Concrete Floor Slabs Research Articles

Advanced finite element analysis of a complex deep excavation case history in Shanghai

The construction of the North Square Shopping Center of the Shanghai South Railway Station is a large scale complex top-down deep excavation project. The excavation is adjacent to several current and newly planned Metro lines, and influenced by a neighboring Exchange Station excavation. The highly irregular geometry of this excavation greatly increases the complexity in 3D Finite Element modeling. The advanced numerical modeling described in this paper includes detailed structural and geotechnical behavior. Important features are considered in the analysis, e.g., 1) the small-strain stiffness of the soil, 2) the construction joints in the diaphragm wall, 3) the shrinkage in the concrete floor slabs and beams, 4) the complex construction sequences, and 5) the shape effect of the deep excavation. The numerical results agree well with the field data, and some valuable conclusions are generated.

Solar Active Building with Directly Heated Concrete Floor Slabs

A new concept for solar active houses is presented within this paper. In contrast to existing solar house solutions, the solar collec- tor heat gains are distributed in a temperature-optimized way to three different heat sinks – a significantly smaller storage tank, concrete floor elements directly fed by the solar circuit and a ground heat exchanger which also serves as the heat source of a heat pump, which is the backup heater. This new layout should reduce the today's usual extra system costs of solar houses by about 25%.System simulations prove the functionality of the concept and show even higher solar fractions and energy savings as simulated for the existing solar active house concept. One of the main components in the new concept is the controller which has to decide which heat sink will be charged. A control strategy was developed which evaluates the potential outputs of the collector opera- ting to each heat sink. Simulations allow determining the optimal control parameters for this approach. While the thermal activa- tion is able to compensate the decreasing solar input to the smaller storage tank, the effects of the regeneration of the ground heat exchanger are significantly smaller. However, the regeneration avoids a long-term temperature decrease in the ground and may allow a reduction of the heat exchanger area.

Investigations of the processes of structure formation in concrete conditions on winter concreting

Early as antifreeze additive for concreting construction company uses traditional additive sodium nitrite. While the concrete using the same stacking technology and warming gaining strength in the project deadlines. To determine the causes of degradation of concrete specialists VPO UGNTU studies were carried out samples of slabs structures by X-ray analysis and simultaneous thermal analysis (TG DSC). X-ray analysis was carried out on rentgenogram received diffractometer “D2 Phaser” (Bruker), treated with a licensed version of the program “Diffrac. Eva” using licensed databases “PDF- 2”. Simultaneous thermal analysis was carried out on material obtained by simultaneous thermal analysis instrument “STA 449 F3 Jupiter” and mass spectrometer “QMS 403 C Aeolos” (Netzsch). The results were processed using licensed programs “NetzschProteus. ProteusAnalysis” and “Aeolos. Dispsav”. Investigation of the processes of structure formation of concrete floor slabs in connection with their destruction due to changes in the composition and technology of concrete when designing the winter concreting on one of the construction sites in the city of Ufa. Methods of x-ray phase analysis and simultaneous thermal analysis effectively an examination of the structures of concrete and found out the reason of its destruction. Proven change in the composition of concrete in its design, due to the introduction of other supplements to replace the current. Research efforts showed that by X-ray analysis and simultaneous thermal analysis can be efficiently set up kinds of additives used in concrete, and use methods under consideration for the examination of concrete compositions. Concretes considered in relation to the use of potash has been proven and lignosulfonates in winter concreting.

Two case histories relating to the transmission of noise from mechanical equipment rooms to adjacent noise sensitive spaces

Two recent noise control projects related to the reduction of noise from mechanical equipment rooms to an adjacent conference room and to an adjacent office. For both of these situations, the noise control procedures to be implemented involved the determination of the most significant noise transmission path; air borne noise transmitted through a concrete floor slab or structurally transmitted noise due to lack of proper chiller and pipe vibration isolation in the conference room case, or for the office case airborne noise transmitted through a wall constructed of gypsum wall board and flanking through common floor slabs or structurally transmitted due to lack of suitable pump and piping vibration isolation. A method for determining the most significant noise transmission path and the resulting noise reduction for these two cases will be described.

The effects of pore size distribution and working techniques on the absorption and water content of concrete floor slab surfaces

Pore size distribution in the surface of a concrete floor slab may vary according to the quality of the finishing work, such as trowelling, or with the curing of the concrete. The pore size distribution also influences the water absorbency and water content that modulates the quality of the finished floor. We examined how working techniques, e.g., floor top finishing and curing and the resulting pore distribution on the concrete floor slab surface related to water absorbency and the water content of study specimens. As a result, the more the surface is smoothed, pressing it with a wood or steel trowel (henceforth, Finishing) and the longer the surface is moisture-cured, the more the volume of pores ranging from 10−7 to 10−6 m (100nm to 1μm) in diameter is reduced, while the volume of pores with diameters of 10−7m (100nm) and smaller tended to increase. Furthermore, the study revealed that the quantity of pores exceeding ca. 10−7m (100nm) in diameter strongly affected the water absorbency, while that of pores smaller than 10−8m (10nm) in diameter affected the water content. Thus, the above results demonstrate that a working technique of better quality decreases the water absorbency and increases the water content of a concrete floor slab.

A fire test on continuous reinforced concrete slabs in a full-scale multi-story steel-framed building

To further understand the fire behavior of concrete floor slabs, this paper examines the results of a fire test on continuous concrete floor slabs in a full-scale three-story steel-framed building. The case under experimental study models the reality of fire conditions more closely than previous tests and involves the construction of a special furnace on the building's second floor to heat four panels (two by two) and steel beams on the third floor. The experimental results are investigated in detail and consider the furnace temperature, temperature distribution, vertical and horizontal deflections, and failure patterns of the structural elements during the heating and cooling phases. The testing data indicate that the number and locations of the heated panels in the floor also have a considerable effect on the continuous concrete floor's fire behavior, apart from the boundary constraint conditions provided by the adjacent structural members. In addition, the steel beams exhibit better fire-resistant performance than that observed in standard fire tests depending on their structural integrity and the interaction between structural members. In contrast to its high-strength bolt connections, the building's welded-bolted connections do not cause local buckling of the steel beams subjected to fire.

Enhanced accelerated drying of concrete floor slabs

Concrete floor slabs dry out through a process of evaporation and diffusion provided the ambient environment promotes such drying. Impermeable floor coverings laid on concrete slabs can be subject to damage caused by high levels of residual moisture trapped by premature sealing of the surface. This damage can include timber floor boards buckling, vinyls blistering or tiles lifting. Whether or not it is safe to apply such a covering depends on whether the slab is sufficiently dry. Furthermore, if accelerated drying techniques are employed to reduce the waiting time before covering, the surface relative humidity reduces more rapidly, but there is an increase in the risk of damage to the covering because of higher levels of residual moisture deep within the slab. By using actual data from a variety of specimens to calibrate a non-linear finite-element model of the moisture migration, this paper shows how numerical predictions can be undertaken to determine a safer long-term relative humidity under an impermeable floor covering.

Closure to “Strengthening Two-Way Reinforced Concrete Floor Slabs Using Polypropylene Fiber Reinforcement” by Matthew J. Radik, Ece Erdogmus, and Travis Schafer

Closure to “Strengthening Two-Way Reinforced Concrete Floor Slabs Using Polypropylene Fiber Reinforcement” by Matthew J. Radik, Ece Erdogmus, and Travis Schafer

Discussion of “Strengthening Two-Way Reinforced Concrete Floor Slabs Using Polypropylene Fiber Reinforcement” by Matthew J. Radik, Ece Erdogmus, and Travis Schafer

Discussion of “Strengthening Two-Way Reinforced Concrete Floor Slabs Using Polypropylene Fiber Reinforcement” by Matthew J. Radik, Ece Erdogmus, and Travis Schafer

Analytical Model for Predicting Response and Flexure-Shear Resistance of Composite Beams Combining Reinforced Ultrahigh Performance Fiber-Reinforced Concrete and Reinforced Concrete

The addition of an external layer of reinforced ultrahigh performance fiber-reinforced concrete (R-UHPFRC) on top of reinforced concrete (RC) floor slabs and bridge decks is an emerging technique for strengthening RC structures. As an additional reinforcement, a layer of R-UHPFRC significantly increases the maximum resistance and deformation capacity of RC elements, thus creating a composite element that herein is referred to as RU-RC elements. This paper presents an elastic-plastic fictitious RU-RC composite hinge model for the damage caused by flexural and flexure-shear cracks in the RC element of the composite members. The model accounts for the nonlinear interaction of the two elements due to intermediate-crack-induced debonding (ICD) zone in the near-interface concrete. The model determines the force-deflection response and force in the RU-RC composite tension chord. Furthermore, the contribution of the R-UHPFRC element and the shear resistance envelope of the member are calculated. Comparison with available experimental results shows that the model can accurately predict the member response, resistance and failure mode. A simplified formulation for the shear resistance of the composite members is proposed. The models in this paper are needed for the design of the structural behavior of RC beams strengthened with R-UHPFRC.

How to Select the Fire-Resistant Calculation Model for the Completed Steel Structure

Finite element model of the three-dimension steel frame of sorbic alcohol warehouse is built to study the response of the steel structure on fire. The material nonlinearity and geometrical nonlinearity being aroused by high-temperature are taken into account adequately during this computation. Shell elements are used to model the concrete floor slab，beams as well as columns. The rigid connection and flexible connection between the beams and column are considered respectively. In order to reduce the computing amount, the effects of the completed structure and the neighboring span have been explored under the local fire. It turns out that it has more effects on stresses and deflections in the neighboring span than that in others when the whole structure is under local fire. It has greater deflections when using the rigid connection than using flexible connection between the components. Meanwhile, according to the rules of the stresses and the deflections of the structure, the method of selecting the effective and reasonable simulating areas under the local fire is concluded. The conclusions are important for building the reasonable simulating areas on fire and for further studying the mechanical behaviors of the steel structure, also significant for providing references for the fire-resistant calculation of the completed steel structure.

Experimental Study on Reinforced Concrete Superposed Slabs

With the improvement of the level of architectural science and technology and the modern development of the residential industry higher requirement on building materials and environmental protection was brought forward．Based on the static loading experiment of four reinforced concrete floor slabs, two ordinary and two superimposed with connections, the paper studied their loading mechanism and bending performance, such as deformation, cracks, bearing limit and fail characteristics. Finally, proposals for superimposed slabs' design were put forward, popularization and application of new composite wall plate provides realistic basis.

An advanced FRP floor panel system in buildings

This paper presents the design, modelling analysis and experimental verification of a carbon fibre reinforced polymer (CFRP) floor panel system in buildings. The CFRP panel was designed as a pultruded beam with an open cross-section. The design was carried out using the Eurocodes and supported by the finite element analysis (FEA). Modelling results indicated that the proposed floor panel passed tall design check recommended by Eurocode, and the safety check on both deflection and material strength are important for producing CFRP panel products to meet the dimensional requirements in design of buildings with different design specification. Experimental results of scaled CFRP panel samples were also presented in this paper, which successfully validated the design and modelling analysis. This proposed CFRP floor panel as a primary component in the floor system aims to replace traditional concrete floor slab in buildings. This new CFRP floor panel can be easily installed in buildings because of its lightweight feature, and easily integrated with the suspending ceiling, ventilation and lighting system because of designed shape. This investigation provided a potential building component in the low carbon constructional industry for saving energy and reducing CO2 emission.

Experimental study of the thermal performance of a large institutional building with mixed-mode cooling and hybrid ventilation

The paper explores mixed-mode cooling strategies in buildings with hybrid ventilation and high levels of exposed thermal mass and presents data collected over an extensive period of time using a full-scale experimental set-up in an occupied institutional building with motorized façade openings integrated with an atrium. Night cooling strategies for thermal mass pre-cooling, with variable low temperature setpoint for control of airflow through operation of motorized grilles or a possible variable speed fan, are evaluated. Results for the thermal conditions in the highly-glazed atrium zone and the wind and buoyancy-driven airflow rates show that free cooling covers a significant portion of the building's cooling requirements while maintaining a comfortable indoor environment. The heat removal from concrete floor slabs is 2–5 times higher with the inlet air stream at an average temperature of 12 °C, compared to that with an air stream at 15 °C or 18 °C respectively. These findings provide insights for space conditioning using hybrid ventilation that can support the development of model-predictive control strategies.

Cyclic Seismic Testing of Composite Concrete-Filled U-Shaped Steel Beam to H-Shaped Column Connections

In this study, the cyclic seismic performance of a concrete-filled U-shaped steel beam to H-shaped steel column connections was experimentally evaluated. The concrete-filled U-shaped steel beams were compositely attached to the concrete floor slab. The test was conducted in two stages. The first testing program was carried out on one-sided moment connections to find the most promising connecting scheme. The strengthening scheme, or welding steel plates to the beam bottom flange with minimized stress concentration, was shown to be the most satisfactory, and it was used in the second-stage test on two full-scale cruciform specimens. Considering the unique constructional nature of the proposed composite connections, the critical limit states such as weld fracture, local buckling, concrete crushing, and rebar buckling were carefully addressed in designing specimens. Test results showed that the connection details and design procedures proposed in this study can successfully control the critical limit states mentioned previously. The proposed connection detail successfully pushed the plastic hinging to the tip of the strengthened zone as intended in design, thus effectively protecting the more vulnerable beam-to-column welded joint. The specimens typically exhibited a maximum story drift capacity of more than 5.5% rad, exceeding the minimum limit of 4% rad required of special moment frames. Four of the five specimens tested in this study eventually failed because of a low-cycle fatigue fracture across the beam bottom flange at a high story drift greater than 5.0% rad.

Effects of shrinkage on the long-term stresses and deformations of composite concrete slabs

Composite one-way concrete floor slabs with profiled steel decking used as permanent formwork are commonly used in the construction of floors in buildings. The steel decking supports the wet concrete of a cast in situ slab and, after the concrete sets, acts as external reinforcement. Relatively little research has been undertaken on the time-dependent in-service behaviour of such slabs and little guidance is available to structural engineers for predicting the long-term deflection. The drying shrinkage profile through the thickness of a slab is known to be greatly affected by the impermeable steel deck at the slab soffit, but this has not been quantified to date. This paper presents the results of laboratory measurements of the non-uniform distribution of shrinkage through the thickness of composite slabs, and the resulting effects on the long-term deflection of such slabs are considered. An analytical procedure for the determination of time-dependent stresses and deformations in composite floor slabs is described, and the results of analyses are presented for several common decking profiles using the measured shrinkage profiles.

Towards low carbon homes – A simulation analysis of building-integrated air-source heat pump systems

A comparative transient simulation analysis for domestic buildings with a floor-embedded heating system coupled to a modern air source heat-pump (ASHP) has been carried out using the TRNSYS numerical modeling environment for various UK locations. The effects of heat-pump control during off-peak electricity tariff periods in conjunction with varying building fabric characteristics were analysed and the results show that for the locations investigated, running costs and CO2 emissions were lower for the ASHP platform than for a comparative gas boiler heating system. It was also found that by utilizing the thermal mass of a concrete floor slab or by integrating external insulation, acceptable comfort levels during the heating season were maintained when operating the ASHP solely during off-peak tariff periods. A thinner concrete floor slab containing phase change material (PCM) provided a slightly improved comfort level during winter and also reduced overheating during summer in buildings with a high level of insulation. Finally, when utilising a floor-embedded PCM material, it was found that the thermal properties of the PCM material must be carefully matched with case-specific building fabric thermal performance parameters in order to ensure effective internal environmental control.

Strength and ductility of RC slabs strengthened with hybrid high-performance composite retrofit system

This study presents the details and assessment of the effectiveness of an innovative retrofit methodology aims at improving both the strength and ductility of existing reinforced concrete (RC) floor slabs and bridge decks. The innovative retrofit system comprises of a polymeric hybrid composite system made of high performance concrete (HPC) and a carbon fiber reinforced polymer (CFRP) unidirectional laminates. The proposed retrofit system is designed to avoid the difficulty and restricted accessibility associated with applying conventional steel and fiber reinforced polymeric (FRP) composite systems to the underside of existing floor slabs or bridge decks for positive moment capacity enhancement. The proposed system is applied only to the top of the slabs or decks resulting in a shorter application time and minimizing service disturbance of the lower floor or traffic interruption under the bridge overpass. The flexural enhancing mechanisms of the proposed system to the RC floor or bridge deck sections at both the positive and the negative moment zones are discussed. Three full-scale one-way slabs having two continuous spans were tested. The results showed that the proposed system can be easily installed and that the ultimate flexural capacity and ductility of retrofitted RC slabs can significantly increase.

Seismic behavior of CFRSTC composite frames considering slab effects

This paper reports on an experimental and numerical investigation conducted on the seismic behavior of concrete-filled rectangular steel tubular columns (CFRSTC) composite frames. The experimental study was conducted by subjecting two full-scale composite frames to simulated seismic loads. Both frames were composed of CFRSTC and steel beams. One specimen was placed on a reinforce concrete (RC) floor slab and the other was not. The purpose of the test was to investigate the elasto-plastic performance of the CFRSTC composite frame system and to examine the effects of composite action on the behavior of composite frames. The test results showed that the stiffness, strength and energy-dissipating capacity of the CFRSTC frame increased significantly with the presence of the floor slab. Compared with a bare steel beam, the composite beam experienced a decrease in the rotation capacity from 0.046 rad to 0.026 rad. The shear deformation of the panel zone grew because of the composite action, which delayed the fracture of the beam. Finite element (FE) models were established to simulate the tested frames. The results of the FE model fit well with that of the test model in terms of stiffness, strength, hysteretic behavior and component deformation.

Study on Mechanical Behaviors of New Reinforced Concrete Hollow Floor Slab

In this paper a new type of reinforced concrete four-way rib hollow slab was proposed by the authors first. Further in order to research on the mechanical properties of the new floor slab the other two common slabs were compared with the new one, that was two-way rib hollow slab and solid slab. The rational finite element (FE) models of the three kinds of slabs supported by four corner columns were built up respectively by ANSYS. The deflection and stress of the three kinds of slabs under three load cases were calculated separately, on the basis of which thorough comparisons and analysis were carried out. The study results showed that the new reinforced concrete four-way rib hollow floor slab has superior mechanical properties.