, representing slab operational loads, then thermal loads were applied in accordance with ISO 843 fire curve. Outputs in the form of deflection profile and edge rotation have been extracted out of the models to present slab deformations. A parametric study has been conducted to figure out the significance of various parameters such as; slab depth, slenderness ratio, load ratio, and opening size; regarding slab deformations. It was found that deformational behaviour differs significantly for slabs of thickness equal or below 100 mm, than slabs of thickness equal or above 200 mm. On the other hand considerable changes in slabs behaviour take place after 30 minutes of fire exposure for slabs of thickness equals or below 100 mm, while such changes delay till 60 minutes for slabs of thickness equals or above 200 mm.

A virtual blind spot identification system (VIBSIM) for construction projects

The construction industry is recognized as one of the most hazardous industries. Visibility-related accidents are the cause of a significant portion of the total fatalities within the construction industry. Limited visibility due to construction equipment blind spots and a lack of visibility in construction areas such as slab openings are among the main causes of these fatalities. This study introduces the Virtual Blind Spot Identification System (VIBSIM), which was designed to identify and examine blind spots in construction equipment and construction sites. The VIBSIM consists of a three-dimensional point cloud model that uses 3ds Max software in conjunction with a V-Ray rendering motor. A real case is used to validate the applicability of the proposed system. The results indicate that the system can significantly improve safety applications for construction projects. Moreover, the system can aid construction managers in making decisions regarding the better management of such safety applications for construction projects.

Strengthening of Cutouts in Existing One-Way Spanning R. C. Flat Slabs Using CFRP Sheets

Openings in slabs are usually required for many different applications such as aeriation ducts and air conditioning. Opening in concrete slabs due to cutouts significantly decrease the member stiffness. There are different techniques to strengthen slabs with opening cutouts. This study presents experimental and numerical investigations on the use of Carbon Fiber Reinforced Polymers (CFRP) as strengthening material to strengthen and restore the load carrying capacity of R.C. slabs after having cutout in the hogging moment region. The experimental program consisted of testing five (oneway spanning R.C. flat slabs) with overhang. All slabs were prismatic, rectangular in cross-section and nominally 2000 mm long, 1000 mm width, and 100 mm thickness with a clear span (distance between supports) of 1200 mm and the overhang length is 700 mm. All slabs were loaded up to 30 kN (45% of ultimate load for reference slab, before yielding of the longitudinal reinforcement), then the load was kept constant during cutting concrete and steel bars (producing cut out). After that operation, slabs were loaded till failure. An analytical study using finite element analysis (FEA) is performed using the commercial software ANSYS. The FEA has been validated and calibrated using the experimental results. The FE model was found to be in a good agreement with the experimental results. The investigated key parameters were slab aspect ratio for the opening ratios of [1:1, 2:1], CFRP layers and the laminates widths, positions for cutouts and the CFRP configurations around cutouts.

Experimental Evaluation on Effect of Openings on Behavior of Prestressed Precast Hollow-Core Slabs

Prestressed precast hollow-core slabs are generally machine-cast with prestressing strands as only flexural reinforcement with no shear reinforcement. Various mechanical, electrical, and plumbing service requirements require openings to be provided in these precast slabs. Openings in hollow-core slabs can coincide with the location of strands and may lead to their curtailment. The size of these openings can vary from minimal, causing no change, to very large, causing adverse effects on the structural behavior of the slab. An experimental study was carried out to evaluate the effect of openings in hollow-core slabs. Six full-scale tests were conducted by considering shear span-depth ratio and location of openings as parameters. The strength of concrete, prestressing ratio, and size of opening was kept constant in all slabs. It was observed that the provision of openings not only reduced the cracking and ultimate strength of slabs but also altered the failure modes with change in deformation capacity. Experimental results were compared with predictions of code equations and finite element analysis (FEA) based software. A fair correlation was observed between the test results and finite element (FE) predictions. The FE modeling approach of hollow-core slabs suggested in this study can be used further for parametric studies and to develop design equations.

An Experimental Investigation and Numerical Analysis on The Behavior Of Reinforced Concrete Thick Slabs under Static Loading

This paper presents the testing results and numerical results of nine reinforced concrete thick slabs with and without openings. All slab specimens have the same planar dimensions (1000mm×1000mm) with three different thicknesses of (120mm,100mm,and 80mm).The slabs resting on 4 corner steel columns and tested under concentrated static loading up to failure. These slabs were also analyzed using nonlinear finite element method assuming nonlinear material properties. From the experiments, it was found that, The presence of openings in slabs supported on their four corners decreases the strength and rigidity of slabs to about (12-23) % depending on the slab thicknesses and the shape of these openings. The slabs with (circular opening) recorded a reduction in ultimate strength to about(20) % from those with square openings having an equivalent opening areas. The yielding of main steel reinforcement occurred at load about 85% of the slab ultimate load. The ultimate loads predicted by ANSYS model have showed a good agreement with the experimental results.

Behavior and Strength of Concentrically Loaded Flat Slabs Using Self-Compacting High Strength Concrete With and Without Openings with Steam Curing

Openings in slabs are usually required for plumbing, fire protection pipes, and ventilation ducts and air conditioning. This study presents an experimental investigation on the influence of openings on the punching shear strength of high reinforced concrete flat plates. Five models of slab-column connection of (1000 x 1000 x 70mm) simply supported along the four edges are tested. The slabs are loaded concentrically by a central stub column. The main variables studied are the size(100x100mm and 200x100mm)and location(at 35 mm , at 135mm from center of slab and at the corner of slab) of the openings and used steam curing method. Experimental results are recorded and studied at various stages of loading, deflection at the center of the slab, at distance (150mm) from the center of the slab in two directions and at the edge of the tested slab out of support. First cracking load and ultimate load capacity are also recorded.

Shaking Table Tests on Earthquake Response Characterization of a Complex Museum Isolated Structure in High Intensity Area

Owing to special functional requirements of museum, such as great space and story height for exhibitions, large floor slab openings in plan and long span truss in elevation are becoming increasingly considered in museum design, which leads to challenges to structural safety. The aseismic performance of an isolated museum structure in high earthquake intensity regions was thus studied because of its complexity and irregularity. In order to observe the seismic characteristics and verify isolation effect, shaking table tests of a 1/30-scale structural model with and without base isolation bearings have been carried out under minor, moderate, and major earthquakes. The experimental results show that isolated structure dynamic characteristics and isolation effect are stable and storey peak acceleration responses of superstructure are less than that of fixed structure. Storey drifts of isolated structure meet required limits stipulated in Chinese design code and torsion responses of the bearings are not remarkable. It is suggested that seismic performances of complex museum structures have been effectively improved with isolation in use.

PERFORMANCE OF PRESTRESSED HOLLOWCORE SLABS WITH AND WITHOUT CUTOUTS

PrestressedHollowcore slabs are typicallyprecast using an extruder machine withprestressing strands as the only internal reinforcement. Various building servicesrequire cut-outs to be provided in these precast slabs.Cut-outs/openings in hollowcore slabs can coincide with the location of strands and may lead to their curtailment.An experimental study was carried out to evaluate the effect of cut-outs in hollowcore slabs. Four full scale tests were conducted by consideringtwo shear span to depth ratiosand out of which two slabs had flexural opening. The strength of concrete, prestressing ratio and size of opening was kept constant in all slabs. It was observed that, provision of cut-outs not only reduced the cracking and ultimate strength of slabs, but also altered the failure modeswith change in deformation capacity.

Seismic behavior of RC structures with absence of floor slab constraints and large mass turbine as a non-conventional TMD: a case study

This paper presents a case study on the influence of absence of floor slab constraints and large mass turbine as a non-conventional tuned mass damper (TMD) on the seismic behavior of the structure and members. The investigated structural system is a reinforced concrete (RC) shear wall-frame power plant structure with large slab openings and a large mass turbine. In RC structures, the existence of floor slabs can usually provide strong constraints on beams so as to greatly increase their bearing capacity. However, due to some special functional demands, large area of slabs may have to be removed so that some floor beams will lose the constraints provided by slabs. In such cases, beams could be subjected to complex internal forces and develop unexpected failure modes under earthquake actions. Nonlinear time history analyses are conducted by using the self-developed program COMPONA-MARC Version 1.0. The numerical model employs fiber beam-column elements with distributed plasticity approach which can elaborately simulate the complex seismic behavior of structural members without slab constraints including the significant transverse vibration damage mechanism. For the seismic effectiveness of the turbine as a TMD with large mass ratio, the optimized parameters are discussed and verified by extensive numerical examples under a wide selection of ground acceleration time histories. The acceleration responses of the turbine are analyzed and found to satisfy the corresponding requirements. The dynamic interaction between the structure and turbine is evaluated and the effects of mass ratio and multiple supporting springs on the dynamic response of the turbine are investigated. It is found that the acceleration response of the turbine modeled with multiple supporting springs is evidently larger than that modeled with a single degree-of-freedom system, and the floor response spectrum decreases significantly with the increase of the mass ratio.

Effective flange width of steel–concrete composite beam with partial openings in concrete slab

Openings often existed in the concrete flange of steel–concrete composite floors in practical structures, affecting the mechanical behavior of composite floors, such as bearing capacity, rigidity and stability. In this paper, the effective flange width of steel–concrete composite beams with openings in the concrete slab was studied by finite element method. The predicted results for the entire loading history of composite beams with openings in the concrete slab were verified by test results, and the axial normal stress distribution was analyzed in detail based on finite element analysis results. Then the parametric analysis was carried out for obtaining the practical simplified design method for calculating the effective width of steel–concrete composite beams with openings in the concrete slab. At last, the predicted deflection of composite beams with openings in the concrete slab was compared with test results and finite element analysis results, showing that the simplified method for calculating the effective flange width of steel–concrete composite beams with openings in concrete slab had enough precision and was suitable for practical design.

EFFICIENT THREE-DIMENSIONAL MODELLING OF HIGH-RISE BUILDING STRUCTURES

A multi-storey building is habitually modelled as a frame structure which neglects the shear wall/slab openings along with the inclusion of staircases. Furthermore, the structural strength provided by shear walls and slabs is not precisely incorporated. With increasing building height, the effect of lateral loads on a high-rise structure increases substantially. Inclusion of shear walls and slabs with the frame leads to improved lateral stiffness. Besides, their openings may play imperative role in the structural behaviour of such buildings. In this study, 61 multi-storey building configurations have been modelled. Corresponding analyses are performed to cope with the influence of shear walls, slabs, wall openings, masonry walls and staircases in addition to frame modelling. The finite element approach is used in modelling and analysis. Structural responses in each elemental combination are evaluated through equivalent static and free vibration analyses. The assessment reveals that inclusion of only slab components with frame modelling contributes trivial improvement on structural performance. Conversely, the presence of shear wall slabs with frame improves the performance noticeably. Increasing wall openings decreases the structural responses. Furthermore, it is not recommended to model staircases in addition to frame–slab–shear wall modelling, unless the effect of wall openings and slab openings is adequately considered.

Binalarda Döşeme Boşluklarının Taşıyıcı Sistem Davranışına Etkisi

Effect of Openings in Building Slabs on the Structural System Behavior Openings having various shape and dimensions exist in the slabs of buildings due to architectural and mechanical considerations. There are various requirements and restrictions in the seismic codes related to dimensions of the openings, including the Turkish Seismic Code (TSC Requirements for buildings to be built in seismic zones, 2007). seismic loads to vertical structural elements should be assessed. In this study, behavior of the reinforced concrete buildings with a certain ratio of openings in the slabs are examined; requirements of the seismic codes of various countries related to this irregularity including TSC 2007, are given comparatively, the definition of irregularities and discontinuities in slabs are presented and the corresponding parameters are given in detail. The results of the numerical analysis related to slab opening irregularity and the effects of the numbers of floors, beam continuity, seismic zone, soil type and rigid and non-rigid diaphragm behavior on the results and on the behavior of the structural system are presented in figures. Furthermore the effects of the location and ratio of the slab openings on the structural system are also investigated

Elastic rigidity of composite beams with full width slab openings

Openings often exist in the concrete slab of composite floors due to the functional requirements of structures. The strength and rigidity of steel-concrete composite beams are reduced by openings. Based on three tests of steel-concrete composite beams with full openings in the concrete flange, the elastic rigidity of composite beams is analyzed. Finite element analysis (FEA) considering the slip effect between the steel and concrete is conducted to simulate the composite beams with full openings in the concrete slab, and the results show that the FEA method is reliable. The analytical calculation method for the deflection of composite beams with full openings in the concrete slab is also proposed, and the results are verified by tests. The predicted deflections using the analytical method and FEA method both agree well with the test results. It is further verified that openings near the supports have insignificant effects on the deflection at the mid-span and this effect can be thus ignored. The simplified method to calculate the rigidity reduction factor is developed by a regression analysis. The analytical method and FEA method can be used for the serviceability limit state design of steel-concrete composite beams with full openings in the concrete flange.